19 August 2011 Analysis on the amplitude instability of homodyne coherent demodulation method based on a 3×3 coupler for fiber laser hydrophone
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Abstract
To develop a practical fiber laser hydrophone, demodulation method to get the wavelength shift of the fiber laser hydrophone is a key technology. A homodyne coherent demodulation scheme utilizing a 3×3 coupler has the advantage of passive detection without phase or frequency modulation in the reference arm and wide dynamic range. But the amplitude of phase output from the passive homodyne coherent demodulation system based on a 3×3 coupler for fiber laser hydrophone is instable during a lake test. To solve this problem, the principle of the passive homodyne phase demodulation scheme based on a 3x3 coupler for the fiber laser hydrophone is investigated and a digital demodulation system is built. A unbalanced Mach-Zehnder fiber interferometer based on the 3×3 coupler is employed to transpose the wavelength shift into phase shift of the interferometer. Through theoretical analysis and simulation calculation, the relations between amplitude discrepancies and the phase differences with the phase output are finally educed. The theoretical analysis and simulation calculation shows that the amplitude discrepancies and the phase differences of the three outputs from the interferometer result in the amplitude instability of phase output. To solve these problems, we can get three symmetrical outputs by adjusting the gains of the three outputs. Both the simulation calculate and the underwater acoustic experiment show that the phase output of homodyne coherent demodulation system based on a 3x3 coupler can be steady by adjusting the gains of the three outputs, when the 3×3 coupler is asymmetric.
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Jun-bin Huang, Jun-bin Huang, Yu Li, Yu Li, Hong-can Gu, Hong-can Gu, Ri-zhong Li, Ri-zhong Li, Bo Tan, Bo Tan, Guang Yang, Guang Yang, } "Analysis on the amplitude instability of homodyne coherent demodulation method based on a 3×3 coupler for fiber laser hydrophone", Proc. SPIE 8192, International Symposium on Photoelectronic Detection and Imaging 2011: Laser Sensing and Imaging; and Biological and Medical Applications of Photonics Sensing and Imaging, 81921I (19 August 2011); doi: 10.1117/12.900104; https://doi.org/10.1117/12.900104
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