Patent Application
20070153387
This invention relates in general to lenses and devices for digital image acquisition and relates in particular to a lens of compact configuration with a fixed focal length or variable focal length (zoom lens) for digital image acquisition in mobile information technology devices such as, for example, cell phones or PDAs, as well as a mobile information technology device, especially a data terminal, with such a lens.
Digital image acquisition increasingly necessitates compact lenses, i.e., lenses with a comparatively short overall length. This applies especially to digital image acquisition in data terminals such as, for example, PDAs or cell phones, where as flat a device geometry as possible is desired. With increasing integration density in microelectronics, currently digital image acquisition chips are also available, for example also as CCD image sensors or CMOS image sensors, with several million image acquisition elements on an extremely small surface; this will also make high image definition desirable in the future for comparatively flat mobile devices, such as the aforementioned mobile data terminals. Thus, there is an increasing demand for compact lenses with a short overall length that enable very high image definition and that are to be produced as economically as possible.
Cost-efficient lenses as an imaging optical element are known, particularly in the field of analog single-lens cameras, particularly disposable cameras. Thus, for example, U.S. Pat. No. 5,581,405 discloses an achromatic hybrid lens with a refractive basic element made of convex lens surfaces on the one lens surface of which there are diffractive structures which can be provided by means of press-forming the lens, injection molding from a plastic or by means of reworking of the one lens surface.
EP 1 193 512 A2 discloses a further diffractive optical element and an optical system provided therefrom.
U.S. Pat. No. 6,157,494 and U.S. Pat. No. 2005/0068637 A1 disclose a compact zoom lens which is provided with a diffractive optical element for correcting chromatic aberration. The lens has a comparatively complex structure and consequently is not suitable as a compact lens in the meaning of the present application for digital image acquisition, particularly for digital image acquisition in mobile applications such as, for example, data terminals.
U.S. Pat. No. 6,072,634 discloses a compact lens with a fixed focal length for digital cameras, which comprises four lenses manufactured by injection molding from a plastic, wherein diffractive optical structures are formed on one surface of one of the lenses, in order to suitably affect the chromatic aberration. The diffractive lens surface is disposed close to an aperture provided in the lens. For the exact alignment of the single lenses, they are provided with peripheral structures acting as an alignment flange, which are formed by subsequent twisting away of the structures, which is comparatively complex and expensive.
The object of this invention is to make available a lens with fixed or variable focal length for digital image acquisition that has a compact structure and can be produced economically and easily, and that is designed to enable high image definition, especially for digital image acquisition in mobile applications, for example for digital cameras, in cell phones, mobile data terminals, particularly PDAs, or else for applications in the automotive domain, for example for shoulder detection, for detection of individuals or obstacles, or for lenses for image acquisition when driving in reverse. According to another aspect of this invention, a digital image acquisition device with at least one such lens will also be made available.
According to a first aspect, the invention proceeds from a compact lens having a fixed focal length for digital image acquisition that comprises two or three, preferably two, refractive optical elements and at least one diffractive optical element to image incident light onto a detector array. According to the invention, the lens is characterized in that an imaging refractive optical element is provided as a compound or hybrid lens with a first lens element from a glass or from optical ceramics with a first index of refraction and with a second lens element from a plastic with a second index of refraction, which is smaller than the first index of refraction, wherein the first lens element is disposed in the beam path in front of the second lens element and at a light entry side of the lens. The incident light is therefore already relatively strongly refracted at the light entry side of the lens, which greatly reduces the overall length of the lens and considerably reduces imaging errors of the lens. In the case of such a compound or hybrid lens, the two lens elements are interconnected by material bonding and are preferably provided as single lenses, for example by injection molding plastic lenses or by pressing glass lenses. The material-bonded connection is preferably made by bonding, but can also be made by means of gluing or glass bonding.
According to another aspect the invention proceeds from a compact zoom lens with variable focal length for digital image acquisition, with at least two imaging optical element groups and at least one diffractive optical element, in order to image incident light onto a detector array. According to the invention, the zoom lens is characterized in that a refractive element of an element group at one light entry side of the lens is made as a compound lens with a first lens element from a glass or from optical ceramics with a first index of refraction and with a second lens element from a plastic with a second index of refraction, which is smaller than the first index of refraction, the first lens element being located on the beam path in front of the second lens element and at the light entry side of the lens. By this means the incident light is already relatively highly refracted at the light entry side of the lens, which greatly reduces the overall length of the lens and considerably reduces imaging errors of the lens. In the case of such a compound or hybrid lens, the two lens elements are interconnected by material bonding and are provided preferably as single lenses, for example by injection molding plastic lenses or by pressing glass lenses. The material-bonded connection is preferably made by means of bonding, but can also be achieved by means of gluing or glass bonding.
Suitable material combinations for achieving an advantageously compact lens comprise a glass with an index of refraction n>1.6 as the material with the first index of refraction. Suitable glasses are, for example, glasses with low Tg such as, e.g., N-LASF47 from Schott, K-VC89 from Sumita or S-LAH79 from OHARA, and all other optical glasses, e.g., N-SF6 or else N-SF66 or else LASF35 from Schott. As the material with the second index of refraction, a plastic is expediently provided with an index of refraction n<1.6. Such a plastic can be selected in particular from a group of plastics comprising the following: polymethylmethacrylate (PMMA), polycarbonate (PC), polymethylmethacrylimide (PMMI), polystyrene (PS), poly(styrene-co-acrylonitrile) (SAN), cycloolefin copolymers (COC), cycloolefin polymers (COP), methylpentene copolymers (PMP), polyethylene terephthalate (PET), polyurethanes, aliphatic polyurethanes, and silicones.
According to another embodiment, at least one diffractive optical element is provided on a refractive optical element. Expediently, such a refractive optical element is an optical lens, or else a compound or hybrid lens, which comprises two material-bonded interconnected single lenses. Since according to the invention only two or three refractive optical elements, particularly lenses, are provided, the lens according to the invention can be produced with a very short overall length which, compared with lenses with more lenses, results in a substantial reduction of the construction volume. Further significant costs can thus be saved according to the invention. At the same time imaging errors can be effectively compensated by means of the at least one diffractive element.
According to another embodiment, at least one diffractive optical element is made or provided directly on or at a transparent cover of a detector array. By this means the light imaged onto the detector array can more suitably be corrected directly in front of the detector array; this further increases important features of the lens, such as, e.g., imaging quality, image contrast and signal intensity, since the light sensitivity of the conventional detector arrays, especially of CCD chips or CMOS chips, is ordinarily highly dependent on the angle of incidence of the incident light. The higher sensitivity makes possible lenses with a smaller overall length.
In particular, lenses with comparatively small diameters can also be realized according to the invention, which at the same f-number of the lens contributes to a further reduction of the lens length. The arrangement or making of a diffractive optical element directly in front of or on the transparent cover also makes possible a still more effective compensation of the chromatic aberration of the lens.
According to another embodiment the diffractive optical element is made integral with the transparent cover. This can be implemented by, for example, making a diffraction grating, a Fresnel zone plate, from phase-active structures or the like in or on the transparent cover. The diffractive optical structures can be implemented by stamping, especially hot stamping, or by other suitable hot forming of the surface of the transparent cover or by other surface structuring processes such as etching (WCE, RIE, IBE, CAIBE) or else by laser ablation processes (UV laser, femto-second laser) or else by additive vapor deposition processes. According to another embodiment, a plastic or glass film can also be applied to the transparent cover and is further structured by stamping, especially hot stamping, or by other suitable hot forming in order to make a diffractive optical element.
According to another embodiment, the two lens elements of the compound lens are made as single lenses and are interconnected by material bonding.
According to another embodiment, an overall length L of the lens is smaller than or equal to a focal length f of the lens: L≦f. The lens according to the invention is therefore clearly below the conventional design limits for the design of compact lenses with a fixed focal length.
According to another embodiment the two diffractive optical elements are provided or made at or on mutually opposing boundary surfaces (interfaces) of two adjacent optical elements, of which one optical element is a refractive optical element.
According to another embodiment, two diffractive optical elements are provided in the lens at or on boundary surfaces (interfaces) of two adjacent optical elements, which surfaces face away from one another, one optical element being a refractive optical element.
According to another embodiment, the two diffractive optical elements in the lens are made from a material with the same index of refraction, an intermediate space between the two adjacent optical elements being filled with a transparent filler material with an index of refraction and an Abbe coefficient that is different from—is in particular smaller than—the index of refraction of the two diffractive optical elements and the two adjacent optical elements. With the transparent filler material, according to the invention another parameter is available for suitably influencing the imaging properties of the lens, especially the chromatic aberration and chromatic diffraction efficiency.
According to another embodiment, the index of refraction and the Abbe coefficient of the transparent filler material are selected such that the relationship between the light diffraction of the two diffractive optical elements and the wavelength of the light to be imaged is made uniform.
According to another embodiment, the filler material in the intermediate space is a plastic or a polymer whose Abbe coefficient is smaller than the Abbe coefficient of the material of the diffractive optical elements so that the transparent filler material dictates a comparatively strong dispersion.
According to another embodiment, the diffractive optical elements are made from a plastic.
According to another embodiment, the diffractive optical elements are made from a plastic that is selected from a group comprising the following: polymethylmethacrylate (PMMA), polycarbonate (PC), polymethylmethacrylimide (PMMI), polystyrene (PS), poly(styrene-co-acrylonitrile) (SAN), cycloolefin copolymers (COC), cycloolefin polymers (COP), methylpentene copolymers (PMP), polyethylene terephthalate (PET), polyurethanes, aliphatic polyurethanes, and silicones; and the intermediate space is filled with another plastic or polymer that is selected from the aforementioned group.
According to another embodiment, the diffractive optical elements are made from a glass with a low processing temperature Tg, preferably with a processing temperature Tg<1000° C., and more preferably with a processing temperature Tg<700° C.
According to another embodiment, the diffractive optical elements are formed from a glass with a low Tg that is selected from a group comprising: glass with low Tg such as, e.g., N-LASF47 from Schott, K-VC89 from Sumita or else S-LAH79 from OHARA, and all other optical glasses such as, e.g., N-SF6, N-SF66 or else LASF35 from Schott; and the intermediate space is filled with a plastic or polymer that is selected from a group comprising the following: polymethylmethacrylate (PMMA), polycarbonate (PC), polymethylmethacrylimide (PMMI), polystyrene (PS), poly(styrene-co-acrylonitrile) (SAN), cycloolefin copolymers (COC), cycloolefin polymers (COP), methylpentene copolymers (PMP), polyethylene terephthalate (PET), polyurethanes, aliphatic polyurethanes and silicones.
According to another embodiment, the diffractive optical elements are formed from raised diffractive sections whose maximum height H is given by: H≦Nλ/Δn, wherein λ designates a minimum wavelength of the light to be imaged, Δn is an absolute value of a difference of the index of refraction of the material of the diffractive optical elements and of the filler material, and N is an integer number between N=1 and N=20.
According to another embodiment, the diffractive optical element is made in each case by hot forming, especially by hot stamping, or by other surface structuring processes such as etching (WCE, RIE, IBE, CAIBE) or else by laser ablation processes (UV laser, femto-second laser) or else by additive vapor deposition processes of a surface of an optical lens or an optical element.
Another aspect of the present invention relates to a digital image acquisition device, especially a cell phone camera, with a solid body detector in the form of a detector array for digital image acquisition, with a lens as described above.
The invention will be described below by way of example and with reference to the attached drawings, from which other advantages, features and objects to be achieved will become apparent and wherein:
a and 12b show schematically in a top view and in a lateral view a cell phone with camera optics according to the present invention;
In all the figures identical reference numberals denote identical or equivalent elements or element groups.
According to
The use of glass for the first lens element 1 and of a plastic for the second lens element 2 has proven expedient. The second lens element 2 can thus be made by simple forming, particularly injection molding, of a plastic onto the planar rear side of a plano-convex lens base element and by stamping the plastic at a temperature below a softening temperature or processing temperature Tg of the glass of the first lens element 1, thereby reducing the manufacturing costs. The first lens element 1 also makes it possible to provide a particularly stable and non-susceptible lens surface, which is in particular comparatively scratch-resistant and attracts few contaminants, at the lens entry surface of the lens, which is of advantage especially for applications without a protective transparent cover in front of the lens.
To achieve a small overall length of the lens for the compound lens made from the first and second lens elements 1, 2 it has proven particularly expedient to have a combination of a comparatively high refractive glass type or even of optical ceramics and a low refractive plastic. By way of example the following material combinations for the material of the first and second lens elements 1, 2 are specified below: the material with the first index of refraction can be a glass with low Tg, for example a glass which has been selected from a group comprising: glasses with a low Tg, such as, e.g., N-LASF47 from Schoft, K-VC89 from Sumita or else S-LAH79 from OHARA, and all other optical glasses, such as, e.g., N-SF6, N-SF66 or else LASF35 from Schott, or else optical ceramics such as, e.g., Lumicera from Murata; and the material with the second index of refraction can be, e.g., a plastic, preferably selected from a group of plastics, comprising: polymethylmethacrylate (PMMA), polycarbonate (PC), polymethylmethacrylimide (PMMI), polystyrene (PS), poly(styrene-co-acrylonitrile) (SAN), cycloolefin copolymers (COC), cycloolefin polymers (COP), methylpentene copolymers (PMP), polyethylene terephthalate (PET), polyurethanes, aliphatic polyurethanes and silicones.
According to
To realize a compact lens design the intermediate spaces 8, 9 between the lenses are kept minimal. According to another embodiment, at least one of the intermediate spaces 8, 9 is filled with a plastic or polymer. The dispersion properties of this “filler material” can further affect the optical imaging properties of the lens advantageously. The dispersion of the filler material can further strengthen, or at least partially compensate, the wavelength dependency of the at least one DOE provided in the lens (reference number 6 according to
The lens intermediate spaces 8, 9 are advisably filled with a plastic or polymer with a smaller Abbe coefficient than the material of the element bounding the respective lens intermediate space, in order to be able to achieve even greater dispersion.
The elements of the lens are rotationally symmetric and are accommodated in a tubular lens tube (not shown). Although not shown in the figures, suitable apertures can basically be provided in the lens intermediate spaces 8, 9, particularly for reducing scattered light. To manufacture the lens, initially the optical elements with refractive action are provided. Subsequently the at least one DOE is made available, expediently by making or disposing it directly on one surface of one of the diffractive optical elements or of the transparent cover of the detector array. The optical elements and the transparent cover are aligned along the optical axis and disposed exactly parallel to one another. Subsequently the lens intermediate spaces are filled with a suitable plastic or polymer. By means of this measure the selected aligned and parallel arrangement of the optical elements is permanently fixed. In this manner a lens with a fixed focal length is made according to the invention.
The two intermediate spaces according to
Although not set forth above in more detail, when studying the above description one skilled in the art will easily see that the curved surfaces of the refractive optical elements 1-3 can optionally be made as spherical, aspherical or as free-form surfaces.
The diffractive structures can be made as surface phase elements according to the invention. For example, Fresnel zone plates or polynomial-shaped phase elements are mentioned, which consist on the surface of an arrangement of binary or else blazed or else saw-tooth structures of changing period. The raised sections project into the adjacent lens intermediate space filled with a plastic or polymer. For the maximum height H of the raised sections the following applies: H≦Nλ/Δn, wherein λ designates a minimum wavelength of the light to be imaged, Δn is an absolute value of a difference of the index of refraction of the material of the diffractive optical elements 5, 6 and of the filler material, and N is an integer number between 1 and 20.
The diffractive structures according to the invention can be made by structuring a surface of a diffractive optical element, for example of an optical lens or of a transparent glass or plastic cover of a detector array. Manufacturing processes are listed by way of example as: precision molding, etching including WCE (wet chemical etching), dry etching, IBE (ion beam etching), CAIBE (chemically assisted ion beam etching), mechanical working, injection molding, hot stamping, laser ablation. For the purpose of hot stamping by way of example another glass or plastic layer can be applied to the surface of a glass or plastic substrate, e.g., of an optical lens or of a transparent cover of a detector array, in particular it can be spun on or pressed on, which melts at a lower temperature than the substrate material. Naturally other structuring processes are also possible in principle for forming the diffractive optical structures.
By comparing
As will become apparent to a person skilled in the art when studying
As can be seen with ease by one skilled in the art, the lens according to the invention can be used in any optical devices in the fields of consumer optics, industrial optics or even in the automotive domain. By way of example the following is listed: lenses of mobile digital devices, such as for example cell phones, PDAs, portable data terminals.
Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The following preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever.
In the foregoing and in the following examples, all temperatures are set forth uncorrected in degrees Celsius and, all parts and percentages are by weight, unless otherwise indicated.
The entire disclosure[s] of all applications, patents and publications, cited herein and of corresponding German application No. 102005033746.5, filed Jul. 15, 2005, and U.S. Provisional Application Ser. No. 60/772,541, filed Feb. 13, 2006 are incorporated by reference herein.
The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding examples. From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.
Upon further study of the specification and appended claims, further objects and advantages of this invention will become apparent to those skilled in the art.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2005 033 746.5 | Jul 2005 | DE | national |
| Number | Date | Country | |
|---|---|---|---|
| 60772541 | Feb 2006 | US |
