Dynamic range for a heterodyne optical channel monitor

An optical channel monitor (OCM), comprising:

• a local oscillator (LO) to provide an LO output;
• a first mixer to generate a first pair of mixed optical signals based on mixing a first portion of the LO output and a first input optical signal,
• the first input optical signal being associated with a first port;
• a second mixer to generate a second pair of mixed optical signals based on mixing a second portion of the LO output and a second input optical signal,
• the second input optical signal being associated with a second port;
• a first optical detector to provide, based on the first pair of mixed optical signals, a first electrical signal corresponding to a coherent mixture of the first input optical signal and the first portion of the LO output;
• and
• a second optical detector to provide, based on the second pair of mixed optical signals, a second electrical signal corresponding to a coherent mixture of the second input optical signal and the second portion of the LO output.

A method, comprising:

• modulating, by modulator of an optical channel monitor (OCM) and using a modulation signal, a local oscillator (LO) signal to create a modulated LO signal;
• mixing, by a mixer of the OCM, a portion of an input optical signal and a portion of the modulated LO signal to create a pair of mixed optical signals;
• providing, by an optical detector of the OCM and based on the pair of mixed optical signals, a first electrical signal corresponding to a coherent mixture of the portion of the input optical signal and the portion of the modulated LO signal;
• and
• providing, by a synchronous demodulator, a second electrical signal based on the first electrical signal and the modulation signal,
• wherein the second electrical signal is representative of an optical power spectrum of the portion of the input optical signal.