Fixed Focus Grating Reflector Based on Hybrid Optimization Method

In this letter, we proposed a hybrid design method based on rigorous coupled wave analysis (RCWA) and velocity varying climbing particle swarm optimization (VVCPSO) to realize a focal shift eliminating grating reflector. we proved that the focusing reflector obtained by the hybrid design method can eliminate the focal shift of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5\mu $ </tex-math></inline-formula>m (the focal length is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$100\mu $ </tex-math></inline-formula>m), improve the reflectivity and focusing efficiency by 14% and 17%, and achieve a full width at half maxima (FWHM) of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.52\mu $ </tex-math></inline-formula>m, which is considerably smaller than the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3.5\mu $ </tex-math></inline-formula>m of the focusing reflector obtained solely through RCWA. Therefore, this method has a far-reaching influence on the design of fixed focus grating structure.