What is OTDR's Live Testing？

When testing with the wavelength of 1310nm, 1490nm, and 1550nm of ordinary OTDR, it is necessary to require that there is no communication light signal in the measured line. Forcibly Live Testing will burn the internal detector of the OTDR. Live testing is when testing, you can stop the light signal in the line, and OTDR can still complete the test.

Why can't ordinary OTDR live testing?

In the communication lines of OLT and ONT, the uplink signal is 1310nm, and the downlink signal is 1490nm or 1550nm, which is like the three lanes of the light signal occupied 1310/1490/1550nm. When testing the line with ordinary OTDR, it will emit 1310nm/1490nm/1550nm light signal. This is exactly the same lane as the light signal, which will inevitably cause conflicts, as shown in the figure below:

FIG1-Test Schematic Diagram

What are the types of live testing?

There are two types of live testing:

1) 1310nm and 1550nm Live Testing: This type of Live Testing built -in filter will filter a certain interference signal. However, this type of Live testing has certain restrictions on the light signals and power in the line.
2) 1610nm, 1625nm, 1650nm Live Testing: This type of Live Testing on the light signal in the line. There are basically no restrictions, but the power of the light signal is also limited. Specific as shown in the table below:

What is the difference between the difference between the Live Testing OTDR and the ordinary version of OTDR?

Difference: The ordinary OTDR on the market cannot be measured in the optical signal in the fiber when measured. The light test version has a built -in filter to filter out other signal light in the fiber. You can directly test it on the user's light cat. You do not need to run to the Fiber Optic Terminal Box to pull off the fiber, which greatly facilitates the investigation of faults such as the loss of time loss.

Same: In the case of optical fiber without light signals, use exactly the same.

 FIG2-Test Schematic Diagram

Why is it still not tested sometimes?
There are two main reasons for this:
     1) This has a certain relationship with the wavelength of the laser used. Light signals and testing light signals are not point light sources in the strict sense. They are FP types of laser. They all have certain spectral width. For example, 1550nm with light test OTDR, it should actually be 1550nm±20nm.It is 1530nm~1570nm; Similarly, if the light signal in the line is 1490nm±20nm,its wavelength range may be 1470nm~1510nm, -20dB spectrum width is 55nm. The hot drift effect of the laser wavelength (as the temperature rises, the laser wavelength will fluttering), which overlaps with the OTDR test light signal, so OTDR still cannot test.
     2) It is related to the power of the light signal in the line. Any Live Testing has certain restrictions. When the power in the line exceeds a certain value, Live Testing will be affected and cannot complete the LIVE TESTING.
The specific table below:

Suggestion: If the Live Testing model is selected, when there is a light signal in the instrument prompt line, you can first use the optical power meter function to test the signal power in the lower line.

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