Wavefront Control Of Transmissive Optical Field Based On Sub-wavelength Silicon Waveguide Array

Optical metasurface has many unconventional properties,like sub-wavelength feature sizes,transmissive responses which natural materials can not have.Therefore it becomes a hot field for optical integration and flat optical devices as soon as its concept is proposed.And reports of all-dielectric metasurface have extended the transmissive metasurfaces to visible and near-infrared frequencies as it avoids the ohm loss of metal materials.The key points for designing metasurfaces are the choices for unit structures.At present,most designs of all-dielectric metasurface are based on Mie theory or PB phase.In this paper,we novelly demonstrate a new idea to control the transmissive optical field at 1550 nm by using sub-wavelength silicon waveguides as unit structures.In our work,all results are given based on theoretical analyses and numerical simulations.First,we investigate the all-dielectric metasurface based on 2D sub-wavelength silicon waveguide arrays.We first analyze whether it's rational using 2D sub-wavelength silicon waveguides as unit structures.Then we realize beam deflection and convergence for normally incident and linear polarized plane wave respectively.By combining these two functions together,we skillfully realize beam convergence after it deflects from the normal direction.What's more,in this paper,we make a special effort to study Dammann grating-a typical binary optical element,and we investigate the design of 1D Dammann grating in this part and get a 1 × 5 spot array.Then we extend the 2D structures to 3D structures and investigate the all-dielectric metasurface based on 3D sub-wavelength silicon waveguide arrays.First we discuss the optical propogation and resonance properties of 3D sub-wavelength silicon waveguide and prove the feasibility of using 3D sub-wavelength silicon waveguides as unit structures.Then we realize vortex beam generation for input plane wave which is normally incident and linear polarized and discuss the interference between the vortex beam and plane wave.At last,we design a polarization independent Dammann grating generating a 5 × 5 spot array in the far field and demonstrate its broadband response and robustness.