Hitoshi Hatayama

Light-curing of dental resins with GaN violet laser diode: The effect of photoinitiator on mechanical strength

The purpose of this study was to evaluate whether a Gallium Nitride (GaN) -based violet laser diode (VLM500) could be used as a light source for light-cured dental resins. Three experimental unfilled resins containing different photoinitiators (camphorquinone, CQ; phenyl propanedione, PPD; or mono acylphosphineoxide, MAPO) were evaluated. These resins were light-cured with a VLM500 laser diode, and their ultimate micro-tensile strengths (μTS) were compared to those cured with three different LED light sources (Curenos, G-Light Prima-normal mode and G-Light Prima-PL mode). The VLM500 produced high μTS values in all three resins, and we concluded that this violet laser diode can be used as a light source for light-cured dental resin materials.

Variable attenuation slope compensator (VASC) using silica-based planar lightwave circuit technology for active gain slope control in EDFAs

A novel planar lightwave circuit device called variable attenuation slope compensator (VASC) is proposed for active gain slope control in EDFAs. Its attenuation slope is electrically controllable with the average attenuation unchanged.

Light-curing efficiency of dental adhesives by gallium nitride violet-laser diode determined in terms of ultimate micro-tensile strength

The purpose of this study was to evaluate whether violet-laser diode (VLD) can be used as light-curing source. The ultimate (micro-)tensile strength (μTS) of three adhesives was determined when cured by VLD in comparison with curing by two different types of commercial LED light-curing units. One VLD (VLM 500) and two LED units (Curenos and G-Light Prima) were used to cure the adhesive resin of the two-step self-etch adhesives Clearfil SE Bond, Tokuso Mac Bond II, and FL-Bond II. A 0.6-mm thick acrylic mould was filled with adhesive resin and cured for 60 s. After 24-h water storage, specimens were trimmed into an hourglass shape with a width of 1.2 mm at the narrowest part, after which the μTS was determined (n=10). In addition, the light transmittance of each adhesive was characterized using a UV-vis-NIR spectrometer. No significant difference in curing efficiency between VLD and LED were observed for both Tokuso Mac Bond II and FL-Bond II (p>0.05). For Clearfil SE Bond, the μTS of VLD-cured specimens was higher than that of the specimens cured by the LED Curenos unit (p<0.05). Spectrometry revealed that this marked difference must be attributed to a different light transmittance of Clearfil SE Bond for visible blue light versus for the lower area of UV and visible violet light. In conclusion, A GaN-based violet laser diode can be used as light-curing source to initiate polymerization of dental resins.

Effects on soft tissue produced by a visible violet diode laser

A violet laser with an oscillating wavelength of 405 nm has recently been developed in industry. Laser irradiation at this wavelength penetrates tissue less aggressively than Nd:YAG and diode laser irradiation at wavelengths of 810 nm, and more aggressively than irradiation by carbon dioxide laser. Further, protein is reported to absorb this 405 nm wavelength at high rates. This study was conducted to evaluate the effect of the violet laser on soft tissue in vitro. A prototype violet diode laser produced by Sumitomo Electric Industries was used. This laser irradiates with a continuous wave at a wavelength of 405 nm. Soft tissue samples were irradiated by the device at output powers in a range from 850 mW to 2400 mW as the irradiated samples were conveyed at a scanning speed of 1 mm/sec. The beam diameter was about 270 μm. The irradiated samples were observed by a stereoscopic microscope, fixed with a 10% neutral formalin aqueous solution, and histologically examined. Irradiation by the device vaporized a U-shaped section of tissue to a depth of about 350 to 900 μm. A denatured layer measuring 300 to 450 μm in width was observed under the carbonization layer. The depth of vaporization increased in proportion to the power. These results indicate that a violet laser has good potential to become an effective laser for the cutting and coagulation of soft tissue.

Wide-dynamic-range and channel-count-free thulium doped fiber amplifiers employing variable slope attenuation compensators designed for photonic networks

This paper presents the unique behavior of thulium doped fiber amplifiers (TDFAs) under circumstantial changes in the multi-wavelength photonic networking systems, namely in the span loss, the channel count, and the environmental temperature. Unlike EDFAs, TDFAs exhibit the dynamic gain-profile variation even when the gain-magnitude is fixed under the automatic gain control (AGC). In addition, it has been shown that the dynamic gain variation is less serious in the up-conversion pumping scheme. As a means to maintain the gain-profile of the up-conversion pumped TDFA, three techniques have been introduced and compared, namely: (i) the auxiliary pump around 1.56 μm, (ii) the mid-stage variable optical attenuator (VOA), and (iii) the mid-stage variable slope attenuation compensator (VASC). Employing the VASC, the output signal level has been successfully maintained within the error of 0.2 dB for the dynamic range of 8 dBp-p and the channel count from 4 to 32. Moreover, it has been shown that the temperature change also induces the gain tilt, which has been successfully compensated by the VASC with the level variation of less than 0.3 dB. In summary, the adjustable slope-compensating device will be useful to control the TDFAs under the various circumstantial changes.

Comparison of violet diode laser with CO 2 laser in surgical performance of soft tissues

The violet diode laser (405nm) has recently begun to be studied for surgical use and authors reported the soft tissue could be effectively incised by irradiation power of even less than 1W. The wavelength of this laser is highly absorbed by hemoglobin, myoglobin or melanin pigment. Cutting or ablating soft tissues by lower irradiation power might be preferable for wound healing. The CO2 laser is known to be preferable for low invasive treatment of soft tissues and widely used. The CO2 laser light (10.6μm) is highly absorbed by water and proper for effective ablation of soft tissues. In this paper, we report the comparison of the violet diode laser with the CO2 laser in surgical performance of soft tissues. Tuna tissue was used as an experimental sample. In the case of the violet diode laser, extensive vaporization of tissue was observed after the expansion of coagulation. Carbonization of tissue was observed after the explosion. On the other hand, consecutive vaporization and carbonization were observed immediately after irradiation in the case of CO2 laser. The violet diode laser could ablate tissue equivalently with the CO2 laser and coagulate larger area than the CO2 laser. Therefore the violet diode laser might be expectable as a surgical tool which has excellent hemostatis.

Dispersion flattened fiber with large-effective-core area more than 50 /spl mu/m/sup 2/

Summary form only given. In summary, we have presented the design of dispersion-flattened fibers with relatively large-effective-core areas employing the triple-cladding profile and successfully fabricated quasi-dispersion-flattened fibers exhibiting the dispersion slopes 55 /spl mu/m/sup 2/.