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Abstract
For the first time, to the best of our knowledge, the design and characterization of a 3 × 1 fused fiber combiner based on multimode step-index fluoroindate optical fibers (InF3) has been performed. Several efforts to develop a well-consolidated normalization procedure and a fabrication protocol have been required due to the low melting temperature and the mechanical properties of fluoroindates. Fabrication results demonstrate repeatability and absence of crystallization. Therefore, the described fabrication process paves the way for manufacturing fluoroindate devices. The electromagnetic design of the combiner is carried out through modal investigation and beam propagation method by computing the transmission efficiency. The experimental results agree with the simulation and demonstrate the device feasibility to operate in the mid-infrared spectral range.
© 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
1. Introduction
Over the last decade, mid-infrared (Mid-IR) optics has attracted interest due to its potential applications in several fields including Mid-IR light sources, optical spectroscopy, biological sensing, environmental sensing, medical surgery and Mid-IR comb generation [1–10]. Soft-glasses such as heavy metal fluoride [11–13], halide polycrystals [14], and chalcogenide [15–18], can be employed for all-in fiber Mid-IR optical devices [9].
Although the chalcogenide glasses have been widely investigated for their excellent transparency until the wavelength $\lambda = 16\; \mu m$, the potential related to these unique properties is restricted by some peculiar aspects. The reflection losses in optical free propagation at fiber end facets, due to high refractive index, and propagation losses in some bands, such as the absorption peak around wavelength $\lambda = 4\; \mu m$ typical of sulfide glass, can limit their feasibility for specific applications [19,20].
Fluoride glasses constitute a mature technology, suitable to transmit light in the ultra-violet (UV), visible, near-infrared (NIR) and Mid-IR spectral range [21–27]. The technological improvement of fluoride glasses has led to the production of commercial low loss fibers with outstanding optical properties [28,29]. The main types of fluoride glasses are based on zirconium, indium, barium, or gallium [30]. The indium fluoride (IFG) optical fibers, also known as fluoroindate fibers, compared with zirconium fluoride (ZFG) ones, have a wider transmission window which extends fro $\lambda = 0.3\; \mu m$ up to $\lambda = 5.5\; \mu m$. They exhibit high performances in terms of high transparency and low attenuation [1]. The development of fluoride optical fiber has not been accompanied by a corresponding development of components such as combiners, couplers and splitters due to difficulty in their manufacturing. Bulk high-power lasers in the Mid-IR wavelength range are available on market but they do not provide high quality beams. Indeed, most of the quantum cascade lasers (QCLs) and interband cascade lasers (ICLs) need fiber pigtailing to this aim. The increasing demand to expand the power and spectral range of sources is strengthening the need to develop all-fiber platforms based on fused fiber devices [31–38].
Regarding fiber components based on fluorides, very precise control of melting temperature is needed for an effective glass processing without crystallization. Ad-hoc developed glass processing systems have been proposed for fused optical components based on fluoride glasses [36,39,40]. However, fluoride glass processing is still challenging [36,41]. In addition, for chalcogenide glasses few components such as optical couplers [42–45], and combiners [46], have been developed by employing custom fusion workstation for low melting temperature or side-polished bonding technique.
Fluoroindate pump and signal combiners can be employed for the fabrication of broadband sources and systems with multi-watt output powers in the Mid-IR. They enable the combination of input powers and/or multiple wavelengths of distinct light sources [46–48]. Indeed, they permit to improve compactness and robustness, compared with free-space beam combining, overcoming the vibration control for the alignment of several beams with bulk optics and the thermal stability requirements.
In this paper, for the first time, the design and fabrication of a 3 × 1 fluoroindate combiner for laser combining application is reported. Three multimode step-index optical fibers are stacked inside a fluoroindate capillary with lower refractive index. The entire structure is heated through graphite filament and tapered, achieving an adiabatic transition from multimode inputs to a single multimode output. The fusion technique with Vytran glass processing system has been used to achieve a fused fiber combiner with fluoroindate glasses. The device feasibility to operate at wavelengths until $\lambda = 5.00\; \mu m$ is numerically and experimentally investigated. The device per-port transmission efficiency has been measured at the wavelength $\lambda = 1.55\; \mu m$, by employing temporary connector and SLED source. The transmission efficiencies agree with simulation results. Furthermore, the flat behavior of the simulated transmission efficiencies versus wavelength $\lambda $ is experimentally confirmed over the wavelength range from $\lambda = 1.00\; \mu m$ to $\lambda = \; 5.00\; \mu m$, by employing a halogen lamp and a monochromator. These results demonstrate the fabrication feasibility of high quality and low-loss fluoroindate fiber devices using commercial glass workstations. In particular, the construction of combiners enables the wavelength and power scaling, without bulk optics components and free-space optical setups.
The paper is organized as follows. Section 1 reports the introduction; Section 2, the 3 × 1 fluoroindate combiner description and the electromagnetic design; Section 3, the fabrication challenges, the developed fabrication process and the experimental characterization; Section 4, prospects and conclusion.
2. Electromagnetic design and numerical results
2.1 Design approach
The 3 × 1 fluoroindate combiner design is performed for beam combining application over the Mid-IR spectral range. The adiabatic taper criterion and the beam brightness principle are the main constraints to be considered when designing an optical combiner [49,50]. In particular, the electromagnetic design is carried out through i) a preliminary modal investigation, considering both the untapered and tapered cross-sections, see Fig. 1(a) and Fig. 1(b); and ii) the Beam Propagation Method (BPM) for evaluating the electromagnetic power propagation/coupling. The geometrical parameters have been chosen a) to ensure the electromagnetic field confinement in a single core, over the entire wavelength range from $\lambda = 1.00\; \mu m$ to $\lambda = \; 5.00\; \mu m$, when only one of the three optical fibers is excited; b) to fulfill the adiabatic taper criterion [49,50]. Moreover, the BPM has been employed to simulate the net transmission efficiency ${\eta _{s,net}}(z )= {P_p}(z )/{P_{in}}$, defined as the ratio between the power along the propagation direction ${P_p}(z )$, i.e., along the $z$-axis direction of the combiner, and the power launched in one of the three input fibers ${P_{in}}$ ($z = 0$), excited one at a time, for different wavelengths $\lambda $ and different waists ${B_w}$ of the input gaussian beam.
Fig. 1. (a) 3 × 1 fluoroindate combiner sketch; (b) longitudinal section in the y-z plane of the 3 × 1 fluoroindate combiner with linear down-taper.
2.2 Design of the 3 × 1 fluoroindate combiner
The designed 3 × 1 fluoroindate combiner is made of three multimode step-index fluoroindate optical fibers arranged at the vertices of an equilateral triangle and surrounded by a low-index fluoroindate capillary. In Fig. 1(a), a 3D sketch of the device is shown.
Both optical fibers and capillary are manufactured by the company Le Verre Fluoré, France [29]. The fluoroindate optical fibers IFG MM (0.30) 100/160 have a core diameter ${d_{co}} = 100\,\mu m$ and a cladding diameter ${d_{cl}} = 160\,\mu m$. The capillary has an internal diameter of ${d_{inner,cap}} = 360\,\mu m$ and an external diameter of ${d_{outer,cap}} = 580\,\mu m$. The material used for core and cladding is InF3 glass with different stoichiometries. The core and cladding refractive index, at the wavelength $\lambda = 1.55\,\mu m$, are respectively ${n_{co}} = 1.504$ and ${n_{cl}} = 1.474$, resulting in a numerical aperture $NA\,\sim \,0.30$. The capillary is not commercially available and it is ad-hoc designed and fabricated to have a refractive index ${n_{cap}} = 1.472$ lower than cladding refractive index ${n_{cl}}$. The simulations consider the actual dispersion curves of fluoroindate glasses, provided by Le Verre Fluoré and reported in Fig. 2.
Fig. 2. Refractive index n as a function of the wavelength $\lambda $; core refractive index ${n_{co}}$ (solid line), cladding refractive index ${n_{cl}}$ (dotdash line), capillary refractive index ${n_{cap}}$ (dotted line).
In Fig. 1(b), the sketch of the longitudinal section of the 3 × 1 combiner is reported. The straight input section has length ${L_{IN}} = 1\,cm$, the linear down-taper section has length ${L_{DT}} = 1.5\,cm$ while, the waist section has length ${L_W} = 2.5\,cm$. The total length of the combiner can be defined as ${L_{out}} = {L_{IN}} + {L_{DT}} + {L_W} = 5\; cm$. The structure, having a diameter ${d_{in}} = {d_{outer,cap}} = 580\,\mu m$ is tapered with a scaling factor $SF = 5$. This corresponds to an output diameter ${d_{out}} = {d_{outer,cap}}/SF = 116\,\mu m$. The waist diameter dimension ${d_{out}}$ is compatible with the typical inner cladding diameters of many double cladding fibers. This allows to splice the combiner output with a double cladding fiber to improve the beam quality and obtain a better delivering of the total power. In Fig. 3, the refractive index profile distribution at the output cross-section of the combiner (i.e., $z = {L_{out}}$) is reported.
Fig. 3. Refractive index distribution, greyscale, of the simulated 3 × 1 fluoroindate combiner at the output cross-section ($z = \; {L_{out}}$) at the wavelength $\lambda = 1.55\; \mu m$ (x-y plane).
The outer low-index capillary (white colored) surrounds both the cladding (light grey colored) and the core (dark grey colored) of the three optical fibers.
2.3 Numerical results
The 3 × 1 fluoroindate combiner operation, from NIR to Mid-IR, is numerically investigated for the wavelengths $\lambda = \{{1.00,\,1.55,\,3.20,\,5.00} \}\,\mu m$ for beam waist ${B_W} = 70.0\,\mu m$. The beam waist ${B_W} = 70.0\,\mu m$ is chosen to highlight the device performance by considering a suitable excitation condition, which is a trade-off for maximizing the net transmission efficiency ${\eta _{s,net}}$ at the four wavelengths of interest. In addition, for a comparison/validation with the experimental results, the 3 × 1 fluoroindate combiner operation at the wavelength of $\lambda = 1.55\,\mu m$ is simulated by considering a beam waist ${B_W} = 10.4\,\mu m.$ The net transmission efficiencies ${\eta _{s,net}}$, simulated with BPM, at the wavelength $\lambda = 1.55\,\mu m$ for beam waist ${B_W} = 10.4\,\mu m$ and ${B_W} = 70.0\,\mu m$, are reported in Fig. 4. The beam waist ${B_W} = 10.4\,\mu m$ is typical of Corning SMF-28 silica optical fiber and it corresponds to the one employed in the experiment at NIR wavelength. Table 1 illustrates the net simulated transmission efficiencies ${\eta _{s,net}}(z )$ fluoroindate, at the output section of the 3 × 1 fluoroindate combiner e.g., $z = {L_{out}}$, for the aforementioned wavelength $\lambda $. The obtained results confirm the compliance with the adiabatic criterion for multimode fiber tapering [51]. The simulations emphasize the possibility to obtain a device with high net transmission efficiency ${\eta _{s,net}}({{L_{out}}} )$ over a wide range of wavelength from NIR to Mid-IR. The power losses over the wavelength $\lambda $ given by the taper are negligible. Table 1 suggests a flat behavior of net transmission efficiency ${\eta _{s,net}}({{L_{out}}} )$. This is explained by the normalized frequency V value of each optical fiber, constituting the 3 × 1 fluoroindate combiner. At the output cross-section, the core diameter of each optical fiber is ${d_{co,t}} = {d_{co}}/SF = 20\,cm$ with numerical aperture $NA = 0.3$. Therefore, at the upper bound of the wavelength range (i.e., $\lambda = 5\,\mu m$), the normalized frequency is $V\,\sim \,3.77$, high enough to support not only the fundamental mode but also a few higher order modes. The simulation confirms that the power coupling between the optical fibers occurs, but it is negligible due to limited optical tunneling [47]. It is in agreement with the modal analysis results.
Fig. 4. BPM simulation of transmission efficiency ${\eta _{sim}}(z )$ along the propagation direction ($z$-axis), for beam waist ${B_W} = 10.4\; \mu m$ (dashed line) and ${B_W} = 70\; \mu m$ (dotted line) at the wavelength $\lambda = 1.55\; \mu m$.
Table 1. Simulated transmission efficiencies ${{\boldsymbol \eta }_{\boldsymbol {s},\boldsymbol {net}}}({{\boldsymbol {L}_{\boldsymbol {out}}}} )$ of the 3×1 fluoroindate combiner
3. Fabrication and measurements
3.1 Fabrication challenges
The 3 × 1 fluoroindate combiner is constituted by the optical fibers and capillaries described in Sect. 2 (produced by Le Verre Fluoré). It is fabricated through fusion technique by employing Vytran GPX-2400 glass filament processing system at Politecnico di Bari. Processing fluoroindate glass is challenging due to the material fragility and the unique thermal properties [52], i.e., low melting temperature, narrow glass-transition, and steep viscosity/temperature characteristic. Figure 5 shows the typical viscosity/temperature of fluoroindate glass. The steep profile justifies the need for strict temperature control [39].
A fine temperature monitoring is necessary to avoid geometric inhomogeneities and surface crystallization. To reach a precise temperature control during combiner manufacture, an ad-hoc normalization procedure of the Vytran GPX-2400, making use of fluoride glass, is developed. In addition, parameters such as filament power, applied tension, pull velocity of the translation stage and argon flow rate have been optimized by carrying out several tests. The manufacturing of high quality fluoroindate optical components is strictly dependent on these crucial aspects. Ultimately, a reliable and controlled fabrication process is obtained.
3.2 Fabrication method
Before inserting the optical fibers into the capillary, they are stripped of their polymer coating using a specific stripping gel, cleaned with isopropyl alcohol and manually threaded into the capillary. To avoid refractive index inhomogeneities and additional losses, during the tapering process great attention is devoted toward many aspects. No dust or coating residuals are left onto the fibers and within the capillary. Generally, to facilitate fibers insertion, the capillary has an internal diameter higher than the needed one and is pre-tapered before inserting fibers. In the case of fluoroindate glasses, this procedure is to be avoided since the repetition of the tapering procedure can easily lead to glass surface crystallizations. For this reason, the inner capillary size, i.e., diameter ${d_{inner,cap}}$, is identified as an opportune trade-off. It is large enough to permit a manual threading of the three fibers but, at the same time, an arrangement without significant air gaps is ensured. A commercial FTAT3 graphite filament is used as heating source and properly normalized to work at a softening point close to the glass transition temperature ${T_g} = {275^\circ }C$ (measured by differential thermal analysis at $10^\circ C/min$). During the whole fabrication process, the glass has to be accurately maintained at the softening point. The main consequences of an excessive amount of heat transmitted to the combiner under construction are surface crystallization, waist diameter smaller than the desired one or completely fused waist. On the contrary, an amount of heat lower than that required to reach the softening point of the glass, leads to larger waist diameter or capillary breaking.
The diameter of the combiner under construction tends to decrease due to the tapering process. Therefore, the amount of heat provided by the filament during the manufacturing process must decrease as well (via a reduction of the filament power along the taper process) to keep the softening glass temperature. As an alternative, a non-constant fiber holding block pull velocity ${v_{block}}$ can be imposed. A larger (smaller) fiber holding block pull velocity ${v_{block}}$ results in smaller (larger) amount of heat absorbed by the combiner under fabrication. However, the use of non-constant fiber holding block pull velocity ${v_{block}}$ can lead to low quality taper. Therefore, a constant fiber holding block pull velocity ${v_{block}} = 0.5\,mm/s$ is exploited and the initial filament power ${P_f}\sim 12\,W$ is reduced during the process. The initial filament power ${P_f}$ should be finely tuned since it is slightly dependent on ambient temperature when working with fluoroindate optical fibers. The pull velocity ${v_{block}}$ is controlled with a repetition time $\Delta t = 0.1\,s$. The structure is clamped between the two translation fiber holders. Before starting the fusion process i) the entire structure is pre-tensioned, moving one fiber holding block, to approximately $L = 15\; g$, ii) an argon flow is employed to purge the fusion region, to prevent the glass crystallization and extend the graphite filament lifetime, iii) any excess of isopropyl alcohol is removed through the vacuum pump Linicon LV-125A. Before the fabrication process it is necessary to purge the filament for a pre-purge duration time ${t_{pp}} = 20\; s$ considering a pre-purge flow rate ${F_{pp,R}} = 0.80\; L/min$. The argon flow rate during the process, dependent on the adopted filament and kind of glass, is ${F_R} = 0.35\; L/min$.
The vacuum pump is also used during the tapering process to promote capillary collapse and, thus, a homogenous cross-section without trapped air [53]. The tension was monitored during the tapering using Vytran GPX-2400 built-in sensor. The tension monitor is a useful tool to understand how to set the parameters of the manufacturing process. In particular, if the tension L goes to large negative values, i.e., the glass is heated over the softening temperature, the filament power ${P_f}$ should be decreased or the fiber holding block pull velocity ${v_{block}}$ increased. If the tension $\textrm{L}$ goes to large positive values, the glass has not reached the softening temperature. In this case, the filament power ${P_f}$ should be increased or the fiber holding block pull velocity ${v_{block}}$ decreased. Figure 6 shows the tension varying during the automatic tapering and drawing process. The trend of the tension indicates that no issues occurred during the process [53]. Figure 7 shows an image captured with an external digital microscope (Dino-Lite camera) during the fabrication process.
Fig. 7. Longitudinal view of the 3 × 1 fluoroindate combiner, captured with Dino-Lite camera, during a stage of the fabrication process. At left, the FTAT3 graphite filament of the Vytran GPX-2400 workstation.
3.3 Fabrication results
The output cross-section, the longitudinal view and the dimensions of the final 3 × 1 fluoroindate combiner were captured and measured using Vytran GPX-2400 microscope camera. The device was cleaved at the center of the waist region via Vytran cleaver LDC-400.
Figure 8 shows the combiner output cross-section. The obtained results show that the use of a fluoroindate capillary with a melting temperature lower than that of the optical fibers and the use of vacuum pump during the process helps to obtain a homogeneous output cross-section.
Fig. 8. Output cross-section of the 3 × 1 fluoroindate combiner, captured with Vytran GPX-2400 microscope camera.
In Fig. 9, the microscope images of the longitudinal view of the 3 × 1 fluoroindate combiner, at different stages of the tapering process, are shown. The down taper transition of the combiner has a length ${L_{DT}} = \; 1.5\; cm$ while the waist has a length ${L_W} = \; 2.5\; cm$.
Fig. 9. Longitudinal view of the 3 × 1 fluoroindate combiner, captured with Vytran GPX-2400 microscope camera, at different stages of the tapering process.
The desired combiner dimensions have been obtained ensuring high glass quality (e.g., without surface crystallization), long adiabatic transition and a scaling factor $SF = 5$. Different tapering ratios and transitions length can be reached by working on filament power and pulling speeds.
3.4 Output power measurements
Two different experimental set-ups are developed to evaluate the performances of the 3 × 1 fluoroindate combiner in the NIR and Mid-IR spectral range. The first set-up, sketched in Fig. 10, is constituted by a light source Exalos SLED EBD-5200 which emits a signal having wavelength around $\lambda = 1.55\; \mu m$, a silica single-mode 50:50 coupler and two power meters (Newport, Optical Power Meter, Model 840). Bare fiber terminators (BFTs) are employed to connect the two arms of the silica single-mode 50:50 coupler to the fluoroindate optical fibers. This set-up is employed to characterize the combiner in terms of per-port net transmission efficiency ${\eta _{m,net}}$ at the wavelength $\lambda = 1.55\; \mu m$. The net transmission efficiency ${\eta _{m,net}} = {P_{out,comb}}/{P_{probe,IFG}}$ is defined as the ratio between the power measured at the output section of the combiner ${P_{out,comb}}$ and the power at the output section of a probe IFG 100/160 optical fiber ${P_{probe,IFG}}$; ${P_{probe,IFG}}$ being equal to the power launched in the IFG 100/160 optical input fiber of the combiner. Since both 3 × 1 IFG 100/160 fluoroindate input fibers of the combiner and the probe IFG 100/160 optical fiber are connectorized by using bare fiber terminators (BFTs), the transmission efficiency ${\eta _{m,net}}$ is net, i.e., evaluated without the coupling losses introduced by temporary connectors. The measured power levels by injecting the light at the different input ports ${P_i}$ with $i = \{{1 \div 3} \}$ and the net transmission efficiencies ${\eta _{m,net}}$ are reported in Table 2. The measured net transmission efficiency ${\eta _{m,net}}$ for a gaussian input beam with waist ${B_W} = 10.4\; \mu m$ at the wavelength $\lambda = 1.55\; \mu m$ is in excellent agreement with the simulated one ${\eta _{s,net}}({{L_{out}}} )$.
Fig. 10. Sketch of the experimental set-up used to characterize 3 × 1 fluoroindate combiner transmission efficiency ${\eta _{m,net}}$ at the wavelength $\lambda = 1.55\; \mu m$. The silica optical fibers are represented in black, the fluoroindate optical fibers in yellow.
Table 2. Measured power levels and 3×1 combiner transmission efficiencies at $\mathbf{\lambda } = 1.55\; \mathbf{\mu m}$
The measurements from NIR to Mid-IR are performed by employing the set-up sketched in Fig. 11, with the aim to investigate the combiner operation over the wavelength range from $\lambda = 1.00\; \mu m$ to $\lambda = \; 5.00\; \mu m$.
Fig. 11. Schematic of the experimental set-up used for 3 × 1 fluoroindate combiner characterization from NIR to Mid-IR.
The second set-up is constituted by halogen lamp, Horiba iHR550 monochromator to select the wavelength $\lambda $ and In-Sb-detector in combination with a lock-in amplifier. A number of 3 × 1 fluoroindate combiner have been fabricated and exhibited similar characteristics, proving a high repeatability. As an example, the characterization of the 3 × 1 fluoroindate combiner shown in Fig. 8, performed by exciting one of the input fibers, is reported. They are affected by coupling losses due to the axial/angular misalignment and due to the beam-quality degradation. Ultimately, the set-up in Fig. 11, differently from the one reported in Fig. 10, is not compensated and allows to measure the overall transmission efficiency ${\eta _{m,overall}}$. The overall transmission efficiency ${\eta _{m,overall}} = {P_{out,comb}}/{P_{in}}$ is defined as the ratio between the power measured at the output section of the combiner ${P_{out,comb}}$ and the input power ${P_{in}}$ delivered by the IFG 100/160 optical fiber, free space coupled with the optical source.
While the net transmission efficiency ${\eta _{m,net}}$ provides the actual performances of the 3 × 1 fluoroindate combiner the overall transmission efficiency ${\eta _{m,overall}}$ includes both the transmission losses of the combiner and those introduced by free propagation coupling. Despite these drawbacks, the qualitative measurement in Mid-IR is significant to demonstrate the 3 × 1 fluoroindate combiner operation over the entire wavelength range.
The measurement of the power at the output section of the combiner ${P_{out,comb}}$, by neglecting the power guided by the capillary, is relevant. Therefore, in order to dissipate the light power guided through the capillary (at the air-capillary interface, since no coating was applied on the combiner), a graphite adhesive, alcohol based solution, acting as absorber, is applied on the combiner. The overall transmission efficiency ${\eta _{m,overall}}$ with (dotdash line) and without graphite covering (solid curve) are illustrated in Fig. 12. It is worth noting that the measured overall transmission efficiencies ${\eta _{m,overall}}$ with graphite covering has an almost flat behavior from NIR to Mid-IR wavelength range. The same can be asserted for the net transmission efficiency ${\eta _{m,net}}$. Indeed, the overall transmission efficiency ${\eta _{m,overall}}$ is the net transmission efficiency ${\eta _{m,net}}$ reduced by the coupling losses.
Fig. 12. Overall transmission efficiency ${\eta _{m,overall}}$ measured in the Mid-IR wavelength range; 3 × 1 fluoroindate combiner without graphite covering (solid line), with graphite covering (dotdash line).
We conclude that the actual net transmission efficiency ${\eta _{m,net}}$ exhibits, as expected by simulations of Table 1 for larger beam waist ${B_W} = 70\; \mu m$, an almost flat behavior from $\lambda = 1\,\mu m$ to $\lambda = 5\,\mu m$. The mean value of this net transmission efficiency is expected to be larger than ${\eta _{m,net}} = 80.6\,{\%}$, which is the value accurately measured in the worst case of beam waist ${B_W} = 10.4\; \mu m$ at the wavelength $\lambda = 1.55\; \mu m$ via a balanced/compensated system.
In other words, the measurement with the broadband source proves a net transmission efficiency flat from NIR to Mid-IR reasonably close to the simulated value ${\eta _{s,net}}\,\sim \,98\,{\%}$.
3.5 Output beam measurements
A beam profiler Ophir Pyrocam IV has been employed to perform a far-field measurement of the beam at the output of the 3 × 1 fluoroindate combiner. One of the three input optical fibers have been excited with an SLED source operating at the wavelength $\lambda = 1.55\,\mu m$. A calibration is performed to compensate the ambient light intensity. Figure 13(a) reports the far-field measurement of the captured beam at the output of the combiner. Figure 13(b) reports near-field measurement of the beam at the output of 3 × 1 fluoroindate combiner, captured, at the wavelength $\lambda = 0.635\,\mu m$, by the CCD microscope camera of the Vytran GPX-2400, for the same input optical fiber of Fig. 13(a).
Fig. 13. (a) Far-field measurement of the beam at the output of the 3 × 1 fluoroindate combiner captured with the camera beam profiler Ophir Pyrocam IV at the wavelength $\lambda = 1.55\,\mu m$; (b) near-field measurement of the beam at the output of the 3 × 1 fluoroindate combiner captured, at the wavelength $\lambda = 0.635\,\mu m$, by the CCD microscope camera of the Vytran GPX-2400.
4. Conclusion
For the first time, a 3 × 1 fluoroindate combiner for Mid-IR wavelength range has been designed and fabricated. A customized fabrication and normalization technique, employing a Vytran GPX-2400 glass processing system has been developed. This result constitutes a first important step towards reliable further fused glass components based on fluoroindate (InF3) optical fibers. The characterization at the wavelength $\lambda = 1.55\,\mu m$ demonstrates a maximum per-port net transmission efficiency of ${\eta _{m,net}} = 80.6\,{\%}$ in agreement with simulations. The measurement with the broadband source proves a net transmission efficiency flat from NIR to Mid-IR reasonably close to the ${\eta _{s,net}}\,\sim \,98\,{\%}$. Our work paves the way for the fabrication of high quality and low-loss fluoroindate fiber combiners using commercial glass workstations, enabling wavelength and power scaling, eliminating the need for bulk optics components and free-space optical setups.
Funding
Ministero dell’Istruzione, dell’Università e della Ricerca (ARS01_00254, ARS01_01215); Horizon 2020 Framework Programme (101016956).
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.
References
1. A. M. Loconsole, M. C. Falconi, V. Portosi, and F. Prudenzano, “Numerical Design of a Gain-Switched Pulsed Laser at 3.92 µm Wavelength Based on a Ho3+-Doped Fluoroindate Fiber,” J. Lightwave Technol. 39(10), 3276–3283 (2021). [CrossRef]
2. Y. Wang, T. T. Fernandez, P. Tang, N. Coluccelli, S. D. Jackson, M. C. Falconi, F. Prudenzano, P. Laporta, and G. Galzerano, “Mid-IR tunable CW and passively Q-switched laser operation of Dy-doped fluoride fiber,” Opt. Mater. Express 12(4), 1502–1511 (2022). [CrossRef]
3. E. Baudel, A. Gutierrez-Arroyo, M. Baillieul, J. Charrier, P. Němec, L. Bodiou, J. Lemaitre, E. Rinnert, K. Michel, B. Bureau, J. L. Adam, and V. Nazabal, “Development of an evanescent optical integrated sensor in the mid-infrared for detection of pollution in groundwater or seawater,” Adv. Device Mater. 3(2), 23–29 (2017). [CrossRef]
4. S. Dupont, C. Petersen, J. Thøgersen, C. Agger, O. Bang, and S. R. Keiding, “IR microscopy utilizing intense supercontinuum light source,” Opt. Express 20(5), 4887–4892 (2012). [CrossRef]
5. B. Kuyken, T. Ideguchi, S. Holzner, M. Yan, T. W. Hänsch, J. Van Campenhout, P. Verheyen, S. Coen, F. Leo, R. Baets, G. Roelkens, and N. Picqué, “An octave-spanning mid-infrared frequency comb generated in a silicon nanophotonic wire waveguide,” Nat. Commun. 6(1), 6310 (2015). [CrossRef]
6. M. A. Ettabib, L. Xu, A. Bogris, A. Kapsalis, M. Belal, E. Lorent, P. Labeye, S. Nicoletti, K. Hammani, D. Syvridis, D. P. Shepherd, J. H. V. Price, D. J. Richardson, and P. Petropoulos, “Broadband telecom to mid-infrared supercontinuum generation in a dispersion engineered silicon germanium waveguide,” Opt. Lett. 40(17), 4118–4121 (2015). [CrossRef]
7. P. Ma, D. Y. Choi, Y. Yu, X. Gai, Z. Yang, S. Debbarma, S. Madden, and B. Luther-Davies, “Low-loss chalcogenide waveguides for chemical sensing in the mid-infrared,” Opt. Express 21(24), 29927–29937 (2013). [CrossRef]
8. C. R. Petersen, N. Prtljaga, M. Farries, J. Ward, B. Napier, G. R. Lloyd, J. Nallala, N. Stone, and O. Bang, “Mid-infrared multispectral tissue imaging using a chalcogenide fiber supercontinuum source,” Opt. Lett. 43(5), 999–1002 (2018). [CrossRef]
9. O. Benderov, I. Nechepurenko, B. Stepanov, T. Tebeneva, T. Kotereva, G. Snopatin, I. Skripachev, M. Spiridonov, and A. Rodin, “Broadband mid-IR chalcogenide fiber couplers,” Appl. Opt. 58(26), 7222–7226 (2019). [CrossRef]
10. M. C. Falconi, D. Laneve, V. Portosi, S. Taccheo, and F. Prudenzano, “Design of a multi-wavelength fiber laser based on Tm: Er: Yb: Ho co-doped germanate glass,” J. Lightwave Technol. 38(8), 2406–2413 (2020). [CrossRef]
11. I. D. Aggarwal and G. Lu, Fluoride Glass Fiber Optics (Academic Press, 2013).
12. H. C. de Sousa Pereira Menezes e Vasconcelos and M. C. Gonçalves, Overall Aspects of Non-Traditional Glasses: Synthesis, Properties and Applications (Bentham Science Publishers, 2016).
13. D. Tran, G. Sigel, and B. Bendow, “Heavy metal fluoride glasses and fibers: a review,” J. Lightwave Technol. 2(5), 566–586 (1984). [CrossRef]
14. L. N. Butvina, E. M. Dianov, N. Lichkova, V. Zavgorodnev, and L. Kuepper, “Crystalline silver halide fibers with optical losses lower than 50 dB/km in broad IR region and their applications,” Proc. SPIE 4083, Advances in Fiber Optics (2000).
15. M. Churbanov, G. Snopatin, V. Shiryaev, V. Plotnichenko, and E. Dianov, “Recent advances in preparation of high-purity glasses based on arsenic chalcogenides for fiber optics,” J. Non-Cryst. Solids 357(11-13), 2352–2357 (2011). [CrossRef]
16. A. Zakery and S. Elliott, “Optical properties and applications of chalcogenide glasses: a review,” J. Non-Cryst. Solids 330(1-3), 1–12 (2003). [CrossRef]
17. J. Sanghera and I. Aggarwal, “Active and passive chalcogenide glass optical fibers for IR applications: a review,” J. Non-Cryst. Solids 256-257(6–16), 1 (1999). [CrossRef]
18. J. J. Nunes, Ł. Sojka, R. W. Crane, D. Furniss, Z. Q. Tang, D. Mabwa, B. Xiao, T. M. Benson, M. Farries, N. Kalfagiannis, E. Barney, S. Phang, A. B. Seddon, and S. Sujecki, “Room temperature mid-infrared fiber lasing beyond 5 µm in chalcogenide glass small-core step index fiber,” Opt. Lett. 46(15), 3504–3507 (2021). [CrossRef]
19. M. El-Amraoui, J. Fatome, J. C. Jules, B. Kibler, G. Gadret, C. Fortier, F. Smektala, I. Skripatchev, C.F. Polacchini, Y. Messaddeq, J. Troles, L. Brilland, M. Szpulak, and G. Renversez, “Strong infrared spectral broadening in low-loss As-S chalcogenide suspended core microstructured optical fibers,” Opt. Express 18(5), 4547–4556 (2010). [CrossRef]
20. X. Liang, M. Zhong, T. Xu, J. Xiao, K. Jiao, X. Wang, Y. Bin, J. Liu, X. Wang, Z. Zhao, S. Bai, S. Li, D. Du, Y. He, Q. Nie, and R. Wang, “Mid-Infrared Single-Mode Ge-As-S Fiber for High Power Laser Delivery,” J. Lightwave Technol. 40(7), 2151–2156 (2022). [CrossRef]
21. K. J. Linden, “Fiber laser with 1.2-W CW-output power at 2712 nm,” IEEE Photonics Technol. Lett. 16(2), 401–403 (2004). [CrossRef]
22. S. Tokita, M. Hirokane, M. Murakami, S. Shimizu, M. Hashida, and S. Sakabe, “Stable 10 W Er:ZBLAN fiber laser operating at 2.71–2.88 µm,” Opt. Lett. 35(23), 3943–3945 (2010). [CrossRef]
23. S. D. Jackson, M. Pollnau, and J. Li, “Diode pumped erbium cascade fiber lasers,” IEEE J. Quantum Electron. 47(4), 471–478 (2011). [CrossRef]
24. J. Li, L. Wang, H. Luo, J. Xie, and Y. Liu, “High power cascaded erbium doped fluoride fiber laser at room temperature,” IEEE Photonics Technol. Lett. 28(6), 673–676 (2016). [CrossRef]
25. M. C. Falconi, D. Laneve, M. Bozzetti, T. T. Fernandez, G. Galzerano, and F. Prudenzano, “Design of an Efficient Pulsed Dy3+: ZBLAN Fiber Laser Operating in Gain Switching Regime,” J. Lightwave Technol. 36(23), 5327–5333 (2018). [CrossRef]
26. P. Tang, Y. Wang, E. Vicentini, F. Canella, L. M. Molteni, N. Coluccelli, P. Laporta, and G. Galzerano, “Single-Frequency Dy:ZBLAN Fiber Laser Tunable in the Wavelength Range From 2.925 to 3.250 µm,” J. Light. Technol. 40(8), 2489–2493 (2022). [CrossRef]
27. Y. Wang, F. Jobin, S. Duval, V. Fortin, P. Laporta, M. Bernier, G. Galzerano, and R. Vallée, “Ultrafast Dy3+:fluoride fiber laser beyond 3 µm,” Opt. Lett. 44(2), 395–398 (2019). [CrossRef]
28. S. Cozic, S. Poulain, and M. Poulain, “Low Loss Fluoride Optical fibers: Fabrication and Applications,” in Advanced Photonics (2018).
29. Le Verre Fluoré, Catalog (2022), Bruz, Brittany, France. [Online]. Available: https://leverrefluore.com/wp-content/uploads/2022/01/LVF-Catalog-2022.pdf.
30. F. Gan, “Optical properties of fluoride glasses: a review,” J. Non-Cryst. Solids 184, 9–20 (1995). [CrossRef]
31. I. S. Choi, J. Park, H. Jeong, J. W. Kim, M. Y. Jeon, and H. S. Seo, “Fabrication of 4× 1 signal combiner for high-power lasers using hydrofluoric acid,” Opt. Express 26(23), 30667–30677 (2018). [CrossRef]
32. F. Min, L. Zhixian, W. Zefeng, C. Zilun, and X. Xiaojun, “Research on a 4× 1 fiber signal combiner with high beam quality at a power level of 12 kW,” Opt. Express 29(17), 26658–26668 (2021). [CrossRef]
33. Y. Liu, K. Liu, Y. Yang, M. Liu, B. He, and J. Zhou, “High power pump and signal combiner for backward pumping structure with two different fused fiber bundle designs by means of pretapered pump fibers,” Opt. Express 29(9), 13344–13358 (2021). [CrossRef]
34. C. Lei, Y. Gu, Z. Chen, Z. Wang, P. Zhou, Y. Ma, H. Xiao, J. Leng, X. Wang, J. Hou, X. Xu, J. Chen, and Z. Liu, “Incoherent beam combining of fiber lasers by an all-fiber 7× 1 signal combiner at a power level of 14 kW,” Opt. Express 26(8), 10421–10427 (2018). [CrossRef]
35. T. Theeg, H. Sayinc, J. Neumann, L. Overmeyer, and D. Kracht, “Pump and signal combiner for bi-directional pumping of all-fiber lasers and amplifiers,” Opt. Express 20(27), 28125–28141 (2012). [CrossRef]
36. G. Stevens and T. Woodbridge, “Mid-IR fused fiber couplers,” Proc. SPIE 9730, 973007 (2016). [CrossRef]
37. R. R. Gattass, L. B. Shaw, and J. S. Sanghera, “Broadband Watt-Level Mid-Infrared Fiber-Coupled Variable Optical Attenuator,” IEEE Photonics Technol. Lett. 25(20), 2007–2009 (2013). [CrossRef]
38. C. Florea, J. S. Sanghera, B. Shaw, and I. D. Aggarwal, “Fiber Bragg gratings in As2S3 fibers obtained using a 0/−1 phase mask,” Opt. Mater. 31(6), 942–944 (2009). [CrossRef]
39. É. Ducharme, S. Virally, R. I. Becerra-Deana, C. Boudoux, and N. Godbout, “Viscosity of fluoride glass fibers for fused component fabrication,” Appl. Opt. 61(17), 5031–5039 (2022). [CrossRef]
40. L. Sójka, L. Pajewski, S. Lamrini, M. Farries, T. M. Benson, A. B. Seddon, and S. Sujecki, “High peak power Q-switched Er: ZBLAN fiber laser,” J. Lightwave Technol. 39(20), 6572–6578 (2021). [CrossRef]
41. R. R. Gattass, R. Thapa, F. H. Kung, L. E. Busse, L. B. Shaw, and J. S. Sanghera, “Review of infrared fiber-based components,” Appl. Opt. 54(31), F25–F34 (2015). [CrossRef]
42. B. Stepanov, O. Benderov, T. Tebeneva, G. Snopatin, and I. Scripachev, “Chalcogenide optical fiber couplers made by FBT method,” J. Non-Cryst. Solids 480, 23–27 (2018). [CrossRef]
43. F. Tavakoli, A. Rekik, and M. Rochette, “Broadband and Wavelength-Dependent Chalcogenide Optical Fiber Couplers,” IEEE Photonics Technol. Lett. 29(9), 735–738 (2017). [CrossRef]
44. I. Tugendhaft, A. Bornstein, Y. Weissman, and A. A. Hardy, “Directional multimode fiber couplers in the mid-infrared,” Opt. Eng. 34(10), 2846–2849 (1995). [CrossRef]
45. F. Tavakoli, A. Rekik, and M. Rochette, “Fused taper infrared optical fiber couplers in chalcogenide glass,” J. Lightwave Technol. 15(12), 2242–2245 (1997). [CrossRef]
46. R. R. Gattass, L. B. Shaw, F. H. Kung, D. J. Gibson, V. Q. Nguyen, G. D. Chin, L. E. Busse, I. D. Aggarwal, and J. S. Sanghera, “Infrared Fiber N x 1 Multimode Combiner,” IEEE Photonics J. 5(5), 7100905 (2013). [CrossRef]
47. P. Baer, P. Cebeci, M. Giesberts, and Oliver Fitzau, “Design and fabrication of a fused 7× 1 35/50 µm into 125/250 µm fiber combiner,” OSA Continuum 2(4), 1106–1112 (2019). [CrossRef]
48. A. Kosterin, V. Temyanko, M. Fallahi, and M. Mansuripur, “Tapered fiber bundles for combining high-power diode lasers,” Appl. Opt. 43(19), 3893–3900 (2004). [CrossRef]
49. L. S. Mendes, D. Pontes Nacaratti, R. E. Samad, and C. Costa Motta, “Theoretical Analysis of the Efficiency of a 7 × 1 End-Pumped Power Combiner,” SBMO/IEEE MTT-S International Microwave and Optoelectronics Conference (IMOC), 1–3 (2021).
50. D. Stachowiak, “High-power passive fiber components for all-fiber lasers and amplifiers application - Design and fabrication,” Photonics 5(4), 38 (2018). [CrossRef]
51. C. Lei, Z. Chen, Y. Gu, H. Xiao, and J. Hou, “Loss mechanism of all-fiber cascaded side pumping combiner,” High Power Laser Sci. Eng. 6, e56 (2018). [CrossRef]
52. S. Cozic, S. Boivinet, C. Pierre, J. Boulet, S. Poulain, and M. Poulain, “Splicing fluoride glass and silica optical fibers,” EPJ Web Conf. 215, 04003 (2019). [CrossRef]
53. J. J. Davenport, M. Diab, P. J. Deka, A. Tripathi, K. Madhav, and M. M. Roth, “Photonic lanterns: a practical guide to filament tapering,” Opt. Mater. Express 11(8), 2639–2649 (2021). [CrossRef]
