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

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.