Glass microspheres with add-on structures for optical resonators

Tellurite glass microspheres having whispering gallery modes (WGMs) were fabricated on a substrate by using a localized-laser heating technique, and nano- or micro-structures were added on the micro spheres to modify the resonance modes. Efficient coupling between the modes inside microspheres and pumping light was realized by the add-on structure; terrace, bubble, or plasmonic array. We fabricated an Nd3+-doped tellurite glass microsphere laser on a substrate by using a localized laser heating technique. The microsphere was pumped by free-space direct pumping of a tunable continuous-wave Ti: sapphire laser with a wavelength of 780 to 830 nm. The terrace structure acted as an entrance of the pumping light for the microsphere to decrease the laser threshold, and reduce the number of the laser emission laser peaks. The bubble structure also decreased the laser threshold and showed numerous peaks at a broad wavelength range in the excitation spectra due to non-degenerated WGMs. The microsphere laser on a plasmonic array modified both emission and excitation spectra. The highest-intensity laser emission mode was changed, and numerous peaks on a broad wavelength range were also observed. These results indicate that the add-on structures were useful for efficient utilization of broadband light like light-emitting diode and sunlight into laser light due to the modification of WGMs in a true sphere.