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.
COHERENT OPTICAL TIME DOMAIN REFLECTOMETRY CODED BASED ON DETECTION FREQUENCY