A frequency mixer is a nonlinear device that combines electromagnetic waves to create waves at new frequencies. Mixers are ubiquitous components in modern radio-frequency technology and microwave signal processing. The development of versatile frequency mixers for optical frequencies remains challenging: such devices generally rely on weak nonlinear optical processes and, thus, must satisfy phase-matching conditions. Here we utilize a GaAs-based dielectric metasurface to demonstrate an optical frequency mixer that concurrently generates eleven new frequencies spanning the ultraviolet to near-infrared. The even and odd order nonlinearities of GaAs enable our observation of second-harmonic, third-harmonic, and fourth-harmonic generation, sum-frequency generation, two-photon absorption-induced photoluminescence, four-wave mixing and six-wave mixing. The simultaneous occurrence of these seven nonlinear processes is assisted by the combined effects of strong intrinsic material nonlinearities, enhanced electromagnetic fields, and relaxed phase-matching requirements. Such ultracompact optical mixers may enable a plethora of applications in biology, chemistry, sensing, communications, and quantum optics.
nonlinear metasurfaces leading to high-efficiency optical
second harmonic generation (SHG) are highly desirable for optical
sensing, imaging, and quantum photonic systems. Compared to traditional
metal-only metasurfaces, their hybrid counterparts, where a noncentrosymmetric
nonlinear photonic material is incorporated in the near-field of a
metasurface, can significantly boost SHG efficiency. However, it is
difficult to integrate such devices on-chip due to material incompatibilities,
thickness scaling challenges, and the narrow band gaps of nonlinear
optical materials. Here, we demonstrate significantly enhanced SHG
in on-chip integrated metasurfaces by using nanometer thin films of
ferroelectric Y:HfO2. This material has the merit of CMOS
compatibility, ultraviolet transparency up to 250 nm, and significant
scalability down to sub-10 nm when deposited on silicon. We observe
a 20-fold magnitude enhancement of the SHG intensity from the hybrid
metasurface compared to a bare ferroelectric HfO2 thin
film. Moreover, a 3-fold SHG enhancement is observed from the hybrid
metasurface compared to a control structure using nonferroelectric
HfO2, demonstrating a major contribution to the SHG signal
from ferroelectric Y:HfO2. The effective second-order nonlinear
optical coefficient χ(2) of Y:HfO2 is
determined to be 6.0 ± 0.5 pm/V, which is comparable to other
complex nonlinear photonic oxide materials. Our work provides a general
pathway to build an efficient on-chip nanophotonic nonlinear light
source for SHG using ferroelectric HfO2 thin films.
ABSTRACT:The process of developing two types of virtual hydraulic experiment supporting animations used in courseware are described: (1) schematic diagram-based 2D virtual hydraulic circuits using Flash, and (2) VRMLbased 3D virtual hydraulic equipments. The effects and students' attitudes on the two approaches are surveyed and analyzed. ß
Ant Colony Optimization algorithms have been successfully applied to solve the Traveling Salesman Problem (TSP). However, they still have a tendency to fall into local optima, mainly resulting from poor diversity, especially in those TSPs with a lot of cities. To address this problem, and further obtain a better result in big-scale TSPs, we propose an algorithm called Multiple Colonies Ant Colony Optimization Based on Pearson Correlation Coefficient (PCCACO). To improve the diversity, first, we introduce a novel single colony termed Unit Distance-Pheromone Operator, which along with two other classic ant populations: Ant Colony System and Max-Min Ant System, make the final whole algorithm. A Pearson correlation coefficient is further employed to erect multi-colony communication with an adaptive frequency. Besides that, an initialization is applied when the algorithm is stagnant, which helps it to jump out of the local optima. Finally, we render a dropout approach to reduce the running time. The extensive simulations in TSP demonstrate that our algorithm can get a better solution with a reasonable variation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.