T. Hamano

Bio: T. Hamano is an academic researcher from Tokyo Institute of Technology. The author has contributed to research in topics: Spontaneous emission & Laser. The author has an hindex of 3, co-authored 6 publications receiving 267 citations.

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%. >

Spontaneous emission factor of a microcavity DBR surface emitting laser. II. Effects of electron quantum confinements

Abstract: For pt.I see ibid., vol.27, p.1347-58 (1991). A method for the theoretical analysis of the spontaneous emission factor (C factor) has been developed for microcavity distributed Bragg reflector (DBR) surface emitting lasers having various quantum-well active regions. It is shown that the C factor can be enlarged by the enhancement of mode density, the anisotropic emission, and the narrow spectral width in quantum wells. C approximately 0.6 may be obtained with GaAs-AlAs DBRs, 0.55 mu m*0.55 mu m cross section of the cavity, three times vertically long cross section of quantum-wire active regions, and the spectral width of several nanometers at room temperature. This value can be further increased by utilizing a narrower spectral width expected at low temperature. >

Spontaneous emission factor and lifetime of a microcavity distributed Bragg reflector surface-emitting laser with quantum-wire structure

Abstract: Control of spontaneous emission in a microcavity is of great interest for considering future device performances of vertical microcavity surface-emitting lasers (SEED),1,2 Several reports have suggested unique features owing to remarkable enhancement/inhibition of spontaneous emission in the microcavity (e.g., a thresholdless lasing operation, a coherent and low noise spontaneous emission light.)3-5 These reports predicted that such features can be conspicuously observed if the spontaneous emission factor (C factor)6 could approach unity, while C ranges 10-5 ~ 10-6 in conventional LDs.

Driving level dependence of spontaneous emission factor in microcavity DBR surface emitting lasers

Abstract: Ultra low-threshold surface emitting (SE) lasers are attractive for large scale integration scheme into two-dimensional laser arrays. The control of spontaneous emission using a microcavity is one of the viable methods to realize such ultra low-threshold lasers. We have obtained the enhanced spontaneous emission factor (C factor) in three-dimensional microcavity DBR SE lasers. Recently, several groups have estimated the C factor of the microcavity SE lasers by fitting the calculated threshold curves of output-input characteristics where they assumed that the C factor was constant. However, the C factor must be changing against driving levels. In this study, we would like to show that the variable C factor provides the substantial difference in the L-I characteristic of a microcavity SE laser. >

Vertical-cavity surface-emitting lasers: Design, growth, fabrication, characterization

Abstract: The authors have designed, fabricated, and tested vertical-cavity surface-emitting lasers (VCSEL) with diameters ranging from 0.5 mu m to>50 mu m. Design issues, molecular beam epitaxial growth, fabrication, and lasing characteristics are discussed. The topics considered in fabrication of VCSELs are microlaser geometries; ion implementation and masks; ion beam etching packaging and arrays, and ultrasmall devices. >

Optical Processes in Microcavities

Abstract: Studies of optical microresonators with dimensions between 0.1 and 10 microns are now under way in a wide variety of condensed matter systems. Ideally, one can isolate a single mode of the optical field in a cube a halfwavelength on a side with perfectly reflecting walls. Liquid droplets, polymer spheres and semiconductor Fabry‐Perot microcavities with dielectric mirrors are examples of microresonators with which one can approach this ideal limit and nearly isolate a few modes of the electromagnetic field from the continuum of surrounding free‐space modes.

Impact of planar microcavity effects on light extraction-Part I: basic concepts and analytical trends

Abstract: We address the long-standing issue of extracting light as efficiently as possible from a high-index material, n/spl ges/2, where as little as 2%-10% of light not suffering total internal reflection is extracted at standard plane faces due to the small critical angle /spl sim/1/n. Using a planar microcavity to redirect spontaneous emission toward the surface, constructive interferences can bring 15%-50% of the light out, enhancing brightness and efficiency. In this first of two papers, an approximate approach is used showing the importance of small cavity order m/sub c/ and of the m/sub c//n/sup 2/ ratio. We define a condition for microcavity regime as m/sub c/<2n/sup 2/. It is shown that most of light extraction is usually attained for moderate mirror reflectivities /spl sim/1-m/sub c//n/sup 2/ typically below 90%, and without strong directionality. Balance between emission directionality, radiance (brightness), and spectral narrowing is discussed. We define a brightness enhancement factor B given by Bm/sub c//spl Delta//spl Omega/=4/spl pi/ where /spl Delta//spl Omega/ is the largest internal solid angle of either the cavity mode or that deduced from the material emission linewidth. Design rules are applied to distributed dielectric mirrors yielding an optimal number of periods. The underlying physical competition between emission into guided modes, Fabry-Perot modes and the so-called "leaky modes" is analyzed.

Strong Purcell effect for InAs quantum boxes in three-dimensional solid-state microcavities

Abstract: A strong enhancement of the spontaneous emission rate (Purcell effect) has been observed for self-assembled InAs/GaAs quantum boxes inserted in GaAs-based pillar microcavities (/spl times/5) and microdisks (/spl times/15) using time-resolved as well as c.w. photoluminescence experiments. We show that the magnitude of the Purcell effect can be quantitatively understood by considering both the Purcell figure of merit F/sub p/ of such cavities (F/sub p//spl Gt/1) and the spatial/spectral distribution of the inhomogeneous collection of atom-like emitters. These results open the way to the development of single-photon devices such as photon-guns or photon-turnstiles, able to emit photons one-by-one in a deterministic way.

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.