Direct laser writing (DLW) enables arbitrary three-dimensional nanofabrication. However, the diffraction limit poses a major obstacle for realizing nanometer-scale features. Furthermore, it is challenging to improve the fabrication efficiency using the currently prevalent single-focal-spot systems, which cannot perform high-throughput lithography. To overcome these challenges, a parallel peripheral-photoinhibition lithography system with a sub-40-nm two-dimensional feature size and a sub-20-nm suspended line width was developed in our study, based on two-photon polymerization DLW. The lithography efficiency of the developed system is twice that of conventional systems for both uniform and complex structures. The proposed system facilitates the realization of portable DLW with a higher resolution and throughput.
Recently, glass-free light field displays of multi-layer architecture have gradually entered the commercial stage. However, for near-eye displays, light field rendering still suffers from expensive computational costs. It can hardly achieve an acceptable framerate for real-time displays. This work develops a novel light field display pipeline that uses two gaze maps to reconstruct display patterns of foveated vision effect. With the acceleration of GPU and the emerging eye-tracking technique, the gaze cone can be updated instantaneously. The experimental results demonstrate that the proposed display pipeline can support near-correct retinal-blur with foveated vision and high framerate at low-computation.
In this paper, a novel microscopic imaging technology, termed light field Fourier ptychographic microscopy (LFFPM), is presented which enables the reconstruction of wide-field, high-resolution images with the depth information by utilizing a light-emitting-diode (LED) illumination matrix.Conventional light field microscope lacks the ability of high lateral resolution because it sacrifices its lateral resolution to its angular resolution. Compared to conventional light field microscope, LFFPM enhances the lateral resolution with no need for the object to be in focus. Using LFFPM, the result shows that the lateral resolution is more than 2 times better than light field microscopy in simulation and 1.5 times in the experiment. Furthermore, the simulation result also shows that the ability of LFFPM to recovery the information of the phase and amplitude.Thus, this technology has a wide prospect of various biomedical applications such as neuroanatomy and haematology.
Assessing tissues’ inhomogeneous optical properties is helpful for diagnosis, but high-cost measurement and experimental setups limit its development, data collecting and applications. In this paper, a portable microscope is proposed to assess the inhomogeneous optical properties of the sample. With a LED illumination, accurate quantitative phase (QP) map can be recovered from 5 intensity images captured at different axial positions. Then based on the scattering-phase theorem and statistical dispersion relation (SDR), the inhomogeneous optical properties of the sample can be quantitatively assessed from these QP maps. In contrast to DHM and SLIM, our setup is cost-effective, use-flexible, and with a small amount of data acquisition, thus having the potential to promote the development of assessing tissues’ inhomogeneous optical properties, especially in resource-limited areas.
Crop population growth information can more fully reflect the state of crop growth, eliminate individual differences, and reduce error in judgment. We have built a suitable plant population growth information online monitoring system with the plant chlorophyll fluorescence and spectral scanning imaging to get the crop growth status. On the basis of the fluorescence image detection, we have studied the early drought diagnosis of cucumber. The typical chlorophyll fluorescence parameters can not reflect the drought degree significantly. We define a new indication parameter (DI). With the drought deepening, DI declines. DI can enlarge the early manifestation of cucumber drought (3-5 days), indicate more significantly in the early drought diagnosis of cucumber.
Laser beam shaping requires controlling the intensity and phase profile of the input laser beam simultaneously. In this paper, a method for designing double freeform surfaces is presented to solve the laser beam shaping problem. Based on Snell’s law and conservation law of energy, a mathematical model is established to convert the double surfaces design problem into an elliptic Monge-Ampère equation with a nonlinear boundary problem by imposing a constraint on the optical path length between the input and output wavefronts. Two different configurations of the beam shaping system are discussed and the good results show clearly the Monge–Ampère equation method provides an effective tool in solving the challenging problem of laser beam shaping.
In many applications, the emitting light from LEDs with different colors need to be mixed together on a large scale target plane and this illumination mode is usually generated with the help of a diffuser. Abandoning the traditional method, we proposed a LED color mixing method which can produce an illumination pattern with both high color uniformity and irradiance uniformity. This method is composed of the two main aspects: arrangement of irradiance array and design of LED lens. With the method, an independent rectangular irradiance distribution is generated by each lens unit, and the large scale color uniform illumination is obtained by arraying the irradiance distribution. A 3×3 array of LED module units consisting of 36 LED lens units with 4 different colors are designed, and a desired result with high color uniformity is obtained. This color mixing method is feasible and practical, and is superior to the existing methods.
Large-scale psychophysical experiments are carried out on two types of mobile displays to evaluate the perceived image quality (IQ). Eight perceptual attributes, i.e., naturalness, colorfulness, brightness, contrast, sharpness, clearness, preference, and overall IQ, are visually assessed via categorical judgment method for various application types of test images, which were manipulated by different methods. Their correlations are deeply discussed, and further factor analysis revealed the two essential components to describe the overall IQ, i.e., the component of image detail aspect and the component of color information aspect. Clearness and naturalness are regarded as two principal factors for natural scene images, whereas clearness and colorfulness were selected as key attributes affecting the overall IQ for other application types of images. Accordingly, based on these selected attributes, two kinds of empirical models are built to predict the overall IQ of mobile displays for different application types of images.
KEYWORDS: 3D displays, Light emitting diodes, LED displays, 3D image processing, 3D acquisition, 3D volumetric displays, 3D vision, Displays, Image processing, Cameras
A volumetric display system based on a rotating light-emitting diode (LED) array panel can realize a three-dimensional (3-D) display truthfully in the space, but the drawback is missing the occlusion of a 3-D image. We propose an omnidirectional 3-D display with correct occlusion based on a direction-selective LED array panel, which is realized by setting a direction-convergent diaphragm array in front of the LED array. Every diaphragm restricts a light-emitting characteristic of every LED. By using direction-convergent diaphragm array, the observer around the display system can only see one image displayed by the LED array at the corresponding position. With the high-speed rotation of the LED panel, a series of views of a 3-D scene are displayed every angle patch in one circle. We set up an acquisition system to record 180 views of the 3-D scene with a rotating camera along a circle, and then the 180 images are displayed sequentially on the rotating direction-selective LED array to get a 360 deg 3-D display. This 3-D display technology has two main advantages: easy to get viewer-position-dependent correct occlusion and simplify the 3-D data preprocessing process which is helpful to real-time 3-D display.
The reproduction of computer-generated hologram (CGH) with white light source was realized using a liquid crystal panel instead of holographic film. The Burch-coding CGH was achieved by simulating the interference of a digital image and virtual reference light, displayed on liquid crystal displays and illuminated by a white light-emitting diode. The system is compact and the reconstructed images include full parallax. The full-parallax images of the Fresnel hologram computed with our algorithm were compared with the reproduced images by the rainbow hologram. The results implied this method was ready for the development of real-time three-dimensional color digital holography.
We investigate the beam splitting phenomena under the case that light is incident obliquely on thin film Fabry-Perot filter and the dispersion diagram of Fabry-Perot filter is shown; Gaussian beam propagating in the structure is analyzed by Fourier decomposition in angular field, transmitted band is calculated by characteristic matrix arithmetic in optical thin film theory. At last, the thin film Fabry-Perot filter device was fabricated by e-beam deposition in vacuum and measured from 782 to 787 achieved by the tunable Ti-sapphire laser. We show the variation of the distance between the splitting spots at different wavelengths by the image of splitting beams we detected, demonstrating the distance achieve maximum at the peak transmittance wavelength because of the largest group delay. And the experimental result is in good agreement with our interpretation.
It is a difficult task to measure the optical uniformity of an optical coating with very large aperture. Here an automatic near-UV/VIS/NIR spectrophotometer has been developed for spectrum analysis of optical coatings on very large aperture optical elements. It can give two-dimensional scanning result of a sample with substrate surface size of 600mm*350mm and 70mm thickness. The testing beam can be s- or p-polarized, at an incident angle from 0° to 70°. The equipment is composed of optical system, mechanical structure, photo-translating module and computer control system. Because of the light deflection after passing through the very thick sample, an integrating sphere and a sphere moving structure was involved. The measuring beam is guided in a quartz fiber with a special interface that can improve coupling efficiency from the monochromator to fiber. The two-dimensional scanning work platform has the position accuracy about 0.05mm and a reproducibility of 0.01mm. The beam incident angle accuracy is controlled within 0.1°. The measurement results show that in the near-UV/VIS/NIR region, the overall photometric accuracy can get 0.1% and 0.2% for transmittance and reflectance, respectively. The wavelength scale is accurate to be within 0.4nm with a reproducibility of 0.05nm.
A lower-cost monochrome CCD camera, which can detect the twenty-five frames of picture in one second, provides a rapid method to measure two-dimensional luminance distributions of the screen. According to the two-dimensional luminance distribution ratios of three primary colors captured by the CCD camera and the chromaticity coordinates of R, G, and B calibrated by the spectrometer, the chromaticity coordinates of combination colors of the LCD projector can be
computed quickly. The algorithm of removing the black stimulus values and the precise calibration in five gray levels of CCD are employed to diminish the error. The two-dimensional distribution maps of chromaticity coordinates of combination colors of five levels are represented in this paper. The data show that the maximum difference between the chromaticity coordinate measured by CCD-based system and by the spectrometer is 0.009, which can present the color uniformity of LCD projector properly.
An auto-focusing and auto-alignment system based on digital image processing and the computer control technology was developed for 3-LCD projector manufacture. We analyzed the imaging characteristic of the optical system, and developed a mathematical model to realize the accurate focusing of each LCD panel and accurate alignment among three LCD panels. Based on the model, the experimental facility was set up, which is compose of five CCD detectors that are placed on the screen at different filed of view to capture images and regulating mechanism of LCD’s six-dimensional degree of freedom droved by stepper motors. Appropriate defocusing evaluation function and alignment algorithm were also presented in this paper. The images captured by CCDs are processed to get the defocusing amount of every panel by the variance function and displacement amount of the three LCD panels by the gravity model approach. Then commands are sent to regulating mechanism to control the movement of each panel. After several turns of auto-correction, all the panels are in the proper position. Experiment results show that with the proper algorithm, the system can provide high accuracy and good performance in projector manufacture. The whole focusing and alignment process can be finished within ten minutes which is far superior to that made by man more than half an hour. With this system, completely automatic product lines can be established, which can provide 3-panel LCD projector light engines with considerable focusing and alignment accuracy.
The tunable optical filter used for WDM system was fabricated by employed the birefringence of liquid crystal. When the driver voltage changed, the refractive index of the liquid crystal was altered, which inverted to change the effective thickness of the cavity of the filter based on the Fabry-Perot etalon, so the peak of the transmittance was shifted and the filter achieved the tunable performance. The experiment result of the device was achieved to the tunable range from 1534.5nm to 1562.5nm and the full width of the half maximum is nearly 0.8nm and was in agreement with the design one.
A simple and low-cost solution for interleaver used in optical communication, based on multi-cavity Fabry-Perot optical thin film filters, is presented. The analyses on this kind optical interleaver reveal the influencing factors that would affect the thin film interleaver performance, including the cavity's spacer thickness, ambient temperature variation, dispersion for the refractive index of deposited material depending on wavelength and the numbers of cavity that is important for passband flatness and isolation. The interleaver achieved to 100GHz-spaced channels, at wavelength around C band, with adjacent channel's cross-stalk less than —25dB and the minimum insertion loss nearly 0.4dB or so.
F-P optical thin film filter based on glass was designed and built using thin film coating and RIE technology. Photoresist was the sacrificial layer and later was removed by dry etching.
A compact LCD projection display system and its optical performance are discussed in this paper. In order to improve optical performance, two flyingeye lens have been employed in the system. It can improve the brightness uniformity of display image. Also, a polarized light transformer, which involves two functions: polarizing light radiation and converting unpolarized light into the same polarization direction light beam for LCD panels, has been developed to increase the optical efficiency and contrast ratio. Moreover, color separation and combination system has been designed and developed. Under these construction, the system with good optical performance and outstanding picture quality has been achieved.
Liquid crystal light valve is composed by hybrid multilayer thin films. Its performance depends critically on both optical and electrical properties of each film consisted. The relation of optical-electrical between thin films and the device will be presented in this paper, and the experimental results of the LCLV device will also be introduced.
The CdS/CdSe Liquid-Crystal Light Valve (LCLV) has been investigated, especially the switching ratio, contrast, and response time have been analyzed and calculated. Moreover, the optical-electronic properties of the LCLV have been measured. Such devices have been successfully used for large-screen display.
A kind of liquid crystal light valve (LCLV) based on a CdS-CdSe photoconductor that can convert visible image to infrared at video rate is introduced in this paper. A prototype of a visible to infrared dynamic image converting system using a CO2 laser as the infrared source is built with this device. Results of the converter are presented in this paper.
The effect of doping with copper and chlorine on various properties of vacuum-evaporated CdS and CdSe double layers has been studied. The properties specifically studied were: (1) the dark conductivity and photoconductivity as functions of the doping concentration and the ratio of copper to chlorine, (2) the response time of various photoconductive films and (3) the optical absorption and spectral response. It was found that the dark conductivity decreases and the photoconductivity increases significantly if the ratio of Cu to Cl is suitable. The response time was about 5 - 10 ms for doping films and more than 100 ms for undoping ones. The optical absorption increases and the spectral response moves to a longer wavelength as the concentration of CdSe increases. The response wavelength can be changed by adjusting the thickness ratio of CdS to CdSe.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.