光纤水听器时分复用系统通过3×3耦合器信号解调的一种新算法

A New Demodulation Method for Time Division Multiplexing System of Fiber-Optic Hydrophone Using a 3×3 Coupler

提出了在光纤水听器时分复用系统中采用3×3耦合器解调信号的一种新算法。在该方案中,光纤水听器仍为2×2耦合器结构,3×3耦合器作为匹配干涉仪,利用其三路输出的线性组合和数字反正切技术实现信号解调,解调中使用的参数通过奇异值分解和椭圆拟合得到。该方案不需要载波调制,可实现光纤水听器近似等臂干涉,有利于抑制系统相位噪声。算法的运算量小且适用于一般的非对称3×3耦合器,解调的动态范围很大。最终利用该方案实现了两路光纤水听器时分复用的实验系统,在1 kHz时,系统的噪声本底为31μrad/Hz,动态范围超过125 dB,串扰小于64 dB。

A new demodulation method is proposed for time division multiplexing system of fiber-optic hydrophone using a 3 × 3 coupler. In such a scheme, the fiber-optic hydrophone is made by a 2× 2 coupler and 3× 3 coupler is used as path-matched differential interferometer. The signal is demodulated by linear combination of the three outputs and digital inverse arctangent approach. Parameters used in demodulation are estimated by singular-value decomposition and ellipse fitting. There is no carrier in this demodulation scheme. In addition, fiber-optic hydrophone can form a nearly zero path difference interferometer which is good for reducing system phase noise. The demodulation method is very simple and feasible for a general asymmetric 3× 3 coupler. Correspondingly, it is easy to get a large dynamic range for the demodulated signal. A time division multiplexing experiment system with two sensors is set up. At 1 kHz noise floor, dynamic range, and cross talk are less than 31μrad/√Hz, more than 125 dB, less than 64 dB, respectively.