High-Efficiency Visible Transmitting Polarizations Devices Based on the GaN Metasurface

Compact all-dielectric metasurface for full polarization detection at the long-wavelength infrared region

Metasurfaces have been extensively demonstrated in engineering and detection of polarization of light from the visible to terahertz regions. However, most of the previous metasurfaces for polarization detection are spatially divided into different parts, and each of the parts focuses on different polarization components, resulting in large metasurface size and hindering their integration development. In this paper, a compact all-dielectric metasurface is proposed and numerically demonstrated to achieve full polarization detection at the long-wavelength infrared region (LIR). First, we design the metasurface at a wavelength of 10 µm, which can converge incident beams to specific positions corresponding to different polarization states. In this design, the metasurface is based on an oblique alternant double-phase modulation method, which arranges meta-atoms with the ability to control as many as possible different polarizations in a limited region, ensuring the high efficiency of polarization detection while giving more freedom and flexibility to the metasurface. Second, the intensity distributions of the electric field of different polarization components are simulated at wavelengths of 9.4 µm and 10.5 µm, verifying the broadband performance of the proposed metasurface. The proposed method has potential applications in integrated multifunctional devices and multispectral polarization imaging.

Quasi-Freeform Metasurfaces for Wide-Angle Beam Deflecting and Splitting

Metasurfaces attracted extensive interests due to their outstanding ability to manipulate the wavefront at a subwavelength scale. In this study, we demonstrated quasi-freeform metasurfaces in which the radius, location, and height of the nanocylinder building blocks were set as optimized structure parameters, providing more degrees of freedom compared with traditional gradient metasurfaces. Given a desired wavefront shaping objective, these structure parameters can be collectively optimized utilizing a hybrid optimized algorithm. To demonstrate the versatility and feasibility of our method, we firstly proposed metasurfaces with deflecting efficiencies ranging from 86.2% to 94.8%, where the deflecting angles can vary in the range of 29°-75.6°. With further study, we applied our concept to realize a variety of high-efficiency, wide-angle, equal-power beam splitters. The total splitting efficiencies of all the proposed beam splitters exceeded 89.4%, where a highest efficiency of 97.6%, a maximum splitting angle of 75.6°, and a splitting uniformity of 0.33% were obtained. Considering that various deflecting angles, and various splitting channels with different splitting angles, can be realized by setting the optical response of metasurfaces as the optimization target, we believe that our method will provide an alternative approach for metasurfaces to realize desired wavefront shaping.

Influencing Effects of Fabrication Errors on Performances of the Dielectric Metalens

Despite continuous developments of manufacturing technology for micro-devices and nano-devices, fabrication errors still exist during the manufacturing process. To reduce manufacturing costs and save time, it is necessary to analyze the effects of fabrication errors on the performances of micro-/nano-devices, such as the dielectric metasurface-based metalens. Here, we mainly analyzed the influences of fabrication errors in dielectric metasurface-based metalens, including geometric size and shape of the unit element, on the focusing efficiency and the full width at half maximum (FWHM) values. Simulation results demonstrated that the performance of the metasurface was robust to fabrication errors within a certain range, which provides a theoretical guide for the concrete fabrication processes of dielectric metasurfaces.

Review of Metasurfaces and Metadevices: Advantages of Different Materials and Fabrications

Flat optics, metasurfaces, metalenses, and related materials promise novel on-demand light modulation within ultrathin layers at wavelength scale, enabling a plethora of next-generation optical devices, also known as metadevices. Metadevices designed with different materials have been proposed and demonstrated for different applications, and the mass production of metadevices is necessary for metadevices to enter the consumer electronics market. However, metadevice manufacturing processes are mainly based on electron beam lithography, which exhibits low productivity and high costs for mass production. Therefore, processes compatible with standard complementary metal–oxide–semiconductor manufacturing techniques that feature high productivity, such as i-line stepper and nanoimprint lithography, have received considerable attention. This paper provides a review of current metasurfaces and metadevices with a focus on materials and manufacturing processes. We also provide an analysis of the relationship between the aspect ratio and efficiency of different materials.

Numerical analysis of an ultra-broadband and highly efficient beam splitter in the visible region

We report a quasi-continuous beam splitter with highly efficient equal-power beam splitting in a wide spectral range. It consists of rhombic aluminum antimonide nanorods standing on a silica substrate. Firstly, a beam splitter based on discrete structures is designed, and the structures are optimized to obtain the quasi-continuous beam splitter. The beam splitter achieves a splitting efficiency of over 80% within the region of 675-786 nm (bandwidth = 111 nm), where the splitting angle can vary in the range of 97.2°-121.8°. In particular, the splitting efficiency reaches 93.4% when the wavelength is 690 nm. Overall, the proposed beam splitter potentially paves the way for realizing broadband metasurfaces and high-performance quasi-continuous metasurface-based devices.

Spherical Aberration-Corrected Metalens for Polarization Multiplexed Imaging

We present a terahertz spherical aberration-corrected metalens that uses the dynamic phase to achieve polarization multiplexed imaging. The designed metalens has polarization-dependent imaging efficiencies and polarization extinction ratios that exceed 50% and 10:1, respectively. Furthermore, opposite gradient phases can be applied to orthogonal polarizations to shift the imaging of the two polarized sources in the longitudinal and transverse directions. Indeed, we find that the metalens has a smaller depth-of-focus than a traditional metalens when imaging point sources with limited objective lengths. These results provide a new approach for achieving multifunctional beam steering, tomographic imaging and chiroptical detection.

Novel Bilayer Micropyramid Structure Photonic Nanojet for Enhancing a Focused Optical Field

In this paper, synthetically using refraction, diffraction, and interference effects to achieve free manipulation of the focused optical field, we firstly present a photonic nanojet (PNJ) generated by a micropyramid, which is combined with multilayer thin films. The theory of total internal reflection (TIR) was creatively used to design the base angle of the micropyramid, and the size parameters and material properties of the microstructure were deduced via the expected optical field distribution. The as-designed bilayer micropyramid array was fabricated by using the single-point diamond turning (SPDT) technique, nanoimprint lithography (NIL), and proportional inductively coupled plasma (ICP) etching. After the investigation, the results of optical field measurement were highly consistent with those of the numerical simulation, and they were both within the theoretical calculation range. The bilayer micropyramid array PNJ enhanced the interference effect of incident and scattered fields; thus, the intensity of the focused light field reached 33.8-times that of the initial light, and the range of the focused light field was extended to 10.08λ. Moreover, the full width at half maximum (FWHM) of the focal spot achieved was 0.6λ, which was close to the diffraction limit.

High-Efficiency Spin-Related Vortex Metalenses

In this paper, one spin-selected vortex metalens composed of silicon nanobricks is designed and numerically investigated at the mid-infrared band, which can produce vortex beams with different topological charges and achieve different spin lights simultaneously. Another type of spin-independent vortex metalens is also designed, which can focus the vortex beams with the same topological charge at the same position for different spin lights, respectively. Both of the two vortex metalenses can achieve high-efficiency focusing for different spin lights. In addition, the spin-to-orbital angular momentum conversion through the vortex metalens is also discussed in detail. Our work facilitates the establishment of high-efficiency spin-related integrated devices, which is significant for the development of vortex optics and spin optics.

Tunable Thermal Camouflage Based on GST Plasmonic Metamaterial

Thermal radiation control has attracted increasing attention in a wide range of field, including infrared detection, radiative cooling, thermal management, and thermal camouflage. Previously reported thermal emitters for thermal camouflage presented disadvantages of lacking either tunability or thermal stability. In this paper, we propose a tunable thermal emitter consisting of metal-insulator-metal (MIM) plasmonic metamaterial based on phase-change material Ge₂Sb₂Te₅ (GST) to realize tunable control of thermal radiation in wavelength ranges from 3 μm to 14 μm. Meanwhile, the proposed thermal emitter possesses near unity emissivity at the wavelength of 6.3 μm to increase radiation heat dissipation, maintaining the thermal stability of the system. The underlying mechanism relies on fundamental magnetic resonance and the interaction between the high-order magnetic resonance and anti-reflection resonance. When the environmental background is blackbody, the tunable emitter maintains signal reduction rates greater than 80% in middle-IR and longer-IR regions from 450 K to 800 K and from room temperature to 800 K, respectively. The dependences of thermal camouflage on crystallization fraction of GST, incident angles and polarization angles have been investigated in detail. In addition, the thermal emitter can continuously realize thermal camouflage for various background temperatures and environmental background in atmospheric window in the range of 3–5 μm.

Generation of subdiffraction longitudinal bifoci by shaping a radially polarized wave

Lenses with two or more foci along the longitudinal direction exhibit immense potential in several optical applications. In this study, we propose an approach for generating subdiffraction longitudinal bifoci by binary-phase bifocal super-oscillatory lenses (SOLs), which are realized by simple AND operation between two single-foci SOLs with different focal lengths. Three bifocal SOLs with radiusRlens=70λ are designed at an operating wavelength of λ=118.8µm. Simulation results demonstrate that the minimum full width at half maximum (FWHM) is 0.397λ, and the maximum FWHM is 0.449λ, which is still smaller than the Abbe diffraction limit of 0.510λ, while all the sidelobe ratios are small (<15.1%). By properly choosing the focal length of the single-foci SOLs in the design process, the distance between the two foci can be easily controlled. Significantly, the generated bifoci with relatively uniform intensity contain a strong longitudinal electric field, which indicates their excellent prospects in optical imaging, particle acceleration, and other optical applications. In addition, the proposed bifoci-SOLs are based on the binary phase modulation, which facilitates easy fabrication compared with other approaches. These outstanding properties indicate the wide application prospects of bifocal SOLs.

Tunable Beam Steering, Focusing and Generating of Orbital Angular Momentum Vortex Beams Using High-Order Patch Array

In this paper, a tunable patch array based on high-order is proposed at the frequency of 300 GHz, achieving active controllable beam steering, focusing and generation of orbital angular momentum vortex beams. It has been demonstrated that the patch array can achieve wide beam scanning angle by controlling the phase of array elements with tunable phase shifters. Meanwhile, beam focusing on the specified position can also be realized by phase modulation of array elements based on the focusing theory. In addition, we also designed a patch array to generate vortex beams with multiple topological charges by high-order modes. The performances show that the patch antenna array we designed has a good application prospect.

Ultracompact biosensor based on a metalens with a longitudinally structured vector beam

The refractive index is one of the essential parameters in describing biochemical reactions and biomedical diagnostics, and in situ measurement of the refractive index is very important for the micro total analysis system. We proposed an ultracompact biosensor based on a high numerical aperture metalens that was designed as two parts for generating the Pancharatnam-Berry phase and propagation phase, respectively, by using zinc sulfide nanofins, and nanopillars. Then incident light was modulated into a right-circularly polarized vortex beam and a left-circularly polarized vortex beam in the focal spot. The superposition of both beams can generate a structured vector beam with various polarization states along the focus direction. The polarization is sensitive to the difference of optical path, which has a potential application in index detection and biochemical analysis.

Spin-Selected Dual-Wavelength Plasmonic Metalenses

Several novel spin-selected dual-wavelength metalenses have been proposed and investigated based on the plasmonic metasurface consisting of two kinds of rotary rectangle gap nanoantennas (RGN), which are designed based on merging two or four polarity-inverse lenses corresponding to different wavelengths (765 and 1300 nm). The spin-selected dual-wavelength metalenses with two similar and two different vertical and lateral focal points have also been proposed respectively, which can focus two wavelengths with inverse spin states to arbitrary special positions. The three-dimensional metalens with four focal points have also been proposed, which can focus four beams with inverse spin states and different wavelengths to preset positions. Moreover, a spin-dependent achromatic metalens has also been proposed, which can focus left circularly polarized (LCP) incidence with different wavelengths to the same position. Our work opens up new avenues toward establishing novel spin-selected and wavelength-selected metadevices, and is significant for the development of spin-controlled photonics and particles manipulation. In addition, it provides a new idea for solving the problem of data transmission from optical fiber communication to visible light communication.

Visible-broadband Localized Vector Vortex Beam Generator with a Multi-structure-composited Meta-surface

We demonstrate a vortex beam generator meta-surface that consists of silver structures and graphene layers. The miniature material is just a few microns in size and the working part is only a few hundred nanometers thick. With the incidence of the linearly polarized beam, the meta-surface generates high-localized vector vortex beam with a high proportion of the longitudinal component. Being compared with the constituent part of the meta-surface, the multi-structure-combined meta-surface increases the localization by 250% and the longitudinal component proportion by 200%. Moreover, the above artificial material can generate vortex beams in broadband within the visible light range. These novel optical properties have the potential to improve the precision and sensitivity of nanoparticle manipulation. The study serves as a foundation in optical miniaturization and integration, nanoparticle manipulation, high-efficiency optical and quantum communication, and light-driven micro-tools.

High numerical aperture multifocal metalens based on Pancharatnam-Berry phase optical elements

A high numerical aperture multifocal metalens was proposed based on well-designed Pancharatnam-Berry phase optical elements. Both circularly and linearly polarized incident lights could be tightly focused into diffraction-limited focal spots. Right and left circularly polarized focal spots could be realized simultaneously by illuminating a linearly polarized beam. The highest numerical aperture reached to 0.84 with full width at half-maximum of 263 nm. Moreover, we also presented a metalens whose optical elements are hybrid arranged and the metalens can realize spin-independent focusing with a numerical aperture of 0.8. The presented metalens has significant potential applications in particles manipulation and high-resolution imaging.

Actively Tunable Terahertz Switches Based on Subwavelength Graphene Waveguide

As a new field of optical communication technology, on-chip graphene devices are of great interest due to their active tunability and subwavelength scale. In this paper, we systematically investigate optical switches at frequency of 30 THz, including Y-branch (1 × 2), X-branch (2 × 2), single-input three-output (1 × 3), two-input three-output (2 × 3), and two-input four-output (2 × 4) switches. In these devices, a graphene monolayer is stacked on the top of a PMMA (poly methyl methacrylate methacrylic acid) dielectric layer. The optical response of graphene can be electrically manipulated; therefore, the state of each channel can be switched ON and OFF. Numerical simulations demonstrate that the transmission direction can be well manipulated in these devices. In addition, the proposed devices possess advantages of appropriate ON/OFF ratios, indicating the good performance of graphene in terahertz switching. These devices provide a new route toward terahertz optical switching.