32 dB modal gain in Er:LiNbO₃ waveguide amplifiers with Er,Yb:Al₂O₃ cladding layer via bidirectional pumping scheme

Lithium niobate on insulator (LNOI) holds substantial promise for applications in integrated photonic systems. Waveguide amplifiers are fundamental photonic components within integrated photonic platforms. In this paper, we report a high-gain erbium-doped lithium niobate (Er:LiNbO 3 ) waveguide amplifier coated with an erbium and ytterbium co-doped aluminum oxide (Er,Yb:Al 2 O 3 ) cladding layer. The ridge waveguide dimensions and cladding thickness were optimized via finite element method (FEM) simulations of electric field distributions, with further analysis of the impacts of optical confinement factor (Γ) and effective mode area ( A eff ) on device performance. This paper further validates the advantages of a bidirectional pumping scheme in suppressing amplified spontaneous emission (ASE) and reducing noise figures (NF). Numerical simulations based on an Er 3+ -Yb 3+ co-doped theoretical model demonstrate that under an Er 3+ concentration of 3×10 20 cm −3 , Yb 3+ concentration of 2.7×10 21 cm −3 , and a signal power of −30 dBm, the amplifier achieves a modal gain of 32 dB. This work establishes a theoretical foundation for the monolithic integration of compact Er 3+ -Yb 3+ co-doped waveguide amplifiers on the LNOI platform through systematic optimization of waveguide dimensions and doping ratios.