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Proceedings Paper

Phase demodulation of Fabry-Perot interferometer-based acoustic sensor utilizing tunable filter with two quadrature wavelengths
Author(s): Hao Liao; Ping Lu; Li Liu; Deming Liu; Jiangshan Zhang
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Paper Abstract

A phase demodulation method for short-cavity extrinsic Fabry-Perot interferometer (EFPI) based on two orthogonal wavelengths via a tunable optical filter is proposed in this paper. A broadband light is launched into the EFPI sensor and two monochromatic beams with 3dB bandwidth of 0.2nm are selected out from the reflected light of the EFPI sensor. A phase bias is induced between the two interferential signals due to the wavelength difference of the two beams. The wavelength difference will have an affect on the sensitivity of demodulated signal, which has been theoretically and experimentally demonstrated. The maximum sensitivity can be obtained when the phase bias is 0.5π corresponding to the wavelength difference of 1/4 FSR of the EFPI spectrum. The acoustic wave induced phase variation can be interrogated through an optimized differential cross multiplication (DCM) method. A normalization process is induced into the traditional DCM method to eliminate the influence of ambient temperature and pressure fluctuation induced spectrum shift on output signal. This means that, once the wavelength difference is fixed, the wavelength variation of each individual beam will have little influence on the amplitude of demodulated signal. The EFPI sensing head is formed by a 3μm-thick aluminum diaphragm, which has a SNR of more than 53dB. Through the proposed demodulation scheme, a large dynamic range and good linearity is acquired and Q-point drift problem of traditional EFPI sensor can be solved. The demodulation scheme can be applied to other kinds of short-cavity EFPI based acoustic sensors.

Paper Details

Date Published: 20 February 2017
PDF: 5 pages
Proc. SPIE 10110, Photonic Instrumentation Engineering IV, 101101J (20 February 2017); doi: 10.1117/12.2251749
Show Author Affiliations
Hao Liao, Huazhong Univ. of Science and Technology (China)
Ping Lu, Huazhong Univ. of Science and Technology (China)
Li Liu, Huazhong Univ. of Science and Technology (China)
Deming Liu, Huazhong Univ. of Science and Technology (China)
Jiangshan Zhang, Huazhong Univ. of Science and Technology (China)

Published in SPIE Proceedings Vol. 10110:
Photonic Instrumentation Engineering IV
Yakov G. Soskind; Craig Olson, Editor(s)

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