Atomic layer deposition-enabled few-mode erbium-doped waveguide amplifiers with low differential mode gains

We present a novel and efficient methodology for obtaining high-gain on-chip few-mode erbium-doped waveguide amplifiers, which exhibit a moderate differential mode gain (DMG). The efficiency of the device is validated by an optimized algorithm that theoretically models the gain performance of the six lowest-order optical modes, namely TE₀, TM₀, TE₁, TM₁, TE₂, and TM₂. Notably, these six signal modes achieve internal net gains exceeding 22 dB within a 5-cm-long waveguide, while maintaining the DMG at a mere 2 dB. This DMG value represents a significant reduction of 5 dB compared to the non-optimized uniform doping configuration. Furthermore, a maximum saturated output power of 150 mW has been achieved. As a practical demonstration, we also propose a feasible fabrication process utilizing atomic layer deposition (ALD) along with standard complementary metal-oxide semiconductor (CMOS) techniques. These results demonstrate the superiority of our methodology in enhancing the performance of few-mode optical waveguide amplifiers.