Sub-micron period relief grating structures inscribed on erbium doped Ta2O5 waveguides using 213 nm, 150 ps laser radiation

The inscription of sub-micron period relief gratings of period 360 nm by interferometric ablation of erbium doped tantala (1 wt% Er₂O₃) rib waveguides using 213 nm, 150 ps Nd:YAG laser radiation is presented in this paper. The principal objective of this study is to establish the feasibility and conditions for writing sub-micron period grating structures in thin film erbium doped tantala waveguides, where thermal diffusion effects play a deleterious role, and use those gratings as output couplers for lasing applications in the 1520-1550 nm wavelength band. Volume damage and relief gratings were written on the waveguides using an elliptical Talbot interferometer, and real time diffraction efficiency measurements allowed study of grating depth growth and ablation threshold. AFM scans show formation of shallow relief gratings both below and above the ablation threshold.