Triple-Doped Rare-Earth Nanoemitters for Two-Photon 3D Printing of Chip-Scale Polymer Optical Waveguide Amplifiers

Polymers with gain media can enable 3D printing of chip-scale optical amplifiers and lasers. In this work, a 3D-printable resin containing uniform dispersion of core/shell erbium–ytterbium–cerium codoped rare-earth nanoparticles (RENPs) is designed, synthesized, and characterized. The core/shell RENPs (NaYF4:Er3+,Yb3+,Ce3+@NaYF4) are synthesized by a high-temperature thermal decomposition method. Uniform dispersion at high concentrations of the RENPs in a 3D printable resin is achieved by selectively polymerizing methyl methacrylate on the surface of the RENPs, which prevents nanoparticle agglomeration. It is observed that codoping with Ce3+ ions facilitates nonradiative energy transfer between the upper excited states of Er3+ ions to the Ce3+ ions, significantly suppressing up-conversion pathways and leading to an order of magnitude increase in the down-conversion (1.53 μm) to up-conversion (0.536 μm) ratio using a 980 nm pump. The resin is used in a two-photon lithography 3D printer to fabricate ultrashort chip-scale spiral optical waveguide amplifiers in the telecommunication C-band. The fabricated amplifier exhibited a relative gain of 7.7 dB for a 1.5 mm long spiral waveguide, with a pump power operating below 130 mW. The subcentimeter length of the amplifiers enables high small-signal gain to be achieved with low pump power for amplifying signals in the microwatt range, making them suitable for integration into chip-scale devices.