The variation of ambient refractive index and ambient temperature is the main factor affecting the error of optical fiber strain measurement. In this paper, a strain sensor based on the dual-mode fiber (DMF) long period fiber grating (LPFG) is designed. The sensor model structure was designed, and the sensor samples with optimized parameters were produced. The experiment tested the response of the DMF-LPFG sensing structure to the strain, temperature and refractive index in the external environment. Through the Bragg grating (fiber Bragg grating, FBG) written on the single-mode fiber with a UV laser, the cross effect of the ambient temperature is solved. The results of the axial strain experiment show that the axial strain sensitivity of the new structure sensor can reach -5.4 pm/με in the strain range of 0 με~840 με, which is greatly improved compared to the ordinary LPFG. The sen-sitivity is 58.86 pm/℃ in the temperature range of 25 ℃~80 ℃, showing good linearity. At the same time, the sensor is insensitive to changes in ambient refractive index. The dual-parameter matrix is used to process the strain and temperature sensitivity of the few-mode LPFG and FBG to achieve dual-parameter simultaneous demodulation. The new composite grating structure has good sensing performance and engineering application prospects.
Refractive index insensitive two parameter sensor based on dual mode LPEG
First published at:Mar 22, 2021
 Vengsarkar A M, Lemaire P J, Judkins J B, et al. Long-period fiber gratings as band-rejection filters[J]. J Lightwave Technol, 1996, 14(1): 58–65.
 James S W, Tatam R P. Optical fibre long-period grating sensors: characteristics and application[J]. Meas Sci Technol, 2003, 14(5): R49–R61.
 Liao C R, Wang Y, Wang D N, et al. Femtosecond laser inscribed long-period gratings in all-solid photonic bandgap fibers[J]. IEEE Photonics Technol Lett, 2010, 22(6): 425–427.
 Martinez-Rios A, Monzon-Hernandez D, Torres-Gomez I. Highly sensitive cladding-etched arc-induced long-period fiber gratings for refractive index sensing[J]. Opt Commun, 2010, 283(6): 958–962.
 Bai Z Y, Zhang W G, Gao S C, et al. Compact long period fiber grating based on periodic micro-core-offset[J]. J Lightwave Technol, 2013, 25(21): 2111–2114.
 Rego G, Okhotnikov O, Dianov E, et al. High-temperature stability of long-period fiber gratings produced using an electric arc[J]. J Lightwave Technol, 2001, 19(10): 1574–1579.
 Jiang Y H, Fu H W, Zhang J L, et al. Simultaneous measurement of transverse pressure and temperature based on multi-core fiber cascaded with fiber Bragg grating[J]. Acta Photonica Sin, 2017, 46(1): 0106002.
蒋友华, 傅海威, 张静乐, 等. 基于多芯光纤级联布喇格光纤光栅的横向压力与温度同时测量[J]. 光子学报, 2017, 46(1): 0106002.
 Chu J L, Shen C Y, Feng Q, et al. Simultaneous measurement of strain and temperature based on a long-period grating with a polarization maintaining fiber in a loop mirror[J]. Opt Fiber Technol, 2014, 20(1): 44–47.
 Yang M W, Wang D N, Wang Y, et al. Long period fiber grating formed by periodically structured microholes in all-solid photonic bandgap fiber[J]. Opt Express, 2010, 18(3): 2183–2189.
 Liu Q, Bi W H, Fu X H, et al. Refractive index sensing characteristic of superimposed long period gratings on few mode fiber[J]. Acta Photonica Sin, 2018, 47(1): 0106001.
刘强, 毕卫红, 付兴虎, 等. 基于少模光纤长周期光栅叠栅的折射率传感特性[J]. 光子学报, 2018, 47(1): 0106001.
National Programs for Science and Technology Development (61327012), National Natural Sciene Foundation of China (61735014), National Key Scientific Instrument and Equipment Development Project (61927812), and National Key Research and Development Plan (2017YFB0405502)
Get Citation: Wang Xiangyu, Qiao Xueguang, Yu Dakuan. Refractive index insensitive two parameter sensor based on dual mode LPEG[J]. Opto-Electronic Engineering, 2021, 48(3): 200247.