OTDR is an Optical Time-domain reflectometer. It is the main device 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 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-to-multipoint 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 cost-effective 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 the 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 at the end of each ONU branch by detecting whether the reflected OTDR test signal exists and the intensity of the optical signal. Therefore, it can easy to determine whether the optical link from the OLT side to the ONU side is normal. By detecting the reflected signal through OTDR, it can accurately grasp the fiber breakage, loss anomalies, fault location, and locate the error quickly.
The end-to-end OTDR measurement from the OLT to the ONT is usually difficult because the splitter brings high losses and complex networks. The application of optical fiber reflector is a cost-effective solution to help OTDR detection and is the best way to realize real-time end-to-end (OLT to ONT) monitoring of optical networks in FTTx networks.
