Light-amplification-assisted sum-frequency generation in erbium-doped thin-film lithium niobate optical waveguides

Erbium-doped thin-film lithium niobate (Er³⁺:TFLN) enables integrated photonic devices through its efficient photoluminescence. However, the fixed transition energies of erbium ions intrinsically restrict emission to the telecommunications C-band (1530-1565 nm), limiting spectral versatility. To transcend this constraint, we engineered periodically poled Er³⁺:TFLN waveguides that concurrently integrate optical amplification and nonlinear frequency conversion. Within this platform, we harnessed erbium ions stimulated emission under 980 nm pumping to achieve net optical gain (0.8 dB) at 1538.2 nm. Simultaneously, we exploited the quasi-phase-matching (QPM) capability of the poled structure to perform sum-frequency generation (SFG) between the 976.0 nm pump and the amplified 1538.2 nm signal. This dual-process yielded visible emission at 597.1 nm with 84 nW output power and a normalized conversion efficiency of 68 % W^-1 cm^-2. Critically, this work demonstrates-for the first time in Er³⁺:TFLN-spectral extension beyond the C-band through synergistic pump amplification and nonlinear mixing. Our monolithic architecture establishes a new paradigm for broadband on-chip photonics, enabling applications including multi-wavelength laser sources, quantum entangled photon pair generators, and on-chip biophotonic sensing systems.