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The configuration of plasmonic circuits comprising SiO2-load waveguides and their characteristics within the nanophotonic range are presented and compared with electronic and lightwave circuits in 1300 and 1550 nm wavelength bands. In the nanophotonic range of less than $1~\mu \text{m}$ , plasmonic signals propagate in narrow waveguides with cross-sections less than a few hundred square nanometers, while lightwaves exhibit only slight propagation in high-refractive-index (i.e., Si) waveguides owing to the transmission loss increase via the cut-off wavelength of the waveguide. Additionally, the plasmonic signal transmission loss is lower than that of electric signals for transmission lengths less than a few hundred micrometers. During signal transmission, a narrow spectral width of the plasmonic signals is needed to suppress any signal shape deformation induced by the frequency dependence of the collective oscillation of electrons in plasmonic signals. In the nanophotonic range, the degree of integration for plasmonic circuits is not governed by the transmission loss but by the leak distance of the plasmonic signal optical field from the side-walls of the waveguides and components. Employing a metal/insulator/metal structure in plasmonic circuits is a valid way to heighten the integration density, and its effectiveness is numerically and experimentally confirmed in a plasmonic multiplexer less than $1~\mu \text{m}$ in length. On the basis of these results, the feasibility of plasmonic circuits is discussed and it can be said that plasmonic circuits including waveguides and components are promising photonic techniques for signal transmission in the nanophotonic range

Feasibility of fabricating plasmonic circuits by complementary metal–oxidesemiconductor (CMOS) compatible processes is presented, and the circuit performances are numerically and experimentally discussed from the viewpoint of operating speed and energy loss. The transmission speed of plasmonic signals, which is governed by the dispersion of circuits, is calculated to be about two orders of magnitude higher than that of electric signals. The energy loss per single transmitted-bit is estimated using shot-noise limits, and it is clarified that plasmonic signals are superior to electric ones if the transmitted distance is set to an area within a few hundred micrometers. Based on these results and the experimental results of each plasmonic components, the feasibility of plasmonic circuits are demonstrated. In addition, the feasibility of the functional expansion of plasmonic circuits, such as wavelength-division-multiplexing networks, is discussed using experimental values of plasmonic components fabricated by CMOS-compatible processes. These plasmonic circuits and networks can be merged into silicon integrated circuits on a silicon substrate using CMOS compatible processes.

Laser diodes are the main optical source in various optical fiber communication systems and indispensable for our daily lives. The wavelength of the laser diodes are set at 1300 nm or 1550 nm for most communication systems, including submarine systems corresponding to the low loss window of silica fiber. Laser diodes used in such wavelength bands are usually InGaAsP/InP lasers. Wavelength in 850-nm band is also used for short-range communication, such as intraoffice systems. The laser diodes used for the wavelengths are AlGaAs/GaAs laser diodes. In these systems, high reliability is required for those laser diodes since the communication systems are serious lifelines, and the operating conditions have been severe year by year. In those applications for communication systems, high-speed operation for trunk systems and long-term stable wavelength operation for wavelength division multiplexing (WDM) systems are required. For subscriber systems, high and wide operating temperature are required, corresponding to the environmental conditions of applications. In addition to those applications, some laser diodes have begun to be used in space for satellite communications and sensing systems. The environmental conditions of space applications are quite different from those of terrestrial applications such as land and submarine communication systems. Compared with the operating conditions in terrestrial systems, there are large variations in the ambient temperature in space, and laser diodes are possibly exposed to severe irradiation by high-energy particles and ultraviolet rays. These environmental factors are inherent features in space applications and have been added to the reliability issues of terrestrial applications. The basic reliability of laser diodes used in the communication systems is usually determined by optical output characteristics. The stability of lasing wavelength and spectral linewidth are also important in these applications.

Plasmonic signal transmission via nanoscale plasmonic waveguides is a new technique with the potential to increase the information transfer capacity in silicon integrated circuits (ICs). During propagation, surface plasmon polaritons (SPPs) exhibit characteristics of a lightwave whose transmission loss is mainly determined by the collective oscillation of electrons. Using this lightwave aspect of SPPs, information can be transmitted using plasmonic signals and optical transmission circuits and networks can be built at the micro/nanoscale. This size scale correlates well with that of electronic circuits comprising metal-oxide-semiconductor field-effect transistors (MOSFETs). In this article, the feasibility of on-chip interconnects and other circuits were discussed and confirmed on the basis of previously developed plasmonic components. The first example examined herein was a wavelength-division-multiplexing circuit comprising a multiplexer and demultiplexer (in 1310 and 1550 nm-wavelength bands), discussed based on the experimental results for each component. Multiplexed signals at the multiplexer were guided into a single-mode waveguide, divided at the demultiplexer and then passed to the electronic circuits. The transmitted plasmonic signals were converted to electric signals at the slits etched on the gate electrode, thereby driving the MOSFET without photodetectors, whereupon the MOSFET-amplified signals were outputted to the electronic circuits. The second example was coherent signal transmission via plasmonic circuits. The signal transmission was performed using micro/nanoscale plasmonic circuits in a manner similar to those of optical fiber transmission systems. These coherent signal transmissions via plasmonic signals were experimentally confirmed, being detected and converted to electric signals at the slits etched on the gate electrode of the MOSFET and then outputted therefrom. These experimental examples confirmed the feasibility of plasmonic circuits integrated with MOSFETs. In plasmonic circuits, signal transmission loss is generally high compared to that of electric and lightwave signals. Herein, it was numerically confirmed again that the plasmonic signal transmission losses were lower than those of electric signals transmitted in electric circuits for plasmonic circuits not exceeding an area of a few hundred square micrometers. The loss of lightwave signals (e.g., transmitted in silicon waveguides) was much lower than those of plasmonic signals. However, as the waveguide width approached the cut-off wavelength, the loss quickly increased to be greater than that of plasmonic signals. This work indicates that plasmonic circuits have an advantage in nanoscale circuits. The circuits presented herein are currently too primitive for actual silicon IC applications, but are adequate to indicate the feasibility of merging plasmonic circuits with silicon ICs.

Wet-electrospun (WES) polymer micron and submicron fibers are promising building blocks for small, flexible optical fiber devices, such as waveguides, sensors, and lasers. WES polymer fibers have an inherent cylindrical geometry similar to that of optical fibers and a relatively large aspect ratio. Furthermore, WES fibers can be produced using low-cost and low-energy manufacturing techniques with large-area fabrication and a large variety of materials. However, the high propagation loss in the fibers, which is normally on the order of tens or thousands of decibels per centimeter in the visible light region, has impeded the use of these fibers in optical fiber devices. Here, the origin of propagation losses is examined to develop a comprehensive and versatile approach to reduce these losses. The excess light scattering that occurs in fibers due to their inhomogeneous density is one of the primary factors in the propagation loss. To reduce this loss, the light transmission characteristics were investigated for single WES polymer fibers heated at different temperatures. The propagation loss was significantly reduced from 17.0 to 8.1 dB cm–1 at 533 nm wavelength, by heating the fibers above their glass transition temperature, 49.8 °C. In addition, systematic verification of the possible loss factors in the fibers confirmed that the propagation loss reduction could be attributed to the reduction of extrinsic excess scattering loss. Heating WES polymer fibers above their glass transition temperature is a versatile approach for reducing the propagation loss and should be applicable to a variety of WES fibers. This finding paves the way for low-loss WES fiber waveguides and their subsequent application in small, flexible optical fiber devices, including waveguides, sensors, and lasers.

We have analyzed the propagation behavior of 1.31-and 1.55-μm-wavelength-band surface plasmon polaritons (SPPs) for three simple Si-based plasmonic waveguides: the Au stripe waveguide, the SiO2 stripe waveguide, and the Au/SiO2 stripe waveguide on a Si substrate. The SPP propagation length in the waveguide varied depending on the waveguide structure and propagation lengths for waveguides with different structural parameters are summarized. The energy that was required for SPP detection after propagation along the waveguides for the 1.31- and 1.55-μm-wavelength bands was calculated for intensity-modulation direct-detection and heterodyne frequency-shift keying systems. The results demonstrate that SPPs can propagate with lower energy consumption than conventional electric wiring below a specific interconnect length. A wavelength-selective structure for SPPs that comprised nano-slits in an Au film on an Si substrate was fabricated. The device can selectively detect 1.31-μm-wavelength SPPs as electrical signals and transmit 1.55-μm-wavelength SPPs. Experimental photoresponses and transmittances were measured and compared with calculated results. Magnitude correlation of the measured and calculated photoresponses and transmittances showed good agreement. Evaluation of the SPP propagation behavior and the wavelength-selective structure are important considerations for the development of optoelectronic integrated circuits that use SPPs and electrons as signal carriers.

Dye-doped, submicron fiber waveguides composed of hole- and electron-transport materials, with a mean diameter of 480–660 nm were fabricated and their waveguiding properties studied. Dye emitted photoluminescence was guided in the fibers and the loss coefficient was calculated to be 1.2 × 10−3–3.9 × 10−3 μm−1 at a wavelength of 540 nm, which is lower than previously reported for optically active polymer submicron fibers. Finally, a feasible method to couple the fibers with counter electrodes is presented using phase segregation of an insulating polymer. These submicron fiber waveguides, composed of optically and electrically active materials, can be used to produce OLED-waveguides, which are applicable in the fields of textile optoelectronics, lab-on-a-chip, and optogenetics.

This paper presents a plasmonic circuit that has been monolithically integrated with electronic devices on a silicon substrate and then discusses the concept behind this circuit. To form the proposed circuit, two plasmonic waveguides and a detector are integrated with metal–oxide–semiconductor field-effect transistors (MOSFETs) on the substrate. In the circuit, intensity signals or coherent plasmonic signals are generated by coherent light at an operating wavelength at which silicon is transparent, and these signals propagate along the waveguides before they are converted into electrical signals by the detector. These electrical intensity and coherent signals then drive the MOSFETs during both DC and AC operation. The measured performances of the devices indicate that surface plasmon polaritons propagate on the metal surface at the speed of light and drive the electronic devices without any absorption in the silicon.

This paper presents a feasibility study of optical interconnections using surface plasmon polaritons (SPPs) as coherent carrier waves in a silicon-based electrical circuit. A gold film plasmonic waveguide and a gold/silicon Schottky-type plasmonic detector were monolithically integrated with an electrical circuit based on metal–oxide–semiconductor field-effect transistors on a silicon substrate. A 1550-nm-band laser source was used for SPP excitation, and the photocurrent generated by the plasmonic detector was amplified 16 000 times by the monolithically integrated electrical circuit after SPPs carrying the optical intensity signal propagated over the gold film surface for a distance of 100 μm. The integrated circuit detected an optical beat signal by using a delayed self-homodyne technique, thus demonstrating that SPPs can be used as coherent carrier waves in the circuit. Additionally, optical amplitude- and frequency-modulated signal transmission in a gold film plasmonic waveguide and optical heterodyne detection by amplification of the signal intensity in a gold/silicon Schottky-type plasmonic detector were also demonstrated.

A plasmonic integrated circuit configuration comprising plasmonic and electronic components is presented and the feasibility for high-speed signal processing applications is discussed. In integrated circuits, plasmonic signals transmit data at high transfer rates with light velocity. Plasmonic and electronic components such as wavelength-divisionmultiplexing (WDM) networks comprising metal wires, plasmonic multiplexers/demultiplexers, and crossing metal wires are connected via plasmonic waveguides on the nanometer or micrometer scales. To merge plasmonic and electronic components, several types of plasmonic components were developed. To ensure that the plasmonic components could be easily fabricated and monolithically integrated onto a silicon substrate using silicon complementary metal-oxide-semiconductor (CMOS)-compatible processes, the components were fabricated on a Si substrate and made from silicon, silicon oxides, and metal; no other materials were used in the fabrication. The plasmonic components operated in the 1300- and 1550-nm-wavelength bands, which are typically employed in optical fiber communication systems. The plasmonic logic circuits were formed by patterning a silicon oxide film on a metal film, and the operation as a half adder was confirmed. The computed plasmonic signals can propagate through the plasmonic WDM networks and be connected to electronic integrated circuits at high data-transfer rates.

Objective: The aim of this study was to investigate the effect of laser irradiation on root surface demineralization caused by local drug delivery systems (DDS), and to evaluate the effect of sealing on drug retention. Background data: The duration of supportive periodontal treatment (SPT) has increased with increasing life expectancy. Repeated root planing and DDS application during SPT should be reconsidered with regard to their effects on the root surface. Methods: Extracted human teeth were collected, cut into 3×3×2 mm root dentin specimens, and divided randomly into eight groups with various combinations of Nd:YAG laser power (0, 0.5, 1, and 2 W), with and without DDS (minocycline HCl). Specimen microhardness and calcium (Ca) solubility were measured after treatment. The specimens (control and laser and DDS groups) were examined by scanning electron microscopy. Forty SPT patients were recruited, to assess the effect of periodontal pocket sealing on drug retention. Results: Laser irradiation increased the microhardness of root specimens in an energy-dependent manner. Calcium solubilities decreased from the 0 W+DDS group to the 2.0 W+DDS group. The mean Ca solubilities in the 1.0 W+DDS and 2.0 W+DDS groups were significantly lower than in the 0 W+DDS group (p

Background Antimicrobial photodynamic therapy (aPDT) is a new treatment method for the removal of infectious pathogens using a photosensitizer and light of a specific wavelength, e.g., toluidine blue with a wavelength of about 600 nm. We explored a new photosensitizer and focused on indocyanine green (ICG), which has high absorption at a wavelength of 800–805 nm. We investigated the bactericidal effect of PDT on Porphyromonas gingivalis using a new photosensitizer, ICG-loaded nanospheres with an 805 nm wavelength low-level diode laser irradiation. Methods We designed ICG-loaded nanospheres coated with chitosan (ICG-Nano/c) as a photosensitizer. A solution containing Porphyromonas gingivalis (108 CFU/mL) with or without ICG-Nano/c (or ICG) was prepared and irradiated with a diode laser or without laser irradiation as a negative control. The irradiation settings were 0.5 W with a duty ratio of 10%, for 3–100 ms in repeated pulse (RPT) or continuous wave mode. CFU were counted after 7 d of anaerobic culture. Results We observed that ICG-Nano/c could adhere to the surface of P. gingivalis. When ICG-Nano/c was used for aPDT, irradiation with RPT 100 ms mode gave the lowest increase in temperature. Laser irradiation with ICG-Nano/c significantly reduced the number of P. gingivalis (i.e., approximately 2-log10 bacterial killing). The greatest bactericidal effect was found in the RPT 100 ms group. However, laser irradiation (RPT 100 ms) with ICG, as well as without photosensitizer, had no effect on the number of bacteria. Conclusions Within the limits of this study, ICG-Nano/c with low-level diode laser (0.5 W; 805 nm) irradiation showed an aPDT-like effect, which might be useful for a potential photodynamic periodontal therapy.

We introduce a novel multimode-interference-based plasmonic phase adjuster, which simplifies cascaded photonic-integrated-circuit (PIC) patterns. A cascaded plasmonic half-adder circuit that includes the proposed phase adjuster is demonstrated using scanning near-field optical microscopy. The proposed phase adjuster will be indispensable for future PIC technologies.

We investigate the detection efficiency of a metallic-grating-based plasmonic detector composed of a Schottky diode and multiple plasmonic waveguides. We then demonstrate a metal-oxide-semiconductor field-effect transistor that includes the plasmonic detector and two plasmonic waveguides.

The three-dimensional finite-difference time-domain method was used to demonstrate a novel structure for coupling whispering gallery mode (WGM) with surface plasmons (SPs). As for this structure, a micrometer-sized optical resonator composed of a silver film coated on a silica microsphere containing apertures is set on a glass substrate. The SPs couple with higher-order WGM, and their intensity is clearly enhanced by this structure.

We propose an on-chip excitation structure for orthogonal-polarized gap plasmons in polarization multiplexing photonic integrated circuits. The structure consists of a Au nanostripe and tapered gap for refractive index matching to a nano-scale gap plasmonic waveguide; it was fabricated on the top surface of a dielectric-stripe-type waveguide. The excitation ratio from the dielectric-stripe-surface mode to the metallic-gap mode was estimated to be 0.79 using the finite-difference time-domain method for a 100-nm-wide, 100-nm-thick gap waveguide. We experimentally observed the gap mode plasmonic intensity distribution using scanning near-field optical microscopy and confirmed the conversion.

This in vitro study was performed to determine the appropriate power output setting for an erbium, chromium-doped:yttrium, scandium, gallium, and garnet (Er,Cr:YSGG) laser used in periodontal pocket irradiation by examining the morphologic alterations of the root surfaces and the efficiency of calculus removal.Sixty-five non-carious extracted human teeth were used in this study. For morphologic analysis of the root surface, the clean, single roots of 22 teeth were separated into 91 pieces, and these pieces were immersed in acrylic resin. The specimens with root-surface exposure were prepared and divided randomly into three groups: a control group (N=8), an irradiation without water group (no water [NW] group; N=39), and an irradiation in water to simulate the conditions in a periodontal pocket group (in water [IW] group; N=44). The power output settings for laser irradiation were 0.5, 1.0, 1.5, and 2.0 W for each group. The roughness (Ra), depth (Z), and width (X) of the disk specimens were determined after laser irradiation. Eight other single-rooted teeth were examined by scanning electron microscopy (SEM) after laser irradiation under the same conditions. Thirty-five single- or multirooted teeth with heavy subgingival calculus were used to test the efficiency of laser scaling. The efficiency of calculus removal was quantified by measuring the time needed to remove the calculus completely using the laser.The mean Ra and Z values in the IW group were significantly higher than in the NW group with the same power output. In addition, these values with 0.5- and 1.0-W power output settings were significantly lower than with 1.5- and 2.0-W settings in the NW and IW groups. No obvious morphologic differences could be found between the 0.5- and 1.0-W power output specimens under SEM. Additionally, thermal alterations, i.e., carbonization or melting, were completely absent in the IW group. Regarding the efficiency of calculus removal, the 0.5-W setting (0.11+/-0.036 mm2/second) was significantly inferior to the 1.0-W setting (0.27+/-0.043 mm2/second). However, there was no significant difference between 1.0- and 1.5-W (0.36+/-0.11 mm2/second). The 2.0-W setting (0.63+/-0.272 mm2/second) was much more efficient but resulted in significant morphologic alterations.Based on these findings, it is appropriate to use a 1.0-W power output setting with an Er,Cr:YSGG laser for root scaling. This may be done without any conspicuous morphologic alterations to the root surface and with acceptably efficient removal of calculus.

The present paper reports the fabrication of long thin holes with a high aspect ratio of 100 (diameter: 10 μm, depth: 1 mm) in biodegradable polymer material (polylactic acid, referred to herein as PLA) using a UV excimer laser. Holes having diameters of 10, 20 and 50 μm are fabricated from the side surface of a PLA sheet, and their fabricated shapes are observed using an optical microscope. These holes are compared with holes fabricated in other polymer sheets. It is proven that a long thin hole can be fabricated in PLA material, although at a lower fabrication rate compared that for epoxy material. This laser fabrication is applied to a PLA microneedle, which is fabricated by the micromolding technique. A hole is fabricated along the centerline of the newly developed microneedle, and it is confirmed experimentally that blood plasma is taken into this hole by capillary force.

This paper presents a type of plasmonic circuit that is monolithically integrated with electronic devices on a silicon substrate and discusses the concept behind this circuit. Surface plasmon waveguides and detectors are integrated with metal-oxide-semiconductor field-effect transistors (MOSFETs) on the substrate. In the circuits, surface plasmon signals are generated by light at a wavelength at which silicon is transparent, and propagate along the waveguide before being converted into electrical signals by the detector. These electrical signals drive the MOSFETs during both dc and ac operation. The measured performances of these devices indicate that the surface plasmons propagate on the metal surface at the speed of light and drive the electronic devices without any absorption in silicon.

We present a promising design for low-loss asymmetric plasmonic crystal waveguides. The plasmonic crystal consists of Au cylinders, and the waveguide is introduced by eliminating a single line of cylinders on Au metal.

The optimum structure of bent SiO2-loaded surface plasmon polariton waveguides was investigated using simulations and experiments to reveal that it yielded 8.0 µm radius of curvature and 30° bending angle.

We designed and fabricated a plasmonic integrated circuit having multiple waveguides for surface plasmon polaritons and confirmed its coherent operation.

Reliability of semiconductor lasers used in recent systems and equipment is reviewed from an aspect of the degradation mechanisms. The degradation mechanisms clarified for last three decades still govern the reliability though the operating conditions of the lasers and requirements to the lasers are quite severe as the application fields diffuse widely. Based on the mechanisms, the laser reliability is briefly discussed for new application including future systems.

The purpose of this in vivo study was to examine morphologic alterations in the periodontal pocket epithelium with presence or absence of clinical inflammation following the use of the Neodymium: Yttrium-Aluminum-Garnet (Nd:YAG) laser irradiation.Subgingival Nd:YAG laser irradiation has been proposed as an alternative technique for treatment of chronic periodontitis. Several published studies have reported the clinical outcomes of such treatment.Twenty patients, diagnosed with moderate chronic periodontitis, were selected for the study. A total of 32 sites was identified and divided into a control (n=18) and laser-treated test groups (n=14). Probing depth (PD) and bleeding on probing (BOP) were recorded for all sites. Test sites were irradiated with an Nd:YAG laser using parameters of 2 W, 200 mJ pulse energy, and 10 pps delivered through a 320 μm diameter tip. Total laser treatment time ranged from 1 to 2 min. Following treatment, all specimens were harvested via biopsy and processed for scanning electron microscopy (SEM) and histologic examination.Control group specimens, depending upon initial PD, exhibited either a relatively smooth and intact epithelium with little desquamation (PD≤3 mm), or increasing degrees of epithelial desquamation and leukocytic infiltration at a PD of ≥4 mm. In the laser-treated test group, the specimens with PD≤3 mm that were BOP negative (-) exhibited a thin layer of epithelium that was disrupted. In the specimens with initial PD of ≥4 mm, complete removal of the epithelium whose extent and degree were increasing, was observed in the inflamed portion, while epithelium remained in the uninflamed portion.The SEM and histologic findings demonstrated the feasibility of ablating pocket epithelium with an Nd:YAG laser irradiation using parameters of 2 W of power (200 mJ, 10 pps). Furthermore, the presence or absence of clinical inflammation appeared to have an impact on the degree of laser-mediated epithelial ablation.

We fabricated electrospun polymer nanofiber waveguides composed of a poly(methyl methacrylate) nanofiber core doped with an organic dye and a Cytop cladding. Photoluminescence (PL) spectra are measured at the end face of individual cores with increasing distance ( d ) between the end face and the point of irradiation by the excitation laser beam. PL intensity at a wavelength of 700 nm decreases according to the relationship ~exp(− αd ) where the loss coefficient ( α ) is 17–75 cm −1 . The value of α is lower in waveguides with cladding than in those without. Reabsorption of emission by the dye is also evaluated to be 3.9 cm −1 . We confirm that the propagation loss in the waveguide results mainly from the losses inherent to the PMMA fiber itself.

Based on the degradation modes and mechanisms clarified in 1980s and 1990s, reliability of laser diodes and photodiodes is discussed for application to current optical fiber networks such as communication systems employing wavelength-division-multiplexing technique (WDM), high-frequency modulation technique, etc.

We have developed near-infrared imaging equipment that can detect small organic substances in foodstuffs with thicknesses of more than 1 mm. The equipment is composed of a high output laser diode and a CMOS camera. The irradiated light power distribution was highly uniform with a maximum optical density of 1.3 W/cm 2 . A 0.3-mm-diameter wooden stick covered with a 2-mm-thick layer of ha m can easily be distinguished in the images. The bones in fish and in chicken wing sticks could also be distinguished. The thicknesses of the fish and the chicken wing sticks were approximately 30 mm and 20 mm, respectively. We eliminated the low spatial frequency components from the images to improve the image contrast. Keywords: near-IR imaging, optical equipment, food contaminan t detection, foreign substance, spatial frequency filter 1. INTRODUCTION In our daily lives, foreign substances in foods can cause se rious problems because they can badly affect human health 1 . Various systems, including X-ray computed tomography and metal detectors, have been used to detect these contaminant substances. In mass production lines in food processing factories, X-ray computed tomography is generally used to detect foreign substances in foods, including metal articles and high-density materials such as stones. However, organic materials, such as hairs and wooden sticks, are difficult to detect when using X-ray computed tomography or metal detectors. A contaminant detection technique that uses near-i nfrared (NIR) light has been a ttracting attentio n because the technique enables transmission images to be monitored at high speed. For example, detection systems based on NIR hyperspectral imaging spectroscopy can detect impurities in cereals

This paper demonstrates the monolithic integration of a plasmonic device with metal-oxide-semiconductor field-effect transistors (MOSFETs) on a Si substrate. The plasmonic device consists of a waveguide and a detector, and is fabricated by a simple process. We confirmed that surface plasmon polaritons (SPPs) propagate for a distance of 100 μm on the Au surface, and are detected as a photocurrent. In addition, an integrated circuit containing the plasmonic device and the MOSFETs was operated by the photocurrent converted from the SPPs.

Infection after a periodontal surgical site has been prepared for guided tissue regeneration (GTR) is one of the common complications that can compromise healing. The purpose of this study was to assess the effect of repeated local antimicrobial therapy following GTR for improving clinical attachment gains, and to histologically evaluate the various cell populations and bacterial contamination of the retrieved expanded polytetrafluoroethylene membrane (ePTFE).Forty periodontal intrabony defects in 40 patients were treated by a flap procedure that included the use of ePTFE membranes to allow GTR. Patients were randomly assigned to 2 treatment groups: 20 patients were treated with the ePTFE alone (control group), and the other 20 were treated with the ePTFE combined with the administration of a weekly repeated local application of minocycline ointment for 8 weeks after membrane placement (test group). The membranes were retrieved 6 weeks after the initial surgery and sectioned serially in a coronal-apical plane. The sections were then divided into 9 fields and examined by light microscopy for the presence of inflammatory cells and oral bacteria. Clinical measurements were taken at the time of baseline examination and at a 6-month follow-up examination after removal of the ePTFE.At the 6-month follow-up examination, control and test groups showed significant improvement; i.e., reduction in the probing depth and increased clinical attachment gain compared with the values at the baseline examination. However, the mean clinical attachment gain of the test group (3.0+/-0.3 mm) was significantly (P = 0.03) greater than that of the control group (2.0+/-0.5 mm). Histologically, the total number of the cells of both groups was similar. In both groups, mononuclear cells were dominant and fibroblasts, neutrophils, and plasma cells were rarely encountered. There was a tendency for the number of macrophages to be somewhat higher in the control group. The total number of bacteria in the test group was significantly less than that in the control group. The number of bacteria in both control and test groups decreased toward the apical portion.In the present study, clinical attachment gain of intrabony defects following GTR was favorable with repeated local administration of minocycline ointment. However, a complete microbial eradication was not achieved.

The failure modes and failure mechanisms in optoelectronic devices, such as laser diodes, Light-emitting diodes, and photodiodes, are reviewed through a historical overview of device reliability and their future reliability is briefly discussed.

Changes in the threshold current and wavelength tuning characteristics due to the degradation of the active region and passive region in buried heterostructure (BH) distributed Bragg reflector (DBR) lasers are experimentally investigated. These changes are caused by the decrease in recombination carrier lifetime due to degradation. It is shown that the decrease in the carrier lifetime is mainly accelerated as a result of increased carrier density. This suggests that the degradation of the active region depends more strongly on the threshold current density than on the operating current. On the other hand, the degradation of the passive region is related to the injected current density, which affects the stability of the wavelength tunability of DBR lasers.

Facet degradation mechanisms of a 980-nm InGaAs/GaAs strained-quantum well laser are analyzed by monitoring the optical-beam induced current. It is clarified that the behavior of defects around the facets govern the long-term stability as well as catastrophic-optical damage generation during operation.

This paper investigates the degradation mode and reliability of planar waveguide photodiodes (WGPD's) for the optical hybrid module for subscriber systems. From electroluminescence topography observations and current-voltage characteristics, it is clarified that the degradation mode for early failure is caused by the concentration of electric field or a microplasma at the edge of p-n junction. The condition for screening the devices likely to fail early without a bias-temperature test is determined by investigating the degradation mode. From optical beam induced current images, it is clarified that wear-out degradation, which governs the lifetime of WGPD's, occurs at the p-n junction perimeter on a cleaved facet. Estimation of activation energy, extrapolated lifetime under a practical use condition, and failure rates for wear-out and random failure show that the WGPD has sufficient reliability for optical subscriber systems.

Cost-effectiveness is essential in developing optical access network systems. To reduce system costs, both improved system and component technologies are required. Reducing the costs of optical devices and modules in an optical network unit is especially necessary. In this paper, the requirements for optical devices in optical access networks and modules are clarified. Moreover, we also review the recent progress in technologies for semiconductor optical devices and hybrid integration for low-cost optical modules in access networks.

Optical circuits are needed to achieve high-speed, high-capacity information processing. An optical waveguide is an essential element in optical circuits. Electrospun polymer fibers have diameters in the nanometer range and high aspect ratios, so they are prime candidates for small waveguides. In this work, we fabricate uniform electrospun polymer nanofibers and characterize their optical waveguiding properties. Poly(methyl methacrylate) (PMMA) solutions of different concentration that contain a small amount of Nile Blue A perchlorate (NBA) are electrospun. Uniform PMMA/NBA nanofibers are obtained from the 10 wt% solution. The fibers are covered with transparent cladding and their ends cut vertically. A laser beam with a wavelength of 533 nm is irradiated onto the fiber from the direction vertical to the fiber axis so that it scans along the fiber. Photoluminescence (PL) at the end face of individual fibers is then measured. The PL intensity decreases with increasing distance (d) between the end face of a fiber and irradiating point of the laser beam as ~exp(-αd) with a loss coefficient (α). Measurements of five individual fibers reveal α is in the range of 17–75 cm -1 .

A gold/silicon Schottky-type plasmonic detector was monolithically integrated with two metal-oxide-semiconductor field-effect transistors (MOSFETs) on a silicon substrate. The output current from the detector was amplified 14000 times by using the MOSFETs.

We clarified the degradation behavior of semi-insulating buried heterostructure lasers in which mesa structures were fabricated by RIE and then buried by MOVPE. The degradation rate and mode correlated with the quality of the BH interface. Based on the correlation, a condition for highly stable SIBH lasers was demonstrated and confirmed experimentally and statistically.

The degradation behavior and the reliability of 980 nm lasers and 1480 nm lasers are reviewed and discussed. In addition, packaging problems for the high power lasers are also discussed from the application viewpoint. For 980 nm lasers the reliability in laser chip is limited mainly by the instability of an interface between the laser material (facet) and the anti-reflecting coating film, and for most 1480 nm lasers the reliability of the laser chip is determined mainly by the instability of a buried heterointerface. These reliability problems have been solved, however, by examining the material properties and improving device fabrication technology. The main packaging problem is a packaging-induced failure (PIF) causing sudden failure in 980 nm lasers sealed in dry N2 or Ar, but packaging problems have also been suppressed or eliminated. The device technology and packaging technology needed to make high power pump laser modules have been established, and erbium-doped fiber amplifiers pumped by these lasers are indispensable components of many optical transmission systems.

We have experimentally and theoretically demonstrated a suitable design for optical antennas with nanorods on a Si substrate to realize plasmonic integrated circuits (PICs). We show that the reflectance measurement results for gold nanorods arranged on the Si substrate correspond to the results calculated by the finite-difference time-domain (FDTD) method. Based on these studies, we designed a structure for the arrangement of aluminum nanorods for Si-PICs for a wavelength range of 800–2000 nm, to match the wavelengths of 1300 nm and 1550 nm that are commonly used in optical communication systems.

We present a new slot-in type of optical correlator that is more compact than the previous types. The correlator can fit inside the cabinet of commercial personal computers and is fully controllable with windows-based software. The correlator is a Joint Transform type (JTC) and its optical system fits inside a metal box measuring 140 mm (W) x 220 mm (L) x 40 mm (H). The optical source is a 650-nm-band laser diode of the kind used in DVD systems. A spatial light modulator and a CMOS camera are installed in the metal box with the passive optical components required for the JTC. The collimated light from the laser diode is illuminated on the spatial light modulator displaying reference and data to be examined. The light reflected from the modulator is Fourier-transformed by a lens on the plane of the CMOS camera. The computer reads the power spectrum recorded by the camera and modulates the spatial light modulator. This process is repeated. We found that these JTC processes could be performed with the prototype developed in this study.

The performances of a random-metal dielectric film composed of silver and fused silica balls were analyzed experimentally under optical AM and FM signal transmission. Optical AM and FM signals emitted from a 1550-nm-band laser diode were clearly transmitted in the random metal-dielectric film and through the optical near field generated on the film. Based on these signal transmission results, the feasibility of using this film to transmit optical AM and FM signals was experimentally confirmed in detail.

A reliability study has been made on 0.98 μm InGaAs/GaAs strained quantum well ridge waveguide lasers for pumping erbium‐doped fiber optical amplifiers (EDFAs). Analysis of a constant power long‐term aging test over 104 h shows that the degradation rate is proportional to the square root of the aging time irrespective of operating output power. A simple relationship is found between degradation rate and both operation current density and optical density. The change in light‐current characteristics and emission wavelength during constant current aging are also investigated. It is found that emission wavelength exhibits a blue shift for an identical operation current accompanied by laser degradation due to an increased threshold carrier density. In constant‐power mode aging, on the other hand, the shift is found to be rather complicated because of an additional factor of an increase in junction temperature causing a red shift. The influence of the wavelength shift on amplification characteristics in EDFAs is also discussed.

Aging tests were carried out on as‐cleaved InGaAs/GaAs strained quantum‐well ridge waveguide lasers. Although the lasers have immunity to sudden failure and have degradation rate as low as 2×10−5 h−1, after over 6000 h of operation, they readily suffered facet oxidation. The measured oxidation rate was comparable to that of GaAs quantum‐well lasers and one order of magnitude higher than that of lattice‐matched InGaAs/InP lasers. This high oxidation rate is considered to be caused by light absorption in the vicinity of the facet where the band gap is reduced because of the stress variation from biaxial to uniaxial.

The degradation modes during long term aging over 10 000 hours are clarified for over 1 500 InGaAsP/lnP buried heterostructure lasers. The degradation of buried heterostructure interface is the main cause of wear-out failure and greatly influences aging behaviour such as the rate of increase in operating current. Additionally, it is confirmed that the instability of the bonding solder metal is a cause of sudden failure.

Background: The options for medical use of signaling molecules as stimulators of tissue regeneration are currently limited. Preclinical evidence suggests that fibroblast growth factor (FGF)-2 can promote periodontal regeneration. This study aimed to clarify the activity of FGF-2 in stimulating regeneration of periodontal tissue lost by periodontitis and to evaluate the safety of such stimulation. Methodology/Principal Findings: We used recombinant human FGF-2 with 3% hydroxypropylcellulose (HPC) as vehicle and conducted a randomized double-blinded controlled trial involving 13 facilities. Subjects comprised 74 patients displaying a 2- or 3-walled vertical bone defect as measured ?3 mm apical to the bone crest. Patients were randomly assigned to 4 groups: Group P, given HPC with no FGF-2; Group L, given HPC containing 0.03% FGF-2; Group M, given HPC cotaining 0.1% FGF-2; and Group H, given HPC Containing 0.3% FGF-2. Each patient underwent flap operation during which we administered 200 μL of the appropriate investigational drug to the bone defect. Before and for 36 weeks following administration, patients underwent periodontal tissue inspections and standardized radiography of the region under investigation. As a result, a significant difference (p = 0.021) in rate of increase in alveolar bone height was identified between Group P (23.92%) and Group H (58.62%) at 36 weeks. The linear increase in alveolar bone height at 36 weeks in Group P and H was 0.95 mm and 1.85 mm, respectively (p = 0.132). No serious adverse events attribute to the investigational drug were identified. Conclusions: Although no statistically significant differences were noted for gains in clinical attachment level and alveolar bone gain for FGF-2 groups versus Group P, the significant difference in rate of increase in alveolar bone height (p = 0.021) between Groups P and H at 36 weeks suggests that some efficacy could be expected from FGF-2 in stimulating regeneration of periodontal tissue in patients with periodontitis., PLoS ONE, 3(7), e2611; 2008

The laser characteristics of 1.3 μm tensile-strained InGaAsP/InP multi quantum well (MQW) lasers were studied. The tensile strain of well layers ranged from 0.5% to 1.8%. The level of the strain dependence of the threshold current shows that the threshold current decreases drastically with increase in the tensile strain from 0.5% to 1.3%, while it stays almost constant in the 1.45%–1.8% range. Among all the samples, the 1.3% tensile-strained MQW laser shows superior performance in terms of minimum threshold current and maximum differential gain (∂g/∂N). The 1.3% tensile strain is the optimum level for the tensile-strained MQW buried-heterostructure lasers.

The feasibility of a pigtail type laser module entirely moulded in plastic is demonstrated from the viewpoint of reliability. Stable operation for this module is confirmed under various long-term aging tests, high humidity high temperature tests (85% humidity and 85/spl deg/C) and temperature cycling tests (-40-70/spl deg/C). This type of laser module is potentially suitable for low cost optical transmitters.