Few-mode polymer optical waveguide amplifier for mode-division multiplexed transmission

We propose a few-mode erbium-ytterbium codoped polymer optical waveguide amplifier employing mode-selective photonic lanterns capable of multiplexing and demultiplexing. A reconfigurable pump configuration scheme is adopted to balance the modal gain per mode. A square few-mode waveguide amplifier supporting LP₀₁, LP₁₁, and LP₁₁ modes is designed and fabricated. The crosstalk effect and modal profiles are characterized. An average gain of 10.4 dB per mode is obtained in a 1.5 cm waveguide at 1555 nm through pumping of the LP₀₁ mode at 320 mW and the LP₂₁ mode at 120 mW at 976 nm. The ultralow differential modal gain is 0.4 dB. In addition, simultaneously amplified LP₀₁, LP₁₁, and LP₁₁ modes are also demonstrated across the whole C-band with low noise figures. To the best of our knowledge, this is the first report of an experimental realization of a few-mode optical waveguide amplifier.