Photonic molecules: tailoring the coupling strength and sign.

S Haddadi,J A Levenson,A M Yacomotti,C Sauvan,I Sagnes,P Lalanne,P Hamel,G Beaudoin

doi:10.1364/oe.22.012359

Abstract

We demonstrate a large tuning of the coupling strength in Photonic Crystal molecules without changing the inter-cavity distance. The key element for the design is the "photonic barrier engineering", where the "potential barrier" is formed by the air-holes in between the two cavities. This consists in changing the hole radius of the central row in the barrier. As a result we show, both numerically and experimentally, that the wavelength splitting in two evanescently-coupled Photonic Crystal L3 cavities (three holes missing in the ΓK direction of the underlying triangular lattice) can be continuously controlled up to 5× the initial value upon ∼ 30% of hole-size modification in the barrier. Moreover, the sign of the splitting can be reversed in such a way that the fundamental mode can be either the symmetric or the anti-symmetric one without altering neither the cavity geometry nor the inter-cavity distance. Coupling sign inversion is explained in the framework of a Fabry-Perot model with underlying propagating Bloch modes in coupled W1 waveguides.

Highlights

Coupled micro and nanocavities, called photonic molecules [1], are being investigated with increasing interest due to their relevance in applications such as laser optimization [2], delay lines [3], optical strong coupling [4], optical equivalent of EIT [5], as well as a testbed for the exploration of advanced nonlinear and quantum regimes [6,7,8]
Evanescently coupled optical cavities can be regarded as multiple potential well systems which, in the presence of nonlinearities, may allow the demonstration of fundamental phenomena such as Josephson oscillations, optical self-trapping or even spontaneous symmetry breaking [9, 10]
3D-Finite Difference Time Domain (FDTD) simulations have been performed in order to obtain a better approximation of the real system, as well as to account for optical losses, Q-factors in membrane-based cavities

Summary

Introduction

Called photonic molecules [1], are being investigated with increasing interest due to their relevance in applications such as laser optimization [2], delay lines [3], optical strong coupling [4], optical equivalent of EIT [5], as well as a testbed for the exploration of advanced nonlinear and quantum regimes [6,7,8] In this context, evanescently coupled optical cavities can be regarded as multiple potential well systems which, in the presence of nonlinearities, may allow the demonstration of fundamental phenomena such as Josephson oscillations, optical self-trapping or even spontaneous symmetry breaking [9, 10]. We numerically show that the use of L3 optical defects makes this technique compatible with high Q-factor (Q ∼ 5 × 104) nano-cavities

Barrier engineering

Experimental results

Conclusions