Double circular erosion patterns on dielectric target in magnetron sputtering.

In rf magnetron sputtering, a circular erosion pattern forms on the surface of a circular metal conductor target with permanent magnets on its back. In this case, the theory behind the erosion pattern has been established. However, in the case of a dielectric target, a double circular erosion pattern is formed. So far, this pattern has been phenomenologically recognized by experimenters; however, it has not yet been investigated. In this study, we performed a magnetron sputtering experiment with a SiO2 dielectric target, and confirmed the formation of a double circular erosion pattern. The dimensions of the double circular erosion pattern varied depending on the insulation resistance or the thickness of the SiO2 target. Furthermore, we found that the dimensions of a double circular erosion pattern changed by making a gap between the SiO2 target and guard ring. Based on the experimental results, we have proposed a qualitative model to explain the formation mechanism of double circular erosion patterns.

Dynamic evolution of the spectrum of long-period fiber Bragg gratings fabricated from hydrogen-loaded optical fiber by ultraviolet laser irradiation.

Long-period fiber Bragg gratings fabricated by exposure of hydrogen-loaded fiber to UV laser light exhibit large-scale dynamic evolution for approximately two weeks at room temperature. During this time two distinct features show up in their spectrum: a large upswing in wavelength and a substantial deepening of the transmission minimum. The dynamic evolution of the transmission spectrum is explained quantitatively by use of Malo's theory of UV-induced quenching [Electron. Lett. 30, 442 (1994)] followed by refilling of hydrogen in the fiber core and the theory of hydrogen diffusion in the fiber material. The amount of hydrogen quenched by the UV irradiation is 6% of the loaded hydrogen.

Thermal tuning of mechanically induced long-period fiber grating.

We have developed a wideband tunable optical filter that uses a long-period fiber grating (LPFG) in which both resonance wavelength and its signal attenuation can be adjusted. We create the grating mechanically by pressing a spring coil to an optical fiber. We achieve continuous fine tuning of wavelength and attenuation by varying the temperature of the LPFG. The adjustable ranges of the LPFG are more than 200 nm in resonance wavelength and more than 10 dB in signal attenuation.