Numerical investigation of Al 0.3 Ga 0.7 N waveguide grating couplers with depth gradients for mode controlled light coupling

Abstract The numerical simulation demonstrates a depth-gradient etched grating coupler integrated into a planar Al 0.3 Ga 0.7 N waveguide, where the groove depth progressively increases to achieve smooth scattering modulation. The simulation results revealed that the design supports ∼36% transmittance, ∼17% upward coupling, and ∼12% reflectance for the TE 0 mode, while TE 2 and TE 3 modes yield ∼20% and ∼18% vertical extraction, respectively. Although binary gratings reach ∼48% peak efficiency for TE 2 , but they depict higher reflectance sensitivity and require a large footprint nearly nineteen times. Up to the best of our knowledge, the proposed depth-gradient approach is presented for the first time and offers a compact, fabrication-tolerant, and reflectance-controlled solution for Al 0.3 Ga 0.7 N based visible and ultraviolet photonic interfaces with promising applications in on-chip lasers, biosensing, and visible light communication.