Integrated optical network design for a retinal projection concept based on single-mode Si3N4 waveguides at 532 nm

We recently presented a novel retinal projection concept based on the combination of integrated optics and holography. Our lens-free optical system uses disruptive technologies to overcome the limitations of current devices such as a limited field-of-view and bulky optical assemblies. An integrated optical network of Si3N4 waveguides has been designed in the visible range in order to control the intensity of an optical field originating from an emissive point distribution (EPD) at a glass surface. In addition, the phase and orientation of the optical field are controlled by incorporating a pixelated holographic layer. The Si3N4 waveguides are transparent, allowing ambient light to pass through the device for augmented reality applications. This study focuses on the design of the components used for the optical circuit at lambda = 532 nm (hologram laser recording wavelength): single-mode waveguides, bent waveguides, cross-talk, diffraction grating couplers, MMI splitters (MultiMode Interference) and directional couplers. The parameters of the components are optimized with various numerical methods. Furthermore, an optical circuit used as the first test structure is presented. An optical set-up based on a goniometric configuration has been built to characterize the efficiency of our components with a particular focus on the angular properties. Future work will focus on the hologram recording process that will involve interferences between the EPD output beams and free-space planar light waves.