Design of a Low-Crosstalk Sub-Wavelength-Pitch Silicon Waveguide Array for Optical Phased Array

In this work, a compact sub-wavelength-pitch silicon waveguide array with low crosstalk is proposed and analyzed. The crosstalk is suppressed by periodic silicon nano-blocks symmetrically arranged along the silicon strip waveguides. The silicon nano-blocks are properly designed to work in the resonant region as a high-reflection boundary so that the evanescent fields of the silicon waveguide, which directly contribute to the coupling between waveguides, can be truncated. Meanwhile, the nano-blocks periodically perturb the evanescent fields to form a weak-radiating grating, leading to a millimeter-long effective radiation length required for highly directive optical phased arrays. Simulation results show that the crosstalk between the waveguides in the proposed design is at least 10 dB lower than traditional waveguide array with identical sizes within the 1500-1590 nm bandwidth. Furthermore, the proposed design achieves an effective radiation length up to 1.47 mm, resulting in a theoretical narrow beam width of 0.052 degrees. Combining both the low crosstalk and the long effective radiating length, our design offers a promising platform for high-performance two-dimensional scanning optical phased array with a large field of view and a narrow beam width.