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, LP11a, and LP11b 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 LP21b mode at 120 mW at 976 nm. The ultralow differential modal gain is 0.4 dB. In addition, simultaneously amplified LP01, LP11a, and LP11b 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.