Integrated laser detector

A PIC-based integrated laser detector comprising:

• two or more sub-systems and one or more phase tuners, the subsystems and the one or more phase tuners fabricated on a common substrate;
• wherein each sub-system comprises:
• first, second and third elements;
• wherein the first element comprises a structure supporting efficient coupling of one or more free-space optical modes of light incident on the first element into one or more waveguide guided optical modes;
• wherein the second element comprises an on-chip interferometer comprising:
• an input optically coupled to the waveguide guided optical modes;
• one or more arms;
• and
• one or more outputs;
• and
• wherein the third element comprises one or more light detecting structures optically coupled to the one or more outputs of the second element, such that variation in optical power in the one or more outputs is detected, providing a determination of coherence characterizing the incident light;
• wherein one of the one or more phase tuners is shared between two or more of the sub-systems, being configured to change optical path length in one or more of the arms in the corresponding two or more interferometers.

A method of assessing coherence of incident light comprising one or more free space optical modes;

• the method comprising:
• intercepting the one or more free space optical modes with a PIC-based integrated laser detector comprising:
• first, second and third elements fabricated on a common substrate;
• wherein the first element comprises a structure supporting efficient coupling of the one or more free-space optical modes into one or more waveguide guided optical modes;
• wherein the second element comprises an on-chip interferometer comprising:
• an input optically coupled to the waveguide guided optical modes;
• one or more arms;
• one or more outputs;
• and
• a phase tuner configured to change optical path length in one or more of the arms;
• and
• wherein the third element comprises one or more light detecting structures optically coupled to the one or more outputs of the second element;
• operating the phase tuner, such that an optical path length of at least one arm of the interferometer is adjusted;
• receiving one or more signals from the one or more light detecting structures as the phase tuner is operated;
• and
• providing a measure of coherence of the incident light, based on analysis of the received one or more signals.