DE102020105201A1 - Compact telephoto lens with a diffractive optical element - Google Patents

Abstract

An objective (1) for a camera (40) is described which has an optical axis (2), a focal length (f), an overall length (TL) in the direction of the optical axis (2), a number of refractive optical elements ( 11-15), a diaphragm (3) with a maximum diameter (D) and at least one diffractive optical element (4, 7). The focal length (f) of the lens (1) is in the range between 10 millimeters and 6 millimeters (10mm ≥ f ≥ 6mm) and the ratio of the focal length (f) to the maximum diameter of the aperture (D) is in the range between 2 and 4 ( 2 ≤ f / D ≤ 4). The ratio of the overall length (TL) to the focal length (f) is less than 0.9 (TL / f <0.9) and the focal length of the at least one diffractive optical element (FDOE) is greater than the focal length by a factor of at least 10 (f) of the lens (fDOE ≥ 10 * f).

Description

The project that led to this patent application was part of the Marie Sklodowska-Curie grant agreement No. 675745 funding from Horizon 2020 European Union research and innovation program received.

The present invention relates to a lens for a camera, a camera and a mobile device, for example a smartphone.

Numerous mobile devices, in particular smartphones, typically have a camera. A high quality camera is predominantly desired. In addition, there is a need for cameras with the largest possible zoom range. However, the overall length of smartphone lenses is very limited. At the same time, however, there is a need for systems with long focal lengths ( f ) in order to be able to cover a larger zoom area with different camera modules. However, the increase in the focal length required for this while the overall length (L) remains the same, in particular the implementation of focal lengths which are greater than the overall length, is difficult. This is due, among other things, to the low refractive indices of polymers from which the lenses used are typically made. Examples of lenses with focal lengths in the range of the overall length are for example in the documents US 9,223,118 B2 , US 10,306,031 B2 , US 10,288,845 B2 , US 10,261,288 B2 and US 2019/0056570 A1 described.

In general, photo objectives with efficiency achromatized diffractive optical elements (DOEs) are known. The efficiency achromatized diffractive optical elements serve to reduce the chromatic aberration.

Diffractive optical elements are used, for example, for the spectral splitting of light and for the deflection of light. Such elements are based on the principle of diffraction of light waves and are designed to deflect light of a certain wavelength in a certain direction with the aid of a diffractive structure, i.e. with the aid of a diffraction grating. The diffraction efficiency of a diffractive optical element is a measure of the proportion of the light transmitted through the grating structure that is diffracted into a certain order of diffraction, i.e. the desired direction. The diffraction efficiency represents the ratio of the energy flow propagating in the desired diffraction order through the entire transmitted energy flow. Basically, for a certain wavelength, the so-called design wavelength of the diffractive optical element, neglecting shadowing effects, all light with the design wavelength is diffracted in the same order of diffraction and thus deflected in the same direction, so that a diffraction efficiency of 1 ( or 100%) can be achieved (so-called blaze grille or echelette grille). However, this does not apply to wavelengths that deviate from the design wavelength. Light with a wavelength deviating from the design wavelength is deflected into different diffraction maxima and thus in different directions. In the case of diffraction of polychromatic light, this leads to scattered light outside the diffraction order and thus to loss of resolution.

Diffractive optical elements have therefore been developed which are able to achieve a high diffraction efficiency in a certain order of diffraction - mostly the first order of diffraction - for all wavelengths from a certain wavelength range. Such diffractive optical elements are called efficiency achromatized diffractive optical elements. Efficiency-achromatized diffractive optical elements are accordingly diffractive optical elements in which a high diffraction efficiency is achieved for all wavelengths of a certain wavelength range for a certain diffraction order.

There are different approaches to the production of efficiency achromatized diffractive optical elements. For example, in U.S. 6,873,463 , U.S. 9,696,469 , US 2001/013975 and U.S. 5,487,877 proposed the use of multilayer diffractive optical elements in order to bring about an efficiency achromatization. the end DE 10 2006 007 432 A1 , US 2011/026118 A1 , U.S. 7,663,803 , U.S. 6,912,092 , US2013 / 057956 A1 , US 2004/051949 A1 and U.S. 5,847,887 It is also known to adapt the refractive index of one of the layers in multilayer diffractive optical elements in such a way that the dispersion of another layer is canceled. the end US 2011/090566 A1 , U.S. 9,422,414 , U.S. 7,031,078 , U.S. 7,663,803 , U.S. 7,196,132 and U.S. 8,773,783 diffractive optical elements are known in which materials with anomalous dispersion are used in order to bring about an efficiency achromatization.

In the case of diffractive optical elements with periods that are very large compared to the wavelength of the light to be diffracted, single-layer diffractive optical elements can be designed in such a way that theoretically a diffraction efficiency of 100% is achieved for a given design wavelength (λ ₀ ). However, if the wavelength deviates from this design wavelength, the diffraction efficiency decreases sharply with increasing deviation from the design wavelength. This leads to undesired scattered light in optical imaging systems and thus prevents the Use of such diffractive optical elements in broadband optical systems. This problem can be solved by adding an additional diffractive layer made of a material with a different refractive index, as shown for example in FIG US 6,873,463 B2 , US 9,696,469 B2 , U.S. 5,847,877 and US 2001/0013975 A1 , as D. Werdehausen et al. "Dispersion-engineered nanocomposites enable achromatic diffractive optical elements", OSA Publishing, Optica, Volume 6, Issue 8, pages 1031-1038 (2019) (https://doi.org/10.1364/OPTICA.6.001031) and D. Werdehausen et al. "General design formalism for highly efficient flat optics for broadband applications" OSA Publishing, Optics Express, Volume 28, Issue 5, page 6452-6468 (2020) (https://doi.org/10.1364/OE.386573). The two layers can have different profile heights, which can be adapted to one another in order to maximize the average diffraction efficiency in the desired wavelength range, as is the case, for example, from BH Kleemann et al. in "Design-Concepts for broadband high-efficieny DOEs", Journal of the European Optical Society-Rapid publications 3 (2008) is described. On the other hand, through a suitable choice of the second material, the average diffraction efficiency can be maximized in the desired wavelength range with the same profile height of the layers. While diffractive optical elements with different profile heights are typically called multilayer DOEs, diffractive optical elements with the same profile height of the layers are usually called “common depth DOEs”. In order to implement a common depth DOE, material combinations must be selected whose dispersion compensate each other as well as possible. For example, common depth DOEs are in DE 10 2006 007 432 A1 , US 2011/0026118 A1 , U.S. 7,663,803 , U.S. 6,912,092 , US 2012/0597741 A1 , US 2004/051949 A1 and U.S. 5,847,877 described. Both approaches have already been implemented in commercially available camera lenses. Diffractive optical elements can be implemented, for example, with inclined surfaces, as is the case in the aforementioned multilayer DOEs and common depth DOEs. An alternative approach to making diffractive optical elements is to periodically vary the index of refraction within the element as a function of location. This gives a so-called gradient index DOE, also known as GRIN DOE for short. However, the diffraction efficiency of a graded index DOE is highly dependent on the wavelength. This problem is known from other single-layer diffractive optical elements and can be circumvented by applying a second GRIN-DOE layer analogously to a multilayer DOE, as is described, for example, in the publication by BH Kleemann already cited. This in turn gives a two-layer diffractive optical element, which increases the height of the overall system.

The use of diffractive optical elements in connection with ordinary camera lenses is for example in the documents US 2018/0 373 004 A1 , US 7,800,842 B2 , U.S. 6,101,035 , JP 2016-102852 A ( JP 20140239895 ), JP 2019-028317 A ( JP 20170148612 ) and JP 2018 - 189878 A ( JP 20170093783 ) described. Smartphone lenses with diffractive optical elements are used, for example, in DE 10 2005 009 238 A1 , DE 10 2005 033 746 A1 , US 2010/0188758 A1 , US 2009/0002829 A1 , US 2010/309367 A1 , US 2015/293370 A1 and CN 107894655 A described.

Against the background described, it is the object of the present invention to provide an improved compact lens for a camera which is particularly suitable for mobile devices such as smartphones and is designed as a telephoto lens. Further tasks are to provide an advantageous camera and an advantageous mobile device.

The first object is achieved by an object for a camera according to patent claim 1. The second object is achieved by a camera according to claim 14 and the third object is achieved by a mobile device according to claim 15. The dependent claims contain further advantageous embodiments of the present invention.

The lens according to the invention for a camera comprises an optical axis, a focal length f , with length TL in the direction of the optical axis, a number of refractive optical elements, for example 3 to 5 lenses, an aperture with a maximum diameter D. , so a diameter D. in the completely open state of the diaphragm, and at least one diffractive optical element, for example one or two or at least two diffractive optical elements. The focal length f of the lens is in the range between 10 millimeters (10mm) and 6 millimeters (6mm) (10mm f 6mm), for example in the range between 10 mm and 8 mm, in particular in the range between 10 mm and 7 mm. The ratio of the focal length f to the maximum diameter of the aperture D. lies in the range between 2 and 4 (2 ≤ f / D ≤ 4). The ratio of the overall length TL to the focal length f is less than 0.9 ( TL / f <0.9), preferably less than 0.8. The focal length of the at least one diffractive optical element f _DOE is greater than the focal length by a factor of at least 10 f of the lens (F _DOE ≥ 10 * f).

The objective according to the invention has the advantage that it is very compact and at the same time powerful telephoto lens. The functionality of a telephoto lens is guaranteed despite the short overall length compared to the focal length. In other words, the lens is designed as a telephoto lens. The lens is preferably designed for a camera for a portable mobile device, for example for a smartphone camera or for a camera for a tablet or a smartwatch or data glasses. In this context, in particular a telephoto lens for a smartphone camera or a camera for another portable mobile device can be implemented.

The at least one diffractive optical element preferably has a focal length in the range between 1000 millimeters and 100 millimeters (1000 mm f _DOE 100 mm). In an advantageous variant, the focal length of the diffractive optical element is greater by a factor of between 10 and 200, in particular by a factor of between 30 and 100, than the total focal length of the objective. The selection of a suitable diffractive optical element makes it possible to achieve a focal length which is significantly greater than the overall length of the objective.

Advantageously, at least one diffractive optical element is arranged in relation to the overall length of the objective starting from an object side in the direction of an image side in the first third of the objective and / or at least one diffractive optical element in the second half, for example in the third third, of the objective. In a further variant, the minimum distance between the sections Amin of the at least one diffractive optical element forming the grating can be between 10 and 500 micrometers (10 μm _min 500 μm). In the case of at least two diffractive optical elements, for example, a first diffractive optical element can be arranged in the first third of the objective and have a minimum distance between the sections forming the grating between 30 and 500 micrometers and a second diffractive optical element in the second half, for For example, be arranged in the third third of the objective and have a minimum distance between the sections forming the grating of between 10 and 200 micrometers. Such a configuration achieves focal lengths of the diffractive optical elements which are at least ten times as high as the total focal length of the objective.

Furthermore, the lens can have a field of view (FOV) over the full diagonal in the range between 40 degrees and 25 degrees (40 ° FOV 25 °). The at least one diffractive optical element and / or at least one, preferably all, of the refractive optical elements can comprise a polymer or consist of a polymer. The use of polymers has the advantage that the corresponding components are, on the one hand, designed to be light and robust. The following compositions, for example, can be used as polymers: polymethyl methacrylate (PMMA), cyclo olefin polymer (COP), cyclo olefin copolymer (COC; brand name ZEONEX), polycarbonate (PC), polystyrene (PS) and styrene acrylonitrile (SAN).

The properties mentioned enable a compact and lightweight construction of a simultaneously powerful telephoto lens.

In an advantageous variant, the objective comprises between three and five, for example 3 or 4, refractive optical elements. The refractive optical elements can be lenses, for example. By combining at least one diffractive optical element with a maximum of five, four or three lenses, a particularly small, comparatively simply constructed lens with a low weight is made available.

The at least one diffractive optical element can be introduced into at least one of the refractive optical elements, for example a lens, or permanently connected to it. The at least one diffractive optical element can be introduced directly into a surface of the refractive optical element, for example as a gradient index element. Alternatively, the at least one diffractive optical element can be applied to a surface of one of the refractive optical elements, for example glued or cemented onto a refractive optical element as a layer. In a further alternative, the at least one diffractive optical element can be arranged in the form of a plate, for example in the form of a free-standing plate. The plate is arranged at a suitable position in the beam path of the objective.

The diffractive optical element can be made up of two layers, the first layer having a first refractive index n ₁ (λ) and the second layer having a second refractive index n ₂ (λ) _{different from the first refractive index n 1.} Additionally or alternatively, the at least one diffractive optical element can be designed as a gradient index element. In the case of an embodiment as a gradient index element, there is a continuous transition from a first refractive index n ₁ (λ) to a second refractive index n ₂ (λ).

The at least one diffractive optical element is preferably designed to be efficiency achromatized. This means that it diffracts at least 95% of the transmitted light for all wavelengths within a specified spectral range Example within the visible spectral range, in one order of diffraction. In order to achieve efficiency achromatization, the diffractive optical element, as already described above, can be made up of two layers and / or designed as a gradient index element. In the cases mentioned, the refractive indices in n ₁ (λ) and n ₂ (λ) are preferably optimized so that the difference between the two, i.e. Δn (λ) = n ₁ (λ) -n ₂ (λ), is practically linear from the Depends on the wavelength (see the aforementioned publication by BH Kleemann et al. in "Design-Concepts for broadband high-efficieny DOEs", Journal of the European Optical Society-Rapid publications 3 (2008) ). For this purpose, n ₁ (λ) must have a higher refractive index at the d-line (n _d = n (587.56nm)) and a higher Abbe number (ν _d ) than n ₂ (λ).

Additionally or alternatively, it is possible for the at least one diffractive optical element to be constructed as a meta-surface, ie from individual elements that are smaller than a specific wavelength. In this case, n ₁ (λ) and n ₂ (λ) represent the effective refractive indices of the waveguides, or in the case of very dense elements of the averaged medium.

The at least one diffractive optical element preferably has a height H of less than 20 micrometers (h <20 μm), for example a height of less than 10 micrometers (h <10 μm). This has the advantage that sufficiently high efficiencies can be achieved with inclined incidence of light and small grating periods.

The diffractive optical element (DOE) can have a single, diffractive structure with a spatial variation in the refractive index. The spatial variation in the refractive index forms a sequence of adjoining sections within which the refractive index varies in each case and which form a diffractive structure. The diffractive optical element is thus a GRIN-DOE. The sequence of adjoining sections forms a structure with variable lateral dimensions of the sections, which leads to a diffraction angle that varies in a defined manner depending on the location on the diffractive structure, for example, in addition to the deflecting effect of the structure, for example, a focusing, a defocusing, an aberration compensating effect or to achieve another visual effect.

The diffractive structure can have a diffraction efficiency averaged over this spectral range of at least 0.95 over a spectral range extending at least over 300 nm and preferably over at least 350 nm. The spectral range can be a section of the visible spectral range, in particular the spectral range can be the entire visible spectral range, i.e. the spectral range from 400 to 800 nm or, to be more narrowly specified, from 400 to 750 nm.

The diffractive optical element can be characterized in that the value is the diffraction efficiency averaged over the spectral range of at least 300 nm of at least 0.95 by a single single-layer diffractive structure with a combination of at least one optimized maximum refractive index nmax and an optimized minimum refractive index n _min and at least one optimized high Abbe number ν _max and an optimized low Abbe number ν _{min is implemented} within each section of the sequence of adjacent sections.

The diffractive optical element can be produced with a low profile height due to the fact that the diffraction efficiency averaged over the spectral range of at least 0.95 can be achieved by a single single-layer diffractive structure. The lower the profile height of the diffractive structure, the lower the shadowing effects caused by the profile height. The lower the shadowing effects, the slower the diffraction efficiency drops when the angle of incidence of the light is increased and / or when the lateral extent of the sections of the sequence of adjoining sections is reduced.

In an advantageous embodiment of the diffractive optical element, the value of the diffraction efficiency averaged over the spectral range of at least 300 nm is at least 0.95 due to a single single-layer diffractive structure with at least one combination of an optimized maximum refractive index n _max at a certain wavelength of the spectral range of at least 300 nm, an optimized minimum refractive index n _min at the specific wavelength of the spectral range of at least 300 nm, an optimized high Abbe number ν _max and an optimized low Abbe number ν _min and optionally an optimized first partial partial dispersion and an optimized second partial dispersion Partial dispersion realized within each section of the sequence of adjacent sections.

The refractive index is a variable that depends on the wavelength, the wavelength of which can be described, for example, by the Cauchy equation, particularly in the visible spectral range. Therefore, two differently parameterized Cauchy equations are necessary to describe the wavelength dependency of the optimized maximum refractive index n _max and the optimized minimum refractive index n _min. Since the The wavelength dependency of the Cauchy equation can be determined in a sufficient approximation by the value of the refractive index at a certain wavelength together with the value of the Abbe number and the value of the partial partial dispersion, this configuration allows the optimization of the wavelength-dependent maximum refractive index n _max as well as the wavelength-dependent one minimum refractive index n _min by optimizing six parameters, namely the maximum refractive index n _max at the specific wavelength, the minimum refractive index n _min at the specific wavelength, the high Abbe number ν _max , the low Abbe number ν _min , the first partial Partial dispersion and the second partial partial dispersion. Since the dependence of the Cauchy equation on the partial partial dispersion has less of an effect on the value of the diffraction efficiency averaged over the spectral range of at least 300 nm, partial partial dispersions can each be kept at a given value without varying them in the optimization.

With the optimized values for the maximum refractive index n _max at the specific wavelength of the spectral range, for the minimum refractive index n _min at the specific wavelength of the spectral range, for the high Abbe number ν _max and for the low Abbe number ν _min and optionally for the first partial partial dispersion and for the second partial partial dispersion the difference Δn (λ) = n _{max (} λ) _{−n min} (λ) runs largely linearly as a function of the wavelength λ over the spectral range of at least 300 nm.

In the diffractive optical element, the optimized high Abbe number ν _{max is} preferably in the area with the optimized maximum refractive index n _max and the optimized low Abbe number ν _{min is} preferably in the area with the optimized minimum refractive index n _min . This is contrary to the trend of optical materials to have a lower Abbe number with increasing refractive index and is made possible, for example, by the use of doped or mixed optical materials.

It is advantageous if the refractive index difference Δn between the optimized maximum refractive index n _max and the optimized minimum refractive index n _{min has} at least a value of 0.005, in particular at least a value of 0.01 and preferably at least a value of 0.015, at least at the specific wavelength, since the profile height of the diffractive structure can be kept lower, the greater the refractive index difference Δn.

It is also advantageous if the Abbe number difference Δν between the optimized high Abbe number ν _max and the optimized low Abbe number ν _{min has} at least a value of 8, in particular at least one value 15th and preferably at least one value 30th having. The higher the Abbe number difference Δν, the higher the refractive index difference Δn can be, with which the diffraction efficiency averaged over the spectral range of at least 0.95 can be achieved, which in turn enables lower profile heights of the diffractive structure to be achieved.

In the diffractive optical element, at least two maxima of the spectral diffraction efficiency can be present in the spectral range extending at least over 300 nm, preferably over at least 350 nm. While the diffraction efficiency averaged over the spectral range of at least 300 nm represents a value for the diffraction efficiency averaged over the spectral range, the spectral diffraction efficiency represents the diffraction efficiency as a function of the wavelength of the diffracted light. If the spectral diffraction efficiency has at least two maxima, a uniform course of the spectral diffraction efficiency over the spectral range can be achieved for a certain value of the diffraction efficiency averaged over the spectral range of at least 300 nm, in particular if the wavelengths differ in the case of two maxima of the spectral diffraction efficiency , at which the maxima lie, differ from one another by at least 150 nm, preferably by at least 200 nm. In the case of more than two maxima, in particular when the wavelengths at which the two outer maxima are located differ from one another by at least 150 nm, preferably by at least 200 nm.

The diffractive structure of the diffractive optical element can consist of a doped material or a material mixed from at least two materials with different refractive indices. The spatial variation in the refractive index is then based on a variation in the doping or a variation in the mixing ratio. The production of the diffractive structure can then take place relatively easily by introducing spatially varying doping or by 3D printing with a mixing ratio of the mixed material that is fed in that varies over time. If a printer with several print nozzles is used, instead of a mixing ratio that varies over time, a mixing ratio that varies over the nozzles can also be used.

The described variants of an embodiment of the at least one diffractive optical element make it possible to achieve a particularly large focal length compared to the overall length of the objective with a simultaneous correction various aberrations, such as a chromatic aberration, and other aberrations. A very high quality and at the same time very compact telephoto lens is thus made available with regard to the image quality.

The camera according to the invention comprises a previously described lens according to the invention. The mobile device according to the invention comprises a camera as described above. The mobile device is preferably a smartphone or a tablet or a smartwatch or data glasses. The camera according to the invention and the mobile device according to the invention, in particular the smartphone, have the same properties and advantages as the lens according to the invention already described.

The present invention has the following advantages overall: A compact telephone lens for smartphones, in particular with a focal length which is greater than the overall length (f> TL), is made available. The objective can be constructed at least partially from polymers, which means that it has a low weight. Furthermore, less refractive optical elements, in particular lenses, are required within the scope of the objective according to the invention in order to realize a powerful objective. In addition, the complexity of the aspheres is reduced, making them less sensitive to manufacturing tolerances.

The invention is explained in more detail below on the basis of exemplary embodiments with reference to the accompanying figures. Although the invention is illustrated and described in more detail by the preferred exemplary embodiments, the invention is not restricted by the disclosed examples and other variations can be derived therefrom by the person skilled in the art without departing from the scope of protection of the invention.

The figures are not necessarily true to detail and to scale and can be enlarged or reduced in order to provide a better overview. The functional details disclosed here are therefore not to be understood as restrictive, but merely as an illustrative basis that offers the person skilled in the art in this field of technology guidance in order to use the present invention in a wide variety of ways.

• 1 zeigt schematisch eine erste Variante eines erfindungsgemäßen Objektivs.
• 2 zeigt schematisch eine zweite Variante eines erfindungsgemäßen Objektivs.
• 3 zeigt schematisch eine dritte Variante eines erfindungsgemäßen Objektivs.
• 4 zeigt schematisch eine vierte Variante eines erfindungsgemäßen Objektivs.
• 5 zeigt schematisch eine fünfte Variante eines erfindungsgemäßen Objektivs.
• 6 zeigt schematisch eine sechste Variante eines erfindungsgemäßen Objektivs.
• 7 zeigt schematisch eine siebente Variante eines erfindungsgemäßen Objektivs.
• 8 zeigt ein erstes exemplarisches Ausführungsbeispiel für ein diffraktives optisches Element.
• 9 zeigt in einer schematischen Darstellung eine Linse mit einem integrierten diffraktiven optischen Element.
• 10 zeigt ein zweites exemplarisches Ausführungsbeispiel für ein diffraktives optisches Element.
• 11 zeigt ein drittes exemplarisches Ausführungsbeispiel für ein diffraktives optisches Element.
• 12 zeigt ein viertes exemplarisches Ausführungsbeispiel für ein diffraktives optisches Element.
• 13 zeigt schematisch eine erfindungsgemäße Kamera.
• 14 zeigt schematisch ein erfindungsgemäßes mobiles Gerät.

The term "and / or" as used herein, when used in a series of two or more items, means that any of the listed items can be used alone, or any combination of two or more of the listed items can be used. For example, if a composition is described that it contains components A, B and / or C, the composition A alone; B alone; C alone; A and B in combination; A and C in combination; B and C in combination; or A, B, and C in combination.

• 1 shows schematically a first variant of an objective according to the invention.
• 2 shows schematically a second variant of an objective according to the invention.
• 3 shows schematically a third variant of an objective according to the invention.
• 4th shows schematically a fourth variant of an objective according to the invention.
• 5 shows schematically a fifth variant of an objective according to the invention.
• 6th shows schematically a sixth variant of an objective according to the invention.
• 7th shows schematically a seventh variant of an objective according to the invention.
• 8th shows a first exemplary embodiment for a diffractive optical element.
• 9 shows a schematic representation of a lens with an integrated diffractive optical element.
• 10 shows a second exemplary embodiment for a diffractive optical element.
• 11 shows a third exemplary embodiment for a diffractive optical element.
• 12th shows a fourth exemplary embodiment for a diffractive optical element.
• 13th shows schematically a camera according to the invention.
• 14th shows schematically a mobile device according to the invention.

In the following, the 1 until 7th various embodiments for lenses according to the invention 1 described. The lenses are in the 1 until 7th Shown enlarged to scale. In addition, the beam path is shown for different angles of incidence, ie field points, and in all figures with the reference number 10 marked.

All lenses shown 1 each have an optical axis 2 , Focal length f and a length TL along the optical axis 2 on. The lenses 1 also include a bezel 3 , three or four refractive optical elements 11-14 in the form of lenses and at least one diffractive optical element 4th , 7th . They also include the lenses shown 1 an image plane 5 and one in the beam path in the direction from an object plane to the image plane 5 immediately in front of the image plane 5 arranged plane-parallel plate 6th . The refractive optical elements 11-14 each point one to the object plane or to the diaphragm 3 pointing front 8th and one to the picture plane 5 pointing back 9 on.

In the direction of the beam path from the object plane to the image plane are in the 1 The variant shown is the bezel 3 , a first lens 11 , a second lens 12th and a third lens 13th and in the 2 until 6th in addition a fourth lens 14th in front of the plane-parallel plate 6th and the image plane 5 arranged. The lenses shown 11-14 are preferably shaped aspherically. The refractive optical elements or lenses can basically be convex, concave, spherical or aspherical or any combination thereof. Free-form lenses or Fresnel lenses can also be used.

Within the scope of the lens according to the invention 1 In principle, refractive and / or diffractive optical elements made up of polymers can be used.

The ones in the 1 , 2 and 6th shown lenses 1 have a first lens 11 with a convex front 8th and a concave back 9 on. The ones in the 3 until 5 and 7th shown lenses 1 have a first lens 11 with a convex front 8th and a convex back 9 on. The second through fourth lenses 12-14 are in the 1 until 6th aspherically shaped.

The ones in the 1 and 2 objectives according to the invention shown schematically 1 have a length of 6 millimeters (TL = 6mm), a focal length f of 7 millimeters (f = 7.0mm), a ratio of the focal length f to the maximum diameter D. the aperture of 2.8 (f / D = 2.8) and a field of view of 36 degrees. That in the 2 shown lens 1 points in contrast to that in the 1 shown lens 1 four lenses on. The second lens 12th and the third lens 13th can be designed as a composite lens or glued together.

A diffractive optical element 4th with a minimum distance between the sections forming the grating of more than 40 micrometers is in the first third of the beam path in relation to the overall length starting from the diaphragm 3 in the direction of the image plane 5 arranged, for example at the rear 9 the first lens 11 or in the first lens 11 integrated. Variants for a configuration of the diffractive optical element 4th are described below using the 7th until 12th explained in more detail.

The ones in the 3 and 4th objectives according to the invention shown schematically 1 have 4 lenses, a length of 6 millimeters ( TL = 6mm), one focal length f of 8 millimeters (f = 8.0mm), a ratio of the focal length f to the maximum diameter D. the aperture of 2.8 (f / D = 2.8) and a field of view of 31.5 degrees. In the in the 3 The example shown is a diffractive optical element 4th with a minimum distance between the sections forming the grid of more than 90 micrometers in the first third of the overall length starting from the diaphragm 3 in the direction of the image plane 5 arranged, for example at the rear 9 the first lens 11 or in the first lens 11 integrated. In the in the 4th The example shown is a diffractive optical element 4th with a minimum distance between the sections forming the grating of more than 15 micrometers in the second half of the beam path in relation to the overall length starting from the diaphragm 3 in the direction of the image plane 5 arranged, for example at the rear 9 the third lens 13th or integrated into them.

the 5 shows an embodiment with 4 lenses and two diffractive optical elements, of which a first diffractive optical element 4th with a minimum distance between the sections forming the grating of more than 100 micrometers in the first third of the beam path in relation to the overall length, for example at the rear 9 the first lens 11 , and a second diffractive optical element 7th with a minimum distance between the sections forming the grating of more than 35 micrometers in the second half of the beam path in relation to the overall length, for example at the rear 9 the third lens 13th , is arranged.

That in the 5 shown lens 1 has a focal length of 8 millimeters (f = 8 mm), an overall length of 6 millimeters (TL = 6 mm), a ratio of the focal length to the maximum aperture of 2.8 (f / D = 2.8) and a field of view of 31 .5 degrees (FOV = 31.5 °). That in the 6th shown lens 1 with a diffractive optical element 4th in the first Third of the beam path in relation to the overall length has a focal length of 9 millimeters (f = 9 mm), an overall length of 6 millimeters (TL = 6 mm), a ratio of the focal length to the maximum aperture of 3.6 (f / D = 3 , 6) and a field of view of 28 degrees (FOV = 28 °).

That in the 7th shown lens 1 comprises 5 lenses, the fifth lens having the reference number 15th is marked. The objective 1 has a focal length of 8 millimeters (f = 8 mm), an overall length of 6 millimeters (TL = 6 mm), a ratio of the focal length to the maximum aperture of 2.5 (f / D = 2.5) and a field of view of 31 .4 degrees (FOV = 31.4 °). A first diffractive optical element 4th with a minimum distance between the sections forming the grating of more than 70 micrometers is arranged in the first third of the beam path in relation to the overall length, for example on the rear 9 the first lens 11 . A second diffractive optical element 7th with a minimum distance between the sections forming the grating of more than 42 micrometers is arranged in the second half of the beam path in relation to the overall length, for example at the rear 9 the fourth lens 14th .

In principle, the at least one diffractive optical element can 4th , 7th either on a surface of one of the lenses, preferably the first lens 11 , on or in, cemented on as an additional layer or placed as a free-standing plate in the beam path. Alternatively, it is also conceivable to introduce a diffractive optical element into a lens as a gradient index DOE (GRIN DOE). This is explained below. The diffractive optical element 4th has a focal length in all cases f _DOE , which is very much larger, for example by a factor between 10 and 200, preferably by a factor between 30 and 100, than the focal length f of the entire lens. The focal length of the diffractive optical element is preferably located 4th as a single element f _DOE in the range between 1000 mm and 100 mm.

The at least one diffractive optical element 4th , 7th in the lens 1 is preferably efficiency achromatized. This means that it diffracts at least 95% of the transmitted light for all wavelengths within a specified spectral range, for example within the visible spectral range, for example between 400 μm and 800 μm, into a diffraction order. For this purpose, it can be made up of two layers. A first layer has a first refractive index n ₁ (λ) and a second layer has a second refractive index n ₂ (λ). Such a configuration is shown schematically in FIG 10 shown. In the case of a GRIN-DOE, on the other hand, there is a continuous transition from n ₁ (λ) to n ₂ (λ). In all cases, n ₁ (λ) and n ₂ (λ) have to be optimized in such a way that Δn (λ) = n ₁ (λ) - n ₂ (λ), i.e. the difference in the refractive indices, depends practically linearly on the wavelength.

Alternatively, it is also possible to build the diffractive optical element as a metasurface, ie from individual elements that are smaller than a certain wavelength, for example smaller than the smallest wavelength used for which the objective is designed, for example the smallest wavelength of visible light . An example of this is given using the 11 explained in more detail. In this case, the refractive indices n ₁ (λ) and n ₂ (λ) represent the effective refractive indices of the waveguides, or in the case of very dense elements of the averaged medium. The total height H , also called the profile height, of the diffractive optical element is preferably less than 20 μm and particularly preferably less than 10 μm.

the 8th shows a section from a diffractive optical element 4th , 7th , which is a diffractive structure 33 which is formed from a sequence of mutually adjacent sections 33A to 33D. The diffractive structure 33 - and thus the optical element - has a profile height H which is not more than 20 µm, in particular not more than 50 µm and preferably not more than 10 µm. In a direction perpendicular to the profile height, the diffractive structure has a spatial variation in the refractive index, by which the sections 33A to 33D are defined. Within each section 33A to 33D, the refractive index decreases from an area represented with a low point density 25th , which represents a region with a minimum refractive index n _min (λ _{0 ) based on a specific wavelength λ 0 of} the diffractive structure, to a region represented with a high point density 27 , which represents a region with a maximum refractive index n _max (λ _{0 ) based on the specific wavelength λ 0} , increases continuously.

Such a diffractive structure is called a gradient index DOE or GRIN DOE for short. Such a grating can be designed in such a way that its spectral diffraction efficiency η (λ) for a specific wavelength λ _des , the so-called design wavelength, theoretically equals the value 1 or 100% achieved. The design wavelength λ _des does not need to _{match the specific wavelength λ 0} , but a match of specific wavelength λ ₀ and design wavelength λ _des is can simplify the design of the diffractive structure if a high diffraction efficiency over the entire visible spectral range and a low profile height of the diffractive structure is to be achieved.

In the present exemplary embodiment, the continuous increase in the refractive index n (λ ₀ ) at the specific wavelength λ _{0 is} due to a linear increase from that in the range 25th present minimum refractive index n _min (λ ₀ ) at the specific wavelength λ ₀ to that in the area 27 present maximum refractive index n _max (λ ₀ ) at the specific wavelength λ ₀ characterized. The minimum refractive index n _min (λ ₀ ) and the maximum refractive index n _max (λ ₀ ) at the specific wavelength λ _{0 of} the diffractive structure 33 are chosen so that light with the design wavelength λ _des experiences a phase shift of j × 2π when transmitted through the area with the maximum refractive index n _max (λ ₀ ) compared to a transmission through the area with the minimum refractive index n _min (λ ₀₎ , where j represents the diffraction order. In the present exemplary embodiments, j = 1 is chosen so that the light in the first order of diffraction is deflected. However, it is also possible to choose j> 1 - and thus a higher diffraction order - or j <0 - and thus a negative diffraction order. In the case of a negative diffraction order, 25th the maximum refractive index n _max (λ ₀ ) and in the range 27 the minimum refractive index n _min (λ ₀ ) is present.

The minimum refractive index n _min (λ ₀ ) and the maximum refractive index n _max (λ ₀ ) at the specific wavelength λ ₀ have such values that the maximum refractive index n _max (λ ₀ ) at the specific wavelength is at least 0.005, in particular at least 0.01 and preferably at least 0.015 higher value than the minimum refractive index n _min (λ ₀ ) at the specific wavelength. If the specific wavelength λ _{0 is} also the design wavelength λ _{des of} the diffractive structure, the refractive index difference Δn (λ _des ) = n _max (λ _des ) - n _min (λ _des ) between the maximum refractive index and the minimum refractive index determines the profile height H the diffractive optical structure according to the following equation (in the first order of diffraction): $$\text{H}={\mathrm{\lambda }}_{\text{of}}\text{/}\Delta \text{n}\left({\mathrm{\lambda }}_{\text{of}}\right)\text{.}$$

gegen. Wenn die bestimmte Wellenlänge λ₀ von der Designwellenlänge λ_des der diffraktiven Struktur abweicht, müssen die Brechungsindices n_max(λ₀) und n_min(λ₀) bei der bestimmten Wellenlänge zuerst in die Brechungsindices n_max(λ_des) und n_min(λ_des) bei der Designwellenlänge λ_des umgerechnet werden, um die Profilhöhe der diffraktiven Struktur berechnen zu können.The profile height would be in the jth order of diffraction H accordingly $$\text{H}=\text{j}{\mathrm{\lambda }}_{\text{of}}\text{/}\Delta \text{n}\left({\mathrm{\lambda }}_{\text{of}}\right)\text{.}$$

against. If the specific wavelength λ ₀ deviates from the design wavelength λ _{des of} the diffractive structure, the refractive indices n _max (λ ₀ ) and n _min (λ ₀ ) at the specific wavelength must first be converted into the refractive indices n _max (λ _des ) and n _min ( λ _des ) can be converted at the design wavelength λ _{des in} order to be able to calculate the profile height of the diffractive structure.

In the present exemplary embodiment, the specific wavelength λ ₀ is equal to the design wavelength λ _of the diffractive structure and has the value 587.56 nm. It thus corresponds to the d-line of helium. In principle, however, any other wavelength than the specific wavelength λ ₀ can also be used, for example the wavelength of the e-line of mercury (546.07 nm), provided that this is in the wavelength range for which efficiency achromatization of the diffractive structure is to take place. This wavelength range is in the present embodiment, the visible wavelength range, which is the wavelength range between 400 and 800 nm, or somewhat specified narrower nm 400-750. The specific wavelength λ ₀ is therefore to 587.56 nm in the present exemplary embodiment, more or less in the Center of the visible wavelength range.

About the efficiency achromatization of the diffractive structure 33 In the present exemplary embodiment, the material from which it is made has a maximum refractive index n _max (λ ₀ ) of 1.700 and a minimum refractive index n _min (λ ₀ ) of 1.695, so that a refractive index difference Δn (λ ₀ ) = n _max (λ ₀ ) - n _min (λ ₀ ) of 0.005 is present. Also lies in the areas 27 with the maximum refractive index n _max (λ ₀ ) an Abbe number ν _max of 50 and in the areas 25th with the low refractive index n _min (λ ₀ ) an Abbe number ν _min of 42, so that an Abbe number difference Δν with the value 8th is present. These values come from an optimization in which the combination of values (n _max (λ ₀ ) = 1.7000; ν _max = 50) was recorded and the values for n _min (λ ₀ ) and for ν _min , and thus the refractive index difference Δn ( λ ₀ ) and the Abbe number difference Δν, have been optimized with regard to a high diffraction efficiency averaged over the visible spectral range. Instead of the values for n _max (λ ₀ ) and ν _max , the values for n _min (λ ₀ ) and ν _min can alternatively be recorded. It is also possible to optimize the values for the maximum refractive index n _max (λ ₀ ), the minimum refractive index n _min (λ ₀ ), the Abbe number ν _max and the Abbe number ν _min , so that none of these values is being held.

berechnet werden kann, wobei die spektrale Beugungseffizienz η(λ) durch die Gleichung $$\eta \left(\lambda \right)=\text{sinc}\left(\frac{h\mathrm{\Delta }n\left(\lambda \right)}{\lambda }-1\right)$$

gegeben ist, sofern Abschattungseffekte vernachlässigt werden können. In der j-ten Beugungsordnung wäre die „-1“ durch „-j“ zu ersetzen. Dabei stehen sinc für den Sinus cardinalis, h für die Profilhöhe der diffraktiven Struktur, Δn(λ) = n₁(λ) - n₂(λ) für die wellenlängenabhängige Brechungsindexdifferenz und λ für die Wellenlänge, wobei n₁(λ₀) = n_max(λ₀) und n₂(λ₀) = n_min(λ₀) gilt.One quantity that can be used to indicate the level of the diffraction efficiency averaged over a spectral range - and thus the degree of efficiency achromatization of the diffractive structure - is the polychromatic integral diffraction efficiency η _PIDE (PIDE: Polychromatic Integral Diffraction Efficiency), which is a specific spectral range - in the present exemplary embodiment over the visible spectral range - is the mean spectral diffraction efficiency η (λ) and that according to the equation $${\eta }_{\text{PIDE}}=\frac{1}{0.8\mathrm{\mu }m-0.4\mathrm{\mu }m}{\int }_{0.4\mathrm{\mu }m}^{0.8\mathrm{\mu }m}\eta \left(\lambda \right)$$

can be calculated, where the spectral diffraction efficiency η (λ) is given by the equation $$\eta \left(\lambda \right)=\text{sinc}\left(\frac{H\mathrm{\Delta }n\left(\lambda \right)}{\lambda }-1\right)$$

is given, provided that shadowing effects can be neglected. In the j-th order of diffraction, the "-1" would have to be replaced by "-j". Here sinc stands for the cardinal sinus, h for the profile height of the diffractive structure, Δn (λ) = n ₁ (λ) - n ₂ (λ) for the wavelength-dependent refractive index difference and λ for the wavelength, where n ₁ (λ ₀ ) = n _max (λ ₀ ) and n ₂ (λ ₀ ) = n _min (λ ₀ ) applies.

insbesondere im sichtbaren Spektralbereich sehr gut angenähert werden. Dabei können die Koeffizienten a, b und c gemäß $$a=n_d-\frac{b}{{\lambda }_d^2}-\frac{c}{{\lambda }_d^4}$$

und $$\left(\begin{array}{c}b\\ c\end{array}\right)=\frac{1}{{\lambda }_{F,C}^2{\lambda }_{g,F}^4-{\lambda }_{F,C}^4{\lambda }_{g,F}^2}\left(\begin{array}{cc}{\lambda }_{g,F}^4& -{\lambda }_{F,C}^4\\ -{\lambda }_{g,F}^2& {\lambda }_{F,C}^2\end{array}\right)\left(\begin{array}{c}\frac{n_d-1}{v_d}\\ \frac{n_d-1}{v_d}{P}_{g,F}\end{array}\right)$$

mit $${\lambda }_{g,F}^2=\frac{1}{{\lambda }_g^2}-\frac{1}{{\lambda }_F^2}$$

$${\lambda }_{F,C}^4=\frac{1}{{\lambda }_F^2}-\frac{1}{{\lambda }_C^2}$$

$${\lambda }_{g,F}^4=\frac{1}{{\lambda }_g^4}-\frac{1}{{\lambda }_F^4}$$

$${\lambda }_{F,C}^4=\frac{1}{{\lambda }_F^4}-\frac{1}{{\lambda }_C^4}$$

durch den Brechungsindex n_d bei der d-Linie von Helium (587,56 nm) die Abbe-Zahl ν_d und die partielle Teildispersion P_g,F ausgedrückt werden.The wavelength-dependent course of the refractive index η (λ) can be determined with the help of the Abbe number and the partial partial dispersion by the Cauchy equation $$n\left(\lambda \right)=a+\frac{\mathrm{<figure-callout\; id="2"\; label="b\; \lambda "\; filenames="DE102020105201A1\_0014.png,DE102020105201A1\_0015.png"\; state="\{\{state\}\}">b</figure-callout>}}{{\lambda }^{}}+\frac{c}{{\lambda }^{\mathrm{4th}}}+0\left({\lambda }^{-\mathrm{6th}}\right)$$

can be approximated very well, especially in the visible spectral range. The coefficients a, b and c can be used according to $$a=n_d-\frac{b}{{\lambda }_d^2}-\frac{c}{{\lambda }_d^{\mathrm{4th}}}$$

and $$\left(\begin{array}{c}b\\ c\end{array}\right)=\frac{1}{{\lambda }_{\mathrm{F.},\mathrm{C.}}^2{\lambda }_{G,\mathrm{F.}}^{\mathrm{4th}}-{\lambda }_{\mathrm{F.},\mathrm{C.}}^{\mathrm{4th}}{\lambda }_{G,\mathrm{F.}}^2}\left(\begin{array}{cc}{\lambda }_{G,\mathrm{F.}}^{\mathrm{4th}}& -{\lambda }_{\mathrm{F.},\mathrm{C.}}^{\mathrm{4th}}\\ -{\lambda }_{G,\mathrm{F.}}^2& {\lambda }_{\mathrm{F.},\mathrm{C.}}^2\end{array}\right)\left(\begin{array}{c}\frac{n_d-1}{v_d}\\ \frac{n_d-1}{v_d}{\mathrm{P.}}_{G,\mathrm{F.}}\end{array}\right)$$

with $${\lambda }_{G,\mathrm{F.}}^2=\frac{1}{{\lambda }_G^2}-\frac{1}{{\lambda }_{\mathrm{F.}}^2}$$

$${\lambda }_{\mathrm{F.},\mathrm{C.}}^{\mathrm{4th}}=\frac{1}{{\lambda }_{\mathrm{F.}}^2}-\frac{1}{{\lambda }_{\mathrm{C.}}^2}$$

$${\lambda }_{G,\mathrm{F.}}^{\mathrm{4th}}=\frac{1}{{\lambda }_G^{\mathrm{4th}}}-\frac{1}{{\lambda }_{\mathrm{F.}}^{\mathrm{4th}}}$$

$${\lambda }_{\mathrm{F.},\mathrm{C.}}^{\mathrm{4th}}=\frac{1}{{\lambda }_{\mathrm{F.}}^{\mathrm{4th}}}-\frac{1}{{\lambda }_{\mathrm{C.}}^{\mathrm{4th}}}$$

_{the Abbe number ν d} and the partial partial dispersion P _{g, F} can be expressed by the refractive index n _d at the d-line of helium (587.56 nm).

wobei das tiefgestellte „d“ bedeutet, dass zur Definition der Abbe-Zahl die d-Line von Helium herangezogen wird. In dieser Definition stehen n_d für den Brechungsindex bei der Wellenlänge der d-Linie von Helium (587,56 nm), n_F für den Brechungsindex bei der Wellenlänge der F-Linie von Wasserstoff (486,13 nm) und n_C für den Brechungsindex bei der Wellenlänge der C-Linie von Wasserstoff (656,27 nm). Andere Definitionen der Abbe-Zahl als ν_d können im Rahmen der vorliegenden Erfindung aber ebenfalls Verwendung finden, bspw. ν_e. Im Falle von ve finden in der obigen Gleichung statt des Brechungsindex n_d bei der Wellenlänge der d-Line von Helium der Brechungsindex n_e bei der Wellenlänge der e-Linie von Quecksilber (546,07 nm), statt des Brechungsindex n_F bei der Wellenlänge der F-Linie von Wasserstoff der Brechungsindex n_F' bei der Wellenlänge der F'-Linie von Cadmium (479,99 nm) und statt des Brechungsindex nc bei der Wellenlänge der C-Linie von Wasserstoff der Brechungsindex n_C' bei der Wellenlänge der C'-Linie von Cadmium (643,85 nm) Verwendung. Da die vorliegende Erfindung nicht von der gewählten Definition der Abbe-Zahl abhängt, wird diese in der vorliegenden Beschreibung lediglich mit v ohne einen Index bezeichnet. Bei einem anderen Spektralbereich als dem sichtbaren Spektralbereich sind statt der Brechungsindices bei den oben beschriebenen Wellenlängen Brechungsindices bei anderen Wellenlängen zu wählen, die innerhalb des Spektralbereichs, für den die Effizienzachromatisierung erfolgen soll, liegen. Dabei braucht keine der gewählten Wellenlängen mit der Designwellenlänge der diffraktiven Struktur übereinzustimmen.The Abbe number is a dimensionless quantity that describes the dispersive properties of an optical material. In the present exemplary embodiment, the following definition of the Abbe number is used $$v_d=\frac{n_d-1}{n_{\mathrm{F.}}-n_{\mathrm{C.}}}\text{,}$$

where the subscript "d" means that the d-line of helium is used to define the Abbe number. In this definition, n _{d stands} for the refractive index at the wavelength of the d-line of helium (587.56 nm), n _F for the refractive index at the wavelength of the F-line of hydrogen (486.13 nm) and n _C for the Refractive index at the wavelength of the C-line of hydrogen (656.27 nm). Definitions of the Abbe number other than ν _d can also be used in the context of the present invention, for example ν _e . In the case of ve, instead of the refractive index n _d at the wavelength of the d-line of helium, the refractive index n _e at the wavelength of the e-line of mercury (546.07 nm) instead of the refractive index n _F at the The wavelength of the F line of hydrogen is the refractive index n _{F '} at the wavelength of the F' line of cadmium (479.99 nm) and instead of the refractive index nc at the wavelength of the C line of hydrogen, the refractive index n _{C '} at the wavelength the C 'line of cadmium (643.85 nm) use. Since the present invention does not depend on the chosen definition of the Abbe number, this is referred to in the present description only with v without an index. In the case of a spectral range other than the visible spectral range, instead of the refractive indices at the wavelengths described above, refractive indices at other wavelengths that lie within the spectral range for which the efficiency achromatization is to take place are to be selected. None of the selected wavelengths need to match the design wavelength of the diffractive structure.

gegeben ist, wobei n_F und n_C dieselben sind wie bei ν_d. Auch bei der partiellen Teildispersion kann eine andere Definition Verwendung finden, in der bspw. die F- und C-Linien von Wasserstoff durch die F'- und C'-Linien von Cadmium ersetzt sind.The partial partial dispersion describes a difference between the refractive indices of two specific wavelengths based on a reference wavelength interval and represents a measure of the strength of the dispersion in the spectral range between these two wavelengths. In the present exemplary embodiment, the two wavelengths are the wavelength of the g-line of Mercury (435.83 nm) and the wavelength of the F line of hydrogen (486.13 nm), so that the partial partial dispersion P _{g, F} in the present exemplary embodiment $${\mathrm{P.}}_{\text{G}\text{, F}}=\frac{{\text{n}}_{\text{G}}-{\text{n}}_{\text{F.}}}{{\text{n}}_{\text{F.}}-{\text{n}}_{\text{C.}}}$$

is given, where n _F and n _{C are the} same as for ν _d . Another definition can also be used in the case of partial partial dispersion, in which, for example, the F and C lines of hydrogen are replaced by the F 'and C' lines of cadmium.

_{The refractive index n d} , which is directly included in the coefficients of the Cauchy equation, at the wavelength of the d-line of helium can also be replaced by a refractive index at a different wavelength, provided that the other wavelength lies within the spectral range for which the efficiency achromatization is to take place. However, the equations for the coefficients a, b and c would have to be adapted to the refractive index at the other wavelength.

The optimization described above can thus be carried out with a view to achieving a predetermined minimum value of the polychromatic integral diffraction efficiency η _PIDE or with a view to achieving a maximum of the polychromatic integral diffraction efficiency η _PIDE . It can be seen that the influence of the partial partial dispersion P _{g, F} on the polychromatic integral diffraction efficiency η _{PIDE is} significantly less than the influence of the Abbe number ν, so that one for the polychromatic integral diffraction efficiency η _PIDE for a wide range of values of the partial partial dispersion P _{g, F} can achieve a value of 0.95 or higher with the help of an optimization of Δn (λ ₀ ) and Δν or an optimization of n _max (λ ₀ ), n _min (λ ₀ ), ν _max and ν _min . In principle, however, there is also the possibility, instead of optimized values for n _max (λ ₀ ), n _min (λ ₀ ), ν _max and ν _min or optimized values for Δn (λ ₀ ) and Δν, optimized values for n _max (λ ₀ ) , n _min (λ ₀ ), ν _max , ν _min , P _{g, F, 1} and P _{g, F, 2} , where P _{g, F, 1 is assigned to} n _max (λ ₀ ) and ν _max and P _{g, F, 2} n _min (λ ₀ ) and ν _min . If only n _max (λ ₀ ), n _min (λ ₀ ), ν _max and ν _min or Δn (λ ₀ ) and Δν are optimized, two maxima are obtained in the spectral diffraction efficiency η (λ). If, in addition, P _{g, F, 1} and P _{g, F, 2 are} both optimized, three maxima are obtained in the spectral diffraction efficiency η (λ), provided that the difference between P _{g, F, 1} and P _{g, F, 2 is} sufficient becomes large, ie P _{g, F, 1 is} sufficiently large and P _{g, F, 2 is} sufficiently small.

The diffractive structure 33 in the diffractive optical element 4th , 7th exhibits such a variation that in the center of the diffractive structure 33 two horizontally mirrored diffractive structures 33 '33' adjoin each other. With increasing distance from the center of the diffractive structure 33 the lateral dimensions of the sections 33A to 33D or 33A 'to 33D', in which the refractive indices _{vary from the minimum refractive index n min} (λ ₀ ) to the maximum refractive index n _max (λ ₀ ), decrease. This makes it possible for the diffractive optical element 4th , 7th For example, to design as a diffraction lens, the manner in which the lateral dimensions change with increasing distance from the center of the diffractive structure 33 among other things depends on which focus position is to be achieved.

The minimum refractive index n _min (λ ₀ ) and the maximum refractive index n _max (λ ₀ ) are at the design wavelength λ _of the diffractive structure 33 chosen so that light with the design wavelength λ _des experiences a phase shift of j × 2π when transmitted through the area with the maximum refractive index n _max (λ ₀ ) compared to a transmission through the area with the minimum refractive index n _min (λ _0), where j represents the diffraction order. For sections 33D, 33D 'with a small width, this means that the course of the refractive index from the area 27D, 27D' with the maximum refractive index n _max (λ ₀ ) to the area 25D, 25D 'with the minimum refractive index n _min (λ ₀ ) must be steeper than, for example, in the case of sections 33B, 33B 'with a greater width.

A diffractive optical element 10 as it is in the 8th is shown, for example, in a lens 15th be integrated, as shown schematically in 9 is shown, in particular to thereby add to that on the refraction of the lens 15th based focus point on the diffraction by the diffractive optical element 10 to create based focus points. The lens or the refractive optical element 15th can be considered one of the in the 1 to shown lenses 11 until 14th be used. The diffractive optical element can be designed in such a way that its wavelength dependency compensates for the refractive wavelength dependency of the lens and thus corrects the color error of the lens.

the 10 shows schematically multilayer diffractive optical element 4th , 7th with the same profile height H , which areas are strung together in the lateral direction to the profile height 30th includes. In the variant shown are a first material 31 and a second material 32 Arranged "sawtooth" one above the other. The height of the second material increases in each case in the lateral direction to the profile height 32 within a range 30th linear and the height of the first material 31 correspondingly falls continuously linearly.

the shows a variant embodiment of a diffractive optical element 4th , 7th , which is designed as a meta-surface. The meta-surface consists of individual elements, the dimensions of which are smaller than a certain specified wavelength. Adjacent elements consist of materials that differ in their refractive index, for example materials 31 and 32 as related to the one in the 10 described embodiment. In the in the 11 variant shown take the dimensions of the second material 32 within a range 30th from left to right and the dimensions of each element of the material 31 left to right too.

In the 10 and 11 are the individual areas 30th for simplification shown with the same lateral dimensions of the adjacent areas. In order to achieve a focusing effect, however, the dimensions must vary, for example as in connection with the 8th explained above.

the 12th shows schematically an efficiency achromatized diffractive optical element 4th , 7th in the form of a diffractive lens. The shown diffractive lens has a profile height in the z-direction H of a little less than 4 µm. Starting from a center, in particular a center axis, the diffractive lens is constructed symmetrically in the x direction. The figure is based on the central axis 29 the radial distance r is plotted in millimeters on an x-axis. The dimensions of the individual sub-areas increase with increasing distance r from the central axis 29 away. As already in connection with the 10 described, the diffractive lens is composed of two layers, namely a first layer 31 with a refractive index n ₁ (λ) and a second layer 32 with a refractive index n ₂ (λ). The boundary between the two layers, especially that in the 12th shown boundary line between the first layer 31 and the second layer 32 point in the starting from the central axis 29 first subregions or sections have a parabolic or parabolic shape. In other words, for transition points between the two layers, the respective position in the z direction is characterized by a parabola as a function of the distance r from the central axis, that is to say z (r) is proportional to r ² . In the in the 12th The variant shown are the two layers mentioned on a substrate 28 upset.

the 13th shows schematically a camera according to the invention, for example a camera for a mobile device, for example a smartphone. The camera 40 comprises an objective according to the invention 1 , for example one related to the 1 until 7th explained lens.

the 14th shows schematically a mobile device 41 , which can be a smartphone, for example. The mobile device 41 comprises a camera according to the invention 40 .

List of reference symbols

1

lens

2

optical axis

3

cover

4th

diffractive optical element

5

Image plane

6th

plane-parallel plate

7th

diffractive optical element

8th

front

9

back

10

Beam path

11

first refractive optical element

12th

second refractive optical element

13th

third refractive optical element

14th

fourth refractive optical element

15th

refractive optical element, lens

16

fifth refractive optical element

23

diffractive structure

25th

Low refractive index area

27

High refractive index area

28

Substrate

29

Central axis

30th

area

31

first material, element

32

second material, element

33

diffractive structure

40

camera

41

mobile device

f

Focal length

fDOE

Focal length of the diffractive optical element

H

Profile height

TL

Overall length

D.

maximum diameter of the aperture

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

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• JP 20170093783 [0009]
• DE 102005009238 A1 [0009]
• DE 102005033746 A1 [0009]
• US 2010/0188758 A1 [0009]
• US 2009/0002829 A1 [0009]
• US 2010309367 A1 [0009]
• US 2015293370 A1 [0009]
• CN 107894655 A [0009]

Non-patent literature cited

• Marie Sklodowska-Curie grant agreement No. 675745 funding from Horizon 2020 [0001]
• D. Werdehausen et al. "Dispersion-engineered nanocomposites enable achromatic diffractive optical elements", OSA Publishing, Optica, Volume 6, Issue 8, page 1031-1038 (2019) [0008]
• D. Werdehausen et al. "General design formalism for highly efficient flat optics for broadband applications" OSA Publishing, Optics Express, Volume 28, Issue 5, pages 6452-6468 (2020) [0008]
• BRA. Kleemann et al. in "Design-Concepts for broadband high-efficieny DOEs", Journal of the European Optical Society-Rapid publications 3 (2008) [0008, 0021]

Claims (16)

Objective (1) for a camera (40), which has an optical axis (2), a focal length (f), an overall length (TL) in the direction of the optical axis (2), a number of refractive optical elements (11-15) , a diaphragm (3) with a maximum diameter (D) and at least one diffractive optical element (4, 7), the focal length (f) of the objective (1) being in the range between 10 millimeters and 6 millimeters (10mm ≥ f ≥ 6mm) and the ratio of the focal length (f) to the maximum diameter of the diaphragm (D) is in the range between 2 and 4 (2 ≤ f / D ≤ 4), characterized in that the ratio of the overall length (TL) to the focal length ( f) is less than 0.9 (TL / f <0.9) and the focal length of the at least one diffractive optical element (F _DOE ) is greater by a factor of at least 10 than the focal length (f) of the objective (F _DOE ≥ 10 * f). Lens (1) Claim 1 , characterized in that the at least one diffractive optical element (4, 7) has a focal length in the range between 1000 millimeters and 100 millimeters (1000 mm f _DOE 100 mm). Lens (1) Claim 1 or Claim 2 , characterized in that the focal length of the at least one diffractive optical element (4, 7) is greater than the focal length of the objective by a factor between 10 and 200 (30 and 100). Lens (1) according to one of the Claims 1 until 3 , characterized in that at least one diffractive optical element (4, 7) in relation to the overall length of the objective (1) starting from an object side in the direction of an image side in the first third of the objective (1) and / or at least one diffractive optical element ( 4, 7) is arranged in the second half of the lens (1). Lens (1) according to one of the Claims 1 until 4th , characterized in that the minimum distance between the sections Amin of the at least one diffractive optical element (4, 7) forming the grating is between 10 and 500 micrometers (10 µm Λ _min 500 µm). Lens (1) according to one of the Claims 1 until 5 , characterized in that the lens (1) has a field of view (FOV) in the range between 40 degrees and 25 degrees (40 ° ≥ FOV ≥ 25 °). Lens (1) according to one of the Claims 1 until 6th , characterized in that the at least one diffractive optical element (4, 7) and / or at least one refractive optical element (11-15) comprises a polymer. Lens (1) according to one of the Claims 1 until 7th , characterized in that the objective (1) comprises between three and five refractive optical elements (11-15). Lens (1) according to one of the Claims 1 until 8th , characterized in that the at least one diffractive optical element (4, 7) is introduced into one of the refractive optical elements (11-15) or is applied to a surface of one of the refractive optical elements (11-15) or in the form of a plate is designed and arranged in the beam path. Lens (1) according to one of the Claims 1 until 9 , characterized in that the at least one diffractive optical element (4, 7) is designed as a gradient index element or is composed of at least two layers (31, 32) with different refractive indices or of individual elements (31, 32) with Dimensions that are smaller than a certain wavelength is built. Lens (1) according to one of the Claims 1 until 10 , characterized in that the at least one diffractive optical element (4, 7) is efficiency achromatized. Lens (1) according to one of the Claims 1 until 11 , characterized in that the at least one diffractive optical element (4, 7) has a height (h) of less than 20 micrometers (h <20 µm). Lens (1) according to one of the Claims 1 until 12th , characterized in that the objective (1) comprises at least two diffractive optical elements (4, 7). Camera (40) which has an objective (1) according to one of the Claims 1 until 13th includes. Mobile device (41) which has a camera (40) according to Claim 14 includes. Mobile device (41) according to Claim 15 , characterized in that the mobile device (41) is a smartphone or a tablet or a smartwatch or data glasses.

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