Novel technique for fabrication of nanoparticle structures in KNbO ₃-TeO₂ glass for photonic integrated circuits

We succeeded in fabricating novel nanoparticle structures on KNbO ₃-TeO₂ glass induced by ultraviolet (UV) laser irradiation and found that the size and size distribution could be controlled by the conditions of laser irradiation, such as fluence, pulse repetition rate, and the temperature of the glass specimen by heat assistance (HA). Nano-sized particles are an interesting new material, because they will be able to open the door to the invention of photonic circuits of extremely small size, which transfer optical signals through optical near-field energy operating by a completely different principle. The particle diameters may be controlled from approximately 200 nm up to 500 nm by modifications of UV laser fluence and the repetition rate of pulses. When using HA with a glass specimen during laser irradiation, it has been found that nanoparticle formation is activated and particle size increased as the temperature of the glass increased, and the uniformity of particle size is markedly improved by HA treatment. The standard deviation of particle size is 20 nm at 100°C. A 60% improvement in the size variation of particles is possible in comparison with laser irradiation without HA. These results suggest that heat is involved in nanoparticle formation during UV laser irradiation, which means that the overall history of heating with pulsed laser irradiation is critically important to control the form of the particles. Furthermore, periodic structures with an 800 nm pitch constructed by lines of ordered nanoparticles with diameters of approximately 150-300nm were successfully fabricated by laser irradiation through a phase mask. This is a significant advancement towards the realization of nanophotonic circuits.