Fiber Bragg grating-tuned feedback laser flow sensor system

In this paper, a fiber Bragg grating (FBG) air flow sensor system using an all-fiber feedback laser is proposed. The operating principle of the feedback laser is based on the mode-locking mechanism between a Sagnac loop multi-grid filter and a tunable FBG single-wavelength filter. A shift in the lasing wavelength is attributed to the change in the heat energy of the coil heater. This is because the flow sensor depends on the variations in the heat energy of the coil heater surrounding the FBG, thereby causing a shift in the Bragg wavelength owing to a thermo-optic effect. In order to investigate the spectral response as a function of the flow speed of air, a simple and cost-effective intensity-based demodulation technique using a micro-optic band-pass filter is demonstrated. The flow sensitivity of the sensor system was 0.7 dB/(l/min) within a linear region.