Tunable Optical Transmission Research Articles

Tunable extraordinary optical transmission spectrum properties of long-wavelength infrared metamaterials.

Metamaterial filters represent an essential method for researching the miniaturization of infrared spectral detectors. To realize an 8-2µm long-wave infrared tunable transmission spectral structure, an extraordinary optical transmission metamaterial model was designed based on the grating diffraction effect and surface plasmon polariton resonance theory. The model consisted of an Al grating array in the upper layer and a Ge substrate in the lower layer. We numerically simulated the effects of different structural parameters on the transmission spectra, such as grating height (h), grating width (w), grating distance (d), grating constant (p), and grating length (S 1), by utilizing the finite-difference time-domain method. Finally, we obtained the maximum transmittance of 81.52% in the 8-12µm band range, with the corresponding structural parameters set to h=50n m, w=300n m, d=300n m, and S 1=48µm, respectively. After Lorentz fitting, a full width at half maximum of 0.94±0.01µm was achieved. In addition, the Ge substrate influence was taken into account for analyzing the model's extraordinary optical transmission performance. In particular, we first realized the continuous tuning performance at the transmission center wavelength (8-12µm) of long-wave infrared within the substrate tuning thickness (D) range of 1.9-2.9µm. The structure designed in this paper features tunability, broad spectral bandwidth, and miniaturization, which will provide a reference for the development of miniaturized long-wave infrared spectral filter devices.

Tunable comb-like optical transmission spectrum resulting from equilateral polygonal networks

Tunable comb-like optical transmission spectrum resulting from equilateral polygonal networks

Nonlinearly tunable extraordinary optical transmission in a hybird metamaterial

Dielectric metamaterials are promising for significantly enhanced optical nonlinearity for their strongly localized Mie-resonant mode. Here, we theoretically and experimentally studied a hybrid metamaterial exhibiting extraordinary optical transmission (EOT) behavior, in which the transmission amplitude and frequency can be modulated. The EOT of the perforated metal sheet with subwavelength aperture is induced with a dielectric cuboid by setting them in a close proximity and exploiting the first-order Mie-resonant mode. The electromagnetic wave is effectively coupled to the subwavelength aperture by properly placing the dielectric cuboid, and the transmission intensity can be enhanced more than 150 times. Meanwhile, we employed the nonlinear effect of the dielectric cuboid to modulate the operation band of the EOT. Hopefully, our work can inspire innovations for the research of light–matter interactions, electromagnetic light switching devices and filter devices.

Scalable Inkjet Printing of Electrochromic Smart Windows for Building Energy Modulation

Electrochromic smart windows are promising for green buildings due to energy efficiency, long optical memory effect, and tunable optical transmission. However, their wide application in buildings is impeded by challenges in scalability, cost‐effectiveness, and limited optical contrast. Quantitative field study of energy savings enabled by electrochromic smart windows in buildings is also lacking. Herein, with the established inkjet printing procedures, electrochromic smart windows (900 cm2) are fabricated. With large optical contrast (≈60%), fast switching kinetics (tc = 43 s, tb = 70 s), and long optical memory retention (transmittance <10% for 7 h), when installed onto the outdoor testbed, these electrochromic smart windows can effectively reduce the internal temperature, especially in summer tropical weather. The energy savings brought by electrochromic smart windows are found to be higher in sunny days than in rainy days. Specifically in a sunny day, the heat gain reduction can reach 42.3%, and for a comfortable targeted indoor temperature of 25 °C, the cooling load savings can be 28.9% compared to regular double‐glazing units‐based reference testbed. This study demonstrates the scalability of inkjet printing technique for fabricating large‐area electrochromic devices and the substantial energy savings obtained from testbed results.

Tunable Extraordinary Optical Transmission with Graphene in Terahertz

Tunable extraordinary optical transmission (EOT) with graphene is realized using a novel metallic ring–rod nested structure in the terahertz frequency regime. The generated double-enhanced transmission peaks primarily originate from the excitation of localized surface plasmon resonances (LSPRs). On using graphene, the resonating surface plasmon distribution changes in the reaction plane, which disturbs the generation of LSPRs. By regulating the Fermi energy (Ef) of the graphene to reach a certain level, an adjustment from bimodal EOT to unimodal EOT is obtained. As the Ef of the graphene integrated beneath the rod increases to 0.5 eV, the transmittance of the peak at 2.42 THz decreases to 6%. Moreover, the transmission peak at 1.77 THz virtually disappears due to the Ef increasing to 0.7 eV when the graphene is placed beneath the ring. The significant tuning capabilities of the bimodal EOT indicate its promising application prospects in frequency-selective surfaces, communication, filtering, and radar.

A novel tunable optical transmission structure designed by ε-near-zero media filled with multiple nested dielectric dopants

The next generation of the advanced optic devices points toward a dynamic control of the wavefront, which will have a ground-breaking impact on optical manipulation technologies. In this paper, a novel tunable optic transmission structure has been designed by epsilon-near-zero media filled with multiple nested dielectric dopants. In this structure, the multiple nested dielectric dopants which consist of a cylindrical air cavity and a dielectric cylinder nested in the air cavity is embodied in ENZ media. Under the condition of varying parameters, the optical control ability of the proposed structure is analyzed comprehensively and verified by EM full-wave simulations. The analysis results show the proposed structure is able to manipulate properties of transmission wave in real-time, such as phase and magnitude by replacing or moving the internal dielectric cylinder nested in the air cavity. As an example, the proposed structure is realized by rectangle wave guide at microwave frequency. This work provides a novel way for the development optical (electromagnetic) wavefront tunable device.

Magnetically Tunable Liquid Crystal-Based Optical Diffraction Gratings

We present a theoretical analysis of optical diffractive properties of magnetically tunable optical transmission gratings composed of periodically assembled layers of a polymer and a ferromagnetic liquid crystal (LC). The orientational structure of the LC layers as a function of an applied magnetic field is calculated by minimization of the Landau-de Gennes free energy for ferromagnetic LCs, which is performed numerically and also analytically by using the one-constant approximation and the approximations of the high and the low magnetic fields. Optical diffractive properties of the associated diffraction structure are calculated numerically in the framework of rigorous coupled-wave analysis (RCWA). The presented methodology provides a basis for designing new types of diffractive optical element based on ferromagnetic LCs and simulating their operation governed by the in-plane magnetic field.

Temperature tunable optical transmission using IR based 1D photonic crystals of VO2 nanostructures

The effect of 1D photonic crystals on the optical transmission of VO2 is studied by depositing thin films of VO2 nanoparticles on SiO2/TiO2 distributed Bragg reflectors (DBRs) in the near-infrared (IR) spectrum as per the earlier theoretical predictions of Rashidi et al (2018 J. Phys. D: Appl. Phys. 51 375102). Monoclinic VO2 nanoparticles with tuned crystallinity are synthesized using a facile solution processing method. Moderately crystalline (MC) and highly crystalline (HC) VO2 nanostructures are obtained by varying the synthesis temperature and post-growth annealing conditions. Both the MC VO2 and HC VO2 films exhibit the expected reduction in optical transmission in the IR region due to the structural phase transition from monoclinic (insulator) to rutile (metallic) around the critical temperature of 68 °C. By combining VO2 films on a 40% transmitting DBR structure, the average optical transmission decreases further to ~20%. The number of stacks of DBRs plays a key role in such an effective reduction of optical transmission in the IR. When the number of stacks of DBRs is further increased from 4 to 7, the optical transmission of metallic VO2 films on DBRs nearly vanishes in the near-IR spectrum in such vanadium dioxide 1D photonic crystal based composite photonic structures. Such a temperature-controlled, enhanced, broad band optical response could provide a promising design for VO2 nanoparticle based hybrid photonic absorbers for various smart window applications.

Tunable optical transmission of magnetic microsphere colloids.

We demonstrate the tunable transmission of core-shell magnetic microsphere colloids (MMC) and report its modeling by effective medium approximation (EMA). Transmission from the MMC was measured experimentally at various filling factors. Using the EMA, the relations between transmission of the colloids, their filling factor, and the applied magnetic field are quantified. Using an electromagnetic actuator, it was shown that the transmission can be reproducibly tuned by controlling the duration as well as the strength of the applied magnetic field. By choosing proper values of applied magnetic field strength, application duration, and optical path length, dynamic properties of the tunable optical switch are studied. These results are useful to the design of tunable optical switches and windows based on magnetic colloids.

Liquid crystal metasurfaces on micropatterned polymer substrates.

Formation of photonic liquid crystal metasurfaces on rubbed polyimide substrates patterned by focused ion beam is demonstrated. Modulation of the surface anchoring conditions with periods from 1 to 6 micrometers gives rise to periodic deformation of the nematic liquid crystal director field. The exact periodicity is confirmed by the light diffraction measurements. Distinct colors originating from the specific zero-order diffraction spectra are observed and qualitatively explained in terms of an analytical model within the one-constant approximation. Quantitatively accurate optical spectra are obtained by the full scale numerical simulations taking into account all relevant material parameters. The results pave the way for hybrid liquid-crystal-based metasurfaces with tunable optical transmission, diffraction, and lasing.

Magnetically Responsive Elastomer-Silicon Hybrid Surfaces for Fluid and Light Manipulation.

Stimuli-responsive surfaces with tunable fluidic and optical properties utilizing switchable surface topography are of significant interest for both scientific and engineering research. This work presents a surface involving silicon scales on a magnetically responsive elastomer micropillar array, which enables fluid and light manipulation. To integrate microfabricated silicon scales with ferromagnetic elastomer micropillars, transfer printing-based deterministic assembly is adopted. The functional properties of the surface are completely dictated by the scales with optimized lithographic patterns while the micropillar array is magnetically actuated with large-range, instantaneous, and reversible deformation. Multiple functions, such as tunable wetting, droplet manipulation, tunable optical transmission, and structural coloration, are designed, characterized, and analyzed by incorporating a wide range of scales (e.g., bare silicon, black silicon, photonic crystal scales) in both in-plane and out-of-plane configurations.

Acoustically tunable optical transmission through a subwavelength hole with a bubble

Efficient manipulation of light with sound in subwavelength-sized volumes is important for applications in photonics, phononics and biophysics, but remains elusive. We theoretically demonstrate the control of light with MHz-range ultrasound in a subwavelength, 300 nm wide water-filled hole with a 100 nm radius air bubble. Ultrasound-driven pulsations of the bubble modulate the effective refractive index of the hole aperture, which gives rise to spectral tuning of light transmission through the hole. This control mechanism opens up novel opportunities for tuneable acousto-optic and optomechanical metamaterials, and all-optical ultrasound transduction.

Conformal Coating of a Phase Change Material on Ordered Plasmonic Nanorod Arrays for Broadband All-Optical Switching.

Actively tunable optical transmission through artificial metamaterials holds great promise for next-generation nanophotonic devices and metasurfaces. Plasmonic nanostructures and phase change materials have been extensively studied to this end due to their respective strong interactions with light and tunable dielectric constants under external stimuli. Seamlessly integrating plasmonic components with phase change materials, as demonstrated in the present work, can facilitate phase change by plasmonically enabled light confinement and meanwhile make use of the high sensitivity of plasmon resonances to the variation of dielectric constant associated with the phase change. The hybrid platform here is composed of plasmonic indium-tin-oxide nanorod arrays (ITO-NRAs) conformally coated with an ultrathin layer of a prototypical phase change material, vanadium dioxide (VO2), which enables all-optical modulation of the infrared as well as the visible spectral ranges. The interplay between the intrinsic plasmonic nonlinearity of ITO-NRAs and the phase transition induced permittivity change of VO2 gives rise to spectral and temporal responses that cannot be achieved with individual material components alone.

Electronically tunable extraordinary optical transmission in graphene plasmonic ribbons coupled to subwavelength metallic slit arrays.

Subwavelength metallic slit arrays have been shown to exhibit extraordinary optical transmission, whereby tunnelling surface plasmonic waves constructively interfere to create large forward light propagation. The intricate balancing needed for this interference to occur allows for resonant transmission to be highly sensitive to changes in the environment. Here we demonstrate that extraordinary optical transmission resonance can be coupled to electrostatically tunable graphene plasmonic ribbons to create electrostatic modulation of mid-infrared light. Absorption in graphene plasmonic ribbons situated inside metallic slits can efficiently block the coupling channel for resonant transmission, leading to a suppression of transmission. Full-wave simulations predict a transmission modulation of 95.7% via this mechanism. Experimental measurements reveal a modulation efficiency of 28.6% in transmission at 1,397 cm−1, corresponding to a 2.67-fold improvement over transmission without a metallic slit array. This work paves the way for enhancing light modulation in graphene plasmonics by employing noble metal plasmonic structures.

Electrically controllable extraordinary optical transmission in gold gratings on vanadium dioxide.

Highly tunable optical transmission through one-dimensional gold gratings patterned on top of a film of the phase transition material, vanadium dioxide (VO2), is demonstrated. Dense electrical integration is enabled by grating features that also function as electrical contacts to the VO2. Extraordinary optical transmission is observed in the VO2 insulator phase, and the optical transmission is extinguished by up to about 6 dB in a 170 nm thick VO2 film. Measurements of gratings with varying duty cycles demonstrate the dependence of the optical transmission and tuning on the device geometry.

A mechanically driven form of Kirigami as a route to 3D mesostructures in micro/nanomembranes

Assembly of 3D micro/nanostructures in advanced functional materials has important implications across broad areas of technology. Existing approaches are compatible, however, only with narrow classes of materials and/or 3D geometries. This paper introduces ideas for a form of Kirigami that allows precise, mechanically driven assembly of 3D mesostructures of diverse materials from 2D micro/nanomembranes with strategically designed geometries and patterns of cuts. Theoretical and experimental studies demonstrate applicability of the methods across length scales from macro to nano, in materials ranging from monocrystalline silicon to plastic, with levels of topographical complexity that significantly exceed those that can be achieved using other approaches. A broad set of examples includes 3D silicon mesostructures and hybrid nanomembrane-nanoribbon systems, including heterogeneous combinations with polymers and metals, with critical dimensions that range from 100 nm to 30 mm. A 3D mechanically tunable optical transmission window provides an application example of this Kirigami process, enabled by theoretically guided design.

Hybrid co-deposition of mixed-valent molybdenum–germanium oxides (MoxGeyOz): A route to tunable optical transmission

Mixed-valent oxides of molybdenum and germanium were deposited simultaneously using reactive magnetron co-deposition within an oxygen–argon environment. The films' stoichiometry, optical, and physical properties were varied through changes in oxygen partial pressure induced by systematic variation of the potential applied to the molybdenum cathode. The oxygen partial pressure was determined from the drop in pressure as measured by a capacitance manometer, assuming constant argon partial pressure. To facilitate deposition, a constant power of 100W DC was applied to the germanium cathode, while power was applied to the molybdenum target using a modulated pulse power supply. Modulated pulse power magnetron sputtering was used due to its ability to generate high target power densities, allowing for rapid reduction of oxygen on the surface of the “oxygen poisoned” molybdenum cathode, as well as for its highly metallic plasma resulting in increased oxygen-gettering capability. Changes in the modulated pulse power supply's capacitor bank voltage load, stepped from settings of 300 to 380V, resulted in films ranging from mixtures of transparent GeO2 (Ge4+) and MoO3 (Mo6+) to the introduction of various absorptive ionic species including Mo5+, Mo4+, Ge2+ and Ge0, as determined from X-ray photoelectron spectroscopy. The presence of each of the aforementioned ions results in characteristic changes in the films' band energies and optical absorption. As deposited MoxGeyOz thin films grown using this method have been shown to have optical gap energies that are able to be tailored between 3.57eV and 0.18eV, spanning useful ranges for devices operating in the visible and near-infrared.

Tuning the peak position of subwavelength silica nanosphere broadband antireflection coatings.

Subwavelength nanostructures are considered as promising building blocks for antireflection and light trapping applications. In this study, we demonstrate excellent broadband antireflection effect from thin films of monolayer silica nanospheres with a diameter of 100 nm prepared by Langmuir-Blodgett method on glass substrates. With a single layer of compact silica nanosphere thin film coated on both sides of a glass, we achieved maximum transmittance of 99% at 560 nm. Furthermore, the optical transmission peak of the nanosphere thin films can be tuned over the UV-visible range by changing processing parameters during Langmuir-Blodgett deposition. The tunable optical transmission peaks of the Langmuir-Blodgett films were correlated with deposition parameters such as surface pressure, surfactant concentration, ageing of suspensions and annealing effect. Such peak-tunable broadband antireflection coating has wide applications in diversified industries such as solar cells, windows, displays and lenses.

Tunable Extraordinary Optical Transmission in a Metal Film Perforated with Two-Level Subwavelength Cylindrical Holes

We propose a novel plasmonic metal structure composed of a silver film perforated with a two-dimensional square array of two-level cylindrical holes on a silica substrate. The transmission properties of this structure are theoretically calculated by the finite-difference time-domain (FDTD) method. Double-enhanced transmission peaks are achieved in the visible and infrared regions, which mainly originate from the excitation of localized surface plasmon resonances (LSPRs), the hybridization of plasmon modes, and the optical cavity mode formed in the holes. The enhanced transmission behaviors can be effectively tailored by changing the geometrical parameters and dielectric materials filled in the holes. These findings indicate that our proposed structure has potential applications in highly integrated optoelectronic devices.

High tunable optical properties of monolayer corrugated hetero-colloidal crystals

We design and fabricate a novel quasi-three dimensional corrugated hetero-colloidal crystal. Both measured and calculated results show a high tunable optical transmission response of the proposed structure via changing the geometry parameters of the coated dielectric film. Two different dielectric materials with low and relative higher refractive index are used as the coated films and different optical responses are achieved. Dual largely deepened transmission dips with a much bigger frequency shift are observed in the structure with a dielectric film consisting of higher dielectric constant materials. Our findings could provide potential applications in light harvesting and optical circuits.