Receive Optical Power Is Normal But a Large Number of Bit Errors Exist on N2SL64
Bit errors occur on the STM-64 signal board in a long-distance project, due to the impacts of the sensitivity, dispersion and distortion of the fiber. Hence, notice the impacts of the sensitivity, dispersion and distortion of the fiber on the system in a long-distance project.
On an STM-64 link, the line board is the SSN2SL6416 (V-64.2b, LC). The corresponding BPA (14) is used. The receive optical power of the line board is -13.00 dBm. The link has the required DCU board, but bit errors still occur in the fiber.
According to the specifications of the SSN2SL6416 (V-64.2b, LC), the receive optical power is within the normal range. Since the DCU board is used, it is determined that the problem should not be with the receive optical power or the DCU board. Compare the input power and the output power of the relevant BPA. It is found that the power of the pre-amplifier is -26.90 dBm. This is why the problem occurs.
The power of the laser on the STM-64 signal board should not exceed -27.00 dBm. When the power of the laser approaches -27.00 dBm, the laser is distorted and thus bit errors occur.
Query the performance of the line board to check whether the power of the laser is within the normal range (between the overload point and the sensitivity).
Replace the DCU board to check whether the problem can be solved by adjusting the dispersion and attenuation.
Check the performance of the BPA. The input power of the two ports on the V-64.2b board should exceed -26 dBm (with a margin of 1 dBm).
It is found that the problem is with the sensitivity, dispersion, and distortion.
To solve the problem with distortion, check whether bit errors exist on the other side. If yes, replace the original fiber or the BPA (for example, replace the BPA-17 with the BPA-14).
If no bit error exists on the other side, detect the reason for the excessive attenuation (the difference within 1 dBm to 3 dBm is normal). The excessive attenuation may be caused by the fiber connector, fiber, or fiber head.
The STM-64 signal is sensitive. Hence, notice the sensitivity (use the BPA), dispersion (use the DCU) and distortion (the power of the laser should not be lower than -27 dBm) of the fiber in the case of a long-distance project. Ensure that no bit error will be caused due to impacts of the sensitivity, dispersion and distortion of the fiber.
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