This article describes the principle of wavefront coding (WFC) technology and the role it plays in optical system. The infrared optical system in tokamak includes three parts: (1) the combination of the concave aspher...
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This article describes the principle of wavefront coding (WFC) technology and the role it plays in optical system. The infrared optical system in tokamak includes three parts: (1) the combination of the concave aspheric mirror and flat mirror;(2) the Cassegrain system;(3) the relay group lenses. Because of the application of wavefront coding, the optical system is less sensitive to the change of the temperature and the depth of field is enlarged. Comparing the modulation transfer function (MTF) of the original optical system and the improved system in different temperatures, the results show that the new system can be used in a larger range of temperature. (C) 2012 Elsevier B.V. All rights reserved.
In wave-front coded imaging system, the phase mask placed in the pupil plane of the imaging system aims to reshape the PSF (point spread function) or OTF (optical transfer function) to realize DOF (depth of field) ext...
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ISBN:
(纸本)9781510622333
In wave-front coded imaging system, the phase mask placed in the pupil plane of the imaging system aims to reshape the PSF (point spread function) or OTF (optical transfer function) to realize DOF (depth of field) extension. How to design a suitable phase mask to provide a highly controlled response of system PSF or OTF is crucial to computational imaging application. Traditionally, AF (ambiguity function) is a powerful tool to assess the DOF extension effect generated by phase masks with known phase function. However, in this paper, we investigate an iterative optimization based procedure to recover the unknown phase mask using AF in a backward way. First, a set of desired PSFs or OTFs at different defocus planes is combined together to construct an initial estimate of AF. Second, the corresponding mutual function is calculated through Fourier transform. Third, SVD (singular value decomposition) is applied to the mutual function. Fourth, only the term corresponding to the biggest eigenvalue is kept and inverse Fourier transform is used to generate a new estimate of AF. Fifth, the input desired OTFs are used to update the newly estimated AF. This procedure iterates until the OTFs extracted from the estimated AF are highly consistent with the input ones using the MSE (mean-square-error) as criterion. In the paper, we systematically study this powerful procedure using numerical simulation and investigate the probability of recovering the rectangular non-separable phase masks. After that, experiments are carried out to justify the effectiveness of the procedure.
This paper is devoted to designing of hybrid refractive/diffractive optics for high-quality imaging with improved depth of focus (DoF). The novelty of the concept is in sharing of the optical power of the refractive l...
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ISBN:
(纸本)9781538668979
This paper is devoted to designing of hybrid refractive/diffractive optics for high-quality imaging with improved depth of focus (DoF). The novelty of the concept is in sharing of the optical power of the refractive lens between the lens and a multilevel phase mask (MLM) as a diffractive optical element (DOE). The efficiency of the design is confirmed by numerical results. Broadband multiwavelength test-images are exploited for the design and testing of the system. It is shown that the obtained hybrid optical system in combination with computational inverse imaging provides both a better image quality (due to the robustness of the designed optics to chromatic aberrations) and an extended depth of focus as compared with the refractive lens and the diffractive lensless design with MLM.
Since the concept of wavefront coding was proposed, many types of phase masks have been reported to extend the depth-of-field of imaging system. Unfortunately there exist some unpleasant image artifacts in the final d...
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ISBN:
(数字)9781510622906
ISBN:
(纸本)9781510622906
Since the concept of wavefront coding was proposed, many types of phase masks have been reported to extend the depth-of-field of imaging system. Unfortunately there exist some unpleasant image artifacts in the final decoded images, especially for asymmetric phas(1)e masks. In this paper, we illustrate a technique that involve shifting a phase mask laterally in pupil plane to introduce axial defocus to an imaging system, which can further be used to determine the defocus map according to the amount of image artifacts. This eventually enables recovery of extended depth-of-filed, artifacts-free decoded images together with a range map. Theoretical analyses and experimental results indicate the effectiveness of this method.
Our goal is to design a radiation resistant camera lens for color imaging capable to withstand ionizing radiations up to total doses of a few MGy. The latter cause damages in the internal structure of glass which can ...
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ISBN:
(数字)9781510619180
ISBN:
(纸本)9781510619180
Our goal is to design a radiation resistant camera lens for color imaging capable to withstand ionizing radiations up to total doses of a few MGy. The latter cause damages in the internal structure of glass which can affect its optical transmission and refractive index (RI). On the one hand, the radiation-induced attenuation (RIA) mainly causes the glass darkening and image signal-to-noise ratio degradation and can be partially handled by choosing the most appropriate materials. On the other hand, the radiation-induced RI change (RIRIC) causes the blurring of the image which can be more harmful to the viewing applications. Indeed, typical RIRIC magnitudes of 10(-4) to 10(-3) mainly induce defocus on the image. Yet, no motorized elements have been shown to be resistant to radiations at the aimed dose levels. Similarly to thermal defocus in non-cooled thermal imaging, the impact of the RIRIC has to be studied during the design step of the camera lens. However, until comprehensive measurements on different glasses and under different types of radiations, the easiest way to foresee the lens behavior with respect to the RIRIC is to perform a parametric study of its response. We studied RIA and RIRIC effects on a dummy lens and show that a self-compensation of the lenses RI changes appears as possible. As this problem is very similar to the constraint of increased depth of field, we also studied the technique of wavefront coding to increase the lens tolerance to RIRIC.
wavefront coding is a hybrid technology designed to increase depth of field of conventional optics but it can also be used to compensate for other aberration and ease tolerancing. The goal of our research is to apply ...
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ISBN:
(纸本)9781467320009;9781467319980
wavefront coding is a hybrid technology designed to increase depth of field of conventional optics but it can also be used to compensate for other aberration and ease tolerancing. The goal of our research is to apply this technology to panoramic imager. Panoramic imagers suffer from an increase level of aberration due to the large field of view and it is also subject to a special tolerance process. They also typically have a wide variation of the point spread function (PSF) across the field of view and suffer from non-symmetric aberration like coma and astigmatism. To obtain the best result using wavefront coding, the PSF should be as invariant as possible over the whole field of view. Asymmetric phase masks, when used in systems having non-negligible asymmetric aberrations, generate variations in the final image quality. For that reason, a model that predicts the final image quality of wavefront coded system is needed. The possibility of using two surfaces for wavefront coding has been studied. The final results were analysed using a variance based image quality criterion. From these results, it is possible to optimize phase mask for panoramic imager and predict the resulting image quality.
The wavefront coding is a widely used in the optical systems to compensate aberrations and increase the depth of field. This paper presents experimental results on application of the wavefront coding paradigm for data...
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ISBN:
(纸本)9780819490766
The wavefront coding is a widely used in the optical systems to compensate aberrations and increase the depth of field. This paper presents experimental results on application of the wavefront coding paradigm for data encryption. We use a synthesised diffractive optical element (DOE) to deliberately introduce a phase distortion during the images registration process to encode the acquired image. In this case, an optical convolution of the input image with the point spread function (PSF) of the DOE is registered. The encryption is performed optically, and is therefore is fast and secure. Since the introduced distortion is the same across the image, the decryption is performed digitally using deconvolution methods. However, due to noise and finite accuracy of a photosensor, the reconstructed image is degraded but still readable. The experimental results, which are presented in this paper, indicate that the proposed hybrid optical-digital system can be implemented as a portable device using inexpensive off-the-shelf components. We present the results of optical encryption and digital restoration with quantitative estimations of the images quality. Details of hardware optical implementation of the hybrid optical-digital encryption system are discussed.
A simple graphical interpretation at the pupil of an optical system is proposed to analyse the properties of the cubic-phase wavefront-coding function. The approach explains the invariance achieved against optical def...
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A simple graphical interpretation at the pupil of an optical system is proposed to analyse the properties of the cubic-phase wavefront-coding function. The approach explains the invariance achieved against optical defocus of wavefront coding imaging systems with simplicity and clarity. Next, an analytical approximation of the modulation-transfer function of general wavefront coding systems is derived and used, in combination with the graphical interpretation, for selecting the optimal strength of the cubic-phase encoding function. (C) 2012 Elsevier Ltd. All rights reserved.
wavefront coding is a hybrid technology designed to increase depth of field of conventional optics but it can also be used to compensate for other aberration and ease tolerancing. The goal of our research is to apply ...
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ISBN:
(纸本)9781467320009
wavefront coding is a hybrid technology designed to increase depth of field of conventional optics but it can also be used to compensate for other aberration and ease tolerancing. The goal of our research is to apply this technology to panoramic imager. Panoramic imagers suffer from an increase level of aberration due to the large field of view and it is also subject to a special tolerance process. They also typically have a wide variation of the point spread function (PSF) across the field of view and suffer from non-symmetric aberration like coma and astigmatism. To obtain the best result using wavefront coding, the PSF should be as invariant as possible over the whole field of view. Asymmetric phase masks, when used in systems having non-negligible asymmetric aberrations, generate variations in the final image quality. For that reason, a model that predicts the final image quality of wavefront coded system is needed. The possibility of using two surfaces for wavefront coding has been studied. The final results were analysed using a variance based image quality criterion. From these results, it is possible to optimize phase mask for panoramic imager and predict the resulting image quality.
A pupil filter is a useful technique for modifying the light intensity distribution near the focus of an optical system to realize depth of field (DOF) extension and superresolution. In this paper, we proposed a new d...
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A pupil filter is a useful technique for modifying the light intensity distribution near the focus of an optical system to realize depth of field (DOF) extension and superresolution. In this paper, we proposed a new design of the phase only pupil filter by using Zernike polynomials. The effect of design parameters of the new filters on DOF extension and superresolution are discussed, such as defocus Strehl ratio (S.R.), superresolution factor (G) and relative first side lobe intensity (M). In comparison with the other two types of pupil filters, the proposed filter presents its advantages on controlling both the axial and radial light intensity distribution. Finally, defocused imaging simulations are carried out to further demonstrate the effectiveness and superiority of the proposed pupil filter on DOF extension and superresolution in an optical imaging system.
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