Showing papers on "Optical microcavity published in 2004"

Strong coupling in a single quantum dot–semiconductor microcavity system

Abstract: Cavity quantum electrodynamics, a central research field in optics and solid-state physics, addresses properties of atom-like emitters in cavities and can be divided into a weak and a strong coupling regime. For weak coupling, the spontaneous emission can be enhanced or reduced compared with its vacuum level by tuning discrete cavity modes in and out of resonance with the emitter. However, the most striking change of emission properties occurs when the conditions for strong coupling are fulfilled. In this case there is a change from the usual irreversible spontaneous emission to a reversible exchange of energy between the emitter and the cavity mode. This coherent coupling may provide a basis for future applications in quantum information processing or schemes for coherent control. Until now, strong coupling of individual two-level systems has been observed only for atoms in large cavities. Here we report the observation of strong coupling of a single two-level solid-state system with a photon, as realized by a single quantum dot in a semiconductor microcavity. The strong coupling is manifest in photoluminescence data that display anti-crossings between the quantum dot exciton and cavity-mode dispersion relations, characterized by a vacuum Rabi splitting of about 140 microeV.

Kerr-nonlinearity optical parametric oscillation in an ultrahigh-Q toroid microcavity

Abstract: Kerr-nonlinearity induced optical parametric oscillation in a microcavity is reported for the first time. Geometrical control of toroid microcavities enables a transition from stimulated Raman to optical parametric-oscillation regimes. Optical parametric oscillation is observed at record low threshold levels (174 micro-Watts of launched power) more than 2 orders of magnitude lower than for optical-fiber-based optical parametric oscillation. In addition to their microscopic size (typically tens of microns), these oscillators are wafer based, exhibit high conversion efficiency (36%), and are operating in a highly ideal "two photon" emission regime, with near-unity (0.97±0.03) idler-to-signal ratio.

Cavity cooling of a microlever

Abstract: The prospect of realizing entangled quantum states between macroscopic objects and photons1 has recently stimulated interest in new laser-cooling schemes2,3. For example, laser-cooling of the vibrational modes of a mirror can be achieved by subjecting it to a radiation2 or photothermal4 pressure, actively controlled through a servo loop adjusted to oppose its brownian thermal motion within a preset frequency window. In contrast, atoms can be laser-cooled passively without such active feedback, because their random motion is intrinsically damped through their interaction with radiation5,6,7,8. Here we report direct experimental evidence for passive (or intrinsic) optical cooling of a micromechanical resonator. We exploit cavity-induced photothermal pressure to quench the brownian vibrational fluctuations of a gold-coated silicon microlever from room temperature down to an effective temperature of 18 K. Extending this method to optical-cavity-induced radiation pressure might enable the quantum limit to be attained, opening the way for experimental investigations of macroscopic quantum superposition states1 involving numbers of atoms of the order of 1014.

A three-dimensional optical photonic crystal with designed point defects.

Abstract: Photonic crystals1,2,3 offer unprecedented opportunities for miniaturization and integration of optical devices. They also exhibit a variety of new physical phenomena, including suppression or enhancement of spontaneous emission, low-threshold lasing, and quantum information processing4. Various techniques for the fabrication of three-dimensional (3D) photonic crystals—such as silicon micromachining5, wafer fusion bonding6, holographic lithography7, self-assembly8,9, angled-etching10, micromanipulation11, glancing-angle deposition12 and auto-cloning13,14—have been proposed and demonstrated with different levels of success. However, a critical step towards the fabrication of functional 3D devices, that is, the incorporation of microcavities or waveguides in a controllable way, has not been achieved at optical wavelengths. Here we present the fabrication of 3D photonic crystals that are particularly suited for optical device integration using a lithographic layer-by-layer approach15. Point-defect microcavities are introduced during the fabrication process and optical measurements show they have resonant signatures around telecommunications wavelengths (1.3–1.5 µm). Measurements of reflectance and transmittance at near-infrared are in good agreement with numerical simulations.

Whispering gallery modes in nanosized dielectric resonators with hexagonal cross section.

Abstract: The size dependence of whispering gallery modes in dielectric resonators with hexagonal cross section has been observed within the visible spectral range for cavity diameters comparable to the light wavelength. As a model system single, tapered, high aspect ratio zinc oxide nanoneedles were analyzed. They enable systematic investigations as a function of the resonator diameter down to the nanometer regime. A simple plane wave interference model without free parameter describes the spectral positions and the linewidths of the modes in good agreement with the experiment.

Optical-fiber-based measurement of an ultrasmall volume high- Q photonic crystal microcavity

Abstract: A two-dimensional photonic crystal semiconductor microcavity with a quality factor $Q\ensuremath{\sim}40,000$ and a modal volume ${V}_{\mathrm{eff}}\ensuremath{\sim}0.9$ cubic wavelengths is demonstrated. A micron-scale optical fiber taper is used as a means to probe both the spectral and spatial properties of the cavity modes, allowing not only measurement of modal loss, but also the ability to ascertain the in-plane localization of the cavity modes. This simultaneous demonstration of high-$Q$ and ultrasmall ${V}_{\mathrm{eff}}$ in an optical microcavity is of potential interest in nonlinear optics, optoelectronics, and quantum optics, where the measured $Q$ and ${V}_{\mathrm{eff}}$ values could enable strong coupling to both atomic and quantum dot systems.

Strong exciton-photon coupling and exciton hybridization in a thermally evaporated polycrystalline film of an organic small molecule

Abstract: We demonstrate strong exciton-photon coupling in an optical microcavity containing a thermally evaporated polycrystalline organic thin film. Microcavity polaritons result from coupling between the 0-0 excitonic transition of 3,4,7,8 napthalenetetracarboxylic dianhydride and a cavity photon. For thicker films, the 0-1 transition also couples to the cavity mode, as vibronic relaxation is overcome by the short Rabi period for strong coupling. To our knowledge, this is the first report of strong coupling between a cavity photon and multiple vibronic transitions in a single material, made possible by the pronounced vibronic absorption features characteristic of crystalline organic materials.

Current-injection spiral-shaped microcavity disk laser diodes with unidirectional emission

Abstract: A spiral-shaped microcavity heterojunction laser diode fabricated with InGaN multiple quantum wells is demonstrated to operate under current injection conditions and emit unidirectionally. Room-temperature laser operation was achieved for microcavity disk radii ranging from 50 to 350 μm and threshold current densities as low as 4.6 kA/cm2. Unidirectional laser emission is clearly revealed in the far-field pattern with the lateral divergence angle ranging from 60° to 75°. Output power of more than 25 mW was obtained for emission wavelengths near 400 nm.

Distributed and localized feedback in microresonator sequences for linear and nonlinear optics

Abstract: Sequences of optical microresonators can be used to construct densely integrated structures that display slow group velocity, ultrahigh or low dispersion of controllable sign, enhanced self-phase modulation, and nonlinear optical switching. We consider four archetypal geometries consisting of effectively one-dimensional sequences of coupled microresonators. Two of these cases exhibit distributed feedback such as is found in a traditional multilayered structure supporting photonic bandgaps. The other two exhibit localized feedback and resonant enhancement but are free from photonic bandgaps. All of these structures offer unique properties useful for controlling the propagation of light pulses on a chip.

Time reversal of light with linear optics and modulators.

Abstract: We introduce a new physical process that can perform a complete time-reversal operation on any electromagnetic pulse. The process uses only small refractive index modulations of linear optical elements. No nonlinear multiphoton effects such as four-wave mixing are required. The introduced process can be implemented on chip with standard semiconductor materials. Furthermore, the same process can be used to compress or expand the spectrum of electromagnetic waves while completely preserving the coherent information. We exhibit the time-reversal process by first-principles simulations of microcavity complexes in photonic crystals.

Quantum Feedback Control of Atomic Motion in an Optical Cavity

Abstract: We study quantum feedback cooling of atomic motion in an optical cavity. We design a feedback algorithm that can cool the atom to the ground state of the optical potential with high efficiency despite the nonlinear nature of this problem. An important ingredient is a simplified state-estimation algorithm, necessary for a real-time implementation of the feedback loop. We also describe the critical role of parity dynamics in the cooling process and present a simple theory that predicts the achievable steady-state atomic energies.

Quasiscarred resonances in a spiral-shaped microcavity.

Abstract: We study resonance patterns of a spiral-shaped dielectric microcavity with chaotic ray dynamics. Many resonance patterns of this microcavity, with refractive indices n=2 and 3, exhibit strong localization of simple geometric shape, and we call them quasiscarred resonances in the sense that there is, unlike conventional scarring, no underlying periodic orbits. It is shown that the formation of a quasiscarred pattern can be understood in terms of ray dynamical probability distributions and wave properties like uncertainty and interference.

Erbium-implanted high-Q silica toroidal microcavity laser on a silicon chip

Abstract: Lasing from an erbium-doped high-Q silica toroidal microcavity coupled to a tapered optical fiber is demonstrated and analyzed. Average erbium ion concentrations were in the range 0.009–0.09 at. %, and a threshold power as low as 4.5 µW and an output lasing power as high as 39.4 µW are obtained from toroidal cavities with major diameters in the range 25–80 µm. Controlling lasing wavelength in a discrete way at each whispering-gallery mode was possible by changing the cavity loading, i.e., the distance between the tapered optical fiber and the microcavity. Analytic formulas predicting threshold power and differential slope efficiency are derived and their dependence on cavity loading, erbium ion concentration, and Q factor is analyzed. It is shown that the experimental results are in good agreement with the derived formulas.

Ultralow loss, high Q, four port resonant couplers for quantum optics and photonics.

Abstract: We demonstrate a low-loss, optical four port resonant coupler (add-drop geometry), using ultrahigh Q (>10(8)) toroidal microcavities. Different regimes of operation are investigated by variation of coupling between resonator and fiber taper waveguides. As a result, waveguide-to-waveguide power transfer efficiency of 93% (0.3 dB loss) and nonresonant insertion loss of 0.02% (<0.001 dB) for narrow bandwidth (57 MHz) four port couplers are achieved in this work. The combination of low-loss, fiber compatibility, and wafer-scale design would be suitable for a variety of applications ranging from quantum optics to photonic networks.

Semiconductor microcavity as a spin-dependent optoelectronic device

Abstract: We demonstrate experimentally that stimulated scattering of exciton--polaritons in a semiconductor microcavity in the strong coupling regime results in a dramatic build-up of the circular polarization degree of light emitted by the cavity. Moreover, we show that the polarization of the emitted light can be different from the polarization of the pumping light, e.g., pumping with a linearly polarized beam we detect a circularly polarized emission. This proves that the stimulated scattering of polaritons selects and amplifies a given polarization and inhibits all spin-relaxation processes. We believe that strong coupling microcavities can be used as building blocks for spin-dependent optoelectronic devices aimed at manipulations with the polarization of light on a micro- to nano-scale.

Photonic molecules doped with semiconductor nanocrystals

Abstract: We report on coherent cavity field coupling in linear chains and arrays of exactly size-matched spherical microcavities doped with $\mathrm{CdSe}$ quantum dots. The spatial distribution and the dominant polarization type of both the weakly and strongly coupled cavity resonances are studied spectrally and spatially resolved in various coupled resonator geometries. Both experiment and theory show strong photon mode coupling with pronounced mode splitting as well as weak coupling with no significant loss in $Q$-factor depending on the emitter position and orientation.

Determination of the Number of Atoms Trapped in an Optical Cavity

Abstract: The number of atoms trapped within the mode of an optical cavity is determined in real time by monitoring the transmission of a weak probe beam Continuous observation of atom number is accomplished in the strong coupling regime of cavity quantum electrodynamics and functions in concert with a cooling scheme for radial atomic motion The probe transmission exhibits sudden steps from one plateau to the next in response to the time evolution of the intracavity atom number, from Ngreater than or equal to 3 to N=2-->1-->0 atoms, with some trapping events lasting over 1 s

Dynamics of the excitations of a quantum dot in a microcavity

Abstract: We study the dynamics of a quantum dot embedded in a three-dimensional microcavity in the strong coupling regime in which the quantum dot exciton has an energy close to the frequency of a confined cavity mode. Under the continuous pumping of the system, the confined electron and hole can recombine either by spontaneous emission through a leaky mode or by stimulated emission of a cavity mode that can escape from the cavity. The numerical integration of a master equation including all these effects gives the dynamics of the density matrix. By using the quantum regression theorem, we compute the first- and second-order coherence functions required to calculate the photon statistics and the spectrum of the emitted light. Our main result is the determination of a range of parameters in which a state of cavity modes with Poissonian or sub-Poissonian (nonclassical) statistics can be built up within the microcavity. Depending on the relative values of pumping and rate of stimulated emission, either one or two peaks close to the excitation energy of the dot and/or to the natural frequency of the cavity are observed in the emission spectrum. The physics behind these results is discussed.

Ring-laser optical flip-flop memory with single active element

Abstract: We present a novel optical flip-flop configuration that consists of two unidirectional ring lasers with separate cavities but sharing the same active element unidirectionally. We show that in such a configuration light in the lasing cavity can suppress lasing in the other cavity so that this system forms an optical bistable element. Essential for obtaining the bistability is the presence of an additional feedback circuit that is shared by both lasers. We show experimentally that the flip-flop can be optically set and reset, has a contrast ratio of 40 dB and allows low optical power operation. We also present a model based on roundtrip equations. Good agreement between theory and experiments is obtained.

Spectral shift and Q change of circular and square-shaped optical microcavity modes due to periodic sidewall surface roughness

Abstract: Radiation loss and resonant frequency shift due to sidewall surface roughness of circular and square high-contrast microcavities are estimated and compared by use of a boundary integral equations method. An effect of various harmonic components of the contour perturbation on the whispering-gallery (WG) modes in the circular microdisk and WG-like modes in the square microcavity is demonstrated. In both cases, contour deformations that are matched to the mode field pattern cause the most significant frequency detuning and Q-factor change. Favorably mode-matched deformations have been found, enabling one to manipulate the Q factors of the microcavity modes.

Wide-range tuning of polymer microring resonators by the photobleaching of CLD-1 chromophores.

Abstract: We present a simple and effective method for the postfabrication trimming of optical microresonators. We photobleach CLD-1 chromophores to tune the resonance wavelengths of polymer microring resonator optical notch filters. A maximum wavelength shift of ~8.73 nm is observed. The resonators are fabricated with a soft-lithography molding technique and have an intrinsic Q value of 2.6 x 10^4 and a finesse of 9.3. The maximum extinction ratio of the resonator filters is ~34 dB, indicating that the critical coupling condition has been satisfied.

Electro-optic modulator on rib waveguide

Abstract: An electro-optic modulator is formed on a silicon-on-insulator (SOI) rib waveguide. An optical field in the modulator is confined by using an electrically modulated microcavity. The microcavity has reflectors on each side. In one embodiment, a planar Fabry-Perot microcavity is used with deep Si/SiO 2 Bragg reflectors. Carriers may be laterally confined in the microcavity region by employing deep etched lateral trenches. The refractive index of the microcavity is varied by using the free-carrier dispersion effect produced by a p-i-n diode formed about the microcavity. In one embodiment, the modulator confines both optical field and charge carriers in a micron-size region.

Time-resolved sensing of chemical species in porous silicon optical microcavity

Abstract: Time-resolved measurements of red-shifts in the reflectivity spectra of porous silicon multi-layer microcavities, due to exposure to vapor of chemical species, give deep insight about the spatial concentration of the liquid condensed into the pores. Results clearly indicate that capillary condensation starts immediately and proceeds homogeneously all over the stack, yielding a uniform concentration distribution.

Three-dimensional wavelength-scale confinement in quantum dot microcavity light-emitting diodes

Abstract: We introduce a microcavity light-emitting diode (LED) structure that uses submicrometer oxide aperture and a quantum dot active region to achieve strong three-dimensional confinement of both the carrier distribution and the optical field. Light–current curves show optical emission for devices as small as 400nm in diameter. Spectroscopy on electrically pumped LEDs, with apertures ranging from 2.5 down to 0.7μm, show several spectral lines corresponding to cavity modes. A strong blueshift of the resonant modes for smaller apertures demonstrates the role of the oxide aperture in confining laterally the optical wave in a volume comparable to (λ∕n)3. Due to the high quality factors and low mode volumes, the devices could be good candidates for the demonstration of the Purcell effect under electrical pumping.

Exciton-polaritons in a crystalline anisotropic organic microcavity

Abstract: Investigation of polaritons in organic microcavities with strong light-matter interaction is of fundamental and practical interest. In the paper we study for the first time the dispersion of exciton-polaritons in a microcavity utilizing anisotropic organic crystals with one and two molecules per unit cell as optically active material. It is known that in bulk anisotropic organic crystals (like anthracene, tetracene and similar ones) the energies of Coulomb excitons are non-analytical functions of their wave vector k at small k (i.e. the energy of the exciton is different for different directions of the wave vector in the limit k → 0). We show that this is not the case in a planar microcavity where Coulomb exciton states are two-dimensional and the energy of Coulomb excitons at small wave vectors is an analytical function. Also, in contrast to widely used inorganic microcavities, in an anisotropic organic microcavity the cavity photon modes with both possible polarizations mix with the exciton states in the formation of polariton states. We demonstrate that these two factors result for small wave vectors in an almost isotropic dispersion of polaritons in an anisotropic organic crystalline microcavity, which can be observed in reflection, transmission and photoluminescence spectra of organic microcavity.

Surface-emission laser diode and surface-emission laser array, optical interconnection system, optical communication system, electrophotographic system, and optical disk system

Abstract: A surface-emission laser diode includes an active layer, a pair of cavity spacer layers formed at both sides of the active layer, a current confinement structure defining a current injection region into the active layer, and a pair of distributed Bragg reflectors opposing with each other across a structure formed of the active layer and the cavity spacer layers, the current confinement structure being formed by a selective oxidation process of a semiconductor layer, the pair of distributed Bragg reflectors being formed of semiconductor materials, wherein there is provided a region containing an oxide of Al and having a relatively low refractive index as compared with a surrounding region in any of the semiconductor distributed Bragg reflector or the cavity spacer layer in correspondence to a part spatially overlapping with the current injection region in a laser cavity direction.

Dye-doped cholesteric-liquid-crystal room-temperature single-photon source

Abstract: Fluorescence antibunching from single terrylene molecules embedded in a cholesteric-liquid-crystal host is used to demonstrate operation of a room-temperature single-photon source. One-dimensional (1-D) photonic-band-gap microcavities in planar-aligned cholesteric liquid crystals with band gaps from visible to near-infrared spectral regions are fabricated. Liquid-crystal hosts (including liquid crystal oligomers and polymers) increase the source efficiency, firstly, by aligning the dye molecules along the direction preferable for maximum excitation efficiency (deterministic molecular alignment provides deterministically polarized output photons), secondly, by tuning the 1-D photonic-band-gap microcavity to the dye fluorescence band and thirdly, by protecting the dye molecules from quenchers, such as oxygen. In our present experiments, using oxygen-depleted liquid-crystal hosts, dye bleaching is avoided for periods exceeding one hour of continuous 532 nm excitation.

Organic polariton laser

Abstract: The present invention relates to organic lasers. More specifically, the present invention is directed to an organic laser that provides a self-stimulated source of coherent radiation originating from organic microcavity polaritons. The organic polariton laser of the present invention comprises a substrate, a resonant microcavity comprising an organic polariton emission layer; and an optical pump. In preferred embodiments the optical pump is a microcavity OLED allowing for the fabrication of a self-contained or integrated device.

Tunable resonant optical microcavities by self-assembled templating

Abstract: Micrometer-scale optical cavities are produced by a combination of template sphere self-assembly and electrochemical growth. Transmission measurements of the tunable microcavities show sharp resonant modes with Q factors of >300 and 25-fold local enhancement of light intensity. The presence of transverse optical modes confirms the lateral confinement of photons. Calculations show that submicrometer mode volumes are feasible. The small mode volumes of these microcavities promise to lead to a wide range of applications in microlasers, atom optics, quantum information, biophotonics, and single-molecule detection.