FMCW Lidar with a diffractive waveguide

Optical sensing apparatus, comprising:

• a substrate;
• a transmitter, which is disposed on the substrate and is configured to emit frequency-modulated (FM) coherent optical radiation along a transmit axis toward a target;
• a receiver, which is disposed on the substrate alongside the transmitter and comprises an array of detectors of optical radiation;
• an objective optic configured to focus the optical radiation that is reflected from the target onto the receiver along a receive axis;
• and
• a transparent slab, which is disposed over the transmitter and the receiver and has a first face facing the substrate and a second face opposite the first face, and which comprises:
• a first diffractive structure, which is disposed in a first location intercepting the transmit axis and is configured to deflect a part of the FM coherent optical radiation to form a local beam propagating diagonally within the transparent slab and reflecting from the second face toward the receive axis;
• and
• a second diffractive structure, which is disposed in a second location intercepting the receive axis and is configured to deflect and project the reflected local beam onto the array of detectors, whereby the local beam mixes at the array with the optical radiation reflected from the target.