Confined optical modes in small photonic molecules with semiconductor nanocrystals

Abstract

We report on the coherent coupling of whispering gallery modes (WGMs) in a photonic molecule formed from two melamine-formaldehyde spherical microcavities coated with a thin shell of light-emitting CdTe nanocrystals (NCs). Utilizing different excitation conditions, the splitting of the WGM resonances originating from bonding and antibonding branches of the photonic states is observed, and fine structure consisting of very sharp peaks resulting from lifting of the WGM degeneracy has been detected. Time-resolved measurements showed a slight increase in the spontaneous emission rate of NCs in a photonic molecule when compared to the spontaneous emission rate for NCs coating a single microsphere.

Photonic atoms and molecules

“…One of the serious drawbacks of small WGM cavities in terms of biosensing is their moderate Qfactor: 10 3 -10 5 for microspheres of 3-6 µm size [23,70,71]. For smaller sphere sizes (2 µm) the Q-factor drops down to $ 10 2 [72]. Such a low Q-factor strongly reduces the resolving power of the system, so that microspheres of 2 µm or less have not been considered for biosensing applications so far.…”

“…This phenomenon has been demonstrated in a system of two square, photonic dots coupled by a narrow channel [78], in a dye-stained bisphere system [71,80,81], in photonic dots with semiconductor QDs [70,82] and in chains of polymer-blend microparticles [83]. However, recent theoretical considerations [84] and experimental studies [70,72] Recent proposals for coupled resonator optical waveguides [85], high-order optical filters [86], and optical delay elements [87,88] stimulated further interest in systems of optically coupled microspheres such as linear chains, two-dimensional arrays or three-dimensional crystal structures [18,83]. In these systems a "photon-hopping" transport between adjacent spheres should occur at the frequencies of the WGMs, providing the possibility of manipulating light paths as well as light dispersion on a microscopic scale.…”

“…Recently, a new approach to control the alignment of the spheres constituting the PM have been developed [70,72] utilizing a polystyrene substrate containing a three-dimensionally ordered array of pores of $ 5 µm in size prepared through a thermocapillary convection process [89]. The ordered structures are formed by evaporating solutions of polystyrene in a volatile solvent, in the presence of moisture with forced airflow across the solution surface.…”

The Fabrication, Fluorescence Dynamics, and Whispering Gallery Modes of Aluminosilicate Microtube Resonators

“…Time-resolved studies in the literature have focused on the modification of the spontaneous recombination dynamics in 3D microcavities, [37][38][39][40][41] or the investigation of cavity-enhanced excitation energy transfer. [37,42] Knowledge of the emission dynamics under amplification conditions should provide impor- …”

Photonic molecules modes in resonantly coupled spherical microcavities with semiconductor nanocrystals

“…This phenomenon has been demonstrated in a system of two square, photonic dots coupled by a narrow channel 7 in a dye-stained bisphere system 9,11,12 , in photonic dots doped by CdSe nanocrystals (NCs) 13 and in chains of polymer-blend microparticles 14 . However recent theoretical considerations 10 and experimental studies 15,16 reveal complex internal distribution of density of photonic states of PM originating from lifting of degeneracy of PM modes with respect to the azimuthal index.…”