MEASURING SIGNAL TO NOISE RATIO OF A WDM OPTICAL SIGNAL

摘要

A WDM optical signal is transmitted through a tunable optical filter and is polarization-nulled to find optical signal to noise ratio of individual WDM channels. The polarization nulling can be performed using a heuristic multipoint extrema search method, such as Nelder-Mead method. A plurality of checkpoints can be included in the search to verify the progress and to improve the overall robustness of a real-time polarization nulling.

主权项

1. A device for measuring OSNR of a WDM optical signal including a plurality of wavelength channels, the device comprising:
an input port; an optical train coupled to the input port and including serially connected
a tunable optical filter for selecting a wavelength channel of the plurality of wavelength channels,a polarization controller for adjusting a polarization state of the selected wavelength channel,a polarization selector disposed in the optical train downstream of the polarization controller, for selecting a polarization state of the selected wavelength channel, anda photodetector disposed in the optical train downstream of the tunable optical filter, the polarization controller, and the polarization selector, for detecting a first optical power level of the selected wavelength channel and in the selected polarization state; and a control unit coupled to the tunable optical filter, the polarization controller, and the photodetector, and configured to tune the optical filter to the selected wavelength channel; adjust the polarization controller to reach a target control point, at which the first optical power level is minimized or reduced; and compute the OSNR of the selected wavelength channel from a polarization extinction defined as a ratio of a second optical power level upstream the polarization selector to the first optical power level; wherein the control unit includes a computer processor and a non-transitory memory configured for causing the computer processor to perform a heuristic iterative search of the target control point by performing a plurality of iterations including a first iteration and a second iteration after the first, wherein a plurality of control points of the second iteration are selected based on optical power levels detected by the photodetector at a plurality of control points of the first iteration.