干涉型光纤水听器相位载波调制-解调中信号混叠产生的机理及解决方案

信号混叠是制约基于相位载波调制-解调的光纤水听器系统走向应用的一个关键问题。对信号混叠产生的机理进行了详细的理论分析和仿真,结果表明,提高光源调制频率和降低探头灵敏度都无法有效解决光纤水听器实际应用中遇到的高频干扰引起的混叠问题。基于声学滤波器原理,提出了一种新颖的声低通滤波解决方案。设计并加工制作了一种简单的声低通滤波光纤水听器,在驻波罐中对其声压灵敏度频响进行了测量。实验结果表明,该光纤水听器在测量频带上具有较好的声低通滤波特性,低频声压灵敏度约为-140 dB(0 dB=1 rad/μPa),高频衰减大于20 dB,对高频干扰有较强的抑制能力。该方案十分简单经济,能从根本上有效地解决相位载波调制-解调中的信号混叠问题。

Physical Mechanism and Solution of Aliasing in Phase Generated Carrier Modulation-Demodulation of Interferometric Fiber-Optic Hydrophone

Signal aliasing is one of puzzling questions of a practical fiber-optic hydrophone system based on phase generated carrier (PGC) modulation-demodulation. The physical mechanism of signal aliasing is analyzed theoretically and simulated by computer. The results show that increasing the modulation frequency and lowering the sensitivity of the fiber-optic hydrophone cannot effectively resolve the signal aliasing induced by high-frequency interfering signal. A novel acoustic low-pass filtering scheme is proposed based on the principle of acoustic low-pass filters. A simple fiber-optic hydrophone with an acoustic low-pass filter is designed and fabricated. The acoustic pressure phase sensitivity is measured in a standard standing-wave duct. The experimental results show that the fiber-optic hydrophone has fine characteristics of acoustic low-pass filtering, and can restrain the high-frequency interfering signal strongly. The low-frequency acoustic sensitivity is about -140 dB (0 dB=1 rad/μPa), the attenuation of high frequency is bigger than 20dB. The scheme is very simple and economical, can be used to eliminate the signal aliasing in a practical phase generated carrier modulation-demodulation system effectively.