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I-OSNR Solution
PhotonCom develops custom test solution to serve customers requiring specific test fixtures. PhotonCom’s experience in providing customers with the appropriate test equipment for their specific needs has lead to the development of an alternative testing solution for In-band Optical Signal to Noise Ratio (I-OSNR). Alternative testing solution for In-band Optical Signal to Noise Ratio
This solution being less portable is better adapted for the lab environment. The main outcome of this solution is the possibility to re-use the OSA and Polarization Controller as needed for other types of measurements besides the I-OSNR. The highest resolution (0.02 nm) of this OSA combined with the extra fast sweep capability make this equipment ideal when measurement precision and repeatability is required. PhotonCom has developed an application based on the information provided by Yokogawa on making I-OSNR with polarization nulling technique using a manual polarization controller.
This procedure was developed for measuring I-OSNR on channels with a spacing of 50 GHz being modulated at 40 Gbit/s.  In order to make accurate I-OSNR measurements, the noise level within the channel needs to be visualized by the OSA. The noise (N) being essentially un-polarized and the modulated signal (S) being highly polarized, passing the complete signal (S + N) by a Polarization Controller enable the Noise to be measured by the OSA. This technique is called Polarization Nulling since the polarized signal is minimized by the Polarization Controller leaving the noise portion to go through. The remaining noise level after the Polarization Controller is 50 % of the total noise level since 50% of the noise is blocked (assuming perfect un-polarized noise and perfect polarization extinction of the Polarization Controller) . Using this technique, a complete I-OSNR measurement require 2 sets of data points.
The analysis portion starts immediately after the acquisition of the second series of data points. The application selects the WDM dual trace analysis option on the OSA.
Analysis results for each channel are then displayed on the OSA and by the application. PhotonCom used an automated test configuration to characterize the I-OSNR measurement parameters. This approach enables the injection of precise noise level that will be compared with the noise measurement tool. Multiple tunable filter stages create sharp noise envelop edges minimizing the injection of this noise in the adjacent channels. The Full Width at Half Maximum (FWHM) of the noise = 0.16 nm. The variable attenuator controls the amount of noise being injected in a particular channel.  This test configuration allows the evaluation of different I-OSNR measuring equipments by simply changing the output connection of the 50/50 coupler. When quantifying the injected noise level, the signal output going to the 50/50 coupler input is disconnected and the measurement is made at the coupler output. The signal noise level is also measured independently from the injected noise and will be considered in the final calculation. The impact of the signal noise level is greater at low noise injected level since it becomes the minimum noise threshold. The Insertion Loss (IL) of the Polarization Controller needs to be quantified to obtain the channels power level and the noise level express in dBm / Noise Bandwidth. But the I-OSNR values are independent of the IL since I-OSNR = Level (channel total power in dBm) – Noise (express in dBm/NBW). Adding the IL on both readings will not change the I-OSNR result. To characterize the Polarization IL using the OSA Connect the source directly into the OSA and run the application. Note: The goal is to get the total power level at the RES = 0.20 nm. The data from trace A = MIN HOLD + MAX HOLD Therefore 3 dB needs to be subtracted from trace A since without the Polarization Controller, the MIN HOLD = MAX HOLD = actual input power level. Repeat the measurement while connected to the Polarization Controller. This time the value of trace A will be used as is since the total power = Min Hold + Max Hold. Subtract the before and after values to get the IL applicable to the Polarization Controller. The WDM Analysis setting can be set remotely by the application or directly at the OSA. Note the value of Noise Area = 0.1 nm for the interpolation setting and the Noise bandwidth = 0.1 nm.   Example of C-band measurement with zoom of 2 nm span, the injected noise is on channel 11 
Preliminary test data: The variation on the I-OSNR measurement is 0.16 dB using scan rates from 1 to 8 and stop scan. The test duration was also varying from 2 to 10 minutes. This demonstrates a high tolerance to polarization state variation of the modulated signal. For a 2 minutes scan of the full C-band, compared to a 10 minutes scan, the I-OSNR measurement variation of the reference channel (containing the added noise) was 0.09 dB. For noise levels varying from -8 to -30 dB, the maximum I-OSNR measurement variation was 0.15 dB. To test the accuracy of the I-OSNR, the Noise and Signal were independently measured and then combined to perform an I-OSNR measurement. This measurement was compared with the predicted calculated value using the Noise and Signal independent measurement. The variation between the signal and noise measurement before and after the polarization controller Agilent 8169A was 0.23 dB. Specification of the I-OSNR PhotonCom solution
Reference links: AQ6370 Optical Spectrum Analyser http://kb.us.yokogawa.com/Network%20Solutions/TMI/COMM/AQ6370/bu7353-01e.pdf High bit rate modulated signal OSNR measurement http://www.yokogawa.com/de/tm/optische/pdf/APPLICATION_OSNR.pdf AQ6370 User Manual: Appendix 4 section http://www.photoncom.com/specs/Yogokawa_AQ6370_WDM Analysis.pdf AQ6370 User Manual http://kb.us.yokogawa.com/Network%20Solutions/TMI/COMM/AQ6370/IM735301-01E_020.pdf AQ6370 vs Competitors http://kb.us.yokogawa.com/Network%20Solutions/TMI/COMM/AQ6370/AQ6370vsCompetitors/AD_Auto.avi http://kb.us.yokogawa.com/Network%20Solutions/TMI/COMM/AQ6370/AQ6370vsCompetitors/AG_Auto.avi http://kb.us.yokogawa.com/Network%20Solutions/TMI/COMM/AQ6370/AQ6370vsCompetitors/AR_Auto.avi Statement: All technical information and specifications are based on the information provided by the equipment manufacturers and on experimentation done up to date. Additional test data will lead to specification review or addition. All risks and liability in connection to the usage of the products and application is assumed by the user. All trademarks are the property of their respective holders. If you would like more information or to get a quote on our I-OSNR measurement solution contact us using the following form: |
