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Real-time and fast trapping and tagging of microfeatures, such as microparticles and cells, are of great significance for biomedical research.

Metasurface is a kind of sub-wavelength artificial electromagnetic structure, which can resonate with the electric field and magnetic field of the incident light, promote the interaction between light and matter, and has great application value and potential in the fields of sensing, imaging, and photoelectric detection. Most of the metasurface-enhanced ultraviolet detectors reported so far are metal metasurfaces, which have serious ohmic losses, and studies on the use of all-dielectric metasurface-enhanced ultraviolet detectors are rare. The multilayer structure of the diamond metasurface-gallium oxide active layer-silica insulating layer-aluminum reflective layer was theoretically designed and numerically simulated. In the case of gallium oxide thickness of 20 nm, the absorption rate of more than 95% at the working wavelength of 200-220 nm is realized, and the working wavelength can be adjusted by changing the structural parameters. The proposed structure has the characteristics of polarization insensitivity and incidence angle insensitivity. This work has great potential in the fields of ultraviolet detection, imaging, and communications.

Adopting the direct $Z$ -transform ( $\text{D}Z\text{T}$ ) method due to its higher accuracy instead of the approximate $Z$ -transform ( $\text{A}Z\text{T}$ ) methods and efficient and switchable truncations between the 1st- and 2nd-order uniaxial perfectly matched layers (UPMLs) with the complex-frequency-shifted (CFS) scheme are shown to terminate the relevant finite-difference time-domain (FDTD) regions. The proposed $\text{D}Z\text{T}$ -CFS-UPML formulations can possess the switchable function in terms of relevant FDTD problems so that the optimal performance can be obtained with the tradeoff among memory requirement, CPU time, and absorption accuracy. For the FDTD problem with the strong evanescent and weak low-frequency propagating waves, the proposed $\text{D}Z\text{T}$ -CFS-UPML formulations can be switched to the 1st-order PML truncation, and for the other cases with both low-frequency propagating and strong evanescent waves, the 2nd-order PML is the best choice. Two numerical simulations have been carried out to illustrate the validity and flexibility of the proposed approach.

The absorption spectrum of metasurface absorbers can be manipulated by changing structures. However, narrowband performance absorbers with high quality factors (Q-factor) are hard to achieve, mainly for the ohmic loss of metal resonators. Here, we propose an all-dielectric metasurface absorber with narrow absorption linewidth in the mid-infrared range. Magnetic quadrupole resonance is excited in the stacked Ge-Si3N4 nanoarrays with an absorption of 89.6% and a Q-factor of 6120 at 6.612 µm. The separate lossless Ge resonator and lossy Si3N4 layer realize high electromagnetic field gain and absorption, respectively. And the proposed method successfully reduced the intrinsic loss of the absorber, which reduced the absorption beyond the resonant wavelength and improved the absorption efficiency of Si3N4 in the low loss range. Furthermore, the absorption intensity and wavelength can be modulated by adjusting the geometric parameters of the structure. We believe this research has good application prospects in mid-infrared lasers, thermal emitters, gas feature sensing, and spectral detection.

Broadband absorption is critical for the applications of metamaterial absorbers. In this work, a broadband long-wave infrared (LWIR) absorber with classical metal-dielectric-metal configuration is numerically demonstrated. The absorber consists of single-sized cut-wire arrays that show broadband and high extinction ratio, attributed to polarization-selective simultaneous excitation of propagated and localized surface plasmon resonances. The average absorption rate of the TM wave reaches 91.7% and 90% of the incident light is absorbed by the resonator in the wavelength range of 7.5–13.25µm so that the average extinction ratio in the resonator layer reaches 125. The polarization insensitive broadband absorption can be obtained by a cross resonator which can be treated as a pair of cut-wires perpendicular to each other. Our metamaterial absorber with single-sized resonators shows spatially concentrated broadband absorption and may have promising applications for hot-electron devices, infrared imaging, and thermal detection.

We present a novel ultra-broadband, polarization-independent, and wide-angle metamaterial absorber whose metal–insulator–metal cavities are embedded into bulk insulator nanodisks. The hybridization of multiple embedded cavity modes generated by the combination of dielectric-loaded surface plasmon polaritons waveguide and cavity modes contributes to large bandwidth and high absorption in the long wavelength infrared (LWIR) region. The proposed structure exhibits more than 94% absorbance in the interval from 8 μ m to 16 μ m ; and more than 95% absorbance over the whole LWIR band (8– 14 μ m ), which is superior than the initial MIM structure (absorption greater than 90% from 8.10–14. 33 μ m ) and similar kinds of metamaterial absorber based on noble metal. In addition, a nearly perfect absorbance (more than 99%) is obtained in the 11.22–12. 46 μ m and 13.26–14. 59 μ m wavebands. Moreover, results show that the resonant wavelength and operating bandwidth can be adjusted flexibly by varying related geometry parameters. Thus, the wavelength-selective metamaterial absorber is promising for thermal emitters, energy harvester and microbolometers.

A dual-band (mid- and long-wave infrared) polarization-selective plasmonic absorber was designed and numerically investigated. This absorber traps definite polarization light and reflects light that is perpendicular to the polarization direction. It is extremely sensitive to polarization angle and can keep robustness to oblique incidence. The extinction rate does not reduce when the incident angle is even near 80°and rate value keeps above 130 for both resonance peaks. The absorber can respond to mid- and long-wave infrared atmospheric windows simultaneously and achieve near-unity absorption at 3.3 μ m and 9.8 μ m for specific polarization under normal radiation. The resonance condition is tuned by altering the geometric design. Owing to its high absorptivity and fine polarization properties, the absorber combines the advantages of a light absorber and a polarizer, and can be utilized in an uncooled infrared polarization detector, which simplify the optical system design and avoid the polarization information reconstruction error caused by the misplacement between the polarizer and the pixel.

As an emerging anisotropic two-dimensional (2-D) material, few-atomic-layer black phosphorus (BP) has shown some promising potentials for infrared optoelectronics. Engineering and enhancing its light-matter interaction is significant for many advanced photonic devices. In view of this, we aim to achieve extremely high infrared absorption in monolayer BP with/without subwavelength patterning. By optimizing the polarization and angle of the incident light, the dielectric thickness, and the n -type doping concentration, respectively, infrared radiation can be sufficiently coupled to optical absorption of the monolayer BP in a multiscale photonic structure. The anisotropic infrared absorbance ratios of the unpatterned monolayer BP are enhanced up to 98.2% and 96%, respectively, in inequivalent crystal directions. Moreover, monolayer BP with a design of metasurface and optimized doping can reach near-unity anisotropic infrared absorption under a smaller incident angle. This paper provides a simple and efficient scheme to trap infrared light for developing promising optoelectronic devices based on monolayer BP and potentially other anisotropic 2-D materials.

We design and numerically analyze a Fano resonance device based on periodical all-dielectric “lucky knot” shaped nanostructure in the mid-infrared region with high sensitivity, which is insensitive to polarization and incident angle. The proposed nanostructure is sensitive to the change of the refractive index of the substance to be tested. We established the correspondence between the change of the refractive index and the peak position of the reflection spectrum. And then we propose an optical refractive index sensor with a sensitivity of 986 nm/RIU, and a maximum figure of merit of 32.7, which is much higher compared to the sensor based on metallic materials. The maximum Q-factor can reach 520. This study may provide a further step in optical sensing, biosensing and environmental monitoring.

Cointegration and coupling a perfect metamaterial absorber (PMA) together with a film bulk acoustic wave resonator (FBAR) in a monolithic fashion is introduced for the purpose of producing ultracompact uncooled infrared sensors of high sensitivity. An optimized ultrathin multilayer stack was implemented to realize the proposed device. It is experimentally demonstrated that the resonance frequency of the FBAR can be used efficiently as a sensor output as it downshifts linearly with the intensity of the incident infrared irradiation. The resulting sensor also achieves a high absorption of 88% for an infrared spectrum centered at a wavelength of 8.2 μm. The structure is compact and can be easily integrated on a CMOS-compatible chip since both the FBAR and PMA utilize and share the same stack of metal and dielectric layers.

Broadband metamaterials absorbers with high absorption, ultrathin thickness and easy configurations are in great demand for many potential applications. In this paper, we first analyse the coupling resonances in a Ti/Ge/Ti three-layer absorber, which can realise broadband absorption from 8 to 12 μm. Then we experimentally demonstrate two types of absorbers based on the Ti/Ge/Si3N4/Ti configuration. By taking advantage of coupling surface plasmon resonances and intrinsic absorption of lossy material Si3N4, the average absorptions of two types of absorbers achieve almost 95% from 8 to 14 μm (experiment result: 78% from 6.5 to 13.5 μm). In order to expand the absorption bandwidth, we further propose two Ti/Si/SiO2/Ti absorbers which can absorb 92% and 87% of ultra-broadband light in the 14–30 μm and 8–30 μm spectral range, respectively. Our findings establish general and systematic strategies for guiding the design of metamaterial absorbers with excellent broadband absorption and pave the way for enhancing the optical performance in applications of infrared thermal emitters, imaging and photodetectors., Ultra-broadband metamaterials absorbers with high absorption, ultrathin thickness and easy configurations are designed and demonstrated, which pave the way for enhancing the optical performance in applications of infrared thermal emitters, imaging and photodetectors.

Infrared broadband absorbers are in great demand in various applications, such as integration into uncooled infrared detectors and microbolometers. In this thesis, we demonstrate and compare three different design methods: coupling multi-sized resonators, inlaying metallic structures in the dielectric layer and choosing laminated dielectric layers made of lossless and lossy materials. Due to their absorption mechanisms, we initially propose a W/ZnTe/W/Ge/W and an embedded Ti/Si/Ti absorber, both of which can achieve ultra-broadband absorption from 8 to 14 μm, with average absorptions of 88% and 92%. We further propose a Ti/Ge/Si3N4/Ti absorbers which can realise near-perfect absorption in the LWIR band, with average absorptions of 95% where all absorption curves exceed 90%. Our study provides the broadband LWIR absorbing structures in addition to providing new insight into the understanding of the interaction of propagating and localised surface plasmon resonances, with the prospect of expanding to other absorbing-structure designs from visible to THz regimes.

A polarization sorting metamaterial with polarization filtering and absorption is proposed. When unpolarized incident light strikes the metamaterial, one polarization component is completely absorbed, and the other polarization component is completely transmitted. We achieved an absorption extinction ratio of up to 350 and a transmission extinction ratio of 425 simultaneously in the LWIR. Unlike the 50% energy utilization limit of other polarization absorbers due to the complete reflection of another polarization component, our proposed metamaterial can be composed of layered polarization selective absorption devices to achieve more than 90% energy utilization. Therefore our design can provide a new solution for real-time polarization detection.

Two types of ultra–broadband long wavelength infrared (LWIR) absorbers with small period and super thin thickness are designed. The absorption with high absorptivity and large bandwidth is achieved through combined propagating and localized surfaced plasmon resonances. We first design a three-layer absorber with a Ti–Ge–Ti configuration, the period of the structure is only 1.4 µm (nearly 1/8 of the center wavelength), the thickness of its dielectric is only 0.5 µm (1/22 of the center wavelength), and the average absorption is 87.9% under normal incident from 8µm to 14µm. Furthermore, the four-layer absorber with a Ti–Ge–Si3N4–Ti configuration is designed to obtain more average absorption increasing to 94.5% from 8 µm to 14µm under normal incident, the period of the structure increases to 1.6 µm and the total thickness of dielectric increases to 0.6µm. The proposed absorber is polarization–independent and possesses a good tolerance of incident angle. We calculate that the average absorption of the four-layer absorber for both TE– and TM–modes still exceeds 90% up to an incident angle of θ = 40° (90.7% for TE–mode, 91.9% for TM–mode), and exceed 80% up to an incident angle of θ = 60° (80.2% for TE–mode, 82.1% for TM–mode).

A wavelength-selective, ultrathin, broadband infrared metal–insulator–metal (MIM) absorber with multi-sized Ti–Ge cubes is proposed. By flexibly combining different sizes of Ti–Ge cubes, stacking upward and reasonably filling the border, all the resulting 3 structures that we propose show an average absorptivity of at least 90% over a wide spectral range in the infra-red, extending from 6. 3 μ m to 14. 8 μ m . The absorptivity is further increased up to 99% when considering narrower spectral ranges such as 7.96-8. 34 μ m and 11.02-11. 75 μ m wavebands, which is superior than the previous work in long wavelength infrared band based on the MIM structure. Those characteristics vary depending on the 3 designs considered and studied in this work: single-layer structure, double-layer structure and modified structure. The intrinsic strong energy dissipation caused by highly lossy metal Ti (here Titanium) and excited low-Q cavity modes are key factors contributing to such efficient broadband absorption. The polarization and angle insensitivity are demonstrated by analysing the absorption performance with oblique incidences for both transverse electric wave (TE) and transverse magnetic wave (TM). Moreover, flexible combinations of different resonators allow trade-offs between the absorption bandwidth and the absorbance, which makes the operating waveband of the metamaterial absorber adjustable through proper design. The proposed broadband absorbers have many potential applications, including microbolometers, thermal emitters, and plasmonic sensors.

The structural parameters of low-stepped mirror which is the core component of a light Fourier transform infrared spectrometer (FTIRS) have important influence on the performance of the instrument. A simple method of multiple deposition is proposed to fabricate a low-stepped mirror with step height of 625 nm, for its high precision, high efficiency and miniaturization. So the film stress will be introduced in the process of coating, which can lead to step deformation. We build a bending model of the low-stepped mirror and analyze the influence of its deformation. The light intensity and spectrum are changed by the step deformation. Therefore, the film stress should be reduced in order to ensure the accuracy of the spectral information. Increasing the thickness of substrate is proposed in this paper to reduce the step deformation, besides adjusting the coating temperature and adding sub-layer. Our results reveal that the basic requirements of the system are satisfied when the thickness of the substrate is 5 mm in the appropriate coating environment. An FTIRS based on stepped mirrors and grid beam splitter is assembled and corresponding experiment is carried out to obtain the spectrum curve of acetonitrile.

In this paper, we describe the design of a small-period ultra-wideband long-wavelength infrared metamaterial absorber. The two-layer metal (titanium) resonators and the underlying metal reflective layer are vertically stacked, and the layers are filled with a dielectric (silicon), where the two cross-shaped resonators have slightly different sizes. The absorption spectrum of the structure reaches absorbance values above 90% in the wavelength interval of 8 µm and 13.15 µm in the case of normal incidence. Through a field distribution analysis, we found that the propagation surface plasmons and localized surface plasmons excited by titanium resonators caused two broad absorption peaks (8.5 µm and 12.2 µm), which were close to each other, to obtain the final broadband absorption. Furthermore, the thickness of the structure is less than 1/13 of the centre wavelength (11 µm), and the period is only 1/5 of the centre wavelength (11 µm), which makes the structure easy to integrate on small-pixel detectors. Therefore, such designs may be useful in infrared imaging, thermal detection, and thermal emitters.

Broadband perfect infrared wave absorption of unpolarized light over a wide range of angles in an ultrathin film is critical for applications such as thermal emitters and imaging. Although many efforts have been made in infrared broadband absorption, it is still challenging to cover the perfect absorption of broadband in the long-wave infrared band. We propose a long-wave infrared broadband, polarization, and incident angle insensitivity metamaterial absorber based on the supercell with four rings of two sizes. Broadband absorption covering the long-wave infrared band is realized by combining four PSPRs and LSPRs absorption peaks excited by the supercell structure. The absorptivity of our absorber exceeds 90% in the wavelength range of 7.76∼14µm, and the average absorptivity reaches 93.8%. The absorber maintains more than 80% absorptivity as the incident angle of unpolarized light reaches 60°, which may have promising applications for thermal emitters, infrared imaging, thermal detection.

The atmospheric window in the infrared (IR) band primarily consists of mid-wave (MWIR, 3-5 μm) and long-wave IR (LWIR, 8-12 μm) bands, also known as the working bands in most of the IR devices. The main factor affecting the device capability includes the absorption efficiency, hence, the absorption material. Herein, a dual-band absorber based on the composite cross structure (CCS) in both MWIR and LWIR bands was proposed, with absorption peaks of 4.28 μm and 8.23 μm. The obtained absorber is with high scalability in the MWIR and LWIR region respectively by tuning the structural parameters. A quadrupole polarization model is proposed for further understanding of the uneven distribution of electromagnetic field that was caused by the change of the center spacing of the embedded structure. Meanwhile, it was shown that the two absorption peaks exhibited good incident angle stability. In addition, as the incident angle of the TM mode increases, a waveguide is formed between the embedded structure and the surface structure, leading to another strong absorption in the LWIR band. The results showed that absorption increases as the incident angle increases. The proposed absorber can be a good candidate for applications in thermal emission, detection and solar energy harvesting.

Capturing polarization information has long been an important topic in the field of detection. In this study, two polarization-dependent broadband absorbers based on a composite metamaterial structure were designed and numerically investigated. Unlike in conventional metamaterial absorbers, the bottom metallic film is functionalized to achieve a polarization response or broadband absorption. The simulation results show that the type I absorber exhibits TM polarization-dependent broadband absorption (absorptivity>80%) from 8.37 µm to 12.12 µm. In contrast, the type II absorber presents TE polarization-dependent broadband absorption (absorptivity>80%) from 8.23 µm to 11.93 µm. These devices are extremely sensitive to the change of polarization angle. The absorptivity changes monotonically with an increase of the polarization angle, but it is insensitive to oblique incidence. This design paves the way for realizing broadband polarization-dependent absorption via a simple configuration. It has bright prospects in thermal detection applications and imaging fields.

The strategy for fabricating bendable micro-light emitting diode arrays is presented and the mechanical properties of bent arrays are analysed in this paper. The key procedures of the fabrication process consist of grooving the wafer, welding the upside electrode with an indium tin oxide current-spreading layer, integrating the micro-pixels, removing the substrate, electroplating the backside electrode, and encapsulating the device. In order to prevent potential physical destruction and improve the reliability and fatigue of the arrays, the position of the neutral mechanical plane was calculated. Strain and stress distributions in bent LED arrays showed that strain concentrated in the polymers and the generated stress preferentially concentrated in the electrodes and semiconductor. These results indicate that physical destruction, rupture, or delamination may first occur in the electrodes or semiconductor interface. Display Omitted A strategy for fabricating polymer-integrated bendable micro-LED arrays is presented.Potential physical destructions likely occur in the regions around LED pixel edges.Bent the sample with radius of 10mm found no observable degradation.

This paper describes a novel finite element thermal analysis model for an AlGaInP-LED micro-array device. We also conduct a transient analysis for the internal temperature field distribution of a 5×5 array device when a 3×3 unit is driven by pulse current. In addition, for broader applications, a simplified thermal analysis model is introduced and its accuracy is verified. The internal temperature field distribution of 100×100 units is calculated using the simplified model. The temperature at the device center reaches 360.6 °C after 1.5 s. In order to solve the heat dissipation problem of the device, an optimized heat dissipation structure is designed, and the effects of the number and size of the heat dissipation fins on the thermal characteristics of the device are analyzed.

Pd-loaded SnO2 hollow microspheres have been successfully prepared via a facile one-pot hydrothermal route and subsequent Pd-loaded treatment without involving any templates, surfactants, or capping agents. The morphological and structural characterization confirms that Pd-loaded SnO2 hollow microspheres are hierarchically constructed of numerous well-aligned rodlike SnO2 subunits with ultrathin diameter of about 5–10 nm and monodisperse Pd particles with several nanometers in size. The time-dependent investigation demonstrates that the formation of hierarchical SnO2 hollow spheres is driven by Ostwald-ripening mechanism. Furthermore, gas sensors based on pure and Pd-loaded SnO2 have been fabricated. The Pd-loaded SnO2 hollow microspheres exhibit relatively lower operating temperature, higher response and selectivity to toluene in comparison with that of pure SnO2. Besides structural merits of ultrathin nanorod-assembled hollow and porous structure, the promotion of sensing performances can also be attributed to the contribution of catalytic Pd particles.

A 300 μm×300 μm light emitting diode (LED) chip is divided into nine 80 μm×80 μm units with 30 μm spacing between adjacent ones. After arraying, the total saturation light output power and the maximum injection current are enhanced by 5.19 times and nearly 7 times, respectively. In addition, the test results demonstrate that the illuminance uniformity on the receiving surface reaches the optimum when the spacing between the arrays is equal to the maximum flat condition. The larger the number of arrays, the greater the area with uniform illuminance on the receiving surface.

Pure and Pd-loaded SnO2 cubic nanocages with hierarchically nanoparticle-assembled and porous shells have been successfully fabricated through a straightforward multi-step route. The synthetic step-dependent structure evolution and the formation mechanism have been discussed. Furthermore, the toluene-sensing performances of these Pd-loaded SnO2 nanocages are elaborated and compared with those of pure SnO2. The toluene sensing results demonstrate that Pd-loaded SnO2 nanocages with the optimal loading amount of 1.0 mol% show a low detection limit (0.1 ppm) with response of 41.4–20 ppm toluene at the working temperature of 230 °C with the fast response time of 0.4 s, and improved selectivity. The improvement of toluene sensing properties is not only attributed to the effective utility of hollow and porous architecture, but also due to the dramatic sensitization of the loaded Pd nanoparticles.

International audience; We present the Near-Infra-Red (NIR) and Mid-Infrared (MIR) absorption properties of Ultra-Black Silicon obtained by wafer-level cryogenic plasma processing. We found that when using highly-doped silicon, the spectral range of near-unity full absorption of light is extended from the visible range till a wavelength of 10 µm. This MIR wavelength range coincides with that of the maximum of black-body radiation from room temperature up to a few thousand Kelvin. Therefore, according to Kirchhoff's Law, we take advantage of the enhanced properties of black silicon to realize ultra-compact light-sources of high efficiency, which are operated in combination with a MEMS-FTIR spectrometer.

Express Wavenet is an improved optical diffractive neural network. At each layer, it uses wavelet-like pattern to modulate the phase of optical waves. For input image with n2 pixels, express wavenet reduce parameter number from O(n2) to O(n). Only need one percent of the parameters, and the accuracy is still very high. In the MNIST dataset, it only needs 1229 parameters to get accuracy of 92%, while the standard optical network needs 125440 parameters. The random shift wavelets show the characteristics of optical network more vividly. Especially the vanishing gradient phenomenon in the training process. We present a modified expressway structure for this problem. Experiments verified the effect of random shift wavelet and expressway structure. Our work shows optical diffractive network would use much fewer parameters than other neural networks. The source codes are available at https://github.com/closest-git/ONNet., Comment: 5 pages,4 figures

All-dielectric metamaterials are a promising low-loss alternative to plasmonic metamaterials for near-infrared perfect reflection, but the working bandwidth is still limited. Here we propose an ultra-wideband all-dielectric metamaterial perfect reflector that has a compact structure consisting of the subwavelength high-index grating, connection layer, and multilayer stack. Such a perfect reflector combines the advantages of quarter-wave design and resonant leaky mode, and covers an extremely wide wavelength range from 966 to 2203 nm under the normal incidence of transverse magnetic wave. By engineering the connection layer, the reflection band can be split with an ultra-narrowband tunneling of light transmission. These achievements demonstrate the promising potential of all-dielectric metamaterials as ultra-wideband reflectors for extensive applications in optical devices and systems.

Metalens have been recently introduced to overcome shortcomings of traditional lenses and optical systems, such as large volume and complicated assembly. As a proof-of-principle demonstration, we design an all-dielectric converging cylindrical metalens (CML) for working in long-wave infrared regions around 9 µm, which is made up of silicon-pillar on MgF2 dielectric layer. We further demonstrate the focusing effect of an orthogonal doublet cylindrical metalens (ODCM). Two CMLs are combined orthogonally and a circular focusing spot was demonstrated. This proves that within a certain size range, the focusing effect achieved by the ODCM is similar to that of a traditional circular metalens.

A new type of nonspherical yolk-shell structures in the case of SnO2 has been successfully prepared by a simple anneal-etching strategy without employing any additional templates or capping agents. The morphological and structural characterization reveals that SnO2 yolk-shell particles have a hierarchical architecture with penetrable multi-walled surfaces and cuboctahedral shape, where the secondary building blocks are numerous nanoparticles. The synthetic step-dependent evolution process of SnO2 yolk-shell cuboctahedra is investigated and the possible formation mechanism is also discussed. To demonstrate the merit of unique structure for the fast mass transfer, sensor based on SnO2 products has been fabricated and the results exhibit excellent sensing performances for toluene detection. It is found that our SnO2 yolk-shell structures have a response of 28.6–20 ppm toluene at the optimal working temperature of 250 °C, and the response time and recovery time are within 1.8 and 4.1 s, respectively.