Highly Tunable Polarized Chromatic Plasmonic Films Based on Subwavelength Grating Templates

Abstract

by the nanoarrays, which lead to extraordinary transmission through dielectric apertures below diffraction limits [13,14] ; 3) the plasmonic waveguiding of dielectric slits, which supports broadband polarized transmission of transverse magnetic (TM) light, while prohibits the propagation of transverse electric (TE) light. [15] Utilizing these mechanisms, the spectra of metallic nanoarray can be flexibly tuned to meet a variety of applications by engineering the metal thickness, profile of the unit cells, and the period. For example, by tailoring the profile of the nanounit cell to be asymmetric (linear, elliptical, or rectangular), polarization-dependent tunability can be imposed on the PSC to make integrated colorfilters and polarizers [16,17] for more compact and lower power-consumption liquid crystal displays (LCDs). Recently, actively tunable PSCs based on elastomeric substrates have been reported. By stretching the substrates, the pitch and therefore scattering colors of PSCs can be modified in a wide range, which makes them promising as novel display devices. [18] Besides the structure, the permittivity of the metal materials also strongly affects the spectrum characteristics. For instance, with small damping factors, gold and silver metallic nanoarrays have sharp surface plasmon resonance dips that are suitable for high figure of merit biosensing. [19] While aluminum (Al) has a large absolute value of complex permittivity and a large plasmon frequency to maintain plasmonic characteristics at wavelength down to ultraviolet, thus it is suitable to make broadband nanowire polarizers with high extinction ratio of TM over TE light in the transmission. In addition, Al has been widely used in the packaging, decoration, and laser hologram tags to enhance the reflection of diffraction gratings. [19][20][21] In this work, we propose a kind of transmission films of 1D metallic nanowire gratings (MNGs), which show polarization-dependent PSC over broad spectrum. Such films can be used as a new type of high-security and more recognizable anti-counterfeiting tags: polarized chromatic plasmonic tags (PCPTs). The physical mechanisms responsible for the polarization-dependent chromaticity are revealed, which are used in the device design. In Section 2, the fabrication of the films and tags is presented and their transmission spectra are described as a function of the MNG parameters and incident light parameters. In Section 3, a physical model is presented to describe the polarization-dependent chromaticity. The paper concludes with a summary in Section 4.A kind of polarized chromatic plasmonic film is proposed based on subwavelength grating structure, which enables "blue transmission" for the transverse electric light and "red transmission" for the transverse magnetic light. Metal-insulator-metal plasmonic waveguiding and metallic nanowire scattering are revealed to be responsible for the chromatic shift. Based upon the unique transmission spectrum characteristics of such films, polarized chromatic plasmonic tags (PCPTs) ca...

Vivid Structural Color Macropatterns Created by Flexible Nanopainting of Ultrafast Lasers

“…The physical-based structural colors have arisen from the light interaction with the spatially ordered sub-micrometer structures, which widely exist in natural biological systems. − Since the electron microscope was introduced into biology in the 1940s, the artificial structural colors began to be investigated by researchers. The generation strategies of artificial structural colors, such as multilayer films, photonic crystals, metasurfaces, and diffraction gratings, have been widely studied over the past few decades, − which demonstrate the structural color exhibiting unique properties of high brightness, fadeless appearance, eco-friendly management, and spectral tunability. It greatly enriches its utilization in both industry and research fields.…”

“…However, this method can only be arranged regularly along the substrate surface, which is a challenge for the arbitrary design and composite patterns. , Nanoimprinting is also a mass-productive and high-resolution method, but it is difficult to become a general method as a result of the limitation of imprinting on flexible materials, such as polymers. Otherwise, it is susceptible to be damaged during the transfer process. ,, Although focused electron or ion beam lithography enables the preparation of complex, high-precision structures, the fabrication is often confined within a very small scale as a result of the limitations of complicated procedures and high cost, leading to the structural color observation usually with the help of a microscope. , In contrast to the aforementioned situations, the recent years of ultrafast laser manufacturing development strongly demonstrates its unique advantages in the structural color fabrication, showing a flexible, one-step, and contactless procedure and remarkably suitability for a wide scope of materials. ,− The direct laser writing process is a prominent fabrication method, producing nanostructures that are often featured with high resolution, ,− and suitable for integration applications, such as optical storage. However, although a tight focus of the laser beam can act as a “pensile” to have a micro- or nanoscale fabrication in a mask-free and flexible way, the point-by-point processing still makes it confined, especially in work efficiency. , The spatial light modulator (SLM) has been used by many research groups for ultrafast laser manufacturing with more efficiency. , However, during such SLM-assisted laser processing, a tight focus of the laser beam spot was often demonstrated, which still limits its capability for further improvements.…”

“…Otherwise, it is susceptible to be damaged during the transfer process. 13,19,20 Although focused electron or ion beam lithography enables the preparation of complex, highprecision structures, the fabrication is often confined within a very small scale as a result of the limitations of complicated procedures and high cost, leading to the structural color observation usually with the help of a microscope. 15,21 In contrast to the aforementioned situations, the recent years of ultrafast laser manufacturing development strongly demonstrates its unique advantages in the structural color fabrication, showing a flexible, one-step, and contactless procedure and remarkably suitability for a wide scope of materials.…”