bluuebunny/crossref_metadata_2025 huggingface dataset:
New Restoration Techniques for Images Degraded by Poisson Noise
Authors: Jiang Shiaw-Shiang , Sawchuk Alexander A.
Published: February 2023

Under low light level conditions, photon noise is a fundamental limitation of detected images. Photon noise can be modeled as a Poisson point process given by (1) where f(i, j) is the original image, λ is a proportionality factor determining the SNR, and Poisson(·,·) is a Poisson random number generator. The probabilistic description of a Poisson process is given by (2) The normalized observation is given by (3) Eq. (3) can be rewritten as [1], [2] (4) where (5) is recognized as the noise part of the Poisson process.
Low Light Level Imaging with CCDs
Authors: Tyson J.A.
Published: February 2023

High quantum-efficiency, excellent linearity, and low noise make frame-transfer silicon Charge-Coupled Devices (CCDs) ideal imagers at very low light levels in the UV to 900 nm range. Scientific-grade CCDs are now available with less than 10e noise from at least four manufacturers. In astronomy these CCDs on large and small telescopes enable studies of objects 100 times fainter than is possible using photographic and video-camera techniques. This is due both to the high quantum efficiency and the photometric stability of the CCD. Chopping techniques, taking advantage of this stability, allow cancellation of low-level systematics. Detection levels of 2×10-5 photons m-2 nm-1 sec-1 pixel-1 have been achieved. Faint galaxies and stars of 30th magnitude are detected in 6 hours integration on a 4 meter telescope, corresponding to 0.02 photons/sec/pixel. Soon the efficiency of large telescopes for survey studies will be improved by the use of CCD mosaics, covering the entire usable focal plane.
Solid State Photomultiplier Arrays
Authors: Stapelbroek M. G.
Published: February 2023

One- and two-dimensional arrays of solid-state photomultipliers, based on arsenic-doped silicon, capable of counting individual photons of wavelength between 0.4 and 28 microns have been demonstrated.
Maximizing the Information Transfer in a Quantum Limited Light Scattering System
Authors: Lading Lars
Published: February 2023

The purpose of the light scattering systems considered here is to obtain information about the macroscopic movements of the scatterer. We shall here be confined to systems based on quasi-elastic scattering - i.e. systems where any change in the frequency of the scattered light is caused only by possible macroscopic motions of the scatterer. A light scattering system can conveniently be divided into three parts (Fig. 1): a transmitter, a receiver, and a signal processor. The transmitter generates a characteristic field (or intensity) distribution in the measuring volume. The receiver collects the scattered light and converts it to an electronic signal (or signals). On the basis of the temporal characteristics of the electronic signal the signal processor will give estimates of the dynamics (e.g. velocity) of the scatterer. The spatial intensity distribution as seen by the receiver when a point scatterer (or set of scatterers) moves through the measuring volume defines the code of the instrument. The code defines how the information about the dynamics of the scatterer is encoded.
Neural Network for Adaptive Processing of Quantum Limited Images
Authors: Perlovsky Leonid I.
Published: February 2023

Processing of quantum limited images requires optimal utilization of all the available information: all the registered photons, prior information such as geometrical and intensity model of imaged objects formulated in terms of relatively small number of parameters, and real time and a posteriori information that could be available from experts or from other sensors. Such an approach to adaptive information fusion image processing is presented here based on maximum likelihood neural network developed previously by the author for adaptive classification and sensor fusion[1,2,3].
Models of Speckle Image Recovery for Complicated Objects*
Authors: Beletic James W. , Goody Richard M.
Published: February 2023

We present two models which predict the image quality obtained by astronomical speckle imaging as a function of object, atmospheric conditions, telescope and imaging camera.
Low Light Level Limits to Tracking Atmospheric Fringe Wander
Authors: Buscher David
Published: February 2023

The low-light-level performance of algorithms for tracking fringe motions in an astronomical Michelson interferometer is investigated using numerical simulations of atmospheric phase disturbances.
Maximum likelihood noise reduction
Authors: Meinel Edward S.
Published: February 2023

The main purpose of processing a degraded image is to determine as closely as possible what object created that image. There are a number of factors which govern the quality of the processing: the severity of the degradation; the amount of noise; the sampling interval; the background estimate; the processing algorithm itself. However, the noise in the image will generally limit the ability to do further processing. We would like to be able to reduce the effects of the noise without degrading the underlying image.
Red (639-661nm) InAlGaAs Vertical Cavity Surface Emitting Laser Diodes†
Authors: Lott J. A. , Schneider R. P.
Published: February 2023

The first electrically injected visible InAlGaP/AlGaAs vertical cavity surface emitting lasers (VCSELs) are reported. The structures consist of an InAlGaP optical cavity active region surrounded by AlAs/AlGaAs distributed Bragg reflectors. Pulsed room temperature lasing is achieved from 639 to 661 nm with test devices fabricated on unrotated wafers. Beam divergence is 6.5° (full angle) and device on-resistance is less than 15 Ω. At 650 nm, a current threshold of 30 mA at 2.7 V is measured with peak output power exceeding 3.3 mW for devices with a 20 μm emitting diameter.
Fabrication of GaAs Quantum Wires (~ 10nm) by MOCVD Selective Growth
Authors: Tsukamoto S. , Nagamune Y. , Nishioka M. , Arakawa Y.
Published: February 2023

Low dimensional semiconductor structures such as quantum wires have recently received great attentions since new physical phenomena with applications to semiconductor lasers and other functional optical devices are expected[1,2]. To fabricate these quantum microstructures, selective growth on patterned substrates is one of the most attractive techniques[3-5]. In order to obtain real quantum wire devices, the structures with lateral width less than 15nm must be achieved. In this paper, we report a successful fabrication of the GaAs triangular-shaped quantum wires with ~10nm lateral width, showing both photoluminescence(PL) measurement and a high-resolution scanning electron micrograph(SEM) observation. The fabrication technique employed here is based on the MOCVD selective growth technique which we have developed recently[6].
Thermal and Coherent Carrier Escape from Quantum Wells in an Electric Field
Authors: Fox A. M. , Ispasoiu R. G. , Foxon C. T.
Published: February 2023

In this work we investigate the mechanism of carrier escape from GaAs/Al0.33Ga0.67As quantum wells in an electric field using CW photocurrent and photoluminescence (PL) techniques. The photocurrent generated with a fixed intensity light source depends strongly on both the applied field and the temperature (T). At low fields the photocurrent increases with T, as expected for a thermally-activated escape mechanism. At higher fields, however, the photocurrent actually decreases with T up to about 100K, and then starts to increase again. The most likely explanation of this is the reduction of a coherent component of the tunneling current, associated with a reduction in the wave function coherence length with increasing temperature.
Optical Nonlinearities Associated with Piezo-Electric Field Screening in [111] Strained-Layer InGaAs/GaAs Quantum Wells
Authors: Smirl Arthur L. , McCallum D. S. , Cartwright A. N. , Boggess Thomas F. , Moise T. S. , Guido L. J. , Barker R. C. , Wherrett B. S.
Published: February 2023

Optical switching and logic devices require a large optical nonlinearity (absorptive or refractive) per absorbed photon, combined with a rapid excitation recovery time. The accumulated absorptive (or index) changes during a laser pulse are proportional to the shorter of either the pulse duration or the excitation lifetime. Optimally the two are matched, in which case the switching energy (power-time product) is determined primarily by the absorption (or refraction) cross-section; that is, the change in absorption coefficient per photogenerated carrier-pair. Any mechanism that is purported to enhance the cross-section is therefore of considerable interest. It has been suggested that the in-well screening of the piezoelectric field present in certain strained-layer quantum well structures could provide such an enhancement1.
Microcavity VCSELs
Authors: Jewell J.L. , Scherer A. , Van der Gaag B. , Schiavone L.M. , Harbison J.P. , Florez L.T.
Published: February 2023

Microcavity lasers potentially will have ultra-low thresholds in the micro ampere range or even lower. The vertical-cavity surface-emitting laser (VCSEL) structure represents the most straightforwardly produceable device which can scale down to ultra-small cavity dimensions and active material volumes. By a simple scaling, one can calculate that a single-quantum-well (SQW) microcavity VCSEL, given a 100 A/cm2 threshold current density, would have a 200 nA threshold if scaled down to a 0.5 μm diameter. This calculated threshold does not rely on any enhancement of spontaneous emission, which could further reduce the threshold. The spontaneous emission factor in a GaAs/AlAs microcavity VCSEL of this diameter is predicted to be greater than 0.1, even at room temperature, compared to ~10-4 for conventional laser diodes [1], or ~10-2 for cryogenic-temperature planar microcavity VCSELs [2]. It is questionable, however, whether such a device is feasible. A SQW microlaser cavity must have extremely low loss, well under 1 % per pass. At some minimum diameter, almost certainly above 0.2 μm, diffraction and scattering due to sidewall roughness and the mirror-layer interfaces will cause losses to be excessively high. For an ultra-small microlaser to be electrically pumped with practical efficiency formidable fabrication challenges must be overcome.
Coherent Exciton Effects in Quantum Wells
Authors: Göbel E. O.
Published: February 2023

Resonant excitation of excitons by short optical laser pulses creates a macroscopic polarization which decays in the simplest case with a constant rate described by the dephasing time T2. In semiconductors and semiconductor quantum well structures this dephasing time is of the order of 1ps. Thus, subpicosecond time resolution is required to study coherent exciton effects in quantum wells. We have applied femtosecond Four-Wave-Mixing (FWM) spectroscopy in our studies. As more than one exciton state is excited simultaneously, the coherent dynamics and interaction of these exciton states can be studied.
AC-Stark shift of the Fermi edge singularity in modulation doped quantum wells
Authors: Brener I. , Knox W.H. , Cunningham J.E. , Chemla D.S.
Published: February 2023

AC-Stark shifts of the electronic states are observed when a semiconductor is excited by ultrashort, below band-gap laser pulses. So far, all the studies have been performed in undoped samples [1,2], and the effect has been called "excitonic AC-Stark effect". It has been explained by means of the interaction of "virtual" excitons created by the pump beam with the real excitons created by the weak probe beam [3]. In this talk, we will describe our work on the AC-Stark shifts observed in the absorption spectra of modulation doped quantum wells (MDQW). This effect occurs in a new regime, as the absorption edge in MDQW samples at low temperatures is governed by the "Fermi edge singularity" (FES).
Femtosecond Studies of Ultrafast Large-Angle Polarization Rotation in GaAs/AlxGa1-xAs Multiple Quantum Wells Under Uniaxial Stress
Authors: Wraback M. , Shen H. , Pamulapati J. , Dutta M. , Newman P. , Lub Y.
Published: February 2023

Due to symmetry considerations, polarization rotation is not possible for light incident normal to a lattice matched or pseudomorphic multiple quantum well (MQW) structure. However, it has been shown1 that a uniaxial stress applied in the plane of the structure breaks the rotation symmetry, which should result in an anisotropic excitonic absorption due to the mixing of the heavy and light hole states in the MQW In this paper we show for the first time that the bleaching of this absorption creates an ultrafast large-angle polarization rotation which may have applications in the field of high speed, high contrast ratio spatial light modulators (SLM).
Semiconductor Laser with Dispersive Loss: Quantum Noises and Amplitude squeezing
Authors: Nabiev R.F.
Published: February 2023

In the recent paper 1 semiclassical treatment of semiconductor laser (SL) with dispersive loss element (DLE) inside the cavity was presented. In SL with frequency dependent photon life time τ
p
(
τ
p
−1=τp0−1+2Cφ, φ is the slowly varying phase of an electromagnetic field) phase and amplitude noises were shown to be decreased (1 + Cα)2 / (l +α2) and (1 + Cα)2 / (1 + C2) (α is the linewidth enhancement factor) times, respectively, comparing to the conventional SL (C=0). At the same time, he low frequency portion of current modulation response is unchanged. Possible values of parameter C 1 can be ~10 and some dozens in the case of atomic absorption cell and the weak coupling of SL to an external high-finesse Fabry-Perot etalon, respectively.
Narrow Linewidth Long Wavelength Phase-Locked Laser Array with Mode Controlling Grating Filter
Authors: Dong Jie , Arai Shigehisa , Ikeda Tetsu
Published: February 2023

Single-longitudinal-mode (DSM) semiconductor lasers have been widely investigated for achieving low chirping and narrow linewidth characteristics. Various schemes such as corrugation-pitch-modulated distributed feedback lasers1, DBR2 or DR3 lasers with passive regions and quantum wire or box lasers with small α parameter4 have been reported. High power and small spontaneous emission factor further reduce the spectral linewidth. For achieving high power and small spontaneous emission factor, phase-locked laser arrays5,6 are attractive as well as for narrow beam operation. We report in this paper a single mode and narrow linewidth characteristics of a five-element 1.5μm GaInAsP/InP phase-locked laser array with a mode controlling grating filter (GFA).
Limitations of Surface Related Optical and Carrier Losses in Microcavity Lasers
Authors: Thibeault B. J. , Strand T. A. , Peters M. G. , Wipiejewski T. , Young D. B. , Scott J. W. , Coldren L. A.
Published: February 2023

There is much interest in exploring the physics associated with micro-cavity lasers. These lasers can have very low threshold currents because the number of cavity modes is limited and a large portion of the spontaneous emission must be coupled to the lasing mode. To achieve such a structure a very small ( < 1 μm diameter ) optical cavity must be used. The index-guided vertical- cavity surface-emitting laser (VCSEL) is a prime candidate for this goal. However, due to the effects of waveguide scattering loss, diffraction loss, and surface recombination, electrically pumped diameters have been limited to > 2 μm [1]. In this paper, we first explore the issues limiting size reduction of the index-guided VCSELs through modelling and experiment. We then show how the issue of surface-recombination can be resolved through in-situ etching and regrowth.
Low Threshold Microcavity Lasers using a Half-Wave Cavity Spacer
Authors: Huffaker D.L. , Shin J. , Deppe D.G.
Published: February 2023

Data will be presented characterizing a microcavity laser structure which uses a half- wavelength cavity (HWC) spacer layer surrounding a single quantum well (QW) active region. Initial results demonstrate a continuous-wave (CW) room-temperature lasing threshold current of 91μA for a 2μm device (Jth=2.3kA/cm2), and 220μA for an 8μm device (Jth=344A/cm2). The HWC laser, as illustrated in Fig.1, uses 26 pairs of n- AlAs/GaAs distributed Bragg reflectors (DBRs) for the bottom mirror, a half-wavelength cavity spacer composed of an n-AlAs layer beneath the QW and p-AlAs layer on top, and a p-GaAs cap layer.
Measurements of Spontaneous Emission Factor in Electrically Pumped Microcavity Lasers
Authors: Ram Rajeev J. , Goobar Edgard , Peters Matt , Coldren Larry A. , Bowers John E.
Published: February 2023

Enhancement of spontaneous emission coupling (β) into the lasing mode has promised significant reductions in lasing thresholds and absolute intensity noise for microcavity lasers [1,2]. This control is typically achieved by employing high finesse, wavelength scale resonators. Measurements of β have been made in optically pumped devices with various resonator geometries: These include planar DBR resonators (β=0.009 at 4 K [2]), large-diameter post resonators (β=0.004 at 4 K [2]), hemispherical microcavities (β=0.01 at 4 K [3]) and micro-disk lasers (β=0.23 at 77 K [4]). This paper reports the first measurements of β in electrically pumped vertical cavity devices as well as the first measurement of β in surface emitting lasers with strong transverse photon confinement.
Ultrathin Porous Silicon Films: Physics & Device Applications
Authors: Fauchet P.M. , von Behren J. , Tsybeskov L. , Kostoulas Y. , Ucer K.B.
Published: February 2023

We have manufactured thin films of light-emitting porous silicon (LEPSi) by electrochemical etching in HF and subsequently lifted them off the silicon wafer by an electropolishing step [1]. The film thickness was varied from 100 μm to 0.1 μm and the porosity ranged from < 40% to ≥ 90%. To insure the structural integrity of the thinner, higher porosity films, they were deposited on sapphire windows where they remain attached by van der Waals or electrostatic forces, in a manner reminiscent of earlier work with ultrathin film of III-V semiconductors [2]. The microstructural, chemical and optical properties of these films have been investigated using a variety of tools, including AFM, XRD, FTIR, cw and time-resolved absorption and luminescence measurements. These films are optically flat, do not scatter light, and show pronounced Fabry-Perot interference fringes in the transparency region which can extend to photon energies well above the bandgap of crystalline silicon (see Fig. 1). The refractive index can be lower than 1.3 for high porosity films, in qualitative agreement with the predictions of a simple effective medium theory.
Fabrication of Quantum Dots and Nano-scale Observation of Electron-Photon Interaction
Authors: Arakawa Yaushiko
Published: February 2023

Various technological approaches have been performed to fabricate quantum dot structures which are potentially useful for optoelectronic device application and basic physics[1]. One of main goals is to manipulate both electrons and photons in nanostructures and microcavities. Towards this goal, it is important to develop nanofabrication and nano-scale optical characterization techniques.
Quantum Wire Fractional Layer Superlattice Microcavity Lasers
Authors: Chavez-Pirson Arturo , Ando Hiroaki , Saito Hisao , Kanbe Hiroshi
Published: February 2023

Semiconductor quantum wires are attracting attention not only because they exhibit interesting one-dimensional optical physics but also because they may improve the performance of optical devices. The increased quantum confinement in the quantum wires concentrates the electronic density of states into a narrow wavelength region resulting in enhanced optical properties. For example, lasers using quantum wires are expected to exhibit lower current thresholds, higher modulation bandwidths, and narrower spectral widths compared to quantum well or bulk lasers. This makes quantum wire lasers attractive devices for a variety of applications in communications, optical processing, and optical interconnects.
Electronic Picosecond-pulse Interferometer Probing the Millimeter-wave Response of a Quantum-Dot System
Authors: van der Weide D.W. , Blick R.H. , Keilmann F. , Haug R.J.
Published: February 2023

As a sensing mechanism for broadband (contactless) millimeter-wave spectroscopy of planar mesoscopic systems at cryogenic temperatures, bolometric detection or the photoconductive response of the sample is usually employed. Conventional sources of radiation, such as backward-wave oscillator tubes or Gunn diodes, are then modulated for lock-in detection. In most cases, the output power from these sources varies as they are tuned, changing the thermal load on the system being studied. Furthermore, such conventional sources rarely offer over a decade of frequency coverage, limiting the range available for probing these systems.
Tunable Transversely-Pumped Counterpropagating Optical Parametric Oscillators Based on Semiconductor Structures
Authors: Ding Yujie J. , Khurgin Jacob B. , Lee Seung-Joon
Published: February 2023

Since backward parametric oscillations were proposed [1] in the parallel propagation configuration, such a fundamental nonlinear process has never been observed due to the lack of appropriate materials for achieving quasi-phasematching. Recently, following Ref. [2], quasi-phasematching were achieved based on GaAs/AlGaAs multilayers [3] or asymmetric quantum-well domain structures [4-6]. Here, for the first time to the best of our knowledge, we propose to use second-order optical nonlinearities of multilayers or asymmetric quantumwell domain structures in a vertical cavity to achieve tunable and efficient transversely-pumped counterpropagating optical parametric oscillations (TPCOPOs). Similar to Refs. [3-6], the quasi-phasematching can be achieved in these structures by spatially modulating the second-order susceptibility along the growth direction.
Quantum Mechanical Capacitance in a Scanning Tunneling Microscope
Authors: Botkin D. , Weiss S. , Ogletree D.F. , Salmeron M. , Chemla D.S.
Published: February 2023

One of the most spectacular manifestations of quantum mechanics is tunneling between closely spaced conductors. The DC I-V characteristics in different types of tunnel junctions, such as metal-vacuum-metal junctions (MVM), metal-insulator-metal junctions (MIM), Josephson junctions, and quantum point contacts in a two dimensional electron gas, are well understood. High frequency transport in these systems is much less understood, and has been the subject of intense research in recent years[1,2].
Excitonic versus electronic Bloch oscillations
Authors: Dekorsy T. , Leisching P. , Ott R. , Bakker H. J. , Kurz H. , Köhler K.
Published: February 2023

We present the first comparative study of the interband and intraband dynamics of coherent Bloch oscillations in the Wannier-Stark regime of GaAs/AlxGa1-xAs superlattices. Transmittive electro-optic sampling (TEOS) and degenerate four-wave mixing (FWM) experiments, which are sensitive towards the electronic intraband and excitonic interband dynamics, respectively, are performed simultaneously. Frequency differences in both experiments are observed with a pronounced dependence on the electric field. This effect shows that the Bloch oscillations observed are mainly performed by excitonic states in FWM and by continuum states in TEOS. The observation of non-excitonic Bloch oscillations is of prime importance for electrically driven Bloch oscillations and for the observation of Bloch oscillations at room temperature.
Quantum Cascade Whispering Gallery Lasers
Authors: Gmachl Claire , Faist Jérôme , Capasso Frederico , Sirtori Carlo , Sivco Deborah L. , Cho Alfred Y.
Published: February 2023

Low threshold, single-mode quantum cascade whispering gallery lasers with emission wavelengths from 5.0 to 11.5 micrometer are reported. Their potential for true microcavities is discussed.
Type-II Superlattices for Infrared Optoelectronics and Lasers
Authors: Miles R. H. , Flatté M. E.
Published: February 2023

Interest in broken-gap, type-II heterostructures for optoelectronic applications is predicated largely on their promise as infrared lasers, detectors, and modulators appreciably outperforming conventional devices. Cryogenic imaging arrays based on these structures are projected to perform with higher detectivities and/or at higher operating temperatures than competing systems based on HgCdTe or extrinsic materials. Lasers in the 3-5μm spectral band are expected to operate at or near room temperature with significant output powers, and modulators with unusually low insertion losses and high dynamic range have been proposed. Brought to maturity, applications of such devices would be numerous, ranging from environmental monitoring systems to short-link, high bandwidth optical communications.
Field-Dependent Transverse Confinement within Selectively Oxidized Microcavities
Authors: Choquette Kent D. , Hadley G. R. , Hou H. Q. , Geib K. M. , Hammons B. E.
Published: February 2023

Buried oxide apertures within microcavities such as vertical-cavity surface emitting lasers (VCSELs)1,2, are effective to transversely confine both carriers and photons within the cavity.3,4 For small cross section area microcavities, the buried oxide layers will also introduce additional optical loss due to aperture scattering.5,6 To reduce the index confinement and optical scattering, the oxide apertures can be thinned and/or pulled away from the optical cavity to diminish the interaction between the fields and the oxide layers.5,6 We show that the induced transverse index confinement from the oxide apertures is dependent upon the relative overlap of the oxide with the longitudinal standing wave intensity within the cavity, regardless of the position or thickness of the oxide layers. The index confinement induced by the oxide apertures is determined from examination of the "oxide" lasing modes present under the oxide layers.3,7
Red-Emitting Semiconductor Quantum Dot Lasers
Authors: Fafard S.
Published: February 2023

The latest results will be presented on stimulated emission in electrically-injected laser structures based on an active region with O-dimensional density-of-states obtained by self-assembled growth.
An All-Silicon Integrated Light Emitter Technology
Authors: Hirschman K.D. , Tsybeskov L. , Duttagupta S.P. , Fauchet P.M.
Published: February 2023

The need for optoelectronic devices that are compatible with integrated circuit manufacturing technology has stimulated research in all-silicon light-emitting devices. Since crystalline silicon is an indirect bandgap semiconductor, its luminescence efficiency is low (~10-6%). Several approaches have been proposed to correct this deficiency [1,2], but so far porous silicon, which produces high-efficiency room-temperature visible photoluminescence [3], has attracted the most interest. Figure 1 shows the range of wavelengths over which strong luminescence can be achieved [4]. A major limitation of this material is that it is very reactive and inherently fragile, and thus cannot readily be integrated with conventional silicon process technology. We have overcome these limitations and we show that silicon-rich silicon oxide (SRSO) prepared by partial oxidation of porous silicon appropriate light-emitting and carrier transport properties and is compatible with conventional processing techniques. SRSO-based visible light-emitting devices (LEDs) have been successfully integrated into a standard bipolar fabrication sequence. This is the first demonstration of an all silicon visible light emitter / bipolar transistor optoelectronic integrated circuit.
Observation of Photonic Bandgap in GaAs 2D Crystal Fabricated by Selective Growth
Authors: Hamano T. , Hirayama H. , Aoyagi Y.
Published: February 2023

Photonic bandgap (PBG) crystals, consisting of periodic structures of two or more materials and with sizes on the order of optical wavelength have recently been extensively studied due to interest in both their physical properties and also in their possible applications to optoelectronic devices [1,2]. Analysis has shown that a 3-dimensional PBG crystal with designed-in phase shifts will control the direction of spontaneous emission due to its strong couping to localized optical modes in the bandgap. Thus a laser using a PBG crystal as its optical cavity can be expected to have a highly directional radiation pattern or high output efficiency [3]. A 1-dimensional crystal has already been utilized as a distributed Bragg reflector (DBR), and so it is necessary to demonstrate that 2-dimensional (2D) PBG crystal without phase shifts can be used as a reflector and then that a PBG crystal with inherent phase shifts may be fabricated inside a laser cavity.
Subwavelength Multilayer Binary Grating Design for Implementing Photonic Crystals
Authors: Tyan Rong-Chung , Sun Pang-Chen , Salvekar Atul A. , Chou Hou-Pu , Cheng Chuan-Cheng , Xu Fang , Scherer Axel , Fainman Yeshayahu
Published: February 2023

Subwavelength multilayer binary gratings (SMBG) can be seen as a 2-D periodic structures (see Fig.1a) with two periodic directions along the grating vector and the multilayer cascading direction. Such structures combine strong form- birefringence1,2 of the subwavelength grating with high reflectivity due the multilayer structure allowing us to design polarization sensitive microdevices, such as polarization selective mirror and polarizing beam splitter. Recently3 we introduce a new polarizing beam splitter (PBS) microdevice design built of SMBGs. Not only this novel design increases the angular and spectral range of the PBS microdevice in comparison to conventional PBS designs, but most importantly, our microdevice can operate with normally incident light, acting as a high-efficiency polarization-selective mirror. Microdevice with such features are critical for microlaser designs. Since the SMBG is a 2-D periodic structure, it can also be used to design a 2-D photonic crystal. In this manuscript, we summarize the design, modeling, and characterization of the SMBG structure designed to implement polarization sensitive microdevice, and also introduce and discuss a 2-D photonic crystal design based on SMBG.
Microfabrication Of Photonic Crystal Mirrors For Optoelectronic Devices.
Authors: Scherer A. , O’Brien J. , Cheng C.C. , Painter O. , Lee R. , Yablonovitch E. , Yariv A.
Published: February 2023

Photonic bandgap crystals are expected to be useful in defining microcavities for modifying spontaneous emission and as high reflectivity mirrors. Here, we use these photonic crystals as end-mirrors of edge-emitting GRINSCH lasers. These single quantum well lasers were grown by molecular beam epitaxy (MBE) and consist of waveguide structures which are in excess of 1.5 micrometers in thickness. To define a high-reflectivity photonic crystal mirror on the edge of these laser stripes, we use a surface mask of PMMA on top of an epitaxially deposited AIAs masking layer. After electron beam exposure of the resist and definition of the 100nm diameter holes through the GaAs cap layer and the 200 nm thick AIAs mask layer, high temperature field oxidation of the AIAs is performed at 340°C for 1.5 hours. This oxidizes the AIAs and forms a very robust etch mask. The hexagonal arrays of 100nm holes are then transferred to a depth of 2 microns through the laser waveguide structure so as to overlap with the optical field in the laser (Figure 1). The output mirror for the laser stripe consists of a standard cleaved facet.
New interpretation of quantum wire luminescence using a non standard description of the valence band states
Authors: Filipowitz F. , Marti U. , Glick M. , Reinhart F.K. , Wang J. , von Allmen P. , Leburton J.P.
Published: February 2023

Theoretical predictions1 have shown that confined structures, quantum wires (QWR) or quantum dots (QD), should have higher gain and absorption, compared to quantum wells, owing to the discontinuity in the joint density of states. We use a non standard description of the valence band states2 to evaluate the absorption of V-shaped quantum wires close to the band edge. We choose the projection axis of the angular momentum of the valence band states along the non-confined direction of the wire. This description has two advantages: (i) the masses are isotropic along the two confined directions and (ii) the light hole (lh) and heavy hole (hh) states are decoupled at kz=0, if the kinetic energy of the confined holes is the same along both confined directions and the energy separation between the {lh,hh}i and {lh,hh}i+1 subbands is high. This description is particularly advantageous close to the band edge where transitions are mostly excitonic. Photoluminescence (PL) and photoluminescence excitation (PLE) measurements made on V-shaped quantum wires are reinterpreted: the lowest energy transition is a e1-lh1 excitonic transition and the second lowest is a e1-hh1 excitonic transition. This new interpretation is the first to explain the lower intensity of the lowest energy peak observed in PL and PLE measurements. To assess the impact of the non-uniformity of the wires, we evaluate the absorption of V-shaped QWR (V-QWR) grown by MBE deposition over a non-planar substrate3.
Uni-Directional Radiation of Spontaneous Emission from 3D-Photonic Bandgap Crystal Cavity Laser
Authors: HIRAYAMA Hideki , HAMANO Tetsuko , AOYAGI Yoshinobu
Published: February 2023

3-dimensional(3D) photonic bandgap crystal is very attractive for the realization of thresholdless light sources because of controlling the lifetime and the radiation pattern of spontaneous emission by forming the localized impurity mode in the absolute forbidden band[1-3]. We proposed novel surface emitting laser diode consist of a 3-dimensional(3D) photonic bandgap crystal cavity[4]. The spontaneous emission is controlled to radiate into the lasing direction with narrow radiation angle by introducing a plane phase shift region into the photonic crystal. In this report, we for the first time show uni-directional radiation of the spontaneous emission from a 3D photonic bandgap crystal cavity laser by using a plane-wave method.
Time-Domain Measurements of Light Propagation in Dielectric Spheres
Authors: Whitten W. B. , Shaw R. W. , Barnes M. D. , Ramsey J. M.
Published: February 2023

There has been increasing fundamental and practical interest in the properties of dielectric microspheres in recent years. High-Q structural resonances that occur when the round trip optical path is an integral number of wavelengths can be exploited for quantum measurement and the observation of cavity QED effects. The spherical microparticle is also an important component of the earth’s atmosphere, contributing both to visual displays and global change. In this paper, we describe theoretical and experimental applications of optical pulse techniques to the characterization of dielectric spheres.
Practical Microcavities?
Authors: Jewell Jack
Published: February 2023

Summary not available.
Excitation- and Disorder-induced Reduction of the Superradiant Excitonic Decay in GaAs Quantum Well Bragg Structures
Authors: Kuhl J. , Hübner M. , Stroucken T. , Grote B. , Knorr A. , Koch S.W. , Hey R. , Ploog K.
Published: February 2023

The theoretically predicted rapid superradiant decay of coherent 2D
excitons on a time scale of approximately 10 ps [1] is expected to be
strongly enhanced in multiple QW (MQW) Bragg structures consisting of
N identical QWs separated by (Ga,Al)As barriers the thickness of which
was adjusted so that the QWs had a distance d equal to one half of the
heavy-hole exciton resonance wavelength λ in the medium [2]. This
enhancement originates from efficient radiative coupling of excitons
excited in different wells via the exchange of transverse photons.
Recently we have published [3] degenerate-four-wave-mixing experiments
with fs optical pulses on GaAs QW Bragg structures which demonstrate
that the radiative lifetime in high-quality GaAs single QWs (SQW) is
approximately 5 ps and decreases to less than 2 ps in Bragg samples
with N=10. These studies revealed that radiative recombination
provides the dominant contribution to the homogenous linewidth of the
2D exciton in high-quality samples and exceeds nonradiative
contributions caused by scattering with sample imperfections in
contrast to previous assumptions.
Wannier-Stark Wavefunction Spectroscopy in GaAs/GaAlAs Superlattices
Authors: Barrau J. , Khirouni K. , Than Do Xuan , Amand T. , Brousseau M. , Laruelle F. , Etienne B.
Published: February 2023

Rich structures of photocurrent spectra of GaAs/GaAlAs periodic superlattices under electric field allow detailed studies of the electronic Wannier-Stark wavefunction by comparison with simple calculations.
Physics of In(Ga)As-Based Heterostructures
Authors: Bastard G. , Ferreira R.
Published: February 2023

The In(Ga)As-based heterostructures appear promizing for the implementation of monolithic opto-electronic devices operating in the 1.5 μm wavelength. In (Ga)As-InP and In(Ga)As-In(Al)As are the two main families which are lattice-matched to InP substrates and which can be fabricated by Molecular Beam Epitaxy or Metal-Organic-Chemical-Vapor Deposition. These growth techniques allow the formation of abrupt interfaces which separate the well-acting (Ga(In)As) from the barrier-acting materials (InP or Al(In)As).
Femtosecond dynamics of excitonic absorption in the infrared InGaAs quantum wells
Authors: Wegener M. , Bar-Joseph I. , Sucha G. , Islam M.N. , Sauer N. , Chang T.Y. , Chemla D.S.
Published: February 2023

Excitons in III-V quantum wells (QW) are strongly coupled to polar longitudinal optical (LO) phonons. The binding energies of the quasi 2D excitons (Eb ≈ 1-10 meV) are smaller than the energies of the LO-phonons (ℏΩLO=30-40meV). Excitons are thus unstable against LO-phonon collisions which can ionize them and release a free electron hole pair with substantial excess energy. It is clear that this process is temperature dependent. At high temperature the collision rate increases and the excitonic life time can be reduced significantly. An experimental investigations of the dynamics of excitonic nonlinearities in GaAs QWs using femtosecond spectroscopic techniques, was able to time resolve the room temperature exciton ionization . An unexpected finding of these experiments was that a population of excitons is more efficient than electron-hole (e-h) plasma in reducing the strength of the exciton resonances. The experimental findings in GaAs QWs were qualitatively explained by a theory2 that accounts only for the effects of the Fermi statistic and completely neglects the long range screening. An extension of this theory was recently presented by Zimmermann3 which uses an elegant technique to performe exact infinite summations over all excitonic states (bound and unbound).
Density dependence of recombination rates in a gated GaAs/AlGaAs modulation doped quantum well
Authors: Peter G. , Fischer R. , Göbel E.O. , Liu H.W. , Delalande C. , Bastard G. , Voos M. , Brum J.A. , Weimann G. , Schlapp W.
Published: February 2023

During the last years the physical properties of modulation doped quantum wells (MDQW) have attracted much attention from both a device as well as from a fundamental physics point of view. With these structures a degenerate one and more component Fermi system of reduced dimensionality can be realized, and e. g. many body effects can be investigated by means of optical spectroscopy /1-4/. In this paper we report on experimental studies of the carrier density dependence of the recombination dynamics. We have investigated a 13 nm wide n-type single MDQW by means of picosecond photoluminescence (PL) spectroscopy at low temperature (T = 4K). An external voltage perpendicular to the quantum well layer can be applied via a Schottky contact (evaporated on the surface of the sample) in order to vary the electron concentration in the quantum well between ns = 0 up to about 3 • 1011 cm-2 (details are reported in ref. /2,5,6/). Consequently, we can cover the regime where excitonic recombination takes place up to densities where the optical properties are governed by a one component free carrier plasma. We thereby have avoided the crucial disadvantage of comparing different samples, where the sample to sample variations of well width, interface quality, PL efficiency etc. complicate the physical interpretation.
Enhancement of the Radiative Lifetime of 2D Excitons in a GaAs Quantum Well by Dephasing Collisions
Authors: Kuhl J. , Honold A. , Schultheis L. , Tu C.W.
Published: February 2023

The nonlinear optical properties and the ultrafast dynamics of excitons in semiconductors are a major field of present semiconductor research. This interest is explained by the potential applications of excitonic nonlinearities as ultrafast optical switching devices in future optical communication systems. In a recent theoretical paper Hanamura /1/ discussed the advantages of excitons in a quantum well (QW) as a nonliner optical medium combining large 3rd order nonlinear susceptibility χ(3) with a fast response. The strong enhancement of is χ(3) explained as a consequence of both the macroscopic transition dipole moment of the exciton in a QW and the rapid radiative decay of the confined excitons. Hanamura calculated that an exciton in a QW should decay superradiantly through its macroscopic dipole transition moment within a few picoseconds. This superradiant decay requires, however, a coherent polarization of the material and will be strongly reduced if the spatial and temporal coherence of the excited excitons is destroyed by interaction of the excitons with their environment. Such a tight connection between the radiative lifetime τ
r
and the dephasing T2 has been recently predicted by Feldmann et al. /2/.
Two-photon Absorption Spectroscopy in GaAs Quantum Wells
Authors: Tai K. , Fischer R. J. , Slusher R. E. , Cho A. Y. , Mysyrowicz A.
Published: February 2023

Two-photon absorption spectroscopy1,2 is a powerful method of investigating electronic properties of solids. Because the transition selection rules are different from those for linear absorption, levels which are not accessible in conventional one-photon spectroscopies can be observed. In this letter, we apply two-photon absorption spectroscopy to the study of quantum well structures.3 In GaAs/AlGaAs quantum wells, spectral features due to two-photon transitions and specific to quantum confinement were seen. The results demonstrate that the two-photon technique is well suited for extracting several important parameters of these artificial structures.
Optimum Electroabsorption in Quantum Wells as a Compromise between Exciton Confinement and Linewidth Broadening
Authors: Jelley K.W. , Engelmann R.W.H. , Alavi K. , Lee H.
Published: February 2023

The dependence of electroabsorption in GaAs/AlxGa1-xAs multiple quantum well (MQW) structures on well width (Lz) is of considerable importance in optimizing optical modulation devices.1,2 However, a complete characterization including the narrow well width limit has still been lacking. Previously, we have reported that for GaAs/Al0.32Ga0.68As MQWs with 100 Å barriers the maximum obtainable change in the absorption coefficient (Δαmax) increases monotonically with decreasing Lz (from 260 to 50 Å) at the cost of an increasing applied electric field (εmax).2 It was predicted that a peak value would be reached near Lz = 25 Å, being limited at lower Lz by either dielectric breakdown or reduced carrier confinement in the well. In order to determine the complete well width dependence of band edge electroabsorption in GaAs/AlxGa1-xAs MQW structures, our experiments were extended to cover the range from 47 to 17 Å. We demonstrate that this range does indeed contain an optimum value of Lz that provides a peak value in Δαmax. But contrary to our prediction, we shall show that enhanced broadening of the heavy hole excitonic resonance, resulting from phonon scattering at small Lz, is responsible for this result.
Two Dimensional Band Gap Engineering in III-V Compounds Semiconductors: Aplications to Quantum Wire Structures and Devices.
Authors: Petroff P.M.
Published: February 2023

Two dimensional band gap modulation in GaAs-AlGaAs structures grown by MBE is demonstrated using several approaches. In the first method a tilted superlattice (TSL) having interface planes tilted with respect to the substrate surface is directly grown by MBE. The growth process and the growth kinetics will be described in detail. The luminescence properties of undoped quantum wells grown by the TSL method will be reported. This method has been used to produce directly by MBE quantum wire superlattices which show the effects of the 2 dimensional carrier confinement in their polarization excited luminescence spectra. These effects will be described and compared to theory. Finally, we will describe the luminescence characteristics of quantum wire and quantum box dense arrays produced by Focused Ion Beam enhanced interdiffusion in GaAs-AlAs quantum well structures. Applications of these various structures to optoelectronic devices will be discussed.
Quantum-Well SEED Optical Pulse Generator
Authors: Giles C. R. , Wood T. H. , Li Tingye , Burrus C. A.
Published: February 2023

Some photonic circuits require optical pulse generators to provide clock pulses for optical logic elements. For example, a recently reported all-optical regenerator [1] used an injection-locked self-electro-optic-effect-device (SEED) oscillator [2] to recover optical clock pulses. The SEED oscillator is a simple optical circuit, consisting of only a quantum-well SEED electrically biased through a resonant LC circuit. By illuminating the SEED with cw light, it can exhibit negative conductance, causing the electrical circuit to oscillate. The voltage oscillations modulate the SEED’S-optical absorption so that light is transmitted through the SEED as a train of pulses.
InGaAs-GaAs Strained Layer Quantum Well Buried Heterostructure Lasers (λ> 1 μm) by Metalorganic Chemical Vapor Deposition
Authors: York P. K. , Beernink K. J. , Fernández G. E. , Coleman J. J.
Published: February 2023

The buried heterostructure (BH) laser1 is one of the most attractive index guided stripe geometry semiconductor lasers because of the combination of strong lateral index guiding and absolute current confinement provided by a heterostructure discontinuity in the lateral direction. This structure is difficult to fabricate, however, because of the need for processing high quality narrow stripe etched mesas with a high quality regrowth interface at the edges of the active region. The regrowth is especially difficult2 for AlGaAs-GaAs BH lasers having higher aluminum composition confining layers. Various1,3-8 AlGaAs-GaAs BH laser structures have been reported. In this work, we report the characteristics of long wavelength (λ> 1 μm) strained layer InGaAs-GaAs-AlGaAs quantum well buried heterostructure lasers9-11 formed by wet chemical etching and a two-step MOCVD growth process. The relatively low aluminum composition of the confining layers allows for high quality regrowth interfaces and effective use2,12 of a silicon dioxide mask for selective epitaxy limited to the etched regions. The structures reported here have active region stripe widths of ~3.5 μm, an emission wavelength of λ ~ 1.074 μm, and threshold currents of less than 7 mA (cavity length 405 μm). Output powers in excess of 130 mW per uncoated facet with total differential quantum efficiencies of greater than 60% have been observed. Near-field patterns indicate that the lasers are operating on a fundamental lateral mode and are stable to more than thirty times laser threshold.