Single-Mode Rb⁺-K⁺ Ion-Exchanged BK7 Glass Waveguides with Low Losses at 1550 nm

Single-mode Rb⁺-K⁺ ion-exchanged channel waveguides operating at 1550-nm wavelength have been demonstrated in BK7 glasses. The ion-exchange process was carried out using RbNO₃ molten bath; the melt temperature ranged from 420 °C to 480 °C, and the exchange time from 30 to 120 h. The waveguide properties were characterized optically, and the stress-induced index change and waveguide birefringence were also studied. The propagation losses of annealed channel waveguides were measured to be ∼0.4 dB/cm, and the diffusion constant and the activation energy of Rb ⁺ in BK7 glasses are calculated to be 3.65 × 10^-17 m²/s and 4.23 kJ/mol, respectively.