Improvement of differential modal gain in a ring-core few-mode erbium-doped polymer optical waveguide amplifier.

A few-mode erbium-doped waveguide amplifier (FM-EDWA) with a confined Er3+ doped ring structure is proposed to equalize the differential modal gain (DMG). The FM-EDWA amplifying three spatial modes (LP01, LP11a and LP11b) is optimized by genetic algorithm and fabricated using precise lithography overlay alignment technology. We observe gain values of over 14 dB for all modes with DMG of 0.73 dB at 1529 nm pumped only with LP01 for the power of 200 mW. Furthermore, a flat gain of more than 10 dB is demonstrated across 1525-1565 nm, with a sufficiently low DMG of less than 1.3 dB.

Few-mode polymer waveguide amplifier with a dual-layer coronal refractive index profile.

A novel, to the best of our knowledge, few-mode waveguide amplifier with a dual-layer coronal core is first proposed. Reconfiguring the refractive index profile is adopted to equalize the modal gains pumped in a single mode. The polymer in terms of the prominent advantages of simple processing and the ease of adjusting refractive index is utilized. The waveguide supporting LP01, LP11a, and LP11b is optimized by the genetic algorithm and fabricated by accurate alignment mask. The crosstalk effect and modal profiles are characterized. The modal gains with different signal power and pumping modes are revealed. The schemes in forward and backward pumps are represented. An average gain of 11.84 dB per mode and an ultralow differential modal gain of 0.36 dB are obtained in a 0.3 cm waveguide at 1526 nm through backward pumping of the LP21b mode at 240 mW for an input signal power of 0.1 mW.