Achieving spatiotemporal control of light at high speeds presents immense possibilities for various applications in communication, computation, metrology, and sensing. The integration of subwavelength metasurfaces and optical waveguides offers a promising approach to manipulate light across multiple degrees of freedom at high speed in compact photonic integrated circuit (PIC) devices. Here, we demonstrate a gigahertz-rate-switchable wavefront shaping by integrating metasurface, lithium niobate on insulator photonic waveguides, and electrodes within a PIC device. As proofs of concept, we showcase the generation of a focus beam with reconfigurable arbitrary polarizations, switchable focusing with lateral focal positions and focal length, orbital angular momentum light beams as well as Bessel beams. Our measurements indicate modulation speeds of up to the gigahertz rate. This integrated platform offers a versatile and efficient means of controlling the light field at high speed within a compact system, paving the way for potential applications in optical communication, computation, sensing, and imaging.

Optical frequency conversion based on the second-order nonlinearity (χ(2)) only occurs in anisotropic media (or at interfaces) and thus is intrinsically polarization-dependent. But for practical applications, polarization-insensitive or independent operation is highly sought after. Here, by leveraging polarization coupling and second-order nonlinearity, we experimentally demonstrate a paradigm of TE/TM polarization-independent frequency upconversion, i.e., sum frequency generation, in the periodically poled lithium niobate-on-insulator ridge waveguide. The cascading of quasi-phase-matched polarization coupling and nonlinear frequency conversion is exploited. With a proper transverse electric field, TE and TM mode fundamental waves can be frequency-upconverted with an equal efficiency in the frequency converter. The proposed method may find ready application in all-optical wavelength conversion and upconversion detection technologies.

The microring resonator based on lithium niobate on insulator (LNOI) is a promising platform for broadband nonlinearity process because of its strong second-order nonlinear coefficients, the capability of dispersion engineering, etc. It is important to control the energy transmitted into the resonator at different wavelengths, as this becomes difficult for two bands across an octave. In this Letter, we study the effect of different pulley bus-resonator configurations on phase mismatching and mode field overlap. We achieve the control of energy transmission coefficients at different wavebands simultaneously and provide a general design methodology for coupled structures for broadband applications. This paper can contribute to quantum and classical optical broadband applications based on LNOI microring resonators.

绝缘体上铌酸锂薄膜凭借铌酸锂晶体优异的光学性能和薄膜器件的易加工和可集成特性，被视为理想的集成光学平台。除了波导、调制器等传输、控制器件方面的研究之外，最近铌酸锂薄膜激光器的研究也取得了显著的进展。文中将对最近迅速发展的铌酸锂薄膜微腔激光器的研究现状进行综述。首先，介绍铌酸锂晶体和铌酸锂薄膜稀土离子掺杂的主要技术方案，以及近期有关于稀土离子掺杂铌酸锂薄膜微纳光学器件制备方面的探索；其次，总结近年来掺铒铌酸锂薄膜微盘腔、微环腔激光器方面的研究进展；然后，阐述微腔激光器体系几种常见的实现单模激光器方法的工作机理，介绍研究者们利用“游标效应”调制模式损耗等方式实现掺铒铌酸锂薄膜单模激光器的研究进展；最后，基于目前报导的铌酸锂薄膜激光器研究成果，对目前研究存在的局限性以及未来的研究方向进行了探讨。

We study the effect of dimension variation for second-harmonic generation (SHG) in lithium niobate on insulator (LNOI) waveguides. Non-trivial SHG profiles in both type-0 and type-I quasi-phase matching are observed during the wavelength tuning of the fundamental light. Theoretical modeling shows that the SHG profile and efficiency can be greatly affected by the waveguide cross-section dimension variations, especially the thickness variations. In particular, our analysis shows that a thickness variation of tens of nanometers is in good agreement with the experimental results. Such investigations could be used to evaluate fabrication performance of LNOI-based nonlinear optical devices.

Lithium niobate on insulator (LNOI), as an emerging and promising optical integration platform, faces shortages of on-chip active devices including lasers and amplifiers. Here, we report the fabrication of on-chip erbium-doped LNOI waveguide amplifiers based on electron beam lithography and inductively coupled plasma reactive ion etching. A net internal gain of ～30 dB/cm in the communication band was achieved in the fabricated waveguide amplifiers under the pump of a 974 nm continuous laser. This work develops new active devices on LNOI and may promote the development of LNOI integrated photonics.