First Demonstration of Gain-Equalized Six-Mode Waveguide Amplifier

We present the first experimental demonstration of a gain-equalized six-mode waveguide amplifier featuring a dual-layer ring-core architecture. By synergistically optimizing the refractive index profile, doping concentration gradient, and pump configuration, we enabled balanced amplification across the LP01, LP11a, LP11b, LP21a, LP21band LP02signal modes. A genetic algorithm was employed to define the optimal structural parameters for the waveguide amplifier, which was subsequently fabricated using a high-precision alignment technique. The pump scheme was refined through a discrete search algorithm, identifying a dual-pump combination of the LP01mode at 180 mW and LP02mode at 90 mW as the most effective. This configuration yields an average gain for six-mode of 10.72 dB and a low differential modal gain of just 0.8 dB at 1550 nm, establishing a key building block for high-capacity on-chip mode-division multiplexing.