Patent ID: 8306438

Claim:
A coherent receiver, comprising: digital circuitry configured to receive an input signal representing a quadrature modulated signal; and iterative updating circuitry configured to determine and correct for any of optical angle and phase magnitude imbalance and for delay imbalance between quadrature paths of the input signal; wherein the input signal comprises a real part and an imaginary part, and wherein the iterative updating circuitry is configured to process the real part and the imaginary part to form an output signal; wherein, to determine and correct for delay imbalance between quadrature paths, the iterative updating circuitry is configured to: process the real part of the received input signal with a first delay and the imaginary part of the received input with a second delay; and iteratively update at least one of the first delay and the second delay responsive to the output signal; and wherein the first delay comprises a fixed delay of two samples; wherein the second delay comprises a variable delay connected to a switch, the switch configured to connect the variable delay to the real part if a delay, δ, is less than or equal to zero or to the real part through a fixed delay of one sample if the delay is greater than zero; and wherein outputs from the first delay and the second delay are connected to an update block that iteratively determines the delay, δ, that in turn is used to set the variable delay.