Luke J. Bissell

Resonance in quantum dot fluorescence in a photonic bandgap liquid crystal host

Microcavity resonance is demonstrated in nanocrystal quantum dot fluorescence in a one-dimensional (1D) chiral photonic bandgap cholesteric-liquid crystal host under cw excitation. The resonance demonstrates coupling between quantum dot fluorescence and the cholesteric microcavity. Observed at a band edge of a photonic stop band, this resonance has circular polarization due to microcavity chirality with 4.9 times intensity enhancement in comparison with polarization of the opposite handedness. The circular-polarization dissymmetry factor g(e) of this resonance is ~1.3. We also demonstrate photon antibunching of a single quantum dot in a similar glassy cholesteric microcavity. These results are important in cholesteric-laser research, in which so far only dyes were used, as well as for room-temperature single-photon source applications.

Organic photonic bandgap microcavities doped with semiconductor nanocrystals for room-temperature on-demand single-photon sources

We report the first experimental observation of fluorescence from single semiconductor nanocrystals (colloidal quantum dots) in microcavities. In these room-temperature experiments we observed photon antibunching from single CdSe nanocrystals doped into a chiral one-dimensional photonic bandgap liquid-crystal microcavity. The chirality resulted in high-purity, circular polarization of definite handedness of the emitted single photons. We also report the fabrication of chiral microcavities for telecom wavelengths doped with PbSe nanocrystals as well as a solution-processed-polymer microcavity with a defect layer doped with CdSe nanocrystals between two distributed Bragg reflectors. These systems with their low host fluorescence background are attractive for on-demand single-photon sources for quantum information and communication.

Room-temperature single photon sources with definite circular and linear polarizations

We report experimental results of two room-temperature single photon sources with definite polarization based on emitters embedded in either cholesteric or nematic liquid crystal hosts. In the first case, a cholesteric 1-D photonic bandgap microcavity provides circular polarization of definite handedness of single photons from single colloidal semiconductor quantum dots (nanocrystals). In these experiments, the spectral position of the quantum dot fluorescence maximum is at the bandedge of a photonic bandgap structure. The host does not destroy fluorescence antibunching of single emitters. In the second case, photons with definite linear polarization are obtained from single dye molecules doped in a planar-aligned nematic liquid crystal host. The combination of sources with definite linear and circular polarization states of single photons can be used in a practical implementation of the BB84 quantum key distribution protocol.

Room temperature source of single photons of definite polarization

A definite polarization in fluorescence from single emitters (dye molecules) at room temperature is demonstrated. A planar-aligned, nematic liquid-crystal host provides definite alignment of single dye molecules in a preferred direction. Well-defined polarized fluorescence from single emitters (single photon source) is important for applications in photonic quantum information. Polarized single-photon sources based on single emitters, for example, are key hardware elements both for absolutely secure quantum communication and quantum computation systems.

Absorption characteristics of mid-wave infrared type-II superlattices

Recently, a new strategy used to achieve high operation temperature (HOT) infrared photodetectors including III-V compound materials (bulk materials and type-II superlattices) and cascade devices has been observed. Another method to reduce detector’s dark current is reducing volume of detector material via a concept of photon trapping detector. The barrier detectors are designed to reduce dark current associated with Shockley-Read (SR) processes and to decrease influence of surface leakage current without impeding photocurrent (signal). In consequence, absence of a depletion region in barrier detectors offers a way to overcome the disadvantage of large depletion dark currents. So, they are typically implemented in materials with relatively poor SR lifetimes, such as all III-V compounds. From considerations presented in the paper results that despite numerous advantages of III-V barrier detectors over present-day detection technologies, including reduced tunneling and surface leakage currents, normal-incidence absorption, and suppressed Auger recombination, the promise of a superior performance of these detectors in comparison to HgCdTe photodiodes, has not been yet realized. The dark current density is higher than that of bulk HgCdTe photodiodes, especially in MWIR range. To attain their full potential, the following essential technological limitations such as short carrier lifetime, passivation, and heterostructure engineering, need to be overcome.

Quantum Dot Fluorescence in Photonic Bandgap Glassy Cholesteric Liquid Crystal Structures: Microcavity Resonance under CW-Excitation, Antibunching and Decay Time

Nanocrystal quantum dot (NQD) fluorescence in 1-D glassy cholesteric liquid crystal host is investigated: (1) Microcavity resonance is obtained under cw-excitation demonstrating coupling between NQD fluorescence and a cholesteric microcavity. Observed at a band edge of a photonic stopband, this resonance has circular polarization due to microcavity chirality with 4.9 times intensity enhancement in comparison with polarization of the opposite handedness. (2) Photon antibunching of a single NQD in a similar microcavity was observed. (3) Fluorescence decay time constants were measured at different excitation powers. These results are important in developing cholesteric lasers and single-photon sources for secure quantum communication.

Single photon source on demand based on single-colloidal-quantum-dot fluorescence in chiral photonic bandgap liquid crystal hosts

A single-photon source based on single CdSe quantum-dot fluorescence in a chiral-photonic-bandgap liquid-crystal host manifests itself in observed fluorescence antibunching. Chiral-photonic bandgap structures will provide deterministically handed, circular-polarized fluorescence, even for emitters without a dipole moment.

Nanocrystal fluorescence in photonic bandgap microcavities and plasmonic nanoantennas

Results are presented here towards robust room-temperature single-photon sources based on fluorescence in nanocrystals: colloidal quantum dots, color-center diamonds and doped with trivalent rare-earth ions (TR3+). We used cholesteric chiral photonic bandgap and Bragg-reflector microcavities for single emitter fluorescence enhancement. We also developed plasmonic bowtie nanoantennas and 2D-Si-photonic bandgap microcavities.

Resonance in quantum dot fluorescence on a band-edge of a 1-D photonic bandgap cholesteric structure under cw-laser excitation

Microcavity resonance is demonstrated in nanocrystal quantum dot fluorescence in a 1-D chiral photonic bandgap cholesteric liquid crystal host. The resonance demonstrates coupling between quantum dot fluorescence and the cholesteric microcavity. Observed at a band edge of a photonic stopband, this resonance has circular polarization due to microcavity chirality with 4.9 times intensity enhancement in comparison with polarization of the opposite handedness. The circular polarization dissymmetry factor ge of this resonance is ~1.3. We also demonstrate photon antibunching of a single quantum dot in a similar glassy cholesteric microcavity. These results are important in cholesteric laser research, in which so far only dyes under pulsed excitation were used, as well as for room-temperature single-photon source applications.

Room-temperature single-photon sources with definite circular and linear polarizations based on single-emitter fluorescence in liquid crystal hosts

Definite circular and linear polarizations of room-temperature single-photon sources, which can serve as polarization bases for quantum key distribution, are produced by doping planar-aligned liquid crystal hosts with single fluorescence emitters. Chiral 1-D photonic bandgap microcavities for a single handedness of circularly polarized light were prepared from both monomeric and oligomeric cholesteric liquid crystals. Fluorescent emitters, such as nanocrystal quantum dots, nitrogen vacancy color centers in nanodiamonds, and rare-earth ions in nanocrystals, were doped into these microcavity structures and used to produce circularly polarized fluorescence of definite handedness. Additionally, we observed circularly polarized resonances in the spectrum of nanocrystal quantum dot fluorescence at the edge of the cholesteric microcavitys photonic stopband. For this polarization we obtained a ~4.9 enhancement of intensity compared to the polarization of the opposite handedness that propagates without photonic bandgap microcavity effects. Such a resonance is indicative of coupling of quantum dot fluorescence to the cholesteric microcavity mode. We have also used planar-aligned nematic liquid crystal hosts to align DiI dye molecules doped into the host, thereby providing a single-photon source of linear polarization of definite direction. Antibunching is demonstrated for fluorescence of nanocrystal quantum dots, nitrogen vacancy color centers, and dye molecules in these liquid crystal structures.