Erbium-doped waveguide amplifiers (EDWAs) applied in on-chip photon integration fields have been widely studied over the past two decades owing to their low cost, compensation for optical loss, and potential applications in integrated optical systems. Due to the limitations of traditional inorganic EDWA research methods, 976 nm or 1480 nm lasers are usually chosen as pump sources to pump polymer EDWAs, which achieves a radiative transition (⁴I_13/2→⁴I_15/2) through the intrinsic absorption (⁴I_15/2→⁴I_11/2 or ⁴I_13/2) of Er³⁺ ions. However, the intrinsic absorption cross-section of Er³⁺ ions in polymers is small, and high-power laser pumping can easily cause damage to polymer waveguides, which limits the development of polymer EDWAs. In this work, a low-power blue violet LED is used as the pump source instead of a traditional semiconductor laser. By utilizing the strong absorption performance of organic ligands in the blue violet light band and the intramolecular energy transfer mechanism between ligands and Er³⁺ ions, the efficient luminescence of Er³⁺ ions at 1550 nm is achieved.

Using the chelating phosphine oxide ligands DBFDPO as the neutral ligand and β-diketone ligand DBTTA as the anionic ligand, respectively, the erbium complex Er(DBTTA)₃(DBFDPO) is synthesized and doped into polymethylmethacrylate (PMMA) to prepare active polymer films. The absorption spectra, photoluminescence (PL) spectra, and atomic force microscope (AFM) image of the film are measured at room-temperature. A passive SU-8 channel waveguide with a cross-sectional size of 4 μm×4 μm is fabricated via a one-step lithography process, using a 3-μm-thick Er(DBTTA)₃(DBFDPO)-doped PMMA as the active top cladding to prepare a polymer optical waveguide amplifier. With the 365 nm LED vertical top-pumping method, optical gains at 1550 nm are achieved in the waveguide based on the evanescent-wave amplification principle.

By using a 462 mW 365 nm LED as the pump source instead of conventional 976 nm or 1480 nm semiconductor lasers, a relative gain of 7.4 dB/cm at 1550 nm is achieved in a 0.9 cm-long waveguide. The output optical intensity increases as the pump power increases when the 1550 nm signal power at the input waveguide facet is 1.8 μW. For a fixed signal power, the relative gain increases as the pump power increases. This approach is expected to reduce the commercialization costs of the waveguide amplifier by utilizing LED pumping for optical gain in the C-band of optical communication.

Based on the intramolecular energy transfer mechanism among the chelating phosphine oxide ligands DBFDPO, β?diketone ligand DBTTA and the central Er³⁺ ions, the optical gain of 7.4 dB/cm is demonstrated at 1550 nm by using a 365 nm LED instead of 976 or 1480 nm lasers as the pump source in complex Er(DBTTA)₃(DBFDPO)-doped PMMA waveguides. In this way, the waveguide thermal damage caused by traditional laser pumping can be overcome. Moreover, the erbium complex Er(DBTTA)₃(DBFDPO)-doped PMMA polymer in this work can be conveniently spin coated on different types of low loss waveguides to compensate for losses in optical links, which greatly improves the universality of materials in planar photonic integration. The LED vertical top-pumping method is expected to reduce commercial costs, and it is expected to be widely applied in the field of planar photon integration.