Edge-Coupling Device on Lithium-Niobate-Integrated Photonic Chips(Invited)
Thin-film lithium niobate(TFLN)exhibits excellent electro-optic and optical nonlinear properties,and is an important platform for research on electro-optic modulators and nonlinear optical frequency converters.However,the significant difference in mode field sizes between the optical waveguides on TFLN films and optical fibers severely restricts efficient coupling between them.Consequently,high efficiency end couplers are valuable for breaking through the application bottleneck of TFLN-integrated optical chips.In this paper,a systematic review of the research progress of TFLN edge couplers is presented.First,the common characteristics of optical fibers involved in edge coupling are introduced.Subsequently,the typical structures of lithium niobate edge-coupling waveguides,such as single layer or multilayer inverse-tapered waveguides and wedge waveguides,are discussed.The selection and fabrication methods for related cladding materials are also described.Finally,the current research status and existing challenges in using edge couplers are summarized,and directions for potential future development are proposed.
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