Lipovac Adriana, Lipovac Vlatko, Hamza Mirza, Batoš Vedran
Department of Electrical Engineering and Computing, University of Dubrovnik, 20000 Dubrovnik, Croatia.
Department of Telecommunications, Faculty of Electrical Engineering, 71000 Sarajevo, Bosnia and Herzegovina.
Sensors (Basel). 2021 Nov 2;21(21):7303. doi: 10.3390/s21217303.
Optical time-domain reflectometer (OTDR) enables simple identification and localization of a plethora of refractive and reflective events on a fiber link, including splices, connectors and breaks, and measuring insertion/return loss. Specifically, large enough OTDR dynamic range (DR) and thus high signal-to-noise-ratio (SNR) enable clear far-end visibility of longer fibers. We point out here that, under such conditions, the optical bit-error-rate (BER) floor is dominantly determined by reflective events that introduce significant return loss. This complements the OTDR legacy tests by appropriate optical BER floor estimation in the field. As high SNR implies inter-symbol interference as dominating error generating mechanism, we could apply the classical time-dispersion channel model for the optical BER floor determined by the root-mean-square (rms) delay spread of the actual fiber channel power-delay profile. However, as the high-SNR condition is not always fulfilled mostly due to insufficient DR, we propose here inserting a low-noise optical preamplifier as the OTDR front-end to reduce noise floor and amplify the backscattered signal. In order to verify the model for the exemplar test situation, we measured BER on the same fiber link to find very good matching between the measured BER floor values and the ones predicted from the OTDR trace.
光时域反射仪（OTDR）能够简单地识别和定位光纤链路上的大量折射和反射事件，包括熔接、连接器和断点，并测量插入/回波损耗。具体而言，足够大的OTDR动态范围（DR）以及因此产生的高信噪比（SNR）能够实现对较长光纤的清晰远端可见性。我们在此指出，在这种情况下，光误码率（BER）底限主要由引入显著回波损耗的反射事件决定。通过在现场进行适当的光BER底限估计，这对OTDR传统测试起到了补充作用。由于高SNR意味着符号间干扰是主要的错误产生机制，我们可以将经典的时间色散信道模型应用于由实际光纤信道功率延迟分布的均方根（rms）延迟扩展所确定的光BER底限。然而，由于高SNR条件并不总是能够满足，主要是因为动态范围不足，我们在此提出插入一个低噪声光前置放大器作为OTDR前端，以降低噪声底限并放大后向散射信号。为了验证示例测试情况下的模型，我们在同一光纤链路上测量了BER，发现测量的BER底限值与从OTDR迹线预测的值非常匹配。
