Toward Perfect Optical Diffusers: Dielectric Huygens' Metasurfaces with Critical Positional Disorder

Ultra-broadband microwave absorber based on disordered metamaterials

Metamaterial absorption technology plays an increasingly important role in military and civilian sectors, serving crucial functions in communication, radar technology, and electromagnetic cloaking. However, traditional metamaterial absorbers are predominantly composed of periodic structures, thus limiting their absorption bandwidth, polarization, and angular flexibility. This study employs disordered structures, utilizing their randomness and diversity, to optimize and enhance the performance of periodic structure metamaterial absorbers. Building upon a well-designed periodic perfect absorption structure, a uniform distribution function is introduced to analyze the effects of positional and size disorder on the absorptive properties of the metamaterial. The mechanisms of the disorder are further investigated through simulation analysis. Subsequently, an innovative approach based on disorder engineering for broadband enhancement of metamaterial absorbers is proposed. Numerical simulation results and experimental validations demonstrate that absorbers constructed using this method significantly broaden the absorption bandwidth while maintaining excellent angular and polarization stability. This research not only offers a new method for the design and performance optimization of metamaterial absorbers but also provides a theoretical foundation for the development of metamaterial self-assembly techniques.

Revisiting the Design Strategies for Metasurfaces: Fundamental Physics, Optimization, and Beyond

Over the last two decades, the capabilities of metasurfaces in light modulation with subwavelength thickness have been proven, and metasurfaces are expected to miniaturize conventional optical components and add various functionalities. Herein, various metasurface design strategies are reviewed thoroughly. First, the scalar diffraction theory is revisited to provide the basic principle of light propagation. Then, widely used design methods based on the unit-cell approach are discussed. The methods include a set of simplified steps, including the phase-map retrieval and meta-atom unit-cell design. Then, recently emerging metasurfaces that may not be accurately designed using unit-cell approach are introduced. Unconventional metasurfaces are examined where the conventional design methods fail and finally potential design methods for such metasurfaces are discussed.

Stretchable Optical Diffuser Constructed by Alternate Procedure of Interfacial Complexation and Thermal Crosslinking

Stretchable optical diffuser is an indispensable photon management element in wearable display devices. Herein, a novel optical diffuser constructed by interfacial hydrogen bonding complexation of methylcellulose (MC), poly(ethylene oxide) (PEO), and polymer complex nanoparticles (PCNP) on transparent polydimethylsiloxane (PDMS) substrate is proposed. The introduction of PEO can toughen the complex film and endow the coating with stretchability. With proper thermal treatment, the polymer complex can be crosslinked through esterification which shows an improved optical diffusion performance and durability. The optimized film exhibits 92% of transmittance (T), 93% of haze (H), and 73% of elongation. It also presents a desirable optical diffusion effect about 88% of T and 93% of H in the stretching state. Moreover, the resulting complex film shows excellent anti-fatigue capacity which maintains 90% of T and 90% of H after 10 000 stretching cycles. The reported polymer complex film broadens the application of interfacial complexation and demonstrates potential to apply in the integrated wearable optical devices.

Tailorable Switching of Transmission Modes between Waveguide and Spoof Surface Plasmon Polariton for Flexible and Dynamic Control of Phase Shift

Programmable metamaterials are suitable for their dynamic and real-time control capabilities of electromagnetic (EM) functions in radars and antenna communications, but it remains a challenge to achieve dynamic modulation of arbitrary transmission phase with high transmission efficiency. Here, we propose a paradigm to tailor transmission phase shift in real time by switching modes between waveguide and SSPP based on the voltage-driven PIN diodes. Step-like phase shift is achieved by the "ON" and "OFF" states of PIN diodes, while continuous phase regulation is by the characteristic of the nonlinear region between those two states. As validations, three systems with programmable functionalities are implemented, including the multibeam generator, the dual-beam scanner, and the active phased-array antenna. The experimental results are consistent with simulation, which verify the feasibility of the proposed approach. Our work offers an alternative route for transmission full-phase modulation and provides unprecedented potential for high-gain, real-time, and multidimensional EM capabilities in applications such as active phased array radars, self-adaption radomes, smart beam shaping.

Responsive photonic nanopixels with hybrid scatterers

Metallic and dielectric nanoscatterers are optical pigments that offer rich resonating coloration in the subwavelength regime with prolonged material consistency. Recent advances in responsive materials, whose mechanical shapes and optical properties can change in response to stimuli, expand the scope of scattering-based colorations from static to active. Thus, active color-changing pixels are achieved with extremely high spatial resolution, in conjunction with various responsive polymers and phase-change materials. This review discusses recent progress in developing such responsive photonic nanopixels, ranging from electrochromic to other color-changing concepts. We describe what parameters permit modulation of the scattering colors and highlight superior functional devices. Potential fields of application focusing on imaging devices, including active full-color printing and flexible displays, information encryption, anticounterfeiting, and active holograms, are also discussed.