A Phase Generation Carrier Demodulation System Based on FPGA

Abstract

The invention discloses an FPGA-based phase generation carrier demodulation system, and relates to the technical field of optical fiber phase demodulation. The PGC demodulation system uses an FPGA asa signal processor, and can improve the operation rate and demodulation speed of the system. The PGC demodulation system comprises a PGC demodulation module, a data caching module and an asynchronouscommunication module which are connected in sequence. The input to-be-demodulated data is directly input into the data cache module for storage. The PGC demodulation module adopts an improved PGC demodulation algorithm to demodulate the data to be demodulated. A disturbance removing unit is introduced into the PGC demodulation module. The division operation is carried out in the disturbance removal unit to eliminate signals containing alternating current items and modulation depths. Therefore, the output item only has the tangent value of the phase signal. The dependence of the demodulation result on the modulation depth introduced by an external carrier is reduced. The uncertainty of the demodulation result caused by unstable factors such as a light source can also be avoided. The accuracy and the stability of system demodulation are improved.

Description

technical field [0001] The invention relates to the technical field of optical fiber phase demodulation, in particular to an FPGA-based phase generation carrier demodulation system. Background technique [0002] Optical fiber sensors have the characteristics of high sensitivity, high linearity, small size, anti-electromagnetic interference, and large dynamic range, and are widely used in optical fiber underwater acoustic detection, seismic wave detection and other fields. The interferometric optical fiber sensor uses the phase change in the optical path to measure physical quantities. The random phase fading of the interferometer will lead to random fluctuations in the signal-to-noise ratio of the output signal. The phase change in the optical path needs to be solved by a specific algorithm. The phase generated carrier (PGC ) algorithm is a more classical demodulation method. [0003] The early PGC demodulation algorithm was completed on the PC side of the upper computer. W...

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Problems solved by technology

However, there is no detailed description on how to reduce the influence of light intensity disturbance and modulation depth drift on the PGC algorithm and harmonic suppression

Tsinghua University uses the triple frequency of the carrier instead of the fundamental frequency to avoid the generation of the DC term, which is still affected by the modulation depth, and the sampling frequency is relatively high; The influence of light intensity reduces the total harmonic distortion to a certain extent, but there are many division operations in the algorithm, and when the divisor is zero in actual demodulation, it will cause numerical distortion and demodulation error (PGC Demodulation Technique With High Stabilityand Low Harmonic Distortion); Yang Jun of Harbin Engineering University and others combined the PGC algorithm with the fixed phase shift method of the 3×3 coupler (CN 201510293444.3), and used ellipse fitting to correct the parameters; Gao Xiaowen et al. Invented a demodulation method for normalizing low-pass filtered signals (CN 201710941759.3)

However, the above algorithm increases the complexity of the system structure, makes the signal processing time longer, and reduces the real-time performance of the system.

For the PGC demodulation system, on the basis of improving the system operation rate and demodulation speed, it is of great significance and practical value to eliminate the influence of modulation depth and light intensity disturbance while suppressing harmonic distortion and reducing signal distortion. no good solution

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