Imaging detector of temporally coherent radiation

We present an optical architecture and image processor capable of detecting and locating temporally coherent radiation that may be dominated by incoherent background radiation. The optical architecture makes use of a coherent light modulator that modulates light of sufficient coherence length while it leaves light of short coherence length unmodulated. The design of the coherent light modulator offers a substantially wider field of view than did past designs, permitting its application within an imaging system. The image processor synchronously detects the modulation imposed on coherent light while it rejects incoherent light fluctuations. Results of a laboratory test are presented. The system tested in the laboratory had a 26 degrees field of view and was able to detect and locate coherent radiation >30 dB below the background incoherent light level.     

White-light implementation of the Wigner-distribution function with an achromatic processor

A temporally incoherent optical processor that combines diffractive and refractive components is proposed for performing two different operations simultaneously: an achromatic image along an axis and an achromatic one-dimensional Fourier transformation along the orthogonal axis. These properties are properly employed to achieve the achromatic white-light display of the Wigner-distribution function associated with a one-dimensional real signal, with high redundancy and variable scale.     

Extended depth of field through wave-front coding

We designed an optical-digital system that delivers near-diffraction-limited imaging performance with a large depth of field. This system is the standard incoherent optical system modified by a phase mask with digital processing of the resulting intermediate image. The phase mask alters or codes the received incoherent wave front in such a way that the point-spread function and the optical transfer function do not change appreciably as a function of misfocus. Focus-independent digital filtering of the intermediate image is used to produce a combined optical-digital system that has a nearly diffraction limited point-spread function. This high-resolution extended depth of field is obtained through the expense of an increased dynamic range of the incoherent system. We use both the ambiguity function and the stationary-phase method to design these phase masks.     

Real-time three-dimensional object recognition with multiple perspectives imaging

A novel system for recognizing three-dimensional (3D) objects by use of multiple perspectives imaging is proposed. A 3D object under incoherent illumination is projected into an array of two-dimensional (2D) elemental images by use of a microlens array. Each elemental 2D image corresponds to a different perspective of the 3D object. Multiple perspectives imaging based on integral photography has been used for 3D display. In this way, the whole set of 2D elemental images records 3D information about the input object. After an optical incoherent-to-coherent conversion, an optical processor is employed to perform the correlation between the input and the reference 3D objects. Use of micro-optics allows us to process the 3D information in real time and with a compact optical system. To the best of our knowledge this 3D processor is the first to apply the principle of integral photography to 3D image recognition. We present experimental results obtained with both a digital and an optical implementation of the system. We also show that the system can recognize a slightly out-of-plane rotated 3D object.     

Hybrid Image Processing for Feature Extraction and Constant Variance Enhancement

Hybrid image processing using a digital image processing system together with a simple incoherent optical technique is described. By using such hybrid processing, feature extraction and constant variance enhancement of dislocation lines in electron micrograph images are shown. Experimental results show the usefulness of such hybrid processing for current applications.     

Design of a multichannel, multiresolution smart imaging system

This paper presents the design of a multichannel imaging system where the different optical channels have a different angular resolution and field-of-view. Such an imaging system is able to resolve fine details in a small region of interest through the channel that has the highest angular resolution (0.0096°) while controlling the surrounding region through the channel that has the widest field-of-view (2×40°). An interesting feature of such a multichannel, multiresolution imaging system is that various image processing algorithms can be applied at different segments of the image sensor. We have designed a three channel imaging system where each optical channel consists of four aspheric lens surfaces. These three imaging channels share a single image sensor with a resolution of 1440×960 and a 10 μm pixel size. All imaging channels have diffraction-limited performance ensuring good overall image quality.     

Professor Dennis Gabor,C.B.E., F.R.S., Nobel Laureate

Texture differences in a picture are difficult to analyse by digital techniques, but can be identified readily by optical spatial filtering. However, purely optical processors have several disadvantages. A low-cost system is described in which the output from an optical processor is digitized and processed by a microcomputer to produce a colour-coded image. This makes it possible to use the parallel processing capability of the optical processor for preliminary data reduction, while retaining the flexibility and interactive capability of a digital computer.     

Incoherent fractional Fourier transform and its optical implementation

The fractional Fourier transform is redefined for working with incoherent light. As a real transformation, the incoherent fractional Fourier transform overcomes coherent system disadvantages such as the speckle effect and the need for incoherent-coherent conversion. It also might have some applications for digital image and signal processing owing to its decreased computing complexity. An incoherent optical implementation of the new transform based on the shearing interferometer is suggested. Laboratory experimental results are given.     

Image identification system based on an optical broadcast neural network processor

We describe the implementation of a vision system based on a hardware neural processor. The architecture of the neural network processor has been designed to exploit the computational characteristics of electronics and the communication characteristics of optics in an optimal manner, thus it is based on an optical broadcast of input signals to a dense array of processing elements. The vision system has been built by use of a prototype implementation of a neural network processor with discrete optic and optoelectronic devices. It has been adapted to work as a Hamming classifier of the images taken with a 128 x 128 complementary metal-oxide semiconductor image sensor. Its results, performance characteristics of the image classification system, and an analysis of its scalability in size and speed, with the improvement of the optoelectronic neural processor, are presented.     

用于人脸识别的非相干光形态学处理器

设计了一个用于人脸图像光学识别处理的非相干光形态学处理器。系统中采用互补编码击中击不中变换以改善传统光学相关器的性能。基于该方法，构建了一个紧凑性的人脸光学识别非相干光系统，图象库中存有96幅人脸图象，可以达到每秒钟10幅的识别速度，识别正确率大于90％，对于8°以内的旋转畸变、30％以内的Gauss噪声干扰以及50％以内的图像缺损具有相当好的容错能力。     

Automated Astroposition Determination Using Sensor Array Systems

A new method to determine the astronomic longitude is described. The standard optical micrometer of the T-4 theodolite is substituted by an optical sensor array system that is placed in the focal plane of the T-4. The image of a star is projected on the sensor array and converted into an electrical signal. The signal is consequently processed in a signal processor and accurately recorded. The signal processing procedure is designed to eliminate the need for an observer. Longitude determinations using stars of various magnitudes are described resulting in an accuracy of ±0.5?.     

Developed, binary, image processing in a dual-channel, optical, real-time morphological processor

A developed, binary, image-processing technique is proposed, and a dual-channel, optical, real-time morphological processor is developed. Nine binary image processings can be realized fully in parallel. The measures for compensating scale and rotation distortion for pattern recognition are provided. Some applications of optical, morphological binary image processing are studied and experimental results are listed.     

Feature-extracted joint transform correlation

A new technique for real-time optical character recognition that uses a joint transform correlator is proposed. This technique employs feature-extracted patterns for the reference image to detect a wide range of characters in one step. The proposed technique significantly enhances the processing speed when compared with the presently available joint transform correlator architectures and shows feasibility for multichannel joint transform correlation.     

Reduced depth of field in incoherent hybrid imaging systems

A hybrid imaging system combines a modified optical imaging module and a digital postprocessing step. We define what to our knowledge is a new metric to quantify the blurring of a defocused image that is more suitable than the defocus parameter for describing defocused hybrid imaging systems. We use this metric to design a pupil phase grating to reduce the depth of field, thereby increasing the axial resolution, of an incoherent hybrid imaging system using quasi-monochromatic illumination. By introducing this grating at the exit pupil and digitally processing the output of the detector, we reduce the depth of field by more than a factor of 2. Finally, we examine the effect of using a CCD optical detector, instead of an ideal optical detector, on the reduction of the depth of field.     

Kinoform filter for an incoherent optical processor

Fabrication and testing of a kinoform filter is described, for use in a real-time incoherent optical processor designed for track recognition in high-energy physics experiments. Composition of the filter as a mosaic of kinoforms with different random diffusers improves the quality of the restoration.     

Synthetic aperture superresolution with multiple off-axis holograms

An optical setup to achieve superresolution in microscopy using holographic recording is presented. The technique is based on off-axis illumination of the object and a simple optical image processing stage after the imaging system for the interferometric recording process. The superresolution effect can be obtained either in one step by combining a spatial multiplexing process and an incoherent addition of different holograms or it can be implemented sequentially. Each hologram holds the information of each different frequency bandpass of the object spectrum. We have optically implemented the approach for a low-numerical-aperture commercial microscope objective. The system is simple and robust because the holographic interferometric recording setup is done after the imaging lens.     

Optical scanning cryptography for secure wireless transmission

We propose a method for secure wireless transmission of encrypted information. By use of an encryption key, an image or document is optically encrypted by optical heterodyne scanning and hence encryption is performed on the fly. We call this technique optical scanning cryptography. The output of the heterodyne encrypted signal is at radio frequency and can be directly sent through an antenna to a secure site for digital storage to be prepared for decryption. In the secure site, an identical optical scanning system to that used for encryption is used, together with a decryption key, to generate an electrical signal. The electrical signal is then processed and sent to a computer to be used for decryption. Utilizing the stored information received from the encryption stage and the electrical information from the secure site, a digital decryption unit performs a decryption algorithm. If the encryption key and the decryption key are matched, the decryption unit will decrypt the image or document faithfully. The overall cryptosystem can perform the incoherent optical processing counterpart of the well-known coherent double-random phase-encoding technique. We present computer simulations of the idea.     

Achromatic fourier processor with holographic optical lenses

An optical Fourier processor that allows the use of broadband light sources and colored inputs is designed, fabricated, and tested. We develop a design technique based on phase manipulation in the Fourier plane to construct an image processor that provides a chromatically corrected image making use of the good aberrations behavior of symmetrical optical systems. Only a small number of diffractive lenses and one achromatic refractive lens are required to obtain a real image. We verify our design experimentally using holographic lenses, which are presented, owing to their versatility, as a good alternative to expensive blazed diffractive elements.     

Optical Fourier processor and point-diffraction interferometer for moving-object trajectory estimation

A hybrid optical-digital signal processing system that estimates the trajectory of moving targets in a two-dimensional field at video frame rates was developed and constructed. The hybrid system is particularly well suited to the trajectory estimation of small, barely discernable, moving objects of unknown position and velocity in high-resolution image sequences. The system uses an optical Fourier processor and a point-diffraction interferometer to calculate the frequency-domain representation of moving objects from which their trajectory is estimated by use of conventional electronic processing techniques. In a series of experiments, target velocities were estimated to within 4% of their actual value and direction was estimated to within 3 deg.     

Compact optical temporal processors

Optical signal processing can be done with time-lens devices. A temporal processor based on chirp-z transformers is suggested. This configuration is more compact than a conventional 4-? temporal processor. On the basis of implementation aspects of such a temporal processor, we did a performance analysis. This analysis leads to the conclusion that an ultrafast optical temporal processor can be implemented.