There are multiple challenges to realize waveguide-based Surface Relief Gratings (SRG) for combiners in Augmented Reality (AR) applications: fabricability, efficiency and diffraction uniformity are among the most important ones. Interdigital develops SRG using Edge Waves (EW) to design highly efficient gratings with a high angular robustness. An EW is generated by a diffraction phenomenon appearing at the interface between two dielectric media and its direction of propagation is controlled by the index ratio between the two media and the direction of the incident plane wave. Combining different edges together, we optimize the elementary geometry, i.e., the building block of an SRG, to diffract into the direction defined by the grating equation, optimizing the power transfer of the incident light into the direction of interest. Our approach enables symmetrical structures with low aspect-ratio, optimized for coupling very efficiently into the first or second order modes, the latter leads to over-wavelength pitch sizes. Moreover, our SRG is designed to angularly tile the exit pupil of the light engine without losses, making our structures adapted to any sort of light engines. Based on our unique design concept, we present in-couplers using two waveguides with a field of view of 130 degrees and RGB operation, and a one waveguide system with 90 degrees of field of view and RGB operation, both with a wafer having also an index of refraction of about 1.7. We believe this will pave the way to new DOE combiners for future AR glasses.
In this work we have developed new type of color splitters, which separate spectrally and spatially the light reaching image sensors by exploiting the nanojet (NJ) beam phenomenon. The goal is to channel respective R, G and B (red, green and blues) spectra to corresponding pixels, and to replace absorbant color filters for a better light efficiency management. The proposed method relies on light diffraction on the edges of constitutive parts of the studied multimaterial elements. Diffraction of light on the edge of a dielectric microstructure forms a tilted focused beam whose characteristics depend on the ratio of refractive indexes between the materials of the elements creating this edge. Combination of two or more dielectric materials with different refractive indexes leads to the creation of multiple NJs with different angles of deviation, lengths and intensities. The possibility to split color-bands of the incident light by combining two or more dielectric materials is discussed. In this way the generated NJ beams create a spectrally dependent NJ pattern in the near zone. We demonstrate that the proposed topologies of multi-material microlenses help to reduce the size of the color splitting element as well as the optical crosstalk through the dielectric layer.