We introduce and compare two methods to produce the phase-shift patterns, which are widely generated in the near-field
lithography, in the optical far field. The key component of the two methods is a phase-only diffractive optical element, a
similar function found in the maskless lithography. The technique to produce a smaller feature size was a major
improvement beyond the diffraction limit.
We proposed a method, which is the first to our knowledge, to realize the phase-shift patterns of the near-field
lithography in the optical far field. The key component of the optical Fourier system was a phase-only diffractive optical
element which generated a diffracted light field of a semi-phase-only complex-valued function. The achieved feature size
was beyond the diffraction limit. The advantages of the proposed method included the capability to generate the
complicated patterns, spatial parallelism, and low cost.
We present a novel optimal phase quantization method for phase-only diffractive optical elements (DOEs) by taking into account both amplitude and phase information that are able to generate an arbitrary target pattern. In our approach, the MSE function was modified in which both the amplitude and the phase of the perfect wavefront were combined into the probability density function. The amplitude and the phase information could be obtained from a phase transmittance of a transparent lens incident by a Gaussian beam (providing the amplitude information), for example, or be directly constructed from the inverse Fourier transform of an arbitrary target pattern. By using the modified MSE function, the influence of the phase elements corresponding to larger amplitude values was emphasized and the optimal phase levels were calculated appropriately. Significant improvement was achieved for the construction of two-, four-, and eight-level Fresnel zone plates with a focal length of 8 m and an aperture of 6.2 mm, which was incident by a Gaussian beam with a 1/e-width of 1.4 mm were calculated. By use of the proposed algorithm, efficiency improved by 26.4% and SNR by 18.2% over the uniform quantization method for binary DOE's.
In this paper, we present a design of a phase-only diffractive optical element (DOE), which is capable of producing two distinct diffractive patterns for two wavelengths with high and equal diffraction efficiencies. The DOE is constructed by two one-sided surface profiles that are stacked together and in contact with a thin focusing lens. One is designed for a wavelength of the incident light to generate a pattern on the back focal plane, and the other is for the second wavelength to generate a different diffractive pattern without affecting the first pattern. The second profile simply provides a multiple of 2(pi) phase delay for the first wavelength and thus has no effect on the first pattern. In the proposed algorithm, the iterative Fourier transform algorithm with the stepwise quantization method is modified to calculate the two phase profiles simultaneously in the iterations. High and equal diffraction efficiency (74.5%) for the two wavelengths was achieved with 2 phase profiles of 4 uniform phase levels. In addition, a method of multiple bounding controls was proposed to increase the SNR in the regions of interest so as to improve the chromatic performance of the double wavelength design. Different SNR's (5.7 dB and 1.7 dB) were achieved at signal and noise regions.
Spatial resolution is one of the main characteristics of electronic imaging devices such as the digital still-picture camera. It describes the capability of a device to resolve the spatial details of an image formed by the incoming optical information. The overall resolving capability is of great interest although there are various factors, contributed by camera components and signal processing algorithms, affecting the spatial resolution. The spatial frequency response (SFR), analogous to the MTF of an optical imaging system, is one of the four measurements for analysis of spatial resolution defined in ISO/FDIS 12233, and it provides a complete profile of the spatial response of digital still-picture cameras. In that document, a test chart is employed to estimate the spatial resolving capability. The calculations of SFR were conducted by using the slanted edge method in which a scene with a black-to- white or white-to-black edge tilted at a specified angle is captured. An algorithm is used to find the line spread function as well as the SFR. We will present a modified algorithm in which no prior information of the angle of the tilted black-to-white edge is needed. The tilted angle was estimated by assuming that a region around the center of the transition between black and white regions is linear. At a tilted angle of 8 degree the minimum estimation error is about 3%. The advantages of the modified slanted edge method are high accuracy, flexible use, and low cost.
In this paper, the techniques as well as the measurement results of the performance of commercial digital still- picture cameras are presented. The key parameters such as the camera Opto-Electronic Conversion Function (OECF), the noise based ISO speed, and the spatial frequency response (SFR) are reported. The camera OECF is defined as the relationship between the input luminance and the grayscale or digital output from the camera, which was measured by using a test chart with twelve squares of various luminances. The ISO speed was calculated from the exposure time, the effective f-number, and the luminance at different incremental signal-to-noise ratios. In general, the exposure time is not obtainable from a commercial digital camera unless a destructive measurement is undergoing. In this study, a device was setup to obtain the exposure time when the OECF test chart was recording. A modified slanted-edge method was employed to estimate the SFR by imaging a pattern with a black-to-white edge tilted at an arbitrary angle. There are seven digital still picture cameras as our test samples whose CCD sensor contains VGA-size and million pixels. The camera OECF of these cameras did not show significant difference under a large range of illumination. However, the ISO speed and the SFR were of great variation.
Commercial electronic still picture cameras need a low-cost, systematic method for evaluating the performance. In this paper, we present a measurement method to evaluating the dynamic range and sensitivity by constructing the opto- electronic conversion function (OECF), the fixed pattern noise by the peak S/N ratio (PSNR) and the image shading function (ISF), and the spatial resolution by the modulation transfer function (MTF). The evaluation results of individual color components and the luminance signal from a PC camera using SONY interlaced CCD array as the image sensor are then presented.
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