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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.

As a solution to provide a small-size and low-cost 100-Gb/s optical module, direct optical coupling between a lens-integrated surface-emitting DFB laser (LISEL) array and a single-mode fiber (SMF) array is demonstrated. A very-small far-field angle ( $\sim 2$ °) was obtained by monolithic integration of an InP lens with a laser chip. As a result, each channel of the LISEL array can directly couple to an SMF without any additional external optical components. The measured misalignment tolerance between the LISEL array and an SMF array was sufficiently large, namely, $\pm 5.5~\mu \text{m}$ , at excess loss of 1 dB over all four channels with the maximum coupling efficiency of 8.4 dB. These measurement results are in good agreement with a theoretical calculation based on Gaussian optics. These results demonstrate that high coupling efficiency (−3 dB) can be achieved while large misalignment tolerance ( $\pm 4.5~\mu \text{m}$ ) at excess loss of only 1 dB is maintained.

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.

Technologies for creating cost-effective light-emission optical sub-assemblies (OSAs) are discussed from the point of view of laser diodes. A lens-integrated surface-emitting laser (LISEL), consisting of a DFB laser, integrated mirror, and integrated convex lens, has the potential to achieve light-emission OSAs. An OSA based on the LISEL is proposed, and the capabilities of direct and passively aligned optical coupling, isolator-free operation, non-hermetic packaging, and on-wafer testing are introduced.

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.

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 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 (

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.

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 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.

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.

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.

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 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