Photonic pattern fabrication in fused silica, BK7, and Ge-doped borophosphosilica glass by a femtosecond laser

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 mu J 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 pm (fused silica) and 11 mu m (BK7) at an input fluence of 71 J/cm(2). 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 x 10(-3) Was obtained for 20,000 laser shots of 73 mJ/cm(2) per pulse. It is thought that the index modification occurs through the defect formation by the fs-laser irradiation.