Motoshi Ohama

Generation of second harmonics in Ge-doped SiO2 thin films by ultraviolet irradiation under poling electric field

Thin films of Ge-doped silica were prepared by radio-frequency sputtering in a controlled atmosphere of Ar and O2 and then subjected to ultraviolet irradiation under poling electric field (UV poling). Effects of oxygen mass flow content during the sputtering on the second-order nonlinearity of the films were investigated. Second harmonic generation (SHG) was observed and its intensity was found to depend greatly on the oxygen mass flow content with an optimum at 1 cm3/min. The annealing in a vacuum enhanced SHG intensity and values as high as 12.5±0.6 pm/V have been achieved with films containing 50 mole % of GeO2. This is on one hand, and we also found that loading thin films with hydrogen prior to UV poling largely improved the decay of SHG. A decay time as long as 7 years has been obtained. The change in second-order optical nonlinear properties of the films is discussed based on structural defects.

Crystallization of GeO 2 –SiO 2 glass by poling with ArF-laser excitation

We report on crystallization of 15.7GeO(2) 84.3SiO(2) (in mol.%) glass by poling with ArF-laser excitation. The UV intensity was 100(mJ/cm (2))/pulse , and the number of shots was 10(4) . The crystallites that were observed in the glass were approximately 15-20microm in diameter. The crystallization feature was dependent on the poling electric field, showing a threshold field of ~0.5x10(5)V/cm , beyond which crystallization occurred.

Crystallization and optical nonlinearity in GeO2–SiO2 glass poled with ArF excimer-laser irradiation

We report on crystallization and second- and third-order optical nonlinearities of GeO2–SiO2 glass poled with ArF laser irradiation. With laser power and 100 mJ/cm2/pulse, the treatment generates crystallites in the glass, provided that the poling field strength is greater than 0.5×105 V/cm. Its crystal structure is possibly the cristobalite phase of the Ge–Si–O system. A large coefficient of second-harmonic generation (SHG), d33, is induced in the glass with the crystallite generation, and its value is comparable to d22 of LiNbO3. Moreover, the third-order optical susceptibility χ(3) increases by a factor of approximately 15 compared to that of glass without the crystallites. Even after the d33 coefficient decays out, the crystallites and χ(3) are retained. The result suggests that the large SHG in the glass is not induced from inert second-order nonlinearity of the crystallites, but the main origin of the induction is the associated effective second-order nonlinearity with the formation of the space-cha...

Decay of ultraviolet-induced optical absorption in Ge-doped SiO2 glass

We report quantitative measurements on the decay of optical absorption at various elevated temperatures in ultraviolet (UV)-irradiated SiO2 glasses doped with Ge. From the Arrhenius plots of decay time constants, the activation energy of the Ge E′ center in the UV-irradiated glasses has been determined to be 2.4±0.3 eV, while the reported activation energy of Ge E′ decay in UV-poled glasses is 0.4±0.1 eV. The present experimental results strongly suggest that the decay process of the Ge E′ center induced in UV-irradiated glasses is quite different from that in UV-poled glasses.

Light-Emitting Seal Using Self-Aligned Organic Light-Emitting Structure

A light-emitting seal using a self-aligned organic light-emitting diode (OLED) and a laminate process is proposed and demonstrated. This device has a self-aligned ink-jet-printed structure where an insulating material is dissolved in a solvent, and a mixture of organic materials is formed at the same position as that of the ink-jet-printed region. A cathode electrode is laminated onto the above ink-jet-printed structure. The merits of the device are its simple fabrication without the need for photolithography or any vacuum process, and its lower cost. The typical luminance obtained was 6,810 cd/m2. The concept of the device is useful for light-emitting seals (LES), tags and graphics with noncontact electromagnetic electric supply but no electric supply line.