The fabrication of small size aspheric optical surface, which made of hard brittle materials, usually uses optical cold processing. However, it is difficult to achieve the ideal requirements of the surface accuracy and roughness. In order to solve this problem, the masked ion beam figuring method is used to etch the one-dimension structure on the plat surface which made of hard brittle material. The results show that the expected surface profile is acquired and meanwhile mainly kept the original roughness and mid-frequency. It provides a possible way for fabricating small size aspheric optics which made of hard brittle materials.
Laser has several advantages, such as high brightness, excellent directivity, good monochromatic, good coherence and so on . Therefore, in ranging schemes which combine laser sensor technology and automatic control technology , the laser ranging is most commonly used nowadays . First, we introduce the principle of grating diffraction in this paper, and proposes a method for ranging based on the laser reflection characteristics of target. Let the laser beam reflected from the target through the diffraction grating and lens and image on the CCD. In the horizontal plane perpendicular to the direction of incidence, grating, lens and CCD make up of an imaging device, and which can measure the distance of target for many times by moving itself horizontally. We can calculate the distance through measuring the range between the central point of the CCD and zero diffraction fringe. Then, we analyze the influence from the targets’ scattering characteristics. Lastly, we simulate the different status according to the proportion of mirror reflection of the actual targets’ scattering characteristics and get a conclusion that only the proportion of mirror reflection exceeds a particular ratio can calculate a valid distance.
Parallel binocular stereo vision system is a special form of binocular vision system. In order to simulate the human eyes observation state, the two cameras used to obtain images of the target scene are placed parallel to each other. This paper built a triangular geometric model, analyzed the structure parameters of parallel binocular stereo vision system and the correlations between them, and discussed the influences of baseline distance B between two cameras, the focal length f, the angle of view ω and other structural parameters on the accuracy of measurement. This paper used Matlab software to test the error function of parallel binocular stereo vision system under different structure parameters, and the simulation results showed the range of structure parameters when errors were small, thereby improved the accuracy of parallel binocular stereo vision system.
Sub-aperture stitching is an effective way to extend the lateral and vertical dynamic range of a conventional interferometer. The test accuracy can be achieved by removing the error of reference surface by the absolute testing method. When the testing accuracy (repeatability and reproducibility) is close to 1nm, in addition to the reference surface, other factors will also affect the measuring accuracy such as environment, zoom magnification, stitching precision, tooling and fixture, the characteristics of optical materials and so on. In the thousand level cleanroom, we establish a good environment system. Long time stability, temperature controlled at 22°±0.02°.The humidity and noise are controlled in a certain range. We establish a stitching system in the clean room. The vibration testing system is used to test the vibration. The air pressure testing system is also used. In the motion system, we control the tilt error no more than 4 second to reduce the error. The angle error can be tested by the autocollimator and double grating reading head.
Most of the commercial available sub-aperture stitching interferometers measure the surface with a standard lens that produces a reference wavefront, and the precision of the interferometer is generally limited by the standard lens. The test accuracy can be achieved by removing the error of reference surface by the absolute testing method. When the testing accuracy (repeatability and reproducibility) is close to 1nm, in addition to the reference surface, other factors will also affect the measuring accuracy such as environment, zoom magnification, stitching precision, tooling and fixture, the characteristics of optical materials and so on. We establish a stitching system in the thousand level cleanroom. The stitching system is including the Zygo interferometer, the motion system with Bilz active isolation system at level VC-F. We review the traditional absolute flat testing methods and emphasize the method of rotation-shift functions. According to the rotation-shift method we get the profile of the reference lens and the testing lens. The problem of the rotation-shift method is the tilt error. In the motion system, we control the tilt error no more than 4 second to reduce the error. In order to obtain higher testing accuracy, we analyze the influence surface shape measurement accuracy by recording the environment error with the fluke testing equipment.
Large-aperture optical elements are widely employed in high-power laser system, astronomy, and outer-space technology. Sub-aperture stitching is an effective way to extend the lateral and vertical dynamic range of a conventional interferometer. Most of the commercial available sub-aperture stitching interferometers measure the surface with a standard lens that produces a reference wavefront, and the precision of the interferometer is generally limited by the standard lens. The test accuracy can be achieved by removing the error of reference surface by the absolute testing method. In our paper we use the different sub-apertures as the different flats to get the profile of the reference lens. Only two lens in the testing process which is fewer than the traditional 3-flat method. In the testing equipment, we add a reflective lens and a lens which can transparent and reflect to get the non rationally symmetric errors of the testing flat. The arithmetic is present in this paper which uses the absolute testing method to improve the testing accuracy of the sub-aperture stitching interferometers by removing the errors caused by reference surface.
Thermal properties and dispersive capacity of diffractive optical elements were expounded in this paper, and the conclusion that optothermal expansion coefficient of diffractive optical element is independent of refractive index of the material was derived. The design method to athermalize the hybrid infrared optical system was studied, a new hybrid system with diffractive surface was structured on the foundation of refractive/reflective optical system using optical design software ZEMAX, and the surface was simulated by MATLAB. The image quality was improved obviously compared with the one without diffractive surface. The system worked at 3.7~4.8μm band with its’ effective focal length of 70mm, field of view of 2° and possessed better athermal performance in the temperature range -40°~+60°. The image quality achieved diffractive limit, besides, a compact structure, small volume and light weight were other advantages of the hybrid system.
Requirements for the measurement resolution in the sub-nanometer range have become quite common which includes
not only the repeatability or reproducibility but also the absolute measurement accuracy. The freeform lens for wavefront
compensating contains some medium spatial frequency terms. The wavefront error of lithographic object lens is very
small. One method to reduce the wavefront error of lithographic object lens is to use the freeform lens. The freeform lens
for compensation needs more accuracy than the object lens. We can also use freeform lens of sphere or aspheric for
compensation. The testing accuracy of sphere and aspheric lens are hard to achieve 1nm. The sphere and aspheric will
contain the power term and are hard to find the cat-eye. The ion beam figure system (IBF) is the best polishing machine
for nanometer manufacture which will polish the PV of 2um for several weeks even months. Usually we use the PV
200nm lens for compensation. So the freeform for compensation looks like a flat. In this paper we will show the testing
experiment of the freeform and the testing problem. The freeform surface is created by 66 Zernike polynomials which
are based on the flat lens. The freeform flat is polished by the ion figuring machine of NTG. The environment such as
temperature, vibration, humidity is controlled well. The Zygo's interferometer Verifire Ashpere with absolute testing
method is used to test the freeform. Position Accuracy is a problem in optical testing and manufacture. The high
accuracy testing can’t be determined by one method, we need the different method to compare the result especially these
method will contain some defects. The defects of the recently absolute testing method are discussed.
The absolute testing method can be used to test the freeform lens. There are some spatial frequencies terms can’t be getting by the traditional absolute testing method such as even and odd functions method, rotation shear method, rotated equally spaced position method. In this paper we will show the losing terms in the traditional method. In this paper the freeform surface is created by 300th Zernike polynomials. The freeform lens is based on the flat lens. We use the Zernike polynomial to simulate the two flats and use the freeform surface as the three flat. According to the three flat absolute testing methods, we can simulate the testing result. The freeform flat which we use is polishing by the ion figuring machine of NTG.
In Cartesian coordinate system, a flat can be expressed as the sum of even-odd, odd-even, even-even and oddodd
functions. In the traditional three-flat even and odd function method, odd-odd function is difficult to obtain. In
our paper the odd-odd function can be solved by use the Dove prism which can rotate the optical axis. The odd-odd
function can calculate exactly. The even-odd, odd-even, even-even can be solved by rotating the flat 180°like the
traditional method. Only five configurations are used to test the flats. The theoretical derivation and analysis are
To overcome the accuracy limitation due to the aberration of reference wavefront in the interferometer testing, the point diffraction interferometer (PDI) uses the pinhole to create an ideal diffraction sphere wavefront as the reference wavefront. Because the perfect pinhole is hard to manufacture, then the imperfect pinhole will cause the wavefront errors which will influence the test accuracy. In this paper we use the absolute testing method to test the wave front of the pinhole. Then the testing accuracy of point diffraction interferometer can be improved by subtracting the error of the pinhole. In this paper a Phase-shifting point diffraction interferometer system is designed to testing the pinhole. We use three pinholes to test each other. According the algorithm of the absolute testing method, we can calculate the wavefront error of the pinhole. Then the testing accuracy of point diffraction interferometer can be improved by subtracting the error of the pinhole.
Large-aperture optical elements are widely employed in high-power laser system, astronomy, and outer-space technology. Sub-aperture stitching is an effective way to extend the lateral and vertical dynamic range of a conventional interferometer. With the aim to provide the accuracy of equipment, this paper simulates the arithmetic to analyze the errors. The Selection of stitching mode and setting of the number of subaperture is given. According to the programmed algorithms simulation stitching is performed for testing the algorithm. In this paper, based on the Matlab we simulate the arithmetic of Sub-aperture stitching. The sub-aperture stitching method can also be used to test the free formed surface. The freeformed surface is created by Zernike polynomials. The accuracy has relationship with the errors of tilting, positioning. Through the stitching the medium spatial frequency of the surface can be tested. The results of errors analysis by means of Matlab are shown that how the tilting and positioning errors to influence the testing accuracy. The analysis of errors can also be used in other interferometer systems.
Result of the testing contain the reference surface errors and test surface errors in the high-accuracy Phase shifting
interferometer which test the relative phase between the two surface. The test accuracy can be achieved by removing the
error of reference surface. In this case, one of body of so-called absolute testing must be used which can test the
systematic errors, including the reference surface, of the instrument to be used to improve the test accuracy. The
accuracy of the interferometer needs different methods to determine in the high accuracy testing. Even-Odd function
method and rotation shear method is introduced in this paper. We use the Zygo interferometer Verifire Asphere to do the
experiment and analyze the errors caused by data processing and interpolation. The result of the experiment can
determine the accuracy of our arithmetic.
Requirements for the measurement resolution in the sub-nanometer range have become quite common. Result of the
testing contain the reference surface errors and test surface errors in the high-accuracy Phase shifting interferometer
(PSI) which test the relative phase between the two surface. The test accuracy can be achieved by removing the error of
reference surface. In this case, one of body of so-called absolute tests must be used which can test the systematic errors,
including the reference surface, of the instrument to be used to improve the test accuracy. Unexpected mechanical
vibrations can significantly degrade the otherwise high accuracy of phase-shifting interferometer. The data acquisition is
sensitivity to vibration with a function of the frequency. The influence of the longitudinal vibration is analyzed in this
paper. We use Zernike polynomials to generate 3 plats. Then the Matlab is used to simulate the 4 frames phase-shift
algorithms and absolute testing algorithms. An experiment used the Zygo interferometer to prove the arithmetic and we
can see the vibration errors in the testing.
Recently most of modern absolute measurement methods rotate the flat or sphere in the interferometer. So it is very
important to exactly know how some errors such as angle rotation error, center excursion error influence the metrology.
This paper analyses these errors how to influence testing accuracy by Zernike based on Even-Odd functions. We review
traditional absolute testing of flats methods and emphasize the method of even and odd functions. The flat can be
expressed as the sum of even-odd, odd-even, even-even and odd-odd functions. Through six measurements the profile of
the flat can be calculated. We use 36 Zernike polynomials in polar coordinates to analysis the method. The polynomials
can be separated by even-odd, odd-even, even-even and odd-odd parts. We substitute polynomials for surface data and
change the arithmetic. Then we can analyze the every surface error data and exactly know the calculate accuracy of every
term through the arithmetic. The results of errors analyze by means of Matlab are shown that how the angle rotation error
to influence the accuracy. The errors analysis can also be used in other interferometer systems which have the motion of
the coordinate system.
Recently most of modern absolute measurement rotation the flats or spheres in the interferometer. We review traditional
absolute testing of flats methods and emphasize the method of even and odd functions. The rotation of the lens can lead
to some errors such as angle rotation error, center excursion error and other coordinate system motion error. We analyze
the errors by using Zernike polynomial. The flat or sphere can be expressed as Zernike polynomial which can also be
divided into even-odd, odd-even, even-even and odd-odd functions. We can use 36 Zernike polynomials to generate 3
plats A, B, C. Then the six measurements can be generated from the three plats. For the angle rotation error, we can
simulate the angle error distribution and substitute in the systems. According the error distribution we can change the
arithmetic to improve the measurement accuracy. The results of errors analyzed by means of Matlab are shown that we
can change the arithmetic according the coordinate direction motion errors which can be detected to improve the accuracy. The analysis results can also be used in other interferometer systems which have the motion of the coordinate system.
This paper describes the principle of Digital Micromirror Device-based infrared scene projector system and analyzes the illumination system. We review traditional illumination systems in critical and kola ways. In order to get more uniform and a low cost illumination system, we use CODEV to design a fly-eye illumination system and a reflective fly-eye lens system. Simulation results by means of CODEV were shown. We propose that a fly-eye illumination system can achieve high quality infrared illumination system and a reflective fly-eye lens system can provide a low-loss illuminator.
This paper presents a digital modulation recognition algorithm for classifying digital signals. The algorithm is based on
high order cumulants, signal square spectrum and spectrum envelope. The advantages of this methods lies on no need for
prior knowledge of the signal. We can even estimate its code rate and SNR. Simulation results demonstrate the efficiency
of this method.