Spectroscopic characterization of Pr,Zn:LT and Pr,Zr:LT ridge waveguides, fabricated by high temperature in-diffusion...

Near-surface doping of lithium tantalate crystals with trivalent praseodymium ions (Pr³⁺) with concentrations up to 0.5 at.% was performed using high-temperature in-diffusion. In these substrates, planar waveguides were subsequently fabricated by in-diffusion of thin Zn or Zr metal films. Doping with the latter metals not only increases the refractive index, but also enhances the crystal's resistance to photorefractive damage, in the short visible wavelength range. In the final step of fabrication, ridge waveguides with near-rectangular cross sections were fabricated by diamond-blade dicing, allowing for propagation of visible light. Propagation losses of about 0.3 dB/cm and optical damage thresholds up to several hundreds of milliwatt were achieved for blue light at 405 nm wavelength. The Pr³⁺-doped waveguides were further optically characterized using absorption and fluorescence spectroscopy, and the lifetime of potential upper laser levels was measured. Combination of spectroscopic properties of Pr³⁺-doped lithium tantalate and its high resistance to photorefractive damage due to Zn (Zr) co-doping, makes these LT ridge waveguides what we believe to be a promising novel platform for compact integrated active devices in the visible spectral range.