End-fire passive beam steering enabled by effective refractive index manipulation using gratings

We propose and demonstrate a compact and power-efficient method for end-fire beam steering in Optical Phased Arrays (OPAs) by passively manipulating the effective refractive index (<i>n</i>_eff) of individual waveguides. Unlike conventional approaches that rely on thermo-optic or electro-optic tuning or long delay lines, our technique introduces fixed phase shifts through geometrical modifications of each waveguide. Specifically, we design a grating-assisted waveguide array in which each waveguide is engineered to exhibit a distinct, static <i>n</i>_eff, forming a linear phase gradient across the array. This passive phase profile enables directional control of the output beam via wavelength tuning in an end-fire configuration. Finite-Difference Time-Domain (FDTD) simulations confirm that the engineered phase gradient effectively steers the beam. Beyond beam steering, this design also offers a significant advantage for densely packed waveguide arrays: the differences in <i>n</i>_eff—and consequently in their propagation constants &beta;—help suppress optical crosstalk, making it well-suited for compact photonic integration.