A Coherent Optical Time Domain Reflectometer Based on Detection Frequency Coding

Abstract

A coherent optical time domain reflectometry coded based on a detection frequency comprises a laser (1), a first coupler (2), a frequency coder (3), a radio frequency driver (4), a circulator (5), an optical interface (6), a light filter (7), a second coupler (8), a photoelectric detector (9), an intermediate frequency amplifier (10), a data acquisition module (11), a signal processing module (12), and a display module (13). A laser beam emitted by the laser (1) is frequency-coded by the frequency coder (3) to obtain detection frequency pulsed light and a filled light pulse sequentially complementary to the detection frequency pulsed light. The detection frequency pulsed light and the filled light pulse are different in frequency, and after their backward Rayleigh scattered signals in an optical fiber line are returned, the signals enter the light filter (7) through a third port; a detection optical signal and local oscillation light that are obtained after the filtering are coherent in the second coupler (8), and then the photoelectric detector (9) outputs a coherent intermediate frequency signal; and finally, the intermediate frequency signal is collected and processed to obtain a timing curve reflecting characteristics of the optical fiber line.

Description

technical field [0001] The invention belongs to the communication field, and in particular relates to a coherent optical time domain reflectometer used for optical fiber communication line characterization, event identification and fault location. Background technique [0002] Coherent optical time-domain reflectometry is usually used to monitor multi-relay ultra-long-distance optical fiber communication lines such as transoceanic submarine optical cables. Coherent optical time domain reflectometry uses the principle of lidar to locate the scattering and / or reflection point by injecting a detection light pulse into the optical fiber and recording the return time of the Rayleigh scattered light and / or reflected light of the light pulse in the optical fiber. The pulse width of the optical pulse corresponds to the spatial resolution of the measurement, and the two are proportional to each other. For example, the detection optical pulse width of 1 microsecond corresponds to the ...

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Problems solved by technology

The frequency of the frequency pulse involved in the method jumps with time but the laser power is continuous. Continuous laser light enters the erbium-doped fiber amplifier in the fiber line to suppress the transient effect and avoid optical surges. However, the frequency pulse is a frequency sweep Yes, in order to stabilize the coherent intermediate frequency signal generated by the probe light and the local oscillator light, the frequency of the local oscillator light should be changed accordingly. In addition, the frequency sweep does not change the continuity and linewidth of the laser. The Brillouin of the continuous light Threshold is very low, which limits the peak power of the frequency pulse and thus limits the dynamic range of the measurement

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