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Efficient wave mixers based on lithium-niobate-on-insulator (LNOI) hold great potential for next-generation photonic integrated circuits in both classical and quantum optics. However, achieving high-performance nonlinear photonic devices readily suitable for scalable, fiber-compatible applications remains challenging. Here, we report on the fabrication of LNOI micrometer waveguides, i.e., micro-waveguides, with a combination of ultraviolet lithography and deep dry etching technology for efficient nonlinear photonics applications. We fabricate periodically poled LNOI micro-waveguides with a cross section of ∼3×4µm 2 and demonstrate a fiber–chip–fiber second-harmonic generation conversion efficiency of 1320%/W with an insertion loss of 3.8 dB at the telecommunication band. We also demonstrate high-quality photon pair generation via spontaneous parametric downconversion with a flux of 178 MHz/mW at sub-mW pump power and coincidence-to-accidental ratio >8000 at microwatt pump power. The overall performance in both applications is on par with that of state-of-the-art counterparts using thin-film lithium niobate nano-waveguides. The technique would make micrometer-thick LNOI an attractive platform for ready applications in nonlinear and quantum optics.
Zhang et al. (Tue,) studied this question.