Er-Doped Optical Waveguide Amplifiers in X-Cut Lithium Niobate by Selective Codiffusion

Positive small-signal net gain is demonstrated for the first time in optical waveguide amplifiers in X-cut Y-propagating lithium niobate by selective erbium (Er) and titanium (Ti) codiffusion. First, a planar codiffused sample was prepared for dynamic secondary ion mass spectrometry (SIMS) analysis. An erbium diffusion coefficient of 0.17 ??m²/h was calculated from the SIMS results and from the diffusion theory. Furthermore, the fabrication of optical waveguide amplifiers and the characterization methods are described. In a 3.5-cm-long optical waveguide amplifier, an optical small-signal net gain of 1.4 dB at 1531 nm was measured for the transverse-magnetic mode by optical pumping at 1488 nm with a launched pump power of 90 mW. The codiffusion process shows good net gain efficiency (dB/mW) and an advantage for the fabrication of integrated optical passive and active functions in lithium niobate.