Polarization-Independent Focusing Reflectors Using Two-Dimensional SWG

Planar dielectric reflectors with polarization-independent focusing ability promise to replace conventional free-space components for applications in on-chip optoelectronic integration. A polarization-independent focusing reflector using a square two-dimensional (2D) subwavelength grating (SWG) has been both numerically and experimentally demonstrated. The 2D SWG can provide high focusing power by designing a non-periodic grating pattern to control the wave front of reflected beam while maintaining a high reflectivity. The 2D SWG focusing reflector with a focal length of 6 μm and a grating area of 10.5 μm × 10.5 μm was investigated, which exhibits a focusing ability without polarization sensitivity under normal incident light at wavelength 1.55 μm. In the reflection focal plane, the full-width-half-maximum of the electric field intensity is 1.338 μm. The results show a numerical aperture of 0.66 with a reflectivity over 82%.