Optical design of an imager with wide field-of-view (FOV) and high-resolution utilizes a monocentric objective lens in conjunction with an array of secondary optical lenses to achieve good performance. An intermediate image with uniform residual aberration throughout a wide FOV is obtained on a curved surface by the monocentric objective lens and then relayed to a sensor array by the secondary optical lenses. In this paper, we focus on the study of the monocentric objective lens and the surface type of its obtained curved image. Firstly, the equation of focal length is determined by ray tracing. The achromatic condition is obtained through first-order aberration theory. Accordingly, the initial configuration of the monocentric objective lens is determined, including the surface radii and reasonable glass combination. Secondly, a detailed calculation of the image positions is performed. The results show that the image surface is spherical when the object distance is much larger than the focal length. But it is aspheric when the object distance is comparable to the focal length. Finally, a mono-centric lens is optimumly designed, with a visible working wavelength band of 480-640nm, a focal length of 100mm, a wide FOV of 140°, and a large f-number of 5. Through imaging simulation and the image performance evaluation with ZEMAX, the theoretical calculations are verified.
The multi-focus image fusion technique is to extract the focus regions from source images and compose them together to form a clear image in the full field of view. In order to further improve the accuracy of focus region detection and ensure its efficiency, a novel multi-focus image fusion method in spatial domain, based on guided filter and mixed focus measure, is proposed in this paper. Firstly, a guided filter is employed as an edge-preserving smoothing operator to process the source images, and the difference operator is used between the filtered images and the source images to extract salient feature. Subsequently, the salient feature maps are measured by the mixed focus measure, combining the sum of energy of edge (SEOE) and the sum of local variance (SLV), to detect the focus regions, and the initial decision map is obtained. For holes of different sizes in the initial decision map, the closing operation and the small area removal strategy are used to fill and connect the truncated regions, and then the opening operation and the guide filter are used to optimize the decision map boundary to obtain the final decision map. Finally, the multi-focus fusion image is obtained by the pixel-wise weighted-averaging rule according to the final decision map. Simulation results demonstrate that the method is superior to some existing fusion methods on both subjective visual perception and objective evaluation metrics.
Color filters based on different Fabry-Perot structures are investigated extensively, and incident angle dependency is an important characteristic in practical applications. Here, we investigated a color filter incorporating a Fabry-Perot structure, discussing its reflective angular sensitivity related to refractive index of its dielectric material. By finite difference time domain(FDTD) theory, the refractive index of the dielectric material is found to influence the angular sensitivity greatly while the optical thickness keeps constant. The simulated results shows that the higher the dielectric layer’s refractive index is, the more angular insensitive of the reflection will be obtained and a good angular insensitive will achieved when the refractive index is larger than 2.1. Finally, samples with different dielectric layer are fabricated in experiment and the measured results verify influence of the refractive index of dielectric layer on the spectra angular sensitivity, which is helpful for the application of color filter in color display, image sensors and decoration.
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.
A printable color filter based on the photonic micro-cavity incorporating a nanostructure is proposed, which consists of a nano-metallic grating, a dielectric layer and aluminum (Al) film. According to the resonance induced by different dielectric depths of the micro-cavity, two dielectric heights for the same resonant wavelength are chosen to form the grating heights relative to the Al film. With the contribution of the cavity resonance and the surface plasmon resonance, the proposed structure performs enhanced broadband filtering characteristics with good angular tolerance up to 48° compared to the one of the micro-cavity as well as the one of the metallic grating. Therefore, reflective filters for RGB colors are designed incorporating the proposed structure. Furthermore, for the proposed structure shows great polarization dependence even at normal incidence, it can also be utilized as an anticounterfeiting certificate.
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.
A polarized color filter with good performance is proposed. This device consists of a transparent substrate, a bottom
metal grating, a low refractive index dielectric layer, a high refractive index dielectric layer and a top metal grating. The
bottom metal grating has a small period which is mainly for polarization, and the top metal grating with a large period is
for color-filtering. The parameters that affect the transmission and polarization properties of the device have been
simulated and analyzed by utilizing the finite-difference time-domain (FDTD) method. A polarized color filter having
broadband peak, high transmission and high extinction ratio is designed. The peak wavelengths and the corresponding
transmittances are as follows: 635nm and 78.7% for red, 541nm and 83.2% for green, 452nm and 82.4% for blue.
Extinction ratio above 1000:1 has been achieved within the full width at half maximum (FWHM) range for all the three
colors. This device is suitable for liquid crystal displays.
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.
A theoretical study of transmission color filters with double metal layers for the visible spectrum is presented. The device
consists of five parts: the transparent substrate, the dielectric grating, the first metal layer, the second metal layer and the
cover dielectric layer. The first metal layer is disposed in the trench of the dielectric grating. The second metal layer,
having the same thickness as the first metal layer, overlies on the top surface of the dielectric grating. And the cover
dielectric layer is formed on the metal layers. By using rigorous couple-wave analysis (RCWA), the transmission
characteristics are analyzed as a function of the duty cycle, the thickness of the dielectric grating, the thickness of the
metal layers and the period. Based on the simulation results, a high-performance color filter is designed by optimizing
the structural parameters. The grating periods are 280, 220, and 170nm for the red, green, and blue filters, respectively.
For the red color filter the center wavelength was 650nm and its corresponding transmission 84%, for the green color one
the center wavelength was 550 nm and its corresponding transmission 83%, while for the blue color one the center
wavelength was 440nm and its corresponding transmission 83%. The bandwidths of the filters are about 100nm.
Accordingly, the color filters not only perform better in filtering light but also produce high color purity. Additionally,
each color light has high transmission. They are suitable for filtering in liquid crystal devices.
A novel subwavelength dual-layer metallic nanowire-grid polarizer is designed for visible region. The difference
between the designed and the available nanowire-grid polarizer is that the former adds a high refractive index dielectric
layer between the substrate and the dielectric grating. It is found that the high refractive index dielectric layer can
improve the performance of polarizer. Effects of the thickness of the high refractive index dielectric layer, the incident
angle and the duty cycle on the TM polarization transmission efficiency as well as the extinction ratios are analyzed
using rigorous couple-wave theory. Based on the simulation results, a polarizer with high TM transmission efficiency and
high extinction ratios over a wide incident angle is designed. It gives TM transmission efficiency over 79% and
extinction ratios higher than 56.6dB until the incident angle is
θ= 60°
A novel high-power two-beam laser interference marking system is proposed. It is used to mark diffractive optical
variable image on the surface of the glazed work piece directly. A high-power laser beam is split into two beams with
equal energy. They are focused to form a spot composed of interference light field. The experimental results show that
periodic micro-grating structure can be achieved with a single shot of laser ablation. Diffractive optical variable image,
which is composed of micro-grating structures with different directions and different periods, has diffractive chromatic
dispersion effects under the illumination of white light. The wavelength of the laser is 527nm. The energy of the
single-pulse laser is 1.0mJ@20ns
20ns. The materials can be the stainless steel, the chromium film and other metals. The
experimental results have been given.
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