In PON (Passive Optical Network) networks, particularly within complex point-to-multipoint PON ODN (Optical Distribution Network) topologies, rapid monitoring and diagnosis of fiber faults present significant challenges. Although optical time domain reflectometers (OTDRs) are widely used tools, they sometimes lack sufficient sensitivity for detecting signal attenuation in ODN branch fibers or at ONU fiber ends. Installing a low-cost wavelength-selective fiber reflector on the ONU side is a common practice that enables precise end-to-end attenuation measurement of optical links.
The fiber reflector operates by using an optical fiber grating to reflect the OTDR test pulse back with nearly 100% reflectivity. Meanwhile, the normal operating wavelength of the passive optical network (PON) system passes through the reflector with minimal attenuation because it does not satisfy the fiber grating’s Bragg condition. The primary function of this approach is to precisely calculate the return loss value of each ONU branch termination’s reflection event by detecting the presence and intensity of the reflected OTDR test signal. This enables determination of whether the optical link between the OLT and ONU sides is functioning normally. Consequently, it achieves real-time monitoring of fault points and rapid, accurate diagnostics.
By flexibly deploying reflectors to identify different ODN segments, rapid detection, localization, and root cause analysis of ODN faults can be achieved, reducing fault resolution time while enhancing testing efficiency and line maintenance quality. In a primary splitter scenario, fiber reflectors installed on the ONU side indicate issues when a branch’s reflector shows significantly increased return loss compared to its healthy baseline. If all fiber branches equipped with reflectors simultaneously exhibit pronounced return loss, it indicates a fault in the main trunk fiber.
In a secondary splitter scenario, the difference in return loss can also be compared to accurately pinpoint whether attenuation faults occur in the distribution fiber segment or the drop fiber segment. Whether in primary or secondary splitting scenarios, due to the abrupt drop in reflection peaks at the end of the OTDR test curve, the return loss value of the longest branch link in the ODN network may not be precisely measurable. Therefore, changes in the reflector’s reflection level must be measured as the basis for fault measurement and diagnosis.
Optical fiber reflectors can also be deployed at required locations. For instance, installing an FBG before Fiber-to-the-Home (FTTH) or Fiber-to-the-Building (FTTB) entry points, then testing with an OTDR, allows comparison of test data against baseline data to identify indoor/outdoor or building interior/exterior fiber faults.
Fiber optic reflectors can be conveniently placed in series at the user end. Their long lifespan, stable reliability, minimal temperature characteristics, and easy adapter connection structure are among the reasons they are an ideal optical terminal choice for FTTx network link monitoring. Yiyuantong offers FBG fiber optic reflectors in various packaging types, including plastic frame sleeves, metal frame sleeves, and pigtail forms with SC or LC connectors.
Post time: Sep-11-2025