The high-performance phototransistor based on two-dimensional materials is very attractive in integrated logic function chips and large-scale real-time optical imaging. Recently, graphene-semiconductor composite film phototransistors have already achieved ultrahigh photoconductive gain due to the strong absorption capacity of the semiconductor layer and the strong mobility of graphene. However, low absorption and high dark current limit the photoresponsivity and detective band of the graphene phototransistors. Here, we fabricate a graphene/C60/Sb composite film photo transistor with a broadband response (450 nm - 1500 nm), fast response speed (20 ms) and ultrahigh peak photoresponsivity (3.927 × 105 A/W). The charge transfer mechanism between layers of the device has been analyzed by adjusting Sb layer thicknesses (5 nm, 10 nm, 20 nm). In addition, we observe the positive and negative photocurrent response in the experiment and study the bidirectional response of the device by applying different gate voltages. The ultrathin phototransistor (10 - 20 nm) is compatible with the traditional CMOS and nanoimprinting process to achieve large area and high-precision array integrated devices.
DNA methylation is one of the earliest known modification pathways, and it regulates gene expression, which in turn influences many biological processes. Direct, label-free detection of DNA methylation with high sensitivity remains a great challenge. Surface-enhanced Raman scattering (SERS), a non-invasive and label-free vibration spectroscopy technique, offers sensitive intrinsic chemical information that makes it an attractive option for DNA analysis. In this study, we employed iodide-modified silver nanoparticles to generate highly consistent SERS signals of DNA at micromolar concentrations in aqueous solutions. This enabled the acquisition of single-base sensitive DNA fingerprint details pertaining to base methylations (such as 5-methylcytosine). As a proof of concept, the SER spectra of a DNA and its methylated counterpart were compared and analyzed, resulting in an obvious identification of DNA methylation. In particular, we first designed two DNA sequences, the sole change being that one of the nucleotides, cytosine, is replaced with a 5-methylcytosine. Further SERS experimental study revealed that methylating a single cytosine in the DNA strand caused a subtle but evident alteration in the SERS spectrum. A new Raman peak emerged at 760 cm-1 the Raman peak at 792 cm-1 moved to 790 cm-1, and there was a noticeable drop in the peak intensity ratio between 1572 cm-1 and 1634 cm-1. This approach may provide a novel and easy-to-use tool for the label-free identification of single-molecule DNA mutations or modifications, furthering the advancement of ultra-sensitive genomic research in the future.
The superlens with plasmonic material have important features such as evanescent wave enhancement and subwavelength imaging. However, the intrinsic loss of the material severely limits the resolution and imposes more stringent requirements on imaging conditions. In this work, we discuss the influence of different temporal features on imaging resolution. The exponential illumination corresponds to a definite imaging state, higher imaging resolution can be obtained with greater exponential decay rate of illumination pulse. This conclusion provides a reference for the selection of pulse time-domain waveforms. In addition, we use this method for periodic pattern imaging, validating its potential for practical applications.
Polarized light has various applications in industrial inspection, remote sensing, and other fields. Traditional methods for detecting polarized light typically rely on the polarization properties of optical components or specific materials to detect and analyze light with different polarization states. However, the polarization detection system designed by these methods has a complex optical path, resulting in bulky size and high cost in large-scale integrated applications, thus hindering the development and application of polarization detection. Therefore, it is crucial to develop polarization detectors to meet the requirements of compact and highly integrated optical devices. The optical catenary structure is a kind of continuous metasurface structure, which has continuous, linear phase change and abundant electromagnetic modes. To further miniaturize the polarization detector for on-chip applications, a potential approach is to combine silicon waveguide with metasurface to achieve a compact, high-efficiency polarization detector. In this work, the on-chip beam polarization detector is effectively realized by using one single catenary gold nanostructure loaded atop silicon on an insulator (SOI) waveguide, which is optimized by the Particle Swarm Optimization algorithm. We envision that our finding could facilitate the application of polarization-optical devices and systems in various fields, including sensing, optical communications, imaging, quantum sciences, etc.
With orbital angular momentum, tightly focused vortex beams can impose optical torque on particles through momentum transfer. In this paper, based on the Richards-Wolf vector diffraction theory, we examine the forces and moments exerted on Mie particles by a tightly focused beam, including the impact of the beam's intensity distribution and the topological charge (TC) number on particle trapping stability. Numerical calculations are conducted to assess the effects of corresponding parameters on the characteristics of the optical radiation force and the tight focusing properties. Our results show that the direction of the particle’s rotation is determined by the sign of the TC numbers and that there is a direct relationship between the magnitude of the induced torque and the TCs. Furthermore, the stability of particle control can be improved by OAM beams with small TCs. These results have potential applications in light capture, optical storage, and optical imaging.
Non-reciprocal devices are essential in many field that require unidirectional wave transmission, such as communications, sensor technology and quantum computing. However, most existing devices are constrained by factors including power supply, external magnetic field, efficiency, and bandwidth. We demonstrated an all-passive, broadband and high efficient nonreciprocal metasurface based on vanadium dioxide (VO2). The electromagnetic thermal coupling simulation results show that when the incident light power density is 40-55 kW/cm2, the transmittance is 90% in one direction and nearly 20% in the other direction. Moreover, benefiting from the non-resonant structure of the metasurface, the device can be used at a broadband wavelength of 7-12 μm. Thus, the demonstrated device has the advantages of broadband and high efficiency, offering a simple but effective scheme of all-passive unidirectional devices.
As a type of computational optical imaging technology, Fourier ptychography (FP) imaging technology combines phase recovery algorithm with the idea of synthetic aperture. It is oriented towards a large field of view and high resolution. However, there are still two issues that need to be addressed. First, there is the problem of slow speed of image acquisition and long acquisition time. The large synthetic aperture and high overlap rate between adjacent images significantly increase the number of collected images. Second, for the transmissive FP imaging, when the intensity of the illumination source is constant, the theoretical synthetic aperture size cannot increase unlimited with the increase of the scanning range of the camera array in the focal plane. Therefore, in this paper, we adopt a 3×3 camera array for data acquisition, reducing the data acquisition speed to one-ninth under the same conditions, greatly improving the imaging speed; research was conducted on the transmissive FP imaging experiment, which achieved a 7-fold resolution improvement; At the same time, through system simulation and reverse derivation of experimental results, the actual effective synthetic aperture size was determined under certain lighting source power conditions. Our work has laid the foundation for further imaging distances in the future and contributed new methods for fast subdiffraction computed imaging.
In recent years, the super-oscillatory lens based on optical super-oscillatory phenomenon has been successfully applied to sub-diffraction focusing and imaging. However, most of the previously reported super-oscillatory lens only work in the visible and near-infrared wavelengths, and little research has been done in the ultraviolet. In this paper, a polarization-insensitive ultraviolet super-oscillatory metalens doublet is proposed. The simulation results show that sub-diffraction focusing and imaging with different incidence angles can be achieved at the ultraviolet operating wavelength of 365nm, and the full width at half maximum of the sub-diffraction foci is approximately 0.7 times of the diffraction limit. This metalens doublet has a numerical aperture of 0.4472, a focal length of 0.6896 mm, and a field of view of ±25°. The proposed polarization-insensitive ultraviolet super-oscillatory metalens doublet can be used in the fields of ultraviolet lithography and microscopic imaging.
KEYWORDS: Image resolution, Non line of sight propagation, Imaging systems, Image restoration, Temporal resolution, Signal to noise ratio, Confocal microscopy, Image quality
As an emerging paradigm in computational imaging, non-line-of-sight (NLOS) imaging demonstrates a distinctive capacity to unveil objects hidden outside the conventional line of sight, which has great application potential in fields such as autonomous driving, medical diagnosis, and disaster rescue. Nevertheless, a comprehensive exploration of factors limiting resolution in NLOS imaging remains absent. Here, to addresses this gap, a method is proposed to improve the resolution by increasing the size of the scanning area instead of reducing the time jitter of the imaging system. Both simulations and experiments confirm the feasibility of the method. Additionally, an experiment of NLOS imaging over 10 meters is conducted to demonstrate the potential to expand imaging distance without compromising resolution.
As an important means of contactless manipulation of targets, optical force has significant application prospects in areas such as light sail propulsion and orbital intervention of space debris. Precise measurement of the optical force generated by spatial targets in complex optical fields is crucial for establishing their spatial dynamics model. The torsion balance can be used to measure the optical torque. We use a 5 μm tungsten fiber to build a torsion balance system to measure the extremely weak optical torque less than 1×10-15 Nm, which can help to establish an accurate model of the interaction between objects and optical forces. At the same time, it provides experimental data for the study of spacecraft orbit control and light sail navigation.
Simultaneously achieving a large field of view (FOV) and high-resolution imaging has always been the goal in the design of optical systems. Although traditional optical systems can switch from large-FOV to high-resolution imaging by adjusting the focal length, this method relies on complex mechanical structures and multi-lens combinations, leading to slow switching speed and bulky volume. Planar metasurfaces composed of subwavelength structures can achieve arbitrary wavefront manipulation, but their phase distributions are usually fixed once fabricated. In this paper, we propose a strategy for large-scale pixel-level active control of local phase on demand via cascaded bilayer metasurfaces. This method enables fast switching between the quadratic phase and hyperbolic phase by globally translating one of two layers at a one-lattice interval. Simulation results indicate that the full FOV for the quadratic phase exceeds 80°, and the point spread functions for the hyperbolic phase at various focal lengths closely approach the diffraction limit. Such multifunctional metalenses may find many potential applications, such as surveillance, unmanned vehicles, and medical science.
The geometric phase concept has profound implications in many branches of physics, from condensed matter physics to quantum systems. Although geometric phase has a long research history, novel theories, devices, and applications are constantly emerging with developments going down to the subwavelength scale. Specifically, as one of the main approaches to implement gradient phase modulation along a thin interface, geometric phase metasurfaces composed of spatially rotated subwavelength artificial structures have been utilized to construct various thin and planar meta-devices. In this paper, we first give a simple overview of the development of geometric phase in optics. Then, we focus on recent advances in continuously shaped geometric phase metasurfaces, geometric–dynamic composite phase metasurfaces, and nonlinear and high-order linear Pancharatnam–Berry phase metasurfaces. Finally, conclusions and outlooks for future developments are presented.
We report a lightweight metasurface with wide field of view (FOV), which can calculate incident angle by the focus of the sun for navigation. The solar altitude angle and solar azimuth angle for navigation can be resolved with converting the coordinate system to connect the sun with the focus. The designed metasurface overcomes bulky devices and bad weather owing to the fact that the metasurface operates at short-wavelength infrared band (SWIR) that penetrates smoke and fog.
We designed a broadband achromatic multilevel diffractive lens which is using the nanoparticle composite. Nanoparticle composite is a new artificial material, which has both pattern-transfer capability and high refractive index requirements. The device has good achromatic performance and good focusing performance at the focal plane in the visible band. The simulated average focusing efficiency is over 85% at the visible frequency.
Super-oscillation phenomenon provides an effective solution for realizing far-field non-invasive super-resolution imaging. However, most super-oscillatory lenses are challenging to balance the working bandwidth and working efficiency, which greatly limits the practical applications of super-oscillation lenses in optical systems. In this work, a broadband high-efficiency super-oscillatory metalens for sub-diffraction focusing about 0.75 times the diffraction limit based on the reflective metasurface is proposed for super-resolution imaging in the visible ranging from 400 nm to 700 nm. Moreover, another metalens with a sub-diffraction focusing spot equal to 0.6 times of the diffraction limit is also designed to prove the universal applicability of the proposed method. The proposed method provides an effective pathway for the development of microscopy, holography, and machine vision.
We design a simple catenary metasurface with high efficiency, which could obtain both the degree of circular polarization and the wavelength of incident polarized light by measuring the diffraction intensity and the deflection angle. The catenary decomposes the incidence into left and right circularly polarized light and diffracts them to different predesigned directions with different deflection angles that present the wavelength information. The diffraction efficiency of the designed catenary exceeds 94%, the average diffraction efficiency is up to 97.6% at the wavelength of 8-14μm, and angular dispersion is 0.078°/nm. Moreover, the degree of circular polarization for various incident polarization states can be characterized by diffraction intensities. This work may provide extensive applications for biosensing, DNA structural analysis, stereochemistry, etc.
In this work, we propose a loaded diode frequency reconfigurable ultra-thin metasurface for beam switching. Different bias voltages are applied to the ultra-thin reconfigurable unit to achieve different phase gradients between adjacent units in the x-axis direction. Different voltage configurations are used to achieve stable phase gradient in different working frequencies which ensures the stability of beam scanning and expands the operating bandwidth of the antenna. The characteristics of frequency reconfigurable metasurface have been verified over the frequency band 9.1-10.1 GHz. This study paves a novel strategy of bandwidth expansion with the advantages of reconfigurable frequency and lightweight.
In this paper, we propose an ultra-thin metasurface to achieve simultaneous thermal infrared camouflage and 1.06 μm laser scattering with thermal management. First, the metasurface has an average absorptivity/emissivity of 0.04 in the band of 8~14 μm and a emission peak at 5.62 μm with nearly 100% emissivity. Therefore, camouflage against thermal infrared detectors and effective thermal management can be achieved. Second, the chessboard-like square patches on the top of the meatsurface make it possible to reduce the specular reflection at the laser wavelength of 1.06 μm to less than 2% by redirecting the reflected light to non-normal angles. These excellent simulated results indicate that our proposed metasurface has promising applications in the fields of multi-band infrared camouflage.
Multispectral imaging technology plays an important role in lots of domains, but traditional systems are limited by large volumes and complex constructions. Here, we propose a high-efficiency multispectral integrated imaging system based on metasurfaces, with its spectral range covering two important infrared windows of 3-5 μm and 8-12 μm. This system is composed of the microlens, metasurface, and filter array, hence its volume, weight, and complexity can be greatly decreased. The average efficiencies of the aforementioned two bands are over 96.47% and 97.43%, respectively. The bandwidth of each spectral channel can be tuned flexibly according to realistic requirements, which makes the system more applicable to various circumstances. The proposed design method is universally applicable and has potential applications in many aspects, such as remote sensing, epidemic monitoring, and archeology.
Dielectric metasurfaces is a plane optical device to achieve the desired function by modulating amplitude and phase, polarization for the incident light, and its transmission efficiency is higher than other metasurfaces, these advantages lead to dielectric metasurfaces will be used widely in the future. Nevertheless, the majority of metasurfaces are planar singlelayered structure, which limit seriously the view field and effect of monochromatic imaging. Here, we demonstrate a composed dielectric meta-lens doublet by the electromagnetic simulation can achieve perfectly diffraction-limited monochromatic focus for the polarization-insensitive incident lights at a wavelength of 375 nm, which has the view field of 60°, the numerical aperture of 0.5, and a focal length of 380μm. Due to the dielectric meta-lens doublet has the scaling of subwavelength at ultraviolet light, and the devices have high distinguishability, it can be used widely in nanolithography, imaging with large view field, and other optical domains.
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