载波调制法提高保偏光纤偏振耦合检测的信噪比

Application of carrier modulation in polarization coupling measurement to improve SNR

保偏光纤偏振耦合系统能有效检测保偏光纤中偏振耦合点的空间位置及耦合强度,因而可被广泛地应用于应力、应变、温度和位置的分布式传感中。由于噪声影响,测试系统中的信噪比和耦合强度检测灵敏度会下降。为了改善系统信噪比,提高保偏光纤中弱耦合点的检测能力,将铌酸锂外调制技术应用于白光干涉保偏光纤耦合测试系统。调制后的信号经光电探测器接收,用数字解调算法进行数据处理。实验结果表明:在电机扫描速度为0.75 mm/s,调制频率为9.1 kHz,采样率为140 kHz时,载波调制时信噪比提高了8 dB,解调耗时仅1.12 s。

The position and intensity of polarization coupling points in polarizationmaintaining fibers （PMFs） caused by stress and twist can be detected effectively by Polarization Coupling Measurement（ PCM）, so the distributed PMFs sensing system of stress, strain,temperature and position can be realized. However, the Signal Noise Ratio（SNR） and the detection sensitivity of Polarization Coupling Measurement will decrease due to various noise sources. In order to improve SNR of the measurement system, external carrier modulation using LiNbO3 modulator is implemented. The modulated signal is received by the photodiode and digital demodulation algorithm is used for data processing. The experimental results show that the measurement sensitivity is obviously improved when scanning speed is O. 75 mm/s, modulation frequency is 9.1 kHz and samples frequency is 140 kHz. The gain of SNR is 8 dB and the demodulation algorithm spends only 1.12 s.