查看更多>>摘要：The metalens has attracted remarkable attention due to its ultra-thin and ultra-light characteristics,which indicate great potential for compact imaging.However,the limited efficiency at a large angle incidence severely hinders the application of wide-angle focusing and imaging,which is pursued in the fast-developing imaging systems.Therefore,new strategies to improve the lens performance at large incident angles are in demand.In this work,we propose tilted structures for large-angle focusing with improved efficiency.Metalenses based on dynamic phase and geometric phase are designed and sys-tematically characterized by numerical simulations.We show that tilted structures of unit cells significantly improve the lens performance at oblique incidences.In detail,the focusing efficiency of the metalens with tilted structures is increased over 25％at 30° incidence,as well as the modulation transfer function.In addition,we develop a hybrid metalens array achieving highly efficient wide-angle imaging up to 120°.We believe this design provides a feasible route toward wide-field and high-performance imaging applications.
查看更多>>摘要：Tunability,ultracompact design,high group index,low loss,and broad bandwidth are desired properties for integrated optical delay lines[0DLs].However,those properties are challenging to achieve simultaneously in the visible region.This paper proposes a tunable hexagonal boron nitride topological optical delay line[0DL]in the visible region based on valley photonic crystals.The topological edge state from the beard-type boundary allows the achievement of an ultralow group velocity close to zero,which results in a large group index of 629 at 645 nm.Moreover,we demonstrate tuning of the slow-light wavelength and optical delay times with electrically tunable liquid crystals by applying external voltage.The device has an ultracompact size of 5 μm × 2.7 μm with an optical delay distance of 25a[a is the lattice constant]and a delay time of 12 ps.0ur design can provide a new possibility for designing 0DLs working in the visible region for optical communication and quantum computing systems.
查看更多>>摘要：We propose a method for optimizing the phase stability of microwave signal transmission over long distances.First,the design of the photon link was modified to reduce the radio frequency[RF]signal's baseline noise and increase power.Second,a low-noise driver circuit was developed for a two-section distributed feedback[DFB]laser designed using reconstruction equivalent chirp[REC]technology to create an ultra-stable laser,and its performance was characterized through linewidth data.Test results indicate that the DFB laser achieved narrower linewidth,improving system phase sta-bility.When an injection current[30 mA]is applied to the reflection section of the two-section DFB laser,the laser linewidth will be narrower[1.38 MHz],further enhancing the system's phase transmission stability.At a 1 Hz offset frequency;a residual phase noise of-88.65 dBc/Hz is obtained.The short-term stability with an averaging time of 1 s is 1.60 × 10-14,and the long-term stability over a testing time of 60,000 s is 3.41 × 10-18.Even after incorporating temperature variations,the long-term stability reaches 8.37 × 10-18 at 22 h.
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