A Monolithic Active‐Passive LNOI Photonic Integration Platform via Localized Thermal Diffusion

Abstract Lithium niobate on insulator (LNOI) provides a low‐loss, high‐density, multifunctional material platform for integrated photonics. However, owing to its indirect bandgap, electroluminescence cannot be realized in undoped LNOI. While rare earth (RE) ions doping provides a gain medium for lithium niobate (LN), it also brings about non‐negligible absorption losses. Here, a method for fabricating locally doped LNOI is introduced, and an active‐passive LNOI platform is presented via localized erbium (Er) ions thermal diffusion. The concentration of Er 3+ ions remains uniform at 0.3 mol% throughout the LN film. The intrinsic quality ( Q i ) factors of microring resonators on active and passive regions are 2.64 × 10 5 and 7.48 × 10 5 , respectively. As a demonstration, an integrated amplifier‐assisted microring laser is fabricated on this platform, which is transmitted through the passive region before output, achieving a maximum slope efficiency of 4.09 × 10 −3 %. The monolithic active‐passive LNOI photonic integration platform offers proven stability and compatibility, paving the way for advanced LNOI devices. It will undoubtedly promote the development and industrialization of LNOI integrated photonics.