PHOTONIC PATTERN FABRICATION IN FUSED SILICA, BK7, ANDGe-DOPED BOROPHOSPHOSILICA GLASS BY A FEMTOSECOND LASER

Abstract

Photonic patterns were fabricated in fused silica, BK7, and Ge -doped borophosphosilica glass ( Ge -BPSG) using a focused femtosecond (fs)-laser beam. By focusing tens to hundreds of μJ fs-laser beam with a 10x microscope objective, we inscribed the semi-circular cavity patterns on the fused silica and the BK7. The inscribed hole diameters are 28 μm (fused silica) and 11 μm (BK7) at an input fluence of 71 J/cm2. This circular-cavity patterning is ascribed to the ablation via the multi-photon absorption process. For the application to functional devices, the surface relief gratings (SRGs) were made in fused silica and BK7 by focusing the fs-laser beam on the glass surface with a cylindrical lens and by translating the sample in the direction perpendicular to the focus line. The first-order diffraction efficiencies of the prepared SRGs are 34% (fused silica) and 14% (BK7). A refractive-index grating was also fabricated in the Ge -BPSG by using the two-beam interference method. The maximum index modulation of 2.5 × 10-3was obtained for 20,000 laser shots of 73 mJ/cm2per pulse. It is thought that the index modification occurs through the defect formation by the fs-laser irradiation.