Optimization of complete band gaps for photonic crystal slabs throughuse of symmetry breaking hole shapes

摘要

A complete photonic band gap (PBG) in photonic crystal slab (PCS) devices is desirable for various applications, and a realizable device of this kind demands minimal transmittance in-plane as well as out of plane. While in the past much work has considered this problem, none have held transverse confinement as a prime factor. In order to achieve our goal, square and triangular hole shapes are considered. Looking at sharp featured shapes as well as their fabrication realizable rounded counterparts and an even more rudimentary triangular cluster of circles, we look to break the crystal-mode symmetries for TM photonic bands and, therefore, open a complete band gap between the 1st and 2nd bands for both TE and TM light. TE/TM gap overlap is optimized for single-slab-mode operation, via the effective index method, for hole size, hole orientation, and slab thickness - all as functions of the lattice constant, a, and operational wavelength, λ. It is found that rounded triangular holes and tri-clustered circular holes of size 0.88a and thickness d/λ = 0.112 show identical photonic behavior that provides an optimized gap overlap of 0.0496 (coa/2πc = a/λ) with a 12.81% gap figure of merit (Δω/ω_0).