Showing papers by "Xiang Peng published in 2007"

Direct electron beam writing of kinoform micro-axicon for generation of propagation-invariant beams with long non-diffracting distance

Abstract: To enhance the non-diffracting distance of propagation-invariant beams, fabrication of an axicon with large aperture diameter and height is essential. It is noted, however, that fabrication of continuous surface profile micro-optical elements with a large physical height (thick resist) is prone to various fabrication constraints and errors. We employ the kinoform technique to alleviate such problems in the fabrication of axicons. In this paper kinoform micro-axicons and kinoform micro-double-axicons are designed and fabricated employing electron beam lithography techniques to generate a Bessel beam and a self-imaged bottle beam with long non-diffracting distance. Furthermore, a detailed study of power conversion efficiency of kinoform structures is discussed.

Known-plaintext attack on the double phase encoding and its implementation with parallel hardware

Abstract: A known-plaintext attack on the double phase encryption scheme implemented with parallel hardware is presented. The double random phase encoding (DRPE) is one of the most representative optical cryptosystems developed in mid of 90's and derives quite a few variants since then. Although the DRPE encryption system has a strong power resisting to a brute-force attack, the inherent architecture of DRPE leaves a hidden trouble due to its linearity nature. Recently the real security strength of this opto-cryptosystem has been doubted and analyzed from the cryptanalysis point of view. In this presentation, we demonstrate that the optical cryptosystems based on DRPE architecture are vulnerable to known-plain text attack. With this attack the two encryption keys in the DRPE can be accessed with the help of the phase retrieval technique. In our approach, we adopt hybrid input-output algorithm (HIO) to recover the random phase key in the object domain and then infer the key in frequency domain. Only a plaintext-ciphertext pair is sufficient to create vulnerability. Moreover this attack does not need to select particular plaintext. The phase retrieval technique based on HIO is an iterative process performing Fourier transforms, so it fits very much into the hardware implementation of the digital signal processor (DSP). We make use of the high performance DSP to accomplish the known-plaintext attack. Compared with the software implementation, the speed of the hardware implementation is much fast. The performance of this DSP-based cryptanalysis system is also evaluated.

A pitch-variation moiré fringes method of temporal phase unwrapping profilometry

Abstract: A method of pitch-variation moire fringes is proposed to realize the temporal phase unwrapping for three-dimensional profilometry. On the basis of the principle of moire pattern, we achieve variable spatial frequencies of fringes in a moire pattern by rotating two gratings. Furthermore a five-point fitting method is used to automatically compute the central position of side-lobe spectrum of the moire fringes. Finally, a generalized temporal phase unwrapping algorithm is introduced to process the three-dimensional reconstruction. The theoretical analysis and experimental results show the validity of the proposed method.

Model-based optical metrology and visualization of 3-D complex objects

Abstract: This letter addresses several key issues in the process of model-based optical metrology, including three dimensional (3D) sensing, calibration, registration and fusion of range images, geometric representation, and visualization of reconstructed 3D model by taking into account the shape measurement of 3D complex structures, and some experimental results are presented.

3D optical vortices generated by micro-optical elements and its novel applications

Abstract: In this paper we report on recent development in the areas of optical vortices generated by micro-optical elements and applications of optical vortices, including optical manipulation, radial polarization and secure free space optical communication

A coarse registration method of range image based on SIFT

Abstract: A novel method for the coarse registration of range images is proposed. This approach is based on texture-feature recognition. As the development of optical digitizing technique, it is now able to acquire the range images and associated texture images sequentially or simultaneously. It's possible to identify the range feature points through texture feature points. Scale Invariant Feature Transform (SIFT) is an efficient method for texture feature generation. SIFT transforms texture image into a large collection of local feature vectors, each of which is invariant to image scaling, translation, and rotation. The mismatched correspondence pairs can be discarded using random sample consensus algorithm based on epipolar geometry constraint. We select more than three well-registered texture-feature pairs, with which we could find the associated range-feature pairs of the range images. Initial pose estimation of the two involved range images can be computed by these range pairs, and the fine registration is implemented using iterative closest point (ICP) algorithm. Our approach utilizes the texture information to register the range images, leading to a technique that can be automatically performed while the influence of 3D noise can be avoided. The experiment results demonstrate that the proposed approach is efficient and robust for the registration of multiple range images.

A symbol-map wavelet zero-tree image coding algorithm

Abstract: A improved SPIHT image compression algorithm called symbol-map zero-tree coding algorithm (SMZTC) is proposed in this paper based on wavelet transform. The SPIHT algorithm is a high efficiency wavelet coefficients coding method and have good image compressing effect, but it has more complexity and need too much memory. The algorithm presented in this paper utilizes two small symbol-maps Mark and FC to store the status of coefficients and zero tree sets during coding procedure so as to reduce the memory requirement. By this strategy, the memory cost is reduced distinctly as well as the scanning speed of coefficients is improved. Those comparison experiments for 512 by 512 images are done with some other zerotree coding algorithms, such as SPIHT, NLS method. During the experiments, the biorthogonal 9/7 lifting wavelet transform is used to image transform. The results of coding experiments show that this algorithm speed of codec is improved significantly, and compression-ratio is almost uniformed with SPIHT algorithm.

A generalized temporal phase unwrapping algorithm

Abstract: A generalized temporal phase unwrapping (GTPU) algorithm is proposed for absolute phase measurement of object surfaces with complex topography. Comparing with the classical TPU algorithms, GTPU shows more robust and has better noise immunity and less computational complexity. According to the type of fringe sequence used, the current TPU algorithms proposed by Huntley can be divided into three categories: linear sequence, exponential sequence and reversed exponential sequence. The two types of exponential sequences make use of the fact that the relation between the phase and the number of projected fringes is linear, resulting in a reduction of total number of acquired images compared to linear sequence illumination. Error analysis for the different TPU methods were done firstly, that reveals the problems existed in theses phase unwrapping methods, for example the limitation imposed on the fringe sequence, noise immunity and computational efficiency. In order to overcome these drawbacks, we present a generalized TPU algorithm in this paper. The GTPU can eliminate the limitation on fringe sequence, so that an arbitrary fringe sequence will be used to encode the object surface, leading to a flexible method for phase reconstruction. Computer simulations and experiment results have been also proved that the GTPU has better performance on noise control and computational efficiency.

All-solid-state microscopic interferometer with frequency-variation and phase-shifting capability

Abstract: A novel microscopic interferometry with ability of frequency-variation and phase-shifting is proposed for microstructures testing. By using acousto-optic technique, sequential carriers can be generated with different spatial frequencies so that the temporal phase unwrapping method can be applied for decoding the height information. Combined with phase-shifting technique realized by spatial light modulator, this method is especially suitable for interferometric measurement with high precision and large dynamic range.

The new methods for registration and integration of range images

Abstract: With the improvements in range image acquisition by optical metrology of our group, we also developed a novel method for the registration and integration of range images. The registration approach is based on texture-feature recognition. Texture-feature pairs in two texture images are identified by cross-correlation, and the validity-checking is implemented through Hausdorff distance comparison. The correspondence between the texture image and range image helped acquire the range point-pairs, and the initial transformation of two range images was computed by least-squares technique. With this initial transformation, the fine registration was achieved by ICP algorithm. The integration of the registered range images is based on ray casting. An axis-aligned bounding box for all range images is computed. Three bundles of uniform-distributed rays are cast and pass through the faces of the box along three orthogonal coordinate axes respectively. The intersections between the rays and the range images are computed and stored in Dexels. The KD-tree structure is used to accelerate computation. Those data points in overlapped region are identified with specific criteria based on the distance and the angle of normals. We can obtain a complete non-redundant digital model after removing the overlapped points. The experimental results illustrate the efficiency of the method in reconstructing the whole three dimensional objects.

Three-dimensional imaging with acousto-optic fringe projector and piecewise temporal phase unwrapping

Abstract: We report an approach for three-dimensional (3D) imaging with use of acousto-optic fringe projector (AOFP) and a technique of piecewise temporal phase unwrapping. The AOFP is controlled by direct digital synthesizer to generate a sequence of fringe patterns with different spatial frequencies so that encoding with variable sensitivity can be realized. Furthermore, we present a new phase unwrapping strategy for incremental phase reconstruction with the level of details. The algorithm is developed as a piecewise temporal phase unwrapping with a tolerance of deviation from the condition imposed upon conventional temporal phase unwrapping technique. Preliminary experiment results are given to support proposed approach.

Integrated optical 3D digital imaging based on DSP scheme

Abstract: We present a scheme of integrated optical 3-D digital imaging (IO3DI) based on digital signal processor (DSP), which can acquire range images independently without PC support. This scheme is based on a parallel hardware structure with aid of DSP and field programmable gate array (FPGA) to realize 3-D imaging. In this integrated scheme of 3-D imaging, the phase measurement profilometry is adopted. To realize the pipeline processing of the fringe projection, image acquisition and fringe pattern analysis, we present a multi-threads application program that is developed under the environment of DSP/BIOS RTOS (real-time operating system). Since RTOS provides a preemptive kernel and powerful configuration tool, with which we are able to achieve a real-time scheduling and synchronization. To accelerate automatic fringe analysis and phase unwrapping, we make use of the technique of software optimization. The proposed scheme can reach a performance of 39.5 f/s (frames per second), so it may well fit into real-time fringe-pattern analysis and can implement fast 3-D imaging. Experiment results are also presented to show the validity of proposed scheme.