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Micromilling-assisted fabrication of monolithic polymer ridge-type waveguides with integrated photonic sensing structures

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Abstract

This study demonstrates and discusses a novel approach for the fabrication and rapid prototyping of monolithic photonic platforms comprising a ridge-type waveguide with integrated sensing structures. First, the bulk injection-molded cyclic olefin copolymer substrates are micromilled in order to define the physical extension of the ridge structure. Cross-sections down to 30 × 30 µm2, exhibiting a mean surface roughness of 300 nm, are achieved with this process. Subsequently, UV radiation is used to modify the ridge structure’s refractive index, which leads to the formation of an optical waveguide. By employing a phase mask, it is possible to equip the photonic platform with a Bragg grating suitable for temperature measurements with a sensitivity of −5.1 pm K-1. Furthermore, an integrated Fabry-Pérot cavity, generated during the micromilling step as well, enables refractive index measurements with sensitivities up to 1154 nm RIU-1.

© 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

1. Introduction

Optical polymer planar Bragg gratings (PPBG) have developed to an increasingly interesting sensor concept throughout recent years. Similar to fiber Bragg gratings, a PPBG comprises a waveguide and a periodic refractive index modulation, also denoted as Bragg grating, which acts as a narrowband reflector for light waves propagating within the waveguide. In comparison to classical silica substrates, polymer-based photonic sensing devices offer several general advantages, such as inherent photosensitivity, a reduced Young’s modulus and an increased thermo-optic coefficient [13]. Moreover, polymer planar photonic platforms are easy to handle while they maintain reasonable manufacturing costs and effort [4]. Up to date, a variety of PPBGs based on poly(methyl methacrylate), Ormocer hybrid polymers and epoxy resins were demonstrated, facilitating multiple sensing applications like temperature sensing, multidimensional stress or strain sensing, vital sign monitoring and accelerometry [511]. Additionally, in combination with microfluidic channels and / or appropriate functionalization, PPBGs can serve as a basis for medical lab-on-a-chip devices and other biochemical applications [1214]. In practice, however, PPBGs based on these materials suffer from limited heat deflection properties and / or unwanted cross-sensitivities towards relative humidity changes [15]. This can be overcome by employing cyclic olefin copolymers (COC), a novel high-grade thermoplastic which offers glass transition temperatures up to 250 °C and negligible water absorption [1618]. Thus, COC-PPBGs are able to outlast harsh environments and perform temperature measurements up to 160 °C [19,20].

Usually, fabrication of COC-based PPBGs is achieved by employing a sophisticated single-writing-step (SWS) method, where a stack comprised of a phase mask and an amplitude mask is brought into close contact with the bulk polymer substrate. Afterwards, the sample is exposed to UV radiation generated by a KrF excimer laser. This leads to the simultaneous generation of a waveguide and an integrated Bragg grating structure, buried underneath the COC substrate’s surface. Using this technique, in dependence of the employed UV dosage, PPBGs with a reflection peak exhibiting a reflectivity of 98% and a 400 pm spectral full width at half maximum (FWHM) were demonstrated. A sophisticated discussion of the SWS method as well as the optical and photosensitive properties of COCs is given by the authors elsewhere [21,22]. However, the flexibility of the SWS procedure is limited by the available amplitude and phase masks, which are responsible for defining the waveguide’s shape as well as its width and the resulting wavelength of main reflection, respectively. Furthermore, in order to enable the usage of COC-PPBGs in the outline of microfluidic applications, additional processing technologies, such as femtosecond laser ablation or micromilling, need to be employed to equip the device with microfluidic channels.

Alternatively, it is possible to make use of femtosecond laser direct writing in order to manufacture PPBGs with buried waveguides in bulk COCs. Waveguides as well as grating structures are generated by employing the point-by-point method, whereas a spatial light modulator is used to form a disk-shaped focal volume pixel (voxel) to modify the substrate’s refractive index in a controlled manner. COC-PPBGs fabricated with this method exhibit a reflectivity up to 95% at a FWHM of 288 pm [23]. This technique offers increased flexibility, since the photonic structures can be generated in various depths within the substrate and the Bragg grating period can be adapted by varying the point-by-point inscription parameters. Moreover, femtosecond-laser based processes enable hybrid micromachining, which features the fabrication of photonic structures and microfluidic channels in one processing step [24]. However, this comes with the increased cost of a sophisticated femtosecond laser system.

In contrast, micromilling, already identified as a cost efficient and versatile tool for rapid prototyping of microfluidic devices [25], can also be used for the generation of photonic structures. Bundgaard et al. reported on micromilling-assisted rapid prototyping of COCs, including the fabrication of microfluidic channels and optical waveguides, as a novel alternative manufacturing method for planar polymer-based photonic devices. Nevertheless, the demonstrated platforms still are heterostructures consisting of multiple COC-based layers. Furthermore, the generated 200 × 200 µm2 waveguides exhibit highly multi-modal behavior and are thus suboptimal for Bragg grating sensor concepts [26,27].

Against this background, this article demonstrates and discusses the fabrication of ridge-type waveguides from bulk COC polymers by employing a combination of micromilling and UV-radiation exposure. Lateral cross-sections with dimensions down to 30 × 30 µm2 are reached and, by means of using an additional phase mask during irradiation, Bragg grating structures are integrated within the waveguide. Furthermore, a Fabry-Pérot (FP) cavity, also generated during the micromilling process, enables refractive index measurements.

2. Fabrication process and micromilling parameters

All photonic structures generated in the outline of this study are based on a high-temperature stable COC grade (TOPAS6017-S04, TOPAS Advanced Polymers, Raunheim, Germany). Its glass transition temperature (defined as 178 °C by the manufacturer) is significantly higher than that of previously demonstrated COCs used for milling-based fabrication of photonic devices [26,27]. A desktop micro mill (CNC Mini-Mill/4, Minitech Machinery, Norcross, GA, USA) is used to prepare COC samples out of an injection-molded polymer plate. Except for an air stream directed at the tip of the end mill, no additional cooling is employed throughout all experiments discussed in this contribution. The bulk substrate exhibits a length of 20 mm, a width of 10 mm and a thickness of 1.5 mm. An end mill with a diameter of 1 mm (ES-PS-0100-3-040-40, vhf camfacture, Ammerbuch, Germany) is employed to cut the sample to appropriate size while successive generation of the ridge structure is achieved by removing excess material with a 0.2 mm diameter single-tooth end mill (ES-SC-0020-3-006-40, vhf camfacture). At this point, an optional Fabry-Pérot cavity can be integrated into the waveguide structure using the same process parameters and milling tool. Subsequently, the structure is covered with a phase mask and the sample is irradiated with 248 nm UV radiation generated by a KrF excimer laser (BraggStar Industrial, Coherent Europe B.V., Utrecht, Netherlands). Finally, the PPBG is thermally cured at a temperature of 130 °C for 2 hours. The process results in a monolithic ridge-type waveguide with an asymmetric refractive index profile. Tangentially to the substrate surface (x-direction, see Fig. 1(b)), the light is confined by the physical extension of the micromilled ridge structure. Perpendicular to the substrate surface however (z-direction), the waveguide exhibits an exponential refractive index depth profile which prevents the guided mode from leaking into the untreated polymer substrate. Thus, the optical properties of the generated waveguide are defined by its cross-section, controlled via the micromilling step, and the amount of UV radiation absorbed by the bulk polymer [22]. Please note that there is no additional masking of the laser beam during the process. Thus, a significant amount of UV light hits the milled COC substrate surface next to the ridge. However, it is found that this does not diminish the light-guiding properties of the fabricated waveguide, as long as the induced refractive index increase is large enough to confine the guided light within the elevated structure. A comprehensive process overview as well as an image of multiple ridge-type waveguides on a single substrate and a schematic of their asymmetric refractive index profile is shown in Fig. 1.

 figure: Fig. 1.

Fig. 1. (a) Fabrication process schematic for micromilling-assisted generation of monolithic ridge-type waveguides on a bulk cyclic olefin copolymer (COC) substrate. (b) Image of a finalized specimen comprising three parallel waveguides with integrated Bragg gratings (grating structures are indicated). The zoom in depicts a sketch of the waveguide and schematics of its asymmetric refractive index (RI) profile.

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There are two main challenges for the generation of photonic microstructures by employing a cutting technology with successive contact irradiation. First, the milled ridge needs to exhibit a sufficiently reduced surface roughness to prevent excessive scattering losses. Second, burr and debris forming on the waveguide’s upper edge needs to be omitted in order to guarantee reproducible results when the phase mask is brought into direct contact with the ridge structure during UV irradiation [28,29]. Overall, there is an enormous variety of adjustable milling parameters such as milling strategy, feed rate, rotational speed and end mill composition including style, material, diameter as well as number of flutes or teeth. In consequence and due to the general machinability variance of polymers, especially in the outline of micromilling processes, an application-related parameter study is necessary to gain an elaborate insight into the fabrication method and the quality of the resulting photonic structures [30,31]. Thus, multiple COC specimens are machined with different feed rates vf and rotational speeds N, which results in varying feed per tooth values ft according to

$${\textrm{f}_\textrm{t}}\,\textrm{ = }\,\frac{{{\textrm{v}_\textrm{f}}}}{{\textrm{N} \cdot \textrm{Z}}}.$$

Here, Z represents the number of end mill flutes, which is 1 for all tools employed in this study, as they exhibited superior performance in preliminary experiments on polymer-based waveguides [32]. Thus, this parameter is equal to the feed per revolution, which is also commonly denoted as chip load. Moreover, for micro-scale end mills, the study compares the impact of up-cut milling, also denoted as conventional milling, and down-cut milling. While in the former case, cutting edge travel and workpiece feed are oriented in opposite directions, down-cut milling describes a process where both directions are equal [33,34]. Figure 2(a) depicts a schematic of the side milling procedure while Fig. 2(b) shows the surface roughness resulting from the process, acquired by means of a white-light interferometer (WLI) (ContourGT-I, Bruker, Billerica, MA, USA). The surface roughness is quantified by evaluating the unfiltered arithmetical mean roughness of the surface Sa [35]. Based on the used 50x objective, lateral and height resolution of the WLI are specified as 0.5 µm and less than 0.1 µm, respectively.

 figure: Fig. 2.

Fig. 2. (a) Schematic of the milling process and its parameters. The inset depicts a contour plot of the resulting areal surface profile, acquired via white-light interferometry. (b) Arithmetic mean deviation of the assessed surface profile, or surface roughness, as a function of varying chip loads when using end mills with a diameter of 1 mm and 0.2 mm.

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According to Fig. 2(b), an unambiguous correlation of chip load and the resulting surface roughness of the waveguide’s side walls is observed. Thus, smoother surfaces can be generated by employing a combination of low feed rates and high milling tool rotational speeds. In this case, the number of interactions between tool cutting edge and workpiece is significantly higher over a finite length, as it is the case with a polishing process. Furthermore, increased rotational speeds lead to elevated temperature generation, which possibly has a positive effect on the residual surface characteristics as well. It is also found that, in comparison to down-cut milling, up-cut milling results in reduced Sa values. This behavior is attributed to the fact that down-cut milling implicates increased engagement forces. Furthermore, the force impact is mainly oriented orthogonally with respect to the machining direction when the cutting edge touches the unmachined section of the workpiece once per revolution. Especially when machining ductile materials such as polymers, this may lead to excessive workpiece deformation. In the case of up-cut milling, this effect is mitigated since this strategy features reduced engagement forces which are also oriented in parallel to the machining direction [36]. While the minimum Sa parameter is limited to 300 nm when using an end mill with a diameter of 0.2 mm, employing a tool with a diameter of 1 mm yields surface roughness values down to 200 nm. Furthermore, larger tools generate a comparable surface roughness at increased feed rates. Thus, faster overall fabrication can be achieved by employing an end mill with a larger diameter. However, this means that tool changes are required for the fabrication of microscale structures, such as a microfluidic channel or an FP cavity. Additionally, it is worthwhile to note that only the final tool passage of a side-milling process defines the residual roughness of the resulting surface. At earlier stages, faster milling parameters can be chosen to reduce fabrication time without sacrificing any surface quality. Cross feed Δx and depth feed Δz are set to 10% of the employed tool’s diameter. No noticeable impact of these parameters on the achievable surface quality is observed in this study. In summary, while there is a deviation in the observed absolute surface roughness values, the general relation of surface roughness and chip load compares well to previous micromilling studies conducted with different milling tools and polymers [37,38].

Burr as well as debris appearance on ridge structures, milled with a comparable parameter set, are examined by means of a light microscope (Eclipse LV-N, Nikon, Tokyo, Japan). Figure 3(a) provides a qualitative overview about the employed feed rate / rotational speed combinations, the residual chip load and the resulting quality of the milled waveguide structures. It is observed that reduced chip loads again lead to preferable results, as the occurrence of burr and debris is drastically reduced. Furthermore, an additional finishing step, wherein the cross-feed parameter is reduced from 10% to 1% during the last passage, can further mitigate burr while the abundance of debris is completely omitted. Figure 3(b) depicts the microscope image of a ridge structure fabricated with optimized parameters, namely a feed rate of 50 mm·min-1 and a rotational speed of 50,000 rpm, which results in a chip load of 1 µm. According to the cross-sectional waveguide profile, which is derived from a WLI measurement, width and height of the top burr are determined as 8 µm and 5 µm, respectively. Up-cut milling is used as fabrication process strategy in all cases, since down-cut milling results in excessive top burr formation, as shown in Fig. 3(c). In the case of ridge structures with widths below 100 µm, the whole ridge surface is completely covered with burr. Thus, they are not suitable for the subsequent illumination step. Again, this behavior is attributed to the chip cutting process which is different for both milling strategies. In the case of up-cut milling, burr is generated in travel direction of the tool. Consequently, every subsequent tool revolution removes burr generated by the preceding revolution. In contrast, down-cut milling leads to burr formation at the side of the tool path and thus no automatic burr removal.

 figure: Fig. 3.

Fig. 3. (a) Qualitative analysis of residual top burr and debris in dependence of feed rate and rotational speed of the up-cut milling process. Moreover, the resulting chip load is stated. (b) Microscope image of a waveguide milled with optimized up-cut milling parameters. Furthermore, a cross-sectional height profile of the fabricated ridge structure is depicted. (c) Exemplary comparison of burr formation resulting from up-cut or down-cut milling processes.

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In order to prevent manual tool changes, a single-tooth end mill with a diameter of 0.2 mm is used for the fabrication of all photonic structures demonstrated in this study. The parameter set of the final tool passage always comprises a rotational speed of 50,000 rpm in combination with a feed rate of 50 mm·min-1, which yields a chip load of 1 µm. While a cross feed of 10% tool diameter is employed for most of the process, a final finishing step is realized by reducing this parameter to 1% during the final tool passage. This way, the formation of top burr and debris, as well as the resulting surface roughness parameter of the ridge’s side walls, is minimized.

3. Bragg grating temperature sensor

Multiple ridge structures are milled and subsequently irradiated to generate monolithic ridge-type waveguides (see Section 2). During UV exposure, a +1/-1 order phase mask (Ibsen Photonics, Farum, Denmark), with a grating period of 1032 nm over a length of 10 mm, is aligned and brought into direct contact with the 20 mm long ridges. After thermal curing at a temperature of 130 °C for two hours, the photonic structures are aligned with a pigtailed single-mode fiber to enable quantification of their respective Bragg reflection signals by means of an interrogation unit (HYPERION si155, Micron Optics, Atlanta, GA, USA). A permanent connection between fiber and waveguide is realized by employing a UV-curable adhesive (NOA78, Norland, Cranbury, NJ, USA), which additionally acts as a refractive index matching medium in the fiber-to-waveguide intersection.

It is found that smaller waveguide cross-sections require increased UV dosages during irradiation of the ridge structure (see Fig. 1(a)), in order to obtain comparable and evaluable reflection signals from the integrated Bragg gratings. Depending on the waveguide cross-section, which is quadratic with an edge length of 30, 40 or 50 µm, the specimen is exposed to a fluence of 400, 350 or 300 J cm-2, respectively. At a repetition rate of 200 Hz, the overall exposure is defined by varying the pulse quantity from 30,000 to 40,000 pulses. Thus, the overall irradiation time also varies from 150 s to 200 s. Figure 4(a) to (c) depict an overview on the obtained Bragg peaks as well as the respective waveguide’s mode profile, acquired via beam propagation method simulations (RSoft, Synopsys, Mountain View, CA, USA) [39]. The simulation is based on refractive index depth profiles acquired via phase shifting Mach-Zehnder interferometry [22]. While the demonstrated structures are exposed to various quantities of UV radiation, which implies a different amount of refractive index modification, no straightforward relation between employed fluence F and residual Bragg wavelength λB is present. However, the obtained Bragg signals show that the residual top burr of the ridge structure does not prevent successful contact irradiation through a phase mask. Furthermore, the wavelength of main reflection correlates well to the simulated effective refractive index neff values of the respective waveguide, as dictated by the Bragg relation

$${\mathrm{\lambda }_\textrm{B}}\, = \,2{\textrm{n}_{\textrm{eff}}}\mathrm{\Lambda }.$$
 figure: Fig. 4.

Fig. 4. Bragg peaks and simulated mode profiles of micromilled ridge-type waveguides with cross-sections of (a) 30 × 30 µm2, (b) 40 × 40 µm2 and (c) 50 × 50 µm2. Additionally, the respective fluence F, absorbed by the ridge structure during UV exposure, is given. (d) Simulated mode intensity I profile cross-sections for various waveguide geometries irradiated with a fluence of 300 J cm−2. The inset shows a magnification of the mode cross section near the ridge-structure to polymer-substrate transition region.

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The grating period Λ therein is defined by the employed phase mask, which means this value is constant for all fabricated structures [40].

The inverse proportionality of waveguide cross-section and UV radiation necessary to enable suitable reflection peaks is examined by means of Fig. 4(d). Therein, the simulated vertical intensity distribution of several waveguide geometries, fabricated with a fluence of 300 J cm-2, is shown. It reveals that the mode is propagating closer to the waveguide surface in larger structures. Additionally, smaller ridge cross-sections lead to mode penetration into the bulk, unmachined COC material, where there is no more physical light confinement in the horizontal plane (x-direction). This behavior is attributed to the fact that the fabricated ridge-type waveguides exhibit a large refractive contrast at the upper as well as the lateral COC-to-air interfaces. However, towards the unirradiated COC substrate, the guided light experiences relatively weak modal confinement by the waveguide’s exponential refractive index depth profile. Consequently, when the physical extension of a ridge-type waveguide is reduced, the guided mode will begin to leak through the interface with the smallest refractive index contrast, hence, towards the lower regions of the polymer. This needs to be countered with larger UV radiation doses during fabrication, which increases the waveguide’s residual refractive index modification. Additionally, a steeper refractive index depth profile is generated which, in consequence, leads to increased modal confinement [22]. Therefore, overall irradiation in combination with waveguide cross-section needs to be considered when designing a monolithic ridge-type waveguide since they both influence the resulting effective refractive index of the propagating mode as well as the general functionality of the device. However, the results demonstrate that a variety of monolithic ridge-type waveguides, with cross-sections down to 30 x30 µm2, can be manufactured with the proposed micromilling-assisted fabrication method.

Since both, effective refractive index neff and grating period Λ of a Bragg grating are functions of environmental physical quantities, such as strain and temperature, the fabricated specimens can be used as a sensing device. Thus, an exemplary study is conducted by positioning a sample with a 40 × 40 µm2 waveguide on a hotplate with active temperature control. During the experiment, the temperature is incrementally increased and subsequently held for at least 10 minutes in order to guarantee stable conditions. Figure 5 depicts the Bragg wavelength shift induced by environmental temperatures up to 70 °C.

 figure: Fig. 5.

Fig. 5. Temperature response of a COC-PPBG with monolithic ridge-type waveguide.

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It is found that increasing the temperature leads to a negative Bragg wavelength shift correlated to the negative thermo-optic coefficient of COCs, or polymers in general [41]. Linear regression of the measurement data yields a sensitivity of -5.1 pm K-1, a value which is characteristic for PPBGs based on bulk COCs. Additionally, the observed quality of the Bragg reflection peak is comparable to the signal of COC-PPBGs with buried photonic structures [18,20,42,43]. Hence, the residual top burr has no or negligible influence on the irradiation process and the resulting photonic platform. Conclusively, the device is equally suitable for temperature sensing or, alternatively, for temperature referencing in the outline of other applications.

4. Fabry-Pérot refractive index sensor

Fabry-Pérot interferometers, often denoted as etalons, principally consist of two plane parallel mirrors separated by a cavity. If broadband light traverses the etalon structure, multiple internal reflections lead to characteristic interference fringes in the transmission as well as in the reflection spectrum. Since spectral location and distance of these interference fringes are strongly influenced by perturbations of the cavity’s optical path length, FP-based devices have been successfully developed for various purposes, such as temperature, pressure and refractive index sensing. Within an optical waveguide, etalons can be straightforwardly generated by interrupting the photonic structure in a controlled manner. In this case, the waveguide-to-air interfaces will act as the mirrors of the FP etalon [44,45].

A COC-PPBG with monolithic ridge-type waveguide is fabricated by micromilling a ridge structure with a cross-section of 40 × 40 µm2. During the micromilling process, prior to UV irradiation, the waveguide structure is additionally equipped with a FP cavity (see Fig. 1(a)). After connecting the photonic structure to a pigtailed single-mode fiber, the cavity’s interference-based reflection signal is interrogated (SYS:Lab 2, Stratophase, Hampshire, UK), as shown in Fig. 6(a). In order to optimize signal evaluation, the raw signal is filtered with a digital Butterworth filter via Matlab. Both, raw and filtered reflection signal are depicted in Fig. 6(b). Therein, a microscopic image of the FP cavity is shown as well. According to

$${\mathrm{\lambda }_\textrm{M}}\,\textrm{ = }\,\frac{{\textrm{2}\mathrm{\pi }}}{\mathrm{\delta }}\textrm{2nl,}$$
under the assumption of normal incidence, the wavelength of a reflection minimum λM is linked to the FP cavity’s length l and its internal refractive index n. Thus, for constant phase shifts δ and cavity lengths l, refractive index changes Δn will lead to a linear wavelength shift ΔλM of a reflection minimum following
$$\mathrm{\Delta }{\mathrm{\lambda }_\textrm{M}}\,\textrm{ = }\,\frac{{{\Delta \textrm n}}}{\textrm{n}}{\mathrm{\lambda }_\textrm{M}}\textrm{.}$$

 figure: Fig. 6.

Fig. 6. (a) Schematic of the employed experimental setup. (b) Reflection spectrum of the milled Fabry-Pérot cavity. The raw signal is filtered with a digital Butterworth filter to optimize tracking of the reflection minima. A microscopic image of the cavity is shown in the inset. (c) Wavelength response of the FP reflection minima when filling the cavity with various refractive index liquids.

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As a result, the reflection signal of the milled device can be utilized to determine the refractive index of a medium within its cavity [46].

Multiple refractive index liquids are prepared by mixing distilled water with various weight percentages of sugar. Each solution’s refractive index is determined by employing an Abbe refractometer (DR-M2/1550, Atago, Tokyo, Japan) which is specified to offer a maximum refractive index deviation of ±0.001 at a wavelength of 589 nm. Before every measurement, the solution is stirred to ensure optimum mixing conditions. Subsequently, the sensor is dipped into the liquid, so the cavity is fully immersed. This leads to an immediate shift of the reflection minima, whereas the observed response time cannot be resolved by the 2 Hz sampling rate of the employed interrogation unit. In-between measurements, the FP cavity is purged with nitrogen gas to remove possible residues. Figure 6(c) shows the resulting wavelength shift of the first seven reflection minima of the spectrum’s short wavelength side, when the cavity is flooded with different refractive index liquids. All tracked minima exhibit a positive wavelength shift when the cavity is filled with increasing refractive indices. Linear regression yields a sensitivity between 1141 nm RIU-1, for the shortest wavelength minimum (M1), and 1154 nm RIU-1 for the longest wavelength minimum (M7). The determined shifts of all minima, as well as the wavelength-related sensitivity variation, is in good agreement with the theoretical values obtained by Eq. (4). Consequently, the demonstrated device can be employed in the outline of high-precision refractive index measurement applications.

5. Conclusion

In conclusion, this article demonstrates a novel waveguide generated from a bulk injection-molded cyclic olefin copolymer platform. A combination of micromilling with subsequent UV irradiation enables the fabrication of monolithic ridge-type waveguides. While the milling procedure defines the horizontal extension of the waveguide, light is prevented from leaking into the substrate by means of a graded refractive index depth profile. Thus, in contrast to all other state-of-the-art ridge waveguides, the whole platform consists of only one single bulk material. Additionally, photonic sensing structures, such as Bragg gratings or a Fabry-Pérot cavities, can be integrated.

The study reveals that quadratic ridge structures with edge lengths down to 30 µm can be manufactured via micromilling. By optimizing the parameters of the final tool passages, a mean surface roughness of 300 nm is achieved whereas residual top burr can be reduced to a height of 5 µm and a width of 8 µm. It is additionally demonstrated that it is possible to equip the ridge structure with a Bragg grating by irradiating the waveguide through a phase mask. It is found that the amount of absorbed radiation necessary to achieve comparable Bragg reflection signals reduces with increasing waveguide cross-sections. By means of numerical simulations, this behavior is attributed to modal leakage, which predominantly occurs in smaller waveguides and thus needs to be countered with increased UV radiation. Temperature measurements based on evaluating the Bragg wavelength shift of the integrated structure yield a temperature sensitivity of −5.1 pm K-1, which correlates well to preliminary data based on COC-PPBGs with buried sensing structures. Finally, the study presents that it is possible to employ micromilling in order to equip the ridge with a Fabry-Pérot cavity. By tracking the wavelength shift of the reflection minima, this enables refractive index measurements with sensitivities up to 1154 nm RIU-1.

Therefore, the proposed fabrication method constitutes a promising approach for novel and robust polymer-based photonic platforms. In comparison to state-of-the-art heterostructure ridge waveguides, the demonstrated devices consist of only one single material. Furthermore, in comparison to conventional lithography-based fabrication techniques, employing a micro mill to define the cross-section of the resulting waveguide omits the necessity of inflexible amplitude masks. Thus, the proposed method enables rapid prototyping of novel waveguide designs since dimension and shape can be straightforwardly adapted and directly implemented onto the photonic platform. Furthermore, the fabricated ridge structures can be equipped with a milled Fabry-Pérot cavity for refractive index sensing purposes and a Bragg grating structure for temperature referencing. Consequently, and due to the fact that micro milling is already an established process in the field of microfluidics, this contribution paves the way towards rapid prototyping of polymer-based lab-on-a-chip devices for biomedical sensing applications.

Disclosures

The authors declare no conflicts of interest.

Data availability

Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.

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19. S. Kefer, T. Sauer, S. Hessler, M. Kaloudis, and R. Hellmann, “Microstructure-based fiber-to-chip coupling of polymer planar Bragg gratings for harsh environment applications,” Sensors 20(19), 5452 (2020). [CrossRef]  

20. M. Rosenberger, S. Kefer, M. Girschikofsky, G.-L. Roth, S. Hessler, S. Belle, B. Schmauss, and R. Hellmann, “High-temperature stable and sterilizable waveguide Bragg grating in planar cyclo-olefin copolymer,” Opt. Lett. 43(14), 3321–3324 (2018). [CrossRef]  

21. M. Rosenberger, B. Schmauss, and R. Hellmann, “Influence of the UV dosage on planar Bragg gratings in cyclo-olefin copolymer substrates,” Opt. Mater. Express 6(6), 2118 (2016). [CrossRef]  

22. S. Hessler, M. Rosenberger, B. Schmauss, and R. Hellmann, “Two-dimensional interferometric characterization of laser-induced refractive index profiles in bulk Topas polymer,” Optical Materials 75, 230–235 (2018). [CrossRef]  

23. G.-L. Roth, S. Hessler, S. Kefer, M. Girschikofsky, C. Esen, and R. Hellmann, “Femtosecond laser inscription of waveguides and Bragg gratings in transparent cyclic olefin copolymers,” Opt. Express 28(12), 18077 (2020). [CrossRef]  

24. G.-L. Roth, J. Haubner, S. Kefer, C. Esen, and R. Hellmann, “Fs-laser based hybrid micromachining for polymer micro-opto electrical systems,” Optics and Lasers in Engineering 137, 106362 (2021). [CrossRef]  

25. D. J. Guckenberger, T. E. de Groot, A. M. D. Wan, D. J. Beebe, and E. W. K. Young, “Micromilling: a method for ultra-rapid prototyping of plastic microfluidic devices,” Lab Chip 15(11), 2364–2378 (2015). [CrossRef]  

26. F. Bundgaard, G. Perozziello, and O. Geschke, “Rapid prototyping tools and methods for all-Topas® cyclic olefin copolymer fluidic microsystems,” Proc. Inst. Mech. Eng., Part C 220(11), 1625–1632 (2006). [CrossRef]  

27. F. Bundgaard, Prototyping of Microfluidic Systems with Integrated Waveguides in Cyclic Olefin Copolymer (COC) (Technical University of Denmark, 2006).

28. L. O’Toole, C.-W. Kang, and F.-Z. Fang, “Precision micro-milling process: state of the art,” Adv. Manuf., (2020).

29. B. Z. Balázs, N. Geier, M. Takács, and J. P. Davim, “A review on micro-milling: recent advances and future trends,” Int J Adv Manuf Technol 112(3-4), 655–684 (2021). [CrossRef]  

30. M. A. Câmara, J. C. Rubio, A. M. Abrão, and J. P. Davim, “State of the art on micromilling of materials, a review,” J. Mater. Sci. Technol. 28(8), 673–685 (2012). [CrossRef]  

31. M. Kahrizi, ed., Micromachining Techniques for Fabrication of Micro and Nano Structures, 1st ed. (InTech, 2011).

32. H. Baghsiahi, K. Wang, W. Kandulski, R. C. A. Pitwon, and D. R. Selviah, “Optical waveguide end facet roughness and optical coupling loss,” J. Lightwave Technol. 31, 2659–2668 (2013). [CrossRef]  

33. H. A. Youssef and H. El-Hofy, Machining Technology: Machine Tools and Operations, 1st ed. (CRC Press, 2008). [CrossRef]  

34. R. K. Rajput, A Textbook of Manufacturing Technology: Manufacturing processes for B.E./B. Tech., A.M.I.E.-Section B, and Competitive Examinations, 2nd ed. (Laxmi Publications (P) LTD, 2015).

35. R. Leach, Characterisation of Areal Surface Texture (Springer, 2013). [CrossRef]  

36. J. Ahmad, Machining of Polymer Composites, 1st ed. (Springer US, 2009). [CrossRef]  

37. E. Korkmaz, R. Onler, and O. B. Ozdoganlar, “Micromilling of poly(methyl methacrylate, PMMA) using single-crystal diamond tools,” Procedia Manufacturing 10, 683–693 (2017). [CrossRef]  

38. D. Adeniji, J. Schoop, S. Gunawardena, C. Hanson, and M. Jahan, “Characterization and modeling of surface roughness and Burr formation in slot milling of polycarbonate,” J. Manuf. Mater. Process. 4, 59 (2020). [CrossRef]  

39. K. Okamoto, Fundamentals of Optical Waveguides, 2nd ed. (Elsevier/Academic Press,2006).

40. R. Kashyap, Fiber Bragg Gratings, 2nd ed. (Academic Press, 2010).

41. Z. Zhang, P. Zhao, P. Lin, and F. Sun, “Thermo-optic coefficients of polymers for optical waveguide applications,” Polymer 47(14), 4893–4896 (2006). [CrossRef]  

42. S. Kefer, K. Bischoff, G.-L. Roth, J. Haubner, B. Schmauss, and R. Hellmann, “Tunable bulk polymer planar Bragg gratings electrified via femtosecond laser reductive sintering of CuO Nanoparticles,” Adv. Optical Mater. 4, 2002203 (2021). [CrossRef]  

43. G.-L. Roth, S. Kefer, S. Hessler, C. Esen, and R. Hellmann, “Integration of microfluidic and photonic components within transparent cyclic olefin copolymers by using fs laser,” JLMN 16, 47 (2021). [CrossRef]  

44. M. R. Islam, M. M. Ali, M.-H. Lai, K.-S. Lim, and H. Ahmad, “Chronology of Fabry-Perot interferometer fiber-optic sensors and their applications: a review,” Sensors 14(4), 7451–7488 (2014). [CrossRef]  

45. H. F. Taylor, Fiber Optic Sensors Based upon the Fabry-Perot Interferometer, S. Yin, P. B. Ruffin, and F. T. S. Yu, eds. (CRC Press, 2017), pp. 35–64.

46. S. Pevec and D. Donlagic, “Miniature fiber-optic Fabry-Perot refractive index sensor for gas sensing with a resolution of 5 × 10−9 RIU,” Opt. Express 26(18), 23868–23882 (2018). [CrossRef]  

References

  • View by:

  1. H. Ma, A.-Y. Jen, and L. R. Dalton, “Polymer-based optical waveguides: materials, processing, and devices,” Adv. Mater. 14(19), 1339–1365 (2002).
    [Crossref]
  2. D. J. Webb, “Fibre Bragg grating sensors in polymer optical fibres,” Meas. Sci. Technol. 26(9), 092004 (2015).
    [Crossref]
  3. R. Oliveira, L. Bilro, and R. Nogueira, Polymer Optical Fiber Bragg Gratings: Fabrication and Sensing Applications, 1st ed. (CRC Press, 2020).
  4. M. Rosenberger, G. Koller, S. Belle, B. Schmauss, and R. Hellmann, “Planar Bragg grating in bulk polymethylmethacrylate,” Opt. Express 20(25), 27288–27296 (2012).
    [Crossref]
  5. C. Wochnowski, “UV-laser-based fabrication of a planar, polymeric Bragg-structure,” Optics & Laser Technology 41(6), 734–740 (2009).
    [Crossref]
  6. M. Rosenberger, W. Eisenbeil, B. Schmauss, and R. Hellmann, “Simultaneous 2D strain sensing using polymer planar Bragg gratings,” Sensors 15(2), 4264–4272 (2015).
    [Crossref]
  7. M. Foerthner, M. Rumler, F. Stumpf, R. Fader, M. Rommel, L. Frey, M. Girschikofsky, S. Belle, R. Hellmann, and J. J. Klein, “Hybrid polymers processed by substrate conformal imprint lithography for the fabrication of planar Bragg gratings,” Appl. Phys. A 122(3), 240 (2016).
    [Crossref]
  8. J. Missinne, N. Teigell Benéitez, M.-A. Mattelin, A. Lamberti, G. Luyckx, W. van Paepegem, and G. van Steenberge, “Bragg-grating-based photonic strain and temperature sensor foils realized using imprinting and operating at very near infrared wavelengths,” Sensors 18(8), 2717 (2018).
    [Crossref]
  9. M. Girschikofsky, M. Rosenberger, M. Förthner, M. Rommel, L. Frey, and R. Hellmann, “Waveguide Bragg gratings in Ormocer®s for temperature sensing,” Sensors 17(11), 2459 (2017).
    [Crossref]
  10. T. Guan, G. Keulemans, F. Ceyssens, and R. Puers, “MOEMS uniaxial accelerometer based on EpoClad/EpoCore photoresists with built-in fiber clamp,” Sensors and Actuators A: Physical 193, 95–102 (2013).
    [Crossref]
  11. S. Hessler, P. Bott, S. Kefer, B. Schmauss, and R. Hellmann, “Multipurpose polymer Bragg grating-based optomechanical sensor pad,” Sensors 19(19), 4101 (2019).
    [Crossref]
  12. S. Hessler, S. Knopf, M. Rommel, M. Girschikofsky, B. Schmauss, and R. Hellmann, “Advancing the sensitivity of integrated epoxy-based Bragg grating refractometry by high-index nanolayers,” Opt. Lett. 45, 5510–5513 (2020).
    [Crossref]
  13. M. Girschikofsky, D. Ryvlin, S. R. Waldvogel, and R. Hellmann, “Optical sensor for real-time detection of trichlorofluoromethane,” Sensors 19(3), 632 (2019).
    [Crossref]
  14. S. Kefer, J. Dai, M. Yang, B. Schmauss, and R. Hellmann, “Hypersensitive H2 sensor based on polymer planar Bragg gratings coated with Pt-Loaded WO3-SiO2,” Opt. Lett. 45(13), 3601–3604 (2020).
    [Crossref]
  15. M. Rosenberger, S. Hessler, S. Belle, B. Schmauss, and R. Hellmann, “Humidity-induced effects on polymer planar Bragg gratings,” IEEE Photon. Technol. Lett. 26(16), 1669–1671 (2014).
    [Crossref]
  16. G. Khanarian, “Optical properties of cyclic olefin copolymers,” Opt. Eng. 40(6), 1024–1029 (2001).
    [Crossref]
  17. P. S. Nunes, P. D. Ohlsson, O. Ordeig, and J. P. Kutter, “Cyclic olefin polymers: emerging materials for lab-on-a-chip applications,” Microfluid. Nanofluid. 9(2-3), 145–161 (2010).
    [Crossref]
  18. M. Rosenberger, S. Hessler, S. Belle, B. Schmauss, and R. Hellmann, “Fabrication and characterization of planar Bragg gratings in TOPAS polymer substrates,” Sensors and Actuators A: Physical 221, 148–153 (2015).
    [Crossref]
  19. S. Kefer, T. Sauer, S. Hessler, M. Kaloudis, and R. Hellmann, “Microstructure-based fiber-to-chip coupling of polymer planar Bragg gratings for harsh environment applications,” Sensors 20(19), 5452 (2020).
    [Crossref]
  20. M. Rosenberger, S. Kefer, M. Girschikofsky, G.-L. Roth, S. Hessler, S. Belle, B. Schmauss, and R. Hellmann, “High-temperature stable and sterilizable waveguide Bragg grating in planar cyclo-olefin copolymer,” Opt. Lett. 43(14), 3321–3324 (2018).
    [Crossref]
  21. M. Rosenberger, B. Schmauss, and R. Hellmann, “Influence of the UV dosage on planar Bragg gratings in cyclo-olefin copolymer substrates,” Opt. Mater. Express 6(6), 2118 (2016).
    [Crossref]
  22. S. Hessler, M. Rosenberger, B. Schmauss, and R. Hellmann, “Two-dimensional interferometric characterization of laser-induced refractive index profiles in bulk Topas polymer,” Optical Materials 75, 230–235 (2018).
    [Crossref]
  23. G.-L. Roth, S. Hessler, S. Kefer, M. Girschikofsky, C. Esen, and R. Hellmann, “Femtosecond laser inscription of waveguides and Bragg gratings in transparent cyclic olefin copolymers,” Opt. Express 28(12), 18077 (2020).
    [Crossref]
  24. G.-L. Roth, J. Haubner, S. Kefer, C. Esen, and R. Hellmann, “Fs-laser based hybrid micromachining for polymer micro-opto electrical systems,” Optics and Lasers in Engineering 137, 106362 (2021).
    [Crossref]
  25. D. J. Guckenberger, T. E. de Groot, A. M. D. Wan, D. J. Beebe, and E. W. K. Young, “Micromilling: a method for ultra-rapid prototyping of plastic microfluidic devices,” Lab Chip 15(11), 2364–2378 (2015).
    [Crossref]
  26. F. Bundgaard, G. Perozziello, and O. Geschke, “Rapid prototyping tools and methods for all-Topas® cyclic olefin copolymer fluidic microsystems,” Proc. Inst. Mech. Eng., Part C 220(11), 1625–1632 (2006).
    [Crossref]
  27. F. Bundgaard, Prototyping of Microfluidic Systems with Integrated Waveguides in Cyclic Olefin Copolymer (COC) (Technical University of Denmark, 2006).
  28. L. O’Toole, C.-W. Kang, and F.-Z. Fang, “Precision micro-milling process: state of the art,” Adv. Manuf., (2020).
  29. B. Z. Balázs, N. Geier, M. Takács, and J. P. Davim, “A review on micro-milling: recent advances and future trends,” Int J Adv Manuf Technol 112(3-4), 655–684 (2021).
    [Crossref]
  30. M. A. Câmara, J. C. Rubio, A. M. Abrão, and J. P. Davim, “State of the art on micromilling of materials, a review,” J. Mater. Sci. Technol. 28(8), 673–685 (2012).
    [Crossref]
  31. M. Kahrizi, ed., Micromachining Techniques for Fabrication of Micro and Nano Structures, 1st ed. (InTech, 2011).
  32. H. Baghsiahi, K. Wang, W. Kandulski, R. C. A. Pitwon, and D. R. Selviah, “Optical waveguide end facet roughness and optical coupling loss,” J. Lightwave Technol. 31, 2659–2668 (2013).
    [Crossref]
  33. H. A. Youssef and H. El-Hofy, Machining Technology: Machine Tools and Operations, 1st ed. (CRC Press, 2008).
    [Crossref]
  34. R. K. Rajput, A Textbook of Manufacturing Technology: Manufacturing processes for B.E./B. Tech., A.M.I.E.-Section B, and Competitive Examinations, 2nd ed. (Laxmi Publications (P) LTD, 2015).
  35. R. Leach, Characterisation of Areal Surface Texture (Springer, 2013).
    [Crossref]
  36. J. Ahmad, Machining of Polymer Composites, 1st ed. (Springer US, 2009).
    [Crossref]
  37. E. Korkmaz, R. Onler, and O. B. Ozdoganlar, “Micromilling of poly(methyl methacrylate, PMMA) using single-crystal diamond tools,” Procedia Manufacturing 10, 683–693 (2017).
    [Crossref]
  38. D. Adeniji, J. Schoop, S. Gunawardena, C. Hanson, and M. Jahan, “Characterization and modeling of surface roughness and Burr formation in slot milling of polycarbonate,” J. Manuf. Mater. Process. 4, 59 (2020).
    [Crossref]
  39. K. Okamoto, Fundamentals of Optical Waveguides, 2nd ed. (Elsevier/Academic Press,2006).
  40. R. Kashyap, Fiber Bragg Gratings, 2nd ed. (Academic Press, 2010).
  41. Z. Zhang, P. Zhao, P. Lin, and F. Sun, “Thermo-optic coefficients of polymers for optical waveguide applications,” Polymer 47(14), 4893–4896 (2006).
    [Crossref]
  42. S. Kefer, K. Bischoff, G.-L. Roth, J. Haubner, B. Schmauss, and R. Hellmann, “Tunable bulk polymer planar Bragg gratings electrified via femtosecond laser reductive sintering of CuO Nanoparticles,” Adv. Optical Mater. 4, 2002203 (2021).
    [Crossref]
  43. G.-L. Roth, S. Kefer, S. Hessler, C. Esen, and R. Hellmann, “Integration of microfluidic and photonic components within transparent cyclic olefin copolymers by using fs laser,” JLMN 16, 47 (2021).
    [Crossref]
  44. M. R. Islam, M. M. Ali, M.-H. Lai, K.-S. Lim, and H. Ahmad, “Chronology of Fabry-Perot interferometer fiber-optic sensors and their applications: a review,” Sensors 14(4), 7451–7488 (2014).
    [Crossref]
  45. H. F. Taylor, Fiber Optic Sensors Based upon the Fabry-Perot Interferometer, S. Yin, P. B. Ruffin, and F. T. S. Yu, eds. (CRC Press, 2017), pp. 35–64.
  46. S. Pevec and D. Donlagic, “Miniature fiber-optic Fabry-Perot refractive index sensor for gas sensing with a resolution of 5 × 10−9 RIU,” Opt. Express 26(18), 23868–23882 (2018).
    [Crossref]

2021 (4)

G.-L. Roth, J. Haubner, S. Kefer, C. Esen, and R. Hellmann, “Fs-laser based hybrid micromachining for polymer micro-opto electrical systems,” Optics and Lasers in Engineering 137, 106362 (2021).
[Crossref]

B. Z. Balázs, N. Geier, M. Takács, and J. P. Davim, “A review on micro-milling: recent advances and future trends,” Int J Adv Manuf Technol 112(3-4), 655–684 (2021).
[Crossref]

S. Kefer, K. Bischoff, G.-L. Roth, J. Haubner, B. Schmauss, and R. Hellmann, “Tunable bulk polymer planar Bragg gratings electrified via femtosecond laser reductive sintering of CuO Nanoparticles,” Adv. Optical Mater. 4, 2002203 (2021).
[Crossref]

G.-L. Roth, S. Kefer, S. Hessler, C. Esen, and R. Hellmann, “Integration of microfluidic and photonic components within transparent cyclic olefin copolymers by using fs laser,” JLMN 16, 47 (2021).
[Crossref]

2020 (5)

2019 (2)

M. Girschikofsky, D. Ryvlin, S. R. Waldvogel, and R. Hellmann, “Optical sensor for real-time detection of trichlorofluoromethane,” Sensors 19(3), 632 (2019).
[Crossref]

S. Hessler, P. Bott, S. Kefer, B. Schmauss, and R. Hellmann, “Multipurpose polymer Bragg grating-based optomechanical sensor pad,” Sensors 19(19), 4101 (2019).
[Crossref]

2018 (4)

J. Missinne, N. Teigell Benéitez, M.-A. Mattelin, A. Lamberti, G. Luyckx, W. van Paepegem, and G. van Steenberge, “Bragg-grating-based photonic strain and temperature sensor foils realized using imprinting and operating at very near infrared wavelengths,” Sensors 18(8), 2717 (2018).
[Crossref]

M. Rosenberger, S. Kefer, M. Girschikofsky, G.-L. Roth, S. Hessler, S. Belle, B. Schmauss, and R. Hellmann, “High-temperature stable and sterilizable waveguide Bragg grating in planar cyclo-olefin copolymer,” Opt. Lett. 43(14), 3321–3324 (2018).
[Crossref]

S. Hessler, M. Rosenberger, B. Schmauss, and R. Hellmann, “Two-dimensional interferometric characterization of laser-induced refractive index profiles in bulk Topas polymer,” Optical Materials 75, 230–235 (2018).
[Crossref]

S. Pevec and D. Donlagic, “Miniature fiber-optic Fabry-Perot refractive index sensor for gas sensing with a resolution of 5 × 10−9 RIU,” Opt. Express 26(18), 23868–23882 (2018).
[Crossref]

2017 (2)

E. Korkmaz, R. Onler, and O. B. Ozdoganlar, “Micromilling of poly(methyl methacrylate, PMMA) using single-crystal diamond tools,” Procedia Manufacturing 10, 683–693 (2017).
[Crossref]

M. Girschikofsky, M. Rosenberger, M. Förthner, M. Rommel, L. Frey, and R. Hellmann, “Waveguide Bragg gratings in Ormocer®s for temperature sensing,” Sensors 17(11), 2459 (2017).
[Crossref]

2016 (2)

M. Foerthner, M. Rumler, F. Stumpf, R. Fader, M. Rommel, L. Frey, M. Girschikofsky, S. Belle, R. Hellmann, and J. J. Klein, “Hybrid polymers processed by substrate conformal imprint lithography for the fabrication of planar Bragg gratings,” Appl. Phys. A 122(3), 240 (2016).
[Crossref]

M. Rosenberger, B. Schmauss, and R. Hellmann, “Influence of the UV dosage on planar Bragg gratings in cyclo-olefin copolymer substrates,” Opt. Mater. Express 6(6), 2118 (2016).
[Crossref]

2015 (4)

M. Rosenberger, S. Hessler, S. Belle, B. Schmauss, and R. Hellmann, “Fabrication and characterization of planar Bragg gratings in TOPAS polymer substrates,” Sensors and Actuators A: Physical 221, 148–153 (2015).
[Crossref]

D. J. Webb, “Fibre Bragg grating sensors in polymer optical fibres,” Meas. Sci. Technol. 26(9), 092004 (2015).
[Crossref]

M. Rosenberger, W. Eisenbeil, B. Schmauss, and R. Hellmann, “Simultaneous 2D strain sensing using polymer planar Bragg gratings,” Sensors 15(2), 4264–4272 (2015).
[Crossref]

D. J. Guckenberger, T. E. de Groot, A. M. D. Wan, D. J. Beebe, and E. W. K. Young, “Micromilling: a method for ultra-rapid prototyping of plastic microfluidic devices,” Lab Chip 15(11), 2364–2378 (2015).
[Crossref]

2014 (2)

M. R. Islam, M. M. Ali, M.-H. Lai, K.-S. Lim, and H. Ahmad, “Chronology of Fabry-Perot interferometer fiber-optic sensors and their applications: a review,” Sensors 14(4), 7451–7488 (2014).
[Crossref]

M. Rosenberger, S. Hessler, S. Belle, B. Schmauss, and R. Hellmann, “Humidity-induced effects on polymer planar Bragg gratings,” IEEE Photon. Technol. Lett. 26(16), 1669–1671 (2014).
[Crossref]

2013 (2)

T. Guan, G. Keulemans, F. Ceyssens, and R. Puers, “MOEMS uniaxial accelerometer based on EpoClad/EpoCore photoresists with built-in fiber clamp,” Sensors and Actuators A: Physical 193, 95–102 (2013).
[Crossref]

H. Baghsiahi, K. Wang, W. Kandulski, R. C. A. Pitwon, and D. R. Selviah, “Optical waveguide end facet roughness and optical coupling loss,” J. Lightwave Technol. 31, 2659–2668 (2013).
[Crossref]

2012 (2)

M. A. Câmara, J. C. Rubio, A. M. Abrão, and J. P. Davim, “State of the art on micromilling of materials, a review,” J. Mater. Sci. Technol. 28(8), 673–685 (2012).
[Crossref]

M. Rosenberger, G. Koller, S. Belle, B. Schmauss, and R. Hellmann, “Planar Bragg grating in bulk polymethylmethacrylate,” Opt. Express 20(25), 27288–27296 (2012).
[Crossref]

2010 (1)

P. S. Nunes, P. D. Ohlsson, O. Ordeig, and J. P. Kutter, “Cyclic olefin polymers: emerging materials for lab-on-a-chip applications,” Microfluid. Nanofluid. 9(2-3), 145–161 (2010).
[Crossref]

2009 (1)

C. Wochnowski, “UV-laser-based fabrication of a planar, polymeric Bragg-structure,” Optics & Laser Technology 41(6), 734–740 (2009).
[Crossref]

2006 (2)

F. Bundgaard, G. Perozziello, and O. Geschke, “Rapid prototyping tools and methods for all-Topas® cyclic olefin copolymer fluidic microsystems,” Proc. Inst. Mech. Eng., Part C 220(11), 1625–1632 (2006).
[Crossref]

Z. Zhang, P. Zhao, P. Lin, and F. Sun, “Thermo-optic coefficients of polymers for optical waveguide applications,” Polymer 47(14), 4893–4896 (2006).
[Crossref]

2002 (1)

H. Ma, A.-Y. Jen, and L. R. Dalton, “Polymer-based optical waveguides: materials, processing, and devices,” Adv. Mater. 14(19), 1339–1365 (2002).
[Crossref]

2001 (1)

G. Khanarian, “Optical properties of cyclic olefin copolymers,” Opt. Eng. 40(6), 1024–1029 (2001).
[Crossref]

Abrão, A. M.

M. A. Câmara, J. C. Rubio, A. M. Abrão, and J. P. Davim, “State of the art on micromilling of materials, a review,” J. Mater. Sci. Technol. 28(8), 673–685 (2012).
[Crossref]

Adeniji, D.

D. Adeniji, J. Schoop, S. Gunawardena, C. Hanson, and M. Jahan, “Characterization and modeling of surface roughness and Burr formation in slot milling of polycarbonate,” J. Manuf. Mater. Process. 4, 59 (2020).
[Crossref]

Ahmad, H.

M. R. Islam, M. M. Ali, M.-H. Lai, K.-S. Lim, and H. Ahmad, “Chronology of Fabry-Perot interferometer fiber-optic sensors and their applications: a review,” Sensors 14(4), 7451–7488 (2014).
[Crossref]

Ahmad, J.

J. Ahmad, Machining of Polymer Composites, 1st ed. (Springer US, 2009).
[Crossref]

Ali, M. M.

M. R. Islam, M. M. Ali, M.-H. Lai, K.-S. Lim, and H. Ahmad, “Chronology of Fabry-Perot interferometer fiber-optic sensors and their applications: a review,” Sensors 14(4), 7451–7488 (2014).
[Crossref]

Baghsiahi, H.

H. Baghsiahi, K. Wang, W. Kandulski, R. C. A. Pitwon, and D. R. Selviah, “Optical waveguide end facet roughness and optical coupling loss,” J. Lightwave Technol. 31, 2659–2668 (2013).
[Crossref]

Balázs, B. Z.

B. Z. Balázs, N. Geier, M. Takács, and J. P. Davim, “A review on micro-milling: recent advances and future trends,” Int J Adv Manuf Technol 112(3-4), 655–684 (2021).
[Crossref]

Beebe, D. J.

D. J. Guckenberger, T. E. de Groot, A. M. D. Wan, D. J. Beebe, and E. W. K. Young, “Micromilling: a method for ultra-rapid prototyping of plastic microfluidic devices,” Lab Chip 15(11), 2364–2378 (2015).
[Crossref]

Belle, S.

M. Rosenberger, S. Kefer, M. Girschikofsky, G.-L. Roth, S. Hessler, S. Belle, B. Schmauss, and R. Hellmann, “High-temperature stable and sterilizable waveguide Bragg grating in planar cyclo-olefin copolymer,” Opt. Lett. 43(14), 3321–3324 (2018).
[Crossref]

M. Foerthner, M. Rumler, F. Stumpf, R. Fader, M. Rommel, L. Frey, M. Girschikofsky, S. Belle, R. Hellmann, and J. J. Klein, “Hybrid polymers processed by substrate conformal imprint lithography for the fabrication of planar Bragg gratings,” Appl. Phys. A 122(3), 240 (2016).
[Crossref]

M. Rosenberger, S. Hessler, S. Belle, B. Schmauss, and R. Hellmann, “Fabrication and characterization of planar Bragg gratings in TOPAS polymer substrates,” Sensors and Actuators A: Physical 221, 148–153 (2015).
[Crossref]

M. Rosenberger, S. Hessler, S. Belle, B. Schmauss, and R. Hellmann, “Humidity-induced effects on polymer planar Bragg gratings,” IEEE Photon. Technol. Lett. 26(16), 1669–1671 (2014).
[Crossref]

M. Rosenberger, G. Koller, S. Belle, B. Schmauss, and R. Hellmann, “Planar Bragg grating in bulk polymethylmethacrylate,” Opt. Express 20(25), 27288–27296 (2012).
[Crossref]

Bilro, L.

R. Oliveira, L. Bilro, and R. Nogueira, Polymer Optical Fiber Bragg Gratings: Fabrication and Sensing Applications, 1st ed. (CRC Press, 2020).

Bischoff, K.

S. Kefer, K. Bischoff, G.-L. Roth, J. Haubner, B. Schmauss, and R. Hellmann, “Tunable bulk polymer planar Bragg gratings electrified via femtosecond laser reductive sintering of CuO Nanoparticles,” Adv. Optical Mater. 4, 2002203 (2021).
[Crossref]

Bott, P.

S. Hessler, P. Bott, S. Kefer, B. Schmauss, and R. Hellmann, “Multipurpose polymer Bragg grating-based optomechanical sensor pad,” Sensors 19(19), 4101 (2019).
[Crossref]

Bundgaard, F.

F. Bundgaard, G. Perozziello, and O. Geschke, “Rapid prototyping tools and methods for all-Topas® cyclic olefin copolymer fluidic microsystems,” Proc. Inst. Mech. Eng., Part C 220(11), 1625–1632 (2006).
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F. Bundgaard, Prototyping of Microfluidic Systems with Integrated Waveguides in Cyclic Olefin Copolymer (COC) (Technical University of Denmark, 2006).

Câmara, M. A.

M. A. Câmara, J. C. Rubio, A. M. Abrão, and J. P. Davim, “State of the art on micromilling of materials, a review,” J. Mater. Sci. Technol. 28(8), 673–685 (2012).
[Crossref]

Ceyssens, F.

T. Guan, G. Keulemans, F. Ceyssens, and R. Puers, “MOEMS uniaxial accelerometer based on EpoClad/EpoCore photoresists with built-in fiber clamp,” Sensors and Actuators A: Physical 193, 95–102 (2013).
[Crossref]

Dai, J.

Dalton, L. R.

H. Ma, A.-Y. Jen, and L. R. Dalton, “Polymer-based optical waveguides: materials, processing, and devices,” Adv. Mater. 14(19), 1339–1365 (2002).
[Crossref]

Davim, J. P.

B. Z. Balázs, N. Geier, M. Takács, and J. P. Davim, “A review on micro-milling: recent advances and future trends,” Int J Adv Manuf Technol 112(3-4), 655–684 (2021).
[Crossref]

M. A. Câmara, J. C. Rubio, A. M. Abrão, and J. P. Davim, “State of the art on micromilling of materials, a review,” J. Mater. Sci. Technol. 28(8), 673–685 (2012).
[Crossref]

de Groot, T. E.

D. J. Guckenberger, T. E. de Groot, A. M. D. Wan, D. J. Beebe, and E. W. K. Young, “Micromilling: a method for ultra-rapid prototyping of plastic microfluidic devices,” Lab Chip 15(11), 2364–2378 (2015).
[Crossref]

Donlagic, D.

Eisenbeil, W.

M. Rosenberger, W. Eisenbeil, B. Schmauss, and R. Hellmann, “Simultaneous 2D strain sensing using polymer planar Bragg gratings,” Sensors 15(2), 4264–4272 (2015).
[Crossref]

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H. A. Youssef and H. El-Hofy, Machining Technology: Machine Tools and Operations, 1st ed. (CRC Press, 2008).
[Crossref]

Esen, C.

G.-L. Roth, J. Haubner, S. Kefer, C. Esen, and R. Hellmann, “Fs-laser based hybrid micromachining for polymer micro-opto electrical systems,” Optics and Lasers in Engineering 137, 106362 (2021).
[Crossref]

G.-L. Roth, S. Kefer, S. Hessler, C. Esen, and R. Hellmann, “Integration of microfluidic and photonic components within transparent cyclic olefin copolymers by using fs laser,” JLMN 16, 47 (2021).
[Crossref]

G.-L. Roth, S. Hessler, S. Kefer, M. Girschikofsky, C. Esen, and R. Hellmann, “Femtosecond laser inscription of waveguides and Bragg gratings in transparent cyclic olefin copolymers,” Opt. Express 28(12), 18077 (2020).
[Crossref]

Fader, R.

M. Foerthner, M. Rumler, F. Stumpf, R. Fader, M. Rommel, L. Frey, M. Girschikofsky, S. Belle, R. Hellmann, and J. J. Klein, “Hybrid polymers processed by substrate conformal imprint lithography for the fabrication of planar Bragg gratings,” Appl. Phys. A 122(3), 240 (2016).
[Crossref]

Fang, F.-Z.

L. O’Toole, C.-W. Kang, and F.-Z. Fang, “Precision micro-milling process: state of the art,” Adv. Manuf., (2020).

Foerthner, M.

M. Foerthner, M. Rumler, F. Stumpf, R. Fader, M. Rommel, L. Frey, M. Girschikofsky, S. Belle, R. Hellmann, and J. J. Klein, “Hybrid polymers processed by substrate conformal imprint lithography for the fabrication of planar Bragg gratings,” Appl. Phys. A 122(3), 240 (2016).
[Crossref]

Förthner, M.

M. Girschikofsky, M. Rosenberger, M. Förthner, M. Rommel, L. Frey, and R. Hellmann, “Waveguide Bragg gratings in Ormocer®s for temperature sensing,” Sensors 17(11), 2459 (2017).
[Crossref]

Frey, L.

M. Girschikofsky, M. Rosenberger, M. Förthner, M. Rommel, L. Frey, and R. Hellmann, “Waveguide Bragg gratings in Ormocer®s for temperature sensing,” Sensors 17(11), 2459 (2017).
[Crossref]

M. Foerthner, M. Rumler, F. Stumpf, R. Fader, M. Rommel, L. Frey, M. Girschikofsky, S. Belle, R. Hellmann, and J. J. Klein, “Hybrid polymers processed by substrate conformal imprint lithography for the fabrication of planar Bragg gratings,” Appl. Phys. A 122(3), 240 (2016).
[Crossref]

Geier, N.

B. Z. Balázs, N. Geier, M. Takács, and J. P. Davim, “A review on micro-milling: recent advances and future trends,” Int J Adv Manuf Technol 112(3-4), 655–684 (2021).
[Crossref]

Geschke, O.

F. Bundgaard, G. Perozziello, and O. Geschke, “Rapid prototyping tools and methods for all-Topas® cyclic olefin copolymer fluidic microsystems,” Proc. Inst. Mech. Eng., Part C 220(11), 1625–1632 (2006).
[Crossref]

Girschikofsky, M.

G.-L. Roth, S. Hessler, S. Kefer, M. Girschikofsky, C. Esen, and R. Hellmann, “Femtosecond laser inscription of waveguides and Bragg gratings in transparent cyclic olefin copolymers,” Opt. Express 28(12), 18077 (2020).
[Crossref]

S. Hessler, S. Knopf, M. Rommel, M. Girschikofsky, B. Schmauss, and R. Hellmann, “Advancing the sensitivity of integrated epoxy-based Bragg grating refractometry by high-index nanolayers,” Opt. Lett. 45, 5510–5513 (2020).
[Crossref]

M. Girschikofsky, D. Ryvlin, S. R. Waldvogel, and R. Hellmann, “Optical sensor for real-time detection of trichlorofluoromethane,” Sensors 19(3), 632 (2019).
[Crossref]

M. Rosenberger, S. Kefer, M. Girschikofsky, G.-L. Roth, S. Hessler, S. Belle, B. Schmauss, and R. Hellmann, “High-temperature stable and sterilizable waveguide Bragg grating in planar cyclo-olefin copolymer,” Opt. Lett. 43(14), 3321–3324 (2018).
[Crossref]

M. Girschikofsky, M. Rosenberger, M. Förthner, M. Rommel, L. Frey, and R. Hellmann, “Waveguide Bragg gratings in Ormocer®s for temperature sensing,” Sensors 17(11), 2459 (2017).
[Crossref]

M. Foerthner, M. Rumler, F. Stumpf, R. Fader, M. Rommel, L. Frey, M. Girschikofsky, S. Belle, R. Hellmann, and J. J. Klein, “Hybrid polymers processed by substrate conformal imprint lithography for the fabrication of planar Bragg gratings,” Appl. Phys. A 122(3), 240 (2016).
[Crossref]

Guan, T.

T. Guan, G. Keulemans, F. Ceyssens, and R. Puers, “MOEMS uniaxial accelerometer based on EpoClad/EpoCore photoresists with built-in fiber clamp,” Sensors and Actuators A: Physical 193, 95–102 (2013).
[Crossref]

Guckenberger, D. J.

D. J. Guckenberger, T. E. de Groot, A. M. D. Wan, D. J. Beebe, and E. W. K. Young, “Micromilling: a method for ultra-rapid prototyping of plastic microfluidic devices,” Lab Chip 15(11), 2364–2378 (2015).
[Crossref]

Gunawardena, S.

D. Adeniji, J. Schoop, S. Gunawardena, C. Hanson, and M. Jahan, “Characterization and modeling of surface roughness and Burr formation in slot milling of polycarbonate,” J. Manuf. Mater. Process. 4, 59 (2020).
[Crossref]

Hanson, C.

D. Adeniji, J. Schoop, S. Gunawardena, C. Hanson, and M. Jahan, “Characterization and modeling of surface roughness and Burr formation in slot milling of polycarbonate,” J. Manuf. Mater. Process. 4, 59 (2020).
[Crossref]

Haubner, J.

S. Kefer, K. Bischoff, G.-L. Roth, J. Haubner, B. Schmauss, and R. Hellmann, “Tunable bulk polymer planar Bragg gratings electrified via femtosecond laser reductive sintering of CuO Nanoparticles,” Adv. Optical Mater. 4, 2002203 (2021).
[Crossref]

G.-L. Roth, J. Haubner, S. Kefer, C. Esen, and R. Hellmann, “Fs-laser based hybrid micromachining for polymer micro-opto electrical systems,” Optics and Lasers in Engineering 137, 106362 (2021).
[Crossref]

Hellmann, R.

G.-L. Roth, J. Haubner, S. Kefer, C. Esen, and R. Hellmann, “Fs-laser based hybrid micromachining for polymer micro-opto electrical systems,” Optics and Lasers in Engineering 137, 106362 (2021).
[Crossref]

S. Kefer, K. Bischoff, G.-L. Roth, J. Haubner, B. Schmauss, and R. Hellmann, “Tunable bulk polymer planar Bragg gratings electrified via femtosecond laser reductive sintering of CuO Nanoparticles,” Adv. Optical Mater. 4, 2002203 (2021).
[Crossref]

G.-L. Roth, S. Kefer, S. Hessler, C. Esen, and R. Hellmann, “Integration of microfluidic and photonic components within transparent cyclic olefin copolymers by using fs laser,” JLMN 16, 47 (2021).
[Crossref]

S. Kefer, T. Sauer, S. Hessler, M. Kaloudis, and R. Hellmann, “Microstructure-based fiber-to-chip coupling of polymer planar Bragg gratings for harsh environment applications,” Sensors 20(19), 5452 (2020).
[Crossref]

G.-L. Roth, S. Hessler, S. Kefer, M. Girschikofsky, C. Esen, and R. Hellmann, “Femtosecond laser inscription of waveguides and Bragg gratings in transparent cyclic olefin copolymers,” Opt. Express 28(12), 18077 (2020).
[Crossref]

S. Hessler, S. Knopf, M. Rommel, M. Girschikofsky, B. Schmauss, and R. Hellmann, “Advancing the sensitivity of integrated epoxy-based Bragg grating refractometry by high-index nanolayers,” Opt. Lett. 45, 5510–5513 (2020).
[Crossref]

S. Kefer, J. Dai, M. Yang, B. Schmauss, and R. Hellmann, “Hypersensitive H2 sensor based on polymer planar Bragg gratings coated with Pt-Loaded WO3-SiO2,” Opt. Lett. 45(13), 3601–3604 (2020).
[Crossref]

M. Girschikofsky, D. Ryvlin, S. R. Waldvogel, and R. Hellmann, “Optical sensor for real-time detection of trichlorofluoromethane,” Sensors 19(3), 632 (2019).
[Crossref]

S. Hessler, P. Bott, S. Kefer, B. Schmauss, and R. Hellmann, “Multipurpose polymer Bragg grating-based optomechanical sensor pad,” Sensors 19(19), 4101 (2019).
[Crossref]

M. Rosenberger, S. Kefer, M. Girschikofsky, G.-L. Roth, S. Hessler, S. Belle, B. Schmauss, and R. Hellmann, “High-temperature stable and sterilizable waveguide Bragg grating in planar cyclo-olefin copolymer,” Opt. Lett. 43(14), 3321–3324 (2018).
[Crossref]

S. Hessler, M. Rosenberger, B. Schmauss, and R. Hellmann, “Two-dimensional interferometric characterization of laser-induced refractive index profiles in bulk Topas polymer,” Optical Materials 75, 230–235 (2018).
[Crossref]

M. Girschikofsky, M. Rosenberger, M. Förthner, M. Rommel, L. Frey, and R. Hellmann, “Waveguide Bragg gratings in Ormocer®s for temperature sensing,” Sensors 17(11), 2459 (2017).
[Crossref]

M. Foerthner, M. Rumler, F. Stumpf, R. Fader, M. Rommel, L. Frey, M. Girschikofsky, S. Belle, R. Hellmann, and J. J. Klein, “Hybrid polymers processed by substrate conformal imprint lithography for the fabrication of planar Bragg gratings,” Appl. Phys. A 122(3), 240 (2016).
[Crossref]

M. Rosenberger, B. Schmauss, and R. Hellmann, “Influence of the UV dosage on planar Bragg gratings in cyclo-olefin copolymer substrates,” Opt. Mater. Express 6(6), 2118 (2016).
[Crossref]

M. Rosenberger, S. Hessler, S. Belle, B. Schmauss, and R. Hellmann, “Fabrication and characterization of planar Bragg gratings in TOPAS polymer substrates,” Sensors and Actuators A: Physical 221, 148–153 (2015).
[Crossref]

M. Rosenberger, W. Eisenbeil, B. Schmauss, and R. Hellmann, “Simultaneous 2D strain sensing using polymer planar Bragg gratings,” Sensors 15(2), 4264–4272 (2015).
[Crossref]

M. Rosenberger, S. Hessler, S. Belle, B. Schmauss, and R. Hellmann, “Humidity-induced effects on polymer planar Bragg gratings,” IEEE Photon. Technol. Lett. 26(16), 1669–1671 (2014).
[Crossref]

M. Rosenberger, G. Koller, S. Belle, B. Schmauss, and R. Hellmann, “Planar Bragg grating in bulk polymethylmethacrylate,” Opt. Express 20(25), 27288–27296 (2012).
[Crossref]

Hessler, S.

G.-L. Roth, S. Kefer, S. Hessler, C. Esen, and R. Hellmann, “Integration of microfluidic and photonic components within transparent cyclic olefin copolymers by using fs laser,” JLMN 16, 47 (2021).
[Crossref]

S. Hessler, S. Knopf, M. Rommel, M. Girschikofsky, B. Schmauss, and R. Hellmann, “Advancing the sensitivity of integrated epoxy-based Bragg grating refractometry by high-index nanolayers,” Opt. Lett. 45, 5510–5513 (2020).
[Crossref]

S. Kefer, T. Sauer, S. Hessler, M. Kaloudis, and R. Hellmann, “Microstructure-based fiber-to-chip coupling of polymer planar Bragg gratings for harsh environment applications,” Sensors 20(19), 5452 (2020).
[Crossref]

G.-L. Roth, S. Hessler, S. Kefer, M. Girschikofsky, C. Esen, and R. Hellmann, “Femtosecond laser inscription of waveguides and Bragg gratings in transparent cyclic olefin copolymers,” Opt. Express 28(12), 18077 (2020).
[Crossref]

S. Hessler, P. Bott, S. Kefer, B. Schmauss, and R. Hellmann, “Multipurpose polymer Bragg grating-based optomechanical sensor pad,” Sensors 19(19), 4101 (2019).
[Crossref]

S. Hessler, M. Rosenberger, B. Schmauss, and R. Hellmann, “Two-dimensional interferometric characterization of laser-induced refractive index profiles in bulk Topas polymer,” Optical Materials 75, 230–235 (2018).
[Crossref]

M. Rosenberger, S. Kefer, M. Girschikofsky, G.-L. Roth, S. Hessler, S. Belle, B. Schmauss, and R. Hellmann, “High-temperature stable and sterilizable waveguide Bragg grating in planar cyclo-olefin copolymer,” Opt. Lett. 43(14), 3321–3324 (2018).
[Crossref]

M. Rosenberger, S. Hessler, S. Belle, B. Schmauss, and R. Hellmann, “Fabrication and characterization of planar Bragg gratings in TOPAS polymer substrates,” Sensors and Actuators A: Physical 221, 148–153 (2015).
[Crossref]

M. Rosenberger, S. Hessler, S. Belle, B. Schmauss, and R. Hellmann, “Humidity-induced effects on polymer planar Bragg gratings,” IEEE Photon. Technol. Lett. 26(16), 1669–1671 (2014).
[Crossref]

Islam, M. R.

M. R. Islam, M. M. Ali, M.-H. Lai, K.-S. Lim, and H. Ahmad, “Chronology of Fabry-Perot interferometer fiber-optic sensors and their applications: a review,” Sensors 14(4), 7451–7488 (2014).
[Crossref]

Jahan, M.

D. Adeniji, J. Schoop, S. Gunawardena, C. Hanson, and M. Jahan, “Characterization and modeling of surface roughness and Burr formation in slot milling of polycarbonate,” J. Manuf. Mater. Process. 4, 59 (2020).
[Crossref]

Jen, A.-Y.

H. Ma, A.-Y. Jen, and L. R. Dalton, “Polymer-based optical waveguides: materials, processing, and devices,” Adv. Mater. 14(19), 1339–1365 (2002).
[Crossref]

Kaloudis, M.

S. Kefer, T. Sauer, S. Hessler, M. Kaloudis, and R. Hellmann, “Microstructure-based fiber-to-chip coupling of polymer planar Bragg gratings for harsh environment applications,” Sensors 20(19), 5452 (2020).
[Crossref]

Kandulski, W.

H. Baghsiahi, K. Wang, W. Kandulski, R. C. A. Pitwon, and D. R. Selviah, “Optical waveguide end facet roughness and optical coupling loss,” J. Lightwave Technol. 31, 2659–2668 (2013).
[Crossref]

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L. O’Toole, C.-W. Kang, and F.-Z. Fang, “Precision micro-milling process: state of the art,” Adv. Manuf., (2020).

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R. Kashyap, Fiber Bragg Gratings, 2nd ed. (Academic Press, 2010).

Kefer, S.

S. Kefer, K. Bischoff, G.-L. Roth, J. Haubner, B. Schmauss, and R. Hellmann, “Tunable bulk polymer planar Bragg gratings electrified via femtosecond laser reductive sintering of CuO Nanoparticles,” Adv. Optical Mater. 4, 2002203 (2021).
[Crossref]

G.-L. Roth, S. Kefer, S. Hessler, C. Esen, and R. Hellmann, “Integration of microfluidic and photonic components within transparent cyclic olefin copolymers by using fs laser,” JLMN 16, 47 (2021).
[Crossref]

G.-L. Roth, J. Haubner, S. Kefer, C. Esen, and R. Hellmann, “Fs-laser based hybrid micromachining for polymer micro-opto electrical systems,” Optics and Lasers in Engineering 137, 106362 (2021).
[Crossref]

S. Kefer, T. Sauer, S. Hessler, M. Kaloudis, and R. Hellmann, “Microstructure-based fiber-to-chip coupling of polymer planar Bragg gratings for harsh environment applications,” Sensors 20(19), 5452 (2020).
[Crossref]

G.-L. Roth, S. Hessler, S. Kefer, M. Girschikofsky, C. Esen, and R. Hellmann, “Femtosecond laser inscription of waveguides and Bragg gratings in transparent cyclic olefin copolymers,” Opt. Express 28(12), 18077 (2020).
[Crossref]

S. Kefer, J. Dai, M. Yang, B. Schmauss, and R. Hellmann, “Hypersensitive H2 sensor based on polymer planar Bragg gratings coated with Pt-Loaded WO3-SiO2,” Opt. Lett. 45(13), 3601–3604 (2020).
[Crossref]

S. Hessler, P. Bott, S. Kefer, B. Schmauss, and R. Hellmann, “Multipurpose polymer Bragg grating-based optomechanical sensor pad,” Sensors 19(19), 4101 (2019).
[Crossref]

M. Rosenberger, S. Kefer, M. Girschikofsky, G.-L. Roth, S. Hessler, S. Belle, B. Schmauss, and R. Hellmann, “High-temperature stable and sterilizable waveguide Bragg grating in planar cyclo-olefin copolymer,” Opt. Lett. 43(14), 3321–3324 (2018).
[Crossref]

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T. Guan, G. Keulemans, F. Ceyssens, and R. Puers, “MOEMS uniaxial accelerometer based on EpoClad/EpoCore photoresists with built-in fiber clamp,” Sensors and Actuators A: Physical 193, 95–102 (2013).
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M. Foerthner, M. Rumler, F. Stumpf, R. Fader, M. Rommel, L. Frey, M. Girschikofsky, S. Belle, R. Hellmann, and J. J. Klein, “Hybrid polymers processed by substrate conformal imprint lithography for the fabrication of planar Bragg gratings,” Appl. Phys. A 122(3), 240 (2016).
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Knopf, S.

Koller, G.

Korkmaz, E.

E. Korkmaz, R. Onler, and O. B. Ozdoganlar, “Micromilling of poly(methyl methacrylate, PMMA) using single-crystal diamond tools,” Procedia Manufacturing 10, 683–693 (2017).
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P. S. Nunes, P. D. Ohlsson, O. Ordeig, and J. P. Kutter, “Cyclic olefin polymers: emerging materials for lab-on-a-chip applications,” Microfluid. Nanofluid. 9(2-3), 145–161 (2010).
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Lai, M.-H.

M. R. Islam, M. M. Ali, M.-H. Lai, K.-S. Lim, and H. Ahmad, “Chronology of Fabry-Perot interferometer fiber-optic sensors and their applications: a review,” Sensors 14(4), 7451–7488 (2014).
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J. Missinne, N. Teigell Benéitez, M.-A. Mattelin, A. Lamberti, G. Luyckx, W. van Paepegem, and G. van Steenberge, “Bragg-grating-based photonic strain and temperature sensor foils realized using imprinting and operating at very near infrared wavelengths,” Sensors 18(8), 2717 (2018).
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M. R. Islam, M. M. Ali, M.-H. Lai, K.-S. Lim, and H. Ahmad, “Chronology of Fabry-Perot interferometer fiber-optic sensors and their applications: a review,” Sensors 14(4), 7451–7488 (2014).
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[Crossref]

Ma, H.

H. Ma, A.-Y. Jen, and L. R. Dalton, “Polymer-based optical waveguides: materials, processing, and devices,” Adv. Mater. 14(19), 1339–1365 (2002).
[Crossref]

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J. Missinne, N. Teigell Benéitez, M.-A. Mattelin, A. Lamberti, G. Luyckx, W. van Paepegem, and G. van Steenberge, “Bragg-grating-based photonic strain and temperature sensor foils realized using imprinting and operating at very near infrared wavelengths,” Sensors 18(8), 2717 (2018).
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J. Missinne, N. Teigell Benéitez, M.-A. Mattelin, A. Lamberti, G. Luyckx, W. van Paepegem, and G. van Steenberge, “Bragg-grating-based photonic strain and temperature sensor foils realized using imprinting and operating at very near infrared wavelengths,” Sensors 18(8), 2717 (2018).
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P. S. Nunes, P. D. Ohlsson, O. Ordeig, and J. P. Kutter, “Cyclic olefin polymers: emerging materials for lab-on-a-chip applications,” Microfluid. Nanofluid. 9(2-3), 145–161 (2010).
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L. O’Toole, C.-W. Kang, and F.-Z. Fang, “Precision micro-milling process: state of the art,” Adv. Manuf., (2020).

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P. S. Nunes, P. D. Ohlsson, O. Ordeig, and J. P. Kutter, “Cyclic olefin polymers: emerging materials for lab-on-a-chip applications,” Microfluid. Nanofluid. 9(2-3), 145–161 (2010).
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R. Oliveira, L. Bilro, and R. Nogueira, Polymer Optical Fiber Bragg Gratings: Fabrication and Sensing Applications, 1st ed. (CRC Press, 2020).

Onler, R.

E. Korkmaz, R. Onler, and O. B. Ozdoganlar, “Micromilling of poly(methyl methacrylate, PMMA) using single-crystal diamond tools,” Procedia Manufacturing 10, 683–693 (2017).
[Crossref]

Ordeig, O.

P. S. Nunes, P. D. Ohlsson, O. Ordeig, and J. P. Kutter, “Cyclic olefin polymers: emerging materials for lab-on-a-chip applications,” Microfluid. Nanofluid. 9(2-3), 145–161 (2010).
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E. Korkmaz, R. Onler, and O. B. Ozdoganlar, “Micromilling of poly(methyl methacrylate, PMMA) using single-crystal diamond tools,” Procedia Manufacturing 10, 683–693 (2017).
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F. Bundgaard, G. Perozziello, and O. Geschke, “Rapid prototyping tools and methods for all-Topas® cyclic olefin copolymer fluidic microsystems,” Proc. Inst. Mech. Eng., Part C 220(11), 1625–1632 (2006).
[Crossref]

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Pitwon, R. C. A.

H. Baghsiahi, K. Wang, W. Kandulski, R. C. A. Pitwon, and D. R. Selviah, “Optical waveguide end facet roughness and optical coupling loss,” J. Lightwave Technol. 31, 2659–2668 (2013).
[Crossref]

Puers, R.

T. Guan, G. Keulemans, F. Ceyssens, and R. Puers, “MOEMS uniaxial accelerometer based on EpoClad/EpoCore photoresists with built-in fiber clamp,” Sensors and Actuators A: Physical 193, 95–102 (2013).
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S. Hessler, S. Knopf, M. Rommel, M. Girschikofsky, B. Schmauss, and R. Hellmann, “Advancing the sensitivity of integrated epoxy-based Bragg grating refractometry by high-index nanolayers,” Opt. Lett. 45, 5510–5513 (2020).
[Crossref]

M. Girschikofsky, M. Rosenberger, M. Förthner, M. Rommel, L. Frey, and R. Hellmann, “Waveguide Bragg gratings in Ormocer®s for temperature sensing,” Sensors 17(11), 2459 (2017).
[Crossref]

M. Foerthner, M. Rumler, F. Stumpf, R. Fader, M. Rommel, L. Frey, M. Girschikofsky, S. Belle, R. Hellmann, and J. J. Klein, “Hybrid polymers processed by substrate conformal imprint lithography for the fabrication of planar Bragg gratings,” Appl. Phys. A 122(3), 240 (2016).
[Crossref]

Rosenberger, M.

M. Rosenberger, S. Kefer, M. Girschikofsky, G.-L. Roth, S. Hessler, S. Belle, B. Schmauss, and R. Hellmann, “High-temperature stable and sterilizable waveguide Bragg grating in planar cyclo-olefin copolymer,” Opt. Lett. 43(14), 3321–3324 (2018).
[Crossref]

S. Hessler, M. Rosenberger, B. Schmauss, and R. Hellmann, “Two-dimensional interferometric characterization of laser-induced refractive index profiles in bulk Topas polymer,” Optical Materials 75, 230–235 (2018).
[Crossref]

M. Girschikofsky, M. Rosenberger, M. Förthner, M. Rommel, L. Frey, and R. Hellmann, “Waveguide Bragg gratings in Ormocer®s for temperature sensing,” Sensors 17(11), 2459 (2017).
[Crossref]

M. Rosenberger, B. Schmauss, and R. Hellmann, “Influence of the UV dosage on planar Bragg gratings in cyclo-olefin copolymer substrates,” Opt. Mater. Express 6(6), 2118 (2016).
[Crossref]

M. Rosenberger, S. Hessler, S. Belle, B. Schmauss, and R. Hellmann, “Fabrication and characterization of planar Bragg gratings in TOPAS polymer substrates,” Sensors and Actuators A: Physical 221, 148–153 (2015).
[Crossref]

M. Rosenberger, W. Eisenbeil, B. Schmauss, and R. Hellmann, “Simultaneous 2D strain sensing using polymer planar Bragg gratings,” Sensors 15(2), 4264–4272 (2015).
[Crossref]

M. Rosenberger, S. Hessler, S. Belle, B. Schmauss, and R. Hellmann, “Humidity-induced effects on polymer planar Bragg gratings,” IEEE Photon. Technol. Lett. 26(16), 1669–1671 (2014).
[Crossref]

M. Rosenberger, G. Koller, S. Belle, B. Schmauss, and R. Hellmann, “Planar Bragg grating in bulk polymethylmethacrylate,” Opt. Express 20(25), 27288–27296 (2012).
[Crossref]

Roth, G.-L.

G.-L. Roth, J. Haubner, S. Kefer, C. Esen, and R. Hellmann, “Fs-laser based hybrid micromachining for polymer micro-opto electrical systems,” Optics and Lasers in Engineering 137, 106362 (2021).
[Crossref]

G.-L. Roth, S. Kefer, S. Hessler, C. Esen, and R. Hellmann, “Integration of microfluidic and photonic components within transparent cyclic olefin copolymers by using fs laser,” JLMN 16, 47 (2021).
[Crossref]

S. Kefer, K. Bischoff, G.-L. Roth, J. Haubner, B. Schmauss, and R. Hellmann, “Tunable bulk polymer planar Bragg gratings electrified via femtosecond laser reductive sintering of CuO Nanoparticles,” Adv. Optical Mater. 4, 2002203 (2021).
[Crossref]

G.-L. Roth, S. Hessler, S. Kefer, M. Girschikofsky, C. Esen, and R. Hellmann, “Femtosecond laser inscription of waveguides and Bragg gratings in transparent cyclic olefin copolymers,” Opt. Express 28(12), 18077 (2020).
[Crossref]

M. Rosenberger, S. Kefer, M. Girschikofsky, G.-L. Roth, S. Hessler, S. Belle, B. Schmauss, and R. Hellmann, “High-temperature stable and sterilizable waveguide Bragg grating in planar cyclo-olefin copolymer,” Opt. Lett. 43(14), 3321–3324 (2018).
[Crossref]

Rubio, J. C.

M. A. Câmara, J. C. Rubio, A. M. Abrão, and J. P. Davim, “State of the art on micromilling of materials, a review,” J. Mater. Sci. Technol. 28(8), 673–685 (2012).
[Crossref]

Rumler, M.

M. Foerthner, M. Rumler, F. Stumpf, R. Fader, M. Rommel, L. Frey, M. Girschikofsky, S. Belle, R. Hellmann, and J. J. Klein, “Hybrid polymers processed by substrate conformal imprint lithography for the fabrication of planar Bragg gratings,” Appl. Phys. A 122(3), 240 (2016).
[Crossref]

Ryvlin, D.

M. Girschikofsky, D. Ryvlin, S. R. Waldvogel, and R. Hellmann, “Optical sensor for real-time detection of trichlorofluoromethane,” Sensors 19(3), 632 (2019).
[Crossref]

Sauer, T.

S. Kefer, T. Sauer, S. Hessler, M. Kaloudis, and R. Hellmann, “Microstructure-based fiber-to-chip coupling of polymer planar Bragg gratings for harsh environment applications,” Sensors 20(19), 5452 (2020).
[Crossref]

Schmauss, B.

S. Kefer, K. Bischoff, G.-L. Roth, J. Haubner, B. Schmauss, and R. Hellmann, “Tunable bulk polymer planar Bragg gratings electrified via femtosecond laser reductive sintering of CuO Nanoparticles,” Adv. Optical Mater. 4, 2002203 (2021).
[Crossref]

S. Hessler, S. Knopf, M. Rommel, M. Girschikofsky, B. Schmauss, and R. Hellmann, “Advancing the sensitivity of integrated epoxy-based Bragg grating refractometry by high-index nanolayers,” Opt. Lett. 45, 5510–5513 (2020).
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S. Kefer, J. Dai, M. Yang, B. Schmauss, and R. Hellmann, “Hypersensitive H2 sensor based on polymer planar Bragg gratings coated with Pt-Loaded WO3-SiO2,” Opt. Lett. 45(13), 3601–3604 (2020).
[Crossref]

S. Hessler, P. Bott, S. Kefer, B. Schmauss, and R. Hellmann, “Multipurpose polymer Bragg grating-based optomechanical sensor pad,” Sensors 19(19), 4101 (2019).
[Crossref]

S. Hessler, M. Rosenberger, B. Schmauss, and R. Hellmann, “Two-dimensional interferometric characterization of laser-induced refractive index profiles in bulk Topas polymer,” Optical Materials 75, 230–235 (2018).
[Crossref]

M. Rosenberger, S. Kefer, M. Girschikofsky, G.-L. Roth, S. Hessler, S. Belle, B. Schmauss, and R. Hellmann, “High-temperature stable and sterilizable waveguide Bragg grating in planar cyclo-olefin copolymer,” Opt. Lett. 43(14), 3321–3324 (2018).
[Crossref]

M. Rosenberger, B. Schmauss, and R. Hellmann, “Influence of the UV dosage on planar Bragg gratings in cyclo-olefin copolymer substrates,” Opt. Mater. Express 6(6), 2118 (2016).
[Crossref]

M. Rosenberger, S. Hessler, S. Belle, B. Schmauss, and R. Hellmann, “Fabrication and characterization of planar Bragg gratings in TOPAS polymer substrates,” Sensors and Actuators A: Physical 221, 148–153 (2015).
[Crossref]

M. Rosenberger, W. Eisenbeil, B. Schmauss, and R. Hellmann, “Simultaneous 2D strain sensing using polymer planar Bragg gratings,” Sensors 15(2), 4264–4272 (2015).
[Crossref]

M. Rosenberger, S. Hessler, S. Belle, B. Schmauss, and R. Hellmann, “Humidity-induced effects on polymer planar Bragg gratings,” IEEE Photon. Technol. Lett. 26(16), 1669–1671 (2014).
[Crossref]

M. Rosenberger, G. Koller, S. Belle, B. Schmauss, and R. Hellmann, “Planar Bragg grating in bulk polymethylmethacrylate,” Opt. Express 20(25), 27288–27296 (2012).
[Crossref]

Schoop, J.

D. Adeniji, J. Schoop, S. Gunawardena, C. Hanson, and M. Jahan, “Characterization and modeling of surface roughness and Burr formation in slot milling of polycarbonate,” J. Manuf. Mater. Process. 4, 59 (2020).
[Crossref]

Selviah, D. R.

H. Baghsiahi, K. Wang, W. Kandulski, R. C. A. Pitwon, and D. R. Selviah, “Optical waveguide end facet roughness and optical coupling loss,” J. Lightwave Technol. 31, 2659–2668 (2013).
[Crossref]

Stumpf, F.

M. Foerthner, M. Rumler, F. Stumpf, R. Fader, M. Rommel, L. Frey, M. Girschikofsky, S. Belle, R. Hellmann, and J. J. Klein, “Hybrid polymers processed by substrate conformal imprint lithography for the fabrication of planar Bragg gratings,” Appl. Phys. A 122(3), 240 (2016).
[Crossref]

Sun, F.

Z. Zhang, P. Zhao, P. Lin, and F. Sun, “Thermo-optic coefficients of polymers for optical waveguide applications,” Polymer 47(14), 4893–4896 (2006).
[Crossref]

Takács, M.

B. Z. Balázs, N. Geier, M. Takács, and J. P. Davim, “A review on micro-milling: recent advances and future trends,” Int J Adv Manuf Technol 112(3-4), 655–684 (2021).
[Crossref]

Taylor, H. F.

H. F. Taylor, Fiber Optic Sensors Based upon the Fabry-Perot Interferometer, S. Yin, P. B. Ruffin, and F. T. S. Yu, eds. (CRC Press, 2017), pp. 35–64.

Teigell Benéitez, N.

J. Missinne, N. Teigell Benéitez, M.-A. Mattelin, A. Lamberti, G. Luyckx, W. van Paepegem, and G. van Steenberge, “Bragg-grating-based photonic strain and temperature sensor foils realized using imprinting and operating at very near infrared wavelengths,” Sensors 18(8), 2717 (2018).
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van Paepegem, W.

J. Missinne, N. Teigell Benéitez, M.-A. Mattelin, A. Lamberti, G. Luyckx, W. van Paepegem, and G. van Steenberge, “Bragg-grating-based photonic strain and temperature sensor foils realized using imprinting and operating at very near infrared wavelengths,” Sensors 18(8), 2717 (2018).
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J. Missinne, N. Teigell Benéitez, M.-A. Mattelin, A. Lamberti, G. Luyckx, W. van Paepegem, and G. van Steenberge, “Bragg-grating-based photonic strain and temperature sensor foils realized using imprinting and operating at very near infrared wavelengths,” Sensors 18(8), 2717 (2018).
[Crossref]

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M. Girschikofsky, D. Ryvlin, S. R. Waldvogel, and R. Hellmann, “Optical sensor for real-time detection of trichlorofluoromethane,” Sensors 19(3), 632 (2019).
[Crossref]

Wan, A. M. D.

D. J. Guckenberger, T. E. de Groot, A. M. D. Wan, D. J. Beebe, and E. W. K. Young, “Micromilling: a method for ultra-rapid prototyping of plastic microfluidic devices,” Lab Chip 15(11), 2364–2378 (2015).
[Crossref]

Wang, K.

H. Baghsiahi, K. Wang, W. Kandulski, R. C. A. Pitwon, and D. R. Selviah, “Optical waveguide end facet roughness and optical coupling loss,” J. Lightwave Technol. 31, 2659–2668 (2013).
[Crossref]

Webb, D. J.

D. J. Webb, “Fibre Bragg grating sensors in polymer optical fibres,” Meas. Sci. Technol. 26(9), 092004 (2015).
[Crossref]

Wochnowski, C.

C. Wochnowski, “UV-laser-based fabrication of a planar, polymeric Bragg-structure,” Optics & Laser Technology 41(6), 734–740 (2009).
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D. J. Guckenberger, T. E. de Groot, A. M. D. Wan, D. J. Beebe, and E. W. K. Young, “Micromilling: a method for ultra-rapid prototyping of plastic microfluidic devices,” Lab Chip 15(11), 2364–2378 (2015).
[Crossref]

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H. A. Youssef and H. El-Hofy, Machining Technology: Machine Tools and Operations, 1st ed. (CRC Press, 2008).
[Crossref]

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Z. Zhang, P. Zhao, P. Lin, and F. Sun, “Thermo-optic coefficients of polymers for optical waveguide applications,” Polymer 47(14), 4893–4896 (2006).
[Crossref]

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Z. Zhang, P. Zhao, P. Lin, and F. Sun, “Thermo-optic coefficients of polymers for optical waveguide applications,” Polymer 47(14), 4893–4896 (2006).
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H. Ma, A.-Y. Jen, and L. R. Dalton, “Polymer-based optical waveguides: materials, processing, and devices,” Adv. Mater. 14(19), 1339–1365 (2002).
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Adv. Optical Mater. (1)

S. Kefer, K. Bischoff, G.-L. Roth, J. Haubner, B. Schmauss, and R. Hellmann, “Tunable bulk polymer planar Bragg gratings electrified via femtosecond laser reductive sintering of CuO Nanoparticles,” Adv. Optical Mater. 4, 2002203 (2021).
[Crossref]

Appl. Phys. A (1)

M. Foerthner, M. Rumler, F. Stumpf, R. Fader, M. Rommel, L. Frey, M. Girschikofsky, S. Belle, R. Hellmann, and J. J. Klein, “Hybrid polymers processed by substrate conformal imprint lithography for the fabrication of planar Bragg gratings,” Appl. Phys. A 122(3), 240 (2016).
[Crossref]

IEEE Photon. Technol. Lett. (1)

M. Rosenberger, S. Hessler, S. Belle, B. Schmauss, and R. Hellmann, “Humidity-induced effects on polymer planar Bragg gratings,” IEEE Photon. Technol. Lett. 26(16), 1669–1671 (2014).
[Crossref]

Int J Adv Manuf Technol (1)

B. Z. Balázs, N. Geier, M. Takács, and J. P. Davim, “A review on micro-milling: recent advances and future trends,” Int J Adv Manuf Technol 112(3-4), 655–684 (2021).
[Crossref]

J. Lightwave Technol. (1)

H. Baghsiahi, K. Wang, W. Kandulski, R. C. A. Pitwon, and D. R. Selviah, “Optical waveguide end facet roughness and optical coupling loss,” J. Lightwave Technol. 31, 2659–2668 (2013).
[Crossref]

J. Manuf. Mater. Process. (1)

D. Adeniji, J. Schoop, S. Gunawardena, C. Hanson, and M. Jahan, “Characterization and modeling of surface roughness and Burr formation in slot milling of polycarbonate,” J. Manuf. Mater. Process. 4, 59 (2020).
[Crossref]

J. Mater. Sci. Technol. (1)

M. A. Câmara, J. C. Rubio, A. M. Abrão, and J. P. Davim, “State of the art on micromilling of materials, a review,” J. Mater. Sci. Technol. 28(8), 673–685 (2012).
[Crossref]

JLMN (1)

G.-L. Roth, S. Kefer, S. Hessler, C. Esen, and R. Hellmann, “Integration of microfluidic and photonic components within transparent cyclic olefin copolymers by using fs laser,” JLMN 16, 47 (2021).
[Crossref]

Lab Chip (1)

D. J. Guckenberger, T. E. de Groot, A. M. D. Wan, D. J. Beebe, and E. W. K. Young, “Micromilling: a method for ultra-rapid prototyping of plastic microfluidic devices,” Lab Chip 15(11), 2364–2378 (2015).
[Crossref]

Meas. Sci. Technol. (1)

D. J. Webb, “Fibre Bragg grating sensors in polymer optical fibres,” Meas. Sci. Technol. 26(9), 092004 (2015).
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G. Khanarian, “Optical properties of cyclic olefin copolymers,” Opt. Eng. 40(6), 1024–1029 (2001).
[Crossref]

Opt. Express (3)

Opt. Lett. (3)

Opt. Mater. Express (1)

Optical Materials (1)

S. Hessler, M. Rosenberger, B. Schmauss, and R. Hellmann, “Two-dimensional interferometric characterization of laser-induced refractive index profiles in bulk Topas polymer,” Optical Materials 75, 230–235 (2018).
[Crossref]

Optics & Laser Technology (1)

C. Wochnowski, “UV-laser-based fabrication of a planar, polymeric Bragg-structure,” Optics & Laser Technology 41(6), 734–740 (2009).
[Crossref]

Optics and Lasers in Engineering (1)

G.-L. Roth, J. Haubner, S. Kefer, C. Esen, and R. Hellmann, “Fs-laser based hybrid micromachining for polymer micro-opto electrical systems,” Optics and Lasers in Engineering 137, 106362 (2021).
[Crossref]

Polymer (1)

Z. Zhang, P. Zhao, P. Lin, and F. Sun, “Thermo-optic coefficients of polymers for optical waveguide applications,” Polymer 47(14), 4893–4896 (2006).
[Crossref]

Proc. Inst. Mech. Eng., Part C (1)

F. Bundgaard, G. Perozziello, and O. Geschke, “Rapid prototyping tools and methods for all-Topas® cyclic olefin copolymer fluidic microsystems,” Proc. Inst. Mech. Eng., Part C 220(11), 1625–1632 (2006).
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Procedia Manufacturing (1)

E. Korkmaz, R. Onler, and O. B. Ozdoganlar, “Micromilling of poly(methyl methacrylate, PMMA) using single-crystal diamond tools,” Procedia Manufacturing 10, 683–693 (2017).
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Sensors (7)

S. Kefer, T. Sauer, S. Hessler, M. Kaloudis, and R. Hellmann, “Microstructure-based fiber-to-chip coupling of polymer planar Bragg gratings for harsh environment applications,” Sensors 20(19), 5452 (2020).
[Crossref]

M. Rosenberger, W. Eisenbeil, B. Schmauss, and R. Hellmann, “Simultaneous 2D strain sensing using polymer planar Bragg gratings,” Sensors 15(2), 4264–4272 (2015).
[Crossref]

J. Missinne, N. Teigell Benéitez, M.-A. Mattelin, A. Lamberti, G. Luyckx, W. van Paepegem, and G. van Steenberge, “Bragg-grating-based photonic strain and temperature sensor foils realized using imprinting and operating at very near infrared wavelengths,” Sensors 18(8), 2717 (2018).
[Crossref]

M. Girschikofsky, M. Rosenberger, M. Förthner, M. Rommel, L. Frey, and R. Hellmann, “Waveguide Bragg gratings in Ormocer®s for temperature sensing,” Sensors 17(11), 2459 (2017).
[Crossref]

S. Hessler, P. Bott, S. Kefer, B. Schmauss, and R. Hellmann, “Multipurpose polymer Bragg grating-based optomechanical sensor pad,” Sensors 19(19), 4101 (2019).
[Crossref]

M. Girschikofsky, D. Ryvlin, S. R. Waldvogel, and R. Hellmann, “Optical sensor for real-time detection of trichlorofluoromethane,” Sensors 19(3), 632 (2019).
[Crossref]

M. R. Islam, M. M. Ali, M.-H. Lai, K.-S. Lim, and H. Ahmad, “Chronology of Fabry-Perot interferometer fiber-optic sensors and their applications: a review,” Sensors 14(4), 7451–7488 (2014).
[Crossref]

Sensors and Actuators A: Physical (2)

M. Rosenberger, S. Hessler, S. Belle, B. Schmauss, and R. Hellmann, “Fabrication and characterization of planar Bragg gratings in TOPAS polymer substrates,” Sensors and Actuators A: Physical 221, 148–153 (2015).
[Crossref]

T. Guan, G. Keulemans, F. Ceyssens, and R. Puers, “MOEMS uniaxial accelerometer based on EpoClad/EpoCore photoresists with built-in fiber clamp,” Sensors and Actuators A: Physical 193, 95–102 (2013).
[Crossref]

Other (11)

R. Oliveira, L. Bilro, and R. Nogueira, Polymer Optical Fiber Bragg Gratings: Fabrication and Sensing Applications, 1st ed. (CRC Press, 2020).

M. Kahrizi, ed., Micromachining Techniques for Fabrication of Micro and Nano Structures, 1st ed. (InTech, 2011).

H. A. Youssef and H. El-Hofy, Machining Technology: Machine Tools and Operations, 1st ed. (CRC Press, 2008).
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R. K. Rajput, A Textbook of Manufacturing Technology: Manufacturing processes for B.E./B. Tech., A.M.I.E.-Section B, and Competitive Examinations, 2nd ed. (Laxmi Publications (P) LTD, 2015).

R. Leach, Characterisation of Areal Surface Texture (Springer, 2013).
[Crossref]

J. Ahmad, Machining of Polymer Composites, 1st ed. (Springer US, 2009).
[Crossref]

F. Bundgaard, Prototyping of Microfluidic Systems with Integrated Waveguides in Cyclic Olefin Copolymer (COC) (Technical University of Denmark, 2006).

L. O’Toole, C.-W. Kang, and F.-Z. Fang, “Precision micro-milling process: state of the art,” Adv. Manuf., (2020).

H. F. Taylor, Fiber Optic Sensors Based upon the Fabry-Perot Interferometer, S. Yin, P. B. Ruffin, and F. T. S. Yu, eds. (CRC Press, 2017), pp. 35–64.

K. Okamoto, Fundamentals of Optical Waveguides, 2nd ed. (Elsevier/Academic Press,2006).

R. Kashyap, Fiber Bragg Gratings, 2nd ed. (Academic Press, 2010).

Data availability

Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.

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Figures (6)

Fig. 1.
Fig. 1. (a) Fabrication process schematic for micromilling-assisted generation of monolithic ridge-type waveguides on a bulk cyclic olefin copolymer (COC) substrate. (b) Image of a finalized specimen comprising three parallel waveguides with integrated Bragg gratings (grating structures are indicated). The zoom in depicts a sketch of the waveguide and schematics of its asymmetric refractive index (RI) profile.
Fig. 2.
Fig. 2. (a) Schematic of the milling process and its parameters. The inset depicts a contour plot of the resulting areal surface profile, acquired via white-light interferometry. (b) Arithmetic mean deviation of the assessed surface profile, or surface roughness, as a function of varying chip loads when using end mills with a diameter of 1 mm and 0.2 mm.
Fig. 3.
Fig. 3. (a) Qualitative analysis of residual top burr and debris in dependence of feed rate and rotational speed of the up-cut milling process. Moreover, the resulting chip load is stated. (b) Microscope image of a waveguide milled with optimized up-cut milling parameters. Furthermore, a cross-sectional height profile of the fabricated ridge structure is depicted. (c) Exemplary comparison of burr formation resulting from up-cut or down-cut milling processes.
Fig. 4.
Fig. 4. Bragg peaks and simulated mode profiles of micromilled ridge-type waveguides with cross-sections of (a) 30 × 30 µm2, (b) 40 × 40 µm2 and (c) 50 × 50 µm2. Additionally, the respective fluence F, absorbed by the ridge structure during UV exposure, is given. (d) Simulated mode intensity I profile cross-sections for various waveguide geometries irradiated with a fluence of 300 J cm−2. The inset shows a magnification of the mode cross section near the ridge-structure to polymer-substrate transition region.
Fig. 5.
Fig. 5. Temperature response of a COC-PPBG with monolithic ridge-type waveguide.
Fig. 6.
Fig. 6. (a) Schematic of the employed experimental setup. (b) Reflection spectrum of the milled Fabry-Pérot cavity. The raw signal is filtered with a digital Butterworth filter to optimize tracking of the reflection minima. A microscopic image of the cavity is shown in the inset. (c) Wavelength response of the FP reflection minima when filling the cavity with various refractive index liquids.

Equations (4)

Equations on this page are rendered with MathJax. Learn more.

f t  =  v f N Z .
λ B = 2 n eff Λ .
λ M  =  2 π δ 2nl,
Δ λ M  =  Δ n n λ M .

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