Patent ID: 7130505

Claim:
An optical performance monitor for monitoring an OSNR of an input optical signal comprising a plurality of WDM channels centered at evenly spaced channel frequencies with a channel frequency spacing Δ ch , the optical performance monitor comprising: a dispersive element comprising M input ports and J output ports, wherein M>2 and J>2, a control means disposed to receive the input optical signal for optically coupling said input signal sequentially into each of the M input ports; a photodetector means optically coupled to the J output ports for providing electrical signals related to an optical power in each of the J output ports when the input signal is coupled into one of the M input ports; and, a processing means for determining the OSNR of the input optical signal from the electrical signals provided by the photodetector means; wherein the dispersive element is for optically coupling each of the input ports with each of the output ports at a different central frequency in dependence on respective input and output ports for sampling an optical spectrum of the input optical signal at a plurality of the central frequencies when the input light is sequentially coupled into the M input ports, wherein the J output ports are configured for optical coupling to one of the M input ports at a first set of J of the central frequencies that are evenly spaced by the frequency spacing Δ ch , and shifted from the channel frequencies by a pre-determined fraction of the channel spacing Δ ch for sensing optical noise level between the WDM channels; wherein the M input ports are configured for optical coupling to one of the J output ports at a second set of M of the central frequencies spaced by at least 2·Δ ch/M.