Buried channel waveguides in neodymium-doped KGd(WO4)2 fabricated by low-repetition-rate femtosecond laser writing

Symmetric buried waveguides were fabricated in neodymium-doped KGd(WO₄)₂ by using femtosecond laser writing in the low-frequency regime. Due to stress-induced index changes in the regions surrounding the focal spot, mode guidance was demonstrated and low propagation losses of ∼0.2 dB/cm were obtained. Based on the comparison of the waveguides fabricated with different parameters, we present further significant analysis to get low-loss waveguides with symmetrical mode profiles. According to the reconstructed index profile, the mode distribution was numerically calculated by the beam propagation method, which showed a reasonable agreement with the experimental results.