OSAs can also be used to predict bit-error-rate (BER) results at turn-up. Indeed, we know that the OSNR must be greater than 15 to 18 dB at the receiver to ensure proper signal detection. Optical impairments from ITU-T Recommendation G. 697 (optical monitoring for DWDM networks), sets out the most common optical impairments. The International Telecommunication Union is a standards agency that establishes guidelines in the telecom industry. Indeed, recent 40G/100G coherent systems featuring polarization multiplexing have made some traditional OSA measurements, such as optical signal-to-noise ratio (OSNR), impossible to carry out. These new technologies are certainly beneficial, but they also bring about new test and measurement challenges, in particular for optical spectrum analyzers (OSAs), versatile test instruments that are key to successful DWDM system commissioning and troubleshooting.
In order to meet the constantly increasing need for bandwidth, more and more telecommunications operators are now deploying 40G or 100G coherent systems on long-haul dense wavelength-division multiplexing (DWDM) networks. Optical Signal-to-Noise Ratio (OSNR) Measurement Given that more than 60% of deployment issues are related to CFP or CFP2, it is now critical to test each CFP. EXFO’s CFP health check supports both interfaces with a basic and advanced mode for quick pass/fail validation. EXFO’s CFP2 adapter, which can be inserted into a CFP interface, allows field technicians to validate CFP2 transceivers before deployment, thus minimizing risk. However, this also introduces some new challenges, and at the same time new issues. There is no gearbox in the CFP2-it was moved to the host, reducing the physical size and power consumption. The above tests are also applicable to the upcoming CFP2 interface, which is backward-compatible with CFP technology. For instance, lane 9 as shown in below picture is slightly out of range. In some cases, the CFP is considered the weakest link in the network in such cases, it will be critical to ensure that the CFP is completely functional before conducting any CFP deployment. In some cases, a per-lane view may be required to identify any suspicious lanes that could eventually cause bit errors. The main tests involve analyzing the laser power to ensure that the laser’s transmitted and received optical power is within the specific range as part of the same validation process, the received per-lane frequency will need to be tested. However, a quick validation test is still required before each deployment to analyze the main status of the CFP and ensure that there are no errors. CFP quality is improving, and as a result we are now seeing fewer and fewer issues due to incompatibility or electrical crosstalk.
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