Showing papers on "Optical microcavity published in 1991"

Modification of spontaneous emission rate in planar dielectric microcavity structures.

Abstract: The spontaneous emission rate and radiation pattern for a thin quantum well sheet enclosed by a one-dimensional dielectric microcavity have been calculated. By placing the sheet in the node (antinode) position of the cavity standing wave, the spontaneous emission in the direction normal to the sheet will be decreased (enhanced). In the former case the theory predicts that the spontaneous lifetime can be increased more than a factor of 10. In the latter case both theory and experiments confirm that such a simple structure can couple a substantial amount (30\char21{}90 %) of the spontaneous emission into the cavity resonant mode. In both cases, however, theory predicts that the spontaneous emission lifetime will increase for structures without guided modes.

Spontaneous emission factor of a microcavity DBR surface-emitting laser

Abstract: The spontaneous emission factor (SEF) of a microcavity distributed Bragg reflector (DBR) surface-emitting laser has been obtained theoretically to investigate the possibility of the thresholdless lasing operation. Formulas expressing the spontaneous emission in a three-dimensional microcavity were obtained. By introducing the distribution of mode density in wavevector space, it is shown that the radiation pattern of spontaneous emission is deeply modified by the microcavity and is different from that in free space. Based on this result, the SEF and the emission lifetime are calculated as a function of emission spectral width and the size of the active region. It is found that the SEF exceeds 0.1, even though the spectral width is as large as 30 nm when the transverse size is smaller than 0.5 mu m and the DBR reflectivity is larger than 90%. >

High quantum efficiency, long wavelength InP/InGaAs microcavity photodiode

Abstract: There is an inherent tradeoff between the quantum efficiency and bandwidth of conventional pin photodiodes. In the case of devices based on III-V semiconductors, an absorption region thickness of approximately 2 μm is required to achieve quantum efficiencies greater than 80%, although this limits the transit-time-limited bandwidth to less than 15 GHz. It has recently been shown that a microcavity photodiode can circumvent this performance tradeoff and achieve both high quantum efficiency and large bandwidths. The fabrication of a microcavity pin photodiode with a high quantum efficiency near 1.55 μm is described. An external quantum efficiency of 82% at 1480 nm has been achieved with an InGaAs absorption layer only 2000 A thick embedded in a resonant cavity grown by metal organic vapour phase epitaxy (MOVPE).

Observation of spontaneous emission lifetime change of dye‐containing Langmuir–Blodgett films in optical microcavities

Abstract: We have studied the spontaneous emission properties of Langmuir–Blodgett films containing dye molecules confined in Fabry–Perot microcavity structures having wavelength thickness. The presence of the cavity causes great modifications in the emission spectrum and emission intensity in the direction of the cavity axis. A clear change in spontaneous emission lifetime occurs, which is also attributed to the microcavity effect.

Spontaneous emission from a dipole in a semiconductor microcavity

Abstract: The effect of a semiconductor microcavity on the radiative spontaneous recombination of an electron‐hole pair strategically placed (by virtue of a quantum well) in the microcavity is considered. First‐order perturbation theory is used in the quantum mechanical calculation of the spatially anisotropic radiation rate and shows a strong influence of the cavity, and dipole position in the cavity, on the spontaneous photon emission process. Calculations are compared with previous experiments [T. J. Rogers, D. G. Deppe, and B. G. Streetman, Appl. Phys. Lett. 57, 1858 (1990)].

Apparatus for recording and reproducing optical information and prism coupler

Abstract: An apparatus for recording and reproducing optical information includes an optical integration detecting element arranged on an optical path of light from a laser beam source to an optical information recording medium. The optical integration detecting element has an optical waveguide layer formed on a substrate; a photodetector connected to the optical waveguide layer; a first gap layer formed on the optical waveguide layer and having a refractive index lower than that of the optical waveguide layer; a second gap layer formed on the first gap layer and having an opening portion and a refractive index lower than that of the optical waveguide layer; an adhesive layer having a refractive index higher than that of the optical waveguide layer and adhered to the first gap layer such that the opening portion of the second gap layer is filled with the adhesive layer; and a prism adhesively fixed to an upper portion of the adhesive layer and constructed by a dielectric substance having a refractive index higher than that of the optical waveguide layer.

Optical information storing apparatus and method for production of optical deflector

Abstract: An optical waveguide is comprised of an optical substrate and an optical thin-film optical waveguide layer and formed such that ##EQU1## where θ is an output angle, n o1 is an ordinary refractive index of the optical substrate for an ordinary beam, n e1 is an extraordinary refractive index of the optical substrate for an extraordinary beam, n o2 is an ordinary refractive index of the optical thin-film optical waveguide layer for the ordinary beam and n e2 is an extraordinary refractive index of the optical thin-film optical waveguide layer for the extraordinary beam, and an electrode for generating a surface acoustic wave for diffracting light is formed on the optical waveguide to construct a collinear optical deflector. A method for production of the optical thin-film optical waveguide layer is exemplified wherein a target made of tantalic lilthium niobate or tantalic lithium niobate magnesium and an optical substrate made of lithium tantalate are prepared and an optical thin-film optical waveguide layer having a composition of tantalic lithium niobate or tantalic lithium niobate magnesium is formed on the optical substrate through an ion beam sputtering process into which oxygen can be introduced. Proton substitutes for part of an element constituting the optical thin-film optical waveguide layer.

An Ultimately Low-Threshold Semiconductor Laser with Separate Quantum Confinements of Single Field Mode and Single Electron-Hole Pair

Abstract: A novel semiconductor surface-emitting laser structure is proposed. All spontaneous emission is coupled into a single lasing mode by means of a quantum microcavity, and discrete electron-hole pair emission is made free of absorption by means of a dc-biased quantum dot. The quantum microcavity modifies the angle distribution of a vacuum field fluctuation that is a source of spontaneous emission. The dc-biased quantum dot separates the emission and absorption lines by image-charge-induced change in the electric field. The threshold current of such a semiconductor laser can be reduced to below 100 nA.

High-speed short cavity strained-layer multiple quantum well lasers

Abstract: The high-speed response and optical properties of strained-layer In/sub 03/Ga/sub 07/As four and five quantum-well ridge waveguide lasers fabricated by chemically-assisted ion beam etching (CAIBE) are presented The threshold current variation with cavity length is very similar for the two-layer designs, but the differential gain decreases more quickly with optical loss in the four quantum-well devices Consequently, whereas the 200-400 mu m cavity length lasers from the four quantum-well wafer are superior to those from the five quantum-well layer in terms of high speed performance, the 50- and 100- mu m long devices are nearly identical A CW 3-dB bandwidth of 22 GHz and a record 3-dB bandwidth of 26 GHz under pulsed bias have been measured on 50 mu m long lasers 100- mu m cavity length lasers exhibit excellent modulation efficiency with a typical 3-dB bandwidth of 20 GHz >

Optical wavelength conversion device with high alignment accuracy

Abstract: The optical wavelength conversion device according to the present invention comprises a light source for emitting a fundamental wave, a waveguide type optical wavelength conversion element having an optical coupler to receive said fundamental wave and an optical waveguide made of non-linear optical material for converting the fundamental wave to a secondary harmonic, and a light-focused optical system having an objective lens for converging the fundamental wave to the optical coupler, wherein the light-focused optical system includes an optical tilting means for tilting the optical axis of the fundamental wave with respect to the optical axis of the objective lens. The wavelength conversion device having a simple arrangement of an optical system can guide the fundamental wave to the wavelength conversion element at a high accuracy.

Noise-driven rate equation analysis of quantum-well, microcavity lasers

Abstract: Noise-driven rate equations are used in modeling microcavity, quantum-well, semiconductor lasers. Results for different cavity designs are compared. Particular attention is paid to threshold and noise characteristics. Using attainable dimensions it is seen that threshold current is reduced, relaxation modulation bandwidth is increased and turn-on delay is shortened as previously predicted for devices with enhanced spontaneous emission. In addition, it is shown that the device tends to lose its coherence as the microcavity design is approached, and the microcavity loses its noise advantage as the bandwidth is increased (when external modulation is considered) because of the lack of roll-off in the 100 GHz spectrum presented. >

Vertical-cavity surface-emitting lasers and arrays for optical interconnect and optical computing applications

Abstract: Vertical cavity surface emitting lasers (SELs) offer many desirable features that are suitable for applications in optical interconnect, optical signal processing, and optical computing. We describe a GaAs vertical cavity SEL with a novel structure and discuss those key laser performance characteristics, such as threshold current, power output, efficiency, far field divergence, and modulation response, that are important to these potential applications.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Electrodynamics and controlled spontaneous emission in semiconductor microcavity lasers

Abstract: It is pointed out that controlled spontaneous emission has become a topic of interest and speculation concerning light emission from semiconductors. Recent experiments with GaAs-AlGaAs-InGaAs heterostructures show that such effects are indeed observable, but questions remain as to what role, if any, controlled spontaneous emission may play in current microcavity semiconductor lasers, and in future devices. The authors review the experimental work to date on controlling spontaneous emission in semiconductor microcavities, and present calculations on the microcavity effect on spontaneous emission. In particular, longitudinal cavity effects on the operation of the AlAs-GaAs-InGaAs microcavity Fabry-Perot laser are considered. Cavity enhancement of optical gain is shown to be an immediate benefit of the Fabry-Perot microcavity. The cavity enhancement has been shown to be substantial even for relatively low-contrast DBR (distributed Bragg reflector) mirrors such as occurs with the AlAs-GaAs material. >

Semi-insulating Multiple Quantum Wells As An Optical Imaging Medium

Abstract: Semi-insulating quantum wells provide a unique new mechanism for controlling optically induced space-charge and saturation effects in electro-optic devices. This is achieved by spatially separating space-charge trapped in the quantum barriers from photoconductivity in the quantum wells. To demonstrate this principle, we have grown, processed and characterized photorefractive quantum-well devices that operate with the quantum-confined Franz-Keldysh effect[l,2]. A consequence of this principle for the photorefractive effect is the persistence of photorefractive gratings: the gratings generated by a visible-wavelength pump laser are not erased by a high-intensity infrared probe laser. Therefore a strong signal can be controlled by a weak control beam, which is a requirement of any efficient optical processing system. The film structure for this device was grown in a Varian GEN II molecular beam epitaxy system. The film consists of 8000 8, of AlGaAs layers which can be used as an etch stop for removal of the substrate or to perform lift-off of the eptaxial MQW structure. The MQW consists of 60 periods of 75 8, GaAs wells and 100 8, Alo.sGao.7As barriers for a total photorefractive interaction length of 1.05 pm. On top of the MQW is a 500 8, Alo.3Gao.7As cap. After film growth the MQW structure was implanted with protons of energy 160 KeV and dose 1012 cm-2. The epitaxial side of the wafer was then epoxied to a glass slide and the substrate removed. The MQW structure was now implanted with the same energy and dose of protons but from the other side to ensure that the entire MQW structure was semi-insulating. Gold contact strips of separation 1 mm were formed in order to be able to generate an electric field parallel to the quantum wells. The non-degenerate four wave mixing experiment is illustrated in Fig. 1. A helium neon laser, which can generate electron-hole-pairs (ehp) in the multilayer structure, is used to form an optical grating in the SIMQW. With an electric field applied parallel to the quantum wells, the ehp generated in the light regions will be separated and trapped in the dark regions. An optical probe beam from a Ti:sapphire laser is now diffracted from the absorption and refractive gratings caused by the stored spacecharge pattern in the SIMQW. The diffraction efficiency as a function of wavelength of the Ti:sapphire laser is shown in Fig. 2 at an applied AC field of 4 kV/cm at 290 Ht. The diffraction efficiency peaks at 8x10-5 at a wavelength of 837 nm. When the Ti:sapphire probe laser is tuned below the bandgap of the Al0.3Ga0.7As barriers, ehp are only generated in the GaAs quantum wells and will not erase the stored charge pattern in the barriers. Shown in Fig. 3 is the diffraction signal as a function of the probe intensity for two different wavelengths, 837 nm corresponding to the peak in the diffraction efficiency and 840 nm corresponding to the zero-crossing of the electroabsorption on the low-energy side of the heavy-hole exciton. The Ti-sapphire