Gain optimization of an erbium-ytterbium co-doped amplifier via a Si3N4 photonic platform

Erbium-doped waveguide amplifiers enable the integration of various active functions on a silicon platform. Er³⁺ can provide the basis for efficient optical amplification of photonic integrated circuits, but the gain is limited by cooperative upconversion leading to doping concentration limitations and insufficient optimization of the waveguide structure. In this paper, an erbium-ytterbium co-doped Al₂O₃ amplifier has been innovatively implemented on a low loss Si₃N₄ waveguide by careful design and optimization with the finite difference method. A more accurate and comprehensive theoretical model of erbium-ytterbium co-doping is established, with consideration of upconversions, energy transfer, amplified spontaneous radiation and propagation loss to perform optimization of the high-gain erbium-ytterbium co-doped waveguide amplifier. The optimized waveguide amplifier achieves a small-signal gain of more than 36 dB at 1550 nm under Er³⁺ concentration of 3 × 10²⁰ cm^-3 and Yb³⁺ concentration of 3 × 10²¹ cm^-3. Endowing Si₃N₄ photonic integrated circuits with gain can enable the miniaturization of various on-chip based active devices.