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We report on the highest two-terminal magnetoresistance (MR) ratio at room temperature in semiconductor-based lateral spin-valve devices. From first-principles calculations, we predict energetically stable ferromagnet–semiconductor heterointerfaces consisting of Co2MnSi (CMS) and Ge(111) upon insertion of Fe atomic layers. Using low-temperature molecular beam epitaxy, we demonstrate L21-ordered CMS epilayers at 80 °C on Ge(111), where the CMS layer can be utilized as a spin injector and detector. Two-terminal MR ratios as high as 0.1% are achieved in n-Ge-based lateral spin-valve devices with CMS/Fe/Ge Schottky tunnel contacts annealed at 200 °C. This study will open a path for semiconductor-based spintronic devices with a large MR ratio at room temperature.

We study the electrical properties of pseudo-single-crystalline Ge (PSC-Ge) films grown by a Au-induced layer exchange crystallization method at 250 °C. By inserting the SiNx layer between PSC-Ge and SiO2, we initiatively suppress the influence of the Ge/SiO2 interfacial defective layers, which have been reported in our previous works, on the electrical properties of the PSC-Ge layers. As a result, we can detect the influence of the ionized Au+ donors on the temperature-dependent hole concentration and Hall mobility. To further examine their electrical properties in detail, we also fabricate p-thin-film transistors (TFTs) with the PSC-Ge layer. Although the off-state leakage currents are suppressed by inserting the SiNx layer, the value of on/off ratio remains poor (

We propose a widely tunable and low insertion loss loop filter incorporating two ring resonators and an asymmetric Mach-Zehnder interferometer. A semiconductor optical amplifier, phase control section, and loop filter are monolithically integrated on one chip in the InP-InGaAsP material system. The tuning range of 39 nm with side-mode suppression ratio of over 30 dB was demonstrated. The maximum of the total heater power over the tuning range was 84 mW.

A gap-mirror technology for integrating a functional section onto a laser gain chip is presented. A semiconductor optical amplifier, implementing several functions, is integrated on the gain chip used in an external cavity laser, and demonstrated as a high-performance variable attenuator and data modulator at 2.5 Gb/s. Control of the mirror properties through the gap geometry is demonstrated, and further optimization is realized by a gap-filling technique, which increases the output power to above 100 mW across the C -band.

A theoretical and experimental study of the wavelength channel accuracy of an external cavity wavelength tunable laser (ECTL) with a wavelength reference etalon inside the laser cavity is presented. A feedback control scheme for wavelength locking is proposed based on monitoring of the forward output power. The cavity parameters with an impact on the channel accuracy, using the proposed scheme, are indicated, and guidelines toward optimization of the etalon are proposed. Experimental demonstration of a channel accuracy of less than 0.6 GHz for a full C-band ECTL with a channel spacing of 50 GHz confirms the high potential of this laser configuration

Tunable/selectable-wavelength light sources are beginning to play important roles in dense wavelength-division-multiplexing (DWDM) optical transmission systems. Of the many types of tunable/selectable light sources, we have chosen to develop distributed-feedback (DFB) laser-diode (LD)-array-based "wavelength-selectable" light sources (WSLs) because of their stable and reliable wavelength properties. This paper reviews our recent progress on eight-DFB-LD array WSLs and WSL modules for wide-band DWDM applications. We took full advantage of an advanced form of selective metal-organic-vapor-phase epitaxy (MOVPE), which we call microarray selective epitaxy (MASE), to simultaneously fabricate six types of WSL on two wafers so as to fully cover the S-, C-, and L-bands. These WSLs demonstrated a tunable wavelength range (/spl Delta//spl lambda/) of 15 nm, a high fiber output power of up to about 10 mW, and stable single-mode lasing properties with a side-mode-suppression-ratio greater than 42 dB. We also describe a 94-channel (50-GHz spacing) WSL module that features an integrated multiwavelength locker. A WSL with a band-covering tuning range, i.e., a /spl Delta//spl lambda/ of 40 nm in the L-band, was installed with a compact wavelength locker in a 12.7 mm/spl times/20.8 mm standard-size 22-pin butterfly package. The WSL module has a stable wavelength locking capability with spectral fluctuations of less than 1 pm and less than +/-5 pm against passage of time and variations in case temperature, respectively.

We experimentally demonstrate a flexible thin-film transistor (TFT) with (111)-oriented crystalline germanium (Ge) layers grown by a gold-induced crystallization method. Accumulation-mode metal source/drain p-channel Ge TFTs are fabricated on a polyimide film at ≤ 400 ° C. A field-effect mobility (μFE) of 10.7 cm2/Vs is obtained, meaning the highest μFE in the p-TFTs fabricated at ≤ 400 ° C on flexible plastic substrates. This study will lead to high-performance flexible electronics based on an inorganic-semiconductor channel.

Wire bonding, a process of the connection between a semiconductor chip and a lead frame by a thin metal wire, is one of the important processes of electronic packaging. This paper presents failure estimation of a silicon chip and a GaAS chip during a gold wire bonding process. The gold wire bonding process is carried out by pressing a gold ball made at a tip of the gold wire on a semiconductor chip and vibrating it by ultrasonic. High contact pressure is useful for shortening the process cycle, but it sometimes causes failure of the semiconductor chip. Elastic-plastic large deformation contact analyses are performed and the distributions of the stresses in these semiconductor chips are investigated. The possibility of failure of a semiconductor chip under usual wire bonding pressure is pointed out only for a GaAs chip.

This paper describes a novel epitaxial growth technique, called microarray selective epitaxy (MASE), for fabricating extremely small integrated photonic devices. The MASE technique makes it possible to form densely arrayed (pitch

We have proposed and demonstrated a novel planar-buried-heterostructure laser diode that includes oxidized AlAs current blocking layers exhibiting the overall lasing performance improvement. Superior current blocking characteristics of the insulating layers significantly improve maximum output power compared to a conventional buried heterostructure with a p-n-p-n thyristor configuration. A forward breakover at the current blocking layers was not observed at an injection current of more than 1 A for a 300-/spl mu/m-long device with both cleaved facets. The excellent lasing performance at a threshold current of 6 mA, a slope efficiency of 0.51 W/A under continuous-wave conditions, and a maximum output power of up to 150 mW under pulsed conditions was also demonstrated.

We present a 10-Gb/s InP-based Mach-Zehnder modulator with ruthenium (Ru)-doped buried heterostructure waveguides. C- and L -band operation is demonstrated, including transmission over 100 km of single-mode fiber for 1528-1600 nm.

We present an external-cavity wavelength-tunable laser with a semiconductor optical amplifier-modulator monolithically integrated on the gain chip. The modulator chirp is analyzed, and it is explained how the chirp can be partially cancelled by self-phase modulation in the transmission fiber. Full C-band transmission of 2.5-Gb/s data over 360 km is demonstrated with small power penalty

We investigated experimentally the impact of the cavity spacing on the lasing mode stability of the external cavity wavelength-tunable laser (ECTL) with Fabry-Peacuterot etalon and liquid-crystal-based wavelength-tunable mirror. In the asynchronous mode cavity ECTL, the etalon assists in the suppression of the cavity modes at the neighboring transmission peaks of the lasing wavelength due to the misalignment to the etalon's peak. Therefore, the ECTL with asynchronous mode cavity shows highly mode stable lasing operation. The fabricated ECTL module with optimized asynchronous mode cavity shows excellent lasing property of sidemode suppression ratio more than 59 dB and output power of over 14 dBm for a 45-nm tuning range

We propose a novel external cavity wavelength tunable laser (ECTL) configuration without an etalon inside the cavity. ECTL consists only of a semiconductor optical amplifier with an integrated phase section, and a liquid crystal tunable mirror. We successfully demonstrated excellent performances of the ECTL with fiber coupled output power of more than 50 mW over a 40-nm tuning range, sidemode suppression ratio of better than 45 dB, relative intensity noise of better than -148 dB/Hz, and linewidth of narrower than 2.3 MHz

We have developed a 1310-nm uncooled electroabsorption modulator integrated light source (EML) with an AlGaInAs multiple quantum well (MQW) active/absorption stripe, which was simultaneously grown using the narrow-stripe selective MOVPE technique and was buried with an Fe-doped InP. The Al-content MQW oxidation was effectively inhibited by using the same technique. An experiment-based evaluation of the device's performance revealed that by only changing the modulation bias voltage linearly with temperature, it was possible to achieve 10-Gb/s penalty-free operation at up to 85/spl deg/C over a 23-km single-mode fiber.

High-performance 1.3-/spl mu/m spot-size-converter integrated laser diodes (SSC-LDs) have been developed by using narrow-stripe (

A compact full C-band external cavity wavelength tunable laser is proposed. The cavity contains a fixed etalon and makes use of a liquid-crystal-based tunable mirror. The measurement results show a tuning range of 35 nm with fiber coupled power of more than 15 dBm. The sidemode suppression ratio is higher than 50 dB over the whole range and the relative intensity noise is below -148 dB/Hz. The linewidth is in worst case 700 kHz.

An advanced microarray-selective epitaxy with wider open-stripes has been developed for simple fabrication of distributed-feedback laser diode array-based high-power wavelength-selectable light sources. More than 40-mW fiber-coupled power and 50-dB sidemode suppression ratio over 9.2-nm wavelength were achieved.

Ultraviolet photoelectron spectroscopy (UPS) of C60 thin-film field-effect transistors was measured with biasing gate voltages. A time-dependent change in the electronic structure of the C60 film was observed during the UPS measurement, which has never been observed in a C60 film grown on a conductive substrate. The change was attributed to the accelerated polymerization of C60 by comparing the UPS with that of the photopolymerized C60. The polymerization was associated with the increase in the field-effect electron mobility. This result indicates that mobile carriers produce reactive radicals in organic semiconductors.

We report on the first demonstrated near-complete coverage of the S-, C-, and L-bands using six different ranges of wavelength-selectable microarray light sources (WSLs) based on a distributed-feedback (DFB) laser diode (LD) array. The six devices were fabricated on only two wafers. Each device has a tuning range of more than 15 nm, a sidemode suppression ratio of over 40 dB, and a fiber-coupled power greater than around 10 mW.

A wide-band wavelength-selectable light source module having an integrated multiwavelength locker has been developed. An eight-distributed-feedback (DFB) arrayed monolithic light source was designed to have 40-nm tunable range in the L-band by covering 5 nm per DFB laser diode. A uniquely designed etalon-based wavelength locker achieved very stable operation and uniform locking performance for all channels. Wavelength variation in the short term at room temperature was much less than 1 pm and the locked wavelength stayed within +/-5 pm when the case temperature of the module was varied from -20/spl deg/C to 65/spl deg/C.

The cavity length dependence of the linewidth property of complex coupled (CC) DFB lasers is investigated. In CC-DFB lasers with a fixed geometrical structure of the active region, the cavity length strongly affects the ratio of index coupling strength to the gain coupling one, which results in the variation of the effective linewidth enhancement factor /spl alpha//sub eff/. It is also found that pure gain coupled (GC) DFB lasers have the saturation characteristic in the linewidth power product, with the extension of the cavity length, These results indicate the importance of the selection of the cavity length in CC-DFB lasers. >

With an aim toward a high-saturation power operation, a tapered-waveguide traveling-wave semiconductor laser amplifier (SLA) with a Ga/sub 0.68/In/sub 0.32/As/GaInAsP/InP tensile-strained quantum-well (QW) structure was investigated and realized for the first time. In spite of the high differential gain in the tensile-strained QW active layer, a high-saturation-output power of 18.5 dB (1 mW) (71 mW) and a high-maximum-output power of 20.4 dB(1 mW) (110 mW) were obtained with a narrow single-lobed beam-divergence property. These results indicate that the saturation performances of SLA's with tensile-strained active layers can be improved by the tapered-waveguide structures. >

In this letter, we have simultaneously fabricated five wavelength-selectable microarray light sources (WSLs), each having a different wavelength range integrated with an electroabsorption (EA) modulator on a single wafer. We also introduced a novel device configuration scheme for wavelength-independent modulation. The five EA-WSLs fully covered the entire C-band and had a low uniform threshold current of 6 /spl plusmn/ 1 mA at 25/spl deg/C. Wavelength-independent extinction characteristics were obtained over a tuning wavelength range of 8 nm, and 2.5-Gb/s transmission over 600 km was successfully achieved.

Fairly low threshold current operation was achieved with Ga/sub 0.66/In/sub 0.34/As/GaInAsP/InP tensile-strained (TS) single-quantum-well (SQW) lasers with 30- approximately 40-nm-wide and 70-nm-period wire active region fabricated by a combination of a wet chemical etching and two-step OMVPE (organometallic vapor phase epitaxy) growth. Threshold current as low as 16 mA and threshold current density of 816 A/cm/sup 2/ were obtained under a room temperature CW condition. In comparing the spontaneous emission peak wavelength of the TS-SQW wire laser with that of the TS-SQW film laser, an approximately 10-meV blue shift of the fundamental energy level was observed in the TS-SQW wire laser. >

Improvements in the fabrication of GaInAs(P)/InP devices consisting of an ultrafine structure by using two-step organometallic vapor phase epitaxy (OMVPE) growth, electron beam exposure direct writing, and wet chemical etching are reported. This improved process achieved, for the first time, a room-temperature continuous-wave (CW) operation of GaInAs/InP quantum-wire lasers consisting of 5-nm-thick and 10-30-nm-wide vertically stacked triple quantum-wire active region within the period of 70 nm. A large blue shift of approximately 40 nm was observed in both the lasing and the electroluminescence spectra of Ga/sub 0.3/In/sub 0.7/As/InP compressively strained multi-quantum-well (MQW) wire lasers consisting of a 3-nm-thick and 30-60-nm-wide five-wire active region, which suggests a reduced effective mass of holes along the in-plane direction. >

A design theory is presented to apply inductively coupled superconducting striplines to microwave filters, in which the coupled stripline system is considered as four-port circuitry. By obtaining eigenvalues for impedance, admittance, and scattering matrices, the authors obtained general formulas for designing bandpass filters. The microwave filters using this coupling scheme are simple in design and have advantages of external-modulation capability. Experiments to demonstrate the validity of this coupling scheme have been performed in the frequency range between DC and 300 GHz by investigating the coupling between a Josephson oscillator and an external stripline. >

We developed high-performance distributed feedback array-based wavelength-selectable light sources (WSLs), covering the entire C-band with five simultaneously fabricated devices. We fabricated five different range WSLs on a wafer, each with a unique 8-nm tuning range to cover 40 100-GHz-spaced channels. Uniform characteristics, such as an Ith of 8.3/spl plusmn/1.2 mA, a sidemode suppression ratio of over 45 dB, and a fiber-coupled power greater than 8.5 mW were obtained.

A 10-Gb/s Mach-Zehnder modulator is monolithically integrated with a tunable laser source based on a 2-ring loop-filter with a small device dimension (2.5 × 0.9 mm2). Sufficient static extinction ratio of 16.5 dB was obtained both at 1573.92 and 1595.50 nm.

A room temperature CW operation of Ga/sub 0.3/In/sub 0.7/As/GaInAsP/InP GRINSCH compressive strained MQW lasers with 30 approximately 60 nm wide wire active region was achieved. This device was fabricated by two-step LP-OMVPE growths on p-type InP substrate and wet chemical etching. Threshold current as low as 53 mA (L=910 mu m, J/sub th/=2.9 kA/cm/sup 2/) was obtained at RT-CW condition. The spontaneous emission peak and the lasing wavelength of strained MQW wire lasers exhibited approximately 20-meV blue shift from those of MQW film lasers cut out from the same wafer. >

The effective linewidth enhancement factor alpha /sub eff/ of DFB lasers which have both gain and index coupling coefficients is theoretically analyzed. The unique reduction mechanism of alpha /sub eff/ due to the optical negative feedback of modal phase and modal gain in gain coupled DFB lasers was found for the first time. The numerical result showed that alpha /sub eff/ can be reduced to almost one half of the material defined linewidth enhancement factor alpha when there exists an index coupling coefficient comparable to the gain coupling coefficient. >

We developed compact (1.136 mm/sup 2/) eight-channel wavelength-selectable microarray distributed feedback laser diodes (DFB-LD's) with a monolithically integrated 8/spl times/1 multimode-interference (MMI) optical combiner, a semiconductor optical amplifier (SOA), and an electro-absorption (EA) modulator. By using /spl plusmn/10/spl deg/C thermal tuning, an addressable wavelength range of 15.3 nm with uniform device characteristics and 2.5-Gb/s modulation performance were successfully demonstrated.

The properties and applications of the inductive coupling of a superconducting stripline system, which takes advantage of kinetic inductance of thin superconducting films, are studied. The system, composed of two striplines inductively coupled through a common electrode as a four-port circuit, was formulated by obtaining its scattering coefficients in a general form. The system is characterized with the coupled-mode theory. Based on the analysis, it is proposed that a novel type of kinetic inductance devices for microwave analog components, such as directional couplers, microwave switches, variable filters, and efficient coupling elements for striplines. Experiments on stripline coupling with this scheme are also discussed.

A monolithically integrated wavelength-tunable laser diode based on a novel loop-filter that consists of two ring resonators and an asymmetric Mach-Zehnder Interferometer (AMZI) is demonstrated with 39-nm tuning range over 30-dB SMSR.

A compact 10 Gb/s full C-band tunable transmitter module of external cavity tunable light source with monolithically integrated Mach-Zehnder modulator was developed. Penalty free 10 Gb/s - 80 km transmission over full C-band has been successively achieved.

This paper reviews our recent activities on the development of high performance full-band wavelength tunable lasers. Our approach utilizes an external cavity configuration, which makes use of a liquid crystal (LC) tunable mirror. We also describe a gap mirror technology for integrating a functional section onto a laser gain chip. A semiconductor optical amplifier, implementing several functions, is integrated on the gain chip used in an external cavity laser, and demonstrated as a high-performance variable attenuator and booster amplifier. Control of the mirror properties through the gap geometry is demonstrated, and further optimization is realized by a gap-filling technique, which increases the output power to above 100 mW across the C-band.

We have fabricated organic static induction transistor (SIT) and organic light emitting transistor (OLET) combining SIT with organic light emitting diode (OLED). SIT and OLET have a grid-type Al gate electrode that was formed using a shadow evaporation mask in the organic semiconductor layers. The effective electrode area of SIT and OLET is approximately 4 mm2. By optimizing the device structure, excellent performances of SIT and OLET were obtained. The drain-source current (IDS) at a constant drain-source voltage (VDS) decreases with increasing the gate voltage (VG). The current is controlled by relatively small VG (-10 V) and a typical SIT characteristic is obtained in the OLET. The luminance of OLET also varies corresponding to the I-V characteristics. The maximum current and luminance values were approximately 10 mA and 10,000 cd/m2, respectively. We have also investigated the electrical characteristics of organic SITs having several gate gaps. The organic SIT with gate gap (Dg) less than 200 nm have much smaller off currents and much larger on/off ratios.

We demonstrate large-area (∼600 μm), (111)-oriented, and high-crystallinity, i.e., pseudo-single-crystalline, germanium (Ge) films at 275 °C, where the temperature is lower than the softening temperature of a flexible substrate. A modulated gold-induced layer exchange crystallization method with an atomic-layer deposited Al2O3 barrier and amorphous-Ge/Au multilayers is established. From the Raman measurements, we can judge that the crystallinity of the obtained Ge films is higher than those grown by aluminum-induced-crystallization methods. Even on a flexible substrate, the pseudo-single-crystalline Ge films for the circuit with thin-film transistor arrays can be achieved, leading to high-performance flexible electronics based on an inorganic-semiconductor channel.

We report for the first time different-wavelength modulator-integrated distributed-feedback laser diodes (DFB/MODs) fabricated on a single wafer, whose lasing wavelength cover almost all of the expanded erbium-doped fiber amplifier (EDFA) gain band from 1.527 to 1.593 /spl mu/m. The devices provided uniform and high-performance characteristics such as a threshold current less than 12 mA and successful transmission of 2.5 Gb/s-600 km through a normal fiber.

Organic transistors are promising in the future development of active devices for flexible, low-cost and large-area photoelectric devices . However, conventional filed effect transistors using organic materials have low-speed, low-power, and relatively high operational voltage, and these poor device performances. Vertical type transistors show high-speed and high-current characteristics and are suitable for driver elements of flexible displays.

We present an external cavity wavelength tunable laser with an SOA-modulator monolithically integrated on the gain chip. Full C-band transmission of 2.5 Gb/s data over 360 km is demonstrated with small power penalty.

We present a gap mirror based monolithic integration technology of functional sections on a gain chip for an external cavity wavelength tunable laser (ECTL). The effective reflectivity and coupling coefficient of the gap mirror can be controlled by changing gap length and gap angle. Utilizing this technique, we experimentally demonstrated full C-band ECTL with integrated variable optical attenuator (VOA). Output power of more than 50 mW with VOA operation, SMSR of more than 50 dB were obtained over the entire C-band.

Wideband wavelength tunable lasers are now beginning to play important roles in dense wavelength-division multiplexing (DWDM) optical transmission systems, because these lasers can reduce the required number of inventory lasers and inventory costs. They are also key components in the evolution towards future photonic network systems, particularly in reconfigurable optical add/drop multiplexing (ROADM) systems and optical cross-connect (OXC) systems. However, before the tunable laser can be a viable alternative for the conventional fixed wavelength laser (e.g. DFB laser) it should have the same characteristics over its entire tuning range. Additionally, the device should only be marginally more expensive than its fixed counterpart. This paper reviews our recent activities on the development of high performance full-band wavelength tunable lasers. Our approach utilizes an external cavity configuration, which makes use of a liquid crystal (LC) tunable mirror. We first demonstrate high performance of an external cavity wavelength tunable laser (ECTL) with an intracavity etalon. This ECTL module shows a tuning range of 45 nm and output power of more than 14 dBm. We also explain an approach to realize a more compact ECTL with 40% reduced cavity length by eliminating the intracavity etalon, and show its excellent laser characteristics such as a fiber-coupled power of around 17 dBm, tuning range of over 40 nm, and a sidemode-suppression-ratio (SMSR) greater than 50 dB.

The Photon Factory Advanced Ring (PF-AR) is a synchrotron light source dedicated to X-ray research. Although the PF-AR is usually operated at a stored beam energy of 6.5 GeV, a 5.0 GeV mode is also available for medical application. In the 6.5 GeV mode, the beam current of 60 mA in a single-bunch and the typical lifetime of 15 hrs at the current have been archived. Single-bunch operation for pulsed X-ray and its relatively high beam energy characterize the PF-AR. However, the high-current in single-bunch causes several problems to be solved, such as the temperature rise of some of the vacuum components, a pressure increase in the ring, and a sudden drop of beam lifetime. In order to avoid these problems, developments of new methods have been continued. In this paper, the status and the recent developments of the PF-AR are presented. It concerns: the successful operation with a two-bunch high-current operation at 5.0 GeV; the vertical beam size control for the medical application; modulating the RF acceleration phase in order to elongate the bunch length; stabilizing temperature in the ring tunnel; the study for medium emittance operation with 160 nm · rad; transferring the RF cavities in order to install a new insertion device; an innovative injection scheme using a pulsed quadrupole magnet.

We have fabricated pentacene static induction transistors (SITs) on both Au and indium tin oxide (ITO) formed on glass substrate at room temperature using the vacuum evaporation method.

We have been developing a detector element which includes dipole antennas and a doubly balanced mixer fabricated on a dielectric substrate. This detector is designed for millimeter-wave imaging system on fusion device experiment in order to measure electron temperature distribution. Prototype detector which works in X-band shows ideal characteristics such as axisymmetric field pattern and detection sensitivity as an imaging element. Recently, we have fabricated same type detectors which work in E-band range. We have confirmed that the detectors have sensitivity in this frequency range.

We demonstrated an external cavity wavelength tunable laser using a novel gain chip with monolithically integrated VOA function. Over 15-dBm output power and an output power tuning range of 55 dB were obtained over the whole C-band.

We report for the first time different-wavelength distributed-feedback laser diodes (DFB-LDs) fabricated on a single wafer, whose lasing wavelengths cover the expanded erbium-doped fiber amplifier (EDFA) gain band from 1.52 to 1.59 /spl mu/m with adjusted detuning between lasing-wavelengths and gain-peak-wavelengths. Uniform lasing characteristics such as a low-threshold current of less than 12 mA with stable single-mode oscillation of more than 35-dB side-mode suppression ratio (SMSR) are achieved for the 75-nm wavelength range.