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Abstract
Fiber-optic devices working in the visible and near-infrared windows are attracting attention due to the rapid development of biomedicine that involves optics. In this work, we have successfully realized the fabrication of near-infrared microfiber Bragg grating (NIR-µFBG), which was operated at the wavelength of 785 nm, by harnessing the fourth harmonic order of Bragg resonance. The NIR-µFBG provided the maximum sensitivity of axial tension and bending to 211 nm/N and 0.18 nm/deg, respectively. By conferring the considerably lower cross-sensitivity, such as response to temperature or ambient refractive index, the NIR-µFBG can be potentially implemented as the highly sensitive tensile force and curve sensor.
© 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
1. Introduction
Microfibers are optical fibers with the diameter of several microns, which possess a myriad of advantages, such as large evanescent field, smaller effective mode field diameter, high nonlinearity and pliability, and low-loss interconnection to conventional fibers. It enables wide applications in many fields, for example, passive photonic devices [1–3], sensing [4,5], lasing [6,7], and signal processing [8]. Microfiber Bragg gratings (µFBGs) are formed by introducing periodic variations in refractive index or geometrical tailoring to microfibers. Compared with the conventional counterpart of microfiber-based devices, such as microfiber interferometer, µFBG further compacts the footprint of the device and enables multiplexing by virtue of the monochromatic reflection signal. Therefore, the µFBG is an excellent candidate to serve as the biosensor and have so far been used for label-free detection of nucleic acids [9], proteins [10,11], and cardiovascular biomarkers [12,13]. Chemical etching [14–16], focused ion beam (FIB) milling [17] and femtosecond laser irradiation [18] were exploited for the fabrication of µFBG. In contrast with those fabrication strategies, grating inscription using UV laser and phase mask is more convenient and compatible with widely applied fabrication method. However, both the fabrication and application of µFBGs reported in the previous studies had focused on the C-band [19,20]. Despite the fact that recent research had fabricated the µFBG resonating in the second near infrared (NIR-II) biological window (1000-1350 nm) [4,13,21], further manipulation of the reflection wavelength of the µFBG remains required.
As an important wave band, 800 nm-band is the first optical fiber communication window for low loss light transmission [22]. FBG working in 800 nm-band outweighs its counterpart operated at 1550 nm-band for sensing water-based analytes due to the strong absorption of hydroxyl bonds above 1400 nm [23]. Furthermore, the 800 nm-band rides into the first near-infrared (NIR-I) biological window (700–900 nm) and thus allows for photon-based deep-tissue imaging and therapy [24]. By surveying our previous research focusing on “ harmonic Bragg gratings ” [25], near-visible fiber Bragg grating yielding the resonances at 800 nm-waveband was produced by Talbot-UV-pattern which is created by higher order diffraction of the incident UV laser through a phase mask. The cost and difficulty of manufacturing optical sensors based on wavelength design modulation are decreased by this effective and straightforward inscription technology. However, the µFBG working in the 800 nm-band has not been reported to date.
In this paper, we explore the efficient fabrication of the harmonic near-infrared microfiber Bragg gratings with different diameters. The sensing characteristics of the NIR-µFBGs have been investigated. The temperature sensitivity of 5.93 pm/°C and refractive index sensitivity of 2.689 nm/RIU are revealed by observing the reflected wavelength shift. More importantly, the highest axial tension sensitivity and bending sensitivity could reach 0.211 nm/µm and 0.18 nm/deg, which demonstrates the higher sensitivity and application potential of the sensor for human joint motion monitoring [26–28]. The highly sensitive NIR-µFBGs can endow patients, who suffered from joint issues, with the long-term joint monitoring functionality, which would provide a more objective evaluation on their rehabilitation.
2. Theory and principle
Figure 1 illustrates the phase-mask assisted µFBG inscription. The ultra-violet laser beam incident through the phase mask is diffracted and then interfered, spatially periodic interference patterns are imprinted in the fiber core. However, the commercial phase mask used in the experiments has a small amount of indelible ±2 order diffractions rather than the ideal condition, in which only the ±1 order diffractions exist [29]. The participation of the higher-order diffractions, which gives rise to the modulated pattern with sinusoidally varying energy intensity in the incident direction. The period of function is defined as Talbot length ZT, which is expressed as [30]
where m and n are integers representing diffraction orders and m < n, $G = ({2\pi /{\mathrm{\Lambda }_{pm}}} )$, $k = 2\pi N/\lambda $, N represents the refractive index of the laser propagating medium at the incident UV wavelength λ. As a result, Talbot-UV-pattern is applied to the core, thus leaving periodic refractive index changes on the fiber core.Previous studies have shown that the resonant wavelength for Bragg wavelength is given by the following equation [31]
where ${\lambda _{Bragg}}(j )$ is the reflected wavelength of the j th harmonic of Bragg (j = 1, 2, 3, 4 · · ·), ${N_{eff1}}$ and ${N_{eff2}}\; $ represents the effective index of the forward and backward transverse modes, respectively. A super-pioned modulation structure with two different amplitudes is enabled on the fiber core since the appearance of the Talbot-UV-pattern. The new superstructure modulation period with ${\varLambda _g}$ is ${\varLambda _g}$ =${\varLambda _{pm}}$ instead of ${\varLambda _g}$=${\varLambda _{pm}}$ /2. Under this circumstance, the fourth harmonic resonance (j = 4) reveals itself at the near-visible band (800 nm). Therefore, the fourtharmonic resonance would exist around 1/2 ${\varLambda _{Bragg}}$, which gave the flexibility to design wavelength ranging from approximately 765-800 nm by using C-band phase masks only.3. Experiments
Follow this strategy, the whole signal path is fiber-connected, which is similar to the setup of the grating inscription in the previous report [20]. Corning 62.5/125 multimode fiber was the optimal choice for inscribing NIR-µFBG in the study. The reason is that the fiber would maintain a sizable germanium-doped region after thinned [20]. The substantial photosensitive region of fiber can refrain the light transmission of fundamental mode and ensure the efficiency of µFBG formation under UV inscription. Figure 2(a) shows three sizes of 3 µm, 7 µm and 11 µm micro-nano fibers with a core diameter about half the diameter of a tapered micro-nano fiber. ${Z_T}$ can be calculated to ∼6.5 µm by Eq. (1). The core of the fabricated micro-nano fibers is smaller than ${Z_T}$, which means the NIR-µFBG inscription process has interlaced modulation patterns of contrasting intensity on the fibers.
Fig. 2. (a) Microscopic images of microfibers with the diameters of (1) 3 µm, (2) 7 µm, and (3) 11 µm; (b) Real product of the NIR-µFBG with input of broadband light source; (c) Reflective spectra of NIR-µFBGs for 30 seconds inscription time. (Data File 1 [33])
In this case, in order to avoid the laborious and risky procedure of photosensitive treatment on fiber, e.g., the hydrogen loading, a 193 nm UV excimer laser (Compex 110, Coherent co, Ltd.) was recruited to direct form FBG on the microfiber, in combination with a C-band phase mask (pitch = 1081.55 nm). The repetition rate and energy density of UV radiation were set to 200 mJ/cm2 and 40 Hz, respectively. By conducting a 30 second-exposure, the NIR-µFBG could be fabricated and revealed as the segment with red light diffraction in the Fig. 2(b). Figure 2(c) shows the reflection spectra of the NIR-µFBGs with different diameters. The efficiency of grating inscription between the µFBGs is similar as the microfibers have the diameters in the same order of magnitude. The 11 µm and 7 µm NIR- FBGs presented the spectra with multiple resonances, which are attributed to the intermodal coupling between the fundamental and higher order transverse modes. By contrast, the 3 µm NIR-FBG shows a monochromatic reflection signal with a 3 dB bandwidth of 0.3 nm due to the smaller core diameter (∼1.5 µm), which can support the single mode operation of the fiber. By comparing the fundamental peak wavelengths of the three NIR-µFBGs, we can learn that the peak wavelength of NIR-µFBG could be signed via the control of fiber diameter. The smaller diameter of µFBG would confer a reflection signal at a shorter wavelength.
4. Results and discussion
At first, we had tested the spectral variation of the fourth harmonic NIR-µFBG with respect to the stimulus. The µFBG operates on a similar principle to the FBG, mainly depending on the resonant wavelength shift with regard to a change of external measurand. As shown in Fig. 3 to Fig. 5, the sensing characteristics of NIR-µFBG in different sizes had been investigated experimentally.
The bending responsiveness of the NIR-µFBG was tested. The bending angle was used in the characterization because it relates to joint motion monitoring [26–28]. Figure 3 shows the spectral drifts of NIR-µFBGs that were applied by the process of bending from 0 to the limited angle, at which the signal wavelength was no longer shifted, and then return to the original state. Regarding the NIR-µFBGs had different limited angle due to their diameters, the angle degrees were shown in a relative manner for making the comparison clearly. The resonance wavelength shift exhibits a similar tendency regarding the curvature by presenting a circular arc shape. FBG inscribed on the same type of fiber has low sensitivity near the short wave [25]. Therefore, a normal FBG resonated in 1550 nm band was deployed for establishing the benchmark of the FBG bending sensor. The 3 µm NIR-µFBG held the best bending sensitivity of 0.18 nm/deg with the limited angle of 35 deg. The bending sensitivities of 7 µm- and 11 µm- NIR-FBG sensors are 0.141 nm/deg and 0.107 nm/deg, respectively. Besides, we can observe the limit angle for these two sensors are both 20 deg, which is three quarters to 3 µm-NIR-FBG-sensor. It can be inferred that the smaller diameter NIR-µFBG sensor would exhibit higher bending sensitivity and larger limited angle. Compared with the normal FBG (0.015 nm/deg of sensitivity and 15 deg of limited angle), 3 µm NIR-µFBG sensor presented a one order of magnitude higher sensitivity and a doubled limited angle, respectively.
In the following, we had investigated the tensile force sensing capability of the NIR-µFBGs. In the experiment, one end of the NIR-µFBG was immobilized and the other end was attached on the tensiometer. The axis of the fiber was kept parallel to the tensile direction and the preliminary distance between the two ends was set to 15 cm. Different axial tensions were applied to the sensor, and the center wavelength shift of the sensor was logged accordingly. The preliminary tension on the NIR-µFBG was set to 0.03N to guarantee the linearity of responsiveness of the grating signal. As shown in Fig. 4, the tension sensitivity of 7 µm- and 11 µm- NIR- FBGs are approximately 211 nm/N and 84 nm/N, respectively. As a benchmark, the sensitivity of single-mode FBG is an order of magnitude lower than 11 µm NIR- FBG. And the 7 µm NIR- FBG is two orders of magnitude more sensitive than the single-mode FBG. The sensitivity enhancement of µFBG can be ascribed to the tensile amplified effect, which is resulted from the fiber segment with a smaller cross section area [32]. It can be found that the NIR-µFBG could maintain a high level of sensitivity despite the condition that it was operated at great higher order harmonics. The tensile amplified effect can also be used to explain the high bending sensitivity enabled by NIR-µFBG, where tensile force as well makes an important role.
In the sensing scenario, the cross-talk of sensor is inevitable, which may deteriorate the sensing performance and fidelity of the results. In this regard, the ambient interference, such as fluctuations of temperature and outer refractive index (RI) and are mainly taken into consideration.
The temperature response test was carried out by use of a thermal controller. The spectral evolution of 3 µm-NIR-FBG with the change of temperature from 30 °C to 70 °C was logged in the inset of Fig. 5(a). The increase of temperature resulted in the red-shift of wavelength and increase of the intensity of reflection spectrum due to the thermal expansion and thermal optic effect. By tracing the corresponded wavelength shift, the temperature sensitivity of 3 µm-NIR-FBG can be obtained to 5.93 pm/°C, which is approximately one half of the normal FBG. Figure 5(b) showcases the sensing curves of the 7 µm- and 11 µm- NIR- FBGs and presents the temperature sensitivity to 5.17 pm/°C and 5.06 pm/°C, respectively. It means the temperature sensitivity is also related to the fiber size. However, the gap is not very remarkable regarding that the maximum difference for temperature sensitivity in this test is only 0.87 pm/°C.
In the following, by immersing the grating zone into the solution mixed with deionized water and ethanol, the RI response of the NIR-µFBG can be evaluated. The RI of liquid sample can be simply tuned by a range from 1.335 to 1.360 through altering the volume ratio of the two components. The 3 µm-NIR-FBG conferred the highest RI sensitivity of 2.689 nm/RIU, while the 7 µm- and 11 µm- NIR-FBGs possessed the RI sensitivity of 1.341 nm / RIU and 1.365 nm / RIU, respectively, as is depicted in Fig. 5(c). The RI sensitivity of the NIR-µFBG were also dependent to the fiber diameter, which is in line with the response to bending and tension, but the discrepancy is not very significant due to the higher harmonic resonance can be attributed to the contraction of grating period mediated shorter operation wavelengths, which results in the appearance of a smaller evanescent field.
Fig. 5. Temperature response for (a) 3 µm NIR- FBG or (b) 7 and 11 µm NIR- FBG ; (c) Three sizes of NIR-µFBG spectral variation versus the RI change; (d) The wavelength stability of NIR-µFBG in water at the different temperatures. (Data File 2 [34])
It can be noted that the temperature and refractive index responses of the NIR-µFBGs are both lower in contrast with the µFBG working at C-band. The specific heat capacity of water is 4.2 × 103J/(kg·°C). It means that heat can be transferred more evenly to the grating when the NIR-µFBGs is immerged in water. Therefore, we had tested the stability of the sensor by immersing the 7 µm-NIR- FBG in the deionized water, which can be thermalized by a plate heater. Regarding the NIR- FBG had a small refractive index sensitivity, the water-bath heat will not significantly change the temperature sensitivity, compared with heating in the air. By logging the wavelength signal variation within a duration of 20 minutes, the results can be seen in Fig. 5(d). The benchmark was set by monitoring the Bragg wavelength shift in the water at 20 °C. At higher temperature, the fluctuations were higher, which present the standard deviation in the scale of 6∼7 pm. It shows that the standard deviation of the sensor remains in a small scale when the temperature reaches higher than 50 °C. For the room temperatures, the standard deviation was reduced to the scale of 3∼4 pm. Regarding the room temperature is a more common condition, the NIR-µFBG enables a higher signal-to-noise rate for the wavelength encoded sensing regime. These data, therefore, show that the proposed NIR-µFBG sensor can measure axial tension or curvature with high sensitivity while maintaining low cross-sensitivity.
5. Conclusions
In conclusion, the near-infrared fiber Bragg grating is successfully formed in microfiber following the regime of harmonic resonances. By harnessing the correlation between the core size and the Talbot length, the microfiber Bragg grating possessing a fourth harmonic resonance in 800 nm-band can be obtained by a repeatable and straightforward inscription approach. The NIR-µFBG presented high sensitivity to the tensile force and curvature, which could be up to two orders magnitude higher than the normal FBG (211 nm/ N vs 1.3 nm/N; 0.14 nm/deg vs 0.015 nm/deg). The reason is accounted for by the local strain magnified effect of the microfiber grating structure. On the other hand, the sensitivity of the temperature (5.93 pm/°C) and refractive index (2.689 nm/RIU) were both low, compared with µFBGs operates in the conventional waveband. The proposed NIR-µFBG can expand the operation band of µFBGs, facilitating the full utilization of the optical wavebands. Furthermore, the demonstration of higher-order harmonic microfiber gratings offers the alluring promise of greater flexibility in wavelength design for FBG-based sensors. The sensor also showcases its application potential of the sensor for human joint motion monitoring.
Funding
Science and Technology Research Project of Higher Education of Hebei Province (BJ2021093); Natural Science Foundation of Hebei Province (F2021109003); National Natural Science Foundation of China (62175055).
Disclosures
The authors declare no conflicts of interest related to this article.
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. M. Sumetsky, “Optical fiber microcoil resonator,” Opt. Express 12(10), 2303–2316 (2004). [CrossRef]
2. F. Xu and G. Brambilla, “Embedding optical microfiber coil resonators in Teflon,” Opt. Lett. 32(15), 2164–2166 (2007). [CrossRef]
3. X. Jiang, Y. Chen, G. Vienne, and L. Tong, “All-fiber add-drop filters based on microfiber knot resonators,” Opt. Lett. 32(12), 1710–1712 (2007). [CrossRef]
4. Y. Ran, J. Long, Z. Xu, D. Hu, and B. O. Guan, “Temperature monitorable refractometer of microfiber Bragg grating using a duet of harmonic resonances,” Opt. Lett. 44(13), 3186–3189 (2019). [CrossRef]
5. Y. Ran, L. Jin, L.-P. Sun, J. Li, and B.-O. Guan, “Bragg gratings in rectangular microfiber for temperature independent refractive index sensing,” Opt. Lett. 37(13), 2649–2651 (2012). [CrossRef]
6. Q. Yang, X. Jiang, X. Guo, Y. Chen, and L. Tong, “Hybrid structure laser based on semiconductor nanowires and a silica microfiber knot cavity,” Appl. Phys. Lett. 94(10), 101108 (2009). [CrossRef]
7. X. Jiang, Q. Yang, G. Vienne, Y. Li, L. Tong, J. Zhang, and L. Hu, “Demonstration of microfiber knot laser,” Appl. Phys. Lett. 89(14), 143513 (2006). [CrossRef]
8. Y. Zhang, E. Xu, D. Huang, and X. Zhang, “All-Optical Format Conversion From RZ to NRZ Utilizing Microfiber Resonator,” IEEE Photonics Technol. Lett. 21(17), 1202–1204 (2009). [CrossRef]
9. D. Sun, T. Guo, Y. Ran, Y. Huang, and B. O. Guan, “In-situ DNA hybridization detection with a reflective microfiber grating biosensor,” Biosens. Bioelectron. 61, 541–546 (2014). [CrossRef]
10. P. Xiao, Z. Xu, D. Hu, L. Liang, L. Sun, J. Li, Y. Ran, and B.-O. Guan, “Efficiently Writing Bragg Grating in High-Birefringence Elliptical Microfiber for Label-Free Immunosensing with Temperature Compensation,” Adv. Fiber Mater. 3(5), 321–330 (2021). [CrossRef]
11. Y. Cao, X. Wang, T. Guo, Y. Ran, X. Feng, B.-O. Guan, and J. Yao, “High-resolution and temperature-compensational HER2 antigen detection based on microwave photonic interrogation,” Sens. Actuators, B 245, 583–589 (2017). [CrossRef]
12. T. Liu, L. L. Liang, P. Xiao, L. P. Sun, Y. Y. Huang, Y. Ran, L. Jin, and B. O. Guan, “A label-free cardiac biomarker immunosensor based on phase-shifted microfiber Bragg grating,” Biosens. Bioelectron. 100, 155–160 (2018). [CrossRef]
13. Y. Ran, J. Long, Z. Xu, Y. Yin, D. Hu, X. Long, Y. Zhang, L. Liang, H. Liang, and B. O. Guan, “Harmonic optical microfiber Bragg grating immunosensor for the accelerative test of cardiac biomarker (cTn-I),” Biosens. Bioelectron. 179, 113081 (2021). [CrossRef]
14. A. Iadicicco, A. Cusano, S. Campopiano, A. Cutolo, and M. Giordano, “Thinned fiber Bragg gratings as refractive index sensors,” IEEE Sens. J. 5(6), 1288–1295 (2005). [CrossRef]
15. A. Iadicicco, A. Cusano, A. Cutolo, R. Bernini, and M. Giordano, “Thinned fiber Bragg gratings as high sensitivity refractive index sensor,” IEEE Photonics Technol. Lett. 16(4), 1149–1151 (2004). [CrossRef]
16. W. Liang, Y. Huang, Y. Xu, R. K. Lee, and A. Yariv, “Highly sensitive fiber Bragg grating refractive index sensors,” Appl. Phys. Lett. 86(15), 151122 (2005). [CrossRef]
17. Y. Liu, C. Meng, A. P. Zhang, Y. Xiao, H. Yu, and L. Tong, “Compact microfiber Bragg gratings with high-index contrast,” Opt. Lett. 36(16), 3115–3117 (2011). [CrossRef]
18. X. Fang, C. Liao, and D. Wang, “Femtosecond laser fabricated fiber Bragg grating in microfiber for refractive index sensing,” Opt. Lett. 35(7), 1007–1009 (2010). [CrossRef]
19. Y. Zhang, B. Lin, S. C. Tjin, H. Zhang, G. Wang, P. Shum, and X. Zhang, “Refractive index sensing based on higher-order mode reflection of a microfiber Bragg grating,” Opt. Express 18(25), 26345–26350 (2010). [CrossRef]
20. Y. Ran, Y.-N. Tan, L.-P. Sun, S. Gao, J. Li, L. Jin, and B.-O. Guan, “193 nm excimer laser inscribed Bragg gratings in microfibers for refractive index sensing,” Opt. Express 19(19), 18577–18583 (2011). [CrossRef]
21. Q. Yang, Y. Hao, X. Long, Y. Wu, X. Yue, J. Cai, Z. Xu, Y. Ran, L. Jin, and B. O. Guan, “Third harmonic phase-shifted Bragg grating sensor,” Opt. Lett. 47(8), 1941–1944 (2022). [CrossRef]
22. P. D. Townsend, “Experimental investigation of the performance limits for first telecommunications-window quantum cryptography systems,” IEEE Photonics Technol. Lett. 10(7), 1048–1050 (1998). [CrossRef]
23. G. M. Hale and M. R. Querry, “Optical constants of water in the 200-nm to 200-µm wavelength region,” Appl. Opt. 12(3), 555–563 (1973). [CrossRef]
24. J. Zhao, D. Zhong, and S. Zhou, “NIR-I-to-NIR-II fluorescent nanomaterials for biomedical imaging and cancer therapy,” J. Mater. Chem. B 6(3), 349–365 (2018). [CrossRef]
25. X. Long, Y. Yin, J. Long, Z. Xu, J. Cai, Y. Zhang, Y. Ran, and B. O. Guan, “Near-Visible Fiber Sensing Tandem Exploiting Single-Pulse Modulated Harmonic Bragg Gratings,” J. Lightwave Technol. 39(17), 5650–5656 (2021). [CrossRef]
26. L. Li, R. He, M. S. Soares, S. Savovic, X. Hu, C. Marques, R. Min, and X. Li, “Embedded FBG-Based Sensor for Joint Movement Monitoring,” IEEE Sens. J. 21(23), 26793–26798 (2021). [CrossRef]
27. C. K. Jha, A. L. Chakraborty, and S. Agarwal, “A fiber Bragg grating-based sensing glove with a sensitivity of 18.45 pm/degree to accurately assess finger flexure,” in Optical Fiber Sensors, (Optica Publishing Group, 2018), WB4.
28. X. Yue, R. Lu, Q. Yang, E. Song, H. Jiang, Y. Ran, and B. O. Guan, “Flexible Wearable Optical Sensor Based on Optical Microfiber Bragg Grating,” J. Lightwave Technol. 41(6), 1858–1864 (2023). [CrossRef]
29. K. O. Hill and G. Meltz, “Fiber Bragg grating technology fundamentals and overview,” J. Lightwave Technol. 15(8), 1263–1276 (1997). [CrossRef]
30. J. D. Mills, C. W. Hillman, B. H. Blott, and W. S. Brocklesby, “Imaging of free-space interference patterns used to manufacture fiber Bragg gratings,” Appl. Opt. 39(33), 6128–6135 (2000). [CrossRef]
31. T. Erdogan, “Fiber grating spectra,” J. Lightwave Technol. 15(8), 1277–1294 (1997). [CrossRef]
32. Y. Ran, L. Jin, S. Gao, L.-P. Sun, Y.-Y. Huang, J. Li, and B.-O. Guan, “Type IIa Bragg gratings formed in microfibers,” Opt. Lett. 40(16), 3802–3805 (2015). [CrossRef]
33. Y. Ran, “Reflective spectra of NIR-µFBGs for 30 seconds inscription time.,” figshare (2023).[retrieved 18 April 2023] https://doi.org/10.6084/m9.figshare.22567102
34. Y. Ran, “Temperature response for (a) 3 µm NIR- FBG or (b) 7 and 11 µm NIR- FBG ; (c) Three sizes of NIR-µFBG spectral variation versus the RI change; (d) The wavelength stability of NIR-µFBG in water at the different temperatures.,” figshare (2023).[retrieved 18 April 2023] https://doi.org/10.6084/m9.figshare.22567102
35. Y. Ran, “Responses to the tension of two sizes of NIR-µFBG and single-mode FBG,” figshare (2023).[retrieved 18 April 2023] https://doi.org/10.6084/m9.figshare.22567096
36. Y. Ran, “Bending response for three sizes of NIR-µFBG and single-mode FBG,” figshare (2023).[retrieved 18 April 2023] https://doi.org/10.6084/m9.figshare.22567093
