Spectroscopy of erbium-doped potassium double tungstate waveguides

We report the spectroscopy of crystalline waveguide amplifiers operating in the telecom C-band. Thin films of erbiumdoped gadolinium lutetium potassium double tungstate, KGd x Lu y Er 1-x-y (WO 4 ) 2 , are grown by liquid- phase epitaxy onto undoped potassium yttrium double tungstate (KYW) substrates and micro-structured by Ar + - beam etching. Channel waveguides with erbium concentrations between 0.45–6.35 × 10 20 cm -3 are characterized. The transition cross-sections of interest are estimated. The effect of energy-transfer up-conversion (ETU) is experimentally investigated. Microscopic and macroscopic ETU parameters are extracted from a simultaneous analysis of 20 decay curves of luminescence on the transition 4 I 13/2 → 4 I 13/2 . The correlation between ETU and the doping concentration is studied. Pump excited-state absorption (ESA) on the transition 4 I 11/2 → 4 F 7/2 is investigated via a direct ESA measurement using a double-modulation pump-probe technique. The effect of ESA is studied for different pump wavelengths. The pump wavelength of 984.5 nm is found to be favorable for the complete range of erbium concentrations.