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Achieving a pre-designed scattering pattern from an ultra-compact platform is highly desired for on-chip integration optics, but conventional techniques suffer from the limitations of bulky size, wavelength-scale modulation and low efficiency. Here, we propose a new strategy to efficiently generate arbitrary spin-polarized scattering far-field patterns from surface-wave (SW) excitations on a designer Pancharatnam–Berry (PB) metasurface. We find that a PB meta-atom serves as a subwavelength scatter to decouple impinging SW to a spin-polarized propagating wave (PW) with tailored amplitude and phase, and thus interference among PWs generated by scatterings at different PB meta-atoms can generate a tailored far-field pattern. As a proof of concept, we design and fabricate a series of PB metasurfaces in the microwave regime and experimentally demonstrate that they can generate desired radiation patterns within a broad frequency band, including unidirectional radiation, line/point focusing, vortex beam and hologram. These findings may stimulate important applications in on-chip integrated photonics.

An all-silicon long-wavelength infrared (LWIR) achromatic metalens based on deep silicon etching is designed in this paper. With a fixed aperture size, the value range of the equivalent optical thickness of the non-dispersive meta-atoms constructing the achromatic metalens determines the minimum f-number. The fabrication characteristic with high aspect ratio of deep silicon etching amplifies the difference value of optical thickness between different meta-atoms by increasing the propagation distance of the propagation mode, which ensures a small f-number to obtain a better imaging resolution. A 280-µm-diameter silicon achromatic metalens with a f-number of 1 and the average focusing efficiency of 27.66% has been designed and simulated to validate the feasibility of this strategy. The simulation results show that the maximum focal length deviation percentage from the target value between the wavelength of 8.6 and 11.4 µm is 1.61%. This achromatic metalens design is expected to play a role in the field of LWIR integrated optical system.

This paper reports the design and electromagnetic performance of a new complementary frequency selective surface (CFSS) which shows polarization selectivity and good angular stability. Each CFSS unit cell only consists of a thin substrate sandwiched by a square patch array and its complementary square slot array with lateral displacement. The polarization selectivity of the proposed CFSS is determined by the displacement introduced between two arrays. An equivalent circuit model has been developed for this structure to interpret its polarization selective feature. The CFSS structure has been analyzed with full-wave simulation. The polarization selectivity of the proposed structure was verified by experiment.

In the fields of communication and sensing, resonance bandwidth is a very critical index. It is very meaningful to implement a broadband resonance device with a simple metamaterial structure in the terahertz band. In this paper, we propose a simple metamaterial structure which consists of one horizontal metal strip and two vertical metal strips. This structure can achieve an electromagnetically induced transparency-like (EIT-like) effect in the frequency range of 0.1~3.0 THz to obtain a transparent window with a resonance bandwidth as high as 1.212 THz. When the relative distance between two vertical metal strips is changed, the bandwidth can be effectively controlled. Furthermore, we found that the EIT-like effect can be actively adjusted by replacing vertical metal strips with photosensitive silicon.

Metalens is a planar optical component that uses nanostructures with a thickness on the order of the wavelength to manipulate the wavefront of the incident light. A key problem, especially in color imaging and display applications, is the correction of chromatic aberration, which is an inherent effect caused by the dispersion of periodic lattices and resonance modes. However, the current achromatic metalenses either use the PB phase method that is only valid for circularly polarized light or nanostructures with complex cross sections that are difficult to manufacture. Here, we designed a broadband achromatic metalens for linearly polarized light from 450 to 800 nm. Rectangular titanium dioxide nanofins of various lengths and widths were applied to modulate the phase and dispersion of the incident light. The metalens can fulfill three target phases simultaneously by using an optimization method. The designed metalens has a stable focus from 450 to 800 nm with an average focusing efficiency of 64%. It can be potentially applied in microscopes, lithography machines, sensors, and displays.

Metamaterial is the artificial structure under sub-wavelength dimension and could be designed to manipulate the electromagnetic wave radiation across the broad frequency range through microwave to much higher frequency, such as terahertz and optical regime. Lens antenna can generate the focused beam with high gain and shrink the bulky refractive body and feeds into a shape of flat form. This chapter will discuss the general concepts of metalens and the technology of metalens-based antenna at microwave, terahertz and optical frequency. The recent progress in the research and development of metalens antennas is reviewed with designs principle and typical applications. At last part, some innovative techniques such as dynamic focus-tuning of metalen are discussed in details.

Achromatic focusing is essential for broadband operation, which has recently been realised from visible to infrared wavelengths using a metasurface. Similarly, multi-terahertz functional devices can be encoded in a desired metasurface phase profile. However, metalenses suffer from larger chromatic aberrations because of the intrinsic dispersion of each unit element. Here, we propose an achromatic metalens with C-shaped unit elements working from 0.3 to 0.8 THz with a bandwidth of approximately 91% over the centre frequency. The designed metalens possesses a high working efficiency of more than 68% at the peak and a relatively high numerical aperture of 0.385. We further demonstrate the robustness of our C-shaped metalens, considering lateral shape deformations and deviations in the etching depth. Our metalens design opens an avenue for future applications of terahertz meta-devices in spectroscopy, time-of-flight tomography and hyperspectral imaging systems.

Grating coupled surface plasmon resonance (GCSPR) sensors with wavelength modulation are widely used in many fields, but the low sensitivity holds their practical applications. Here we theoretically analyze the sensitivity limit of GCSPR sensors, provide design methods to reach the maximum sensitivity and the way to increase the sensitivity limit. The theoretical analysis shows that metal gratings with periods as large as possible should be used and the incident angle should be set close to 90∘ in order to maximize the sensitivity for a certain detecting wavelength, moreover the sensitivity limit increases as the detecting wavelength increases. Experimentally, we prepare three gratings with periods of 314 nm, 1470 nm and 6733 nm by stripping commercial optical discs or photolithography. The measured sensitivities of the sensors based on these gratings are 319.96 nm/RIU, 1477.74 nm/RIU and 2077.26 nm/RIU, respectively. The sensitivity achieved in this article is much higher than existing ones due to the use of design method following the theoretical analysis. This work paves the way for the optimal design of GCSPR sensors.

This paper describes a simple H-typed terahertz metamaterial structure consisting of three metal rectangular strips. The structure can convert the Fano effect to the electromagnetically induced transparency (we use its abbreviation EIT instead) effect in the frequency range of 0.1–1.5 THz. The results show that the Fano effect occurs when the symmetry of the H-typed structure is slightly broken, and a narrow and sharp Fano dip occurs at a frequency of 1.05 THz, and the Q value of the Fano dip can reach 43. When the structural asymmetry is increased by moving the metal rectangular strip in the middle, the structure realizes a transition from the Fano effect to the EIT effect, and a transparent transmission with a line width of 0.383 THz occurs at a frequency of 1.0 THz, and the transmittance is as high as 93.66%. In order to illustrate the mechanism of the Fano effect and the EIT effect in this structure, we present the electric fields at several key resonant frequencies and discuss and analyze them. In addition, we also study the effects of structural parameters on the Fano effect and the EIT effect, and make appropriate discussions and summaries. This metamaterial structure enables the functional conversion from Fano to EIT, and the functional conversion device designed by this has potential application value in terahertz sensing technology.

Multiple-band metamaterial absorbers have been widely reported using the co-planar or layered design methods. However, these obtained absorption devices are of complex structure, large unit size, heavy weight, and time-consuming construction steps. Herein, an alternative design strategy is suggested to realize the multiple-band absorption at terahertz frequency. By introducing air gaps into the rectangular metallic patch, the original rectangular resonator can be divided into multiple sub-structures (or separated sections), and the combined effect of the localized resonance response of these sub-structures (or separated sections) gives rise to the multiple-band absorption. More importantly, the size, position and number of air gaps play the important roles in controlling the resonance performance of the absorption peaks and even in regulating the amount of the absorption peaks. Compared with the existing multiple-band absorption design strategies, the proposed approach does not increase the unit size, nor need to stack multiple layers, which provides important guidance for the design of multiple-band terahertz metamaterial absorbers with simple, compact, and easy to fabricate for full details.

Intelligent polymers with tough networks are of considerable significance for thedevelopment of highly proficient polymer science and technology. In this work, polymeric elastomers with integrated stretchable and self-healable characteristics were designed by cross-linking hyperbranched polymers with flexible segments. The hyperbranched polymer with multiple terminal groups provided various cross-linking points, so that mechanically robust networks could be achieved. Driven by the reversibility of imine and disulfide bonds employed, the elastomers exhibited good self-healing property and the healing efficiency reached up to 99% under ambient environments. Furthermore, the dynamic reversibility of the polymers was investigated at molecular level. The imine and disulfide bonds were incorporated into the networks to construct soluble and recyclable hyperbranched polymer with pH and redox responsiveness via A2+B3 approach and Schiff base polymerization. The polymers containing imine bonds could complete the polymerization–depolymerizationtransition and undergo reversible cycles for several times through changing pH. Moreover, in the presence of disulfide bonds, the polymers were provided with redox cleavage property triggered by dithiothreitol. This study may provide new opportunities for the design and application of intelligent polymers with tough networks through regulating topological structures.

Ultraviolet lenses are core components of surveillance cameras, lithography machines and UV microscopes. Traditional refractive UV lenses are bulky, expensive and easy to aging, which hinders their applications in miniaturized and integrated photonic devices. In this paper, we proposed a polarization independent, broadband achromatic metalens that consists of arrays of silicon nitride nanopillars on a flat substrate. In order to simultaneously fulfill the target phases in a wide spectrum range, the phase library is extended to 0-8 π by using tall nanopillars that support high order resonances. The designed metalens has a stable focus across the entire operating wavelength range from 300 nm to 400 nm and the average focusing efficiency is as high as 50%. This polarization independent achromatic metalens can be potentially applied in compact UV cameras, UV microscopes and lithography machines.

Surface plasmon resonance (SPR) sensors based on metal gratings have received much attention for designing compact and portable biosensors. In this paper, we systematically optimize SPR sensors based on sinusoidal and rectangular gratings to improve the performance of this kind of sensors. A parameter (FOM*) is defined to evaluate the sensor performance, which combines the sensitivity, FWHM, and depth of the SPR absorption peak. We find that grating period of 560 nm is suitable to locate the SPR peaks in the optimal response range of silicon detectors and ensures high sensitivity. For sinusoidal gratings, the highest FOM* of 99.25 is achieved at grating depth of 15 nm. The highest FOM* for rectangular grating with continuous metal film is 123.70 when grating depth and duty cycle are 12 nm and 0.3, respectively. With grating depth of 24 nm and duty cycle of 0.8, the highest FOM* of 25.23 is obtained for rectangular grating with discontinuous metal film. These optimization results can be directly used to improve the detection limit of compact SPR sensors.

Dual-band polarization controllable terahertz metamaterial absorber consisting of two horizontal metallic strips and two vertically connected metallic strips is demonstrated. Due to different strip lengths in the two orthogonal directions, two near-perfect absorption peaks are firstly obtained when the incident beam electric field is in the horizontal direction, while two new peaks are next realized when the electric field is selected along the vertical direction. The near-field distributions in two specific directions are provided to investigate the mechanism of polarization controllable dual-band absorption. Our research should have broad application prospects in the selection, control and utilization of polarization-based devices.

A simple and fast optimization method for symmetric multilayer frequency selective surfaces (FSSs) structure is presented in this paper, based on the mutual admittance approach. To elaborate the proposed method, a symmetric bi-planar FSSs structure is selected to explain the optimizing process. After the optimized analysis, the symmetric bi-planar FSSs structure can achieve good characteristics of flat top and sharp roll-off at 70° angle of incidence, with an optimum coupling layer medium (d 2 = 15 mm, e 2 = 1.15). As it is difficult to obtain the material with e = 1.15 by using traditional technique, we design an array of dielectric cylinders to effectively replace the homogeneous medium, based on the theory of periodic waveguide. To verify the optimization method and design idea, a prototype simple of the symmetric bi-planar FSS is fabricated and measured. The measured results of the prototype well coincided with the simulation results, which further shows the validity of the optimization method and the idea of equivalent substitution.

A subwavelength-scale Huygens particle utilizing both electric and magnetic responses is proposed here. As the electric and magnetic responses of the proposed particle are independent of each other, arbitrary complex transmission coefficients covering all magnitudes from 0 to 0.9 and all phases (360°) can be achieved by varying its structural parameters. By properly engineering the distribution of transmission magnitudes and phases, a Huygens metasurface grating with excitation of +1 order harmonic is designed and fabricated. The measurement results are in agreement with the simulations, further demonstrating the validity of the designed Huygens particle and metasurface.

We design and fabricate a deformable frequency selective surface (FSS) structure using shape memory alloys (SMA). The unit cell could “remember” two different geometrical shapes and the shapes convert to each other alternately during heating and cooling, that leads to the drift of resonant frequency. Qualitative analysis by equivalent circuit model and accurate numeric calculation are compared to display the character of the transmission. The measurements show that a tuning range of frequency from 13.07GHz to 16.29GHz is achieved when the morphology of the unit cell changes, making the deformable FSS an attractive choice for tunable filter in different frequency bands with the features of wide tuning range and sharp cut-off.

A novel broadband bi-mode active frequency selective surface (AFSS) is presented in this paper. The proposed structure is composed of a periodic array of convoluted square patches and Jerusalem Crosses. According to simulation results, the frequency response of AFSS definitely exhibits a mode switch feature between band-pass and band-stop modes when the diodes stay in ON and OFF states. In order to apply a uniform bias to each PIN diode, an ingenious biasing network based on the extension of Wheatstone bridge is adopted in prototype AFSS. The test results are in good agreement with the simulation results. A further physical mechanism of the bi-mode AFSS is shown by contrasting the distribution of electric field on the AFSS patterns for the two working states.

A novel wideband, low-profile and second-order miniaturized band-pass frequency selective surface (FSS) made of metallic mesh and its complementary structures with skewed arrays of modified triples is presented in this paper. Compared with traditional second-order bandpass FSSs obtained using λ/4 apart from one another, the novel FSS with an overall thickness of λ/18 is composed of three metallic layers (the outside and middle layers are complementary) separated by two electric thin dielectric substrates. This arrangement can shorten the inter-element spacing and increase the bandwidth, while the up and bottom metallic layers can constitute a symmetric biplanar FSS and thus realize ability of maximally flat second-order bandpass response. The novel FSS has a −3 dB bandwidth about 8.2 GHz (6.9 -15.1 GHz) and a fractional bandwidth exceeds 75%. Moreover, such an FSS has the merits of stable performance for incident angles within 50° and different polarizations. The principles of operation along with guidelines for the design of the proposed FSS, the simulated results by vector modal matching method, and the experimental values of the fabricated prototype are also presented and discussed.

In this paper, we present an infrared transparent frequency selective surface (ITFSS) based on iterative metallic meshes, which possesses the properties of high transmittance in infrared band and band-pass effect in millimeter wave band. Cross-slot units are designed on the iterative metallic meshes, which is composed of two same square metallic meshes with a misplaced overlap. In the infrared band of 3–5 μm, the ITFSS has an average transmittance of 80% with a MgF2 substrate. In the millimeter wave band, a transmittance of −0.74 dB at the resonance frequency of 39.4 GHz is obtained. Moreover, theoretical simulations of the ITFSS diffractive characteristics and transmittance response are also investigated in detail. This ITFSS may be an efficient way to achieve the metamaterial millimeter wave/infrared functional film.

A dual-band flexible frequency selective surface (FSS) with miniaturized elements and maximally flat (Butterworth) response is presented in this paper. It is composed of three metallic layers, which are fabricated on thin flexible polyimide substrates and bonded together using thin bonding films. The overall thickness of the proposed structure is only about 0.3 mm, making it an attractive choice for conformal FSS applications. All the three layers can constitute a miniaturized-element FSS (MEFSS) and produce the first pass-band with miniaturization property, while the up and bottom layers can constitute a symmetric biplanar FSS and produce the second pass-band with maximally flat (Butterworth) response. The two pass-bands are independent and there is a wide band spacing up to 30 GHz between them. The principles of operation, the simulated results by using the vector modal matching method, and the experimental values of the fabricated prototype are also presented and discussed.

This paper presents an infrared transparent frequency selective surface (ITFSS) based on metallic meshes. In this ITFSS structure, periodic cross-slot units are integrated on square metallic meshes empowered by coating and UV-lithography. A matching condition is proposed to avoid the distortion of units. Experimental results show that this ITFSS possesses a good transmittance of 80% in the infrared band of 3–5 μm, and also a stable band-pass behavior at the resonance frequency of 36.4 GHz with transmittance of −0.56 dB. Theoretical simulations about the ITFSS diffractive characteristics and frequency responses are also investigated. The novel ITFSS will attract renewed interest and be exploited for applications in various fields.