Apparatus and methods for timing tone based transmitter skew alignment in an optical communication system

A method of operating an transmitter error compensation device for a digital signal processing circuit in a receiver for an optical communications systems, the method comprising:

• receiving, from an analog front-end, a digital signal vector, wherein the digital signal vector comprises a digital representation of an in-phase (I) component and a quadrature-phase (Q) component of an optical signal received from a transmitter;
• generating, by a MIMO equalizer, a compensated digital vector by compensating for a modulating biasing error of the transmitter;
• generating, by a first SISO equalizer, an I component of the compensated digital vector, wherein the first SISO equalizer is configured in an I signal path with the MIMO equalizer;
• generating, by a second SISO equalizer, a Q component of the compensated digital vector, wherein the second SISO equalizer is configured in a Q signal path with the MIMO equalizer;
• and
• compensating, by the first and second SISO equalizers, for a transmit skew error of the transmitter.

A receiver for an optical communications system, the device comprising:

• an analog front-end configured to convert an analog signal vector representing an optical signal into a digital signal vector, the optical signal having a baud rate that is based on a timing tone, wherein the digital signal vector comprises a digital representation of an in-phase (I) component and a quadrature-phase (Q) component of an optical signal received from a transmitter;
• a digital signal processing circuit configured to process the digital signal vector to recover data from symbols of the optical signal, wherein the symbols change at the baud rate;
• wherein the digital signal processing circuit further comprises a transmitter error compensation system configured to compensate the digital signal vector for at least one of a transmit skew error or a modulator biasing error of the transmitter;
• wherein the transmitter error compensation system comprises:
• a MIMO equalizer configured to receive the digital signal vector from the analog front-end and to generate a compensated digital vector;
• wherein the MIMO equalizer is configured to compensate for a modulating biasing error of the transmitter;
• a first SISO equalizer configured to generate an I component of the compensated digital vector;
• a second SISO equalizer configured to generate a Q component of the compensated digital vector;
• wherein the first and second SISO equalizers are configured to compensate for a transmit skew error of the transmitter;
• an I signal path including the MIMO equalizer and the first SISO equalizer;
• and
• a Q signal path including the MIMO equalizer and the second SISO equalizer.