Light Localization in Woodpile Photonic Crystal Built via Two-Directional Etching Method

Abstract

This paper describes designs, fabrication, and optical properties of subwavelength-scale light localization components in 3-D woodpile photonic crystal materials. Designed microcavities and waveguide geometries can be built with N-directional etching fabrication method (N = 2), which produces structures consisting of a combination of N 2-D air trench geometries. The microcavities and waveguides consist of straight dielectric rods only. In surface reflectance measurements, fabricated woodpile photonic crystals exhibit high reflectivity due to a photonic bandgap in infrared optical wavelength ranging from 1200 nm to about 1550 nm, matching with numerical calculation results. A variety of woodpile photonic crystals are fabricated with 2-D etching method, including (100) and (110) woodpile photonic crystals in silicon and gallium arsenide. This opens up the possibility of designing surface Bloch modes. A high quality factor is expected in the microcavity fabricated by vertical etching on top and side wafer facets. For a dipole mode, the Q factor of 105 requires a woodpile of 9 × 9 × 7 unit cells only. Three types of waveguide designs are studied. In a double-hetero junction woodpile, a self-collimation state is found and analyzed. Single-mode lateral and vertical optical waveguide modes in a complete photonic bandgap are presented, and would become basic components in 3-D integrated optics based on woodpile photonic crystals. Due to the confinement of light in complete photonic bandgap materials, the loss can be suppressed in a large woodpile photonic crystal.