High-speed spectrum demodulation of fiber-optic Fabry–Perot sensor based on scanning laser

A high-speed spectrum demodulation method with a large dynamic range for fiber-optic Fabry–Perot sensor is presented. The demodulation system only consists of a near-infrared distributed Bragg reflector (DBR) laser, a fiber circulator, a photodetector and a signal processing circuit. By quickly cyclically setting the grating current and phase current of the DBR laser, the laser wavelength is scanned with a repetition frequency of 2 kHz. The signal processing circuit controls the current of the laser and performs spectrum demodulation simultaneously. Spectral demodulation mainly includes normalization of interference spectrum, fast Fourier transform, phase estimation and cavity length calculation. The displacement stage and piezoelectric ceramics were used to remove the static cavity length and dynamic cavity length of the Fabry–Perot cavity. Experimental results show that the demodulation resolution reaches 0.15 nm. Benefiting from the high spectral detection resolution, a large demodulation range is achieved to be 0.3–13 mm. Compared with the demodulation systems based on spectrum modules, this solution significantly reduces the cost, simplifies the algorithm and improves the dynamic range.