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We fabricated a p-i-n photodiode (PD) with an integrated microlens, and demonstrated its high performance capabilities including high speed (35GHz), high responsivity (0.8A/W), and large misalignment tolerance (26µm), and an error-free 25-Gbit/s 10-km single-mode fiber transmission by using a 100-Gbit/s Ethernet quadplexer receiver module with the PDs.

As a solution to provide small-footprint and low-cost light sources for silicon platforms, light sources using a lens-integrated surface-emitting laser (LISEL), and a grating coupler fabricated on a silicon-on-insulator substrate is proposed. Light emitted from the LISEL (based on an InP distributed feedback laser) has a narrow far-field pattern, so the LISEL can be directly mounted on the silicon platform with no additional external optical components. The alignment tolerance between the LISEL and grating coupler was experimentally measured. This measurement confirmed large alignment tolerance. The excess loss due to misalignment of ±5 μm is only 1.5 dB.

We proposed a perfectly facet-free surface-emitting 1.3-μm DFB laser toward cost-effective light source, and confirmed the same performances as the usual DFB lasers and an on-wafer measurement.

A simple and practical method for integrating a DFB laser and a silicon photonics platform without additional optical components such as lenses and an isolator is proposed. Optical-coupling and feedback-tolerance characteristics arc experimentally measured.

Low-cost optical assemblies for optical interconnections using lens-integrated surface-emitting laser are proposed. High coupling efficiency with single-mode-fibers of over −1.9dB and RIN below −140dB/Hz with large back reflection and 85°C/85% storage test are demonstrated.

A 50-Gb/s optical transmitter, consisting of a DFB-LD with a bandwidth of 20 GHz and a SiGe BiCMOS LD driver, was developed. At 43-50 Gb/s, it enhanced a LD bandwidth and demonstrated wide eye openings.

A 103.2 (25.8 × 4)-Gb/s optical link using a 1.3-µm lens-integrated surface-emitting laser array was demonstrated. A power penalty after 2-km transmission was small (

In this study, we propose a new process to fabricate electrically conductive alumina by gelcasting and reduction sintering. The process used the conventional gelcasting method except for varying amounts of monomer at 2.8, 5.5, and 8.0 wt.% relative to the weight of the slurry. In the plastic mould, the slurry was under in situ solidification for 3 hrs at 25oC to achieve gelation. The freshly gelled bodies were demolded, carefully dried, and then sintered at 1100oC, 1300oC, and 1550oC in nitrogen atmosphere. The holding times at 1100oC and 1300oC was 2 hours, while at 1550oC were 2, 4, and 6 hrs. The sintered alumina body was characterized by electrical property, X-ray diffraction, and scanning electron microscopy. Results showed that monomer additions and sintering schedule significantly affect in lowering electrical resistance. The low value was 3.6×106 +cm at 8.0wt.% monomer addition and sintering at 1550oC for 2 hrs. The effect of physical properties on electrical conductivity and the corresponding reaction mechanism were discussed in details.

In this study, we propose a new process to fabricate electrically semi-conductive alumina by the combination of gelcasting and reduction sintering. The process is similar to the conventional gelcasting method except for varying amounts of methacrylamide monomer dosages at 2.83, 5.50, and 8.04 wt% relative to the mass of the slurry. Correspondingly, the rheological evaluation of aqueous slurry was conducted. The resulting fluidity exhibited that monomer dosage until 8.04 wt% yielded slurry viscosity of 1628 MPA·s at shear rate of 20 s−1, which was feasible for gelcasting without noticeable casting defects. The freshly gelled bodies were demolded, carefully dried, and then sintered at different schedules in nitrogen atmosphere. The reduction-sintered samples were re-sintered in air for comparative evaluation of physical property. The sintered alumina body was characterized by electrical resistance, X-ray diffraction, and scanning electron microscopy. The results showed that monomer additions and sintering schedule significantly affect in lowering electrical resistivity. The obtained lowest value was 3.6 × 106 Ω-cm with 8.04 wt% monomer dosage and sintering at 1550°C with 2 h holding time. The resulting material is classified as semi-conductive, which is potential for electrostatic shielding applications. The effect of physical property and microstructure on electrical conductivity and the corresponding reaction mechanism were discussed in details.

This work demonstrated an in-situ pyrolysis of gelcast alumina under reduction sintering to make alumina and carbon composite in providing semi-electrical conductivity. To increase the carbon content, the monomer was varied in the premix solution with reduction sintering in nitrogen gas. Two-probe method was used to measure electrical resistance of the sintered samples. The results revealed that the increase of monomer addition and sintering treatment were effective in reducing electrical resistance. The lowest value was 3.6×106-cm, which is a potential candidate for electrostatic shielding application. The reduction-sintered sample was re-sintered in an air in order to gain insight on the conductive path due to carbon network. Further tests such as XRD, TGA/DTA, and scanning electron microscopywere used to explain the semi-conductive property of the material.

A prototype transceiver composed of a 1.3-μm-range lens-integrated laser diode and photodiode as well as a complementary metal-oxide-semiconductor (CMOS) laser diode driver and a CMOS transimpedance amplifier for high-speed optical interconnections was developed. It demonstrated 25-Gb/s error-free 100-m multimode fiber transmission, with power dissipation of only 9 mW/Gb/s, for the first time.

A high-speed large-capacity optical printed circuit board (OPCB) for next-generation high-capacity routers and servers was developed. This OPCB is composed of a multilayer polymer optical waveguide, a receiver optical input/output (I/O) module (with a lens-integrated photodiode and a SiGe transimpedance amplifier), and a low-power (7.1 mW/Gb/s) transmitter optical I/O module consisting of a lens-integrated surface-emitting laser and complementary metal-oxide-semiconductor (CMOS) driver IC. A 1-Tb/s (20 Gb/s/ch × 48 ch per transmitter or receiver) large-capacity OPCB prototype was fabricated and demonstrated 20-Gb/s/ch operation.

40-Gb/s (4-ch x 10-Gb/s) operation of a 1.3-µm lens-integrated surface-emitting laser diode array was demonstrated by a CMOS shunt driver. Clearly opened eyes at 10-Gb/s were obtained for 4 channel simultaneous operation at 95°C.

A lens-integrated surface-emitting laser array has been developed for an optical module compliant with Parallel Single-mode 4-lane Multi-Source Agreement (PSM4 MSA) for 100GbE applications. High-efficiency optical coupling to SMF with two-lens configuration and uncooled 25-Gb/s operation over all four-channels were demonstrated.

A 1.3-μm wavelength optical link, which consists of a lens-integrated laser diode and a CMOS optical receiver, was developed. It achieves 25-Gb/s error-free 100-m multi-mode fiber transmission with sensitivity of −6.3-dBm OMA.

We have successfully grown highly strained GaInNAs/GaAs multiple quantum wells (MQWs) ranging from a single-QW (SQW) structure to a five-QW (5QW) structure without strain-compensation layers or Sb surfactant by molecular beam epitaxy (MBE). High-resolution X-ray-diffraction (HRXRD) measurements showed clear multiple reflections of GaInNAs QWs, which suggests their good structural quality. Photoluminescence (PL) measurements revealed that a triple-QW (TQW) structure had a strong PL intensity proportional to the number of QW layers, while the 5QW structure had a PL intensity that was five times less than that of the SQW structure. We fabricated GaInNAs/GaAs TQW edge-emitting lasers and demonstrated a record low-threshold current of 4.3 mA at a long wavelength of 1.29 μm

A compact 4 25-Gbps optical transceiver for short-reach communications using optical interconnects was developed. Its total power consumption is 2.2 W. A transmission experiment with the transceiver was successfully conducted at 25-Gbps data rate.

As a silicon photonics light source, a lens-integrated surface-emitting laser (LISEL) was integrated on a silicon-waveguide platform for the first time. Excess loss due to misalignment of +/-5 Pm between the LISEL and silicon waveguide is only 1.5 dB.

A high-speed opto-electronic printed circuit board (OEPCB) composed of a polymer waveguide and an optical module is conceptually proposed and prototyped. The fabricated OEPCB prototype provides highly efficient optical coupling characteristics (> -1 dB) and large optical-coupling tolerance (> +/-15 μm). It demonstrated 25-Gbit/s high-speed optical-signal transmission through a 10-cm-long multi-mode polymer waveguide. This performance result indicates that the OEPCB is suitable for next-generation high-speed and high-density chip-to-chip optical interconnection.

40-Gb/s/ch direct modulation of multi-wavelength 1.3-μm surface-emitting laser array is demonstrated. Fabricated laser array consisting of four-channel DFB stripes with modified gratings, 45° mirror, and integrated lens, exhibited clear 40-Gb/s eye openings over all four channels.

A hybrid integration of a surface emitting DFB lasers and a fully integrated transceiver CMOS chip was proposed for compact 100-Gb/s transceivers of optical backplanes and datacenter optical links.

A compact 4 × 25 Gbps optical transceiver has been fabricated for an optical backplane system, which consists of a 4 × 25 Gbps DFB-LD array, a 4 × 25 Gbps PIN-PD array, and a CMOS transceiver chip. These are directly mounted on 9 × 14 mm(2) multi-layer ceramic package with an electromagnetic shield structure to suppress inner-channel crosstalk effectively. The transceiver includes an analog front-end as well as an electrical interface function to interface with the switch LSI or CPU. Power consumption was as low as 20 mW/Gbps, and a transmission experiment was successfully conducted at 25 Gbps.

A compact optical low-power (9 mW/Gbps) transceiver with lens integrated devices and 12-ch flexible waveguides for optical interconnects was developed. It provides high optical-coupling efficiency and large tolerances (>-2.5 dB and >+/-15 μm) and demonstrated 25-Gbps/ch error-free transmission.

Uncooled 25-Gb/s operation of a multi-wavelength 1.3-µm surface-emitting-laser array was demonstrated. This array–consisting of four distributed-feedback (DFB) active stripes, 45° mirrors and integrated lenses–exhibited 25-Gb/s operation up to 85°C over all channels.

A low-power transceiver for optical interconnects, composed of 1.3-um-range microlens-integrated optical devices and CMOS ICs, was developed. It demonstrated 25-Gbit/s error-free transmission with over-100-m multi-mode fiber (MMF) and low-power consumption of 9 mW/Gbit/s.

Multiple-wavelength 25-Gb/s operation of a 1.3-μm-range surface-emitting laser array was demonstrated. The fabricated laser array, which consists of nine distributed-feedback (DFB) active stripes operating between 1260 and 1290 nm at 3.7-nm intervals exhibited clear 25-Gb/s eye openings.

We developed a high-speed (20 Gbps/channel) and large-capacity (1 Tbps/board) optical printed circuit board with a proposed two-lens optical coupling structure and a low-power (7.1 mW/Gbps) optical module using a CMOS IC, and successfully demonstrated 20-Gbps/ch operation in our optical interconnection.

A compact 25-Gbps × 4-channel optical transceiver has been fabricated for optical backplane systems. Power consumption was as low as 20 mW/Gbps. A transmission experiment was successfully conducted at 25 Gbps.

Uncooled 25-Gb/s transmission of a 1.3-µm surface-emitting laser is demonstrated. A fabricated laser, which consists of an InGaAlAs-MQW DFB active stripe and surface-mountable structure, exhibited clear 25-Gb/s eye openings after 2-km SMF transmission up to 85°C.

Four-channel 25-Gb/s direct modulation of a 1.3-µm surface-emitting laser array with a surface mountable device structure was demonstrated. The fabricated laser array, which consists of InGaAlAs-MQW DFB stripes, exhibited a total output of 100 Gb/s with collimated optical outputs.

Recent progress in developing 1.3-um InGaAlAs-MQW directly modulated lasers is reported. Uncooled 25-Gbps operations over a wide temperature range were demonstrated. Clear eye opening up to 100 °C % was successfully obtained.

Recent advances in integrated photonic devices for next-generation Ethernet are described. In particular, 1.3-µm-range uncooled photonic devices (namely, electroabsorption modulator integrated lasers, directly modulated lasers, and lens integrated devices) are focused on. A key technology for uncooled operation is an InGaAlAs multiple quantum well (MQW), which produces a strong electron confinement. The electroabsorption modulator integrated lasers, which incorporated an InGaAlAs-MQW absorption layer, exhibit uncooled 25.8-Gbit/s and 43-Gbit/s single-mode fiber 10-km transmissions. The 1.3-µm directly modulated laser, which consists of an InGaAlAs MQW distributed feedback (DFB) active stripe, exhibits uncooled direct modulation at 25 Gbit/s. To improve the optical coupling of the directly modulated laser, we developed a lens-integrated surface-emitting laser, which incorporates an InGaAlAs DFB active stripe. This lens-integrated laser exhibits 25-Gbit/s direct modulation up to 100°C. Furthermore, the lens-integrated photodiode exhibited high speed (35 GHz), high responsivity (0.8 A/W), and large alignment tolerance (26 µm) for direct coupling to a single-mode fiber. These photonic devices have demonstrated their potential for implementation in cost-effective 100-Gbit/s and 40-Gbit/s Ethernet.

The uncooled 25-Gbit/s direct modulation of a 1.3-µm horizontal-cavity surface-emitting laser was demonstrated. A fabricated laser, which is directly mountable on a high-frequency coplanar line, exhibited 25-Gbit/s eye openings up to 100°C.

We developed a high-speed (20 Gbps) and high-density (480 Gbps/cm2) optical printed circuit board with a new two-lens optical interface for optical interconnections, and successfully demonstrated a 20-Gbps operation in our optical interconnection.

We describe an aspheric-microlens-integrated high-performance PIN photodiode, which exhibits high speed (35 GHz), high responsivity (0.8 A/W), and large alignment tolerance (26 µm) for direct coupling to a flat-ended standard single-mode fiber.

Circular, narrow beam emission of a lens-integrated surface-emitting laser operated at 1.3-µm wavelength was demonstrated. The laser consists of a distributed feedback laser cavity monolithically integrated with an etched 45° total reflection mirror and an etched InP lens. The profile of the etched InP lens was estimated to be a highly symmetrical parabolic shape that is ideal for the collimation of a Gaussian beam. A fabricated lens-integrated surface-emitting laser exhibited a circular, narrow far-field pattern with full-width at half-maximums of 3.9° × 3.5°. A highly efficient direct coupling to a single-mode fiber with a coupling efficiency of − 2.7 dB was also confirmed.

A novel 1.3-µm surface-emitting laser integrated with a monolithic InP bulk lens was demonstrated. The laser achieved very narrow far-field angles of around 2° leading to a −2.7 dB direct coupling to a single-mode fiber.

High-performance GalnNAs/GaAs triple quantum well (TQW) edge-emitting lasers were demonstrated. Al-free molecular beam epitaxy (MBE) is effective to prevent any Al impurity or contamination, which had appeared in previous GalnNAs materials, leading to a significant improvement in the photoluminescence intensity. By using this growth method, we have successfully grown highly-strained GalnNAs/GaAs TQW lasers that exhibit a record low threshold current of 4.4 mA at 25degC and a 40-Gbit/s direct modulation at 5degC. These results indicate that GalnNAs lasers are good candidates for future high-frequency operation cost-effective light sources.

We experimentally demonstrated that a record-low threshold current of 4.3 mA is achieved in long-wavelength, 1.29 μm, GaInNAs-TQW RWG lasers. Moreover, 40-Gb/s direct modulation of the laser is confirmedat 5°C.

In an attempt to isolate genes located on double minute (Dmin) DNA in HL-60 cells, we prepared DNA probe from purified micronuclei. Micronucleation was induced in HL-60 cells by treatment with hydroxyurea. Screening of a cDNA library unexpectedly produced a number of clones containing mitochondrial DNA (mtDNA) sequences. Here, we show that amplified mtDNA sequences were localized in nuclei and micronuclei of HL-60 and COLO 320DM cells, but not in nuclei of WI-38 normal human fibroblasts or peripheral blood T-cells. To unequivocally demonstrate the presence of mtDNA inside of nuclei and micronuclei, we obtained tomographic fluorescence in situ hybridization (FISH) images of mtDNA by confocal microscopy of consecutive sections of paraformaldehyde (PFA)-fixed material. We also located mtDNA in nuclear buds and purified micronuclei. Dmin DNA and mtDNA were always located at similar sites. The mechanisms of nuclear retention of mtDNA and Dmin DNA and the resulting influence on tumorigenesis are discussed.

Monolithically lens-integrated surface-emitting distributed-feedback (DFB) laser arrays and p–i–n photodiode arrays were developed. A combination of dry etching and wet chemical etching was used to fabricate a monolithic InP lens. The lens profile within ±10 µm from the lens center was estimated to be parabolic shape, which is ideal for the collimation of a Gaussian beam. A fabricated lens-integrated surface-emitting DFB laser exhibited a circular, narrow far-field pattern with full-width at half maximums of 3.9×3.5°. An efficient direct coupling of the lens-integrated DFB laser to a single-mode fiber with a coupling efficiency of -3 dB was confirmed. A four-channel lens-integrated surface-emitting laser array and a lens-integrated p–i–n photodiode array were used to fabricate a very compact 100 Gbps (25 Gbps × 4 channel) optical transceiver with 14×9 mm2 footprint.

We proposed tapered pinch discharge as a measure to conduct laboratory astrophysics experiments. Basic behaviors of the plasma have been characterized using a prototype device. Results show that the plasma flux and velocity depend on initial gas density, discharge current and taper geometry. Those behaviors can be illustrated with a simple model considering the pinching dynamics of the current sheet based on a 1 dimensional (1-D) equation of motion. Achievable value of the tapered pinch plasma is estimated and compared with required plasma parameters based on scaling parameters for laboratory astrophysics.

We propose a new type of plasma source using a pinch discharge in a tapered capillary, which generates a dense moving plasma by electromagnetic compression and acceleration. The axial velocity and flux of the moving plasma are controllable and can be maximized by adjusting the taper angle. The behavior can be illustrated with a simple model considering the pinching dynamics of the current sheet.

Low-threshold GaInNAs single-quantum-well (SQW) lasers with emission wavelength over 1.3 mum are demonstrated. Epitaxial layers of the lasers are grown using an aluminium-free gas-source molecular-beam epitaxy (GS-MBE) to prevent any impurity or contamination related to aluminium that might be incorporated into the GaInNAs active layer. The fabricated laser is believed it exhibit the lowest threshold-current density (200 A/cm 2 ) among GaInNAs-SQW lasers grown by MBE. Moreover, record low threshold current (5.2 mA) and long-wavelength (1.31 mum) emission were achieved in a ridge-waveguide laser at 25degC under continuous-wave operation