Analysis of fiber optic common problems

As an important transmission medium of an integrated wiring project, the performance of optical fiber is particularly important, especially for optical fiber cables laid in the sky or underground pipelines. Therefore, before the optical fiber is laid, we have to test the optical fiber and the optical fiber equipment. What problems will we encounter during the test?

Integrated wiring

1. When testing optical fiber, why use a special reference jumper to set the reference value?

Whether the test result is accurate or not is inseparable from the setting of the reference value. If the reference value is not set properly, the test result will be inaccurate or negative. The recommended method is to use a reference optical jumper and adapter when setting the reference value.

In TIA/EIA 568-B.3 and ISO 11801 standards, the loss requirement for a fiber coupling is less than 0.75dB. The performance of fiber optic jumpers and adapters produced by most manufacturers can meet or exceed this requirement. What many people don't know, however, is that the standard has specific requirements for reference jumpers and adapters. According to the IEC 14763-3 standard, when the reference jumper and adapter are used, the coupling loss of multimode fiber is less than 0.1dB, and that of single-mode fiber is less than 0.2dB. Conventional fiber optic jumpers simply cannot meet this requirement. Therefore, it is recommended to purchase special reference jumpers from manufacturers and test instrument manufacturers for testing.

When setting the reference, a fiber optic adapter with a zirconia ceramic ferrule material is required for optimal coupling. The conventional practice is to use a single-mode fiber adapter to set the reference value to obtain the best coupling effect, no matter whether you are testing multi-mode or single-mode fiber links.

2. When doing optical fiber link loss test, what is the importance of warming up the tester?

Generally, the higher the temperature of the light source module, the greater the value of the light source power emitted by it. During the test, the light source module needs to be warmed up for a period of time before the transmitted light source power value can be stabilized. If the reference value is set before the light source module is warmed up, as the temperature of the light source module rises, the test results will gain, thereby affecting the accuracy of the test results.

For example, when the reference value is initially set, the optical power meter receives and stores a power value of -6.00dB. At this time, if the reference value setting model is maintained and the test is carried out directly without adding the link under test, the test result of 0.00dB should be obtained. However, after the optical power module is preheated, the output power will increase, and the power value received by the power meter may rise to -6.20dB. Then test again, you will get -0.2dB gain.

The warm-up time of the light source module is related to the temperature of the test environment. The method to check whether the light source module is stable is very simple. Just complete the reference value setting and test the reference value model. The test value obtained is acceptable between -0.04dB and 0.04dB; if it exceeds this value, you need to wait for a while and reset the reference value.

3. Why is there a negative value when testing loss? Is the link under test not only lossless, but also gaining?

When testing a single-mode optical fiber link, if the length of the tested link is less than 100m, and the entire link is spliced with pigtails, the loss of the entire link may be only 0.15dB. In this case, insufficient warm-up time for the light source module, large changes in the test environment temperature, the coupling effect between the reference jumper and the test instrument, and inaccurate reference value settings may lead to negative test results, such as -0.03dB. At this time, it is necessary to fully warm up the machine and reset the reference value.