Abstract
We present a new Phase Generated Carrier (PGC) demodulating system for optical seismometer and discuss its stability and consistency which is improved by modifying and compensating key parameters. A simple and easy approach to measure key parameters is presented and realized and its measure error and consistency can satisfy practical system's requirement. Several factors affecting the stability and consistency are analyzed theoretically and experimentally. The results prove that laser drive current of Direct Current (DC) bias would severely affect the stability of key parameters, and it fluctuates seriously the Signal-to-Noise-And-Distortion (SINAD) and Total-Harmonic-Distortion (THD) of demodulating result. Besides, different sensors would deteriorate the stability and consistency at a large degree which must be considered. The demodulating results have been compared between respectively modifications and unified. Other factors such as circuit gain and light attenuation also impact on system's stability and consistency, and it could be neglected at a certain extent. In this work, our system's SINAD is better than 45dB and THD is better than 50dB with the maximum fluctuation is ±1.5dB, the noise background is near -100dB/ √Hz and dynamic range has reached 130dB@100Hz.
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