Photofabrication for microphotonics in glass

Large-scale integration of compact photonic devices may be the key technology for the future information age. If optical-waveguide structures with small radius of curvatures are integrated inside a small glass tip along with active devices, a paradigm of microphotonics inside glass may become possible. We will review the fabrication techniques for the waveguides and photonic-band structures inside glass with the ultrashort laser pulses and present our recent results of fabrication experiments. The experimental studies include fabrication of birefringent waveguides, formation of small vacancies called voids, and drilling of a narrow but long hole from the rear side of a glass. We will show the birefringence properties of waveguides that are induced by the lienarly-polarized ultrashort laser pulses of approximately 100 fs duration. Birefringence of the waveguides depends on the polarization states of the fabrication beam. The experimental studies on the stabilities of a void during the fabrication process are also presented. We will show that the voids move during the fabrication process although the beam and sample are fixed. It will be shown that the void moves from pulse to pulse toward the upstream direction along the optical axis. We can currently drill a long hole of more than 200 microns with a diameter of several microns. We also present the results of numerical analysis of optical propagation through photonic structures that are based on the array of voids.