Design of Si3N4 waveguides and components to form an integrated optical network for retinal projection in thin augmented reality glasses

We developed a novel concept of retinal projection for augmented reality (AR) glasses combining optical integrated optics and holography. Our thin and lens-free concept overcomes limitations of current AR devices such as bulky optics and limited field-of-view. The integrated circuit is transparent and guide visible wavelengths by using Si₃N₄ as the core material of the waveguides. This work presents a detailed description of the optical principles behind the concept, including the self-focusing effect. Furthermore, we present the design of the first building blocks used for the optical integrated circuit at a visible wavelength (λ = 532 nm): single-mode waveguides, bent waveguides, cross-talk, grating couplers and MMI splitters (MultiMode Interference). Numerical simulation results of each component are presented. A prototype combining these optical building blocks in a 1024 waveguide array is designed to provide future experimental proof of concept of our retinal projection concept. In addition to this prototype, test structures are inserted on a photolithography mask to experimentally validate the simulations of each optical building block in future work. Next steps of development will include densifying the integrated optical architecture using serial coupling effects and multiple waveguide layers.