Research on vector optimization of laser beam splitter grating

Large angle beam splitter grating is an important optical element but the current design methods are mostly based on the scalar diffraction theory based on Thin Element Approximation approximation, which is difficult to evaluate and calculate well when large angle beam splitting is involved. In this work, a method combining finite difference time domain method with adjoint optimization is proposed. Each iteration only needs two electromagnetic simulations to obtain the gradient distribution of the grating structure region. Using this method, a 1×5 beam splitting grating with a splitting angle of 10 degrees is designed. The final uniformity error is 3.7%, and the total diffraction efficiency is 86.6%. For the two-dimensional splitter , a 3×5 beam splitting grating with a diffraction full angle of 82.4×14 degrees is designed. Under the condition of large angle beam splitting, good uniformity error can still be maintained, and the final uniformity error reaches 23.1%.