Optical coherent imager having shared input-output path and method for sensing coherent light

An apparatus comprising an imaging optics system, a coherent sensor, and a polarization transformer on the coherent sensor, wherein the coherent sensor comprises:

• a photonic substrate;
• a polarization diversified optical coupler disposed on a substrate surface of the photonic substrate to direct optical signals having a first polarization state to and from free space and a first waveguide disposed on the substrate surface and to direct optical signals having a second polarization state to and from free space and a second waveguide disposed on the substrate surface, the first polarization state being orthogonal to the second polarization state;
• and
• one or more photodetectors disposed on the substrate surface and optically coupled to the polarization diversified optical coupler through at least one of the first and second waveguides;
• wherein said optical signals having the first polarization state propagate along a first direction of an optical path after exiting the polarization transformer and before entering the imaging optics system;
• and
• wherein said optical signals having the second polarization state propagate along a second direction of the same optical path after exiting the imaging optics system and before entering the polarization transformer, the second direction being opposite to the first direction.

A method for optical coherent imaging, comprising:

• emitting, from an optical coherent imager having a photonic substrate with a plurality of coherent detection units disposed on the photonic substrate, one or more outgoing optical signals to one or more targets respectively along one or more optical paths in free space corresponding respectively to one or more field-of-view positions of the optical coherent imager, wherein different coherent detection units correspond to different field of view positions;
• receiving, by the optical coherent imager along the one or more optical paths, one or more incoming optical signals reflected from the targets illuminated by the one or more outgoing optical signals;
• converting, by a polarization transformer of the optical coherent imager, each of the one or more incoming optical signals into a first optical component having a first polarization state and a second optical component having a second polarization state, wherein the first polarization state is orthogonal to the second polarization state;
• and
• guiding, by one or more polarization diversified optical couplers disposed on the photonic substrate of the optical coherent imager, the first and second optical components of the one or more incoming optical signals to one or more photodetectors disposed on the photonic substrate of the optical coherent imager so as to perform heterodyne detection at each of the one or more field-of-view positions of the optical coherent imager, thereby determining information of the targets at the one or more field-of-view positions;
• wherein one of the one or more outgoing optical signals corresponding to a first one of the one or more field-of-view positions of the optical coherent imager propagates along a same one of the one or more optical paths as that of one of the one or more incoming optical signals corresponding to said first one of the one or more field-of-view positions of the optical coherent imager.