Method and apparatus for compensating for optical crosstalk in an optical output power feedback monitoring system of a parallel optical transmitter

An apparatus for performing optical crosstalk calibration in a parallel optical transmitter or transceiver to obtain reference values to be used in monitoring and controlling optical output power levels of laser diodes of the parallel optical transmitter or transceiver, the apparatus comprising:

• a memory device;
• and
• a controller configured to perform a calibration process, the calibration process comprising:
• enabling n of the laser diodes and adjusting respective initial reference values applied to the respective second terminals of the respective laser diode driver circuits until average optical output power levels of the laser diodes are being maintained at substantially constant levels, wherein n is equal to or greater than 2;
• storing the adjusted initial reference values as respective original reference values in the memory device;
• enabling j of the laser diodes, where j is a positive integer that ranges in value from 1 to n;
• disabling an ith one of the laser diodes, where i is a positive integer that ranges in value from 1 to n, and where i is not equal to j;
• applying respective original reference values stored in the memory device to respective second terminals of respective laser diode driver circuits of respective feedback control loops of the parallel optical transmitter or transceiver;
• adjusting the respective original reference values being applied to the respective second terminals of the respective laser diode driver circuits until average optical output power levels of the respective laser diodes are being maintained at substantially constant levels, the respective adjusted original reference values corresponding to respective new reference values;
• and
• storing respective difference values in the memory device as respective optical crosstalk terms, the respective optical crosstalk terms corresponding to respective differences between respective adjusted original reference values and respective original reference values.

A method for compensating for optical crosstalk in an optical output power feedback monitoring system of a parallel optical transmitter or transceiver, the method comprising:

• in n feedback control loops, where n is a number of optical transmit channels in the parallel optical transmitter or transceiver and is greater than or equal to 2, enabling n respective laser diodes of respective feedback control loops, each laser diode being driven by a respective laser diode driver circuit of the respective feedback control loop, each laser diode driver circuit having at least first and second input terminals, the first input terminal receiving an electrical feedback signal that is based on an optical output power level of the respective laser diode detected by a respective photodiode of the respective feedback control loop;
• applying respective original reference values to respective second input terminals of respective laser diode driver circuits;
• in a controller of the parallel optical transmitter or transceiver, determining whether or not adjustments need to be made to the original reference values to compensate for a change in an amount of optical crosstalk present in or absent from one or more of the feedback control loops;
• and
• if the controller determines that adjustments need to be made, the controller adjusts the original reference values to produce new reference values and causes respective new reference values to be applied to the respective second terminals of the laser diode driver circuit.