Gain characteristics of a high concentration Er³⁺-doped phosphate glass waveguide

A channel waveguide on an erbium-doped phosphate laser glass was fabricated by a dry silver-film ion exchange technique, and its gain properties were studied experimentally. The propagation loss of the fabricated waveguide was 0.63 dB/cm at 1.3 μm. Er³⁺ concentration of 1×10 ²⁰ ions/cm³ was chosen so that no concentration quenching occurred. This was confirmed by measuring a fluorescence lifetime of 8.4 ms at 1.54 μm. Gain of the fabricated waveguide was measured by using a Ti:sapphire laser at a wavelength of 980 nm and a laser diode of 1.532 μm producing pump and signal beams, respectively. The signal wavelength used for the experiments was shorter than the emission peak, and the measured gain of the 1.8 cm waveguide was comparable to the total loss. However, the model showed that lasing is expected at the emission peak with a 3.6 cm long waveguide fabricated in a similar manner. Calculation results showed that the potential gain of 8.8 dB can be realized with 250 mW pump power, and a 7.2 cm long waveguide provided that mode overlap can be increased by 20% and propagation loss can be reduced by 50%. No significant upconversion effect was observed up to 1.1×10 ⁶ W/cm² pump intensity.