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Optical Engineering

Performance improvement of phase-generated carrier method by eliminating laser-intensity modulation for optical seismometer
Author(s): Qingping Shi; Qian Tian; Liwei Wang; Changdong Tian; Huayong Zhang; Min Zhang; Yanbiao Liao; Honghua Wang; Xiang Zeng; Longjun Huang
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Paper 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.

Paper Details

Date Published: 1 February 2010
PDF: 6 pages
Opt. Eng. 49(2) 024402 doi: 10.1117/1.3294878
Published in: Optical Engineering Volume 49, Issue 2
Show Author Affiliations
Qingping Shi, Tsinghua Univ. (China)
Qian Tian, Tsinghua Univ. (China)
Liwei Wang, Tsinghua Univ. (China)
Changdong Tian, Tsinghua Univ. (China)
Huayong Zhang, Tianjin Univ. (China)
Min Zhang, Tsinghua Univ. (China)
Yanbiao Liao, Tsinghua Univ. (China)
Honghua Wang, China Oilfield Services Ltd. (China)
Xiang Zeng, China Oilfield Services Ltd. (China)
Longjun Huang, China Oilfield Services Ltd. (China)

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