Although there is only one test item of ODN in FTTH access engineering, the testing process is very complicated, including single-disk inspection of optical cable, attenuation test of optical cable, local test of optical shunt, and whole-process test of ODN optical fiber link, in accordance with the requirements of Code for Acceptance of Communication Line Engineering and Code for Acceptance of Broadband Optical Fiber Access Engineering.

1, single disk inspection of optical cable

OTDR is used to test the length and decay characteristics of the fiber in the cable. However, in FTTH access project, few construction units carry out single disk inspection of optical cable.

If the construction unit before the construction of the cable is not a single disk test, in the cable laying if found quality problems, cable manufacturers can be irresponsible.

2, Cable line failure test

The FTTH access project usually involves the construction of multiple optical cable sections. As shown in the figure below, it usually involves the construction of distribution optical cables and incoming optical cables. After laying and installing the cable, each core of each new cable section should be tested for decay.

Lead-in cable because of the connection of the fiber box, there are many differences in the middle, the test is more troublesome. As shown in the figure below, a 12-core optical cable is connected to a total of 6 fiber boxes. When testing, it is necessary to test the backscattering curve of each core by OTDR at the optical intersection of the wiring, and then to test again at each fiber box. If the test is not straight, reverse bidirectional, it is unable to test the size of the joint failure in the line.

Introduction of optical cable if only the light source and optical power meter test, it is unable to judge the size of the cable joint decay.

It seems that the introduction of fiber optic cable decay test is also very troublesome, so, few construction teams to test.

3. Local test of optical shunt

The local test of the optical shunt is to test the plug loss of each port of the optical shunt before installation. Its purpose, one is to see whether the plug loss of each port of the shunt is normal, the other is to see whether the plug loss deviation of each port is normal. The plug loss of each port of the shunt is a certain deviation, for example, the allowable deviation of 1×8 shunt is 1.5dB.

The plug loss test model of the shunt is shown in the figure below. The plug loss is the difference between Pout and Pin.

Although the local test of optical shunt is not complicated, it seems that few construction units have carried out this work.

4. ODN optical fiber link full test

The full-course ODN optical link refers to the optical fiber link from the S/R point on OLT to the R/S point on ONT. However, the user end of an FTTH access project usually ends at the fiber distribution box. Therefore, the testable part refers to the optical fiber link from the service aggregation point ODF to the splitter port in the fiber distribution box.

There are three main testing methods for ODN fiber link:

Method 1: Using OLT equipment PON port and optical power meter test;

Method 2: Test with light source and optical power meter;

Method 3: Test with PON optical time domain reflectometer (OTDR).

For details about the above three methods, see the Optical Fiber to the Home (FTTH) Construction Operation Regulations.

If the new ODN fiber link uses the original PON port, only Method 1 can be used for testing, as shown in the figure below. In this case, only downlink attenuation can be measured. The optical power of the PON port must be extracted from the PON network management system. However, pay attention to the difference between the optical power data of the network management system and the actual test value. Of course, if there are few users of the original PON port, you can disconnect the PON port and read the optical power of the PON port with the optical power meter.

5. Closing Remarks

ODN fiber links do not need to be tested for return loss. Only the fiber links with analog signals need to be tested for return loss.

Although according to the standard requirements, FTTH access projects need to test a lot of content, but in actual projects, few people test the above content, even the most important ODN fiber link test.