A two-thickness subwavelength grating focusing lens for TE polarization light

Abstract

A focusing lens for TE-polarization light based on silicon high-contrast subwavelength gratings (HCGs) with two different thicknesses is proposed. The key point in designing this structure is to obtain a total phase shift of 2π rad continuously by changing the period, duty cycle, and thickness of each grating bar simultaneously for TE polarization light. Meanwhile, a novel two-thickness method is presented to provide more suitable grating bars for the design of HCGs. The properties are numerically studied by the finite element method (FEM). The results show that the focal length is 7.2 µm, the total transmissivity is 72%, and the full-width at half-maximum (FWHM) at the focal plane is 0.8 µm at a wavelength of 1.55 µm. This structure will be potentially integrated into optical devices, such as vertical cavity surface emitting lasers (VCSELs), photodetectors, CCDs, and CMOSs. We also estimate the two-thickness method to be a trade-off between high performances and fabricating accuracy. This lens as an example provides guides for the design of one-dimensional (1D) HCGs and provides suggestions for the design of 2D or 3D HCGs.