Transversal load sensor on addressed fiber Bragg structure with two phase shifts

Abstract

Fiber Bragg gratings (FBGs) have attracted considerable attention and have been used to measure various physical parameters. The best known is the use of FBGs to measure structural strain in a direction parallel to the optical fiber. However, it is also possible to use an FBG to measure the load in the direction transverse to the optical fiber. The paper presents scientifically based principles for constructing and results of experimental demonstration of polarization fiber optic sensors for monitoring of transversal load of a new type built on two addressed fiber Bragg structures (AFBS) with a microwave photonics interrogation. AFBS with two phase shifts have two ultra-narrow transmission peaks in the reflection band, which determine its address, expressed in GHz. When a transverse load is applied to AFBS, the transmission peaks will be divided into two due to the difference in the change of the fiber core refraction indices. The distance between the wavelengths of the separated peaks with two polarizations will change when the transversal force changes. The measured dependence between the value of the transverse force and the frequency of the beat-generated microwave signal shows very good linearity. The new sensor has the possibility to increase the resolution and sensitivity of measurements, as well as temperature compensation through the use of various AFBS of wavelength type. The range of measured forces is up to 100 N, the absolute measurement error is 0.1 N, frequency separation sensitivity is 0.1 GHz/N.