Photonic molecules made of matched and mismatched microcavities: new functionalities of microlasers and optoelectronic components

Abstract

Photonic molecules, named by analogy with chemical molecules, are clusters of closely located electromagnetically interacting microcavities or "photonic atoms". As two or several microcavities are brought close together, their optical modes interact, and a rich spectrum of photonic molecule supermodes emerges, which depends both on geometrical and material properties of individual cavities and on their mutual interactions. Here, we discuss ways of controllable manipulation of photonic molecule supermodes, which improve or add new functionalities to microcavity-based optical components. We present several optimally-tuned photonic molecule designs for lowering thresholds of semiconductor microlasers, producing directional light emission, enhancing sensitivity of microcavity-based bio(chemical)sensors, and optimizing electromagnetic energy transfer around bends of coupled-cavity waveguides. Photonic molecules composed of identical microcavities as well as of microcavities with various degrees of size or material detuning are discussed. Microwave experiments on scaled photonic molecule structures are currently under way to confirm our theoretical predictions.

Symmetric photonic molecules formed from coupled microspheres

“…Our experiments demonstrate that directional emission in the horizontal plane in three well defined directions with the triangular-sphere structure is possible under the condition of perpendicular illumination of the PM with a defocused laser beam. The photonic nanojets develop although it is not a vertical plane wave excitation technique [6].…”

“…Photonic molecule structures consisting of three or more microcavities were studied theoretically by different groups with regards to supermodes with dramatically increased Q-factors, low laser threshold and directional emission [3][4][5][6]. For optimal results, the structure requires a symmetric photonic molecule with size-matched microcavities and optimised gap alignment between the spheres [6]. Apart from microcavities arranged in arrays, chains of coupled microspheres have also been studied for waveguiding purposes [7,8].…”

“…The so called supermodes in a photonic molecule are WGMs which extend over the whole structure of the coupled microcavities. Photonic molecule structures consisting of three or more microcavities were studied theoretically by different groups with regards to supermodes with dramatically increased Q-factors, low laser threshold and directional emission [3][4][5][6]. For optimal results, the structure requires a symmetric photonic molecule with size-matched microcavities and optimised gap alignment between the spheres [6].…”

Chains of coupled square dielectric optical microcavities

“…A variety of concepts exist; among these are series of microring or -disk resonators (Yariv et al 1999;Little et al 2004;Morichetti et al 2007), sequences of defects in photonic crystals or photonic crystal slabs (Bayindir et al 2000;Reynolds et al 2001;Scheuer et al 2005), and coupled dielectric spheres (Astratov et al 2004;Chen et al 2006). Some configurations can also be viewed as specific extended cases of photonic molecules (Boriskina 2005(Boriskina , 2006Boriskina et al 2007). …”

Nanojets and directional emission in symmetric photonic molecules

“…Photonic molecule structures consisting of three or more microcavities were studied theoretically by different groups with regards to supermodes with dramatically increased Qfactors, low laser threshold and directional emission [3][4][5][6]. For optimal results, the structure requires a symmetric photonic molecule with size-matched microcavities and optimised gap alignment between the spheres [6].…”