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Fabrication of SU-8 slab- and ridge-waveguides with holographic grating for DFB laser, effectively utilizing nanoimprint technology (NIL), is presented. Rhodamine-6G-doped SU-8 slab- and ridge-waveguides were embedded in grooves defined by NIL in UV curable resin. Utilization of NIL made it easier to form such a three-dimensional micro structure consisting of ridge stripe and fine corrugation grating. TE-polarized 587nm laser and TE-polarized 594nm light emissions were observed from the slab- and ridge-waveguides, respectively, when the waveguides were irradiated by 532nm pulsed Nd:YAG laser.

We fabricated quantum well (QW) microtubes by rolling up thin films containing QWs and measured their photoluminescence (PL) properties. Before fabricating microtubes, no PL signal is observed in the QW at all, because their band configuration is indirect, i.e., type-II. However, PL signal is detected in the QW microtubes. This result clearly indicates that the transition from type-II to type-I band configuration of QW microtubes is induced by uniaxial-strain effect.

The explicit model of a lateral p–n junction tunneling transistor is developed and the current–voltage characteristics are obtained.

We have developed a system of compositing three-dimensional (3D) video images based on the depth information of the objects. The system consists of the Axi-Vision Camera that can measure object distance in real time and an arithmetic image processor that can synthesize video images according to the depth information. The paper demonstrates how to three-dimensionally synthesize such a scene as an array of computer-generated characters moving around a standing person in real time. The feasibility of using such a signal processor to create realistic TV programs in a broadcasting station has been studied.

Chaotic signals with a flat power spectrum over 20 GHz have been generated using two commercially available semiconductor lasers coupled in a unidirectional master-slave scheme. The master laser has an external optical feedback that induces optical chaos in the laser output. A part of the chaotic light output from the master laser is injected into the slave laser. We experimentally demonstrated the generation of broad-band signals up to 22 GHz using lasers whose relaxation oscillation frequency in the free-running state is only around 6.4 GHz. We also show that the experimental results can be well reproduced by numerical simulations using two coupled rate equations. The numerical investigation shows that the high-frequency broad-band signal generation is owing to two key effects: high-frequency oscillations as a result of beating between the master and slave laser lights, and spectrum flattening due to the injection of the chaotic signal. The flatness, stability, and tunability of the power spectra demonstrated in our experiments suggests that the proposed system can be potentially useful for generation of high-frequency broad-band random signals.

InAs QDs on GaAs substrates were grown by molecular beam epitaxy (MBE). The dot density and properties were studied by atomic force microscopy (AFM). The low temperature photoluminescence (PL) characteristics of InAs QDs with different cap layers are discussed. The results suggest that InAs QDs covered by two InGaAs layers with different indium composition have long wavelength emission without much reduction in the PL intensity.

We experimentally investigate the synchronous response of a semiconductor laser to the injection of a periodic or chaotic oscillating optical signal that is generated by a similar semiconductor laser with optical feedback. We show that there are two different types of synchronous response, appearing in separate regimes of laser frequency detuning and injection strength. They are distinguished by the time lag of the slave-laser response with respect to the injection signal from the output of the master laser. The experimental observations are well described by a numerical model consisting of a set of rate equations. It is revealed that the first type of synchronous response corresponds to the complete synchronization solution of the equations and the second type of response is the result of strong driving. The relevance of these two types of synchronous behavior to a number of recent experiments on chaos synchronization and their implications for data encoding/recovery using chaotic carriers are discussed.

We show that modulated near-infrared radiation can generate terahertz plasma oscillations in the channel of a high-electron mobility transistor. This effect is associated with a temporarily periodic injection of the electrons photoexcited by modulated near-infrared radiation into the transistor channel. The excitation of the plasma oscillations has the resonant character. It results in the pertinent excitation of the electric current in the external circuit that can be used for generation of terahertz electromagnetic radiation.

We study the performance of a lateral p–n junction quantum-well edge-emitting laser-transistor with an extra gate contact. The incorporation of the gate contact provides an opportunity to control the threshold current and output optical power by the gate voltage. The application of negative gate voltages can lead to a substantial decrease in the threshold current. This is due to the confinement of the electrons injected into the p-type portion of the quantum well serving as the active region. Using the developed device model, we calculate the laser-transistor threshold and output characteristics. We also estimate the device cutoff modulation frequency associated with the gate recharging.

We have investigated coherent LO phonon–plasmon coupled (LOPC) modes in an (InAs) 1 /(GaAs) 30 strained-layer superlattice (SL) with a miniband structure. By generating carriers in the miniband, the GaAs-like LOPC modes are observed. In spectrally resolved pump–probe measurements, it is found that the intensity of the lower branch (L − ) of the LOPC mode is enhanced around the transition energies at the miniband critical points, the mini-Brillouin-zone center and edge. In addition, the decay time of the L − mode in the SL hardly depends on the detection energy. These properties of the LOPC mode will be discussed from the viewpoint of the effect of the miniband structure.

We fabricated micro-tubes containing two GaAs/AlGaAs quantum wells (QWs) in a section of the tube layer, and studied the optical properties of the embedded QWs. A multilayer structure composed of GaAs and AlGaAs layers and a lattice-mismatched InGaAs layer was epitaxially grown on a GaAs substrate by MBE. This multilayer structure rolled up by the built-in strain when it was freed from the substrate. By measuring the photoluminescence peak shift of the QWs caused by the uniaxial strain, we were able to determine the radial profile of the strain within the micro-tube wall.

In order to correct the color deviation due to variation of illumination in film shooting, a liquid-crystal filter with dichroic dyes that can control the color temperature of the transmitted light in real time has been developed. By using Planck's radiation rule and the Lambert–Beer law, the absorption spectra of the dyes are designed. It is found that the color balance can be adjusted continuously between 4450 and 2530 K. The time needed for control is about 80 ms. When a liquid-crystal filter is used for actual television film shooting, it is confirmed that the color balance of the image can be corrected naturally. The present device is useful in location film shooting for television when the color temperature of the image changes drastically under such conditions as the lighting changing from indoor light to solar light. © 2001 Scripta Technica, Electron Comm Jpn Pt 2, 84(10): 40–48, 2001

We have investigated coherent longitudinal optical (LO) phonons in GaSb/AlSb superlattices. The coherent AlSb-like LO phonon in the barrier layer and the coherent GaSb-like LO phonon in the well la...

We developed an analytical device model for lateral p-n junction vertical-cavity surface-emitting lasers (LJVCSELs) with a quantum well active region. The model takes into account the features of the carrier injection, transport, and recombination in LJVCSELs as well as the features of the photon propagation in the cavity. This model is used for the calculation and analysis of the LJVCSEL steady-state characteristics. It is shown that the localization of the injected electrons primarily near the p-n junction and the reabsorption of lateral propagating photons significantly effects the LJVCSELs performance, in particular, the LJVCSEL threshold current and power-current characteristics. The reincarnation of electrons and holes due to the reabsorption of lateral propagating photons can substantially decrease the threshold current.

We developed an analytical device model for quantum well lateral p-n junction photodiodes (LJPDs). The model takes into account the features of the carrier transport in LJPDs and their geometry, which ensure short transit times and a low capacitance. This model is used for calculating the LJPD's characteristics as functions of the signal frequency, bias voltage, and structural parameters and for the estimation of the LJPD ultimate performance.

A brightness-enhanced full-color projection display using optically addressed spatial light modulators (SLMs) with light-scattering mode polymer-dispersed liquid crystal has been developed. The SLM can modulate strong unpolarized light efficiently using the light-scattering effect. The projector using SLM with a Schlieren optical system produces bright, high-contrast images. Electrical image compensation of the shading and gamma characteristics of the SLMs carried out in the driving circuits improves the spatial uniformity and grayscale representation of the projected images. The system projects a bright image of more than 1300 cd/m/sup 2/ with a high extinction ratio over 130:1 on a 60-inch screen, which can be viewed in a bright living room under normal lighting conditions.

This paper reports the important effects of frequency-locking in an electro-optical bistable system with long delay. The mechanism of the locking behaviour is discussed from the viewpoint of power spectrum and the linear eigen modes of the system.

A high-speed controllable polarizing filter has been developed to eliminate obstructive polarized light reflected from glass and watery surfaces for image pickup in video media program producing and marine dynamic remote sensing. In this device, the polarization plane of incident light is rotated through 0°, 45°, 90° or 135° by an electrically-controllable polarization rotator composed of 45° and 90° twisted nematic liquid crystal cells, and the polarization component of reflected light is absorbed by a fixed polarizing film. It selectively absorbs more than 80% of incident white light linearly polarized in an arbitrary direction. With the drastic reduction of reflected light, the object images hidden by the bright reflected light are clearly captured in real time. Another type of polarizing filter, using a guest-host liquid crystal cell instead of the polarizing film, controls light absorption as well as polarization angle.

We have been developed a video camera system using an electrically-controllable liquid crystal polarizing filter for television program production, which can quickly reduce undesirable reflected light from a window pane or watery surface, by automatically judging the polarization state of incident light from the change in video signal intensity. More than 80% of linearly-polarized incident light is removable by this method for all incident polarization angles. The time required for detecting and reducing reflected light is approximately 0.3s in our system. The drastic reduction of polarized light reflected from glass and watery surfaces was demonstrated, and object images obscured by bright reflected light were clearly captured in an instant.

Effects of small signal injection on an electro-optical bistable system with a very large delay are theoretically and experimentally investigated from the viewpoint of linear stability analysis. The resonance phenomena and frequency locking are observed when sinusoidal and rectangular small signals are additively injected into the system. Experiments confirm that theoretical results obtained by linear stability analysis are good predictions of the effects of both resonance and frequency-locking phenomena and show the dependence of these phenomena on the system parameters. As an application of the frequency locking phenomenon to the dynamical memory, the phase identification of the memory oscillation using the frame pulse externally injected is successfully executed.

Micromirrors were fabricated by the micro-origami technique. This technique allows the fabrication of simple and robust hinges for movable parts, and it can be applied to any pair of lattice mismatched epitaxial layers, in semiconductors or metals. A multilayer structure, including AlGaAs/GaAs component layers and an InGaAs strained layer, was grown by molecular beam epitaxy on a GaAs substrate. After definition of the hinge and mirror’s shape by photolithography, the micromirrors were released from the substrate by selective etching. They moved to their final position powered by the strain release in the InGaAs layer. Optical actuation was achieved by irradiation with the 488 nm line of an argon laser, and the mirror’s position was measured by sensing the reflection of a He–Ne laser. Continuous wave irradiation with a power density of 450 mW/mm2 produced an angular deflection of the mirror of around 0.5°. The frequency response of the mirrors shows a resonance at 25 kHz.

We fabricated SiGe/Si free-standing micro-objects on a silicon-on-insulator (SOI) substrate using the SiO2 sacrificial layer. SiGe/Si strained films were grown by molecular beam epitaxy on SOI substrates. The films were released from the substrate by selective etching of the SiO2 layer. The released films rolled up due to the elastic strain in the SiGe layer. Microtubes and microspirals with a diameter of about 40 μm were obtained.

We fabricated and experimentally investigated a nanostructure known as a quantum-well (QW) microtube, which is a fine tube with a micron- or nanometer-order diameter fabricated by rolling a semiconductor GaAs QW. Although the wall thickness is only 40 nm, the system retains the quantum properties of a QW, and photoluminescence from the QW subband can be clearly observed. Even though the QW width is sufficiently small to make the QW subband type-II band-aligned, a type-II to type-I transition caused by uniaxial strain in the microtube allows for optical emission.

A "micro-origami" method of surface micromachining has recently been proposed. The method is based on the rolling of thin strained films detached from substrate into tubes or coils. A number of free-standing structures such as a standing plate and a back reflector were fabricated. In this paper we demonstrate an array of corner plates standing at preset different angles as an example of three-dimensional components for micro-electromechanical system.

Edge-emitting InGaAs/GaAs laser diodes were grown on patterned GaAs (311)A-oriented substrates. Due to the amphoteric properties of Si as a dopant in high-index GaAs, a device with a lateral p–n junction was obtained. CW lasing was observed up to 200 K. The dependence of the threshold current with temperature was measured. The characteristic temperatures were T0=180 and T0=57 K for experimental temperatures below and above 100 K, respectively, meaning that the carrier confinement structure must be improved. Quantitative results of the cavity gain were experimentally obtained.

A light-emitting diode array was fabricated using a lateral p–n junction to inject carriers in the InGaAs active layer. The lateral p–n junction is formed in GaAs epilayers doped only with silicon and grown by molecular beam epitaxy on a patterned GaAs (311)A-oriented substrate. This design allows the use of electrically insulating carrier-confining barriers and coplanar contacts while simplifying device process. Light emission is uniform all over the 1200 dpi array and electroluminescence spectrum has a single peak at 960 nm.

A method to make two types of hinges which bend toward opposite directions from the same epitaxial layers using the micro-origami technique is proposed and successfully applied to make standing micro-stages on a GaAs substrate. This method opens a path to fabricate more complex three-dimensional self-positioned micro-machined structures.

We propose an effective method for carrier injection into the high-energy Γ ground state in a narrow quantum well (QW) in asymmetric double QW systems using Γ–X–Γ electron transfer and simultaneous hole tunneling. Although the high-energy state is type-II band-aligned for the electrons, our method enables an efficient injection of both electrons and holes into the same narrow QW, and it thus demonstrates relatively strong light emission from the higher energy state.

We introduce a method to make self-positioned micromachined structures by using the strain in a pair of lattice-mismatched epitaxial layers. This method allows the fabrication of simple and robust hinges for movable parts, and it can be applied to any pair of lattice-mismatched epitaxial layers, in semiconductors or metals. As an application example, a standing mirror was fabricated. A multilayer structure including an AlGaAs/GaAs dielectric mirror and an InGaAs strained layer was grown by molecular-beam epitaxy on a GaAs substrate. After releasing the multilayer structure from the substrate by selective etching, it moved to its final position powered by the strain release in the InGaAs layer.

This paper presents a novel SU-8 polymer-based grating light modulator fabricated using conventional process technology which requires no expensive equipments and materials. A set of fifty 2.5μm-thick SU-8 micro beams of 20μmwidth x 100μm-length is patterned by photolithography on the aluminum sacrificial layer to form a grating. The micro beams are arranged in parallel with an inter-beam gap of 20μm. The wide inter-beam gap tolerates low patterning precision. Narrow air gaps of 0.5μm beneath the micro beams are formed by combination of wet-etching of the aluminum sacrificial layer and freeze drying method, where cyclohexane is chose as sublimation liquid because of the high freezing point and the ease of sublimation. When a voltage is applied across the upper and lower electrodes to attract the micro beams to the substrate, neighboring micro beams are actuated to deflect in phase and the optical path length between the upper electrode/mirror on the micro beam and the lower mirror on the substrate decreases by quarter wavelength, the 0th and 1st order diffracted light intensities vary from maximum and minimum, respectively, or vice versa. The voltage to obtain maximum modulation for HeNe laser beam of 632.8nm wavelength is 70V. The rise and fall response times of the light modulation are 3.08 microsecond and 4.63 microsecond, respectively.

The camera described here makes color TV images that include information about the distance between the camera and the objects in the images. This range information is obtained from two images of the same scene taken under different illumination conditions. The camera does not require scanning, multiple camera units, or complicated computation. Range information for each pixel is acquired fast enough to keep up with the video rate of a TV camera. We describe various operational features and technical specifications such as ranging errors as well as the results of experimental investigations of the dependence on the color and reflectivity of the objects, of the sensitivity to interference from external light, and of the effects of the movement of the objects.

We have developed an improved version of a high-definition real-time depth-mapping Axi-Vision Camera that enhances the speed of the depth detection, reduces external light interference, and is more compact. The new depth-detection method uses a high-resolution, fast-frame-rate CMOS sensor with a rolling shutter. The depth is calculated from four near-infrared light (NIR) images in successive video frames to cancel the effects of external light interference. Therefore, the external light interference immunity is improved so that the depth information can be detected accurately under external light at an intensity up to 30% of that of NIR light illumination. Furthermore, the compact-imaging optical system is achieved by using a specially designed HDTV camera lens, which internally separates only NIR light and provides NIR images on an image intensifier coupled with a CMOS sensor. Further compact sizing of the camera system is achieved by arranging specially developed small, high-power reflection-type LED arrays for the NIR illumination around the camera lens. As a result of this compact sizing, the volume is 1/5 that of the prototype system. We also demonstrated a method to obtain 3-D information from image data captured by this Axi-Vision Camera.

We fabricated quasi-stadium laser diodes whose resonators consist of two concentric curved end mirrors and two straight sidewall mirrors. We observed two lasing modes that correspond to different beam propagations along the cavity axis and along a ring trajectory, and different far-field patterns with wide angular separation. The modes can be selected by control of an electrode pattern. We also show that the far-field patterns numerically obtained by the extended Fox-Li mode calculation method are in good agreement with the experimental results.

Versatile three-dimensional (3D) image data as in the form of I(X,Y,Z) defined in the camera coordinate system are acquired from sets of color image and depth image, which are simultaneously captured at a video frame rate by a 3D camera named Axi-Vision camera. The X and Y coordinates are calculated from the image coordinates (x, y) on the image plane of CCD based on the perspective projection theory. The Z coordinate can be obtained for each pixel of the color image directly from the depth image without any complex processing. Thus, the 3D image data of objects, I(X,Y,Z), is obtained from the relation between the camera coordinate and the image coordinate systems. A stereoscopic video image display is demonstrated using the 3D image data using an integral photography (IP) system, which combines a 4- inch VGA liquid crystal color display panel and a pinhole array. Aliasing, an issue from mismatch of image qualities between the 3D image data and the IP system, is effectively suppressed by pre-processing the color Axi-Vision image data using a two-dimensional lowpass filter, which is designed based on analyses of the maximum spatial frequency of the 3D image transformed appropriate for the LCD size and the Nyquist spatial frequency of the IP system.

Optoelectronic devices based on lateral junctions are particularly interesting because carriers are injected perpendicular to both the optical cavity and the direction of quantum confinement (i.e. the epitaxial growth direction). An edge-emitting InGaAs/GaAs laser diode with a lateral p-n junction was fabricated by MBE on a patterned GaAs (311)A substrate. The injection current dependence of the multimode emission was studied. Experimental results revealed a gain spectrum that favors long-wavelength modes as injection current increases.

We demonstrate up-converted light emission from an asymmetric double quantum well (QW). Carriers in the wide QW, which are photogenerated by a long wavelength light, are transferred and collected into the adjacent narrow quantum well by using /spl Gamma/-X-/spl Gamma/ electron transfer and simultaneous hole tunneling, thus generating short wavelength light emission.

MBE grown self-organised InAs QDs on GaAs (100) and (n11) substrates have been investigated by AFM and PL. The results show that substrate orientations have a strong effect on the properties of QDs. The dependence of PL for different oriented substrates has been examined. It was found that, by reducing the strain and quantum confinement in InAs QDs, long-wavelength PL emission was obtained.

We present a device model for a lateral p-n junction quantum-well edge-emitting laser-transistor with an extra gate contact. Such a contact provides an opportunity to control the confinement conditions of the electrons injected into the active region and, as a consequence, the threshold current and output optical power by the gate voltage. Using the proposed model, we calculate the laser dc characteristics and estimate its modulation performance. We show that the application of negative gate voltages can lead to a substantial decrease in the threshold current. The estimated cutoff modulation frequency associated with the gate recharging can be much higher than those associated with the photon and electron lifetimes.

Micro Opto-Electro-Mechanical Systems (MOEMS) technology is expanding the potential of device technologies in regard to fabrication methods as well as device performance. We proposed and successfully demonstrated a simple method named Micro-Origami to make self-positioning micro-machined three-dimensional structures by using the strain in a pair of lattice-mismatched GaAs/InGaAs epitaxial layers grown on GaAs substrates. Micro-Origami is expected to become a viable fundamental technique for developing MOEMS devices with complex three-dimensional structures. However, the precision of the three-dimensional structures fabricated by Micro-Origami is supposed to be strongly affected by the fabrication process, because of the self-positioning mechanism. In this paper, we report on the fabrication of a free-standing plate and a retro-reflector, as examples of Micro-Origami devices, and discuss the design and fabrication precision.

We have observed lasing in a complicated eigenmode of a quasi-stadium laser diode with an unstable resonator consisting of two curved end mirrors obeying an unstable resonator condition and two straight sidewall mirrors. The laser was fabricated by application of a reactive-ion-etching technique to a molecular beam epitaxy–grown graded-index separate-confinement heterostructure single-quantum-well GaAs/AlGaAs structure. The far-field pattern shows that the lasing mode corresponds to the complicated lowest-loss mode obtained numerically by an extended Fox–Li method.

We present an analytical device model for quantum well lateral p-n junction photodiodes (LJPDs) which takes into account the features of the carrier transport in LJPDs and their geometry. These features ensure short transit times and a low capacitance. The developed model is used to calculate the LJPD characteristics as functions of the signal frequency, bias voltage and structural parameters.

Scar wave functions in a fully chaotic cavity are obtained numerically by an extended Fox-Li method. Lasing on the scar modes are observed in a semiconductor microcavity with a selective excitation of different scars controlled by corresponding shape of electrodes for current injection.

This paper proposes and demonstrates a scheme for generating pseudo-random wavelength hopping sequences in semiconductor lasers by using chaotic dynamics. The system consists of a wavelength tunable light source, a nonlinear wavelength element, and a delayed opto-electric feedback. By feeding back the filter output signal to the light source to control the lasing wavelength, it is possible to achieve periodic or chaotic wavelength variation patterns with a wide variation range covering several longitudinal modes. In experiments, wavelength hopping among up to 10 modes was observed with the hopping frequency about 100 MHz. Synchronization of the wavelength hopping in two separate lasers is performed by coupling part of the feedback signal of one laser into the feedback of a second laser. Synchronization was observed between the on-off intensity modulation patterns of each pair of corresponding longitudinal laser modes.