Due to the loss of the flexibility of the crystalline lens, presbyopia is the most common vision dysfunction for adults after 40. To correct presbyopia, this paper presents a design of a MIOL, which can give extended clear vision range both in photopic vision(3mm pupil diameter) and in the mesopic vision(4.5mm pupil diameter). With a pseudophakic eye model, a multi-configuration with object distance covering a full range of normal visual from 8m to 0.4m was applied. The surfaces of MIOL were aspherical diffractive surface. MIOL was divided into two regions: the inner zone was optimized when the pupil diameter was 3mm and the outer zone was optimized when the pupil diameter was 4.5mm. Finally, we got a 22 diopters (D) MIOL with a central thickness of 0.652mm and an optical diameter of 4.5mm. By evaluating the modulation transfer function, we got optical performance of the pseudophakic eye with this MIOL. When the pupil diameter of pseudophakic eye was 3mm, MTF at 50c/mm and 100c/mm was respectively above 0.4 and 0.15 for the object distance from 8m to 0.4m. When the pupil diameter of pseudophakic eye was 4.5mm, MTF at 50c/mm and 100c/mm was respectively above 0.25 and 0.09 for the object distance from 8m to 0.4m.The visual acuity was above 0.9 for the whole visual range at both of two pupil diameters. Therefore it is safe to say that the new MIOL design provides good optical performance for whole visual range under both of the photopic vision and the mesopic vision.
When the pupil is dilated in dim light the higher-order aberrations increase and degrade badly visual performance.
So it is important that the wave-front aberrations of human eyes for scotopia vision with large pupil were developed.
Rod cells are dominant work for scotopia vision. Rod cells distribute in the periphery. The density of rod cells is
highest at 20ºvisual field and it drops by 50% at 50° visual field. Therefore, from the distribution of rod cells, the
research is significant for monochromatic aberrations of the eye across 50ºhorizontal visual field. Aberrations of the
human eyes in the horizontal visual field were measured with Hartmann-Shack wave front sensor. The
characteristic of third to tenth order Zernike aberration rms both temporally and nasally out to 50° is as follows:
considerable differences occur among subjects in the pattern of aberrations, particularly for the dominating
second-order aberrations; The third to tenth order Zernike aberrations increase with the visual angle, but the
increscent magnitude decreases as the Zernike order increases; in despite of imperfect symmetry, the increscent
magnitude is the same on the whole; the third-order Zernike aberrations increases up to 2.2 times from 0° to ±50°visual angle, the forth-order up to 1.6 times, and the fifth to tenth order up to 1.5 times.
KEYWORDS: Eye, Modulation transfer functions, Contrast sensitivity, Modulation, Monochromatic aberrations, Sensors, Visualization, System on a chip, Americium, Image quality
The quantitative analysis of the effect of aberrations in human eye on vision has important clinical value in the correction
of aberrations. The wave-front aberrations of human eyes were measured with the Hartmann-Shack wave-front sensor
and modulation transfer function (MTF) was computed from the wave-front aberrations. Contrast sensitivity function
(CSF) was obtained from MTF and the retinal aerial image modulation (AIM). It is shown that the 2nd, 3rd, 4th, 5th, 6th
Zernike aberrations deteriorate contrast sensitivity function. When the 2nd, 3rd, 4th, 5th, 6th Zernike aberrations are
corrected high contrast sensitivity function can be obtained.
The variation of the wavefront aberration with accommodation was investigated based on the eye model of
Gullstrand-Le Grand. The anterior lens radius was optimized at different accommodation to focus the image at the retina,
and the RMS and PV wave-front error of human eye were compared at different accommodation. The PV value of
wavefront aberration from 0.718 waves increases gradually to 0.904 waves and RMS value from 0.21 waves to 0.26
waves when accommodative stimuli varies from 0 to - 5 diopters. The change of PV value is 0.186 waves which is less
than the Rayleigh diffraction limit λ/4, and the change of RMS is 0.05 which under Marechal diffraction limit λ/14.
Therefore, the change of the wavefront aberration caused accommodation can be ignored when wavefront aberrations
in the human eye are corrected with surgery or wearing glasses.
In order to understand the relative contribution of the wave-front aberrations of the cornea and the crystalline lens to the retinal image quality in the human eye, we have measured the wave-front aberrations of the anterior corneal surface, the posterior corneal surface and the complete eye with a corneal topographic system (Orbscan) and a Hartmann-Shack wave-front sensor. The 20 subjects selected to participate in the study are all no eye diseases, covering a range of age from 18 to 25. All the subjects have refractive errors of defocus varying from 0.5 D to 5 D and astigmatism varying from 0.1 D to 1.5D. Using the Orbscan, we obtained the discrete set of corneal elevation data in radial distribution over the pupil plane for the anterior and the posterior corneal surfaces directly, and the data are then transformed into wave-front aberrations of both the corneal surfaces. The wave-front aberrations of the two surfaces are then used to acquire the aberrations in whole cornea. The aberration contribution of the crystalline lens is obtained by subtracting the aberrations in the cornea from that in the complete eye. It is shown that the combination of the aberrations between the crystalline lens and the cornea could be either a compensatory or an additive process. The effect of the combination between the anterior and the posterior corneal surface is also complicated, and the aberration compensation, as well as aberration addition can be observed. It is shown from statistics point of view that the anterior corneal surface contributes more lower-order aberrations (astigmatism) to the complete eye, while the posterior corneal surface and the crystalline lens play a more important role in contributing higher-order aberrations.
Wavefront aberrations of human eye are expected to change when the eye accommodates to targets from infinite distance to clear visual threshold distance (25 centimeters distance from target to eye). It is significant to measure and analyze the wavefront aberrations in the accommodated human eye, which helps to evaluate visual performance and has clinical value.
The previous research on the effect of accommodation on the wavefront aberration all adopted subjective measurement technique. In this paper, we firstly adopt Hartmann-Shack wavefront sensor technique, which possesses advantages in comparison with the psychophysical subjective technique such as larger sampling points. Data from 20 eyes are reported in this study. Ages of all subjects range from 19 to 38 and defocus of them range from -6D to +3D. Every pupil size is greater than 5mm for whole eye measurements. No one in this experiment has a record of ocular disease.
Root-mean-square (RMS) and peak-to-valley (PV) values of wavefront aberration have been evaluated. In a comparison between the clear visual threshold condition and the infinite distance condition, the subject DQ has the larger change in RMS wavefront error, from 0.85 μm at infinite distance to 0.43 μm at clear visual threshold distance. The RMS difference is about 0.42 μm which is 50% in proportion to the RMS value at infinite distance. While the subject JL has the smaller change of 23% in RMS wavefront error, just from 0.66 μm to 0.51 μm between two different accommodative conditions. Defocus and astigmatism have been excluded in this paper. It is found that accommodation influences wavefront aberrations of whole eye and the situation varies substantially from individual to individual. We have to consider not only the wavefront aberration at the infinite distance but also that at the clear visual threshold distance during clinical ocular therapy.
In this paper the performance of Hartmann-Shack wave-front sensor in the aberration measurements of human eyes is investigated and the accuracy and repeatability of measurements are presented qualitatively and quantitatively.
Based on the widely used Gullstrand-Le Grand eye model, the individual human eye model has been established here, which has individual corneal data, anterior chamber depth and the eyeball depth. Furthermore the foremost thing is that the wavefront aberration calculated from the individual eye model is equal to the eye's wavefront aberration measured with the Hartmann-shack wavefront sensor. There were four main steps to build the model. Firstly, the corneal topography instrument was used to measure the corneal surfaces and depth. And in order to input cornea into the optical model, high order aspheric surface-Zernike Fringe Sag surface was chosen to fit the corneal surfaces. Secondly, the Hartmann-shack wavefront sensor, which can offer the Zernike polynomials to describe the wavefront aberration, was built to measure the wavefront aberration of the eye. Thirdly, the eye's axial lengths among every part were measured with A-ultrasonic technology. Then the data were input into the optical design software -ZEMAX and the crystalline lens's shapes were optimized with the aberration as the merit function. The individual eye model, which has the same wavefront aberrations with the real eye, is established.
A novel wavefront reconstruction algorithm used in the visual science for the wavefront aberration of the human eye with use of the Hartmann-Shack (H-S) sensor is proposed in this paper. We model the gradients of H-S sensor with the Fried geometry. Iterative discrete Fourier transform and the correspondent inverse filter in spatial frequency domain are introduced. The processing of the boundary condition in our algorithm becomes easy and natural, and it is with no necessary to derive the boundary gradients from the measured data. The simulations and experimental results show that the new iterative algorithm can accurately offer the estimated wavefront and gradient data, especially in high precision measurement where the signal-to-noise ratio is high.
As the micro-display applied to head-mounted display, the optical system not only suits for the small size of the micro-display, but also provides sufficient eye relief and exit pupil, and it becomes perplex. For settling this problem, a head-mounted display, which combines a hybrid diffractive-refractive eyepiece with a reflective relay system using a liquid crystal on silicon (LCOS) with the diagonal size 18mm, was designed. Basing on a Zeiss (60°) eyepiece, and replacing the doublet of it of a diffractive-refractive doublet, a hybrid eyepiece with 20mm eye relief and 10mm exit pupil was designed. The weight greatly reduced and the optical performance improved of the eyepiece compared with the Zeiss one. Considering the space for illuminating source of LCOS, a reflective relay system was used, which includes a flat half mirror and a concave mirror. The magnifying power of the relay system also makes the optical system suitable for the small size of LCOS. The system is with high performance, sufficient exit pupil and eye relief, and reasonable size and weight in the specific application of head-mounted display.
Harmonic diffractive surface element is successfully introduced to the system of infrared dual band in this paper. It has been simultaneously accomplished that the rectification of the Transverse ray, Lateral color and Longitudinal aberration in both band, wave front aberration less ¼ wave length and Modulation Transfer Function of dual band approaching or attaining the diffraction limit. The properties of action spectrum of harmonic diffractive are between refractive element and diffractive, which debased the demand for technical level. The practical design not only shows that the system is compact, few elements and high rates of transmission but also has better weaken-ray aberrations character and 100% cool diaphragm efficiency. The harmonic diffractive element offers a new component for optics designs.
Two-wave mixing properties of a Ce:KNSBN photorefractive crystal is experimentally studied while the ihcoherent erasing technique is applied. As the signal beam is with extraordinary polarization and the polarized direcitn of the pump beam has an angle φ with its extraordinarily polarized direction, the gain of the signal beam is measured with respect to the angle φ. Because of the erasing of the fanning by the ordinary component of the pump beam, the gain enhances at small angle φ and obtains its maximum at φ = 30°. The couple-wave theory with considering of the fanning effect is used to fit the experimental data and the fitting curve is coincident wiht the experimental data very well. The calculated results of the gain as a fucntin of the angle φ for different fanning factor are given out. Finally the enhancement of the gain is experimentally measured with respect to the angle between the signal beam and the normal of the crystal face. While this angle takes θ=11°, the enhancement of the gain obtains its minimum value, which means the minimum fanning.
Properties of degenerate four-wave mixing in a Ce:KNSBN photorefractive fiber-like crystal under the conditions that the angle between the pump beam and the signal beam is smaller and bigger was studied. It is found that there are two interaction regions of degenerate four-wave mixing in the sample when the angle is bigger, and four-times enhancement of the maximum phase-conjugate reflectivity compared with that in smaller angle condition is obtained. The experimental results of the phase-conjugate reflectivity versus the intensity of signal beams, and versus the ratio of the pump beams are presented, which are numerically fitted by theoretical equations. They are coincident quite well. The property of the four-wave mixing gratings and the phase-conjugate response time of Ce:KNSBN photorefractive fiber-like crystal were studied. The response time could be faster, in an order of second in our experimental conditions.
The fanning and the two-wave mixing properties of Ce:KNSBN photorefractive fiber have been studied. The fanning exhibits a strong nonlinear dependence on the incident angle, which differs not only from the bulk Ce:KNSBN crystal but also from the reported photorefractive fiber of other materials. The two-wave coupling gain is also strongly pump beam incident-angle dependent, restricted seriously in a narrow incident angle range, which is attributed to the internal reflection from the side-surface and the fanning effect as well. The numerical fitting method is adopted, which shows to be coincident with the experimental data. The photorefractive fibers have potential applications in signal amplification, holographic storage and phase-conjugation, especially incorporation into optical fiber systems.
The property of phase-mostly modulation of the SVGA1 spatial light modulator, which is manufactured by CRL Ltd. in UK., was investigated and the phase shift of (pi) was achieved. The Dammann grating of binary-phase device for fan-out up to 5x5 was designed and the data of the phase device were fed into the liquid crystal display. The 5x5 array of spots was produced. It has been found that the spatial light modulator can be used as a phase modulated binary optical device to realize some functions in the laboratory.
IN this paper, the advantage and disadvantage of several seal imprint recognition methods have been compared, and an approach for seal imprint recognition based on ring- projecting template matching is proposed. Firstly, the seal important in divided into some rings, and the local and global intrinsic features are extracted. The, the recognition is made, with the border and the words of seal imprint separated, by 1D template matching. The experimental results show that the proposed approach is of adaptability and reliability.
In this paper we present a coherent image processor, which uses the loop-like nonlinear diffraction property of the Ce:KNSBN photorefractive crystal to achieve real-time edge- enhanced optical correlation and optical pattern recognition. The full-width-at-half-maximum of the auto- correlation peak is decreased four times by the edge- enhancement operation. The intensity ratio between auto- correlation peak and the cross-correlation peak is improved nearly two times. As the same time the lobe of the auto- correlation peak and the background 'clutter' noise are obviously suppressed. Therefore the discrimination of this system achieves great improvement.
KEYWORDS: 3D image processing, 3D metrology, CCD cameras, Cameras, 3D modeling, 3D vision, Imaging systems, Image processing, RGB color model, Calibration
We proposed a method for 3D shape measurement of moving human body by use of stereo vision technique. To resolve the matching problem of two images, we use the characteristic of the independence of red, green and blue in color space and propose a color-coded technique used to search the corresponding points of two images in the measurement. Using two sets of optical imaging systems we can obtain the color images of a moving human body in different directions. The corresponding points of two images detected with CCD cameras are found out by computer image processing. The 3D information of a moving human body can be obtained based on the parallax of the corresponding points in the two images. By this means, not only can the 3D shape of human body be measured but also the moving action of human body can be tracked.
Based on the nonlinear property of the moving grating in BSO crystal in four-wave mixing architecture at large fringe modulation, i.e. the enhancement of the reflectivity increases as the incident beam ratio increases and the grating with large pump beam ratio can obtain higher enhancement of the reflectivity, we achieve edge-enhancement and edge-enhanced optical correlation of a binary optical image by applying the moving grating in the Fresnel transform four-wave mixing system. The relative intensity of the edge of the object is enhanced nearly 2 times. The Full- Width-at-Half-Maximum of the auto-correlation peak and the fluctuation noise if obviously suppressed, which indicate that a significant improvement in the discrimination capability of the correlator is achieved.
Fingerprints are usually compared based on the matching of such features as ridge bifurcations and endings. However, when features are extracted from a thinned fingerprint, pseudo-features are usually introduced as well. In this paper, we propose an approach in which points on a fingerprint ridge can be traced and recorded in a chained list with a 3 X 3 window. based on the proposed approach, an algorithm to remove pseudo-features from a thinned fingerprint image is developed. The algorithm is carried into execution using a library of thinned fingerprint images with such pseudo-structures as spurs, bridges and circles, and it is found that the pseudo-features can be correctly and totally removed with high efficiency.
The main goals of the color image enhancement are to sharp contrast the image while preserving the natural appearance of the image. Some works have been done to process color images in luminance, hue and saturation attributes. But there are some problems by using these methods. Other attributes of the image color will been varied if one of its attribute is changed. In this paper, we analysis the true color image processing method, presented that the luminance value of the image color should be adjusted to suitable range, then the saturation enhancement under the certain luminance can be performed in the RGB color space, L*u*v* color space and L*a*b* color space to get the best saturation effect. We calculated some typical color differences produced by the luminance adjustment method and the saturation enhancement method. Then we compared the color differences in these three color spaces. As a result, we concluded that the different method should be chosen according to the different color images. Some images were processed with these methods and the best visual effect were obtained.
Two-wave coupling between orthogonally polarized beams in a Cerium doped potassium sodium strontium barium niobate crystal is studied. The coupling gain coefficient, the response time and the saturation diffraction efficiency of the volume grating are measured with respect to the angle (phi) between the polarized direction of the pump beam and the c-axis of the crystal. It is found that they have the similar variation behavior. In our experimental condition, the maximum coupling gain coefficient is 3.2 cm-1, the maximum response time is about 55 seconds and the maximum saturation diffraction efficiency is about 18.5%. The maximum values are obtained at (phi) =20 degree(s) and (phi) =160 degree(s). Numerical calculated results from the couple-wave equations are given, which are coincident with the experimental data.
The nonlinearity of phase-conjugate beam reflection with four-wave mixing in BSO crystal by the moving grating at large fringe modulation formed by the incident-beams ratio is investigated. The experimental results have shown that the optimum fringe velocity is the incident-beam ratio and the total-light-intensity dependent, the reflectivity at the optimum fringe velocity is the incident-beam ratio and the fringe-spacing dependent. Based on these nonlinear properties, the edge-enhancement of an object is achieved.
Degenerate four-wave mixing in a cerium doped potassium sodium strontium barium niobate photorefractive crystal is studied. The transmission grating is dominated in our experimental geometry that the bisector of the pump beam and the signal beam is normal to the c-axis of the crystal. As the fringe modulation depth of this transmission grating varies, the variation of the conjugated beam intensity forms a loop. Based on this nonlinear property, real-time optical image edge-enhancement processing as well as real-time edge- enhanced optical correlation is obtained without the reverse of the signal-to-pump beam intensity ratio. The full-width- at-half-maximum intensity of the auto-correlation peak is one fifth of that without the edge-enhancement operation. The computer simulation results are given, which are coincident with the experimental data very well.
KEYWORDS: 3D metrology, 3D image processing, CCD cameras, 3D modeling, Imaging systems, Inspection, 3D acquisition, Image compression, Projection systems, Head
A fast and efficient technique for profilometric measurement using color-coded grating is proposed. Four colors are used to code the grating and each color represents only one logical state. There are 48 stripes in one period of the color grating, which is large enough for normal measurement. As compared with the previous techniques, it has the advantages of simple hardware without moving mechanical part, single exposure for obtaining 3D information, little influence of the noise and the nonlinearity of the CCD camera on the measurement accuracy, and higher anti- color-blurring capability. The suggested technique is suitable for on-line inspection and dynamic measurement of moving objects.
The diffraction efficiency of volume grating written by two- wave mixing in Ce:KNSBN photorefractive crystal as a function of the writing beam ratio for different polarized reading beam is experimentally studied. It is found that, the polarization and the incident direction of the reading beam strongly affect the diffraction efficiency. In the selected direction, the extraordinarily polarized reading beam obtains enhanced diffraction and achieves nearly fifteen times larger diffraction efficiency than the ordinarily polarized reading beam. The modified coupled-wave theory is used to fit the experimental data and the fitting result are coincident with the experimental result. We also theoretically examined the realization between the diffraction efficiency and the amplitude coupling constant k of the reading beam and its diffracted beam. As k < 6cm-1, the diffraction efficiency has single maximum and the maximum diffraction efficiency increases as k increases. As k > 6cm-1, the diffraction efficiency curves exhibit two peaks. But the central position of the curves does not change with the variation of k.
In this work, we propose a novel thresholding method to simplify the procedure of the binary joint transform correlator. Unlike the normal binary joint transform correlator which thresholds on the power spectra of both the reference image and the target image, we threshold on the power spectra of the reference image only. With this technique the additional on-line recording of the power spectra of the target is avoided. Therefore the procedure of the recognition is as simple as that of the normal joint transform correlator. We then extend the binary joint transform correlator to circular harmonic expansion to achieve the rotation invariant optical pattern recognition. We use a computer to decompose the reference image into a sum of circular harmonic components and form an input of the joint transform correlator with the first-order circular harmonic component and the target image. By use of this technique, we achieve circular-harmonic-based binary joint transform correlation with good performance merits. Computer simulation results and 3D output correlation profiles are presented.
KEYWORDS: RGB color model, 3D metrology, CCD cameras, 3D modeling, Imaging systems, 3D image processing, Inspection, Image processing, Projection systems, 3D image reconstruction
A color-coded projection grating is used to provide means of measuring 3D surface profiles. In conventional 24 bits RGB model, each color has 256 gray levels, whereas we use only the levels of 0 and 255 to maximize the difference of gray levels. Thus there are eight colors which can be used to code the grating. They are white, red, green, blue, cyan, magenta, yellow, and black. In order to get a large space period grating, we code the grating on a specific order. If we use eight kinds of colors to code the grating, we can get 64 strips in one period. In this case the space period of the projection grating is large enough in the most of measurement of surface profiles. Only one image is needed in 3D measurement and so it is suitable for on-line inspection. In our system the measurement error is less than +/- 1.3 mm.
We attach micro-cylindrical lenses with D/f' equals 4/3 to 300 W Q-CW LD array, pre-compressing the divergent angle in fast-axis plane from 40 degree(s) to 9.6 degree(s). Then we use lens duct as optical coupler in LD array end-pumped Nd:YAG laser. The transfer efficiency is 90%, and well convergent effect is also obtained near the output face of lens duct. At last, we get 37.9% light-light conversion efficiency of 1.06 micrometers light at 1% duty factor, and the output beam is good.
Moving gratings at large fringe modulation and optical bias in photorefractive crystal Bi12SiO20 are investigated. With two-wave mixing architecture, the optimum fringe velocity and the enhancement of the diffraction efficiency exhibit strong nonlinear dependence on the fringe modulations. With four-wave mixing architecture, not only these nonlinear effects still exist but also the optimum pump beam ratio is totally different from a stationary grating. It is also found applying optical bias into moving gratings that the diffraction efficiency exhibits unexpected behavior. Experimental results of these nonlinear effects are presented.
A new spatial filter, the quantized amplitude compensated matched filter is proposed. It is characterized as amplitude modulation only with several discrete grey levels. As compared with the amplitude-compensated matched filter, the Horner efficiency is quite poor. However, the high discrimination is preserved, and an amplitude-modulated spatial light modulator might be accommodated. The circular harmonic version of this filter is also investigated.
Moving grating technique is applied to dynamic holographic recording to overcome the difficulties of the fluctuation of the diffraction efficiency and the funning effect in photorefractive crystal BSO. Various nonlinear effects caused by moving gratings at large fringe modulations are experimentally investigated. It is shown in the application of optical pattern recognition that the probability of an error detection is reduced and the signal-to-noise ratio is considerably enhanced. Experimental results are presented.
Moving gratings is an effective method to improve the diffraction efficiency of dynamic gratings. However there is a sudden drop in the optimum fringe velocity when the fringe modulation is close to unit, which restricts its applications. We experimentally showed that optical bias is an effective method of overcoming this problem. We also found that within a certain range of optical bias, the absolute diffraction efficiency can be higher than that without optical bias, which is not the case when using a stationary grating.
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