Consistent with the present disclosure, a coherent detector is provided that includes an optical hybrid that supplies optical signals including local oscillator light to a balanced detector. The amount of imbalance or “balance error” in the balanced detector is identified by comparing an output of the balanced detector and an output of a photodiode that receives a portion of an input optical signal provided to the optical hybrid. Based on the balance error, electrical signals generated by the balanced detector or the power of optical signals passing through (or output from) the optical hybrid circuit can be adjusted so that the balance error is minimized or reduced to zero. As a result, imbalance associated with the balanced detector is corrected so that unwanted currents and/or related electrical signals are cancelled out or substantially cancelled out. Such unwanted currents and/or related electrical signals are generated in response to noise in the local oscillator light as well as intensity noise associated with non-selected optical signals in a superchannel.