Mode coupling and vertical radiation loss for whispering-gallery modes in 3-D microcavities

The characteristics of whispering-gallery modes (WGMs) in 3-D cylindrical, square, and triangular microcavities with vertical optical confinement of semiconductors are numerically investigated by the finite-difference time-domain (FDTD) technique. For a microcylinder with a vertical refractive index 3.17/3.4/3.17 and a center layer thickness 0.2 mu m, Q-factors of transverse electric (TE) WGMs around wavelength 1550 nm are smaller than 10(3), as the radius R < 4 mu m and reach the orders of 10(4) and 10(6) as R = 5 and 6 mu m, respectively. However, the Q-factor of transverse magnetic (TM) WGMs at wavelength 1.659 mu m reaches 7.5 x 10(5) as R = 1 mu m. The mode coupling between the WGMs and vertical radiation modes in the cladding layer results in vertical radiation loss for the WGMs. In the microcylinder, the mode wavelength of TM WGM is larger than the cutoff wavelength of the vertical radiation mode with the same mode numbers, so TM WGMs cannot couple with the vertical radiation mode and have high Q-factor. In contrast, TE WGMs can couple with the corresponding vertical radiation mode in the 3-D microcylinder as R < 5 mu m. However, the mode wavelength of the TE WGM approaches (is larger than) the cutoff wavelength of the corresponding radiation modes at R = 5 mu m (6 mu m), so TE WGMs have high Q-factors in such microcylinders too. The results show that a critical lateral size is required for obtaining high, Q-factor TE WGMs in the 3-D microcylinder. For 3-D square and triangular microcavities, we also find that the Q-factor of TM WGM is larger than that of TE WGM.

Laterally confined modes in wet-etched, metal-coated, quantum-dot-inserted pillar microcavities

We report the fabrication and the measurement of microcavities whose optical eigenmodes were discrete and were well predicted by using the model of the photonic dot with perfectly reflected sidewalls. These microcavities were consisted of the semiconductor pillar fabricated by the simple wet-etched process and successive metal coating. Angle-resolved photoluminescence spectra demonstrate the characteristic emission of the corresponding eigenmodes, as its pattern revealed by varying both polar (0) and azimuthal (45) angles. It is shown that the metal-coated sidewalls can provide an efficient way to suppress the emission due to the leaking modes in these pillar microcavities.

Mode characteristics of semiconductor equilateral triangle microcavities with side length of 5-20 mu m

Semiconductor equilateral triangle microresonators (ETRs) with side length of 5, 10, and 20 mum are fabricated by the two-step inductively coupled plasma (ICP) etching technique. The mode properties of fabricated InGaAsP ETRs are investigated experimentally by photoluminescence (PL) with the pumping source of a 980-nm semiconductor laser and distinct peaks are observed in the measured PL spectra. The wavelength spacings of the distinct peaks agree very well with the theoretical longitudinal mode intervals of the fundamental transverse modes in the ETRs, which verifies that the distinct peaks are corresponding to the enhancement of resonant modes. The mode quality factors are calculated from the width of the resonant peaks of the PL spectra, which are about 100 for the ETR with side length of 20 mum.

Comparison of free spectral range and quality factor for two-dimensional square and circular microcavities

Free spectral range of whispering-gallery (WG)-like modes in a two-dimensional (2D) square microcavity is found to be twice that in a 2D circular microcavity. The quality factor of the WG-like mode with the low mode number in a 2D square microcavity, calculated by the finite-difference time-domain (FDTD) technique and the Pade approximation method, is found to exceed that of the WG mode in 2D circular microcavity with the same cavity dimension and close mode wavelength.

Quantum computation with coupled quantum dots embedded in optical microcavities

Based on an idea that spatial separation of charge states can enhance quantum coherence, we propose a scheme for a quantum computation with the quantum bit (qubit) constructed from two coupled quantum dots. Quantum information is stored in the electron-hole pair state with the electron and hole located in different dots, which enables the qubit state to be very long-lived. Universal quantum gates involving any pair of qubits are realized by coupling the quantum dots through the cavity photon which is a hopeful candidate for the transfer of long-range information. The operation analysis is carried out by estimating the gate time versus the decoherence time.

Magnetoexciton polaritons in planar semiconductor microcavities

We study the magnetoexciton polaritons in planar semiconductors microcavities by a quantum approach developed in the strong and weak magnetic-field limits. Ht is shown that the vacuum Rabi splittings with different Landau level indices are close to each other and tend to be proportional to B at sufficiently large values of the magnetic field. Also, we show that the calculated results are in good agreement with the experimental observations. [S0163-1829(99)10215-7].

Experimental study of mode characteristics for equilateral triangle semiconductor microcavities

Equilateral triangle semiconductor microcavities with tensile-strained InGaAsP multi-quantum-well asthe active region are fabricated by the inductively coupled plasma (ICP) etching technique. The modecharacteristics of the fabricated microcavities are investigated by photoluminescence, and enhanced peaksof the photoluminescence spectra corresponding to the fundamental transverse modes are observed formicrocavities with side lengths of 5 and 10 μm. The mode wavelength spacings measured experimentallycoincide very well with those obtained by the theoretical formulae.

Mode characteristics of metallically coated square microcavity connected with an output waveguide

Mode characteristics of a square microcavity with an output waveguide on the middle of one side, laterally confined by an insulating layer SiO2 and a p-electrode metal Au, are investigated by two-dimensional finite-difference time-domain technique. The mode quality (Q) factors versus the width of the output waveguide are calculated for Fabry-Peacuterot type and whispering-gallery type modes in the square cavity. Mode coupling between the confined modes in the square cavity and the guided modes in the output waveguide determines the mode Q factors, which is greatly influenced by the symmetry behaviors of the modes. Fabry-Peacuterot type modes can also have high Q factors due to the high reflectivity of the Au layer for the vertical incident mode light rays. For the square cavity with side length 4 mu m and refractive index 3.2, the mode Q factors of the Fabry-Peacuterot type modes can reach 10(4) at the mode wavelength of 1.5 mu m as the output waveguide width is 0.4 mu m.

Structural properties of ne implanted GaN

We report a study on the micro-structural changes in GaN due to neon ion implantation using the x-ray diffraction and Raman scattering techniques. An implantation dose of 10(14) cm(-2) was found unable to produce lattice deformation observable by Raman measurements. For higher doses of implantation several disorder activated Raman scattering centers were observed which corroborate the literature. A new dose dependent feature has been recorded at 1595 cm(-1) for higher implantation doses which is suggested to be the vibrational mode of microcavities produced in the lattice.

Room-temperature photonic crystal laser in H3 cavity on InGaAsP/InP slab

We fabricate and investigate two-dimensional photonic crystal H3 microcavities in an InGaAsP slab. The lasing action at room temperature is observed. The lasering threshold is 7mW under the pulsed pump of 0.75% duty cycle. The Q factor and the lasing mode characteristics are simulated by three-dimensional finite difference time domain method. The simulation result matches well with the experiment.

Design of quantum cascade microcavity lasers based on Q factor versus etching depth

The choice of the etching depth for semiconductor microcavities is a compromise between a high Q factor and a difficult technique in a practical fabricating process. In this paper, the influences of the etching depth on mode Q factors for mid-infrared quantum cascade microcylinder and microsquare lasers around 4.8 and 7.8 mu m are simulated by three-dimensional (3D) finite-difference time-domain (FDTD) techniques. For the microcylinder and the microsquare resonators, the mode Q factors of the whispering-gallery modes (WGMs) increase exponentially and linearly with the increase in the etching depth, respectively Furthermore, the mode Q factors of some higher order transverse WGMs may be larger than that of the fundamental transverse WGM in 3D microsquares. Based on the field distribution of the vertical multilayer slab waveguide and the mode Q factors versus the etching depth, the necessary etching depth is chosen at the position where the field amplitude is 1% of the peak value of the slab waveguide. In addition, the influences of sidewall roughness on the mode Q factors are simulated for microsquare resonators by 2D FDTD simulation. (C) 2009 Optical Society of America

Electrically Driven InAs Quantum-Dot Single-Photon Sources

Electrically driven single photon source based on single InAs quantum dot (QDs) is demonstrated. The device contains InAs QDs within a planar cavity formed between a bottom AlGaAs/GaAs distributed Bragg reflector (DBR) and a surface GaAs-air interface. The device is characterized by I-V curve and electroluminescence, and a single sharp exciton emission line at 966nm is observed. Hanbury Brown and Twiss (HBT) correlation measurements demonstrate single photon emission with suppression of multiphoton emission to below 45% at 80K

Mode quality factor based on far-field emission for square resonators

The quality factors of modes in square resonators are calculated based on the far-field emission of the analytical field distribution. The obtained quality factors are in reasonable agreement with those calculated by the finite-difference time-domain (FDTD) technique and Pade approximation method. The emission power in the square diagonal directions for whispering-gallery-like modes in square resonators is zero due to the interference cancellation caused by the odd field distributions relative to the diagonal mirror planes, so they have larger quality factors than the modes with even field distribution.

Modes in square resonators

Modes in square resonators are analyzed and classified according to the irreducible representations of the point group C-4v. If the mode numbers p and q that denote the number of wave nodes in the directions of two orthogonal square sides are unequal and have the same even-odd characteristics, the corresponding double modes are accidentally degenerate and can be combined into two new distributions with definite parities relative to the square diagonal mirror planes. The distributions with odd parities belong to the whispering-gallery-like modes in square resonators. The mode frequencies and quality factors are also calculated by the finite-difference time-domain technique and Pade approximation method. The numerically calculated mode frequencies agree with the theoretical ones very well and the whispering-gallery-like modes have quality factors much higher than other modes, including their accidentally degenerate counterparts in square resonators.

WG-like modes selectivity in a square cavity with posts

We investigate the characteristics of Whispering-Gallery(WG)-like modes in a square cavity with posts by employing the two-dimentional (2D) finite-difference time-domain (FDTD) technique combined with the effective index method. The results indicate that the posts can result in mode selection in the WG-like modes. The WG-like modes with odd mode numbers are not much sensitive to the sizes of the posts. However, the quality factor (i.e. Q-factor) of the WG-like modes with even mode numbers decreases sharply with the increasing size of the posts. The decreasing Q-factor is attributed to mode leakage and scattering loss due to the presence of the post. The mode selection increases with the mode spacing of square cavity twice in an optimized strucure.