A phase difference detection system for a single target location, the phase difference detection system comprising: - a laser source to generate a laser beam; - a phase difference detector coupled to the laser source and having a multi-layer structure comprising: - a planar waveguide for guiding the laser beam, the planar waveguide having a normal direction and forming a first layer of the multi-layer structure; - a grating coupler to split the laser beam into a reference beam and a measurement beam, wherein the measurement beam is directed towards the target location and the reference beam is directed away from the target location, the reference beam and the measurement beam each being inclined with respect to said normal direction; and - a planar imager array forming a second layer of the multi-layer structure, the planar imager array being placed below the grating coupler, thus reducing the required on-chip area, the planar imager array being configured to detect a fringe pattern generated by said reference beam and an incoming beam, the incoming beam being the result of the measurement beam having been reflected at the target location and having passed through the grating coupler, and an external optical system configured to focus the measurement beam output from the phase difference detector on the single target location and to focus signals reflected at the target location to the phase difference detector. - a laser source to generate a laser beam; - a phase difference detector coupled to the laser source and having a multi-layer structure comprising: - a planar waveguide for guiding the laser beam, the planar waveguide having a normal direction and forming a first layer of the multi-layer structure; - a grating coupler to split the laser beam into a reference beam and a measurement beam, wherein the measurement beam is directed towards the target location and the reference beam is directed away from the target location, the reference beam and the measurement beam each being inclined with respect to said normal direction; and - a planar imager array forming a second layer of the multi-layer structure, the planar imager array being placed below the grating coupler, thus reducing the required on-chip area, the planar imager array being configured to detect a fringe pattern generated by said reference beam and an incoming beam, the incoming beam being the result of the measurement beam having been reflected at the target location and having passed through the grating coupler, and an external optical system configured to focus the measurement beam output from the phase difference detector on the single target location and to focus signals reflected at the target location to the phase difference detector. - a planar waveguide for guiding the laser beam, the planar waveguide having a normal direction and forming a first layer of the multi-layer structure; - a grating coupler to split the laser beam into a reference beam and a measurement beam, wherein the measurement beam is directed towards the target location and the reference beam is directed away from the target location, the reference beam and the measurement beam each being inclined with respect to said normal direction; and - a planar imager array forming a second layer of the multi-layer structure, the planar imager array being placed below the grating coupler, thus reducing the required on-chip area, the planar imager array being configured to detect a fringe pattern generated by said reference beam and an incoming beam, the incoming beam being the result of the measurement beam having been reflected at the target location and having passed through the grating coupler, and an external optical system configured to focus the measurement beam output from the phase difference detector on the single target location and to focus signals reflected at the target location to the phase difference detector.