Radiative transitions and optical gains in Er³/Yb³⁺ codoped acid-resistant ion exchanged germanate glass channel waveguides

K⁺-Na⁺ ion-exchanged channel waveguide amplifiers have been fabricated in Er³⁺/Yb³⁺ codoped acid-resistant aluminum germanate (NMAG) glasses. The Judd-Ofelt parameters indicate high asymmetry and strong covalent environment in the glass substrates. The optical gain and the relative gain (the signal enhancement) of a 2.5 cm long waveguide amplifier were measured to be 9.10 and 8.16 dB, respectively, and after compensating both the propagation loss and the absorption loss, a maximum internal gain of ∼2.0 dB at 1.534 μm was obtained, which reveals the successful employment of the thermal ion-exchange technology on the low phonon energy glasses. Based on this work, ion-exchanged Pr³⁺, Tm ³⁺, and Ho³⁺ doped NMAG glass waveguides will bring surprises in developing O-, S- and U-band waveguide amplifiers, infrared UV-writing grating waveguide lasers, and compact integrated optical devices.