Experimental Demonstration of Robustness and Accuracy of an MZI-based OSNR Monitor under Transmitter Drift and Reconfigurable Networking Conditions for Pol-Muxed 25-Gbaud QPSK and 16-QAM Channels
Optical Fiber Communication Conference
We experimentally demonstrate the robustness of an MZI-based OSNR monitor under reconfigurable network and transmitter drift. The monitor calibration factors for 25 Gbaud PM-QPSK signal are stored after assembly and applied to study the accuracy of the OSNR monitoring unit when different changing scenarios outside the monitor occurred. OCIS codes: (060.2360) Fiber optics links and subsystems; (060.4257) Networks, network survivability 1. Introduction Optical performance monitoring has gained
... h interest for its ability to help determine the relative health of various optical data channels. Such ability can enable: (i) the identification and location of data-degrading effects at different points in the system, and (ii) routing traffic based on the relative "quality" of a given physical route. Such monitoring should optimally be located at many points of the system . A key parameter to measure is the optical signal-to-noise ratio (OSNR), which represents a crucial metric of the health of a data channel at various points around the network. There are different approaches for OSNR monitoring. One method is to measure the noise adjacent to the data channel and interpolating what the noise would be in-band  . This approach is not only an approximation, but it also is problematic the many systems that incorporate wavelength filters and (de)muxes that preferentially reduce the out-of-band noise. Another method that does measure the in-band noise is to use polarization nulling, but it is difficult to use this approach for unpolarized optical data channels  . There have been reports of using a Mach-Zehnder interferometer (MZI) to achieve OSNR monitoring in which the MZI contains a ¼-bit delay in one arm of the interferometer. In this approach, the data signal experiences coherent interference and the noise does not. By measuring the relative output power at the constructive and destructive ports of the delay-line interferometer (DLI), the OSNR can be measured    . Although this single-DLI approach has been shown to provide <0.5 dB error for different modulation formats and can operate on pol-muxed data channels, there are still several critical questions that must be answered in order to enable future deployment in systems. For example, the OSNR monitor must be calibrated after assembly so that it accurately measures signal and noise. However, it is unclear if the monitor will indeed still perform accurate measurements if: (a) the transmitter parameters drift or the data channel is modified, (b) if the data channel originates from a different source transmitter due to reconfigurable networking or transmitter replacement, and (c) if the baud rate or modulation format of the data channel is changed. A laudable goal would be to determine if the OSNR monitor would function properly under changing network conditions with requiring servicing, updating or recalibration. In this paper, we experimentally demonstrate robustness and accuracy of an MZI-based OSNR monitor under transmitter drift and reconfigurable networking conditions for pol-muxed 25-Gbaud QPSK and 16-QAM channels. We initially calibrated the monitor with its signal and noise distribution factors (α and β) once and changed the: (a) error vector magnitude (EVM), (b) baud rate, (c) modulation format, (d) wavelength, and (e) path, to emulate the reconfigurable network and conduct accuracy study (see Fig. 1 ). We show that the monitor is robust and can achieve <0.5dB error at specific baud rate for most of the cases.