Optical fiber strain sensor based on sandwiched long-period fiber gratings with a surface bonding layer

Chia-Chin Chiang,Chien-Hsing Li

doi:10.1117/1.jmm.13.4.043008

Abstract

An optical fiber strain sensor based on sandwiched long-period fiber gratings (OFSS-SLPFG) with a surface bonding layer is proposed. The proposed OFSS-SLPFG is an etched optical fiber that is sandwiched between two thick photoresists with a periodic structure. To prevent the glue effect in the surface bonding process, where glue flows into the SLPFG structure, reducing the coupling strength, a surface bonding layer (thickness: 16 μm) is used as the base layer on the bottom of the OFSS-SLPFG. The OFSS-SLPFG is, therefore, more effective for use as a strain sensor. When external strain loading is applied, the resonant dip loss of the OFSS-SLPFG is reflected linearly. A bending strain calibration experiment is demonstrated by the four-point bending test. The results show an average linearity (R2) of 0.980, with a sensitivity of 0.00788 dB/με. This phenomenon suggests that the OFSS-SLPFG can be utilized as a sensitive strain transducer.

Highlights

Strain sensing is especially important as an engineering application
Small size, and electromagnetic resistance, the long-period fiber grating (LPFG) sensor is more applicable for sensing strain,[1,2,3,4] temperature,[5,6] pressure,[7] and dispersion compensation.[8]
In 2010, the sandwiched long-period fiber grating (SLPFG) was first reported[14] as a loss tunable filter made via the thick photoresist process

Summary

Introduction

Strain sensing is especially important as an engineering application. Normally, the resistance strain gauge is used in strain sensing. Small size, and electromagnetic resistance, the long-period fiber grating (LPFG) sensor is more applicable for sensing strain,[1,2,3,4] temperature,[5,6] pressure,[7] and dispersion compensation.[8]. The SLPFG structure consists of an etched optical fiber that is sandwiched between two thick photoresists with a periodic structure. This process of the SLPFG improves the overall performance of traditional fiber grating, and cuts down on fabrication costs. In a 1992 study on an LPFG-based optical sensor, Vaziri and Chen[1] proposed an etch method to fabricate fiber gratings as a strain gauge. A strain calibration is made on the optical fiber strain sensor based on a sandwiched long-period fiber grating (OFSS-SLPFG) sensor to obtain strain sensitivity

Theory

Processing of OFSS-SLPFG

Experimental Setup

Results and Discussion

Conclusions