Design and fabrication of line-defect waveguides in hexagon-type SOI photonic crystal slabs

We present a novel design approach for line-defect waveguides integrated in a photonic crystal slab (PCS) with hexagonal holes in a triangular lattice (aka 'hexagon-type'). Triangular air inclusions are symmetrically added on each side of the waveguide. Size and position of these inclusions are tuning parameters for the band diagram and can be used for minimizing the distributed Bragg reflection (DBR) effect. The waveguides show single-mode behavior with reasonably high group velocity and large transmission window, inside the gap between even-like modes. Qualitative design rules were obtained from 2D calculations based on effective index approximation and full 3D calculations of the band structure were applied for fine-tuning of structural parameters of these high-index contrast systems. Transmission spectra and losses of finite-sized structures were estimated by means of 3D finite-difference time domain (FDTD) calculations. We present a pattern definition technique, which is an integration of optical lithography with focused ion beam (FIB) high-resolution etching. The mask pattern is transferred into the SOI stack by a subsequent reactive ion etching (RIE) process. The combination of moderate resolution optical lithography and FIB etching provides an excellent tool for fast prototyping of PCS-based devices.