Terahertz radiation imaging has been employed to diagnose the supercurent and vortex distribution in high-Tc superconductive thin film strips. We observe them in the YBCO films patterned into the strip with and without ordered arrays of small antidots. Comparison with the theoretically expected distribution reveals that the present technique can provide a powerful tool for the noncontact, nondestructive, and free-space evaluation of the supercurrent and the vortex distribution with good quantitative agreement. The effect of the antidot formation in the strips is explained by the decrease of the effective critical current. The remanent state after removal of the relatively large magnetic field cannot be explained by the conventional model for the superconductive thin films, and the discrepancy is more notable in the antidot-formed area.

When a single-mode LD is subjected to distant reflection, relative intensity noise and the width of the optical spectrum are drastically increased. This phenomenon is known as 'coherence collapse. ' This letter demonstrates that penalty-free operation is possible at 2.5 Gbit/s even when a DFB-LD is in a state of coherence collapse. In addition, an LD in a state of coherence collapse is applied to a situation where signal light suffers from interferometric crosstalk. The results show that the LD reduces the influence of interferometric noise because of its wide spectral width.

Nonlinear characteristics of a DBR (Distributed Bragg Reflector) Cherenkov laser are investigated with the aid of particle simulation, allowing for the nonlinear properties of the electron beam. Numerical results show that the EM power extracted from the cavity is considerably suppressed by the nonlinear effect of the electron beam. Additionally, the extracted EM power is found to be critically dependent on the reflection coefficient of the DBR at the output end. Thus the DBRs at both ends of the cavity should be carefully designed in order to extract the EM power from the cavity efficiently.

We present novel semiconductor technologies of ZnO epitaxial films with using laser molecular-beam epitaxy method. Exciting optical properties such as room temperature lasing in ZnO nanocrystalline films and quantum size effects in ZnO/MgxZn1-xO superlattices were observed. By developing crystalline quality with using lattice-matched substrates, we could control resistivity of the doped ZnO films from 10-3 Ωcm to 104 Ωcm. These results would provide us an opportunity to construct a monolithic array consisted of light emitting devices and field effect transistors towards a possible flat panel display.

The alignment of a nematic liquid crystal (LC) parallel to the polarization direction of the laser could be induced by three types of polyimide (PI) films, a PI based on aromatic dianhydride and two PIs on alicyclic dianhydride, exposed to polarized pulsed laser at 266 nm at high fluence in air. The UV-visible absorption spectra of the PI films showed that a remarkable chemical change occurred after exposure at the high fluence in air. In contrast, in argon atmosphere the PI based on aromatic dianhydride was radiation-resistant and the exposed PI film could induce alignment of the LC molecules parallel to laser polarization. We estimate that the mechanism of the parallel alignment observed in argon is not the photodegradation but the orientation of the PI molecules.

A Rayleigh lidar (laser radar) system was developed and is now working well for temperature observations of the middle atmosphere at Poker Flat Research Range near Fairbanks, Alaska (65.1 N, 147.5 W). A comparison of lidar data and balloon sonde data showed good agreement in overlapped altitudes. The atmospheric fluctuations are detected in the temperature profiles obtained by the Rayleigh lidar and these are useful for the study of gravity waves. A Rayleigh Doppler lidar for wind measurements of the middle atmosphere is under the phase of development. The expected accuracy in measurements of horizontal winds up to an altitude of 60 km is smaller than 6 m/s in 2 hours observation. The system will be operated at Poker Flat after the completion of development. The combination of these lidars and radars installed at Poker Flat, give us chances of simultaneous observations of the structure and dynamics of the atmosphere in broad range of altitudes. Here, we give descriptions of the Rayleigh lidar and the Rayleigh Doppler lidar for the observations of the Arctic middle atmosphere at Poker Flat.

Topographical changes induced by optical near-field around photo-irradiated nanoparticles were attained using a pulsed laser with a large peak power as a light source. The arrayed structure of nanoparticles was transcribed on urethane-urea azo copolymer film as dent structure. The experiments by the pulsed laser of different wavelength showed that the topographical change was caused by the light absorption. The dent diameter and the dent depth changed depending on the diameter of nanoparticles.

In industrial assembly lines, seam sealing is a painting process used for making watertight seals or for preventing rusting. In the process, sealant is painted on seams located at the joints of pressed metal parts. We developed a sealing robot system that adjusts the sealing gun motion adaptively to the seam position sensed by a range sensor (a scanning laser rangefinder which senses profile range data). In this paper, we propose a high-speed and highly reliable algorithm for seam position computation from the sensed profile range data around the seam. It is proved experimentally that the sealing robot system used with the developed algorithm is very effective, especially for reducing wasted sealant.

Photoacoustic spectroscopy (PAS) has recently received much attention especially for plant photosynthesis research, because this technique is capable of performing non-destructive measurement without any pre-treatment of specimens. So far we have developed a PAS system equipped with an open photoacoustic cell (OPC), which allows in situ and in vivo measurements of plant photosynthesis of intact undetached leaves. In this study, we have measured photosynthesis reaction using OPC and developed a Confocal Scanning Photoacoustic Microscopy (CSPAM) system, in which PAS is combined with confocal scanning laser microscopy. The system allows simultaneous measurement of acoustic signal and another signal such as fluorescence, and also gives two- and three- dimensional intensity distributions of these signals, thereby giving two- and three- dimensional information about photosynthetic activity of plants.

In this paper, a method of fusing ground-based laser range image and CCD images for the reconstruction of textured 3D urban object is proposed. An acquisition system is developed to capture laser range image and CCD images simultaneously from the same platform. A registration method is developed using both laser range and CCD images in a coarse-to-fine process. Laser range images are registered with an assumption on sensor's setup, which aims at robustly detecting an initial configuration between the sensor's coordinate system of two views. CCD images are matched to refine the accuracy of the initial transformation, which might be degraded by improper sensor setup, unreliable feature extraction, or limited by low spatial resolution of laser range image. Textured 3D model is generated using planar faces for vertical walls and triangular cells for ground surface, trees and bushes. Through an outdoor experiment of reconstructing a building using six views of laser range and CCD images, it is demonstrated that textured 3D model of urban objects can be generated in an automated manner.

A 160 GHz colliding-pulse mode-locked laser diode (CPM-LD) was stabilized by injection of a stable master laser pulse train repeated at a 16th-subharmonic-frequency (9.873 GHz) of the CPM-LD's mode-locking frequency. Synchroscan steak camera measurements revealed a clear pulse train with 16-times repetition frequency of the master laser pulse train for the stabilized CPM-LD output, indicating that CPM-LD output was synchronized to the master laser and that the timing jitter was also reduced. The timing jitter of the stabilized CPM-LD was quantitatively evaluated by an all-optical down converting technique using the nonlinearity of optical fiber. This technique is simple and has a wider bandwidth in comparison to a conventional technique, making it possible to accurately measure the phase noise of ultrafast optical pulse train when its repetition frequency exceeds 100 GHz. The electrical power spectra measurements indicated that the CPM-LD's mode-locking frequency was exactly locked by the injection of the master laser pulse train and that the timing jitter decreased as the injection power increased. The timing jitter was reduced from 2.2 ps in free running operation to 0.26 ps at an injection power of 57 mW, comparable to that of the master laser (0.21 ps).

Waveguide characteristics of beam-expanders integrated with laser diodes were numerically analyzed by the beam propagation method (BPM) or the finite-difference time-domain (FD-TD) method. It was demonstrated that the vertically and horizontally hybrid tapered structure or an optimized refractive index in the cladding layer improve the trade-off relationship between fiber coupling efficiency and lasing characteristics. It was also demonstrated that exponentially tapering stripe width can reduce device length without sacrificing device properties.

We describe the fabrication method and characteristics of hybrid external cavity lasers composed of a spot-size converter integrated LD (SS-LD) and a UV written Bragg grating in a planar lightwave circuit (PLC) on a Si substrate. The SS-LD is passively aligned on a Si platform formed in the PLC, and the UV grating is created in the PLC with ArF laser irradiation through a phase mask. This structure enables us to fabricate a stable single-mode laser with a precisely controllable oscillation wavelength. By using the above techniques, we obtained a threshold current of 7-8 mA and a side mode suppression of 37 dB for an external cavity laser operating at 1.3 µm. Moreover, we successfully demonstrated a four-channel external cavity laser with a wavelength interval of 2 nm 0.1 nm by integrating 4 SS-LDs on a PLC and controlling the Bragg wavelengths with ArF laser irradiation without a phase mask.

We propose a device called the Waveguide width abruptly EXpanded Spot-Size-Converter integrated Laser Diode (WEX-SSC-LD) that has been designed to improve lasing characteristics by achieving a steep photoluminescence wavelength change along the cavity. The waveguide parameter was optimized by a three-dimensional beam propagation method to reduce mode conversion and absorption losses. The WEX-SSC-LD's showed superior lasing characteristics such as threshold currents of 5.8 mA at 25C and 19 mA at 85C and operation current of 57.5 mA at an output power of 10 mW for 85C. These excellent lasing characteristics were achieved due to the steeper bandgap-energy shift in the SSC section near the LD section side by introducing the WEX-SSC structure as well as the high-quality MQW active layer grown by selective MOVPE and the precisely controlled pn-pn current blocking structure. The coupling loss to normal single-mode fiber was as low as 1.8 dB while maintaining a large coupling tolerance of 1.8 µm. These excellent coupling characteristics are very promising for passively aligned optical modules.

A theoretical study on high slope-efficiency phase-shifted DFB laser diodes is presented. We have proposed a new grating structure called asymmetrically-pitch-modulated (APM) grating, and calculated its slope- efficiency and single-mode-yield. In order to take into account the modulated grating period; we have developed an F-matrix which directly includes a chirped grating structure. APM phase-shifted DFB laser diodes consist of a uniform grating in one half section of the cavity and a chirped grating in the other half. This structure causes asymmetrical field distribution inside the cavity and the optical output power from one facet is larger than that from the other facet. According to the simulation results, when the normalized coupling coefficient κ L is 3.0, the front-to-rear output power ratio is 2.6, while the single-mode-yield remains at 100%, and simultaneously the slope-efficiency improvement becomes 65% better than that of ordinary quarter-wave phase-shifted DFB lasers of the same κ L value.

Continuous-wave operation at room-tempera-ture has been demonstrated for InGaN multi-quantum-well (MQW) laser diodes (LDs) grown on FIELO GaN substrates with a backside n-contact. This was made possible by introducing important new concept of reducing threading dislocations that occur during the growth of the GaN substrates. We found that InGaN active layers grown on FIELO GaN are superior to those grown on conventional sapphire substrates in terms of their growth mode and the resultant In compositional fluctuation. The fabricated laser diode shows the threshold current, the threshold current density and the threshold voltage were 36 mA, 5.4 kA/cm2 and 7.5 V, respectively, with the lasing wavelength of 412 nm and internal quantum efficiency as high as 98%.

Laser diodes in the (Al, Ga, In) N system are attractive for many applications. Due to the wurtzite crystal structure, cleaved facets are not easily produced. We have investigated distributed feedback (DFB) laser diodes employing embedded dielectric gratings with the grating located above the active region. The dielectric gratings are incorporated via epitaxial lateral overgrowth. The DFB laser diodes had reduced threshold current densities over the etched cavity devices, with a minimum of 15 kA/cm2. The spectral emission width was considerably reduced for the DFB devices. Voltages for the DFB devices were high due to the presence of the Si3N4 grating within the p-type material.

Biological object could be trapped by a single laser beam from an optical fiber end inserted at an angle to a sample chamber. Separation/coupling of an individual biological cell was easily achieved using plural optical fibers. From these experimental results, we verify that fiber optic trapping technology can provide new and novel tools for the manipulation of microorganisms and cells without physical contact.

Optical transverse-mode properties of the GaN-based semiconductor laser-diode is characterized by effective refractive index method. In order to stabilize a transverse-mode in the conventional ridge-waveguide structure, very precise control of ridge-height is found to be necessary. On the contrary, a novel 2-step grown structure with 2-dimensional index guiding has wide feasibility for device parameter, excellent stability of large confinement factor in transverse-mode, and small aspect ratio of beam divergence, under the condition that AlN molar fraction of 0.08 in AlGaN current blocking layer and stripe width of 1.5 µm are used.

We introduce the characteristics for continuous wave operation at room temperature of InGaN laser diodes fabricated on SiC substrates. The threshold current was 60 mA, the threshold voltage was 8.3 V, and the oscillation wavelength was 404.4 nm. The lifetime of the laser diodes with a constant light output of 1 mW at 25 was 57 hours. The heat dissipation of the devices mounted p-side-up on a stem without using a heat sink was shown to be as good as that of devices mounted p-side-down with an external heat sink, owing to the high thermal conductivity of SiC substrates.