Testing the OSNR with the Agilent 86145B optical spectrum analyzer (OSA) using the integral method

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For a 50 GHz/0.4 nm system, follow the procedure below to test the OSNR with an optical spectrum analyzer (OSA) using the integral method:
1. Select the linearity test mode. In the SOFTKEY PANEL area, press the Amplitude key and select Display Mode. In the dialog box that is displayed, select linear. Note: The default testing mode is log, whose values are expressed in dB. The log testing mode is selected by default and is used in most cases. Select linear for linearity test, which is expressed in mW. 2. Set the wavelength range for the test channel. Query the standard wavelength for the to-be-tested wavelength. Take a wavelength of 1560.81 nm in an 80-wavelength system with a bandwidth of 50 GHz/0.4 nm for example. Set the starting wavelength Start WL: 1560.61 nm = 1560.81 �?0.2. Set the ending wavelength Stop WL: 1561.01 nm = 1560.81 + 0.2.
3. Test the total optical power P (mW) in the test channel. Turn on the laser at the transmit end on the OTU for the wavelength. Test the current optical power P. P is the total optical power containing noise.
4. Test the total noise power Pn (mW) in the test channel. Keep the starting wavelength settings in the OSA. Shut down the laser at the transmit end of the OTU of the wavelength. Test the current optical power Pn. Pn is intra-channel noise power.
5. Calculate the signal optical power S using the following formula: S = P �?Pn.
6. Set half of the bandwidth near the center wavelength. Test the noise power Pa for a 0.2 nm channel wavelength that affects services. Set Start WL: 1560.71 nm = 1560.81 �?0.1. Set Stop WL: 1560.91 nm = 1560.81 + 0.1. Obtain the current optical power Pa (mW).
7. Calculate the noise of a 0.1 nm channel: N = Pa/2. N indicates the noise (mW) of a 0.1 nm channel and is required in the calculation of OSNR.
8. According to OSNR definition, calculate the OSNR using the following formula: OSNR = 10lgS/N.
Note:
1. During the entire test process, you must enable the test for other wavelengths to obtain the actual OSNR.
2. For calculating average noise power for wavelengths, select the center wavelength with an offset of ±0.1 nm, which is more accurate than that of ±0.2 nm.
3. The test methods are the same as the 40-wavelength system. The only difference is that the bandwidth of the 40-wavelength system is 0.8 nm. The starting wavelength varies depending on the wavelength bandwidth.
4. When using an OSA to test the OSNR of wavelengths that traverse boards with filters, as filters reduce noise base at the channel edge, note that the OSNR will be inaccurate if the noise of the channel edge is used for reference. Therefore, always test the OSNR of wavelengths that traverse the boards with filters using the integral method.
5. The common boards with filters in WDM systems are as follows: M40, D40, WSM9, WSD9, and ITL.

Other related questions:
Whether an optical spectrum analyzer can be used to test the NPO2 board
No. The NPO2 board does not provide the MON port for light splitting, and therefore cannot be tested using an optical spectrum analyzer.

Can spectrum be analyzed? If yes, how can I analyze it
Airmagent, DingLi WiFi Monitor, WLAN tools of TuZhi Company and sniffer can analyze and simulate spectrum. eSight can also provide detailed spectrum analysis.

Function comparison of optical spectrum analyzer units MCA and WMU on OSN 6800
1. MCA boards are classified into MCA4 and MCA8, which provide four and eight ports respectively. An MCA board is mainly used to detect channel optical power, center wavelengths, optical signal-to-noise ratio (OSNR), and the number of wavelengths on an optical path. Similar to an optical spectrum analyzer, an MCA board reports the detected information to the system control board for fault diagnosis and monitoring. In addition, an MCA board can be used together with other boards to implement the automatic power equilibrium (APE) function. 2. The core function of a WMU board is to work with the system control board to lock wavelengths and monitor the wavelength offset of the transmit-end OTU board. The monitoring information is sent to the system control board by email. Then the system control board determines whether to adjust the wavelengths based on the wavelength configuration table. If wavelength adjustment is required, the system control board sends the adjustment information to the OTU board and then adjusts the wavelength offset. 3. An MCA board can monitor both the transmit end and receive end. 4. A WMU board can be configured only at the transmit end because it must work with the system control board at the local site to adjust the wavelength offset of the OTU board at the local site. 5. An MCA board mainly facilitates maintenance and a WMU board is used for function implementation. If an OTU board with 100 GHz channel spacing is used to implement a C-band 80-wavelength system, a WMU board needs to be configured to lock the operating wavelength of the OTU board. This is because the OTU board with 100 GHz channel spacing cannot satisfy the stability requirements of an 80-wavelength system, but the WMU board can help stabilize the wavelength performance.

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

Functions of spectrum analyzer units MCA and WMU on OSN 6800
Question: When an OSN 6800 device is used to construct a new network, two spectrum analysis units are configured: multi-channel spectrum analyzer unit (MCA) and wavelength monitoring unit (WMU). The functions of these two boards seem to be overlapped. How do we understand these functions? Answer: 1. MCA boards are classified into MCA4 and MCA8, which provide four and eight ports respectively. An MCA board is mainly used to detect channel optical power, center wavelengths, OSNR, and the number of wavelengths on an optical path. Similar to an optical spectrum analyzer, an MCA board reports the detected information to the system control board for fault diagnosis and monitoring. It can also be used together with other boards to achieve the automatic power equilibrium (APE) function. 2. A WMU board works with the system control board to lock wavelengths and monitor the transmit-end OTU wavelength deviation. The monitoring results are transmitted to the system control board through mailbox. Then, based on the wavelength configuration table, the system control board determines whether wavelengths need to be adjusted. If the wavelengths need to be adjusted, the system control board transmits the adjustment information to the OTU board to complete the wavelength deviation adjustment. 3. An MCA board can be configured to monitor the transmit end and receive end.4. A WMU board can be configured only at the transmit end, because it is used to adjust wavelength deviation of the OTU board at the local station with the system control board. 5. An MCA board is easy to maintain. A WMU board provides functions. To use OTU boards with 100 GHz spacing in an 80-channel system in the C band, WMU boards need to be configured to lock the working wavelength of OTU boards. If the working length stability of OTU boards with 100 GHz spacing cannot meet the requirements of an 80-channel system, WMU boards can be used. Suggestion and conclusion: An MCA board is used to monitor optical signals. A WMU board is used to monitor optical signals and lock and control the OTU wavelength with the system control board.

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