Sub-micron grating formation in Ta2O5-waveguides by femtosecond UV-laser ablation

Sub-micron-period surface gratings on Ta2O5 waveguide layers were produced by ablation with a sub-ps-UV-laser. The structure is generated by projection imaging of a primary transmission grating mask. A grating of 500 nm period with a surface modulation depth of 10 nm on a sample area of about 300 mu m x 300 mu m can be produced with a single laser pulse of about 100 mJ/cm(2) at 248 nm. Adjustment of the modulation depth to specific requirements can be accomplished by varying laser fluence or pulse number. The structures can be used as grating couplers. (C) 1999 Elsevier Science B.V. All rights reserved.