Rapidly growing demands for high-performance computing, powerful data processing, and big data necessitate the advent of novel optical devices to perform demanding computing processes effectively. Due to its unprecedented growth in the past two decades, the field of meta-optics offers a viable solution for spatially, spectrally, and/or even temporally sculpting amplitude, phase, polarization, and/or dispersion of optical wavefronts. In this review, we discuss state-of-the-art developments, as well as emerging trends, in computational metastructures as disruptive platforms for spatial optical analog computation. Two fundamental approaches based on general concepts of spatial Fourier transformation and Green’s function (GF) are discussed in detail. Moreover, numerical investigations and experimental demonstrations of computational optical surfaces and metastructures for solving a diverse set of mathematical problems (e.g., integrodifferentiation and convolution equations) necessary for on-demand information processing (e.g., edge detection) are reviewed. Finally, we explore the current challenges and the potential resolutions in computational meta-optics followed by our perspective on future research directions and possible developments in this promising area.
Metasurface is a recently developed nanophotonics concept to manipulate the properties of light by replacing conventional bulky optical components with ultrathin (more than 104 times thinner) flat optical components. Since the first demonstration of metasurfaces in 2011, they have attracted tremendous interest in the consumer optics and electronics industries. Recently, metasurface-empowered novel bioimaging and biosensing tools have emerged and been reported. Given the recent advances in metasurfaces in biomedical engineering, this review article covers the state of the art for this technology and provides a comprehensive interdisciplinary perspective on this field. The topics that we have covered include metasurfaces for chiral imaging, endoscopic optical coherence tomography, fluorescent imaging, super-resolution imaging, magnetic resonance imaging, quantitative phase imaging, sensing of antibodies, proteins, DNAs, cells, and cancer biomarkers. Future directions are discussed in twofold: application-specific biomedical metasurfaces and bioinspired metasurface devices. Perspectives on challenges and opportunities of metasurfaces, biophotonics, and translational biomedical devices are also provided. The objective of this review article is to inform and stimulate interdisciplinary research: firstly, by introducing the metasurface concept to the biomedical community; and secondly by assisting the metasurface community to understand the needs and realize the opportunities in the medical fields. In addition, this article provides two knowledge boxes describing the design process of a metasurface lens and the performance matrix of a biosensor, which serve as a “crash-course” introduction to those new to both fields.
Coherent control is an ingenious tactic to steer a system to a desired optimal state by tailoring the phase of an incident ultrashort laser pulse. A relevant process is the two-photon–induced photoluminescence (TPPL) of nanoantennas, as it constitutes a convenient route to map plasmonic fields, and has important applications in biological imaging and sensing. Unfortunately, coherent control of metallic nanoantennas is impeded by their ultrafast femtosecond dephasing times so far limiting control to polarization and spectral optimization. Here, we report that phase control of the TPPL in resonant gold nanoantennas is possible. We show that, by compressing pulses shorter than the localized surface plasmon dephasing time (<20 fs), a very fast coherent regime develops, in which the two-photon excitation is sensitive to the phase of the electric field and can therefore be controlled. Instead, any phase control is gone when using longer pulses. Finally, we demonstrate pure phase control by resorting to a highly sensitive closed-loop strategy, which exploits the phase differences in the ultrafast coherent response of different nanoantennas, to selectively excite a chosen antenna. These results underline the direct and intimate relation between TPPL and coherence in gold nanoantennas, which makes them interesting systems for nanoscale nonlinear coherent control.
An efficient electro-optic transition control is reported in all-fiber graphene devices over a broad spectral range from visible to near-infrared. The ion liquid–based gating device fabricated onto a side-polished fiber with high numerical aperture significantly enhances the light-matter interaction with graphene, resulting in strong and nonresonant electro-optic absorption of up to 25.5 dB in the wavelength ranging from 532 to 1950 nm. A comprehensive analysis of the optical and electrical properties of the device fabricated with monolayer and bilayer graphene revealed that the number of graphene layers significantly impacts on the performance of the device, including modulation depth and driving voltage. Wavelength-dependent optical response is also measured, which clearly characterizes the electronic bandgap dispersion of graphene. The device exhibited more efficient electro-optic modulation in the longer wavelength region, where the maximum light modulation efficiency of 286.3%/V is achieved at a wavelength of 1950 nm.
Two-dimensional iron phosphorus trichalcogenide (FePS3) has attracted significant attention for its use in electricity, magnetism and optical fields due to its outstanding physical and chemical properties. Herein, FePS3 was prepared using the chemical vapor transportation (CVT) method and then exfoliated by using fast electrochemical exfoliation. After gradient centrifugation, FePS3 nanosheets with thicknesses ranging from 1.5 to 20 nm and lateral dimensions of 0.5–3 μm were obtained. By utilizing the spatial self-phase modulation (SSPM) effect, the relationships between the nonlinear refractive index and the size of the FePS3 nanosheets were investigated in detail which revealed that the nonlinear refractive index can be effectively controlled by the size of the FePS3 nanosheets. It is worth noting that the optimal FePS3 nanosheets (3–5 layers thick and ∼1 μm in lateral dimensions) displayed the highest nonlinear refractive index of ∼10−5 cm2 W−1. This work demonstrates the potential that FePS3 nanosheets have for use in nonlinear optics or nonlinear optical devices.