Detection of the OSNR of a 40G or 100G system using the traditional OSNR detection method

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The optical spectrum of 40G or 100G signals is wider than that of 10G signals. Therefore, the signal spectra of adjacent channels overlap each other. The channel noise includes not only the ASE noise but also the power crosstalk of some signals. Therefore, the OSNR tested using the traditional OSA method is less than the actual OSNR. The traditional OSA method is implemented based on the interpolation of inter-channel noise that is equivalent to in-band noise.
The traditional OSNR detection methods, including the scanning method and the integral method, have the following disadvantages:
Scanning method: applicable only to a system with a 100G channel spacing and without traversing an OEQ node. The detection results have a low precision.
Integral method: When there are a few wavelengths, turning on or off the lasers will cause noise power fluctuation and therefore affect the detection accuracy. In addition, the noise power cannot be measured by turning on or off the laser when there is only one wavelength.

Other related questions:
Whether the MCA802 board supports OSNR detection of 100G systems
The TN11MCA802 board can scan the OSNR of a 100G system when it works with the license of the intelligent wavelength monitoring management system and configures the functions of the OD.

Method used to measure the OSNR on a coherent system
In the coherent system, the OD solution can be used to measure the OSNR. The OD solution can measure the OSNR by modeling OAs and fibers and accurately measuring the signal power and noise power. E2E OSNR measurement is supported for 10G, 40G, and 100G systems in various scenarios.

Formula used to calculate the OSNR
OSNR = 10lg (S/N)

Optimal OSNR value
The requirement on the OSNR varies according to code patterns. Generally, an OSNR value greater than 20 is acceptable except when no FEC code is present.

Possible causes of an OSNR decrease
The possible causes are as follows: Possible cause 1: Any fiber pigtail in a multiplexing part or the optical cable degrades or is physically damaged. As a result, the attenuation of the fiber increases, and the receive optical power decline causes an OSNR decrease. Possible cause 2: The OA board gain at the local or peer site is decreased.

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