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In the past, the polarization-insensitive absorption is realized mainly employing the two-dimensional periodic structure of fourfold rotational symmetry, which greatly increases the manufacturing complexity and cost. Here, we present the numerical design of a polarization-independent near-perfect absorber incorporating one-dimensional embedded aluminum grating. The absorption peaks near 99% at 520-nm wavelength for different polarization angles are achieved. The underlying mechanism associated with the resonance is attributed to the magnetic polariton resonance and the cavity-mode resonance for TM and TE polarization, respectively, and further explained by the inductor-capacitor circuit model and the eigen equation of cavity mode. Furthermore, the effects of geometrical parameters of the nano-cavity on the absorption performance are discussed. The proposed structure may provide a new way to achieve polarization-independent absorption with one-dimensional meta-surface, which has broad applications in plasmonic sensors, photo-detectors, and so on.

The prediction of the lifetime of a PEM fuel cell under a specific electrical load profile is beneficial for automotive applications. An empirical lifetime prediction model coupled with an electrical load profile is presented based on an estimate of the degradation rate of the cell voltage. First, a cause and effect chain-based analysis of the PEM fuel cell's degradation process is presented. Second, a characteristic value is extracted and is treated as a numerical measurement of the effect of load profile on voltage degradation. The characteristic value is defined using both load current and load voltage. Third, an empirical model is proposed, modeling the voltage degradation rate as a linear function of the load profile's characteristic value. Finally, experimental data are used to fit the coefficients and validate the model.

We present a polarization-independent near-perfect absorber in the visible regime based on one-dimensional meta-surface. In this absorber, the dielectric grating layer with high refractive index is essential, which supports strongly localized electromagnetic modes concentrated in the double-metal regions. The simulation results show that absorption peaks are over 99% at the wavelength of 0.45 μm for both TM and TE polarizations. The near-perfect absorptions are attributed to the lateral plasmon cavity resonance and longitudinal Fabry-Perot-like cavity resonance for TM and TE polarization, respectively. Furthermore, theses absorption peaks can maintain almost unchanged within wide ranges of incident and azimuthal angles. Comparing with those meta-material absorbers with complex two-dimensional array and one-dimensional stacked array, this one-dimensional absorber has a very simple geometrical structure which can be integrated into complex photonic devices expediently.

We design and numerically investigate an optical absorber consisting of the sub-wavelength dielectric grating covered by continuous thin aluminum film. In this absorber, the aluminum film act as an efficient absorbing material because of the enhanced electric field in the air nano-grooves, and the absorption spect+rum can be manipulated by Fabry-Perot cavity mode resonance. According to the spectrum manipulation mechanism, the wavelength of absorption peak can be tuned by changing the heights and widths of the air nano-grooves. More importantly, the high absorption is very robust to the incident angle around the designed wavelength. From the nanofabrication point of view, the light absorber can be fabricated more easily without the need for ion or electrochemical etching of metal and it is easy to be integrated into complex photonic devices.

In this paper, we propose a phase modulator based on dot matrix nanogratings for realizing a super multiview display for optical see-through near-eye display applications. The phase information of a three-dimensional scene can be modulated by the phase modulator to form a series of viewing points in front of the human eyes, and the pitch of the viewing points can be confined to be smaller than the pupil diameter of the human eye by designing the diffraction vector of each nanograting in the phase modulator. Here, we fabricated a 2-inch 4-view phase modulator with full coverage of dot matrix nanogratings using continuously variable spatial frequency photolithography. Under the illumination of a collimated laser beam with a wavelength of 532 nm, the emergent light was converted into 4 well-separated viewing points with a separation distance of 2 mm, and the angular divergence of the viewing point was measured to be 1.14° on average, which slightly exceeds the diffraction limit (0.93°). By using a transmissive liquid-crystal panel that loaded the amplitude information of the perspective images of a three-dimensional scene, we experimentally demonstrated that the proposed see-through near-eye display can display three-dimensional images with correct depth cues, enabling observation that is unhindered by the vergence-accommodation conflict and the visual fatigue problem.

Black structural color has attracted particular interest due to its attractive applications in various fields. Until now, however, the reported graphical black structural color (GBSC) devices are mainly realized by means of electron beam lithography or focused ion beam technology, inevitably suffering from the obstacles of high production cost and time-consuming processing. Moreover, the limited and small area of the GBSC constitutes another issue for real applications and little attention has been devoted to flexible GBSC because of the limitations of this manufacturing approach. In this paper, we experimentally demonstrate and theoretically analyze a novel flexible GBSC architecture capitalized on a pixelated embedded nickel cylindrical array using a reliable, low-cost and self-developed continuously variable spatial frequency lithography. The fabricated graphical and large-area flexible GBSC sample (4 cm × 4 cm) exhibits a measured absorbance of ∼92% over the entire visible regime from 400 nm to 700 nm. Furthermore, the desirable absorptivity is well retained at incident angles up to 60°. It is anticipated that the facile, controllable and scalable approach developed here opens new exciting perspectives for industrial production.

A metadielectric nanostructure with narrow cavities is proposed, behaving as a reflective color filter for TM-polarized light while as a broadband reflector for TE-polarized light. By varying the cavity depth or changing the incident light polarization, reflective colors of the proposed structure cover the entire visible spectrum conveniently. In particular, the reflections of this proposed structure show good angular tolerance up to 50° for both polarizations. Furthermore, it can display colors even with two grating slits, which shows high printing resolution up to 70555 dpi, having great potential for applications of a large area color imaging and anticounterfeiting devices.

In this paper, we design and numerically investigate an ultrathin polarization-insensitive, broadband visible absorber based rectangular metagratings. The absorber, consisting of a dielectric grating grown in a metallic substrate with a vertically metallic covering, presents an average absorption of 0.975 for TM polarization and 0.911 for TE polarization at normal incidence in the visible regime, respectively. For the incident angle ranges from 0°to 45°, the high absorption is almost unchanged for both polarizations. Moreover, the physical mechanism of broadband absorption is investigated. The strong absorption effect is derived from the excited SPR and CMR in the uniform nanocavity for TM polarization and TE polarization, respectively. Compared with those metasurface absorbers using a 2D array or 1D complicated structures, our design is efficient for both TM and TE polarizations using a straightforward 1D structure that provides excellent optical performance.

In this paper, we design and numerically investigate ultrathin high-efficiency, variable-color filters. The color filters, based on a cavity resonator covered with a compensated dielectric film, promise an adjustable spectral bandwidth while preserving the same resonant wavelength. A broad color gamut and widely tuned color saturation can be obtained by gradually varying the cavity depth and the top mirror thickness, respectively. The numerical results show that the transmitted peak wavelength remains unchanged with the angle of incident range from 0 to 60°for TM polarization and the transmission efficiency is above 65% at the resonant peak wavelength. Moreover, the physical mechanism of the device is investigated. The light field is mainly concentrated in the cavity, leading to the strong resonant effect. The proposed designs can be fabricated more easily by the deposition methods for the practical applications.

Flexible transparent electrodes (FTEs) with high stability and scalability are in high demand for the extremely widespread applications in flexible optoelectronic devices. Traditionally, thin films of indium thin oxide (ITO) served the role of FTEs, but film brittleness and scarcity of materials limit its further application. This review provides a summary of recent advances in emerging transparent electrodes and related flexible devices (e.g., touch panels, organic light-emitting diodes, sensors, supercapacitors, and solar cells). Mainly focusing on the FTEs based on carbon nanomaterials (e.g., carbon nanotubes and graphene) and metal materials (e.g., metal grid and metal nanowires), we discuss the fabrication techniques, the performance improvement, and the representative applications of these highly transparent and flexible electrodes. Finally, the challenges and prospects of flexible transparent electrodes will be summarized.

A high-performance polarizer based on the double-layer metallic gratings with air-gaps is theoretically investigated. It is observed that the transmission of the TM polarized light greatly exceeds the double-layer metallic gratings without air-gaps. The electric field distributions are plotted to interpret the physical mechanism. The improvement is attributed to the enhanced coupling between the two metal layers. The transmission efficiency and extinction ratio of the proposed polarizer in terms of different structure parameters and the incident angles are discussed. At the period of 100 nm, the optimized structure can reach an extinction ratio higher than 30 dB and the TM transmission efficiency over 80% until the incident angle is 30o. The study presented here is of great importance in designing and fabricating metallic grating polarizer with better performance.

To date, near-perfect light absorbers at visible frequency are still severely impeded by the complicated architecture design and time-consuming costly fabrication procedures. In this work, we design and fabricate a new cost-effective near-perfect absorber at visible frequency based on homogenous meta-surface nickel (Ni) with a two-dimension cylinder array. The simulated and measured average absorption at normal incidence are beyond 94% and 92% over the entire visible wavelength band from 400 nm to 700 nm, respectively. Additionally, the absorbance property was well retained, and the absorptivity still remained beyond 70% when the incident angles vary from 0° to 60°. Our theoretically and experimentally results indicate that the broadband wide-angular absorption can be ascribed to the Rayleigh-Wood anomaly combined with slot modes induced by excited surface plasmon polaritons. Moreover, the low-cost double-beam interference lithography followed by soft nano-imprinting and electroforming technology, which are directly compatible with the cost-effective and high volume manufacturing requirements, are employed to fabricate the proposed absorber. The proposed approach is simple and inexpensive and the obtained ultrathin homogenous meta-surface nickel absorber can be rolled or folded on the surface of various optoelectronics, such as solar system and radiation thermal devices.

A broadband and omnidirectional absorber based on an asymmetric multi-cavity resonance is presented, which is realized by adapting a lossless silicon nitride layer on top, a sandwiched amorphous silicon layer, and a silver mirror at the bottom. Its average optical absorption is 0.92 (0.87, experiment) for wavelengths from 400 nm to 700 nm and still over 0.84 (0.80, experiment) with the incident angle up to 60°. In addition, the developed absorber is suitable for large-scale applications, since only the deposition method is involved in its fabrication. Furthermore, photophysical properties of this absorber for a solar cell device are investigated, where high short-circuit current density and photo-conversion efficiency are obtained, even with the amorphous silicon layer thinning to 22 nm. Therefore, the demonstrated absorber has great application potential in the solar cell.

A broadband absorber based on a one-dimensional metasurface is designed and characterized numerically. In this absorber, the lossless dielectric in non-noble metal nickel (Ni) grating grooves is essential, which supports strongly the localized electromagnetic modes concentrated in the nanocavity formed between two metallic walls. A high absorbance from 380 to 760 nm for either TM or TE polarization is attained. In particular, a nearly perfect absorbance (over 99%) is achieved at λ = 450 nm for TE polarization. Furthermore, the absorption in the visible region remains above 60% at incident angles up to 45° for the two polarizations.

Broadband metamaterial absorber (MA) in the whole visible regime has attracted an enormous amount of attention for its potential applications in thermophotovoltaic cells, thermal emitters, and other optoelectronic devices. Nonetheless, complicated device configuration is still involved in achieving broadband, polarization-independent MA and it results in a cost-ineffective fabrication process. In this paper, a novel MA composed of a periodic array of dielectric cylinder sandwiched by the non-noble metal of nickel (Ni) film is demonstrated. Experimental results show that the proposed MA exhibits strong absorptive behavior independent of polarization in the whole visible regime (400-700 nm). The absorption still remains 80% when the incident angle is 60°. The proposed fabrication method is well compatible with the conventional soft nano-imprinting lithography technique, thus it is economic and scalable for a large-format substrate. These results provide an alternative method for the realization of high-performance visible light absorber and offer new opportunities for potential applications in related fields.