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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.

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.

A 25 Gb/s laser diode (LD) driver has been developed on the basis of standard 65 nm CMOS technology for optical interconnects. The LD driver consists of a main driver capable of providing an average current of 30 mA and a predriver providing a gain of 20 dB. The main driver uses mutually coupled inductors to adjust the inductive peaking to improve eye patterns under various packaging conditions. The predriver uses CMOS active feedback to achieve a wide bandwidth and high gain, despite its small size and low power consumption. The fabricated circuit achieves data rates of 25 Gb/s, consumes 156 mW (6.3 mW/Gb/s) and occupies an area of 0.011 mm2 .

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.

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.