Sub-micron grating formation in Ta O -waveguides by 2 5 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 mm=300 mm can be produced with a single laser pulse of about 100 mJrcm2 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. q1999 Elsevier Science B.V. All rights reserved.