UV inscription of sub-micron periodic structures in "hard" optical materials and waveguides

Interferometric ablation and structural modification of materials using pulsed UV lasers is a powerful technique for the straightforward fabrication of relief structures in "hard" optical materials such as glasses and thin polycrystalline films. In this approach, a high intensity periodic UV radiation pattern, generated using two- or multi-beam interference, directly ablates the exposed material or induces structural modification in the irradiated volume. In the case of volume structural modification, a further step of development by selective chemical etching may employed to reveal the periodic relief pattern. The selectivity between ablation and volume structural modification is controlled by adjusting the exposure energy density and the number of pulses according to the specific material. Selected results in direct and chemically-assisted interferometric ablation patterning of 1D relief Bragg reflectors in thin oxide films and overlaid waveguides are presented and discussed. Characteristics of the inscription process related to material damage, optical loss, stitching errors and strength irregularities and their correlation to the spectral properties of the waveguide gratings are addressed.