We propose a novel structure that can reduce the power consumption and extend the transmission distance of an electro-absorption modulator integrated with a DFB (EADFB) laser. To overcome the trade-off relationship of the optical loss and chirp parameter of the EA modulator, we integrate a semiconductor optical amplifier (SOA) with an EADFB laser. With the proposed SOA assisted extended reach EADFB laser (AXEL) structure, the LD and SOA sections are operated by an electrically connected input port. We describe a design for AXEL that optimizes the LD and SOA length ratio when their total operation current is 80mA. By using the designed AXEL, the power consumption of a 10-Gbit/s, 1.55-µm EADFB laser is reduced by 1/2 and at the same time the transmission distance is extended from 80 to 100km.

We newly propose the first lateral mode selective active multimode interferometer laser diode. The design principle is to arrange identical propagation path of different lateral mode. Thanks to multimode waveguide structure, 0th mode and 1st order mode has individual propagation path within one device. Individual lasing of fundamental mode as well as first mode was confirmed successfully.

We have developed membrane distributed Bragg reflector (DBR) lasers on thermally oxidized Si substrate (SiO2/Si substrate) to evaluate the parameters of the on-Si lasers we have been developing. The lasers have InGaAsP-based multi-quantum wells (MQWs) grown on InP substrate. We used direct bonding to transfer this active epitaxial layer to SiO2/Si substrate, followed by epitaxial growth of InP to fabricate a buried-heterostructure (BH) on Si. The lateral p-i-n structure was formed by thermal diffusion of Zn and ion implantation of Si. For the purpose of evaluating laser parameters such as internal quantum efficiency and internal loss, we fabricated long-cavity lasers that have 200- to 600-µm-long active regions. The fabricated DBR lasers exhibit threshold currents of 1.7, 2.1, 2.8, and 3.7mA for active-region lengths of 200, 300, 400, and 600µm, respectively. The differential quantum efficiency also depends on active-region length. In addition, the laser characteristics depend on the distance between active region and p-doped region. We evaluated the internal loss to be 10.2cm-1 and internal quantum efficiency to be 32.4% with appropriate doping profile.

In order to realize high-yield speckle modulation, we developed a novel spatial light modulator using zinc oxide single crystal doped with nitrogen ions. The distribution of dopants was optimized to induce characteristic optical functions by applying an annealing method developed by us. The device is driven by a current in the in-plane direction, which induces magnetic fields. These fields strongly interact with the doped material, and the spatial distribution of the refractive index is correspondingly modulated via external control. Using this device, we experimentally demonstrated speckle modulation, and we discuss the quantitative superiority of our approach.

An application of laser annealing process, which is used to form the P-type Base junction for high-performance low-voltage power MOSFETs (Metal Oxide Semiconductor Field Effect Transistors), is proposed. An equivalent shallow-junction structure for P-Base junction with uniform impurity distribution is achieved by adopting green laser annealing of pulsed mode. Higher impurity activation for the shallow junction has been achieved by the laser annealing of melted phase than by conventional RTA (Rapid Thermal Annealing) of solid phase. The application of the laser annealing technology in the fabrication process of Low-Voltage U-MOSFET is also examined.

An application of laser annealing process, which is used to form the shallow P-type Base junction for 20-V planar power MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) is proposed. We demonstrated that the fabricated devices integrated with laser annealing process have superior electrical characteristics than those fabricated according to the standard process. Moreover, the threshold voltage variation of the devices applied by the new annealing process is effectively suppressed. This is due to that a uniform impurity distribution at the channel region is achieved by adopting laser annealing. Laser annealing technology can be applied as a reliable, effective, and advantageous process for the low-voltage power MOSFETs.

In this study, our recent research activities on nanophotonic devices with semiconductor quantum nanostructures are reviewed. We have developed a technique for nanofabricating of high-quality and high-density semiconductor quantum dots (QDs). On the basis of this core technology, we have studied next-generation nanophotonic devices fabricated using high-quality QDs, including (1) a high-performance QD laser for long-wavelength optical communications, (2) high-efficiency compound-type solar cell structures, and (3) single-QD devices for future applications related to quantum information. These devices are expected to be used in high-speed optical communication systems, high-performance renewable energy systems, and future high-security quantum computation and communication systems.

Recent small cube satellites use higher frequency bands such as Ku-band for higher throughput communications. This requires high-frequency link in an earth radio station as well. As one of the solutions, we propose usage of bidirectional radio-on-fiber link employing a wavelength multiplexing scheme. It was numerically shown that the response linearity of the electro-absorption modulator integrated laser (EML) is sufficient and that the spurious emissions are lower enough or can be reduced by the radio-frequency filters. From the frequency response and the single-sideband phase noise measurements, the EML was proved to be used in a radio-on-fiber system of the cube satellite earth station.

In recent years, there are many collision accidents between vehicles due to human errors. As one of countermeasures against the collision accidents, automotive radar systems have been supporting vehicle drivers. By the automotive radar mounted on the vehicle, it is possible to recognize the situation around the vehicle. The ranging with automotive infrared laser radar is very accurate, and able to understand the object existence in the observation around the vehicle. However, in order to grasp the situation around the vehicle, it is necessary to be aware of the attribute of the detected object. The information obtained by the automotive radar vehicle is only the direction and the distance of the object. Thus, the recognition of the attribute of the detected object is very difficult. In this paper, we propose a novel vehicle information acquisition method by using 2D reflector code. Through experiments, we show that the proposed method is able to detect 2D reflector code and is effective for vehicle information acquisition.

Optical interfaces have been recently standardized as the main physical layer interfaces for most short length optical communication systems, such as IEEE802.3ae, OIF-VSR, and the Fiber Channel. As interface speed increases, the requirements for forecasting the optical characteristics of direct modulated laser diodes (LDs) also increase because those standards define the specifications for physical layers with optical domains. In this paper, a vertical-cavity surface-emitting laser (VCSEL) equivalent electronic circuit model is described with which designers can simulate the $I-L-V$, S-parameter, and transient characteristics of LDs on a circuit simulator by improving convergence. We show that the proposed VCSEL model can model an 850-nm bandwidth VCSEL with 10-Gbps operation.

We describe wavelength-routed switching technology for 25-Gbit/s optical packets using a tunable transmitter that monolithically integrates a parallel-ring-resonator tunable laser and an InGaAlAs electro-absorption modulator (EAM). The transmitter provided accurate wavelength tunability with 100-GHz spacing and small output power variation. A 25-Gbit/s burst-mode optical-packet data was encoded onto the laser output by modulating the integrated EAM with a constant voltage swing of 2 V at 45$^{circ}$C. Clear eye openings were observed at the output of the 100 GHz-spaced arrayed-waveguide grating with error-free operation being achieved for all packets. The tunable transmitter is very promising for realizing a high-speed, large-port-count and energy-efficient wavelength-routing switch that enables the forwarding of 100-Gbit/s optical packets.

Laser diode capable of high speed direct modulation is one of the key solution for short distance applications due to their low power consumption, low cost and small size features. Realization of high modulation bandwidth for direct modulated laser maintaining the above mentioned feature is needed to enhance the short distance, low cost data transmission. One promising approach to enhance the modulation speed is to increase the photon density to achieve high modulation bandwidth. So to achieve this target, 1.55 $mu$m InGaAsP/InGaAsP multiple quantum well (MQW) asymmetric active multimode interferometer laser diode (active MMI-LD) has been demonstrated [1]. The split pumping concept has been applied for the active MMI-LD and significant enhancement of electrical to optical 3 dB down frequency bandwidth (f$_{mathrm{3dB}})$ up to 8 GHz has been successfully confirmed. The reported high bandwidth for split pump active MMI-LD is around 3.5 times higher than the previously reported maximum 3 dB bandwidth (2.3 GHz) of active MMI-LD without split pumping section. That shows, the splitted multimode pumping section behind the electrically isolated modulation section can potentially improve the modulation bandwidth of active MMI-LD. Clear and open eye diagram had also been confirmed for 2.5 Gbps, (2$^{mathrm{7}}$-1) pseudo random bit sequence (PRBS) modulation.

Excimer laser annealing at 308nm in UV and semiconductor blue laser-diode annealing at 445nm were performed and compared in term of the crystallization depending on electrical properties of Si films. As a result for the thin Si films of 50nm thickness, both lasers are very effective to enlarge the grain size and to activate electrically the dopant atoms in the CVD Si film. Smooth Si surface can be obtained using blue-laser annealing of scanned CW mode. By improving the film quality of amorphous Si deposited by sputtering for subsequent crystallization, both laser annealing techniques are effective for LTPS applications not only on conventional glass but also on flexible sheet. By conducting the latter advanced annealing technique, small grain size as well as large grains can be controlled. As blue laser is effective to crystallize even rather thicker Si films of 1µm, high performance thin-film photo-sensor or photo-voltaic applications are also expected.

We review our recent achievements in monolithic 3D-ICs and flexible electronics based on single-grain Si TFTs that are fabricated inside a single-grain with a low-temperature process. Based on pulsed-laser crystallization and submicron sized cavities made in the substrate, amorphous-Si precursor film was converted into poly-Si having grains that are formed on predetermined positions. Using the method called µ-Czochralski process and LPCVD a-Si precursor film, two layers of the SG Si TFT layers with the grains having a diameter of 6µm were vertically stacked with a maximum process temperature of 550°C. Mobility for electrons and holes were 600cm2/Vs and 200cm2/Vs, respectively. As a demonstration of monolithic 3D-ICs, the two SG-TFT layers were successfully implemented into CMOS inverter, 3D 6T-SRAM and single-grain lateral PIN photo-diode with in-pixel amplifier. The SG Si TFTs were applied to flexible electronics. In this case, the a-Si precursor was prepared by doctor-blade coating of liquid-Si based on pure cyclopentasilane (CPS) on a polyimide (PI) substrate with maximum process temperature of 350°C. The µ-Czochralski process provided location-controlled Si grains with a diameter of 3µm and mobilities of 460 and 121cm2/Vs for electrons and holes, respectively, were obtained. The devices on PI were transferred to a plastic foil which can operate with a bending diameter of 6mm. Those results indicate that the SG TFTs are attractive for their use in both monolithic 3D-ICs and flexible electronics.

Radio over Fiber (RoF) is a promising technology that is suitable for broadband wireless access systems to cover in-building areas and outdoor dead-spots. However, one issue in RoF transmission that should be considered is the nonlinear distortion caused by Electrical/Optical (E/O) converters. Multicarrier RF (Radio Frequency) signal formats such as Orthogonal Frequency Division Multiplexing (OFDM), which are commonly employed in broadband wireless communications, are weak against nonlinearities. To enable the linear transmission of OFDM signal in RoF channel, we propose to employ the Envelop Pulse Width Modulation (EPWM) transmission scheme for RoF channel. Two commonly used E/O converters, Mach-Zehnder modulator and direct-modulation of Distributed Feedback Laser Diode (DFB LD), are employed to validate the proposal. Based on the measured nonlinearities of the E/O converters, they are mathematically modeled and their transmission performance are analyzed. A modified Rapp model is developed for the modeling of the DFB LD. Through simulations and experiments, the proposed scheme is shown to be effective in dealing with the nonlinearities of the E/O converters.

Ultra-high luminance lamps emitting white light with a well-scattered blue spectrum from InGaN/GaN laser diodes and a phosphor-converted yellow spectrum show speckle contrast values as low as LED. Spectral behavior of the laser diodes is analyzed to find the reason why such low values are obtained. As a result, the PWM-driven, multi-longitudinal mode with dynamically broadened line-width is found to have a great effect on reducing speckle contrast. Despite using the lasers, such speckle-free lamps are considered to be very suitable for high-luminance and other various lighting applications.

By using impedance (Z) matching circuits in a low-cost transistor outline (TO) CAN package for a 10 Gb/s transmitter, we achieve a cost-effective and small bidirectional optical subassembly (BOSA) with excellent optical transmission waveforms and a > 40% mask margin over a wide temperature range (-10 to 85). We describe a design for Z matching circuits and simulation results, and discuss the advantage of the cost-effective compensation technique.

We describe 25-Gb/s error-free transmission over multi-mode fiber (MMF) by using a transmitter based on a 1.3-µm lens-integrated surface-emitting laser (LISEL) and a CMOS laser-diode driver (LDD). It demonstrates 25-Gb/s error-free transmission over 30-m MMF under the overfilled-launch condition and over 150-m MMF with a power penalty less than 1.0 dB under the underfilled-launch condition.

The quantum dot optical frequency comb laser (QD-CML) is an attractive photonic device for generating a stable emission of fine multiple-wavelength peaks. In the present paper, 1.0-GHz and 10-ps-order short optical pulsation is successfully demonstrated from a hybrid mode-locked QD-CML with an ultrabroadband wavelength tuning range in the T+O band. In addition, 10-GHz high-repetition intensity-stable short optical pulse generation with a high S/N ratio is successfully demonstrated using an external-cavity QD-CML with a 10th-harmonic mode-locking technique.

To obtain an ultra-short high-intensity pulse source, we investigated the amplification characteristics of two types of pulses (dissipative soliton and stretched pulses) produced by our Yb-doped fiber laser oscillator. Our results show that the dissipative soliton pulse can be amplified with less deterioration than the stretched pulse.