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相干瑞利噪声是制约相干光时域反射(COTDR)探测曲线上事件识别的重要因素,本文实验研究了COTDR系统中激光定时跳频的降噪方案。采用RIO公司的窄线宽外腔式半导体激光器(ECLD),搭建了COTDR系统,实现了一种通过软件控制激光频率的定时跳频方案,在光纤探测长度为25km、探测光脉冲宽度为1μs、峰值功率为20dBm和多点数字平均104次的情况下,进行了10次定时跳频,并与传统的异步跳频和同步跳频进行比较,分析了各探测曲线的衰减系数和衰落噪声大小。研究表明,定时跳频将衰落噪声降为0.150dB,达到了同步跳频的降噪效果,同时将跳频时间缩短为ms级,提高了探测效率,可作为一种简便的跳频方法广泛应用于COTDR在线监测系统。
Coherent Rayleigh noise is an important factor in the event identification of Coherent Optical Time Domain Reflectance (COTDR) detection curves. In this paper, we experimentally studied the noise reduction scheme of laser timing-hopping in COTDR system. Using RIO’s narrow-linewidth external cavity semiconductor laser (ECLD), a COTDR system was set up to implement a timing-controlled frequency-hopping scheme with software-controlled laser frequency. With a fiber length of 25km and a probe pulse width of 1μs, The peak power of 20dBm and multi-point digital average of 104 cases, carried out 10 times the frequency hopping, and compared with the traditional asynchronous frequency hopping and synchronous frequency hopping, analysis of the attenuation coefficient of the sounding curve and the size of fading noise. The research shows that the time-frequency hopping reduces the fading noise to 0.150dB and achieves the noise reduction effect of synchronous frequency hopping, meanwhile shortens the frequency hopping time to ms level, which improves the detection efficiency and can be widely used as a simple frequency hopping method COTDR online monitoring system.