Showing papers on "Optical microcavity published in 1992"

Physics and Device Applications of Optical Microcavities

Abstract: Optical microcavities are resonators that have at least one dimension on the order of a single optical wavelength. These structures enable one to control the optical emission properties of materials placed inside them. They can, for example, modify the spatial distribution of radiation power, change the spectral width of the emitted light, and enhance or suppress the spontaneous emission rate. In addition to being attractive for studying the fundamental physics of the interaction between materials and vacuum field fluctuations, optical microcavities hold technological promise for constructing novel kinds of light-emitting devices. One of their most dramatic potential features is thresholdless lasing. In this way and others, controlled spontaneous emission is expected to play a key role in a new generation of optical devices.

Controlling spontaneous emission and threshold-less laser oscillation with optical microcavities

Abstract: We describe the alteration of spontaneous emission of materials in optical microcavities having dimensions on the order of the emitted wavelength. Particular attention is paid to one-dimensional optical confinement structures with pairs of planar reflectors (planar microcavities). The presence of the cavity causes great modifications in the emission spectrum and spatial emission intensity distribution accompanied by changes in the spontaneous emission lifetime. Experimental results are shown for planar microcavities containing GaAs quantum wells or organic dye-embedded Langmuir-Brodgett films as light emitting layers. Also discussed are the laser oscillation properties of microcavities. A remarkable increase in the spontaneous emission coupling into the laser oscillation mode is expected in microcavity lasers. A rate equation analysis shows that increasing the coupling of spontaneous emission into the cavity mode causes the disappearance of the lasing threshold in the input-output curve. Experimentally verification is presented using planar optical microcavities confining an organic dye solution. The coupling ratio of spontaneous emission into a laser mode increases to be as large as 0.2 for a cavity having a half wavelength distance between a pair of mirrors. At this point, the threshold becomes quite fuzzy. Differences between the spontaneous emission dominant regime and the stimulated emission dominant regime are examined with emission spectra and emission lifetime analyses.

Micro-cavity semiconductor lasers with controlled spontaneous emission

Abstract: The principle and applications of quantum electrodynamics in microcavity semi-conductor lasers are reviewed. The coupling efficiency of spontaneous emission into a lasing mode and the spontaneous lifetime are modified by various microcavity structures. As a consequence of the increased coupling efficiency, those microcavity semi-conductor lasers are expected to feature a low threshold current, high quantum efficiency and broad modulation bandwidth. One remarkable result of the increased coupling efficiency is ‘lasing without inversion’. The other is ‘intensity squeezing at any pump rate’.

Spontaneous emission and optical gain in a Fabry–Perot microcavity

Abstract: The Fabry–Perot microcavity is analyzed in terms of its modification of the spontaneous emission and stimulated emission from a thin gain medium, which is contained between distributed Bragg reflectors. The structures correspond to the vertical‐cavity surface‐emitting semiconductor laser. Gain enhancement due to the cavity is calculated and compared to the case of a large Fabry–Perot cavity. The critical parameters in determining the degree of gain enhancement are the (large cavity) coherence length of the spontaneously emitted wave packet, and reflector design.

Vertical microcavity surface‐emitting ring laser

Abstract: We report the performance of a novel surface‐emitting laser of ring structure (RSEL). The far‐field emission pattern of the RSEL remains a near‐diffraction limited single lobe at 3 times the threshold current level. The structure may also be used to achieve beam width much less than that of the diffraction limit of Gaussian near‐field distribution.

Optical waveguide having a variable refractive index and an optical device having such an optical waveguide

Abstract: A semiconductor optical waveguide comprises a substrate of a semiconductor material doped to a first conductivity type, a multiple quantum well layer provided on the substrate for guiding an optical beam, a clad layer doped to a second conductivity type and provided on the multiple quantum well layer for confining the optical beam, a first electrode provided on the upper major surface of the clad layer for injecting carriers of a first type into the quantum well layer, and a second electrode provided on the lower major surface of the substrate for injecting carriers of a second type into the quantum well layer, wherein multiple quantum well layer comprises an alternate stacking of: a quantum well layer having a composition set to provide a smallest band gap that is possible under a constraint that the quantum well layer maintains a lattice constant with the substrate and a thickness set with respect to the optical energy of the optical beam such that a discrete quantum level of carriers is formed in the quantum well layer at an energy level larger than the optical energy by about 50 meV; and a barrier layer having a band gap substantially larger than the band gap of the quantum well layer.

Optical gain enhancement in Fabry–Perot microcavity lasers

Abstract: Fabry–Perot microcavities are analyzed in terms of their light emission characteristics. The analysis considers full output coupling, and we calculate both spontaneous and stimulated emission dependencies on cavity length, mirror design, and spectral characteristics. The cavities correspond to vertical‐cavity surface‐emitting lasers in the AlAs‐GaAs‐InGaAs material system, and a GaAs cavity with Bragg mirrors of CaF2/ZnSe. We show that considerable gain enhancement depends on the degree of coherence in the spontaneous emission, the microcavity length, and the Bragg reflector design.

Threshold characteristics of microcavity semiconductor lasers

Abstract: The influence of spontaneous emission coupling on the threshold characteristics of microcavity semiconductor lasers is studied using explicit algebraic expressions for the pump rate dependence of photon and carrier numbers. It is shown that fractional spontaneous emission coupling in practical microcavity laser structures imposes limitations on thresholdless lasing operation.

Cavity Quantum Electrodynamics in Semiconductor Laser

Abstract: : A one-dimension (planar) microcavity structure shown in can increase the coupling efficiency Beta of spontaneous emission into a single cavity resonant mode, if the spontaneous emission spectral width Aw. is smaller than the microcavity resonance width Awc and if the refractive-index difference An is fairy large. The loss of spontaneous emission into spurious modes, 1-Beta, are clue to the two (degenerate) orthogonal polarization modes and the leaky guided modes propagating in a plane of the microcavity. A three-dimensional (waveguide) microcavity structure shown in features several advantages over the one-dimensional structure. The increase in Beta is realized without requiring delta(omega sub e) delta(omega sub c) and large delta n. The degeneracy of the two orthogonal polarization mode's can 'be lifted and the leaky guided modes, can be made cut-off by the waveguide structure. Therefore, the spurious spontaneous emission into these modes can be suppressed. The spontaneous emission lifetime T, can be also decreased in the three-dimensional microcavity. On the other hand, the one-dimensional microcavity cannot decrease Tav sub delta but can only increase Tau sub delta.

Calculation of the coupling coefficient of two optical waveguide ends separated by layered medium

Abstract: The coupling coefficient between two optical waveguide ends which are separated by a layered medium is calculated. The coupling is determined between given modes of the waveguides. The optical beam propagating in the three-dimensional structure is represented as an angular spectrum of electromagnetic plane waves. The coupled field is calculated by fulfilling the boundary conditions for the plane wave components at the planes separating the layers. The maximum coupling is calculated by optimizing the characteristic data of the layer between the two waveguides. A two-dimensional example is presented where the attenuation is minimized by optimizing the refractive index and thickness of the separating layer. The attenuation versus the thickness of the separating layer is also calculated. >

Laser Oscillation with Optical Microcavity Structures

Abstract: Principles and experimental examples of controlling spontaneous emission and laser oscillation using optical microcavities are presented. Particular attention is paid to one-dimensional optical confinement structures with pairs of planar reflectors (planar microcavities). A simple analysis shows that a large coupling of spontaneous emission into the cavity mode causes the significant changes in the threshold behavior of the laser oscillation. Differences between the spontaneous and the stimulated emission dominant regimes are discussed. The ultrafast response capability of a microcavity laser is also shown. These laser oscillation properties are experimentally examined employing microcavities containing an organic dye solution.

Control of spontaneous emission in hemispherical microcavity lasers

Abstract: We present results for the modification of spontaneous emission in hemispherical micro-cavity quantum well lasers.