Three-dimensional microphotonic optical systems

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The purpose of this research was 1) the investigation of the mechanism of refractive index changes in photorefractive crystal and Ge-doped silica glass that are induced by ultrashort laser pulses and and 2) fabrication and evaluation of microstructures inside glass such as the waveguides, dividers, couplers and small Bragg reflectors. The results obtained in the research term are listed below.1) Induction of refractive index change by self-trapped filamentsWe induced the refractive index change by using the filaments formed by femtosecond laser pulses (800 nm) focused into the silica glass. The diameter of the area of refractive index change was approximately 2μm and the length was several ten to several hundred mm. The maximum refractive index change was 0.01.2) Fabrication of birefringent microphotonic elementsBy mechanically translating the filament formed by the ultrashort laser pulses, we fabricated optical waveguides with negligible loss (core diameter ; 2μm, length ; 2 mm). We f … More ound that the waveguides had birefringence and evaluated the birefringence by making a grating with these waveguides.3) Optical seizing and mering of voidsWe focused the ultrashort laser pulses by high-NA objectives and formed voids inside glass. We cleaved the glass inside which voids are formed and observed the void by scanning electron-beam microscope. We identified the voids as the vacancies inside the glass. We succeeded in moving the void by approximately 5μm along the optical axis by repeating the irradiation of the ultrashort laser pulse and translation of the focusing lens. We also succeeded in merging the two voids into one.These results do not unfortunately lead to the direct elucidation of the mechanism. However, they provide strong clues to the interpretation of the mechanism of refractive index change in silica glass.A part of this work has been published in Optics Letters and is under preparation for publication. Two patents related to the movement and merger of voids and formation of birefringent optical waveguides are under application by the help of Japan Science and Technology Corporation. The results of movement and merger of voids are picked up by the technical magazine, Laser Focus World (Vol.37, Issue 2, 2001). Less