2018 年 126 巻 7 号 p. 495-503
Surface-tension molding (StM) and localized-laser heating (LLH) techniques were developed for on-chip fabrication of micrometer-size super-hemispherical glass (µ-SSG), which has a truncated spherical shape, and spherical glass. The optical functionalities of these glasses as solid immersion lenses (SILs) and whispering gallery mode (WGM) optical resonators were demonstrated. In the StM method, glass particles on a glassy carbon substrate were heat-treated under an H2/N2 atmosphere and the glass particles were melted and deformed into super-hemispherical shapes that were determined by the wetting property of glass melt on the substrate. The contact angle of the droplet ranged from 120 to 167° depending on the glass composition. We found that the shape of a µ-SSG with a composition of 20Na2O–10CaO–70SiO2 (in mol %) satisfied the optical condition of a SIL and demonstrated super-resolution for µ-SSG fabricated by StM. The LLH technique enables us to make a nearly perfect sphere on a substrate. A micrometer-size Nd3+-doped tellurite glass particle on a transparent substrate was irradiated by a continuous-wave (CW) laser with a wavelength near 810 nm and a power of more than 150 mW, and only the particle was heated and melted into a spherical shape on a transparent substrate at room temperature. The obtained spherical glass had a very smooth spherical surface with high sphericity. The Nd3+-doped microsphere showed WGM resonances to free-space direct pumping of the CW laser with a wavelength of 790–820 nm, and laser emissions were observed with a threshold of a few-milliwatts. Effects of add-on structures, e.g., a terrace or a bubble, on the laser characteristics of the microsphere were also investigated. Both structures acted as an entrance for pumping light and resulted in laser thresholds lower than 1 mW. The terrace structure reduced the emission modes and showed quasi-single mode laser emission. The bubble-containing microsphere laser realized broad excitation spectra due to the modified WGM. These results indicate that a spherical glass with a smooth surface formed from a molten glass droplet on a chip has excellent potential in the field of optics and photonics.