Cellulose Nanocrystals (CNCs) are nanoscale, rigid rod-shaped cellulose fibers, measuring 100-500 nm in length, 2-20 nm in diameter, and with aspect ratios ranging from 5-100. At concentrations below a critical threshold (Critical Concentration I), CNC suspensions maintain isotropic characteristics. Upon surpassing another threshold (Critical Concentration II), the suspension transitions to an anisotropic phase, spontaneously forming chiral nematic structures. These chiral configurations are preserved even after drying the CNC suspensions. CNC photonic films exhibit the optical attributes of chiral nematic liquid crystals, including selective reflection and polarization, which manifest as pronounced structural colors and circular birefringence. This research demonstrates the structure color of CNCs through the conformal assembly with micro-nanostructures. By assembling CNCs at a 0.1 wt% concentration with triangular micro-nanostructures of varied sizes, the resulting structures displayed enhanced polarization characteristics. The conformal assembly technique introduced in this study is pivotal for advancing CNC-based photonic devices, opening new avenues in the realm of optoelectronic and environmentally friendly nanomaterials. These developments hold considerable potential for applications in optical filters, sensors, visual identifiers, and color display technologies.
Thanks to their striking visual appeal, grayscale moiré pattern have a high potential for document, security, art, and decoration. In recent years, researchers have paid extensive attention to using microlens arrays instead of micrographic arrays as the base layer to achieve novel moiré effects in moiré magnifiers. In order to reduce the thickness of the grayscale imaging device and increase the dots per inch (DPI) of the grayscale image, we proposed a reflective grayscale moiré imaging device. By using a curved microcylindrical lens array (CMCLA) with a metal reflector layer deposited on the surface as the base layer, the reflective device achieves a similar grayscale effect as the transmissive device with a smaller offset in the base layer, thereby increasing the fill factor of CMCLA. Applications of such devices can be found in the protection of valuable items against forgery.
Due to its thinness and large focal depth range, micro lens array (MLA) based projectors possess high potential in automotive lighting, traffic signs, and short-distance projection. Recently, researchers have paid extensive attention to projectors that employ micro lens arrays as projection lenses and transmissive chromium layers as masks. In order to expand the application scope of such projectors, we have developed a projection device capable of projecting grayscale images. By specially designing the mask pattern for each micro lens, the projected image from each sub-aperture is different, resulting in varying illuminance levels in different parts of the overlaid image on the image plane. This design method enables the projector to project fine grayscale images without requiring high-precision lithography equipment.
Moiré imaging, achieved by superimposing a layer of microlens array (MLA) and micropattern array (MPA), has already be proven useful in a range of applications from art to engineering. Due to the sensitivity to small variations in the MPA , moiré imaging device require high resolution machine to produce. Here we report a colorful, inkjet-printable, resolution up to 4800 dpi moiré imaging device. By utilizing the RGB inkjet printing technology, full-color moiré image can be produced with strikingly visual effect. Moiré imaging device with large-format (<300mm) can be realized to achieve the visually striking motion and 3D effect as varying the viewing angle. The moiré image is coded as a micropattern packed repeatedly, and the imaging heights is determined by the repeated period of micropattern. Therefore, we achieve moiré image with complex imaging heights by varying the period of the micropattern. Injection molding process for manufacturing MLA, is a technology that has proven to be stable and reliable in actual production. The proposed moiré imaging device, with obvious 3D perception to the naked eye, is inexpensive, mass-producible and convenient for authentication. We demonstrate the quality of the device by theoretical calculation and manufacturing. Such device can find potential applications in the field of anti-counterfeiting, information encryption and decoration, etc.
Micro-nano optical device based on the moiré imaging effect has been widely used in the visual security and anticounterfeiting due to the unique visual effect. However, the micro-pattern array in the state-of-art moiré imaging device is based on nanoimprint lithography and the gravure printing technique which cannot achieve multi-color effect. Even worse, the volatile organic compounds in the printing ink does harm to the environment and human health. Therefore, it is urgently needed to develop a moiré imaging device free of ink. In this paper, we propose to integrate the diffraction grating into the moiré imaging device. Grating MPA is formed by rasterizing the micro-pattern array layer, and combined with the microlens array to construct a moiré imaging device, which was a hybrid refraction-diffraction structure. In the experiment, a diffraction grating with a period of 2 μm and a cylindrical lens array with a focal length of 90 μm were integrated on both sides of a 50 μm thick film to realize the imaging device. A formula that can predict the intensity of diffraction dispersion is derived, and the colorful moiré image related to the orientation of the grating and the position of the light source is achieved, in which the color can cover the whole visible spectrum under different viewing angle.
In recent years, the moiré imaging device has become one of the hot topics in the field of micro optics due to its strikingly visual three-dimensional (3D) effect which can be easily recognized by naked eye. Traditionally, the moiré imaging film is composed of the superposition of a microlens array(MLA)and a micro pattern array (MPA)with high alignment accuracy. By the combination of the nanoimprinting and nanoprinting techniques, we fabricated a moiré imaging film on a large-format substrate characterized by fluorescent enhancement effect under ultraviolet light illumination. By using a novel virtual mask technique, the MPA can contain more information than traditional one. It is worthy to note that the nanostructure is introduced to the MPA to promote the light efficiency of the fluorescent material. A synthetically magnified moiré image with 3D effect is demonstrated. The moiré imaging film has widely potential applications in 3D imaging, optical anti-counterfeiting, packaging, etc.
Micro-focusing moiré imaging has found successful application in security and anti-counterfeiting. It comprises of a micro-lens array and a micro-pattern array to visually present impressive dynamic and stereoscopic visual effects. In this paper a moiré imaging device with new features is fabricated using the well-known techniques such as nanoimprinting and photoresist thermal reflow. The features of the moiré imaging device benefit from the novel configuration of the micro lens array. With the same aperture diameter , the Flat Micro Lens Array can realize moiré imaging on thicker substrate, which has better dynamic effect, compared to the moiré image achieved by the traditional microlens array. The working surface of the MLA is buried in the UV layer, and the microlens moiré device is not easily replicated. The Flat Micro Lens Array surface is flat, hard to worn, even if be worn does not affect the imaging quality. Due to the above features, the proposed moiré device has application in the field of anti-counterfeiting.
With the development of wireless microwave electronic devices, electromagnetic interference (EMI) is a new kind of pollution that is becoming increasingly prevalent and has affected the performance of the electronic devices and the human health. Thus,the transparent EMI shielding film is a key component for many practical applications. Conventional methods for the fabrication of transparent EMI film are time-consuming and costly for their employing expensive vacuum-based process. By combination of the scrape and selective electroplating techniques, a vacuum sputtering/evaporation-free processing is explored for the fabrication of high-performance metal mesh based TCF. The fabricated composite Ag-Ni mesh TCF exhibits ultra-low sheet electrical resistance (Rs=0.07Ω sq−1) at average transmittance of 70% in the visible region. The measured shielding efficiency can be greater than 30dB in X-band. Both experimental and theoretical results are given in the paper. By using the proposed method, TCF based EMI film can be easily fabricated for mass-manufacturing.
An ultra-flexible and low-sheet resistance transparent conductive film is developed from nickel metal-mesh (Ni metal-mesh) embedded in a polyimide (PI) by exploiting selective deposition technique coupled with photolithography and subsequent inverted film-processing method. The fabricated conductive film achieved sheet resistance values as low as 0.15 Ω sq-1, with corresponding optical transmittance as 80% at 550 nm corresponding the figure of merit up to 1.1×104. The film shows excellent adhesion and also preserves its structural integrity and good contact with the substrate for severe bending showing less than 4% decrease of conductivity even after 104 cycles. Finally, employing the fabricated Ni metal-mesh/PI conductive film, a hybrid transparent thin-film heater is demonstrated, which exhibited higher heating temperatures (110°C) under the lower operating voltage (1 V), lower power consumption (79.1°C cm2 W-1), and shorter response time (T < 2 s) than other heaters, as well as stability after repeated test.
We numerically and analytically report an ultra-broadband near perfect absorber based on one-dimensional metal-dielectric-metal grating at visible light for TM polarization. A unit cell of this design is composed of metal-dielectric-metal grating, where the bottom metallic layer and the upper metallic coating are separated from each other by the intermediate dielectric grating. The absorber exhibits an average absorption of over 90% in the range 400-700nm. Moreover, they remain very high over a wide range of incident angle up to 45°.The electromagnetic field distributions are investigated, which reveals that this broadband absorption behavior is ascribed to the combination of surface plasmon resonance and cavity resonance. Furthermore, impedance calculations were carried out to explain the absorption behavior. The ultra-broadband near-perfect angle-robust absorber can be a good candidate for many fascinating applications, including solar-energy harvesting as well as producing artificial colors on a large scale substrate.
With the demanding requirements for light source, light emitting diodes (LED) attracts more and more attention because of its inherent advantages such as low power consumption, high reliability and longevity. However, there are two disadvantages for LED, one is the low light extraction efficiency resulting from the total internal reflection, and the other is the relative large scattered angle. In order to improve the light extraction efficiency and collimate the out-coupling light, a sub-micron Fresnel lens array is introduced and investigated in this paper. The focal length of the proposed Fresnel lens is 3μm and the minimum width of the outmost ring is about 150nm. To calculate and analyze the light extraction efficiency and the scattered angle of LED with such Fresnel lens array structure, we optimize the parameters of the Fresnel lens, such as the depth of the Fresnel lens array structure and the thickness of the p-type gallium nitride layer by using the finite difference time domain method (FDTD). By comparing the discussed patterned GaN-based LED with that traditional flat LEDs, it can be found that significant enhancement factor of the light extraction efficiency, which is improved by 3.5 times, can be obtained and the scattered angle at half maximum can be decreased 50° from 60° with this novel Fresnel lens structure. It will be expected that the proposed sub-micron structure can find wide applications in LEDs industry.
KEYWORDS: Holography, 3D image processing, Printing, 3D displays, Digital holography, Holograms, Fresnel lenses, Diffraction gratings, 3D vision, Diffraction
Micro-nano optics and digital dot matrix hologram (DDMH) technique has been combined to code and fabricate glassfree 3D image. Two kinds of true color 3D DDMH have been designed. One of the design releases the fabrication complexity and the other enlarges the view angle of 3D DDMH. Chromatic aberration has been corrected using rainbow hologram technique. A holographic printing system combined the interference and projection lithography technique has been demonstrated. Fresnel lens and large view angle 3D DDMH have been outputted, excellent color performance of 3D image has been realized.
Autostereoscopic displays are a promising three dimensional display technology for its convenience and compatibility with current display systems which has attracted considerable attention. We describe in detail an autostereoscopic display system with full-parallax using a directional light-guide device with continuously variable spatial frequency sub-micron grating structures. The optimization process of parameters of the multi-direction light-guide is given. A method of implementing sub-micron grating pixels (SMGPs) based on an ultraviolet continuously variable spatial frequency photolithography process has been proposed. The process aims to provide low cost fabrication of variable spatial frequency grating pixels with high efficiency. We fabricate 2 inch backlight plate with nine viewing directions, and the pitch of each diffractive pixel varies between 441 nm and 578 nm. The properties of SMGPs are investigated by the measurement of diffraction efficiency dependence on viewing angle under a collimated 650 nm LED light source at an incidence angle of 60°. The variation of diffraction efficiency with regards to viewing angle is weak. The measured diffraction efficiency is around 6%, which is in good agreement with the simulated value.
A type of tunable liquid crystal diffractive lens (TLCDL) for monochromatic wave base on multiorder diffraction is proposed and demonstrated. Two TLCDLs were designed using patterned indium tin oxide and a conductive surface relief electrode, respectively. The focus tuning mechanism of the lens has been proved using multiorder diffractive structure. One TLCDL with three switchable focal lengths was fabricated using an imprinting technique, which significantly reduced fabrication complexity. Electro-optic performances of the TLCDL were studied with monochromatic illumination. High image quality with low operating voltage and fast response time has been realized.
A cost-effective method, using reactive ion etch (RIE) process to etch Si with Ag nanoparticle mask for fabricating
antireflection structure, is proposed. The formation of Ag nanoparticle adopts wet-chemical method to deposit Ag layer
on Si substrate, and then through rapid thermal annealing of Ag at 200°C-600°Crange, Ag nanoparticle were formed on
Si substrate. Effects of parameters including etching parameters and deposited factors were investigated. According to
analysis result of experiment, a group of high performance antireflection structure parameters was obtained.
A polarizing color filter, combining the function of polarizer and color filter, is proposed and
theoretically investigated. The proposed color filter comprises of a metal grating and a dielectric layer
on a glass substrate. The influence of the geometrical parameters of dielectric layer on the transmission
efficiency are discussed in detail by rigorous coupled-wave analysis (RCWA). The result shows that a
dielectric layer of high equivalent refractive index can enhance its performance effectively. A optimum
tricolor filter with more than 74.1% broadband transmission and a polarization extinction ratio of
8.39dB is obtained.For TE-polarized light, it is reflected and can be recycled in the backlight units to
increase the total energy utility. The numerical result shows that the peak transmission efficiency can
increase 21.5% by using the proposed devices.
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