We propose a novel design of grating couplers to be used as the building blocks of the optical antennas of Lidar systems, designed in the well-established Si3N4-TriPleX platform, that offers low-loss waveguides and allows the integration of the dispersive grating elements with ultra-low-loss and low-energy photonic beamformer circuits. The grating couplers are based on standard asymmetric double-stripe waveguide geometry and are designed with 100nm spectral range around 1550nm. More specifically, we design non-uniform geometry grating couplers, varying the waveguide width and filling factor, targeting constant effective refractive index across the propagation direction, and thus constant emission angle, while optimizing for a uniform emission profile. The designs allow to achieve low theta angle divergence as well as maximum wavelength steering. The reported design showcases theta angle 3dB divergence of 1o, phi angle 3dB divergence of 20o and wavelength steering of 10 o /100nm. The proposed components show low fabrication complexity and are compatible with standard fabrication processes. A comparison between uniform and non-uniform grating designs is also presented, investigating also their performance in an OPA configuration. The described methodology is based on mode solving simulations (Lumerical FDE) and propagation simulations (Lumerical FDTD), while the OPA profile extraction is performed with Matlab Sensor Array Analyzer Toolbox.
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