Birefringent fiber grating sensor and detection system

Abstract

A sensor system comprises a broadband light source, a birefringent sensor, a detection circuit, and a signal processing unit. The preferred detection circuit further includes a variable frequency oscillator, a modulator, and a photodetector. The modulator modulates the output of the birefringent sensor with a modulation signal from the variable frequency oscillator. The modulation produces an interference signal having a variable interference frequency. By determining the frequency of the modulation signal from the variable frequency oscillator that minimizes the interference frequency, the detection system is able to determine the difference in frequency between first and second spectral components of the output of birefringent sensor. The detector may be constructed using entirely solid state optics/electronics. The preferred fiber grating sensor comprises a birefringent optical fiber having a cladding and a core. The cladding has first and second side holes formed therein that extend substantially parallel to the core, and that are substantially coextensively located with respect to each other along the length of the optical fiber. The first and second side holes are preferable positioned such that, in transverse cross section of the optical fiber, a first radial line that extends from the core to the first side hole is substantially perpendicular to a second radial line that extends from the core to the second side hole.