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 projectio n imaging of a primary transmission grating mask. A grating of 500 nm perio d 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 c an 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.