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Vanadium dioxide (VO2) has been one of the most significant functional materials for its prominent property change during phase transition. Here the modulation in crystallinity and morphology of VO2 thin film is achieved by femtosecond laser direct writing. Both the local crystallization from an amorphous phase and self-organized periodical structures are generated due to the well-controlled femtosecond laser energy deposition and controlled accumulation. The dynamic evolution of either the volumetric or surface nano-/micro-structure depends strongly on the femtosecond laser conditions, revealed by changes of the Raman bands and reflectance spectra at visible wavelengths. Based on the distinguishable color display performance of differently processed regions, a four-color-level image has been drawn on a VO2 thin film. This work proposes an elaborate "annealing by light" and optical property modulation method for the VO2, paving the way to producing complex integrated multi-functional devices for color display and data storage. [ABSTRACT FROM AUTHOR]

Leveraging the outstanding nonlinear optical properties and the ultra‐high spatial confinement of light, microresonators based on lithium niobate (LN) thin films have emerged as intriguing elements in various frontiers such as integrated photonic circuits and quantum photonics. A number of applications have been realized based on LN thin‐film microresonators toward various on‐chip devices. In this paper, the recent advances of microresonators based on LN thin films are reviewed, including essential techniques used in fabrication/characterization and a detailed overview of applications, ranging from frequency conversion, electro‐optic modulation, frequency combs, microwave‐to‐optical transducers, quantum photonics, to lasing. A short summary and perspective is presented to indicate possible research topics related to LN thin‐film. [ABSTRACT FROM AUTHOR]

By preparing a sensor system around isolated exceptional points, one can obtain a great enhancement of the sensitivity benefiting from the non‐Hermiticity. However, this comes at the cost of reduction of the flexibility of the system, which is critical for practical applications. By generalizing the exceptional points to exceptional surfaces, it has been theoretically proposed recently that enhanced sensitivity and flexibility can be combined. Here, an exceptional surface is experimentally demonstrated in a non‐Hermitian photonic sensing system, which is composed of a whispering‐gallery‐mode microresonator and two nanofiber waveguides, resulting in a unidirectional coupling between two degenerate counter‐propagating modes with an external optical isolator. The system is simple, robust, and can be easily operated around an exceptional surface. On the one hand, sensitivity enhancement is observed by monitoring the resonant frequency splitting caused by small perturbations. This demonstration of exceptional‐surface‐enhanced sensitivity paves the way for practical non‐Hermitian sensing applications. On the other hand, the suppression of frequency splitting around the exceptional surface is also shown for the first time. [ABSTRACT FROM AUTHOR]

In article number 2000569 by Haitan Xu, Fuchuan Lei, Dong Ruan, Gui-Lu Long, and co-workers, exceptional surfaces are experimentally realized in the higher-dimensional synthetic space. The sensor operating at an exceptional surface combines enhanced sensitivity with flexible experimental conditions. Exceptional Surface-Based Sensors: Experimental Realization of Sensitivity Enhancement and Suppression with Exceptional Surfaces (Laser Photonics Rev. 15(5)/2021). [Extracted from the article]