What is OTDR test with light? When testing with the wavelengths of 1310nm, 1490nm and 1550nm of common OTDR, it is necessary to require that there is no communication optical signal in the line under test. Forcing the test with light will burn out the internal detector of the OTDR. With light test, the OTDR can still complete the test without interrupting the signal light in the line during the test.
Why can't ordinary OTDR test with light? In the communication lines of OLT and ONT, the upstream signal is 1310nm, and the downstream signal is 1490nm or 1550nm, for example, the communication light occupies the three lanes of 1310/1490/1550. When using an ordinary OTDR to test the line, it will emit 1310nm/1490nm/1550nm light, which happens to be the same lane as the communication light, which will inevitably cause conflicts.
What types of light tests are there? There are two types of light tests: 1) 1310nm and 1550nm test with light: this type of test with light has a built-in filter, which will filter out certain interference signals. However, this type of test with light has certain restrictions on the communication light and power in the line; 2) 1610nm, 1625nm, 1650nm with light test: this kind of light test is for the communication light in the line. What are the differences and similarities between the optical test OTDR and the normal OTDR?
Difference: For ordinary OTDRs on the market, when measuring, there is an optical signal in the fiber that cannot be measured. The optical version has a built-in filter to filter out other signal light in the fiber. It can be directly measured at the user's optical cat end, and there is no need to go to the splitter box to unplug the optical fiber, which greatly facilitates the troubleshooting of maintenance time loss and other faults.
The same point: In the case of no optical signal in the fiber, the use is exactly the same. Chose an OTDR with light test, why can't test sometimes? There are two main reasons for this: 1) This has a certain relationship with the wavelength of the laser used. The communication light and test light signal are not point light sources in the strict sense, but FP type lasers, all of which have a certain spectral width. For example, a 1550nm optical test type OTDR should actually be 1550nm ± 20nm, and the wavelength range of the light emitted by the laser should be is 1530nm~1570nm; Similarly, if the optical signal in the line is 1490nm±20nm, its wavelength range may be 1470nm~1510nm, -20d B spectral width is 55nm, the wavelength range of this power point light should be 1435nm~1545nm, plus The thermal drift effect of the upper laser wavelength (as the temperature increases, the laser wavelength will drift to a certain extent) has a certain overlap with the test optical signal of the OTDR, so the OTDR still cannot be tested. 2) It is related to the power of the optical signal in the line. Any test with light has certain restrictions. When the power in the line exceeds a certain value, the test with light will be affected, and the test with light cannot be completed.
Suggestion: If you choose an OTDR with an optical test model, when the instrument prompts that there is an optical signal in the line, you can use the optical power meter function to test the signal power in the line first.
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