Light detection and ranging

A method of determining a parameter for projection of a structured light pattern by a holographic projector;

• said holographic projector being comprised within a light detection and ranging, “LiDAR”, system arranged to make time of flight measurements of a scene, the LiDAR system further comprising a detector and a controller;
• said holographic projector comprising a spatial light modulator arranged to display a light modulation pattern comprising a hologram and grating function having a periodicity, and a light source arranged to illuminate the displayed light modulation pattern and project a structured light pattern corresponding to the hologram on a replay plane;
• wherein the detector has a field of view defined on the replay plane;
• and
• wherein there is a spatial separation between the spatial light modulator and the array of detection elements, such that they have two different respective lines of sight of a target, within the scene;
• the method comprising:
• projecting light from the light source, via the spatial light modulator, towards the scene;
• detecting, by the detector, a reflection of the light from the scene;
• making a determination of distance information related to the scene, based on the detection made by the detector;
• selecting a parameter for a subsequent projection of a structured light pattern, by the holographic projector, based on the determined distance information wherein the step of selecting a parameter for subsequent projection of a structured light pattern comprises determining the periodicity of a subsequent grating function such that the resulting structured light pattern, corresponding to that subsequent grating function, will be located within the field of view of the detector.

A method of controlling a light detection and ranging, “LiDAR”, system arranged to make time of flight measurements of a scene, the LiDAR system comprising a holographic projector and a detector;

• said holographic projector comprising a spatial light modulator arranged to display a light modulation pattern comprising a hologram and grating function having a periodicity, and a light source arranged to illuminate the displayed light modulation pattern and project a structured light pattern corresponding to the hologram on a replay plane;
• wherein the detector has a field of view defined on the replay plane;
• the method comprising:
• providing a control instruction to the holographic projector to project light from the light source, via the spatial light modulator, towards the scene;
• receiving a detection signal, from the detector, indicating a reflection of the light from the scene;
• making a determination of distance information related to the scene, based on the detection signal received from the detector;
• selecting a parameter for a subsequent operation of the holographic projector, based on the determined distance information;
• and
• providing a control instruction to the holographic projector to perform said subsequent operation.