In the PON (Passive optical network, passive optical network) network, especially the complex point-to-multipoint PON ODN (Optical distribution network, optical distribution network) topology environment, the rapid monitoring and diagnosis of optical fiber faults has become a challenging work.
Although optical time domain reflectometer (OTDR) tools are widely used at present, OTDR detection is sometimes not particularly sensitive to the attenuation of optical signals at the ends of some ODN branch fibers or ONU fibers.
Installing a low-cost wavelength-selective optical fiber reflector on the ONU side is often used at present, through which accurate detection of the end-to-end attenuation of the optical link can be achieved.
It mainly uses the fiber grating to reflect the test light pulse sent by the OTDR with a reflectivity of nearly 100%, while the working wavelength of the normal passive optical network (PON) system passes through with a small attenuation because it does not satisfy the Bragg condition of fiber grating.
The main function of this is that, by detecting the existence of the reflected OTDR test signal and the intensity of the optical signal, the return loss value of the reflection event at the end of each ONU branch can be accurately calculated.
Thus, it is judged whether the optical link from the OLT side to the ONU side is normal. This enables real-time monitoring of fault points and fast and accurate diagnosis.
By flexibly deploying the position of the reflector and identifying different ODN sections, the detection and location of the ODN fault point and the cause analysis can be quickly realized, which reduces the fault processing time and improves the test efficiency and line maintenance quality.
In the first-level splitting scenario, if the return loss of the reflector of a certain home fiber branch increases significantly compared with the return loss value of the health file, it indicates that the optical fiber of this branch is There is a problem with the link; if all of the fiber branches with fiber reflectors have significant return loss increase at the same time, it is an indication that the trunk fiber is faulty.
In the secondary optical splitting scenario, the difference of return loss can also be compared to accurately locate whether the attenuation fault has occurred in the distribution fiber segment or the home fiber segment.
Whether it is a first-level or second-level splitting scenario, since the reflection peak will drop sharply at the end of the OTDR test curve, the return loss value of the longest branch link in the ODN network may not be accurately measured, and it is necessary to measure the reflector.
The optical fiber reflector can be conveniently placed in series at the user end. It has the characteristics of long life, stable and reliable, and easy connection of the adapter structure. It is also one of the reasons why the optical fiber reflector is an ideal optical end choice for FTTx network link monitoring.
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