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For a multimode-optical-fiber surface plasmon resonance (SPR) sensor with a gold film supporting surface plasmon waves (SPWs), we have investigated the effects of gold thickness on sensor performance experimentally to find the optimal thickness when a white-light source is used. It is found that the sensor with a thickness of around 65 nm enables most precise measurement of a resonance wavelength and gives relatively high sensitivity, which is 1557 nm/RIU in the refractive index range of 1.333–1.3469. Also, we have confirmed that a simulation model based on meridional rays cannot explain the minimum reflectance of SPR spectra for values below 0.5.

In this paper, we present the fundamental characteristics of a novel dual-colour optical fibre surface plasmon resonance (SPR) sensor for a portable low-cost sensing system. The principle of the proposed SPR sensor is based on the differential reflectance method. Light from two light-emitting diodes (LEDs), which are flashing alternately with different wavelengths, is fed to a sensor via two optical couplers. The reflected light is detected by a photodiode. Changes of reflectance at two wavelengths are proportional to the refractive index change of the medium of interest. Taking the difference in reflectance at two wavelengths improves the sensitivity almost twofold. Measuring ethanol solutions with different refractive indices reveals that the sensor has a linear response to the refractive index change from 1.333 to 1.3616. By measuring the stability in the time response we estimate that the limit of detection (LOD) of the refractive index is 5.2 × 10−4.

Electronic-optical conversion efficiency of 11.4% in a vertical-to-surface-transmission electrophotonic device with a vertical cavity is reported. Reduction of the electrical resistance by the double mesa structure, efficient confinement of carriers in the active region by the proton implanted structure, and photon recycling by sidewall reflectors lead to this high conversion efficiency. Efficiency over 10% is achieved for the first time in surface-emitting devices. >

We realized extremely high absolute thickness controllability around ±0.3% in molecular beam epitaxy growth of distributed Bragg reflectors, using a modified reflection high energy electron diffraction oscillation measurement technique. Very low threshold current density and high efficiency were obtained in InGaAs/AlGaAs surface emitting lasers by using this technique and a new periodically doped distributed Bragg reflectors.

The vertical to surface transmission electrophotonic device has a laser cavity covered with plated gold, which has high reflectivity. The laser light is emitted from the distributed Bragg reflector (DBR) with no gold. Consequently, spontaneous emission remains in the laser cavity, and the carriers are regenerated. The injected carriers are converted to light and spontaneous emission is reconverted to carriers. Due to photon recycling, threshold current density decreases and indistinct threshold laser operation is obtained. In the indistinct threshold operation, the light output is linearly polarized. The submode suppression ratio is larger than 25 dB, and the divergence angle of a far field is as narrow as 6.8 degrees . The indistinct threshold laser characteristics lead to high slope efficiency in low current level. To achieve high slope efficiency in the overall current level, DBR mirrors are designed, and high slope efficiency of 0.32 mW/mA is obtained. >

Surface emitting laser operation and optical switching operation are demonstrated in vertical-to-surface transmission electrophotonic devices using pnpn structures and vertical cavities. Threshold current density as low as 1.4 kA cm−2 for laser operation and optical switching energy as low as 2.2 pJ for optical switching operation are achieved. It is found that optical switching energy can be lowered by multireflections in the vertical cavity. Growth rate calibration and series resistance in the distributed Bragg reflector mirrors are examined for device fabrication.

With the continuing development of biotechnology and nanotechnology, a miniaturized and integrated device that is capable of controlling and measuring a small droplet has become desirable. Using a surface acoustic wave (SAW), a droplet is manipulated. If the sensor is fabricated onto the SAW propagating surface, a novel sensor and actuator integrated system, namely digital microfluidic system, is realized. The integrated device is called a “micro-laboratory.” In this paper, to actualize a disposable micro-laboratory, three-layer structure of sensor plate/ matching layer/ piezoelectric substrate is examined. Droplet manipulation, mixing and measurement are succeeded using the proposed novel micro-laboratory.

In this paper we present practical capability of a dual-color optical fiber surface plasmon resonance (SPR) sensing system for measuring the refractive index (RI) of liquids. The sensor system consists of two LEDs, two optical couplers, a photodiode and an electronics followed by a laptop computer via an A/D converter. Features of the developed system are compact, portable and inexpensive. Principle of the proposed SPR sensing system is based on the differential reflectance method. Changes of reflectance at two wavelengths are proportional to the refractive index change of a sensed medium. Differential of two reflectance gives two-folded sensitivity. Three liquids with different RI ranges were tested. Also the reproducibility of measured data was checked. As a result, it was demonstrated experimentally that the dual-color optical fiber SPR sensing system is capable of measuring the RI of liquids over the range of from 1.329 to 1.36 with the RI resolution of 2.35 × 10-4.

The authors experimentally study the effect of a sidewall reflector on current versus light-output characteristics in a pnpn vertical-to-surface-transmission electrophotonic device with a vertical cavity. The distributed Bragg reflectors that form the vertical cavity for laser oscillation and the sidewall reflector retain spontaneously emitted photons in the optical cavity, and only the photons that have the resonance wavelength of the vertical cavity are emitted. As a result, spontaneously emitted photons are absorbed and the carriers are regenerated; that is, the injected carriers are converted to light, and spontaneous emission is reconverted to carriers. As a result of photon recycling of spontaneous emission, threshold reduction is expected. Threshold reduction by at least a factor of 4 is obtained with a device that has the sidewall reflector. >

The dependence of threshold current density on indium composition in strained InGaAs/AlGaAs quantum well lasers is examined. A threshold current density (J th) as low as 115 A/cm2 is obtained in a chip with a 500 µm long cavity at a lasing wavelength of 950 nm. The J th for a strained InGaAs QW was found to be 35% less than that for a GaAs QW laser with the same cavity length. Time resolved photoluminescence measurement revealed that the improvement in the nonradiative carrier lifetime for quantum wells with higher indium composition was limited to a J th improvement of only 10%. Calculation suggests that the most likely reason for the major portion of the J th improvement is gain enhancement due to a reduction in heavy hole mass.

Bidirectionally cascadable optical pixels that consist of a single-vertical-cavity surface-emitting laser (VCSEL) thyristor and a double-vertical-cavity phototransistor are proposed. Despite almost identical layer structures, each device characteristic can be independently optimized by introducing a lambda /2-spacer layer into the phototransistor section. A lasing threshold of 0.8 mA and a slope efficiency of 0.25 W/A are obtained for the laser thyristor, and a flat-topped photocurrent spectrum over 30 A and a photocurrent gain of 70 A/W are obtained for the phototransistor at the resonant wavelength. This work demonstrates the possibility of monolithic integration using thermal desorption and a regrowth technique and the suitability of these devices for massively parallel optical interconnections. >

We demonstrate the first surface‐emitting laser operation in a vertical‐to‐surface transmission electrophotonic device with a vertical cavity. The thyristor‐like current‐voltage characteristics, which are required for optical and electrical switching, are achieved. Threshold current during the on state is as low as 1.2 mA. All 100 devices, which were randomly extracted from a grown wafer, emit laser light.

We have proposed a structure for optical pixels consisting of a double vertical-cavity detector and single vertical-cavity laser section. This pixel can be formed by simple fabrication processes because the structures of the detector and laser section are almost the same, and the characteristics of the laser and detector sections can be independently optimized by choosing the pair number of each distributed Bragg reflector. We have achieved a spectral bandwidth and peak absorptivity of the double vertical-cavity detector section about five times those of the single vertical-cavity laser section.

We used two‐step molecular beam epitaxial (MBE) growth to integrate monolithically single and double vertical‐cavity structures on a wafer. This technique is useful for making a single vertical‐cavity surface‐emitting laser–thyristor with a low threshold and a double vertical‐cavity heterojunction phototransistor with both a high responsivity and a large spectral bandwidth. Regrowth on a patterned distributed Bragg reflector after thermal desorption of a passivating GaAs layer resulted in the laser in the single‐cavity section having a threshold current density of 1.0 kA/cm2, which is comparable to that of one grown by conventional one‐step MBE. Controlling thickness to within ±0.3% resulted in the regrown double‐cavity section having a bandwidth of 5 nm.

We demonstrate a record low threshold current of 190 µA in a microcavity surface-emitting laser with a 5-µm-diameter airpost, in pulsed operation at room temperature with no heat sink. This low threshold current is attributed to high-quality epitaxial layers and a dry-etched smooth sidewall.

Very smooth and vertical etching of InP by Cl2 reactive ion beam etching has been achieved under high temperature (≈200°C), high ion energy (≈1 keV) and low Cl2 pressure (∼10-5 Torr). The roughness is estimated to be a few nm by scanning tunneling microscopy and no contamination except for Cl was observed by in situ Auger electron spectroscopy. Under these etching conditions, the etched depth is precisely controlled (σ=22 nm) by simply monitoring the electrode curtent of the ion accelerating grid. Other III-V compound semiconductors, such as GaAs, InGaAs, AlGaInP and InAlAs have also been etched smoothly and vertically. Multilayers of these materials, such as InP/InGaAsP, AlGaInP/GaInP, and InAlAs/InGaAs/InP have been etched without steps between the layers on the sidewalls.

Monolithically integrated 8×8 semiconductor optical matrix switches have been successfully fabricated for the first time. They were constructed on GaAs substrates from 64 GaAs/AlGaAs electro-optic directional couplers using a simplified tree architecture. The devices have a chip size of 26.5×3 mm2 and a minimum total loss (excluding coupling loss) of 8.7 dB.

The threshold current dispersion, slope efficiency and lasing wavelength of vertical-to-surface transmission electrophotonic devices with vertical cavities are investigated. The critical number of output distributed Bragg reflectors (DBRs) required to overcome the disturbance due to back-surface reflections for surface-emitting-laser (SEL) structure devices is clarified. >

We demonstrate surface-emitting laser operation in pnpn structure vertical to surface transmission electro-photonic devices (VSTEPs) with a vertical cavity, i.e., VC-VSTEPs. Continuous-wave (cw) laser operation at room temperature is achieved with a VC-VSTEP mounted directly on a glass sheet with no heat sink. The threshold current is 3 mA for a 10 µm square device. In pulsed operation, this device shows current vs light-output characteristics with no definite threshold. The light output spectrum shows single mode operation in which the spectral width is the same value as the resolution of a spectrometer.

A novel electrophotonic mode of operation reduces both the memory holding power and the optical switching energy to 26 fJ at a 9 ns writing period in vertical to surface transmission electrophotonic devices with a pnpn structure (pnpn-VSTEPs). An integration of 1024 pnpn elements in a two-dimensional matrix has been demonstrated for these electrophotonic operations by using a thick metal line process and a low temperature dielectric film deposition for improving characteristics uniformity. >

A perturbed piezoelectric waveguide is constructed from a reference waveguide, which is specified by the eigenvalues and eigenfunctions, by the coordinate transformation, or other methods. In the perturbed waveguide, coupling occurs between normal modes of the reference waveguide. Coupling phenomena are analyzed by transforming Maxwell's and Newton's equations into the variational expression of the phase constant of the normal mode and then by applying the Rayleigh‐Ritz method. As an example, the couplings between purely elastic waveguide modes are discussed; and then the two‐mode approximation is applied in the case when two modes are degenerate or nearly degenerate. Mode conversion phenomena are discussed and from the viewpoint of the network theory, the mode transfer matrix relating the complex amplitudes of the two modes along the waveguide is defined and developed.

A systematic study for evaluating the effect of introducing short‐period superlattice waveguide layers on the threshold current of single quantum‐well diode lasers is reported. The waveguide layers which consist of short‐period GaAs/AlAs superlattices, in place of AlGaAs alloys, resulted in a decrease by a factor of 4–6 in the lasing threshold current density of GaAs/AlGaAs single quantum‐well diode lasers of separate confinement heterostructure. A time‐resolved photoluminescence study of those laser structures revealed that the threshold current reduction was the result of an improvement of overall nonradiative carrier recombination lifetime of single quantum wells by more than a factor of 10.

A photoeletronic bistable device with selectable light output channels has been fabricated for implementation in photonic switching and processing systems. The device is a variation of the vertical to surface transmission electrophotonic device. Output in the stimulated light emission mode was successfully obtained from different waveguide channels by external electronic switching. Output channels could be switched at a rate of 400 Mb/s. The potential versatility of this device has been experimentally confirmed in programmable or switchable optical interconnections.

A pnn double heterostructure optoelectronic switch with dual extractor electrodes was dynamically operated as an optical memory with the resulting achievement of 20 μW holding power. This value represents a reduction in holding power of about three orders of magnitude as compared to that of conventional light‐emitting optical bistable devices. Complete operation, involving optical writing, regeneration, and high‐speed erasing of written data through a dual extractor‐electrodes configuration, was carried out with a simple driving scheme.

Surface‐emitting GaAs/AlGaAs lasers with 45° total reflection mirrors have been successfully produced using a 45° tilted reactive ion beam etching technique. The ratio of surface‐emitted light output power to edge‐emitted light output power was obtained at values as high as 77%. The total reflection mirror was formed within 1° of the desired precise 45° angle. This type of surface‐emitting laser is promising for optoelectronic integrated circuits because of the simplicity of its structure and fabrication.

Previously reported work on optical waveguide bistability in GaAs/AlGaAs has included thermally induced dispersive and increasing-absorption bistability in a slab waveguide1 and increasing-absorption bistability utilizing the self-electro-optic effect in a slab waveguide.2 A more recent report claimed observation of optical switching and dispersive bistability of electronic origin in strain-induced channel waveguides.3 We report here an unambiguous observation of optical bistability of electronic origin in multiple-quantum-well (MQW) strip-loaded waveguides formed by reactive ion etching.

The possibility of using a vertical-cavity surface-emitting laser (VCSEL) as a detector has been investigated. For a 100 Å In0.2Ga0.8As strained quantum-well-layer that serves as both an active and absorption layer, 26% absorption due to the effect of multireflection mirrors and an 8% absorption increase at the resonant wavelength by applying an electric field were demonstrated.

A new periodically doped distributed Bragg reflector is examined. This new structure is expected to reduce the electrical resistivity without optical absorption increase. A very low threshold current density of 450 A/cm2 is obtained in vertical-cavity surface-emitting lasers with periodically doped distributed Bragg reflectors.

Laser-emission surface-normal optical devices with a vertical cavity are expected to be key devices for optical interconnections. Thermal characteristics improvement is necessary for a large-scale-integrated two-dimensional array which increases the number of optical interconnections. To optimize the device structures to obtain good thermal characteristics, the temperature rise of distributed Bragg reflectors and an active layer must be known. Here, we report on the first evaluation of temperature rise in both regions, and it is found that the temperature rise is small for a compact double-mesa structure which allows a single lateral-mode oscillation. In addition, we measured the thermal crosstalk between the above compact devices, and it is found that the thermal crosstalk between one-dimensional array devices is small enough when each device operates at a few milliamperes.

A unique optical self-routing switch, which uses laser mode vertical to surface transmission electrophotonic (VSTEP) devices, is proposed. This optical self-routing switch, in which the light input itself determines the output port by switching on VSTEPs, has a high internal optical gain of more than 20 dB and a wavelength filtering function. The light extinction ratio for the data signals between the on and off state is larger than 30 dB.

We report a high electronic-optical power conversion efficiency of 11.4% in the laser operation of a double-mesa-structure vertical-to-surface transmission electro-photonic device with a vertical cavity. This high conversion efficiency is due to both reduction in the device resistance and increase in light emission efficiency. To reduce electrical resistance, a double mesa structure with a highly doped region is proposed and the resistance reduction is analyzed. To increase light emission efficiency, efficient carrier confinement in the active region by a proton-implanted structure, threshold current reduction by photon recycling, and decreased light absorption by annealing after proton implantation are utilized. Electronic-optical conversion efficiency of over 10% is achieved in surface-emitting devices for the first time to the authors' knowledge.

A small-size matrix switch is required for constructing large scale optical switching systems. An optical gate matrix switch, which consists of optical splitters, combiners and gates, is suitable for above requirement because of its potential in regard to short device length and non-blocking and point-to-multipoint connections ability. However, this kind of switch reported so far is a hybrid /1/. In the hybrid type of optical gate matrix switch, it has seemed difficult to interconnect optical gates with optical circuits efficiently and to make a large-scale matrix switch. Therefore, monolithic integration of optical circuits and optical gates is indispensable for a small-size optical gate matrix switch and large-scale optical switching networks.

Threshold current as low as 1.2 mA has been achieved in GaAs/AlGaAs quantum well (QW) laser diodes. The low threshold current reflects the high quality of the QW crystal and the low level of leakage current attained in the buried heterostructure. This heterostructure was fabricated with a novel self-aligned mesa etching and Si diffusion process on a molecular beam epitaxy grown planer QW structure. Both the low threshold current and the precisely controllable fabrication process make these lasers quite suitable for optoelectronic integration.

Monolithic integration of an InGaAsP PIN photodiode with an n-channel enhancement InP-MISFET is reported. Photo-current amplification characteristics at 1000 Mbit/s have been achieved.

By pumping a small-core single-mode silica fibre with a 1.32 μm CW Nd:YAG laser, continuous-wave Raman amplification of InGaAsP laser diode light, with unsaturated gain as high as 21 dB, has been obtained in both backward as well as forward pumping configurations.