WO2005088354A1 - Element optique variable comprenant des fluides immiscibles - Google Patents

Element optique variable comprenant des fluides immiscibles Download PDF

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Publication number
WO2005088354A1
WO2005088354A1 PCT/IB2005/050760 IB2005050760W WO2005088354A1 WO 2005088354 A1 WO2005088354 A1 WO 2005088354A1 IB 2005050760 W IB2005050760 W IB 2005050760W WO 2005088354 A1 WO2005088354 A1 WO 2005088354A1
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WO
WIPO (PCT)
Prior art keywords
optical
fluid
lens
abbe
lens system
Prior art date
Application number
PCT/IB2005/050760
Other languages
English (en)
Inventor
Bernardus H. W. Hendriks
Stein Kuiper
Original Assignee
Koninklijke Philips Electronics N.V.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Koninklijke Philips Electronics N.V. filed Critical Koninklijke Philips Electronics N.V.
Publication of WO2005088354A1 publication Critical patent/WO2005088354A1/fr

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B3/00—Simple or compound lenses
    • G02B3/12—Fluid-filled or evacuated lenses
    • G02B3/14—Fluid-filled or evacuated lenses of variable focal length
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
    • G02B26/004—Optical devices or arrangements for the control of light using movable or deformable optical elements based on a displacement or a deformation of a fluid
    • G02B26/005—Optical devices or arrangements for the control of light using movable or deformable optical elements based on a displacement or a deformation of a fluid based on electrowetting

Definitions

  • the present invention relates to a variable optical element comprising a first fluid and a second fluid which are in contact over a meniscus, to a lens system including such an optical element, to an imaging system including such an optical lens system, and to a method of designing such a variable optical element, lens system and optical imaging system.
  • a variable lens is a device in which one or more properties of the lens can be controllably adjusted, e.g. in which the focal length or the position of the lens can be altered.
  • the general trend in the development of image sensors for camera modules is that they constantly increase in resolution.
  • low-resolution sensors such as the lOOk-pixels range CIF image sensors and 300k-pixel range VGA image sensors
  • high-resolution, mega-pixels image sensors available. These higher resolutions not only require a focusing function of the optical lens system in order to be able to employ the high resolution over the entire object distance range (e.g.
  • the meniscus of an electrowetting lens is substantially spherical, it will not significantly contribute to removing optical aberrations in the image such as coma, distortion and spherical aberration.
  • the known electrowetting lens has limited magnification, field flattening and aberration reduction possibilities due to the limited number of optical surfaces.
  • the module is only suitable for low-resolution cameras such as CIF and VGA.
  • sensors such as the 500k-pixel range (S)VGA image sensors, the lM-pixel range XGA image sensors and mega-pixel devices this is not sufficient.
  • a camera lens stack containing an electrowetting lens, having flat entrance and exit windows, and containing separate lens groups in front and behind the electrowetting lens.
  • the focusing is performed through movement of the first lens group.
  • the electrowetting lens has a zoom function. It is not contributing to an improvement of other optical performances None of the above disclosures addresses the problem of achromatization, which is needed to achieve a good optical color correction of the imaging lens system.
  • Achromatization is the reduction of the dispersive optical power in an optical system.
  • a dispersive optical power is resulting from the dependence of refractive index n of the materials of the optical elements on the wavelength of the light.
  • the dispersion must be well corrected in order to obtain a high optical quality.
  • Conventional lens systems employ grating structures susceptible to haze, or costly doublet components for color correction.
  • a conventional lens system is rendered achromatic by forming a cemented doublet or by combining an ordinary refractive lens and a diffractive lens.
  • the two elements forming the lens have substantially the same refractive index and different Abbe-numbers.
  • the optical powers Kl and K2 and the Abbe-numbers VI and V2 of the two elements are chosen such that they comply with the equation:
  • achromatic by tuning the optical properties (e.g. Abbe-numbers) of the liquids involved e.g. mixing or dissolving well-chosen substances for the liquids.
  • Fluid-based variable lenses make up a lens system that can be made achromatic. For instance, to make the interface between the fluids achromatic the refractive index n and Abbe-number V for the fluids 'i' and 'n' must obey the relation:
  • an optical element having a chamber having an entrance window, an exit window and an optical axis extending longitudinally through the chamber, the chamber containing a first fluid and a second fluid in contact over a meniscus extending transverse the optical axis, the fluids being substantially immiscible, at least one of the entrance window or exit window comprising a surface being in contact with one of the first or the second fluid, said surface having a curvature, and the Abbe-number of the material of said at least one of the entrance and exit windows having a substantial difference with the Abbe-number of the fluid being in contact with the surface having a curvature.
  • a final overall design of an optical lens system is usually the result of an optimization of all aspects of the imaging in order to meet the system specifications related for example to, resolution, field of view, maximum chief-ray angles and optical aberrations such as distortion, spherical aberration and chromatic aberrations.
  • curved surfaces are allowed for the entrance and/or exit windows of the electrowetting lens, it is also possible to tune these curvatures with respect to the overall optical design of the system for optimizing of other aberrations such as distortion, spherical aberration or field curvature.
  • the curved surfaces can for example be spherical or aspherical.
  • Figure 1 schematically shows an optical lens system according to the invention.
  • Figure 2 shows the wavefront aberrations of an optical lens system design according to the invention.
  • Figure 3 shows the modulus of the optical transfer function for different wavelengths of an optical lens system design according to the invention.
  • Figure 4 illustrates a variable focus image capture device including an optical lens system according to the embodiments of the invention.
  • FIG. 1 schematically shows an optical lens system according to the invention.
  • the optical lens system (200) comprises two lens groups 201 and 202 and a stop 203 located between the first and second lens group.
  • the first lens group 201 comprises a variable lens, such as an electrowetting lens 204, and acts as a variable focus lens.
  • the second lens group 202 determines the optical magnification using a lens 220 to match size of the images with the size of the image sensor 205 located behind the optical lens system. Also it reduces the chief-ray angle by means of a field-flattening lens 206.
  • the image sensor 205 is covered with a transparent cover 207, for example a plane-parallel plate.
  • the electrowetting lens 204 has a chamber 208 provided with an entrance window 209 and an exit window 210, and an optical axis 211 extending longitudinally through the chamber.
  • the chamber contains a first fluid 213 and a second fluid 212 in contact over a meniscus 214 extending transverse the optical axis.
  • the radius of curvature of the surface of the entrance window 217 being in contact with the first fluid 213, has the same sign as the curvature of the meniscus 214 between the first and second fluid.
  • the curvature of the surface of the exit window 219, being in contact with the second fluid 212 has the same sign as the curvature of the meniscus 214 between the first and second fluid. This leads to a reduction of the building height.
  • the windows as well as the lenses can be made of glass, plastic or other suitable material.
  • the two fluids 212 and 213 used are being substantially immiscible.
  • the first fluid 213 is an electrically insulating fluid, such as silicone oil or an alkene referred to herein as oil
  • the second fluid 212 is an electrically conducting fluid, such as water containing a salt solution.
  • the two fluids preferably have an equal density, so that the lens operates independently of its orientation, i.e. without dependency on gravitational effects on the fluids.
  • the design can also lead to a situation in which the first fluid can be the electrically isolating fluid and the second fluid the conducting fluid.
  • a first electrode 215 in the chamber is typically a cylinder with a radius between 1 and 20mm, but can have a different shape, for instance conical, depending on the shape and geometry of the chamber. Electrode 215 is electrically insulated from the fluids by an insulating coating, for instance formed of parylene-N covered with a hydrophobic top coating of AF-1600.
  • a second, usually annular electrode 216 is arranged at an end of the chamber, in this case near the exit window. This second electrode 216 is arranged with at least one part in connection with the second fluid 212. This connection may be a direct contact, or a capacitive coupling over a thin insulating layer.
  • the fluids are in contact over a meniscus 214 having a curvature.
  • the meniscus can be changed to have a smaller or larger radius of curvature by applying a voltage over the electrodes.
  • a plurality of different shapes of the meniscus can be realized, dependent on the configuration of the chamber and the arrangement of the electrodes.
  • the surfaces of the optical element may take part in the overall optical design.
  • the curvatures of the windows may be used as extra number of degrees of freedom for the optical design to optimize the optical performance of the optical lens system.
  • the curvatures of the windows may be adapted for aberration corrections by applying aspherical surfaces and achromatization of the electrowetting lens, the lens group in which it is applied, or even the total optical lens system.
  • the optical element may be used in an optical lens system that can comprise more lenses with optical power. It is the object of the invention that the optical element not only acts as a focusing or zooming device, but that it may also act as chromatic aberration reduction element for the other elements in the optical lens system.
  • a refractive index difference between the materials of the curved window and contacting fluid gives the interface some optical power.
  • a substantially equal refractive index for both materials will result in substantially no optical power of the interface.
  • a difference in Abbe-number will result in a difference in optical power for the different wavelengths.
  • This difference in optical power for the different wavelengths can be used to correct the chromatic aberrations of the system.
  • camera lenses are designed with positive lenses made from a glass or a plastic, and having positive radii and being in contact with air. Air under normal conditions has high Abbe-number of about 90. This results only in positive contributions to the chromatic aberration.
  • Negative contributions for compensation can for example be introduced by applying buried lens-lens interfaces in a doublet with suitable interface radius as well as refractive indices and Abbe-numbers matching the design. The number of usable glasses and plastics are limited, and the use of doublets is not cost effective.
  • the combination of the optical parameters of the fluids and the optical properties of the window materials is used to obtain a cost effective substantial achromatic optical lens system.
  • the optical lens system may comprise the optical element only or the optical element and one or more refractive or diffractive elements.
  • the refractive index of the oil may vary between 1.25 and 1.65.
  • the salt solution used as the other fluid may have a refractive index varying between 1.32 and 1.50.
  • additives to the oil or the salted solution can change the Abbe-number of the fluid.
  • ⁇ V is the difference in Abbe-number of material n and i
  • ⁇ n the difference between the refractive index of material n and i. Allowing a substantial difference in refractive indices also requires a substantial difference in Abbe-numbers for the window and fluid to optimize the design for a substantially achromatized electrowetting lens.
  • the choice of materials for windows, fluids and curvatures may also be optimized for substantially achromatizing the total optical lens system. In that case the requirement as given in formula (2) has to be adapted to for example all surface in the optical lens system. The requirement for an achromatic lens system design then is
  • F/2.8, f 3.97mm auto focus camera lens with 66 degrees field of view, an entrance pupil of 1.42mm and a building height of 6.5mm to be used in combination with a mega-pixel type image sensor.
  • All lenses (209, 210, 220, 206) have aspherical surface in order to optimize the optical quality of the image.
  • the meniscus 214 is substantially spherical.
  • the Abbe-number of the enclosing plastic lenses 209 and 210 of the electrowetting lens 204 is 55.8 and their refractive index is about 1.532 at a 560nm wavelength.
  • the conducting fluid 212 comprises salted water and has an Abbe-number of 38 and a refractive index of 1.376 at 560nm wavelength, while the Abbe-number of the first non-conducting fluid 213, which is a silicone oil, is 28 with a refractive index of 1.552 at 560nm wavelength.
  • the optical system can be made substantially achromatic.
  • Figure 2 shows the wavefront aberrations of the optical lens system according to the above design. Wavefront aberrations W in micrometers versus the normalized entrance pupil coordinate Px respectively Py are plotted for three wavelengths 490nm, 560nm and 625nm.
  • Figure 2a this is shown for a field angle of 0 degrees and in Figure 2b for a field angle of about 33 degrees.
  • the maximum scale in vertical direction of both diagrams is 50 micrometer.
  • Figure 3 shows the calculated modulus of the polychromatic optical transfer function of the optical lens system according to the above design, averaged over three relevant wavelengths 490nm, 560nm and 625nm, as a function of the amount of lines per millimeter for a number field angles up to about 33 degrees for both the Px direction and the Py direction. It shows two groups of lines 301 and 302.
  • the group of line 301 are the polychromatic optical transfer functions in the Py direction for angles of 20, 29 and 33 degrees.
  • the group of lines 302 are the polychromatic optical transfer functions in the Px direction for angles of 0, 10, 20, 29 and 33 degrees, as well as in the Py direction for angles of 0 and 10 degrees. It shows that up to 75 lines/mm the modulation is sufficient for a megapixel imaging application as used in for example a camera in a mobile telephone.
  • all surfaces of both the entrance and exit windows have surface curvatures in order to be able to reduce aberrations, such as distortion and spherical aberration and building height.
  • FIG. 4A illustrates the use of a variable focus image capture device 421 using an optical lens system 400 according to the invention.
  • a measuring signal such as a focusing signal, may be derived from the image sensor 405 using techniques as commonly used in cameras using image sensors.
  • the measuring signal is used as input signal for a voltage driver 422.
  • the output of the voltage driver is connected to the electrodes 415 and 416 of the electrowetting lens 404 in the optical lens system 400 for controlling the shape of the meniscus 414.
  • Figure 4B shows an example of an application with the variable focus image capture device 421 integrated in the back of a mobile telephone 423.
  • Other integration positions are also possible.
  • the optical element is very suitable for use in optical lens systems and optical imaging systems for camera applications.
  • These camera applications can be for example movie or still picture hand-held cameras or mobile telephone cameras for movie or still picture.
  • mobile telephone with camera applications there is an increasing need for devices that are small size, have high optical quality, have a low energy use and are robust. Absence of mechanically moving parts, for e.g. focusing or zooming, makes the optical element according to the invention robust.
  • Optical lens systems and imaging systems that use the optical element according to the invention can fulfill those needs.
  • the above descriptions use an optical lens system suitable for small mobile camera systems such as for mobile telephone, the invention also can be used to achromatize, reduce aberrations and reduce building height of other optical systems, for example in microscopy and optical recording applications.
  • the described invention can for example be used to compensate wavelength dependent aberrations introduced by other optical elements in the optical system of the application.
  • the above embodiment and example on the variable lens element use the electrowetting principle for altering the shape of the meniscus.
  • other methods to change the shape of the meniscus between both fluids are considered to fall within the scope of the invention, for example by means of a pump in combination with a conically shaped electrode arranged to alter controllably the shape and the position of the meniscus.
  • the invention may be applied to fluid-based lenses that work by altering the position of the meniscus instead of the shape.

Abstract

L'invention concerne un élément optique (204) qui comprend une chambre (208) possédant une fenêtre d'entrée (209) et une fenêtre de sortie (210). La chambre comprend deux fluides sensiblement immiscibles (212, 213) qui sont en contact sur un ménisque (214). La fenêtre d'entrée (209) et/ou la fenêtre de sortie (210) comprennent une surface présentant une courbure (217, 219) qui est en contact avec un des fluides. Le nombre d'Abbe du matériau constituant la fenêtre d'entrée (209) et/ou la fenêtre de sortie (210) présente une différence notable avec le nombre d'Abbe du fluide en contact avec la surface présentant une courbure. Par sélection et réglage de paramètres de type rayon, indice de réfraction et nombres d'Abbe associés à ces fenêtres et à ces fluides, il est possible de concevoir un élément optique ou un système de lentille optique sensiblement achromatique.
PCT/IB2005/050760 2004-03-09 2005-03-02 Element optique variable comprenant des fluides immiscibles WO2005088354A1 (fr)

Applications Claiming Priority (2)

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EP04100948 2004-03-09
EP04100948.1 2004-03-09

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7142368B2 (en) 2004-09-01 2006-11-28 Samsung Electro-Mechanics Co., Ltd. Auto-focusing optical system for camera module
EP2239611A1 (fr) * 2008-02-04 2010-10-13 Sony Corporation Système de lentille de capture d'image et dispositif de capture d'image l'utilisant
WO2018013467A1 (fr) * 2016-07-11 2018-01-18 Raymond Miller Karam Lentille liquide à aberration chromatique réduite

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US4958919A (en) * 1988-10-20 1990-09-25 Lockheed Missiles & Space Company, Inc. Color-corrected optical systems with liquid lens elements
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Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7142368B2 (en) 2004-09-01 2006-11-28 Samsung Electro-Mechanics Co., Ltd. Auto-focusing optical system for camera module
EP2239611A1 (fr) * 2008-02-04 2010-10-13 Sony Corporation Système de lentille de capture d'image et dispositif de capture d'image l'utilisant
EP2239611A4 (fr) * 2008-02-04 2011-04-27 Sony Corp Système de lentille de capture d'image et dispositif de capture d'image l'utilisant
WO2018013467A1 (fr) * 2016-07-11 2018-01-18 Raymond Miller Karam Lentille liquide à aberration chromatique réduite
CN109804295A (zh) * 2016-07-11 2019-05-24 康宁股份有限公司 具有降低的色度偏差的液体透镜
US11092802B2 (en) 2016-07-11 2021-08-17 Corning Incorporated Liquid lens with reduced chromatic aberration
CN109804295B (zh) * 2016-07-11 2021-11-05 康宁股份有限公司 具有降低的色度偏差的液体透镜

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