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A lumped-electrode-type EA-DFB with a short-length modulator packaged by using an ultra-short wiring technique achieved bandwidth over 60-GHz in a wide-temperature range, and 100-Gbaud NRZ eye opening up to 80°C was demonstrated for the first time.

To deeply understand interrupting phenomena in high-voltage circuit breakers, it is important to measure the electrical characteristics of switching arcs in high-speed gas flow at current zero. A ring-shaped capacitive probe is proposed to measure a spatial arc voltage distribution. The configuration of the probe is decided by considering the effects of arc position and arc radius. The difference between arc voltage distributions is distinguished for an interrupting current of 12 and 30 kA on interrupting tests using the circuit breaker model.

A cost-effective optical sub-assembly (OSA) for high-speed optical interconnections using lens-integrated surface-emitting lasers (LISELs) is demonstrated. Two concepts of the OSA, one based on a direct-modulation (DM)-LISEL and the other based on a continuous-wave (CW)-LISEL for a silicon-photonics (SiP) platform, are proposed. The design parameters of the integrated lens that enable low fiber-coupling loss and the SiP platform are described. Coupling losses, as low as 4.9 dB for the single mode fiber and 4 dB for the SiP platform, were experimentally confirmed. Furthermore, theoretical and experimental evidence that demonstrates the OSA does not require an optical isolator (i.e., it is “isolator-free”) is presented. A DFB laser used for the LISEL had a low relative intensity noise (less than −140 dB/Hz), even with a back reflection of more than −20 dB. For non-Hermetic packaging, 500 h, 85°C/85% relative humidity storage tests experimentally demonstrated no degradation in the lasing characteristics.

Technologies for high-density integration of optical and electrical components are indispensable for next-generation optical transceivers whose capacity will exceed 400 Gbps. 3-D vertical integration technology with high optical coupling efficiency between a single mode fiber (SMF) array and lens-integrated surface emitting laser (LISEL) array using micro electro mechanical system (MEMS)-based movable micro-mirrors can meet this requirement. Light emitted from the LISEL is reflected at the micro-mirror and coupled to the SMF. Since the micro-mirror can steer the beam emitted from the LISEL to the SMF, the coupling efficiency that depends on the alignment accuracy between the LISEL and SMF is adjustable. After the alignment is completed, the position of the micro-mirror is fixed to keep high coupling efficiency. An optical sub-assembly (OSA) incorporating the LISEL, micro-mirror, and SMF array was fabricated using surface mount technology. All optical components were passively aligned, and the positions of micro-mirrors were adjusted to make a precise optical coupling to the SMFs as a post alignment. To confirm the effectiveness of this post-alignment system, the characteristics of the optical coupling to the SMF array were measured. It was found that the position of the reflected beam could be controlled to sub-micro-meter accuracy.

A movable micro-mirror array is proposed for high-density multi-channel single-mode optical sub-assembly. Adjustable optical-coupling loss of over 2dB was confirmed from experiments of 4-ch array optical-coupling between DFB lasers and single-mode fibers using the micro-mirrors.

A passive optical alignment based on a lens-integrated surface-emitting laser array and a single-mode fiber array was demonstrated. The proposed alignment technique enables better coupling efficiency than that of conventional DFB laser with active alignment.

Two multichannel 1.3-μ m lens integrated surface-emitting laser arrays for massive data links were fabricated. The basic structure of the lasers consists of a short InGaAlAs multiple-quantum-well distributed-feedback (DFB) active-stripe array monolithically integrated with both a 45° total reflection mirror and an aspheric collimation lens. One of them, a four-channel laser array based on this structure, exhibited clear 25-Gb/s eye openings up to 50°C over all four channels and achieved a total output of 100 Gb/s. The other laser, a multiple-wavelength array for wavelength-division-multiplexing applications, produces multiple-wavelength emission thanks to precisely modified DFB gratings by electron beam lithography. It exhibited nine-wavelength stable single-mode operation (side-mode suppression ratio >; 40 dB) between 1260 and 1290 nm at 3.7-nm intervals, and a clear 25-Gb/s eye opening for each wavelength. These two surface-emitting laser arrays have demonstrated their suitability for next-generation multichannel data links (including 100-Gb Ethernet and optical interconnects).

High-speed 1.3-μm directly modulated lasers (DMLs) have been developed to support sharply rising optical communications traffic. The most crucial requirement for these lasers is the ability to operate over a wide temperature range with no power-consuming electric cooler. Due to poor temperature characteristics resulting from its poor electron confinement in the multiquantum well, DMLs with InGaAsP material systems have been replaced by DMLs with InGaAlAs material systems, which have stronger electron confinement. In this paper, progress in uncooled 25-Gb/s 1.3-μm InGaAlAs DMLs is summarized. A 160-μm-long ridge-waveguide-type laser showed a lower threshold current Ith of 14.9 mA at high temperatures up to 95 °C, and a small signal-frequency-response bandwidth f3dB of 14 GHz was achieved at a bias current of 60 mA at 95 °C. Using this laser, clear 25-Gb/s operation was obtained at 95 °C. In addition, stable operation was achieved for up to 4000 h at 85 °C, indicating the basic applicability of the device to next-generation 25-Gb/s data communication systems. Furthermore, the developed technology was applied to a novel uncooled 25-Gb/s 1.3-μm surface-emitting laser for optical interconnects, in which a 45° mirror and a lens were integrated monolithically.

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.

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.