Fabry-Perot liquid crystal tunable filter for interrogation of multiple fibre Bragg grating sensors

In this paper we analyze the performance of a fibre Bragg grating (FBG) interrogation system based on a liquid crystal tunable filter (LCTF), which acts as a channel dropper for multiple FBG sensors coupled to a simple all-fibre ratiometric wavelength measurement scheme in which a macrobending single-mode fibre is utilized as an edge filter. We present a model of the proposed interrogation scheme and analyse the optimum design parameters for the LCTF. From the model, the optimum ratio between the number of FBG sensors and the tunable filter bandpass can be found. Experimental results for the wavelength interrogation system are presented to validate the theoretical predictions. The model should be also suitable for similar interrogation systems using other forms of tunable bandpass filters.