Realization of high-precision phase generated carrier demodulation algorithm with ellipse fitting algorithm based on FPGA

The lasing wavelengths of the fiber lasers are changed by the external strain or temperature, and hence they can be used as sensors by detecting the wavelength shift. Phase generated carrier (PGC) is the earliest optical interferometric phase demodulation algorithm, which is widely applied for interferometric optical fiber sensor, for it is simple and accurate. In this paper, we propose an improved PGC demodulation algorithm based on PGC-Arctangent and ellipse fitting algorithm (EFA) to extend the dynamic rangeenhance the phase resolution and suppress the total harmonic distortion (THD) caused by phase modulation amplitude variation and the laser intensity disturbance (LID) of modulation phase. An experimental system for the fiber optic sensor system is set up to confirm the stability of the PGC algorithm with the EFA. A Mach-Zehnder interferometer (MZI) is employed in the fiber optic sensor system to detectable phase shift, and a phase modulator has been attached to the reference arm. The output phase signal of the MZI is detected by a low-noise photodiode and sampled by 16-bit analog to digital converter (ADC). The digital PGC-Arctangent algorithm and the EFA are realized on ZCU102 Evaluation Board (Zynq Ultrascale + MPSoC, Xilinx). The system optimizes the number of sample points of the EFA to reduce the complexity of the algorithm and make full use of FPGA data processing with the advantage of high speed and parallel. According to the result, the phase error of the interferometer is 3% and the dynamic range of 140 dB@5kHz with 1 MHz carrier frequency and 10 Mbps sample rates. The phase resolution of system is 6.457 × 10
^-6
rad/√Hz@5kHz (-103.8 dB) and the THD is 1%.