The finite difference time domain method (FDTD) is a popular and effective numerical approach for electromagnetic analysis. However, the original explicit FDTD suffers from two primary limitations: the time step is constrained by the Courant-Friedrich-Levy (CFL) condition, and it requires significant amounts of computer memory, particularly when analyzing large objects with fine structures. In this paper, we present a new FDTD algorithm called Reduced-Leapfrog Alternating-Direction-Implicit FDTD (R-Leapfrog ADI-FDTD), which is unconditionally stable and reduces computer memory usage by approximately 23%. The algorithm is based on a conservation formula derived from the conventional electromagnetic divergence. This formula describes the spatial dependence of the field components obtained by the one-step leapfrog ADI-FDTD. By leveraging this spatial dependence, we are able to locally calculate and temporarily store two of the six field components during each iteration, while the remaining four components are stored over the entire 3D spatial grid as usual. Our simulations show that the results are in excellent agreement with those obtained from the original explicit FDTD and one-step leapfrog ADI-FDTD, demonstrating the algorithm’s unconditional stability and accuracy. R-Leapfrog ADI-FDTD is a valuable tool for electromagnetic analysis when computer memory is a critical factor.
Zoom system is an optical system of which the focal length can be changed continuously within a certain range, while the image plane keeps stable and the image quality remains good. Zoom system usually consists of fixed group, variable group and compensation group. However, designing a zoom system can be a complex task due to the large number of variables involved in the optical design. One of the critical challenges is to obtain an effective initial structure of the zoom system. In this paper, a design method based on Delano diagram is proposed to establish the first-order model for the initial structure of the zoom system, which describes the relationship between the zoom ratio, focal length, and other parameters. On the basis of the model, the first-order merit function of the zoom system is analyzed and derived. By controlling the merit function with the help of the algorithm optimization, the first-order solution for the initial structure of zoom system is obtained and can be used for subsequent optimization. In order to further prove the effectiveness of the initial structure, the first-order solution is converted into an actual lens according to the properties of the zoom system. After further optimization, a zoom system with good image quality is obtained, which indicates that the initial structure of the zoom system is of great optimization potential. The final result shows that the design method proposed in this paper provides a helpful approach to solving the problem in obtaining an effective initial structure of the zoom system.
Unlike the conventional design of aspheric shaping systems, in order to provide a laser source for applications such as multi-beam laser interference, which can maintain evenly distributed power over a large distance, the influence of shape parameter and aperture on long-distance propagation performance of Kepler refractive beam shaping system is studied. Current work describes the lens, designed automatically by using ZEMAX programming language (ZPL), and simulations of Kepler refractive shaping systems of flattened Lorenz (FL) beams with different shape parameters and apertures.
The damped least squares (DLS) method is widely used in optical system design due to its great advantages in the speed of convergence and robustness. However, it is easy to get stuck into local minima, which is probably very close to the starting point, leading to a small search range. The particle swarm optimization (PSO) algorithm is one of the most popular intelligent optimization algorithms which is used to handle problems with a large number of variables benefits from its great randomness. It is helpful to use PSO to deal with situations when getting stuck into local minima. It can jump out of the local minima easily for its randomly searching mode. In this paper, we proposed a novel optimization method for the optical system design which is based on the combination of the improved PSO with DLS to achieve a balance between local and global optimization. By combining the improved PSO with DLS, we can prevent the whole system from falling into the local minima and improve the stability of the algorithm. First, we use the improved PSO to search in the planning area randomly. Second, after finishing the process of SA-PSO, the DLS is added to continue optimizing in a small range to find the final solutions. A machine vision lens has been designed by our proposed optimization algorithm, and the results demonstrates that this algorithm is effective for optical system design.
Computer Aided Optical System Design is an engineering practice course for undergraduate students in College of Optical Science and Engineering, Zhejiang University. When the students have just completed Applied Optics course in spring-summer semester, they will take the practice course in a short semester in summer vocation. This is a projectbased practice course, including optical software developing and lens design. The teaching idea is not only to improve the students’ engineering skills but also to connect different knowledge they have studied, to build a comprehensive knowledge structure, and to develop the team spirit, organizational capability, leadership and communication skills. This course is designed as an engineering project with a contract between the teacher group and every design group of 3 students. In this paper we describe the course program and how to provide a chance to combine different knowledge into a project. In every student group, developing ray trace software of good reliability is the teamwork, and each student will design a photographic lens independently. The lens with the best optical performance will be selected as the team’s result, and be drawn into a system diagram and part drawings. The whole process is both competitive and cooperative, and gives the students the experiences of programmers and lens designers. Most of the students appreciated the practice course and named it as “the most memorable short semester”.
In this paper, a method for inspecting the defective lenses is proposed. Defects will not only affect the performance of the system, but also do harm to the experiment. Therefore, it is critical to find them out before lenses are used. The principle we adopted here is the laser diffraction and the light source we employed is a He-Ne laser whose diameter is closed to 0.5 mm when focused on the sample. Cooperated with the platform proposed, a convergent lens is placed to collect the diffracted light from the defects while the normal reflecting light is reflected by the mirror attached to it. Thanks to this, the diffracted light can be separated simply. In addition, a circuit module with the chip named max44009 is applied to detect the intensity of diffractive light. Compared to the intensity data obtained by the computer with the threshold we have set automatically, the machine could judge whether the defect is existing. Moreover, this method can detect lenses with various curvatures and calibers. Finally, the system performance is assessed by conducting a series of tests using commercial lenses.
Fourier ptychographic microscopy (FPM) is a newly developed imaging approach for achieving wide field and high resolution. However, image quality will degraded by the pupil aberration because of the limitation of geometrical optics. In this paper, two correction algorithms of pupil aberration combining original FPM algorithm with ptychographical iterative engine (PIE) are presented and justified. And the standard coefficients of Zernike polynomial are applied for constructing the pupil aberration in the simulation. Compared to original FPM algorithm, these algorithms add constraints to the sample and the pupil during each iteration, so that the image can be reconstructed and the pupil function can be recovered simultaneously. Furthermore, we illustrate that these algorithms can not only improve robustness, but also have faster convergence under different aberrations.
Some imaging optical systems include diffraction elements, both the even reflected stray light and multi-order diffraction stray light need to be considered at the image. They are related to the reflectivity and diffraction efficiency of optical surfaces. In this paper the binary tree is employed to describe the multifurcating tree in which each sampling ray’s information is kept. According to the multi-order diffraction efficiency, paraxial ray and real sampling rays are traced, and the calculating results are applied to analyze the stray light in optical systems including diffraction components, and then the stray light energy distribution at any space especially at the image can be obtained. A new calculated wavelength is used to replace the designing wavelength for binary optical elements to calculate the reflected diffraction stray light. Based on the principles above, the stray light analysis software is developed. By tracing and analyzing all sampling rays the positions of ghosts are shown, especially at image surface. In this procedure, the first surface of the system serves as the entrance pupil or stop, instead of the entrance pupil in original imaging system, so as to collect all sampling rays from all direction, in or out the field of view, and then all possible ghosts are obtained. According to the simulation, the glare shields or control methods can be designed.
An optimized scheme to extract the depth information in the 4D light field data is proposed with the advantage of conciseness. The depth information of a light field scene is estimated according to the disparity of edge pixels. Depths of smooth regions are interpolated after region segmentation. A computer generated light field scene is used as an example to test the validity of our algorithm. We restrict the time complexity of our algorithm to logarithmic linearity, which is available in practical use and is promising in parallel computing.
With the rapid development of security market, the glass-plastic hybrid lens has gradually become a choice for the special requirements like high imaging quality in a wide temperature range and low cost. The reduction of spherical aberration is achieved by using aspherical surface instead of increasing the number of lenses. Obviously, plastic aspherical lens plays a great role in the cost reduction. However, the hybrid lens has a priority issue, which is the large thermal coefficient of expansion of plastic, causing focus shift and seriously affecting the imaging quality, so the hybrid lens is highly sensitive to the change of temperature. To ensure the system operates normally in a wide temperature range, it is necessary to eliminate the influence of temperature on the hybrid lens system. A practical design method named the Athermal Material Map is summarized and verified by an athermal design example according to the design index. It includes the distribution of optical power and selection of glass or plastic. The design result shows that the optical system has excellent imaging quality at a wide temperature range from -20 ℃ to 70 ℃. The method of athermal design in this paper has generality which could apply to optical system with plastic aspherical surface.
Due to diffraction and aberrations, images will be degraded during the imaging process. It is needed to find a way to correct the aberration without changing the structure of imaging system. In this paper, a method for improving image quality and obtaining higher resolution is presented. The process of rebuilding high-resolution image from blurred image illuminated by structured light can be viewed as solving equations. The values of pixels in the clearer picture we want are the unknowns and the value of each pixel on the image plane is the weighted cumulate of them, of which the coefficient is decided by the point spared function of the imaging system. More non-equivalent equations are needed to get the solve because the coefficient-matrix is singular. In this passage, the equations mentioned above are the pictures with structured light. As shown by the simulation and experiment that the image quality is improved markedly. Compared with the image enhancement algorithms like Sobel sharpen, the algorithms with structured illumination can rebuild a more accurate image.
The shape of the aspheric lens changes caused by machining errors, resulting in a change in the optical transfer function, which affects the image quality. At present, there is no universally recognized tolerance criterion standard for aspheric surface. To study the influence of aspheric tolerances on the optical transfer function, the tolerances of polynomial fitting are allocated on the aspheric surface, and the imaging simulation is carried out by optical imaging software. Analysis is based on a set of aspheric imaging system. The error is generated in the range of a certain PV value, and expressed as a form of Zernike polynomial, which is added to the aspheric surface as a tolerance term. Through optical software analysis, the MTF of optical system can be obtained and used as the main evaluation index. Evaluate whether the effect of the added error on the MTF of the system meets the requirements of the current PV value. Change the PV value and repeat the operation until the acceptable maximum allowable PV value is obtained. According to the actual processing technology, consider the error of various shapes, such as M type, W type, random type error. The new method will provide a certain development for the actual free surface processing technology the reference value.
Nowadays with the growing threat of terrorist attacks throughout the world, effective security technologies are of urgent need to protect crowds and critical infrastructure. Terahertz wave has emerged as a more powerful tool in security. Terahertz wave is able to penetrate dielectrics such as plastic and cloth so as to detect weapons and contraband hidden under people's clothing without harming human bodies. Nevertheless, image obtained in this frequency range is pretty poor because the diffraction at their relatively long wavelength cannot be ignored in such case. In this paper, we shall briefly introduce the high-resolution (HR) reconstruction for terahertz imaging utilizing the ideology and methodology of super-resolution (SR) restoration in image processing which aims at recovering a high-resolution image from a single low-resolution image. Through the preliminary feasibility research, we applied the image super-resolution algorithm based on the deep convolutional neural network (CNN) to the single passive terahertz image reconstruction. Our deep CNN demonstrates state-of-the-art restoration quality and achieve fast speed as well. Our results indicate that the processed passive terahertz images have clearer edges as well as outlines and are easier to identify suspicious items than the original ones. On the whole, our method outperforms other methods such as the interpolation method and the learning-based image super-resolution reconstruction algorithm. The results indicate a promising prospect for HR terahertz imaging reconstruction.
Fisheye lens forms a circular image on the image plane which is different from people’s perspective view. This paper introduces two practical methods to correct the fisheye image from distortion. Distorted images can be corrected to the perspective views which are suitable for people to watch by rectilinear projection based on lens functions. This paper extended this method so that it can correct images taken by fisheye lens over 180°. Since the rectilinear projection method has the limitation that it can only correct a ROI, the second method based on an improved cylinder projection is proposed to overcome this limitation. The picture corrected by this method has less deformation compared with traditional cylinder projection method.
In the teaching of design courses, the process of students to complete the designs is considered more important than the final results, and usually there are no standard answers for these designs. Thus, the research on the process evaluation method in design courses is of great significance. Taking the assessments of two design courses in optical discipline as examples, the psychophysical experimental methods are introduced into the process evaluation of the design courses, i.e. the process evaluation given by each student to others in forms of classification, sorting or grading are adopted as one trial of a psychophysical experiment, which generate many experimental data of mutual evaluation. Based on these data, evaluation results are measured scientifically using the statistical method. Furthermore, through correlation analysis and regression analysis of these data, the relationship among various aspects of different process can be studied. It is easier for students to understand and accept their assessment results, and more helpful for teachers to analyze the influencing factors in their teaching process.
In order to realize the sharing of high quality course resources and promote the deep integration of ‘Internet+’ higher education and talent training, a new on-line to off-line specialized courses teaching mode was explored in Chinese colleges and universities, which emphasized different teaching places, being organized asynchronously and localized. The latest progress of the Chinese National Optical Education Small Private On-line Course (CNOESPOC) system set up by Zhejiang University and other colleges and universities having disciplines in the field of optics and photonics under the guidance of the Chinese National Steering Committee of Optics and Photonics (CNSCOP) was introduced in this paper. The On-line to Off-line (O2O) optical education teaching resource sharing practice offers a new good example for higher education in China under the background of Internet +.
Applied optics course in Zhejiang University is a National Excellent Resource Sharing Course in China, and the online to offline teaching strategies have been implemented and shared with dozens of universities and colleges in China. Discussion is an important activity in teaching. In this paper our main consideration is designing the discussion questions and group works so as to develop the students’ critical thinking, cooperative and sharing spirits, and communication abilities in the cosmopolitan era. Typical questions that connect different chapters and help the students to understand the relationship between each sub-system in both field of view and aperture are given for discussion. We inspire the students to complete group works such as ray trace programming by cooperation and then make presentations. All of these create a circumstance for sharing thoughts and developing intelligence and knowledge. A poll shows that the students pay more attention to optical design than before and have made progress in conversation and cooperation.
Self-focusing is observed in nonlinear materials owing to the interaction between laser and matter when laser beam propagates. Some of numerical simulation strategies such as the beam propagation method (BPM) based on nonlinear Schrödinger equation and ray tracing method based on Fermat’s principle have applied to simulate the self-focusing process. In this paper we present an iteration nonlinear ray tracing method in that the nonlinear material is also cut into massive slices just like the existing approaches, but instead of paraxial approximation and split-step Fourier transform, a large quantity of sampled real rays are traced step by step through the system with changing refractive index and laser intensity by iteration. In this process a smooth treatment is employed to generate a laser density distribution at each slice to decrease the error caused by the under-sampling. The characteristics of this method is that the nonlinear refractive indices of the points on current slice are calculated by iteration so as to solve the problem of unknown parameters in the material caused by the causal relationship between laser intensity and nonlinear refractive index. Compared with the beam propagation method, this algorithm is more suitable for engineering application with lower time complexity, and has the calculation capacity for numerical simulation of self-focusing process in the systems including both of linear and nonlinear optical media. If the sampled rays are traced with their complex amplitudes and light paths or phases, it will be possible to simulate the superposition effects of different beam. At the end of the paper, the advantages and disadvantages of this algorithm are discussed.
The split-step Fourier method (SSFM) is introduced to analyze the beam propagation in a relatively large-sized turbulent filed, whose refractive-index profile is already detected. The numerical method is achieved by fast Fourier transform (FFT).To obtain the optimal sampling number, we propose an adaptive spread-spectrum method as an optimization. The SSFM is widely used for solving the nonlinear Schrödinger equation [1].The advantage of the SSFM is apparently its simple formalism and suitability to our situation. The direct numerical solution of the Helmholtz equation, derived from this method, yields detailed information of the spatial and angular properties of the propagation beam. On the other hand, a set of approximations restrict its applicability, the requirements for the accurate application of the method are summarized and a set of formulas is generalized in this paper. The efficiency of the SSFM depends on the sampling number, the adaptive spread-spectrum method yields optimal sampling number to increase the computational efficiency .To testify the accuracy of our algorithm, we use graded-index medium as the turbulent filed, for the reason that the beam propagation in turbulent field with random refractive-index profile is ruleless and has no unified reference. The simulation result testifies our algorithm is tremendously accurate, capable of selecting the optimal N automatically and much more computationally efficient than the original algorithm.
Quite a lot of factors will make effects on beam pointing stability of an optical system, Among them, the element tolerance is one of the most important and common factors. In some large laser systems, it will make final micro beams spot on the image plane deviate obviously. So it is essential for us to achieve effective and accurate analysis theoretically on element tolerance. In order to make the analysis of beam pointing stability convenient and theoretical, we consider transmission of a single chief ray rather than beams approximately to stand for the whole spot deviation. According to optical matrix, we also simplify this complex process of light transmission to multiplication of many matrices. So that we can set up element tolerance model, namely having mathematical expression to illustrate spot deviation in an optical system with element tolerance. In this way, we can realize quantitative analysis of beam pointing stability theoretically. In second half of the paper, we design an experiment to get the spot deviation in a multipass optical system caused by element tolerance, then we adjust the tolerance step by step and compare the results with the datum got from tolerance model, finally prove the correction of tolerance model successfully.
Wavefront Coding is a new method to extend the depth of field, which combines optical design and signal processing together. By using optical design software ZEMAX ,we designed a practical wavefront coded imaging system based on a conventional Cooke triplet system .Unlike conventional optical system, the wavefront of this new system is modulated by a specially designed phase mask, which makes the point spread function (PSF)of optical system not sensitive to defocus. Therefore, a series of same blurred images obtained at the image plane. In addition, the optical transfer function (OTF) of the wavefront coded imaging system is independent of focus, which is nearly constant with misfocus and has no regions of zeros. All object information can be completely recovered through digital filtering at different defocus positions. The focus invariance of MTF is selected as merit function in this design. And the coefficients of phase mask are set as optimization goals. Compared to conventional optical system, wavefront coded imaging system obtains better quality images under different object distances. Some deficiencies appear in the restored images due to the influence of digital filtering algorithm, which are also analyzed in this paper. The depth of field of the designed wavefront coded imaging system is about 28 times larger than initial optical system, while keeping higher optical power and resolution at the image plane.
Since the platform "Coursera" is created by the professors of Stanford University Andrew Ng and Daphne Koller, more and more universities have joined in it. From the very beginning, online education is not only about education itself, but also connected with social equality. This is especially significant for the economic transformation in China. In this paper the research and practice on informatization of optical education are described. Online to offline (O2O) education activities, such as online learning and offline meeting, online homework and online to offline discussion, online tests and online to offline evaluation, are combined into our teaching model in the course of Applied Optics. These various O2O strategies were implemented respectively in the autumn-winter small class and the spring-summer middle class according to the constructivism and the idea of open education. We have developed optical education resources such as videos of lectures, light transmission or ray trace animations, online tests, etc. We also divide the learning procedure into 4 steps: First, instead of being given a course offline, students will learn the course online; Second, once a week or two weeks, students will have a discussion in their study groups; Third, students will submit their homework and study reports; Fourth, they will do online and offline tests. The online optical education resources have been shared in some universities in China, together with new challenges to teachers and students when facing the revolution in the e-learning future.
In high power laser systems, nonlinear effect, one of the key factors of beam wavefront aberration and even
irreversible damage to system, has always been one of the top considerations of researchers for decades. A hybrid
ray-tracing method for both linear media and nonlinear media based on geometric optics is presented in this paper and
realized by programming. In a simple optic system with KDP crystal, an obvious decline of beam quality is observed in
high laser power density conditions and a method taking component intervals as compensation of beam quality is proved
feasible. Considering the complexity of traditional modeling method based on surfaces, a modeling method based on
components is established. Hopefully, the conclusions and flaws of this paper can shed light on relevant work and further
research.
KEYWORDS: Stray light, High power lasers, Laser systems engineering, Optical simulations, Collimators, Error analysis, Reflection, Imaging systems, Reliability, Analytical research
In the high-power laser system, the stray light which is generated by the surface’s residual reflection of optical elements and the multi-pass transmission in the system will lead to temperature increase in part of the system, the optical elements deformation and damage, distortion of wave-front and change of the beam’s divergence angle, which seriously influence the beam’s quality and propagation properties and damage the components in the system. So, it is very important to use the relevant software to analyze the stray light rigorously because the reliability and precision of the software is the guarantee of reliable results. Through two types of software we performed the simulation of the stray light in the system, including ghost’s distribution in the case of different states of rotating defocusing, beam’s pointing. Simultaneously, the impact of processing and assembling errors is analyzed in details. We built a specialized experiment to verify the reliability of results of the software and the related parameters of system are conveniently measured with the device.
In order to achieve a uniform illumination distribution confined to a given rectangular region, a feedback modification
strategy is introduced in the design of free-form optical surface. The whole process of this strategy includes two steps:
solving the initial structure and feedback process.
To solve the initial surface, we first divide the source space along its longitude and latitude direction with uniform angel.
Because the energy of each longitude and latitude micro-belt of free-form surface and each corresponding micro-belt on
the target plane is equal, the target plane can be divided into grids, and then the mapping relationship of source space and
target space is constructed. By using Snell’s Law and tangent plane iterative method, we obtain the coordinates of all grid
nodes and an initial free-form surface can be constructed. Afterwards we use specific feedback algorithm to improve the
illuminating performance. This method is proved to be efficient, the shape of illumination spot is dramatically improved
and the design result is satisfactory.
The entire process of image formation and refocusing of light field photography with microlens array is simulated using
the in-house software OTS based on real ray tracing. The optical system consists of a photographic lens and the
microlens array which are specifically designed. Objects are placed in different distance before the lens, and images of
them on the detector plane are got by imaging simulation algorithm. Utilizing the color, intensity and the corresponding
direction information of light rays on the image plane, pictures focusing at different depth in the image space are
calculated, so that we can refocus at different objects in different distance. The paper also details the basic requirement of
optical system and this simulation process is a fundamental work of research on design method and performance of lens
using in light field photography.
In light-emitting diode (LED) street lamp design, it has always been an obsession that how to achieve an
expected illumination distribution confined to a given region. To solve this problem, a new optimization strategy is
proposed. In view of the practicability of actual production, we select the relatively mature approach that is based
on both the Snell law and the energy conservation law which would obtain coordinate relations between the spaces
the light source and target plane owned respectively and a set of equations to establish the initial construction of
free-form lens. In addition, all the processes of simulation, analysis and optimization as well are accomplished in
software. Generally speaking, for construction method which is in the light of the set of equations, the major
improvement ideology focus on finding out the most suitable mapping relationship between the two coordinate
systems. So does our work.
In order to get better performance, the grid of control points must be modified. Then the core problem lies in
determining the direction and distance of every point’s movement contained in the grid. The rule of changing
direction has a bearing on energy relations while migration length is gained by direct search algorithm.We apply
the method in uniform illumination and get some effect. In short, the optimization strategy provides a practical and
simple way for street lamp design of LED illumination.
Starting from three aspects, the paper introduces the reason and effects of glare and displays a kind of Unified Glare Rating(UGR) measuring system. Our research is dependent on the standard made by CIE and the UGR formula put forward by Sorensen, make use of digital camera, programming and digital image processing and develop a set of UGR measuring system. After testing, we find it able to measure indoor UGR and get repeatable results, which are close to the examples in CIEll7—1995 technical report. Hopefully, what the paper introduces can promote the implement of UGR standard and be avail to the simplification of the process of lighting quality evaluation.
Zernike polynomials have been widely used to fit lens surface figure error and the wavefront aberration of optical systems, for its orthogonality in the unit circle and its corresponding relationships with optical aberrations1. Because the current extensively used Zernike polynomials are just functions of the aperture, without consideration of the field factor, it can only represent single field wavefront aberration. This is incomplete for the description of the wavefront aberration, especially for lithographic lens with a large field and high imaging quality2. Thus, considering the field factor in the description of wavefront aberration becomes very necessary. This paper presents a convenient and practical method to describe the full field wavefront aberration. A rotationally symmetric optical system has been taken as an example, in the scope of normalized full field, taking the Chebyshev zero points as nodes, and applying the Chebyshev polynomials to the fitting of Zernike coefficients of different fields. Meanwhile, the influence of the degree of Chebyshev polynomials and the number of fitting nodes on the fitting accuracy is taken into account. The results show that the fitting method used in this paper is of high accuracy, and this fitting method is very significant for the analysis of full field wavefront aberration.
Point spread function (PSF) defines the intensity of the diffraction image formed by the optical system for a point source. The PSF of an optical system varies with the field of the point source and such variance generally cannot be neglected. This paper proposes a realization method of full-field PSF—incorporating field dependence into the PSF matrix. Two practical optical systems with distinct degree of aberrations are chosen and the PSF using the method proposed with that obtained by direct integration are compared. The result and analysis suggest this method can obtain the PSF in any desired field at a fast speed and with relatively high accuracy.
A short-wave infrared (SWIR) imaging spectrometer with all reflective elements was designed, covering the spectral range 1000-2500nm with a spectral resolution of 10nm. The imaging spectrometer is composed of an off-axis three-mirror anastigmatic (TMA) telescope and an Offner spectral imaging system with convex grating. The design result shows that the system has compact structure, light weight, wide field of view, small smile and keystone, excellent image quality and practical feasibility. The design method is simple and easy-operating.
Region labeling for binary image is an important part of image processing. For the special use of small and multi-objects
labeling, a new region labeling algorithm based on boundary tracking is proposed in this paper. Experiments prove that
our algorithm is feasible and efficient, and even faster than some of other algorithms.
The image quality is the most direct method for evaluating actual optical system's quality. Imaging of standard feather
image, such as resolution plate, comet and so on is also frequently used in lens test in optical industry. The existing
simulation method for optical system can be divided into two categories. One is using ideal optical system model to
simulate image the object formed, but the actual parameters, aberration, processing and assembly of the optical system
cannot be considered. The other can calculate the special field's Spot Diagram, Point Spread Function and Module
Transfer Function by the optical design software. It is widely used for optimization (design) and image restoration. In
this paper, the actual optical system is simulated by our self-developed simulation software, the target image is entered,
the ray tracing method is used and the simulated image is received, which is formed by the object image of the practical
optical system with errors. Known parameters of the optical system are used in this article. The correctness of simulation
results is demonstrated. And the targeted photorealistic images with colors and photometric information can be gotten by
the simulation software, and the more rays be used, the more fields be cut, the simulated image much closer to the actual
image. The errors possible existing in optical system processing and assembly, such as eccentric, tilt or surface error are
considered in our simulation software, and the simulated image we get is affected by these factors. So that we can give
the reasonable tolerances, speed up the development efficiency and reduce cost.
Polarization state of only completely polarized light can be analyzed by some software, ZEMAX for example. Based on
principles of geometrical optics, novel descriptions of the light with different polarization state are provided in this
paper. Differential calculus is well used for saving the polarization state and amplitudes of sampling rays when ray
tracing. The polarization state changes are analyzed in terms of several typical circumstances, such as Brewster
incidence, total reflection. Natural light and partially polarized light are discussed as an important aspect. Further more, a
computing method including composition and decomposition of sampling rays at each surface is also set up to analyze
the energy transmission of the rays for optical systems. Adopting these analysis methods mentioned, not only the
polarization state changes of the incident rays can be obtained, but also the energy distributions can be calculated. Since
the energy distributions are obtained, the surface with the most energy loss will be found in the optical system. The
energy value and polarization state of light reaching the image surface will also be available. These analysis methods are
very helpful for designing or analyzing optical systems, such as analyzing the energy of stray light in high power optical
systems, researching the influences of optical surfaces to rays' polarization state in polarization imaging systems and so
on.
The method of real ray trace for the time characteristic analyzing of laser pulse is presented. By tracing the sampling rays
with optical path or phase initialized by given input pulse and limited by the entrance pupil, the output pulse samples are
calculated including the pulse width and energy distribution and the fitting pulse curve is obtained. Further more, this
method can be also used for analyzing the affection of the tolerance in pulse transmission systems to the beam quality.
Taking some pulse transmission systems as examples in which there are different diffraction components such as
diffraction gratings, binary optical elements and holographic elements, the output pulse curves come from different input
pulse are given, and the functions of different diffraction elements as pulse boarder and compressor are compared. As
shown by the results that the multiple diffraction of binary optical elements will not only generates multiple focus points
at the output space to affect the space quality of laser beam, but also leads to broad the pulse width so as to change the
laser's time characteristics.
The difficulty of tracing rays through the random index medium, like atmosphere, or flowing liquid, lies on how to fast
obtain the refractive index and gradient values of each location along the ray trajectory in space. Recently, the method of
"self-adapting grid" has been developed to efficiently describe such a medium. There are several available numerical
techniques for tracing rays through inhomogeneous medium, such as Taylor method and 3rd order Runge-Kutta method,
the combinations of the self-adapting grid with different ray tracing techniques result in different accuracy and require
different computational effort. In this paper, according to the fundamentals of numerical computation, the derivation of
4th order Runge-Kutta method is presented. For the convenience of comparison, the ray trace through a regular gradient
medium (GRIN) has also been made by these methods, and the results are compared with that from other commercial
lens design codes. The results show that the 4th order Runge-Kutta method has the highest accuracy for the same step
size, but it consumes the longest time. When the ray trace step is relatively large, i. e., one fifth of the GRIN rod size, the
4th Runge-Kutta method is much more accurate than the 3rd method, however, there's few difference of the accuracy
when ray trace with a small step size. Therefore, the 3rd order Runge-Kutta method is the optimum choice for ray tracing
in self-adapting grid when comprehensively considering the accuracy and computational efforts.
The principles and operation plans of research-oriented teaching in the course of computer aided optical design are
presented, especially the mode of research in practice course. This program includes contract definition phase, project
organization and execution, post project evaluation and discussion. Modes of academic organization are used in the
practice course of computer aided optical design. In this course the students complete their design projects in research
teams by autonomous group approach and cooperative exploration. In this research process they experience the
interpersonal relationship in modern society, the importance of cooperation in team, the functions of each individual, the
relationships between team members, the competition and cooperation in one academic group and with other groups, and
know themselves objectively. In the design practice the knowledge of many academic fields is applied including applied
optics, computer programming, engineering software and etc. The characteristic of interdisciplinary is very useful for
academic research and makes the students be ready for innovation by integrating the knowledge of interdisciplinary
field. As shown by the practice that this teaching mode has taken very important part in bringing up the abilities of
engineering, cooperation, digesting the knowledge at a high level and problem analyzing and solving.
KEYWORDS: Infrared radiation, Sensors, Infrared imaging, Thermography, Temperature metrology, Ray tracing, Geometrical optics, Metals, Signal to noise ratio
When the outside temperature rapidly changes, there is graded temperature distribution at optical window in infrared
detection systems and the detection sensitivity will be affected. It is necessary to analyze the response of detector
according to the temperature distribution. In this paper the graded temperature distribution is described in optical system
parameters as environment data, the radial graded temperature function using orthogonal polynomial method is created,
and the temperature of any position at optical window can be calculated easily. Based on the principles of blackbody
radiation, the sampling plans of wavelength and thermal radiation source surface are presented. Having imaged each
surface at object space or image space, the common entrance for infrared radiation from the window is found and named
as thermal pupil, then sampling at the entrance to create millions of rays. These rays are traced through the system with
energy and the power spectral density is calculated. Taken an infrared optical system as an example, the radiation of its
optical window with temperature of 30°C and 55°C±5°C is analyzed. As shown by the example that the radial
temperature gradient will lead to nonhomogeneous noise at the image.
Based on the basic principle of geometrical optics, an analytical method is presented in this paper. Each optical surface is regarded as an infrared source, and all optical surfaces behind it make up a new optical system. The sampling rays carrying certain energy are used to indicate the thermal radiation beams, and they are traced through the optical system to obtain the energy distribution on the image plane. The influence of thermal radiation in the infrared optical system is further analyzed. An infrared optical system is designed, which has been athermalized. The thermal radiations from each optical surface are analyzed and the superposition result is obtained.
Headlamps are installed at the head of automobiles for road lighting. About the illumination and anti-dazzle, some standards such as the standard of ECE are established. Now more and more free face reflective headlamps (FFR headlamps) are applied, and the light distribution design of FFR mirror becomes an important subject in the field of automobile assembling part. In this paper the surface shape of FFR headlamps is analyzed and described as a multi-partition aspherical surface with some simple parameters. According to the fundamental principles of geometrical optics and using the theory of ray transmission with energy, millions of real rays emitted from lower beam filament and high beam filament are traced and the relative intensity of illumination at the test screen with distance of 25m from the automobiles is obtained. In this paper the description of FFR mirrors is discussed, the algorithm of FFR headlamp design is presented, the flow chart is given and the light distribution simulation software with friendly interfaces is developed. In the light distribution graphic interface of the software, the illumination area could be dragged to a certain position while the parameters of current partition at the FFR mirror will be automatically changed. Using this software the FFR headlamps satisfying criteria will be designed very quickly and the 3D coordinates of any points at the mirror will be obtained. This makes CAM of FFR headlamps easy.
KEYWORDS: Stray light, Diffraction, High power lasers, Laser systems engineering, Reflection, Stray light analysis, Reflectivity, Monte Carlo methods, Optical components, Optical instrument design
Diffraction components are applied in high power laser systems for beam shaping and harmonic separation. Because of the multi-order diffraction and multi-reflection to high power laser, the distributions of stray light energy and ghosts are much more completed in the systems than in conventional optical systems. In this paper a data structure of tree is presented for describing the stray light caused by multi-order diffraction and multi-reflection. All the nodes of the tree can be dynamically saved and be deleted, and the intermediate results those are useful for the next calculation step can be reserved in RAM. Using this method the multiple repeated calculations in conventional stray light analysis methods such as Monte Carlo technique are avoided and the analysis time is reduced. According to the paraxial tracing, the software which can be used for analyzing the stray light caused by multi-order diffraction and multi-reflection in high power laser systems is developed and the stray light tree of a laser system based on paraxial tracing is built. As shown by the example that this algorithm is available for quickly analyzing stray light in the systems including diffraction components, and the ghost positions with energy descriptions can be given by the software. The ghosts those are harmful to the important components will be picked.
KEYWORDS: Visualization, Optical amplifiers, Visual analytics, Laser systems engineering, Ray tracing, Complex systems, Optical components, Mirrors, High power lasers, Fusion energy
The technical integration line (TIL), which is the full scale prototype for Shengguang-III laser facility (SG-III), now under construction at CAEP, will contain a neodymium glass laser system with more than 70 large (40-100 cm) optical components. Reflections from these surfaces (so-called ghost reflections) are numerous and extensive computation has been required to track them in the TIL optical system. The tremendous number of ghost paths requires a visualization method that allows overlapping ghosts on optics, and then sums them up to illustrate its potential damage on critical surfaces. Therefore, how to make an effective identification and visualization of multi-order "ghost" has been a major part of the optical design effort. This paper addresses the following aspects of TIL ghost analysis: 1, comparison of several methods for ghost energy simulation. 2, some techniques for visualization of complex optical systems in 3D space including mirrors and pinholes. 3, attempts at visualizing “ghost energy” distribution near some critical surfaces so as to provide detailed references for mitigation of ghost caused damage.
In this paper, the microfluidic chips and the corresponding detection system were briefly introduced. The microfluidic chips have been widely applied nowadays, which can meet the norm of general detection instruments that must have high SNR (signal-to-noise ratio) and can detect the object at the density of 10-9 (Mol/L). The influencing factors in improvement of the SNR were mainly addressed. By studies of various detection principles, the con-focal theory and laser induced fluorescence (short for LIF) which can generate better signal and reduce stray light are finally adopted to improve SNR of the overall system; From the comparison of various optical schemes, the reflection design is chosen due to the improvement of light source efficiency and reduction of stray light; the value of the numerical aperture and the size of pinhole can be calculated by formula to exert influence on the SNR. The fluorescence wavelength scopes, was also analyzed so as to apply appropriate laser, spectral filter and PMT. Because of the need of six-way high voltage for separate control, the amplification system must be analyzed and designed to avoid influencing SNR; for better SNR, software has also been programmed.
Polarization interference filters (PIF) has been widely used in many fields. A successful application is color filter used for color separation and recombination in developing new LCOS projection optical sub-systems. In this paper, several techniques are discussed in order to design PIF with any arbitrary output. We present genetic algorithm (GA) optimization method to specify the desired response at first, and then a new Jones Matrix formulation was introduced to determine the orientation angles of each retarder and analyzer, which are much different from conventional "Optical Network Synthesis." Moreover, the angle property using the extended 2 x 2 Jones Matrix is also analyzed. In particular, the designed Blue/Yellow filter is provided as an illustration.
A zoom lens system is usually composed of several components. Some of the components can be moved to change the focal length or magnification. Zoom lens system design is more complicated than fixed-focus lens design due to the moving of some components. In this paper, an optimization method that is used to design zoom lens systems is presented. Using this method, the Gaussian parameters of zoom lens systems are optimized at first, and then the initial structure parameters in each component are generated and optimized. At last the aberration balance is made using multi-configuration. In this paper the flowchart of optimization design for such complex optical systems is showed and the algorithms are described. As a conclusion, the relationship between power distribution, initial structure and the aberrations is considered at the beginning, the evaluation criteria are reliable and efficiency for designing zoom lens systems.
The principal of this new analytical method is to analytically get the coefficients of exponentials, the sum of which approximates the desired rectangular spectrum function of PIF. An arbitrary desired rectangular spectrum could be approximated by a continuous function with ripples. This function can be written in polynomial mathematically, with many unknown coefficients and known special points, such as extremum points and the point of half transmission. A set of equations could be written for those special points, through the solving of which the unknown coefficients will be determined. The following procedures will be the same as the available synthesis procedures of birefringent networks. This method will greatly simplify the design procedure and give more freedom in control of the design spectrum output. An example is given for 5-piece-birefringent-crystal PIF.
By modifying the illumination of the ordinary microscope, the sectioned image of the object is then available at the image plane but with the unwanted ordinary image superimposed. After processing these composite images by decoding algorithm, the optically sectioned images substantially similar to those obtained by confocal microscope can finally be got. Here in this article, we derive the explicit formula of the image formation by using the mutual intensity theory and thus explain the sectioning ability and the decoding theory of this new sectioning microscope. We can conclude that this kind of selective-illumination microscope is actually a selective-illumination microscope.
Microfluidic chip is used for the biochemical analyses such as DNA sequencing and the separation of the protein or single cell. It has been shown to offer more advantages than the conventional capillary electrophoresis (CE): less reagent, miniaturization, high efficiency and sensitivity. In this paper, a laser induced fluorescence (LIF) detection system based on a 488nm argon ion laser and FITC fluorescent dye, is described for use with the microfluidic chip. The optical path of transmission type is adopted in our experiment. The pinhole is also applied to improve the performance of the whole detection system. There are some factors that influence the signal-to-noise ratio (SNR) of the detection system such as objective lens, the laser intensity and the pinhole. The pinhole plays a vital role in the confocal system and its performance is discussed in detail in our paper. The experimental data are presented and explained to show the relationships of these factors.
All of the light that reaches a position other than the intended position is referred as stray light. Stray light generated in multi-pass amplifier system forms a lot of ghost image, which not only seriously influence the laser beam quality and propagation properties, but also damage optical components, and is one of major risks that high power laser system operate regularly. Based on the basic principle of geometrical optics, the transmission of beam is analyzed, a ray tracing method of ghost analysis is mentioned, the mathematical and physical model for analysis of stray light and ghost images has been set up, the analysis software has been presented. Taken a simple system as example, these ghost images and the energy density of key components in the system is get correctly. The results are instructive to the actual work of multi-pass amplifier laser design.
In this paper, based upon the general law oftransmission ofbasic model Gaussian beam, the reflection and refraction of laser at optical surfaces are analyzed respectively. Using the complex parameters of Gaussion beam, a simple algorithm for researching stray light and ghosts caused by Gaussian beam is presented. Depending on the algorithm, a dynamic data structure of tree which can describe the stray light of the system is built, an energy density superposition algorithm based on the distribution of complex amplitude of Gaussian beam is discussed, and a stray light and ghost analysis software for basic model Gaussian beam is developed. It can be seen from given example that the method describes completely the transmission of basic model Gaussian beam in optical systems and the ghost distribution. For given conditions (e.g. the maximum reflection times), the total energy density of Gaussian beam at certain position in optical systems with high accuracy could be calculated.
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