Method and circuit for reflection cancellation

A reflection cancellation circuit, comprising:

• (a) a tunable tap optically coupled to a laser to receive laser output therefrom;
• (b) a phase shifter optically coupled to the tunable tap to receive a tapped portion of the laser output;
• (c) a mirror optically coupled to the phase shifter and positioned to reflect a feedback signal back towards the laser;
• (d) a first photodetector optically coupled to monitor a magnitude of a resulting signal and generate a corresponding first photocurrent;
• and
• (e) a control circuit communicatively coupled to the tunable tap, the phase shifter, and the first photodetector, wherein the control circuit is configured to perform a method comprising:
• (i) tapping the laser output using the tunable tap;
• (ii) using the phase shifter, generating the feedback signal by phase shifting a tapped portion of the laser output, wherein a magnitude and a phase of the feedback signal are such that superposition of the feedback signal and the parasitic reflection results in the resulting signal, wherein the resulting signal is of lower magnitude than the parasitic reflection entering the laser;
• and
• (iii) in response to the first photocurrent, reducing the magnitude of the resulting signal by adjusting at least one of the magnitude and the phase of the feedback signal by respectively adjusting at least one of the tunable tap and the phase shifter.