Two-dimensional photonic crystals with large complete photonic band gaps in both TE and TM polarizations

Feng Wen,Xavier Checoury,Moustafa El Kurdi,Sylvain David,Philippe Boucaud

doi:10.1364/oe.16.012278

Abstract

Photonic crystals exhibiting a photonic band gap in both TE and TM polarizations are particularly interesting for a better control of light confinement. The simultaneous achievement of large band gaps in both polarizations requires to reduce the symmetry properties of the photonic crystal lattice. In this letter, we propose two different designs of two-dimensional photonic crystals patterned in high refractive index thin silicon slabs. These slabs are known to limit the opening of photonic band gaps for both polarizations. The proposed designs exhibit large complete photonic band gaps: the first photonic crystal structure is based on the honey-comb lattice with two different hole radii and the second structure is based on a "tri-ellipse" pattern in a triangular lattice. Photonic band gap calculations show that these structures offer large complete photonic band gaps deltaomega/omega larger than 10% between first and second photonic bands. This figure of merit is obtained with single-mode slab waveguides and is not restricted to modes below light cone.

Highlights

Photonic crystals are being intensively studied for their ability to confine light in small mode volumes of the order of (λ/n)3 and in optical modes with very high quality factors [1]
We present two designs of photonic crystals based on C3v symmetries: the first design corresponds to the implementation of the ideas of Cassagne et al to the case of silicon membranes perforated following a honey-comb lattice with different hole sizes; the second design corresponds to a “tri-ellipse” pattern in triangular photonic crystals
A honey-comb lattice with two different hole sizes corresponds to a lattice where the mirror symmetry m2 is missing and we can observe in the red band diagram of Fig. 2(b) that the degeneracy is lifted leading to the opening of the band gap

Summary

Introduction

Photonic crystals are being intensively studied for their ability to confine light in small mode volumes of the order of (λ/n) and in optical modes with very high quality factors [1]. Not taking into account the vertical confinement of light, their work showed that a lower C3v symmetry applied to the honey-comb lattice leads to the opening of new photonic band gaps Another way to reduce the symmetries is to tilt patterns in each elementary cell of a traditional lattice [12, 13]. We present two designs of photonic crystals based on C3v symmetries: the first design corresponds to the implementation of the ideas of Cassagne et al to the case of silicon membranes perforated following a honey-comb lattice with different hole sizes; the second design corresponds to a “tri-ellipse” pattern in triangular photonic crystals Both designs lead to complete photonic band gaps between first and second bands with a width larger than.

Photonic crystals with C6v and C3v symmetries

Honey-comb lattices with two different hole sizes

Findings

Conclusion