| CPC G02B 6/4213 (2013.01) [G01S 7/499 (2013.01); G01S 17/34 (2020.01); G02B 6/2706 (2013.01); G02B 6/274 (2013.01); G02B 6/2773 (2013.01); G02B 6/34 (2013.01)] | 24 Claims |

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1. An optical coherent sensor comprising a photonic substrate, a plurality of coherent sensing units disposed on the photonic substrate, and a polarization transformer disposed on the coherent sensing units, wherein each of the coherent sensing units comprises:
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;
wherein said optical signals having the first polarization state propagate along a first direction of an optical path after exiting the polarization transformer; and
wherein said optical signals having the second polarization state propagate along a second direction of the same optical path before entering the polarization transformer, the second direction being opposite to the first direction.
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