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Journal ArticleDOI

High tolerance to spherical aberrations and defects of focus with a birefringent lens

01 Aug 2002-Applied Optics (Optical Society of America)-Vol. 41, Iss: 22, pp 4611-4619
TL;DR: A systematic investigation of the imaging behavior of an optical system consisting of a lens from a uniaxial birefringent crystal sandwiched between two linear polarizers into which primary spherical aberration has been introduced.
Abstract: We report a systematic investigation of the imaging behavior of an optical system consisting of a lens from a uniaxial birefringent crystal sandwiched between two linear polarizers into which primary spherical aberration has been introduced. The proposed system has higher tolerance to primary spherical aberration and has a larger depth of focus than an imaging system found with an isotropic lens. Some specific cases are computed and illustrated graphically.
Citations
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Patent
22 Apr 2007
TL;DR: In this paper, an imaging system and method consisting of an imaging lens unit, an imaging detector, and a birefringent element located between the unit and the imaging detector is presented.
Abstract: An imaging system and method are presented. The system comprises an imaging lens unit, an imaging detector, and a birefringent element located between the imaging lens unit and the imaging detector. The system is thus configure and operable to provide in-focus imaging of objects located at both near-field and far-field ranges. Also provided is an optical device configured to be mounted on an imaging lens, being one of the following: a lens of an individual's glasses, on a contact lens, and an eye internal lens. The optical device is configured to be located between the imaging lens and the retina and comprises a birefringent element, to thereby provide in-focus imaging onto the retina of the objects located at both near-field and far-field ranges therefrom.

45 citations

Journal ArticleDOI
TL;DR: In this paper, a simple comprehensive treatment on the use of free-form optical elements, and of nonuniform optical windows, either for increasing focal depth or for tuning the depth of field, by controlling the influence of focus error on the modulation transfer function.
Abstract: We present a simple comprehensive treatment on the use of free-form optical elements, and of nonuniform optical windows, either for increasing focal depth [by regulating the width of the axial point spread function (PSF)] or for tuning the depth of field [by controlling the influence of focus error on the modulation transfer function (MTF)]. We employ the rising notation of pupil engineering, which incorporates techniques for controlling the spread of the axial PSF, as well as methods for governing the impact of focus errors on the MTF. Our discussion also includes the use of vortex lenses for designing nonconventional optical systems.

34 citations

01 Sep 2002
TL;DR: In this article, wavefront coding is employed to encode the incident wavefront in such a way that the image recorded by the detector can be accurately restored over a large range of defocus.
Abstract: This paper gives a review on the design and use of both amplitude filters and phase filters to achieve a large focal depth in incoherent imaging systems. Traditional optical system design enhances the resolution of incoherent imaging systems by optical-only manipulations or some type of post-processing of an image that has been already recorded. A brief introduction to recent techniques to increase the depth of field by use of hybrid optical/digital imaging system is reported and its performance is compared with a conventional optical system. This technique, commonly named wavefront coding, employs an aspherical pupil plane element to encode the incident wavefront in such a way that the image recorded by the detector can be accurately restored over a large range of defocus. As reported in earlier work, this approach alleviates the effects of defocus and its related aberrations whilst maintaining diffraction-limited resolution. We explore the control of third order aberrations (spherical aberration, coma, astigmatism, and Petzval field curvature) through wavefront coding. This method offers the potential to implement diffraction-limited imaging systems using simple and low-cost lenses. Although these performances are associated with reductions in signal-to-noise ratio of the displayed image, the jointly optimized optical/digital hybrid imaging system can meet some specific requirements that are impossible to achieve with a traditional approach.

30 citations

Journal ArticleDOI
TL;DR: This paper presents a simple approach to obtain extended depth of field for any optical imaging system just by adding a birefringent plate between the lens and the detector.
Abstract: In this paper we present a simple approach to obtain extended depth of field for any optical imaging system just by adding a birefringent plate between the lens and the detector. The width of the plate is properly designed such that one polarization state contains in-focus near field information while the other polarization state contains in-focus far field details. Both images are superimposed one on top of the other and thus an all-optical spatially sharp imaging is obtained containing both fields. The width of the plate is also designed such that there is a longitudinal overlapping of the two regions (the near and the far) such that continuously well focused imaging is generated. The presented approach for extending the depth of focus is significantly simple compared to the use of birefringent and bi-focal lenses published recently. Preliminary numerical as well as experimental results verify the proposed approach.

25 citations

Proceedings ArticleDOI
18 Feb 2004
TL;DR: In this article, wavefront coding is employed to encode the incident wavefront in such a way that the image recorded by the detector can be accurately restored over a large range of defocus.
Abstract: This paper gives a review on the design and use of both amplitude filters and phase filters to achieve a large focal depth in incoherent imaging systems. Traditional optical system design enhances the resolution of incoherent imaging systems by optical-only manipulations or some type of post-processing of an image that has been already recorded. A brief introduction to recent techniques to increase the depth of field by use of hybrid optical/digital imaging system is reported and its performance is compared with a conventional optical system. This technique, commonly named wavefront coding, employs an aspherical pupil plane element to encode the incident wavefront in such a way that the image recorded by the detector can be accurately restored over a large range of defocus. As reported in earlier work, this approach alleviates the effects of defocus and its related aberrations whilst maintaining diffraction-limited resolution. We explore the control of third order aberrations (spherical aberration, coma, astigmatism, and Petzval field curvature) through wavefront coding. This method offers the potential to implement diffraction-limited imaging systems using simple and low-cost lenses. Although these performances are associated with reductions in signal-to-noise ratio of the displayed image, the jointly optimized optical/digital hybrid imaging system can meet some specific requirements that are impossible to achieve with a traditional approach.

20 citations

References
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Journal ArticleDOI
TL;DR: In this paper, the response of a defocused aberration-free optical system to line-frequencies in the object is studied analytically, and curves are given showing the response as a function of line-frequency for a range of values of defect of focus.
Abstract: The response of a defocused aberration-free optical system to line-frequencies in the object is studied analytically. Curves are given showing the response as a function of line-frequency for a range of values of defect of focus. A comparison is made with the results to be expected from geometrical optics. A tolerance for defect of focus is obtained, which accords well with published experimental results. Both circular and rectangular apertures are considered.

489 citations

Journal ArticleDOI
TL;DR: To improve the imaging properties of a defocused optical system, the use of shaded apertures is studied theoretically and experimentally and shows that near focus the OTF for T(A) has higher values in the low frequency region than has either T(B) or T(c).
Abstract: To improve the imaging properties of a defocused optical system, the use of shaded apertures is studied theoretically and experimentally. The study is based on the optical transfer function (OTF). The two shaded apertures studied are the type in which the amplitude transmittance decreases gradually from the center of the pupil toward its rim, T(A), and the type in which the amplitude transmittance decreases from its rim toward the center, T(B). For comparison, the effects achieved with a clear aperture, T(C), are included. The results of the calculations show that near focus the OTF for T(A) has higher values in the low frequency region than has either T(B) or T(c). When the system is defocused, the shaded aperture of the type T(A) yields an improved defocused image that is faithful to the outline of the object. The quality of the defocused image obtained with T(B) is worsened. When the OTF is used as a means for judging the quality of the defocused image, the two necessary conditions on the functions appear to be that the OTF (1) must be a monotonically decreasing function and (2) must be nonnegative. These conditions are confirmed by experiment. Since the transmittance variation of the shaded apertures is achieved by absorption, the effects due to the resultant decreases in light level are also considered.

171 citations

Journal ArticleDOI
TL;DR: A method for designing apodizers that increase the depth of focus and reduce the influence of spherical aberration are proposed.
Abstract: We propose a method for designing apodizers that increase the depth of focus and reduce the influence of spherical aberration. These two properties are explicitly manifested in computer-generated pictures and values of the Strehl ratio for variable spherical aberration.

125 citations

Journal ArticleDOI
TL;DR: It is shown that a zone plate with a prespecified number of foci, which are separated axially by Rayleigh's limit of resolution, can create an arbitrarily high focal depth when used as an apodizer over an otherwise clear aperture.
Abstract: We show that a zone plate with a prespecified number of foci, which are separated axially by Rayleigh’s limit of resolution, can create an arbitrarily high focal depth when used as an apodizer over an otherwise clear aperture. We discuss the resolution and light gathering power of this method.

106 citations

Journal ArticleDOI
TL;DR: It is shown that a certain Lorentzian profile is a quasioptimum solution for a specified light throughput, characterized by a Strehl ratio vs defocus with high focal depth, for aspecified light throughput.
Abstract: Focal depth is assessed by the average value of the square modulus of the slope associated with the complex amplitude along the optical axis. Then, the calculus of variations is used for identifying the optimum apodizer, characterized by a Strehl ratio vs defocus with high focal depth, for a specified light throughput. We show that a certain Lorentzian profile is a quasioptimum solution for the above requirements. This apodizer has real and positive transmittance, and it can be modified to achieve arbitrarily high focal depth. A closed formula relates focal depth to light throughput.

88 citations