DE102016125381A1 - Fresnel lens, lens and digital camera system - Google Patents

Abstract

In order to improve on known lenses, lenses or camera systems and / or to expand their fields of application, the invention provides a Fresnel lens with at least one first and at least one second lens area, wherein the first lens area comprises a first part of the lens surface and the second lens area has a second, The invention further provides a digital camera system and an objective, each having at least one such Fresnel lens. The invention provides for the simultaneous simultaneous imaging of the first and second lens regions Recording of even very different wavelength ranges for the entire image area of a single such camera (and with the only lens used) and thus the exact geometric reference of the image information from strongly unterschiedl Ien wavelength ranges to each other.

Description

The invention generally relates to the imaging of objects in an image plane, and more particularly to a Fresnel lens, a lens, and a digital camera system.

Digital camera systems are used today in a variety of fields, such as in the monitoring of objects or processes or in video telephony. Also in assistance systems of vehicle technology, camera systems are increasingly used, for example in the form of reversing cameras or collision warning systems. Since today typically every smartphone is equipped with a digital camera, every smartphone user constantly carries a digital camera system with him.

A digital camera system serves to detect and record static or moving images by means of an electronic sensor or to provide them via an interface, wherein the recording is typically carried out using a digital storage medium and the provision via an interface, for example, for display on a screen.

In a digital camera system, the image is usually imaged by a lens on an image plane in which the electronic sensor is arranged. An objective is a collecting optical system that produces a real optical image of an object in the image plane. In the simplest case, a lens is formed by a single converging lens. By combining multiple lenses, the imaging quality of a lens can be increased if the lenses and their properties are chosen to reduce certain aberrations. Also, the use of multiple lenses allows for the provision of variable focal length lenses.

Lenses are usually equipped with a diaphragm, with the help of which the light transmission through the lens can be changed. A lens diaphragm is usually designed as a lamellar diaphragm, in which circularly arranged lamellae move into one another such that the light transmission becomes narrower or wider and thus the incident light beam becomes smaller or larger. The aperture is positioned in the beam path in such a way that it acts only as an aperture diaphragm and not as a visual field diaphragm.

Lenses are typically called transparent devices that deflect electromagnetic radiation by refraction at their surfaces, with lenses generally having two refractive surfaces, at least one of which is convex or concave. A distinction is generally made between converging lenses that focus parallel light at one focal point and diverging lenses that expand parallel light.

There are also known as so-called Fresnel lenses. A Fresnel lens, also referred to as a Fresnel Fresnel lens, is a lens which, by dividing into annular areas and reducing the thickness of the lens in those areas, enables a reduction in the weight and volume of the lens. The construction principle of the Fresnel lens makes use of the fact that the electromagnetic radiation is only refracted when passing through the lens surfaces, but the angle of refraction does not depend on the thickness, but only on the angle between the two surfaces. Accordingly, the thickness reduction in the annular portions of the Fresnel lens does not change the focal length, but due to the step structure, the imaging quality is lowered.

Lenses whose imaging properties are based on the refraction of electromagnetic radiation, i. based on refraction, are also referred to as refractive lenses.

Most commonly, lenses are used in the field of classical optics for imaging light. The light is typically referred to as the portion of the electromagnetic radiation visible to the human eye, the range of the light in the electromagnetic spectrum comprising wavelengths of approximately 380 nm to 780 nm.

Also known are lenses for use in other wavelength ranges. Infrared lenses, or IR lenses for short, for use in the infrared wavelength range of about 780 nm to 1 mm are used for example in thermal imaging cameras, night vision devices or in infrared spectroscopy. Ultraviolet lenses, or UV lenses for short, for use in the ultraviolet wavelength range of about 1 nm to 380 nm are used, for example, in laser applications.

It is also known to use so-called Fresnel zone plates for focusing X-radiation with wavelengths in the range from about 0.01 nm to 1 nm. A Fresnel zone plate is typically a plate on which alternating transparent and non-transparent concentric rings are mounted, forming annular gaps where electromagnetic radiation is diffracted and amplified by constructive interference at foci. The diffraction-based focusing is used in X-radiation, as for X-rays, the refractive index of all radiopaque materials is minimally less than 1, so that a converging lens has only minimal focusing.

Lenses whose imaging properties are based on the diffraction of electromagnetic radiation, i. based on diffraction, are also referred to as diffractive lenses. The Fresnel zone plate described above constitutes a diffractive lens.

Depending on which wavelength range a lens is to be used, lens materials with corresponding transmission properties are used, i. Materials that are also sufficiently transparent in the respective desired wavelength range.

The refractive index of lens materials is typically wavelength dependent, with the refractive index typically decreasing with increasing wavelength. Since electromagnetic radiation of different wavelengths is thus refracted to different extents, an aberration which is referred to as chromatic aberration results, and which leads to the fact that a lens can be used only for a limited wavelength range.

The invention has for its object to improve known from the prior art lenses, lenses or camera systems and / or to expand their field of application.

The above technical problem is solved by a Fresnel lens according to claim 1, a digital camera system according to claim 15 and a lens according to claim 16. Advantageous embodiments and further developments are the subject of the respective subclaims.

A central idea of the invention is to provide a Fresnel lens which can be used simultaneously for different wavelength ranges. For this purpose, a Fresnel lens according to the invention comprises at least a first and at least a second lens area, wherein the first lens area comprises a first part of the lens surface and the second lens area comprises a second, different from the first part of the lens surface, and wherein the first and second Lens each having a different material with different transmission properties for electromagnetic radiation.

In other words, the invention relates to a lens for a plurality of selected wavelength ranges, or the structure or construction of such a lens, which forms a necessary basic element in an objective, which is adapted to the information of the object space, which come from strongly different wavelength ranges. to let happen in the picture space in time to be detected there in an image plane.

In the present case, the term image plane is generally intended to designate a detection surface predetermined by a sensor or a sensor component, although this does not necessarily have to be a flat surface but, for example, may also have the shape of a partial spherical surface or spherical cap. The notion of the image plane is thus generally used here in the sense of a pictorial space.

An essential basic idea is to combine at least two different materials in one lens, wherein in particular at least two different substrates with different transmission properties are combined in a common lens. It is also conceivable that the first and / or second lens area is formed by a coating of the Fresnel lens. For example, a substrate material that is transparent to the first and second wavelengths could be used, wherein the first and second lens regions are each formed by a coating of different materials, the material layers being transparent only for the first and second wavelengths, respectively. The use of coatings may be advantageous in lens manufacture.

Advantageously, the first lens region for a first wavelength has a higher transmission than the second lens region, and the second lens region for a second wavelength, which differs from the first wavelength, has a higher transmission than the first lens region.

With particular advantage, the first lens region has a higher transmission for a first wavelength range than the second lens region, and the second lens region for a second wavelength region, which differs from the first wavelength region, has a higher transmission than the first lens region. Preferably, the first and second wavelength ranges are non-overlapping wavelength ranges. The first and / or second wavelength range may each be formed as a contiguous wavelength band or be formed by at least two non-contiguous wavelength bands.

Particularly advantageously, the first lens region substantially blocks electromagnetic radiation of the second wavelength, and the second lens region substantially blocks electromagnetic radiation of the first wavelength. In this way, the first lens region preferably acts as an imaging only for electromagnetic radiation of the first wavelength or of the first wavelength range and thus as a diaphragm for electromagnetic radiation of the second wavelength or the second wavelength range, while the second lens region is preferably imaging for electromagnetic radiation of the second wavelength or of the second wavelength range and acts as a diaphragm for electromagnetic radiation of the first wavelength or of the first wavelength range.

The Fresnel lens can thus advantageously be used simultaneously for two different wavelength ranges, wherein electromagnetic radiation of these two different wavelength ranges can preferably be imaged simultaneously into a common image plane.

The image can be refractive or diffractive. Accordingly, the Fresnel lens is advantageously designed as a refractive and / or diffractive lens.

If the image is due to diffraction, the respective lens region is advantageously designed such that a diffractive Fresnel zone lens is formed.

A Fresnel lens typically has annular regions, which are also referred to below as ring zones. If the image is due to refraction, the respective lens region is advantageously designed as an annular zone of the Fresnel lens.

In an advantageous embodiment, the Fresnel lens further comprises at least a third lens region comprising a third, different from the first and second parts of the lens surface and having a different material from the first and second lens region, wherein the third lens region for a third, of the first and the second different wavelength has a higher transmittance than the first and second lens portions, the first lens portion for the first wavelength has higher transmittance than the third lens portion, and the second lens portion for the second wavelength has higher transmittance than the third lens portion.

Conveniently, it can also be provided in this embodiment that the first lens region has a higher transmission than the second lens region for a first wavelength range and the second lens region has a higher transmission than the first lens region for a second wavelength range which differs from the first wavelength range. In this case, it is preferably provided that the third lens region has a higher transmission for a third, of the first and second different wavelength range than the first and second lens region, the first lens region for the first wavelength region has a higher transmission than the third lens region, and the second lens region for the second wavelength range has a higher transmission than the third lens region.

When providing at least one first, second and third lens region, the Fresnel lens can advantageously be used simultaneously for three different wavelength ranges, wherein electromagnetic radiation of these three different wavelength ranges can preferably be imaged simultaneously in a common image plane. By providing additional lens areas, i. at least one fourth, fifth, etc. lens area, each having a different material with different transmission properties for electromagnetic radiation than the other lens areas, a Fresnel lens can be provided, which can be used simultaneously for a predetermined number of different wavelength ranges, wherein electromagnetic radiation of all predetermined different wavelength ranges can be imaged preferably simultaneously in a common image plane.

The imaging by the third lens area or further lens areas can also be refractive or diffractive, wherein the respective lens area is preferably formed in imaging due to diffraction such that a diffractive Fresnel zone lens is formed, and in imaging due to refraction preferably as an annular zone Fresnel lens is formed.

The first and second, as well as optionally the third wavelength and further wavelengths or the first and second, and optionally the third wavelength range and other wavelength ranges can be arbitrarily selected depending on the purpose, as far as materials with suitable transmission properties are available.

The first wavelength or the first wavelength range is preferably in the visible spectrum between 380 nm and 780 nm and the second wavelength or the second wavelength range is preferably in the infrared spectrum between 780 nm and 1 mm, in particular between 2 .mu.m and 15 .mu.m. In this embodiment, the first lens region advantageously comprises an optical glass, and the second lens region advantageously comprises germanium, in particular pure germanium. The optical glass selected for the first lens region preferably has a low transmission at least in parts of the infrared spectrum.

For example, a borosilicate crown glass can be used as the optical glass for the first lens region, which essentially blocks electromagnetic radiation in the infrared spectrum from a wavelength of about 2 μm. The transmission range of germanium ranges from about 2 .mu.m to 16 .mu.m, so that the first lens portion transmits straight electromagnetic radiation at wavelengths blocked by the second lens portion and the second lens portion transmits electromagnetic radiation at wavelengths blocked by the second lens portion.

A Fresnel lens, which is designed for the simultaneous imaging of electromagnetic radiation in the visible and infrared spectrum, can advantageously be used for example in a vehicle, for example in a reversing camera system or another driver assistance system, since then a single camera with low volume and Weight with respect to the objective at the same time can provide information from different wavelength ranges and in particular for the IR range, even in the dark in visible light no active illumination of the object is needed.

The first, second or third wavelength or the first, second or third wavelength range can also be outside the visible and infrared spectrum, for example in the ultraviolet spectrum between 1 nm and 380 n or even in the X-ray spectrum between 0.01 nm and 1 nm.

In order to enable the use of the Fresnel lens for selected wavelength ranges, desired transmission properties of a lens region, in particular bandpass properties, can also be achieved, for example, by a suitable coating of the corresponding lens region.

Preferably, the first and the second lens area, each with a different focal length, with respect to a predetermined wavelength.

Particularly advantageously, the first lens region, in each case with respect to the first wavelength, for which the first lens region is transparent, and the second lens region, based on the second wavelength, for which the second lens region is transparent, each have the same focal length.

In this way it is made possible that electromagnetic radiation of the first and second wavelengths and the first and second wavelength ranges is substantially imaged in a common image plane.

The same applies if a third lens area or further lens areas are provided, i. each lens area preferably has the same focal length relative to the wavelength assigned to the respective lens area, so that advantageous electromagnetic radiation of the first, second, third and optionally further wavelength or the corresponding wavelength ranges for which the respective different lens areas are transparent Essentially in a common image plane is mapped.

Particularly advantageously, a plurality of first and second lens regions are provided, wherein the first and second lens regions preferably alternate from the lens center to the outside.

When three different lens areas are provided, a plurality of first, second and third lens areas are advantageously provided, wherein the first, second and third lens areas alternate from the center of the lens to the outside. The same applies when providing further lens areas, ie fourth, fifth etc. lens areas.

In the case of refractive imaging by the first lens regions, each of the plurality of first lens regions advantageously forms in each case an annular zone of the Fresnel lens. The same applies to the second lens areas, and optionally for the third and further lens areas.

Each adjacent lens areas are preferably glued together or connected to each other by means of flexible connecting elements.

A digital camera system according to the invention comprises at least one Fresnel lens as described above, as well as a sensor component which comprises at least first sensor elements sensitive to the first wavelength and second sensor elements sensitive to the second wavelength.

When imaging electromagnetic radiation of a first and second wavelength range, the first and second sensor elements are preferably sensitive to substantially all wavelengths in the respective wavelength range.

As sensor elements, for example, photodiodes can be used, wherein the sensor component can be designed as a CCD sensor or CMOS sensor. To specifically detect the desired wavelengths, the sensor component can provide appropriate filter.

A sensor suitable for use as a sensor component is also described in Applicant's patent application entitled "Method for Determining Position and / or Orientation by Simultaneously Capturing Object Space Information from Significantly Different Wavelength Ranges in an Image, Digital Camera System and Mobile electronic device "filed on the same day as the present patent application. The content of this patent application is incorporated in full in the present application.

An objective according to the invention comprises at least one Fresnel lens as described above.

The invention will now be described in more detail by way of example with reference to preferred embodiments and with reference to the accompanying drawings. The same reference numerals in the drawings designate the same or similar parts.

• 1: schematisch die Abbildung eines parallelen Strahlenbündels mit einer halbkonvexen Linse,
• 2: schematisch die Abbildung eines parallelen Strahlenbündels mit einer halbkonvexen Fresnel-Linse, welche die gleiche Brennweite aufweist wie die in 1 dargestellte Linse,
• 3: eine schematische Schrägansicht der in 2 dargestellten Fresnel-Linse,
• 4: schematisch den Querschnitt einer bikonvexen Linse und einer entsprechenden bikonvexen Fresnel-Linse,
• 5: schematisch eine erste bevorzugte Ausführungsform einer Fresnel-Linse mit mehreren ersten und zweiten Linsenbereichen,
• 6: schematisch die Abbildung eines parallelen Strahlenbündels mit der in 5 dargestellten Fresnel-Linse,
• 6a: schematisch die Erzeugung eines reellen Bildes mit der in 5 dargestellten Fresnel-Linse,
• 7: schematisch eine zweite bevorzugte Ausführungsform einer Fresnel-Linse mit mehreren ersten und zweiten Linsenbereichen, welche als Rechtecklinse ausgebildet ist,
• 8: eine schematische Schrägansicht der in 7 dargestellten Fresnel-Linse,
• 9: schematisch eine dritte bevorzugte Ausführungsform einer Fresnel-Linse mit mehreren ersten und zweiten Linsenbereichen,
• 10: schematisch ein digitales Kamerasystem, welches eine erfindungsgemäße Fresnel-Linse umfasst,
• 11: schematisch eine vierte bevorzugte Ausführungsform einer Fresnel-Linse mit mehreren ersten, zweiten und dritten Linsenbereichen,
• 12: schematisch eine fünfte bevorzugte Ausführungsform einer Fresnel-Linse mit mehreren ersten, zweiten und dritten Linsenbereichen,
• 13: schematisch eine sechste bevorzugte Ausführungsform einer Fresnel-Linse mit mehreren ersten und zweiten Linsenbereichen, wobei die ersten Linsenbereiche diffraktiv und die zweiten Linsenbereiche refraktiv wirken,
• 14: eine schematische Schrägansicht der in 13 dargestellten Fresnel-Linse,
• 15: schematisch eine Variante der in 13 dargestellten Fresnel-Linse, wobei die ersten Linsenbereiche eine Beschichtung umfassen,
• 16: schematisch eine weitere Variante der in 13 dargestellten Fresnel-Linse, wobei die ersten Linsenbereiche eine Beschichtung umfassen, und
• 17: schematisch ein Fahrzeug, welches wenigstens ein in 10 dargestelltes digitales Kamerasystem als Teil einer Rückfahrkamera oder eines Fahrer-Assistenzsystems umfasst.

Show it:

• 1 FIG. 2 schematically shows the image of a parallel beam with a semi-convex lens, FIG.
• 2 FIG. 2 schematically shows the image of a parallel beam with a semi-convex Fresnel lens having the same focal length as that in FIG 1 illustrated lens,
• 3 : a schematic oblique view of in 2 represented Fresnel lens,
• 4 FIG. 2 schematically shows the cross section of a biconvex lens and a corresponding biconvex Fresnel lens, FIG.
• 5 FIG. 2 schematically shows a first preferred embodiment of a Fresnel lens having a plurality of first and second lens areas, FIG.
• 6 schematically the image of a parallel beam with the in 5 represented Fresnel lens,
• 6a schematically the generation of a real image with the in 5 represented Fresnel lens,
• 7 FIG. 2 schematically shows a second preferred embodiment of a Fresnel lens having a plurality of first and second lens areas, which is designed as a rectangular lens, FIG.
• 8th : a schematic oblique view of in 7 represented Fresnel lens,
• 9 FIG. 2 schematically shows a third preferred embodiment of a Fresnel lens having a plurality of first and second lens areas, FIG.
• 10 FIG. 2 schematically shows a digital camera system comprising a Fresnel lens according to the invention, FIG.
• 11 FIG. 2 schematically shows a fourth preferred embodiment of a Fresnel lens having a plurality of first, second and third lens regions, FIG.
• 12 FIG. 2 schematically shows a fifth preferred embodiment of a Fresnel lens having a plurality of first, second and third lens areas, FIG.
• 13 FIG. 2 schematically shows a sixth preferred embodiment of a Fresnel lens having a plurality of first and second lens regions, wherein the first lens regions are diffractive and the second lens regions are refractive. FIG.
• 14 : a schematic oblique view of in 13 represented Fresnel lens,
• 15 : schematically a variant of in 13 represented Fresnel lens, wherein the first lens areas comprise a coating,
• 16 : schematically another variant of in 13 represented Fresnel lens, wherein the first lens areas comprise a coating, and
• 17 schematically a vehicle, which at least one in 10 illustrated digital camera system as part of a rear view camera or a driver assistance system includes.

In the 1 to 4 are shown known from the prior art lenses.

1 shows schematically in cross section a conventional semi-convex spherical lens 10 with the focal length f, in which in a known manner a parallel incident beam in the focus F is focused. 2 shows schematically in cross-section to the in 1 shown lens corresponding Fresnel lens 20 with the same focal length f, which focuses a parallel incident beam in the same way in the focus F. The shape of in 2 represented Fresnel lens 20 can in known manner from the shape of in 1 lens formed by the thickness of the lens is reduced in sections while maintaining the surface curvature, wherein in a circular lens through the sections, in particular annular zones of the Fresnel lens 20 be formed. This is schematically in the in 3 shown oblique view of the Fresnel lens 20 illustrated. In the 1 and 2 is an example of a screen 30 shown, wherein in the illustrated setting the aperture 30 the outermost ring zone 21 the Fresnel lens 20 is covered and thus does not contribute to the figure.

In the embodiments presented below, semi-convex lenses are considered for refraction. However, the embodiments may also be applied to other types of lenses, such as biconvex lenses. Biconvex lenses known from the prior art are exemplified in FIG 4 shown, where 4 a ) a biconvex spherical lens 12 and 4 b ) a corresponding biconvex Fresnel lens 22 shows.

In 5 is schematically a first preferred embodiment of a Fresnel lens 210 shown, where 5 a ) is a cross-sectional view and 5 b ) a top view of the Fresnel lens 210 shows. The Fresnel lens 210 has at least a first and at least a second lens area, wherein the first lens area comprises a first part of the lens surface and the second lens area comprises a second, different from the first part of the lens surface, and wherein the first and second lens area each comprise a different material with different transmission properties for electromagnetic radiation.

In the in 5 The example shown has the Fresnel lens 210 several first lens areas 211 - 1 . 211 - 2 . 211 - 3 and 211 - 4 of a first material and a plurality of second lens areas 212 - 1 . 212 - 2 and 212 - 3 from a second material.

As in 5 b ), it is the Fresnel lens 210 around a circular lens, with the lens areas 211 - 1 . 211 - 2 . 211 - 3 . 211 - 4 . 212 - 1 . 212 - 2 and 212-3 are each formed as ring zones of the Fresnel lens.

Advantageously, the first lens areas 211 - 1 . 211 - 2 , 211-3 and 211-4 have a higher transmission for a first wavelength than the second lens areas 212 - 1 . 212 - 2 and 212 - 3 and the second lens areas 212 - 1 . 212 - 2 and 212-3 has a higher transmission than the first lens regions for a second wavelength different from the first wavelength 211 - 1 . 211 - 2 . 211 - 3 and 211 - 4 on.

With particular advantage, the first lens regions 211-1, 211-2, 211-3 and 211-4 substantially block electromagnetic radiation of the second wavelength and the second lens regions 212 - 1 . 212 - 2 and 212 - 3 electromagnetic radiation of the first wavelength. An electromagnetic radiation is preferably substantially blocked if the transmittance for the respective wavelength is less than 25%, in particular less than 10%, in particular less than 5%, in particular less than 1%.

In other words, the first lens regions for the first wavelength are substantially transparent and act as an aperture for the second wavelength substantially, while the second lens regions for the second wavelength are substantially transparent and substantially act as an aperture for the first wavelength.

Preferably, this is true not only for a first and a second wavelength, but for a first and a second wavelength range, wherein the first and second wavelength ranges are advantageously non-overlapping wavelength ranges, and wherein the first and / or second wavelength ranges each as a contiguous wavelength band may be formed or formed by at least two non-contiguous wavelength bands.

The first wavelength or the first wavelength range in the visible spectrum is preferably between 380 nm and 780 nm, and the second wavelength or the second wavelength range is preferably in the infrared spectrum between 780 nm and 1 mm, in particular between 2 μm and 15 μm.

Accordingly, the first lens areas include 211 - 1 , 211-2, 211-3 and 211-4 of the 5 represented Fresnel lens 210 Advantageously, an optical glass, wherein in the 5 illustrated embodiment, the volume of the first lens areas 211 - 1 . 211 - 2 . 211 - 3 and 211 - 4 each completely formed by the optical glass. To achieve transparency in the infrared spectrum, but not in the visible spectrum, the second lens areas comprise 212 - 1 . 212 - 2 and 212 - 3 the in 5 represented Fresnel lens 210 advantageous for example germanium, in particular pure germanium, wherein in the in 5 illustrated embodiment, the volume of the second lens areas 212 - 1 . 212 - 2 and 212 - 3 each completely formed by germanium.

As optical glass, for example, a borosilicate crown glass can be used, which is transparent over the entire visible spectrum and into the near infrared, but substantially blocks electromagnetic radiation in the ultraviolet spectrum, as well as in the infrared spectrum from a wavelength of about 2 microns. The transmission range of germanium ranges from about 2 μm to 16 μm, so that the transmission ranges of the first and second lens regions do not overlap in the example shown. However, other materials with suitable transmission properties can also be selected for the first and second lens regions.

The respective substrate material of the first and / or second lens areas of in 5 represented Fresnel lens, ie the optical glass and / or the germanium may be additionally coated on the lens surface with advantage, for example with an antireflection coating. However, the coating is in particular designed such that it is transparent to the respective desired wavelength range.

The first lens areas 211 - 1 . 211 - 2 . 211 - 3 and 211 - 4 are advantageously designed such that they act refractive and emit electromagnetic radiation having wavelengths in the first wavelength range, ie in the example shown in the visible spectrum, with a predetermined first focal length. In the example shown, the first lens areas thus correspond 211 - 1 . 211 - 2 . 211 - 3 and 211 - 4 corresponding annular zones of a known from the prior art Fresnel lens. The second lens areas 212 - 1 . 212 - 2 and 212 - 3 are advantageously designed such that they act refractive and emit electromagnetic radiation having wavelengths in the second wavelength range, ie in the illustrated example in the infrared spectrum, with a predetermined second focal length.

With particular advantage, the first and second focal lengths are substantially identical, so that through the Fresnel lens 210 electromagnetic radiation of the visible spectrum and the infrared spectrum is imaged in a common image plane. A sufficient equalization or equality of the two focal lengths is achieved by a different surface curvature of the first and second lens areas, wherein the different surface curvatures are not explicitly shown in the figures.

A situation with substantially identical focal lengths is schematically illustrated in FIG 6 shown. 6 shows the Fresnel lens 210 and an incident parallel beam comprising at least rays in the visible and in the infrared spectrum, which are shown schematically and by way of example as lines. Rays with wavelengths in the visible spectrum are solid lines 311 represented and rays with wavelengths in the infrared spectrum as dashed lines 312 , The beams of both wavelength ranges are focused essentially in focus F. Due to chromatic aberration, the focus typically coincides precisely with uncorrected surface curvature only for a selected wavelength of the first wavelength range and a selected wavelength of the second wavelength range. This can be suitably selected depending on the intended use. For example, the average wavelength of a desired wavelength range can be selected or the wavelength corresponding to the center frequency of a desired wavelength range. Also, a wavelength can be selected at which a maximum of the radiation to be imaged is expected.

6a shows an example with the lens 210 Real-image-generated rays P 'of an object P. Rays with wavelengths in the visible spectrum are again shown as solid lines and rays with wavelengths in the infrared spectrum are again shown as dashed lines. Like from the 6a As can be seen, both rays with wavelengths in the visible spectrum and rays with wavelengths in the infrared spectrum contribute to the imaging of the object P. Of course, this only applies if the object P emits radiation in both wavelength ranges.

The refractive index of the optical glass of the first lens region is about 1.5 for electromagnetic radiation in the visible spectrum, for example, while the refractive index of the germanium of the second lens region for electromagnetic radiation in the infrared spectrum is about 4. Since the refractive index of the optical glass of the first electromagnetic radiation lens regions in the visible spectrum is different from the refractive index of germanium of the second electromagnetic radiation lens regions in the infrared spectrum, the first lens regions preferably have a different surface curvature than the second lens regions to have identical focal lengths produce.

It should be noted that in the illustrated example, this does not result in duplicate mapping since a given wavelength can only pass through either the first or the second lens areas.

At the in 5 In the embodiment shown, the lens regions are formed by concentrically arranged annular zones, wherein the material of the annular zones differs.

Each annular zone could consist of a different material, wherein the specific material of the respective annular zone is determined in particular during the production of the lens.

Since the ring zones are arranged in an order from the inside, i. from the lens center, are arranged outwardly, an annular zone can be defined by information (i; k), where the value i indicates the position in the order from inside to outside and k the respective material of the annular zone. To clearly define an annular zone, the width of the annular zone in the direction from the center of the lens to the outside, as well as the focal length with respect to a predetermined wavelength are preferably additionally defined.

Possible materials have already been described above by way of example. It should be noted that a material k of an annular zone does not have to be homogeneous with respect to a single material, but the material k can also be a material mixture of a plurality of materials which, for example, transmits a particular wavelength range particularly well and for a different wavelength range than Full aperture effect or lets this other wavelength range only with less intensity. Also, the desired transmission properties of the respective material can be achieved by a suitable coating.

One possible Fresnel ring combination is a strict alternation of first and second lens areas, as in FIG 5 in order to use the good-quality regions of the lens for two wavelength ranges and their corresponding materials a and b on an equal footing: ( 1 (a) ( 2 (b) ( 3 (a) ( 4 (b) ( 5 (a) ( 6 (b) ( 7 A). This sequence could be continued accordingly.

The number of ring zones provided in the illustrated embodiments is only an example and could also be significantly higher. For example, more than 10, more than 100 or even more than 1000 ring zones could be provided.

It would also be conceivable to choose materials for the first and second lens areas, which are both transparent in a spectral overlap area. In such an embodiment, the first lens areas preferably have a focal length for a first wavelength that is outside of the overlap area, and the second lens areas have the same focal length for a second, different wavelength from the first, which is also outside of the overlap area Preferably, the wavelength is below the overlap region and the second wavelength is preferably above the overlap region.

For example, in the in 5 Example shown instead of the optical glass used as a sapphire material having a transmission range of about 0.3 microns to about 6 microns, so there is an overlap range of about 2 microns to about 6 microns, in which both materials are transparent.

The geometry of the first and second lens regions could then be designed, for example, such that the focal length of the first lens regions for a wavelength of 670 nm coincides with the focal length of the second lens regions for a wavelength in the long-wave infrared of, for example, 10 μm.

Based on a predetermined wavelength in the overlap region, the first and second lens regions then preferably each have a different focal length.

Since, in such an embodiment, electromagnetic radiation having wavelengths which lie in the overlapping region is not focused in the focus F and is also imaged differently by the first and second lens regions, the result is a reduced imaging quality. Such an embodiment is therefore only advantageous if no materials with suitable transmission properties are available for the desired wavelength ranges.

Instead of a circular Fresnel lens 210 as they are in 5 is shown, of course, other lens forms within the scope of the invention. The 7 and 8th show, for example, a Fresnel lens 220 in rectangular shape.

In 7 is the Fresnel lens 220 schematically shown, wherein 7 a ) is a cross-sectional view and 7 b ) a top view of the Fresnel lens 220 shows. In the in 7 As shown, the Fresnel lens 220 has a plurality of first lens areas 221 - 1 , such as 221 - 2a . 221 -3a, 221-4a, 221-2b, 221-3b and 221-4b of a first material and a plurality of second lens portions 222 - 1a . 222 - 2a , 222-3a, 222-1b, 222-2b and 222-3b of a second material. The materials can be as in 5 represented Fresnel lens 210 be elected.

In the 7 illustrated Fresnel lens 220 basically forms a rectangular cutout in the 5 represented Fresnel lens 210 ,

For further illustration, see 8th schematically an oblique view of in 7 represented Fresnel lens 220 shown. There 8th merely serves to illustrate the lens shape, was omitted labeling of the different materials.

Instead of a strict alternation of two materials, any other predetermined arrangement of the annular zones of two materials could be provided, such as (1; a) ( 2 (a) ( 3 (b) ( 4 (a) ( 5 (a) ( 6 (b) ( 7 A). This sequence could be continued accordingly.

This is schematically in 9 shown. The further preferred embodiment of a Fresnel lens shown there 230 includes several first lens areas 231 - 1 . 231 - 2 . 231 - 3 , 231-4 and 231-5, and a plurality of second lens areas 232 - 1 and 232-2 according to the above Fresnel ring combination.

10 schematically shows a digital camera system 400 which is a Fresnel lens 410 which in the illustrated example corresponds to the Fresnel lens 210 described above. In the illustrated embodiment, the digital camera system includes 400 a housing 440 in which the Fresnel lens 410 as well as a sensor component 420 are arranged, wherein the sensor component 420 is arranged in the image plane. For focusing, the Fresnel lens 410 and / or the sensor component 420 be designed to be movable. In the example shown, the sensor component comprises 420 at least first, for the first wavelength sensitive sensor elements and second, sensitive for the second wavelength sensor elements, whereby also special combined sensor elements can be used, which are sensitive for both wavelengths at the same time.

For other embodiments of Fresnel lenses for more than two wavelength ranges, the sensor component 420 preferably comprises further sensor elements which are sensitive to a third or further wavelengths or special combined sensor elements which are sensitive to all relevant wavelengths at the same time.

Advantageously, all the sensor elements of the sensor component 420 are arranged in a common image plane, wherein the sensor elements may be formed, for example, as photodiodes and optionally an upstream filter may be provided which only transmits the wavelengths to the respective sensor element to be detected by the respective sensor element ,

A combined photodiode in the image plane could be known, but also successively perpendicular to the image plane sensitive to different wavelengths and thus enable a high packing density of diodes in the image plane to achieve the highest possible resolutions in the image plane.

In the in 10 As illustrated, the digital camera system further includes one with the sensor component 420 connected interface 430 on, for example, for connecting a display device or for connecting to a control device which is adapted to supply recorded images to a memory and to store there.

A digital camera system could also include multiple lenses, one or more of which may be embodied according to the invention. When using multiple lenses, one or more of them may be designed to be movable for focusing. Several lenses, one or more of which are embodied according to the invention, can advantageously also form an objective according to the invention. The combination of lenses to lenses is not considered in detail, since it largely follows the known rules of commercially available lenses.

In 11 is another preferred embodiment of a Fresnel lens 240 shown, which has several first lens areas 241 - 1 . 241 - 2 and 241 - 3 , several second lens areas 242 - 1 and 242 - 2 , as well as several third lens areas 243 - 1 and 243 - 2 includes, where 11 a ) is a cross-sectional view and 11 b ) a top view of the Fresnel lens 240 shows.

The first lens areas 241 - 1 . 241 - 2 and 241 - 3 preferably comprise a first part of the lens surface, the second lens areas 242 - 1 and 242 - 2 preferably comprise a second, different from the first part of the lens surface, and the third lens areas 243 - 1 and 243 - 2 preferably comprise a third, different from the first and second part of the lens surface. Advantageously, the first lens regions for a first wavelength have a higher transmission than the second and third lens regions, and the second lens regions have a higher transmission for a second wavelength than the first and third lens regions, and the third lens regions have a third wavelength higher transmission than the first and second lens areas.

Furthermore, the first lens regions advantageously block electromagnetic radiation of the second and third wavelengths, while the second lens regions advantageously block electromagnetic radiation of the first and third wavelengths and the third lens regions advantageously block electromagnetic radiation of the first and second wavelengths.

For this purpose, advantageously, the first, second and third lens areas each have different materials.

In the 11 The combination of ring zones shown corresponds to a strict alternation of different materials in order to equally use the good-quality regions of the lens for three wavelength ranges and their corresponding materials a, b and c: ( 1 (a) ( 2 (b) ( 3 (c) ( 4 (a) ( 5 (b) ( 6 (c) ( 7 A). This sequence could be continued accordingly.

In 12 is another preferred embodiment of a Fresnel lens 250 shown, which has several first lens areas 251 - 1 and 251 - 2 , several second lens areas 252 - 1 and 252 - 2 , as well as several third lens areas 253 - 1 . 253 - 2 and 253 - 3 includes, where 12 a ) is a cross-sectional view and 12 b ) a top view of the Fresnel lens 250 shows.

In 13 is yet another preferred embodiment of a Fresnel lens 260 shown, which has several first lens areas 261 - 1 to 261 - 7 and a plurality of second lens areas 262 - 1 to 262 - 6 includes, where 13 a ) is a cross-sectional view and 13 b ) a top view of the Fresnel lens 260 shows.

In this embodiment, the first lens regions 261-1 to 261-7 are diffractive, ie they result in diffraction analogous to a Fresnel zone plate and are made of a material that is transparent to a first wavelength and substantially non-transparent to a second wavelength. The second lens areas 262 - 1 to 262 - 6 on the other hand, they act refractively and emit electromagnetic radiation of a second wavelength onto the image plane, the second lens regions 262 - 1 to 262 - 6 are formed of a material which is transparent to the second wavelength and substantially non-transparent to the first wavelength.

For further illustration, see 14 schematically an oblique view of a section of in 13 represented Fresnel lens 260 shown. There 14 merely serves to illustrate the lens shape, was omitted labeling of the different materials. The in 14 shown section includes the in 13 shown lens areas 261 - 1 to 261 - 5 and 262 - 1 to 262 - 4 , Again 14 it can be seen in this embodiment, the second lens areas 262 - 1 to 262 - 6 shaped according to the annular zones of a Fresnel lens, while the first lens areas 261 - 1 to 261 - 7 have a substantially planar surface.

The 15 and 16 show schematically two variants 260 ' and 260 '' the in 13 represented Fresnel lens 260 , wherein the first lens areas 261 - 1 to 261 - 7 each comprise a coating, which advantageously results in the desired transmission properties.

Diffractive first lens areas can also be advantageously used for imaging electromagnetic radiation in the X-ray spectrum, since the refractive index for X-radiation in all materials is very close to one and X-radiation is also strongly absorbed in solids, and thus refractive imaging in the X-ray spectrum is difficult.

At the in 13 shown lens 260 Accordingly, the first lens areas could 261 - 1 to 261 - 7 transparent to X-rays and the second lens areas 262 - 1 to 262 - 6 be absorbent for X-radiation.

wobei

n

die fortlaufende Nummer der Zone,

λ

die Wellenlänge der Strahlung, z. B. 5 nm für Röntgenstrahlung,

f

die Bildweite, also der Abstand vom Zentrum der Linse zum Bild (Fokus), und

g

die Gegenstandsweite bezeichnet.

For a constructive interference in a focus, the radii of the alternately transparent and absorbing zones in the quadratic approximation must satisfy the following equation: $$r_n=\sqrt{n\cdot \lambda \cdot \frac{f\cdot G}{f+G}}$$

in which

n

the serial number of the zone,

λ

the wavelength of the radiation, z. B. 5 nm for X-radiation,

f

the image width, ie the distance from the center of the lens to the image (focus), and

G

denotes the object's width.

For g »f applies: $r_n=\sqrt{n\cdot \lambda \cdot f},$

Accordingly, for use in imaging X-rays, the lens has a much higher number of ring zones than in 13 shown. This can be achieved, for example, with known methods of microstructuring or nanostructuring.

For example, a lens designed for simultaneous imaging, for example in the X-ray spectrum and in the visible spectrum, can advantageously be used for monitoring purposes in nuclear power plants.

Incidentally, known production techniques can be used for joining the first, the second and optionally the further lens areas, in particular the joining together of adjacent lens areas which comprise different materials.

For example, adjacent lens areas may each be glued together, or adjacent lens areas may be interconnected by means of flexible connecting elements. For example, rubber rings could be used as flexible connecting elements.

Alternatively, a support structure could be provided, for example made of plastic, in which parts of the lens can be used. In this embodiment, it could even be provided to flexibly exchange lens parts which serve to form the first, second or further lens regions in order to flexibly provide different materials for different wavelength ranges.

In 17 is shown an advantageous application for a Fresnel lens according to the invention. 17 shows a vehicle 500 , which in the illustrated embodiment, two digital camera systems 510 and 520 each comprising a Fresnel lens described above and each adapted for simultaneous imaging of electromagnetic radiation in the visible and in the infrared spectrum.

The camera systems 510 is designed as a rear view camera and with a display device 540 connected, causing the driver of the vehicle 500 a consideration is made possible, which is advantageously extended to information in the infrared spectrum, which may be advantageous at night, for example. For the visibility of the rear view object space scene, which is different in the infrared wavelength range, this object space scene of the rear view does not require simultaneous illumination of this scene in the dark in the visible light range by means of a commercial rear light with visible light.

The camera system 520 is with a control device 530 and forms part of a driver assistance system which may be advantageously adapted to automatically detect game located near the roadway using the additional information in the infrared spectrum, while the information in the visible spectrum is conventionally used, for example, for lane detection become.

If nearby game is detected, then the driver can be displayed a corresponding information. For this purpose, the control device 530 preferably with the display device 540 connected. The partial information of the detected game in the infrared range could be suitably processed and in the display device 540 additionally in the image of the visible area of the light of the camera 520 be projected in order to make the driver aware of the danger of wildlife and to give him in addition a good optical position information of the game.

1. a) die Positions- und Orientierungsbestimmung einer digitalen Kamera im Objektraumkoordinatensystem, z.B. WGS84 für GPS oder ein selbstdefiniertes bauwerksfestes System, stark verbessert wird, und wodurch
2. b) Informationen z.B. eines Punktes des Objektraums oder aus einer Richtung aus dem Objektraum, die in verschiedenen Wellenlängenbereichen vorliegen, einfacher und genauer zueinander zugeordnet werden.

The proposed by the invention novel design of Fresnel lenses can be used in digital cameras with CMOS or CCD sensors in the image plane, then in the image plane in a known manner, the different wavelength information can be recorded separately, for example by special filters in front of the individual diodes. The invention provides a wider range of information and this information was then also collected at the same time, whereby the information is also ideally suited for moving cameras and their moving shots and / or moving objects in front of the camera. If this information then refers to the same image plane, ie the same image, then a single parameter set can be used for this image and its position and orientation in space

1. a) the position and orientation determination of a digital camera in the object space coordinate system, eg WGS84 for GPS or a self-defined construction-fixed system, is greatly improved, and thereby
2. b) information such as a point of the object space or from a direction of the object space, which are present in different wavelength ranges, are assigned to each other easier and more accurate.

This can be particularly advantageous for expanding in the German patent application with the file number 10 2016 119 920.6 described method can be used. The content of German patent application with the file number 10 2016 119 920.6 is hereby incorporated in full in the present application.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been 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.

Cited patent literature

• DE 102016119920 [0120]

Claims (16)

Fresnel lens (210, 220, 230, 240, 250, 260, 260 ', 260 ") having at least a first and at least a second lens area, wherein the first lens area (211-1 - 211-4, 221-1, 221-2a - 221-4a, 221-2b - 221-4b, 231-1 - 231-5, 241-1 - 241-3, 251) -1, 251-2, 261-1 - 261-7) comprises a first portion of the lens surface and the second lens portion (212-1 - 212-3, 222-1a - 222-3a, 222-1b - 222-3b, 232-1, 232-2, 242-1, 242-2, 252-1, 252-2, 262-1 - 262-6) comprises a second, different from the first part of the lens surface, and - The first and second lens portion each having a different material with different transmission properties for electromagnetic radiation. Fresnel lens after Claim 1 , wherein the lens is designed as a refractive and / or diffractive lens. Fresnel lens according to one of the preceding claims, wherein the lens areas are formed as annular zones of the Fresnel lens. Fresnel lens according to one of the preceding claims, wherein the first lens region for a first wavelength has a higher transmission than the second lens region, and - The second lens region for a second, different from the first wavelength has a higher transmission than the first lens region. Fresnel lens after Claim 3 wherein the first lens region substantially blocks electromagnetic radiation of the second wavelength and the second lens region substantially blocks electromagnetic radiation of the first wavelength. Fresnel lens according to one of the preceding claims, comprising at least one third lens portion (243-1, 243-2, 253-1-253-3) comprising a third, different from the first and second portions of the lens surface and having a different material from the first and second lens portions, wherein the third lens area has a higher transmission than the first and second lens area for a third, of the first and second different wavelengths, the first lens region for the first wavelength has a higher transmission than the third lens region, and - The second lens region for the second wavelength has a higher transmission than the third lens region. Fresnel lens according to one of the preceding claims, wherein the first wavelength in the visible spectrum is between 380 nm and 780 nm and the second wavelength in the infrared spectrum between 780 nm and 1 mm, in particular between 2 and 15 pm. A Fresnel lens according to any one of the preceding claims, wherein the first lens region comprises an optical glass and the second lens region comprises pure germanium. Fresnel lens according to one of the preceding claims, wherein the first and the second lens region, with respect to a predetermined wavelength, each having a different focal length. Fresnel lens according to one of the preceding claims, wherein the first lens area, with respect to the first wavelength, and the second lens area, with respect to the second wavelength, each having the same focal length (f). A Fresnel lens according to any preceding claim, having a plurality of first and second lens portions (211-1 - 211-4, 261-1 - 261-7; 212-1 - 212-3, 262-1 - 262-6), wherein the first and second lens areas alternate outwardly from the lens center. A Fresnel lens according to any one of the preceding claims having a plurality of first, second and third lens regions (241-1, 241-2, 241-3, 242-1, 242-2, 243-1, 243-2), the first , alternate second and third lens areas from the lens center to the outside. Fresnel lens according to one of the preceding claims, wherein adjacent lens areas are each glued together. Fresnel lens according to one of the preceding claims, wherein adjacent lens areas are interconnected by means of flexible connecting elements. Digital camera system (400) comprising - At least one Fresnel lens (210, 220, 230, 240, 250, 260, 260 ', 260 ") having at least a first and at least one second lens region, wherein the first lens area (211-1 - 211-4, 221-1, 221-2a - 221-4a, 221-2b - 221-4b, 231-1- 231-5, 241-1 - 241-3, 251-1, 251-2, 261-1 - 261-7) a first part of the lens surface and the second lens region (212-1 - 212-3, 222-1a - 222-3a, 222-1b - 222-3b, 232-1, 232-2, 242-1, 242-2, 252-1, 252-2, 262-1 - 262-6) comprises a second, different from the first part of the lens surface, the first and second lens regions each have a different material with different electromagnetic radiation transmission properties, the first lens region for a first wavelength has a higher transmission than the second lens region, and the second lens region has a higher transmission than the first lens region for a second, different wavelength from the first, and a sensor component (420) which comprises first sensor elements sensitive to the first wavelength and second sensor elements sensitive to the second wavelength. Lens comprising at least one Fresnel lens (210, 220, 230, 240, 250, 260, 260 ', 260 ") according to one of Claims 1 to 14 ,

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