What is an OTDR and its basic working principle? OTDR is an Optical Time-domain Reflectometer. It is the main devices in optical fiber measurement. It uses to test detect problems that may exist in fiber links. OTDR is widely used in carrier backbone networks. By analyzing the measurement curve, it can quickly detect the fault location of the optical fiber link and the fiber loss. The working principle is to use a laser light to send a higher power laser or light pulse to the test fiber. OTDR observes the power of the laser signal from each point on the fiber and records these results through a trace diagram. It can calculate the distance by recording the return time and transmission speed. In the PON (Passive Optical Network) network, especially the complex point-tomultipoint PON ODN (Optical Distribution Network) topology applications, rapid monitoring, and diagnosis of fiber fault locations is a challenging subject. At present, optical time-domain reflectometer (OTDR) tools are widely used for monitoring the fiber network. However, OTDR detection may not be so particularly sensitive to the attenuation of optical signals at the ends of some ODN branch fibers or ONU fibers. The application of FTTx terminal splitter to the main cable signal makes the traditional OTDR fiber optical detection techniques unable to achieve on-off detection. So a costeffective and wavelength selective fiber optic reflector is a basic method of implementation of optical layer monitoring on the whole length of an FTTx network from the OLT to the ONT in real-time.
The working principle of the fiber optic reflector is mainly to use Fiber Bragg Grating (FBG) to reflect the test light pulse sent by OTDR with nearly 100% reflectivity. But the wavelength of normal passive optical network (PON) will pass with a small attenuation. The main purpose is to accurately calculate the return loss value of the reflected event