中文摘要：

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。

英文摘要：

Coherent Rayleigh noise is an important factor in restricting event identification on the detection curve of coherent optical time-domain reflection （COTDR）. In this experiment,a noise reduction scheme involving laser timed frequency hopping in a COTDR system is studied. By adopting RIO Company＇s nar- row-linewidth external-cavity semiconductor laser and setting the COTDR system, a timed frequency hopping scheme is proposed by controlling laser frequency with a software. The scheme carries out 10 times of timed frequency hopping with 104 times of averaging for a l~s probe light pulse width and 20 dBm peak power under a 25 km optical fiber detection length. The scheme is further used to analyze at- tenuation coefficient and fading noise in each detection curve by comparison with the conventional asyn- chronous and synchronous frequency hopping schemes. Results show that the timed frequency hopping scheme reduces the fading noise to 0.15 dB,achieves the noise reduction effect of synchronous frequency hopping, and reduces frequency hopping time to millisecond level, which improves the detection efficien- cy. Therefore,our approach can be widely used as a simple and convenient frequency hopping method in COTDR on-line monitoring system.