Yongyou Zhang

Visible whispering-gallery modes in ZnO microwires with varied cross sections

ZnO microwires with hexagonal, dodecagonal, and circular cross sections were achieved by a micro-environment control vapor deposition method. Laser induced micro-photoluminescence spectra of single wires showed separated emission modes in the visible range, and in which the higher the number of sides in cross section for the ZnO MWs, the more resonant modes are induced. Theoretical calculations indicated the nature of resonant whispering-gallery modes, in agreement with the spectral and mapping profiles of these modes. The results demonstrated that the as-prepared ZnO MWs can be used as high-quality microresonators to produce whispering-gallery modes.

Magnetic-field modulated exciton-exciton interaction in semiconductor microcavities

We study the quantum-well magnetoexcitons by the variational method in the strong coupling regime of excitons with microcavity photons. In such strong coupling regime, we find that the coupling between the exciton internal state and center of mass motion can be neglected. Through the calculations, we find that the magnetic field can reduce the exciton exchange interaction to 30% as Lw=30u2002nm with Lw being the quantum well width. This is in contrast to the magnetic-field enhancement in the exciton Rabi splitting. In this work, we obtain that a magnetic field can enhance the exciton Rabi splitting up to 1.6 times in the case of Lw=30u2002nm. They both originate from the local enhancement in the exciton internal state due to the magnetic field. In addition, we analyze the behavior of the magnetic response of the exciton energy, Rabi splitting, and exchange interaction in manipulating the polariton parametric scattering, and widening the microcavity applications.

Group delay of single-photon transmission in a waveguide side coupled with a Jaynes-Cummings chain

Using a real-space model Hamiltonian, we have theoretically studied the single-photon transmission in a waveguide side coupled with a Jaynes-Cummings chain (JCC). The JCC can induce the photon group advancement (GA) and group delay (GD) in different frequency ranges determined by JCC eigenmodes. For GA and GD, there exist different optimal JCC lengths. At certain frequency, the GAs maximum value as usual increases with decreasing the cavity dissipation, whereas the GDs eventually reaches saturation. For a 1.55u2009-μm photon, our calculation indicates that the GDs maximum value is about 400 ps simultaneously with a large transmission.

Tailoring of optical modes of semiconductor microcavities via metal and dielectric gratings

We investigate optical mode tailoring in a semiconductor microcavity with a metal grating on top and a dielectric grating (DG) on the bottom. Strong coupling between microcavity and grating-diffraction modes is explained in the Fano-picture. The Fano resonance shows a weak dependence upon grating height and duty ratio, but is strong upon grating period. The microcavity transmission line shapes are S and anti S-type for the metal and DGs, respectively. Together with these two types of Fano resonances, the transmission spectra have been tailored into very sharp peaks with FWHM being up to 0.1xa0nm. We prove that this optical mode tailoring method is quite applicable for other waveguide-grating structures too.

Multi-Band-Stop Filter for Single-Photon Transport Based on a One-Dimensional Waveguide Side Coupled with Optical Cavities

A model of a multi-band-stop filter is proposed for single-photon transport, using a one-dimensional waveguide side coupled with a series of optical cavities. Its transmission behavior is theoretically studied by a real-space model Hamiltonian and is found to depend on cavity mode frequencies, cavity relative phases, as well as cavity number and the coupling strength between the waveguide and the optical cavities. With proper cavity-mode frequencies and relative phases, the proposed model shows multi-band-stop regions and a rectangular transmission spectrum. Based on these phenomena, optical filters with more than one band-stop regions are simulated with gold material in the THz and communication band.

Optically programmable encoder based on light propagation in two-dimensional regular nanoplates

We design an efficient optically controlled microdevice based on CdSe nanoplates. Two-dimensional CdSe nanoplates exhibit lighting patterns around the edges and can be realized as a new type of optically controlled programmable encoder. The light source is used to excite the nanoplates and control the logical position under vertical pumping mode by the objective lens. At each excitation point in the nanoplates, the preferred light-propagation routes are along the normal direction and perpendicular to the edges, which then emit out from the edges to form a localized lighting section. The intensity distribution around the edges of different nanoplates demonstrates that the lighting part with a small scale is much stronger, defined as 1, than the dark section, defined as 0, along the edge. These 0 and 1 are the basic logic elements needed to compose logically functional devices. The observed propagation rules are consistent with theoretical simulations, meaning that the guided-light route in two-dimensional semiconductor nanoplates is regular and predictable. The same situation was also observed in regular CdS nanoplates. Basic theoretical analysis and experiments prove that the guided light and exit position follow rules mainly originating from the shape rather than material itself.

Disorder-induced transparency in a one-dimensional waveguide side coupled with optical cavities

Disorder influence on photon transmission behavior is theoretically studied in a one-dimensional waveguide side coupled with a series of optical cavities. For this sake, we propose a concept of disorder-induced transparency appearing on the low-transmission spectral background. Two kinds of disorders, namely, disorders of optical cavity eigenfrequencies and relative phases in the waveguide side coupled with optical cavities are considered to show the disorder-induced transparency. They both can induce the optical transmission peaks on the low-transmission backgrounds. The statistical mean value of the transmission also increases with increasing the disorders of the cavity eigenfrequencies and relative phases.

Stable optical-signal emitter based on a semiconductor photonic dot

We propose a polariton hyperparametric oscillator (PHO) based on a semiconductor photonic dot at the micro/nano scale. By theoretical derivations and numerical calculations, we find that the PHO not only amplify weak signals like general large-planar polariton amplifiers, but also depress strong signals unusually. The coexistence of such signal amplification and depression can cause a stable signal emission being almost independent of the excitation instabilities in the strong-excitation regime. It has been verified that the instability of the signal emission, increasing with the increase of the excitation instabilities, is only about one to two percent deviation from its average intensity even under strong instable excitations. Hence, the PHO can serve as a stable optical-signal emitter in micro/nano optical systems.