1 February 2010 Performance improvement of phase-generated carrier method by eliminating laser-intensity modulation for optical seismometer
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Abstract
An improved demodulation method for the phase-generated carrier (PGC) system by eliminating laser-intensity modulation (LIM) is proposed. The influence of LIM is analyzed theoretically and experimentally. Two parameters are used to describe the effect of LIM: the LIM coefficient (LIMC) and the LIM phase delay (LIMPD). Good stability of the LIMC and LIMPD is confirmed by experimentation with an actual system. The demodulation signal using the traditional method has a much greater higher harmonic component than the improved method due to LIM. The increase of the signal-to-total-harmonic ratio (SHR) using the improved method is >23 dB, and there is a corresponding improvement of 19 dB to the signal to noise and distortion (SINAD) and signal-to-noise ratio (SNR). A new prototype system using the improved PGC method for marine seismic sensing capable of demodulating multiple channels in parallel, simultaneously, is demonstrated. The SHR is stable at 56 dB when the LIMC is <0.5. Similar results are obtained for the SINAD and SNR. The demodulated signal's upper limit is ~100 rad at 100 Hz and 12 rad at 1 kHz, giving a dynamic range reaching 130 dB at 100 Hz. The system's SINAD is stable within 1 dB, whereas the SHR is stable within 2 dB in field application.
© (2010) Society of Photo-Optical Instrumentation Engineers (SPIE)
Qingping Shi, Qian Tian, Liwei Wang, Changdong Tian, Huayong Zhang, Min Zhang, Yanbiao Liao, Honghua Wang, Xiang Zeng, Longjun Huang, "Performance improvement of phase-generated carrier method by eliminating laser-intensity modulation for optical seismometer," Optical Engineering 49(2), 024402 (1 February 2010). https://doi.org/10.1117/1.3294878 . Submission:
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