Low-loss Ga:Er:LiTaO₃ optical waveguide for integrated optics

Low-loss gallium(Ga³⁺)-diffused erbium(Er³⁺)-doped LiTaO₃(Ga:Er:LiTaO₃) channel waveguide was fabricated using erbium metal film diffusion followed by photolithographically patterned gallium oxide(Ga₂O₃) strip diffusion. Secondary ion mass spectrometry analysis shows that Er³⁺ concentration follows a Gaussian profile, Ga³⁺ concentration follows a sum of two error functions at the waveguide surface and a Gaussian profile in the depth direction. Optical studies show that the waveguide supports single-mode propagation at 1.5 μm wavelength with a coupling loss <1 dB and a waveguide loss 0.2(0.3) dB/cm for the TE(TM) mode, and with a small polarization dependence in mode field distribution. Stable optical gain of ∼1.0 dB/cm was measured at 1547 nm wavelength with 220 mW pump power of 980 nm wavelength, indicating good photorefractive damage resistance of the waveguide.