The present disclosure generally relates to wavelength tuning, and specifically to wavelength tuning for a structured light projector including one or more diffractive optical elements (DOE).
Structured light projectors are used for depth measurement in head-mounted display (HMD) systems, such as systems used in virtual reality and augmented reality applications. A structured light projector is typically composed of a light source that emits light and a DOE that uses the emitted light to generate a structured light pattern. Performance of DOEs is highly dependent on wavelength, and inconsistencies in manufacturing DOEs and/or light sources may cause an optimal wavelength of DOEs to vary from its design wavelength (i.e., wavelength it is designed to operate at), even between DOEs from the same lot. Examples of inconsistency in manufacturing include incorrect etch depth in e.g., lithographic processes, material shrinkage in compression molding, or incomplete material flow in injection/compression molding applications (e.g., due to trapped gas). Any different in feature period and feature height of a DOE can cause change in its design wavelength. Existing wavelength tuning methods for a structured light projector determine wavelengths calibrated to the light source (e.g., to produce maximum optical power). However, those exiting systems fail to produce optimal structured light patterns because variation in the optimal wavelength can result in a system where light emitted from the source is at different wavelength than the optimal wavelength for the associated DOE.