High-reflectivity Bragg gratings fabricated by 248-nm excimer laser holographic ablation in thin Ta₂O₅ films overlaid on glass waveguides

We demonstrate strong Bragg grating reflection in Ta2O5 (tantalum pentoxide) thin films overlaid on potassium ion-exchanged channel waveguides in BK-7 glass, inscribed using 248-nm excimer laser holographic ablation. The experimental data presented are divided into two sections: the first section refers to the study of the grating ablation process of thin Ta2O5 films with respect to the exposure conditions, while the second focuses on the implementation of these relief gratings in functional waveguide devices. Firstly, experimental data on grating morphology versus exposure conditions, accomplished with scanning electron microscopy microscans, are presented. In the second section diffraction spectra for waveguide gratings are presented and analysed. Spectral notches in transmission of depth -18 dB for the TM polarisation were obtained from 16-mm-long gratings patterned in waveguides overlaid with a 105-nm-thick Ta2O5 film, using 50 pulses of 60 mJ/cm2 energy density