Application on Demodulation of FBG Sensing Signals using Phase Detection Algorithm of Intake and Exhaust

Fiber Fabry-Perot tunable filter (FFP-TF) based fiber Bragg grating (FBG) demodulation has been widely applied in many areas, in which F-P etalon is commonly used as wavelength reference. The traditional demodulation algorithm requires the whole spectrum data of each cycle to calculate the sensing signal wavelength, seriously affecting the real-time performance. The spectrum of the fiber-optic F-P etalon is a uniform comb spectrum with a typical marker, similar to the engine crankshaft signal. When an engine runs at high speed, the intake and exhaust phase needs to be demodulated as soon as possible. In this paper, a low delay FBG sensing demodulation algorithm is proposed, drawing on the experience of the intake and exhaust phase demodulation algorithm. When the scanning speed is 1k Hz, the delay can be reduced more than ten times (e.g., from 0.1ms to 0.01ms).

I. Introduction

Fiber Bragg grating (FBG) sensors are very suitable for structural health monitoring (SHM) of spacecrafts and petrochemicals, because of their small size, lightweight, immune to electromagnetic, anti-corrosion, multiplexing capabilities, and forming network [1]. FBG demodulation algorithm based on the tunable filter is one of the most widely used high-precision algorithms [2],[3]. The demodulation delay is about 1/100 of the scanning period of the light source because each demodulation needs to obtain the whole spectral range data first, and then demodulates according to the filter mark. When the sensing signal changes rapidly, the demodulation delay will seriously affect the authenticity of the signal. Combined with the real-time demodulation algorithm of the intake and exhaust phase in the process of high-speed engine operation, a new FBG demodulation algorithm is proposed in this paper. The proposed algorithm can significantly reduce the demodulation delay.