The OTDR optical time domain reflectometer has a built-in OTDR module, which uses the backscattered light generated when the light propagates in the optical fiber to obtain attenuation information. It can be used to measure fiber attenuation, splice loss, fiber fault location, etc. It is an indispensable tool in fiber optic cable construction, maintenance and monitoring. Through the OTDR module, optical cable monitoring, optical cable construction and maintenance can be achieved.