A new method for measuring the radius of curvature (ROC) of an optical surface having a large radius is proposed. The method combines a Fizeau interferometer and a specially designed zoom lens to form a compact and convenient test setup, so that measurement of the curvatures for both concave and convex surfaces having a large ROC can be done in a simple and quick way. The design of the zoom lenses for this application, principle of the measurement, and calibration of the zoom lenses are discussed. By means of the proposed method, radii of 1.5 m to infinity, concave or convex surfaces, can be measured in compact setups efficiently. The accuracy of the measurements can reach up to 0.04% for a surface having a radius of 10 m.
In a conventional particle tracking system, the depth of field is usually very small because of the use of high power imaging lens. The tracking accuracy may also be affected by the smearing of spot image, caused by focal shift. Increasing the focal depth and keeping uniform spot size in the focal region is highly desirable for a high accurate tracking system. In this report, we study the design of phase apdodizer that could be used to increase the focal depth of a tracking lens. The design is based on the requirements by highly accurate tracking that the point-spread function (PSF) of the lens keep an even and concentrated energy distribution when the lens is defocused. To achieve this purpose, a pure phase-shifting apodizer is introduced on the pupil plane of the lens. The function of the apodizer is to control the energy distribution of the 3D diffraction pattern near the focal region and make the effective spot size uniform or minimum variation along optical axis. The pattern of the 3D PSF of the lens with the apodizer shapes closed to a cylinder. New method used to search and optimize the design of the phase apodizer that meet the requirements of a particle tracking system will be studied. Theoretical analysis and numerical simulation are given in support of the method.
Optical coherent tomography (OCT) is a newly developed optical imaging technology that permits high-resolution cross-sectional imaging of an object. Most of the OCT imaging systems is developed for the biomedical applications, such as diagnostics of ophthalmology, dermatology, dentistry and cardiology. The technique behind these applications is the point scanning of laser beam penetrating into an object to obtain the internal features of the object. In this paper, we study a full-field OCT imaging system for acquiring information from a multi-layer information chip. This new system can be used in document security, identification and industrial inspection.
Differing from the biology related samples, the information chip consists of a number of thin layers with information coded on their surfaces. The surfaces of the layers are flat and specular with moderate reflectance. The information on one layer is retrieved through demodulating interference image of that layer. To obtain the tomography image of all the layers, the images in each layer are acquired and separated. The axial resolution of the system, usually defined by coherent length of light source, determines how close the separation of the two vicinal layers can be resolved. In this paper we explore a new approach to enhance the axial resolution of the OCT system. The method is based on a three-step phase shift algorithm to solve the tomography images from fused interference patterns. Theoretic study and simulation indicate that the method improves the system resolution and quality of retrieved tomography images for the multilayer information chip. Experiment results are also given in support of the proposed method.
Quantum operator algebra related to Jaynes-Cummings model is developed to design multi-reflector resonant bandpass filters for the first time. Transmittance and reflectance spectra of these filters are givens with analytic expressions. The results are found in agreement with those based on the existing filter design method. By selecting parameters such as r and N, designed filters can achieve a target spectrum profile with flat-top, large bandwidth, and minor ripples.
During the past decade, optical coherence tomography (OCT) has been vigorously developed into a powerful tool for biomedical diagnosis applications. Because this technology has the nature of extracting the internal features of an object, its applications can be extended to document security, biometrics identification, and industrial inspection. In addition, its high imaging resolution makes OCT an ideal tool for massive storage/retrieval of 3D data. In this paper, we propose the 2D parallel OCT system and its application for multiple-layer information retrieval. We will study the issues that exist exclusively in this type of application, such as interlayer phase/intensity modulation and the parasitic fringe patterns resulting from the surfaces of the information layer. The basic procedure of the proposed OCT system includes three steps: 1) extraction of cross-section raw images at each layer of an object; 2) removal of the interfering fringes by algorithm derived from multiple phase-shifted images; 3) elimination of interlayer modulations and parasitic patterns. Other issues that may degrade the retrieved images are also discussed. The simulation results and experimental tomography obtained from different testing samples are presented and discussed.
We developed a method of extending the depth of field of a microscope objective specifically used in an imaging system designed for small particle tracking. We extended the depth of field by inserting a quartic phase plate near the aperture stop plane of an objective. An optimum quartic phase plate was designed for a conventional 100X/0.8 microscope objective, and the simulation results predicated that the depth of field of the new objective could be increased more than twofold in comparison with an objective having no such phase plate.
We describe a new method of testing optical surfaces having a very large radius of curvature. The method combines a Fizeau interferometer with a set of specially designed zoom lenses. The zoom lenses make the test setup compact, convenient and flexible in testing optical surfaces having a very large radius of curvature. We review the design of the zoom lenses used for this purpose, and describe their performance, showing that reasonably good reference beams can be provided by these lenses to test optical surfaces having a large and variable range of radii.
We present a novel method of increasing the focal depth of an optical system that can be used in a star tracker. The method is based on a special phase plate that is placed in the vicinity of the aperture stop of an optical system to produce the required spot size over a large focal depth. Phase retardation was applied to a lens system having a focal length of 30 mm, an F-number of 2, a working wavelength range of 0.5~0.75 μm and a view angle of 20 degrees. The performance of a lens having a suitable quartic phase was analyzed, and it was shown that the focal depth of such a lens system can be extended more than threefold as compared to a system having no phase plate.
In this paper we present a normalized method of deriving a phase pupil function to extend the focal depth of imaging systems specially used for small object tracking. The method is based on the concept that the intensity distribution in the vicinity of the focal plane can be controlled and redistributed by means of a phase pupil function. This phase pupil function allows the peak intensity of a point-spread function (PSF) of the imaging system to remain relatively uniform, and the profile of the PSF to be approximately fitted to a Gaussian function in an extended range of the focal depth. A rotational symmetric aspheric phase plate has been designed and fabricated. The imaging system incorporating this pupil plate has extended the focal depth more than twofold compared with a conventional imaging system. Theoretical analyses and experimental results are also presented in support of this method.
We present a simple and effective method of reducing the background noise of a full-field optical coherence tomography system that improves the image quality of the system. The system is based on a modified Michelson interferometer providing such new features as a tilted cubic beam-splitter and a spatial filter incorporated in the back focal plane of an imaging lens. The new arrangement reduces background noise significantly. The effects of the tilted beam-splitter and spatial filter on the optical image are also studied, and experimental results are provided.
A microscope coherent optical processor (M-COP) has been specifically applied to the measurement of registration error in multi-layer integrated circuit wafers. This novel technique has resulted in a simple and elegant method for the inspection of both part- and fully-processed semiconductor wafers. The conventional methods of processed wafer inspection comprise of microscopical examination by skilled operators, extensive electrical parameter testing, and numerical image-processing. To apply any one of these techniques to a single chip on a wafer is extremely time consuming, and the number of samples that can be inspected on a production line is severely limited. However, real-time 100% inspection of wafers is one of the benefits of the inherent high resolution and immense speed of the M-COP. Further benefits are the early detection and location of faults, 100% quality assurance, and continuous condition monitoring.
Microscope coherent optical processor (M-COP) has been configured and used to inspect the micro-patterns on a silicon wafer in real time. A technique for the measurement of the scale change of this pattern has been devised. Theoretical and experimental results showing the viability of this technique are presented.
Inaccurate positioning and low-quality optics introduce position-dependent phase errors into coherent optical processors. For the inspection of composite objects, these lead to interference effects at the correlation plane and in particular the occurrence of blind spots through destructive interference. This in turn may result in a misinterpretation of the output. The circumstances under which this might occur are experimentally investigated.