本文提出了一种基于模式转换增敏的长周期光纤光栅（long period fiber grating,LPFG）气压传感器，该传感器由LPFG和两层聚合物涂层组成。内层聚乙烯醇（polyvinylalcohol,PVA）的高折射率特性可以将LPFG的工作区间调谐至模式转换区。外层聚二甲基硅氧烷（polydimethylsiloxane,PDMS）具有多孔特性，可作为传感器的气压敏感材料。实验结果表明，当PVA厚度为244 nm时，传感器灵感度达612 pm/kPa，比未激发模式转换的LPFG传感器提升约50倍。PVA和PDMS对温度敏感，因此串联了一个光纤布拉格光栅（fiber Bragg grating,FBG）进行温度补偿。利用模式转换增敏的LPFG气压传感器具有灵敏度高、制备简单等优点，有望应用于高精度气压传感领域。
This paper proposes a long period fiber grating (LPFG) pressure sensor based on mode transition, consists of LPFG and two polymer films. The inner layer of polyvinyl alcohol (polyvinyl alcohol, PVA) with high refractive index properties can be tuned to operate within the LPFG’s mode transition region. The outer layer of porous polydimethylsiloxane (PDMS) can be used as a pressure-sensitive material for the sensor. Experimental results show that the sensor achieves a sensitivity of 612 pm/kPa when the PVA thickness is 244 nm, which is approximately 50 times higher than that of a conventional LPFG sensor without excitation mode transition. To address temperature sensitivity inherent in both the PVA and PDMS, a fiber Bragg grating (FBG) is connected in series for temperature compensation. The proposed LPFG pressure sensor based on mode transition exhibits high sensitivity and a simple fabrication process, making it a promising candidate for applications in high-precision pressure sensing.
[1] Melo L, Burton G, Davies B, et al. Highly sensitive coated long period grating sensor for CO2 detection at atmospheric pressure [J]. Sensors and Actuators B: Chemical, 2014, 202: 294-300.
[2] Liu G G, Han M. Fiber-optic gas pressure sensing with a laser-heated silicon-based Fabry-Perot interferometer [J]. Optics Letters, 2015, 40(11): 2461-2464.
[3] Bhatia V, Vengsarkar A M. Optical fiber long-period grating sensors [J]. Optics Letters, 1996, 21(9): 692-694.
[4] Gao H T, Xu D P, Ye Y Y, et al. Fiber-tip polymer filled probe for high-sensitivity temperature sensing and polymer refractometers [J]. Optics Express, 2022, 30(5): 8104-8114.
[5] Li Z Y, Liao C R, Wang Y P, et al. Highly-sensitive gas pressure sensor using twin-core fiber based in-line Mach-Zehnder interferometer [J]. Optics Express, 2015, 23(5): 6673-6678.
[6] Yang X H, Zhao Q K, Qi X X, et al. In-fiber integrated gas pressure sensor based on a hollow optical fiber with two cores [J]. Sensors and Actuators A: Physical, 2018, 272: 23-27.
[7] Liang H, Jia P G, Liu J, et al. Diaphragm-free fiber-optic Fabry-Perot interferometric gas pressure sensor for high temperature application [J]. Sensors, 2018, 18(4): 1011.
[8] Zhao Y J, Liu J X, Li H, et al. An ultra-sensitive gas pressure sensor based on tapered fiber coated with PDMS film working at TAP [J]. Optics & Laser Technology, 2022, 151: 107998.
[9] Zhang B W, Kahrizi M. High-temperature resistance fiber Bragg grating temperature sensor fabrication [J]. IEEE Sensors Journal, 2007, 7(4): 586-591.
[10] Tang D Q, Yang D X, Jiang Y J, et al. Fiber loop ring-down optical fiber grating gas pressure sensor [J]. Optics and Lasers in Engineering, 2010, 48(12): 1262-1265.
[11] Cheng X, Liu Y, Yu C Y. Gas pressure sensor based on BDK-doped polymer optical fiber [J]. Micromachines, 2019, 10(11): 717.
[12] Shu X W, Zhang L, Bennion I. Sensitivity characteristics of long-period fiber gratings [J]. Journal of Lightwave Technology, 2002, 20(2): 255-266.
[13] Deng L F, Jiang C, Hu C J, et al. Highly sensitive temperature and gas pressure sensor based on long-period fiber grating inscribed in tapered two-mode fiber and PDMS [J]. IEEE Sensors Journal, 2023, 23(14): 15578-15585.
[14] Del Villar I, Achaerandio M, Matías I R, et al. Deposition of overlays by electrostatic self-assembly in long-period fiber gratings [J]. Optics Letters, 2005, 30(7): 720-722.
[15] Del Villar I, Matías I R, Arregui F J, et al. Optimization of sensitivity in long period fiber gratings with overlay deposition [J]. Optics Express, 2005, 13(1): 56-69.
[16] Cusano A, Iadicicco A, Pilla P, et al. Mode transition in high refractive index coated long period gratings [J]. Optics Express, 2006, 14(1): 19-34.
[17] Coelho L, Viegas D, Santos J L, et al. Enhanced refractive index sensing characteristics of optical fibre long period grating coated with titanium dioxide thin films [J]. Sensors and Actuators B: Chemical, 2014, 202: 929-934.
[18] Yang J C, Zhou L, Huang J, et al. Sensitivity enhancing of transition mode long-period fiber grating as methane sensor using high refractive index polycarbonate/cryptophane A overlay deposition [J]. Sensors and Actuators B: Chemical, 2015, 207: 477-480.
[19] Esposito F, Zotti A, Ranjan R, et al. Single-ended long period fiber grating coated with polystyrene thin film for butane gas sensing [J]. Journal of Lightwave Technology, 2018, 36(3): 825-832.
[20] Wang Y L, Liu Y Q, Zou F, et al. Humidity sensor based on a long-period fiber grating coated with polymer composite film [J]. Sensors, 2019, 19(10): 2263.
[21] Qu J Y, Zhang H X, Shi X Y, et al. High sensitivity temperature sensing of long-period fiber grating for the ocean [J]. Sensors, 2023, 23(10): 4768.
