Signal to noise ratio estimation in optical communication networks

An optical communication apparatus, comprising:

• a memory that stores data and instructions;
• and
• a processor that reads the instructions from the memory and implements a method for monitoring in-band signal to noise ratio of an optical communication path between a source node at which a source signal ingresses the optical communication path and a test node, the optical communication path comprising at least one additional optical node and an optical transmission medium interconnecting the source node, the test node and the at least one additional optical node, wherein each node a bandlimiting distortion from its input to output, comprising:
• obtaining an estimate of a reference signal at the source node prior to the source signal entering the optical transmission medium at the source node;
• determining an equivalent transfer function through which the source signals traverses before reaching the test node;
• computing a noise level at the test node using the equivalent transfer function;
• and
• reporting an optical signal to noise ratio at the test node as a ratio of energy in signal received at the test node and the estimated noise level.

An optical communication system, comprising:

• a plurality of optical nodes, each optical node configured to carry, from its input to its output, an optical signal along an optical communication path,
• one of the plurality of optical nodes being a source node at which a source signal having a pre-determined signal bandwidth ingresses the optical communication path and a test node at which the optical communication path is monitored,
• wherein at least some of the plurality of optical nodes include a wavelength selective switch (WSS) that introduces a bandlimiting distortion in the source signal;
• and
• a monitoring apparatus that implements a method, comprising:
• obtaining an estimate of a reference signal at the source node prior to the source signal entering the optical transmission medium at the source node;
• determining an equivalent transfer function through which the source signals traverses before reaching the test node;
• computing a noise level at the test node using the equivalent transfer function;
• and
• measuring an optical signal to noise ratio at the test node as a ratio of energy in signal received at the test node and the estimated noise level.