Zoom imaging with a holographic device

Abstract

The invention relates to a system (1) for digital holographic imaging, comprising at least the following components: - a beam splitter (2) with an inlet aperture (E), - a retroreflector array (3) comprising a large number of retroreflector elements (30), - a reference mirror (4), wherein the system (1) is configured to receive object light (100) via the input aperture (E) and to superimpose object light (100) reflected from the reference mirror (4) and from the retroreflector array (3) so that interference patterns are created which can each be assigned to one of the retroreflector elements (30), wherein the system (1) has an optic (7) on the side of the input aperture (E) which includes a magnification optic (70).

Description

[0001] The invention relates to a system for digital imaging according to the features of claim 1.

[0002] Systems for digital holographic imaging are known from the state of the art.

[0003] For example, DE 102021114059 B3 discloses a compact system. With such a system, object light originating from an object can be collected using a converging lens. Part of the collected object light is directed by means of a beam splitter onto a retroreflector array comprising a multitude of retroreflector elements, while simultaneously another part of the object light is directed onto a reference mirror.

[0004] A retroreflector element comprises, in particular, a lens that focuses collimated incident light onto a retroreflector mirror of the retroreflector element and re-collimates light reflected from the retroreflector mirror.

[0005] The beam splitter creates two optical arms, which, after the respective portion of the object light has been reflected back by the retroreflector array or the reference mirror, are superimposed by the beam splitter. On one detection side of the system, the superimposed object light forms interference patterns attributable to the retroreflector elements, which can be recorded, for example, by a camera. Based on the recorded interference patterns or holograms, a three-dimensional representation of a recorded object can be determined through appropriate analysis.

[0006] These systems are typically used to image relatively close objects. When processing image data of objects located several meters away from the system, it becomes increasingly difficult to determine this three-dimensional information with increasing distance, making this system unsuitable for 3D imaging of distant objects.

[0007] Conversely, imaging zoom systems that do not operate holographically, i.e., that perform image reconstruction in spatial space, have various disadvantages when it comes to imaging a distant object "sharply," i.e., in focus.

[0008] For this reason, zoom lenses for such systems operating in spatial space always also have a focusing unit with which a focal plane can be selected in which objects are focused and imaged.

[0009] State-of-the-art zoom lenses comprise a multitude of lenses and moving parts to enable axial displacement of the focal plane and to achieve the most aberration-free imaging of the object possible.

[0010] The object of the invention is to provide a system, a method and a computer program which do not have the disadvantages of the prior art.

[0011] The problem according to the invention is solved by a digital holographic imaging system of the type mentioned above according to claim 1. Advantageous embodiments of the invention are specified in the dependent claims and are described below.

[0012] According to a first aspect of the invention, a digital holographic imaging system comprises at least the following components: - a beam splitter with an inlet aperture, - a retroreflector array comprising a large number of retroreflector elements, - a reference mirror.

[0013] The system is designed to receive object light via the input aperture, to direct the object light proportionally onto the retroreflector array or the reference mirror via the beam splitter, and to superimpose object light reflected from the reference mirror and the retroreflector array, so that interference patterns are created, each of which can be assigned to one of the retroreflector elements.

[0014] According to the invention, the system has optics on the side of the input aperture, which include magnification optics, in particular wherein the system is configured to evaluate the interference patterns in such a way that an image of the object space is determined in a focal plane, wherein a position of the focal plane along the optical axis of the system can be adjusted by a corresponding evaluation of the holograms.

[0015] The system can further be configured to determine a large number of images of the object space from the recording, wherein the focal planes assigned to the images are located at at least two or more different positions along the optical axis, the positions of the focal planes being adjustable by appropriate evaluation of the holograms.

[0016] The magnifying optics are designed to propagate object light that strikes the magnifying optics at an input angle to the beam splitter at an output angle, where the output angle is, in particular, significantly larger than the input angle, i.e., for example, at least five, ten or more than ten times larger.

[0017] Magnifying optics are known from the state of the art.

[0018] A magnifying optic can be assigned a magnification factor greater than 1, which describes an angular magnification of the magnifying optic relative to the outgoing object light.

[0019] In particular, the magnifying optics have a magnification factor of more than five, especially more than ten, which corresponds in particular to a zoom range within the meaning of the invention.

[0020] The advantageous effect of combining a digital holographic imaging system with such magnification optics is explained below.

[0021] The magnifying optics allow the system to capture a spatial volume along the optical axis. The wavefronts of the collected object light carry information about the entire captured spatial volume and are captured in the form of interference patterns attributable to a respective retroreflector element.

[0022] Through appropriate evaluation, it is now possible, in contrast to spatially operating imaging systems that project an image of an object directly onto the detector, such as cameras with zoom lenses, to define a focal plane in which a reconstruction of an image is to be or is to take place based on the interference patterns, so that this reconstructed image corresponds to an image that was set, i.e., focused on this focal plane, using a system operating in spatial space.

[0023] Furthermore, based on the information in the interference patterns, an image corresponding to a different focal plane can now be reconstructed simultaneously or alternatively, completely without mechanical refocusing.

[0024] This means that, similar to a wave field camera that operates in spatial space, the system allows the focal plane to be shifted or defined after the recording.

[0025] Furthermore, the system does not require corrected optics, as aberrations or lens errors are compensated for due to the comparatively small apertures of the retroreflector elements, so that the system is also improved in terms of size and complexity compared to systems operating in real space.

[0026] The inventor recognized that combining a digital holographic imaging system with a magnification optic at the entrance aperture provides significant advantages in the field of zoom imaging, which are not immediately obvious.

[0027] The apparent disadvantage is that a three-dimensional reconstruction of surfaces, for which such systems are typically used, is lost with distant objects, but can be "replaced" by a focal plane selectivity, thus offering the aforementioned advantages compared to zoom systems operating in spatial space.

[0028] The system according to the invention is therefore able to shift the focal plane along the optical axis of the system by appropriately evaluating the interference patterns in a single recording through algorithmic adaptations during the evaluation.

[0029] In the context of this specification, the term retroreflector element refers in particular to an optical element designed to reflect incident object light back onto itself. Specifically, the retroreflector element does not reflect the incident object light according to Snell's law, but rather reflects the object light back along the direction of incidence at essentially the same angle.

[0030] A retroreflector element can include a lens configured to focus collimated object light onto a reflective element, and in particular onto a retroreflector mirror of the retroreflector element, and to re-collimate the object light reflected from there. Each retroreflector element can be associated with an aperture. This aperture is essentially limited by the aperture of the lens of the retroreflector element.

[0031] According to a further embodiment of the invention, the beam splitter with a beam splitter surface defines at least the following sides of the beam splitter: - a first side on which the entrance aperture for collecting object light is located, - a second side to which the collected object light is redirected at the beam splitter surface, in particular partially reflected, i.e. proportionally, - a third page that extends opposite the first page, - a fourth side that extends opposite the second side, so that object light originating from the second and third sides is propagated to the fourth side, and can form the interference patterns on the fourth side.

[0032] In particular, the retroreflector array is arranged on the second or third side, and the reference mirror is arranged on an adjacent side to the retroreflector array, this adjacent side then being the second or third side accordingly.

[0033] In the context of this specification, the term "arm" is sometimes used synonymously with the term "side" in connection with the beam splitter. The term "arm" primarily aims to help a person skilled in the art understand the different beam paths of the beam splitter, while the term "side" emphasizes the geometric arrangement of the components.

[0034] The second arm thus corresponds in particular to the beam path between the beam splitter surface and the second side. The same applies to the further numbering of the arms and sides.

[0035] It is familiar to those skilled in the art how the beam splitter surface of a beam splitter (e.g., a beam splitter cube) is defined as having four sides (first to fourth sides). These four sides correspond, in particular, to sides of the beam splitter that are perpendicular to the optical axes of the beam splitter.

[0036] In the context of this specification, the term "optics" refers to individual optical elements or a combination of optical elements, such as lenses and / or mirrors. An optical system can be assigned a focal length.

[0037] An optical system can have an input focal length along its input aperture and a potentially different output focal length along its output aperture.

[0038] In particular, the focal length(s) of the optics at the entrance aperture of the beam splitter is / are fixed.

[0039] According to a further embodiment of the invention, the magnifying optics comprises a first lens system with a first focal length and a second lens system with a second focal length, wherein the first focal length is greater in magnitude than the second focal length.

[0040] In the context of the invention, the term "in magnitude" refers specifically to the second focal length, i.e., the value of the first focal length is greater than the magnitude of the second focal length. The second lens system can have both positive and negative focal lengths.

[0041] In particular, the first focal length corresponds to the input focal length of the magnifying optics and the second focal length corresponds to the output focal length of the magnifying optics.

[0042] A lens system according to the invention is an arrangement comprising at least one lens. In the lens system, one or more lenses can be arranged at predefined distances from one another, in particular forming an objective lens.

[0043] In particular, the lens systems each have a fixed focal length and are arranged at a fixed distance from each other.

[0044] Magnifying optics with two lens systems are advantageous because aberrations are minimal.

[0045] According to a further embodiment of the invention, the magnifying optics consist of the first and the second lens system.

[0046] The optics of the system may include further optical components, such as filters or corrective optics, but these optical components do not, in particular, contribute to an angular magnification of the object light.

[0047] According to a further embodiment of the invention, the first and second lens systems are arranged as a telecentric system.

[0048] This embodiment is particularly advantageous because the entrance or exit pupil of the telecentric system is located at infinity, thus enabling low-distortion imaging of the object light onto the retroreflector array and the reference mirror. Furthermore, the distortion errors unavoidable in simple lens systems can be optimized by algorithmic corrections.

[0049] In particular, the distance between the first and second lens systems is equal to the sum of the first and second focal lengths.

[0050] The telecentric system can be assigned an angular magnification m, which results from the ratio of the first focal length f1 to the second focal length f2: m=f1f2.

[0051] The second lens was calculated as a positive amount.

[0052] According to a further embodiment of the invention, the first lens system comprises exactly one first lens.

[0053] The term "lens" in the context of this specification includes, in particular, composite lenses made up of several lens elements, such as achromats, apochromats, but also lenses made of only one material. Specifically, according to the specification, the lens has no air gap along the optical axis, even if it is made up of several lens elements.

[0054] This embodiment enables a particularly robust and simple implementation of the invention, without significantly impairing the image quality of a reconstructed image due to aberrations inherent in simple lenses (edge ​​effects, chromatic and spherical aberrations). A system with only one first lens can be built particularly compactly and lightweight.

[0055] In particular, the magnifying optics consist of a first lens and a second lens system comprising one or more lenses.

[0056] According to a further embodiment of the invention, the second lens system comprises a second lens, in particular exactly one second lens.

[0057] According to a further embodiment of the invention, the optics, in particular the magnifying optics, consist of the first lens and the second lens system, especially the second lens. This embodiment allows for a particularly compact and lightweight design of the system.

[0058] A system in which the second lens system comprises multiple lenses and the first lens system comprises only one lens can exhibit a particularly advantageous compromise between compactness, lightness, and optical image quality.

[0059] According to a further embodiment of the invention, the first lens is a convex lens and the second lens is a concave lens.

[0060] According to a further embodiment of the invention, the first and / or the second lens system each comprises one or more lenses selected from the group consisting of: - a metalens, - a holographic lens - a diffractive lens.

[0061] According to a further embodiment of the invention, the optics, in particular the magnifying optics, comprise a fixed focal length ratio.

[0062] The focal length ratio can be determined from the input focal length and the output focal length.

[0063] In particular, the focal length or magnification ratio is determined by the first and second focal lengths. f1f2.

[0064] Such an optic can therefore be designed in particular as a rigid, unchanging optic that does not allow any change in the focal length(s).

[0065] Such a system can therefore be understood as an adaptive zoom system for digital holographic imaging with fixed magnification optics.

[0066] In this context, adaptive means that the focal plane is determined solely through appropriate algorithmic evaluation without any mechanical changes in the distance between lenses, thus allowing focusing on multiple planes.

[0067] According to a further embodiment of the invention, the optics, in particular the magnifying optics, do not include movable optics or focal-length-adjustable optics, e.g. focal-length-changing or movable lenses.

[0068] This embodiment also describes a robust, compact and lightweight system.

[0069] According to a further embodiment of the invention, the components of the magnifying optics are fixedly spaced apart from each other.

[0070] In particular, the first and second lens systems are fixedly spaced apart from each other.

[0071] According to a further embodiment of the invention, the first and second lenses are fixedly spaced apart from each other.

[0072] In particular, neither the first nor the second lens system has components, such as lenses, that can be moved along the optical axis.

[0073] According to a further embodiment of the invention, the magnifying optics have a preset, unchanging focal length.

[0074] In particular, the system's optics feature a preset, unchanging focal length.

[0075] According to a further embodiment of the invention, the system comprises a subband phase structure component configured to imprint wavelength-dependent phases onto object light incident on the retroreflector array according to a subband phase relation assigned to the retroreflector element, wherein the subband phase relations are different for at least some of the retroreflector elements, so that information is encoded in the interference patterns that allows the interference patterns to be evaluated in a subband-specific manner, in particular wherein the interference patterns include subband information that enables the separation of contributions of the subbands to the interference pattern.

[0076] In the context of this specification, the term "imprinting phases" means, in particular, that when the object light originating from one side of the beam splitter, where the reference mirror is located, is superimposed on the object light originating from one side of the beam splitter, where the retroreflector array is located, the subband phase structure component in one or both optical arms causes the object light to travel a longer or shorter optical path, resulting in phase differences in the interference pattern that reflect the intended subband phase relation.

[0077] The same applies to the subband phase relation disclosed in further advantageous embodiments, which causes phase differences of the object light compared to the object light from the reference arm through the retroreflector element.

[0078] For the purposes of this specification, a subband is understood to be, in particular, a contiguous spectral region that may have a width of up to 10 nm. Widths of up to 6 nm, 5 nm, or 3 nm are advantageous.

[0079] Each subband can therefore be assigned a central wavelength, which, for example, lies in the middle of the spectral range encompassed by the subband.

[0080] The spectral range of the object light can therefore be subdivided into a multitude of subbands. These subbands can be contiguous, overlapping, and / or spectrally deficient. The width and number of distinguishable subbands can be determined by the design of the system and its optical components.

[0081] The subband phase structure component can, for example, comprise a multitude of Bragg mirrors, i.e., a Bragg mirror system, arranged at predefined intervals along an optical axis of the retroreflector element. Each Bragg mirror in the system is designed to reflect a specific subband, while the other Bragg mirrors are transparent to the other subbands.

[0082] This causes the object light to travel through subband-specific optical paths of varying lengths within the retroreflector element, thus imparting phases to the object light that correspond to the subband phase relationship assigned to the retroreflector element. This relationship is, in turn, at least partially determined by the spacing of the individual Bragg mirror layers along the optical axis of the retroreflector element. The reference mirror can also be designed as a Bragg mirror system to impart the desired phases to the object light in combination with the retroreflector elements. This can offer advantages in terms of structural engineering and design.

[0083] By using the subband phase structure component, the problem described below for broadband object light, e.g., in spectral regions larger than 10 nm, can be solved. The spatial information of one wavelength corresponds to a compressed or stretched spatial information at another wavelength in the interference pattern, making it seemingly impossible to resolve these apparently identical contributions within the interference pattern. The more broadband the object light, the more these contributions become blurred, so that a satisfactory reconstruction no longer seems possible for broadband object light.

[0084] To solve this problem, the interference pattern would need to yield information that allows a distinction between wavelength and spatial information. If this is not possible, the spatial information becomes increasingly blurred across the spectral range.

[0085] Simulations have shown that, depending on the permissible propagation angle (e.g., < 100 mrad) of the object light relative to the optical axis of the system, a narrowband spectral range, a so-called subband with a width of 5 nm, can be imaged without any problems and without adverse destructive interference. The theory assumes a single wavelength (laser light).

[0086] However, it is desirable to be able to generate spatial information from broader-band object light, for example in the spectral range of 50 nm, which could come from LED light or even daylight. This would improve the signal-to-noise ratio and would also mean that only one image would need to be captured instead of numerous images, which can be extremely advantageous when capturing time-critical images, such as when the object being recorded is moving.

[0087] In this way, various advantageous approaches to utilizing broadband object light could be implemented. On the one hand, a hologram for a speckle-free object image could be generated from a contiguous broadband spectral range. On the other hand, various, particularly non-contiguous, narrowband spectral ranges (e.g., 5 nm wide) (e.g., colors, red, green, blue) could be simultaneously captured and evaluated separately, enabling a color representation of the hologram. Finally, a combination of the two approaches would also be conceivable, in which broadband color channels, each approximately 50 nm wide, are simultaneously captured and evaluated separately.

[0088] Especially when daylight, or a light source consisting of several broadband colored light sources, is to be used, it is essential to be able to utilize at least approximately 30 nm per color in order to capture as much light energy as possible. This should also be possible without the usual color filters, which absorb light energy from other colors and also reduce the effectively usable camera pixels per color. With a 30 nm bandwidth per color, this color band could then be "divided" into, for example, 6 individual sub-bands, so that with three colors, a total of 18 sub-bands would need to be separated.

[0089] The use of the subband phase structure component described above solves this problem, since wavelength-dependent phases are imposed on the object light, corresponding to a subband phase relation assigned to the respective retroreflector element.

[0090] Since the wavelength-dependent phases imprinted on the object light are known for different retroreflector elements, this information (phase matching) in the interference pattern of the respective assigned retroreflector element can be used, especially in conjunction with the interference patterns of the retroreflector elements with other subband phase relations, to distinguish between components in the interference pattern that encode for position information of an object point in object space and components in the interference pattern that are wavelength-dependent.

[0091] According to these embodiments of the invention, the system can therefore be used to determine a digital hologram with object light comprising a plurality of sub-bands, by using object light with spectral widths in the range of 30 nm, 50 nm, and larger for the generation of the digital hologram through wavelength-dependent phase adjustment of the object light via the sub-band phase relations.

[0092] This would not be possible without phase matching.

[0093] The respective subband phase relationships can be determined once before using the system by appropriate test measurements.

[0094] In particular, multiple retroreflector elements can be assigned to a single subband phase relation. This increases the signal-to-noise ratio.

[0095] According to some embodiments of the invention, at least some of the retroreflector elements differ with respect to the subband phase relationship, so that a subband-specific reconstruction of the digital hologram can be performed based on the different phases and the subband phase relationships in the evaluation of the interference patterns assigned to the retroreflector elements. This allows, in particular, the compensation of wavelength-dependent compression or stretching of the interference pattern by additional "re-sampling" measures.

[0096] According to a further embodiment of the invention, each of the at least some retroreflector elements comprises a Bragg mirror system configured to imprint object light phases according to the subband phase relation associated with the retroreflector element, wherein the Bragg mirror systems are part of the subband phase structure component.

[0097] According to a further embodiment of the invention, the system comprises an incidence angle-phase structure component, wherein the incidence angle-phase structure component has an associated incidence angle-phase relation for each of a predefined plurality of incidence directions of the object light, wherein the incidence angle-phase structure component is configured to imprint phases on the object light for each of these plurality of incidence directions according to the associated incidence angle-phase relation, so that the interference patterns contain information with which a hologram reconstructed accordingly from these interference patterns has an improved resolution.

[0098] The inventive concept of this embodiment is that predefined phases are imposed on the object light via the angle-of-incident phase structure component, depending on the angle of incidence. These phases are defined by a multitude of angle-of-incident phase relationships that depend on the direction of incidence. Due to the different phases, the interference patterns include higher spatial frequencies (and lose information about lower spatial frequencies in the opposite direction in the frequency domain). By knowing the respective angle-of-incident phase relationship—which can be determined, for example, by targeted measurements or based on the known system design—this information can be used in the reconstruction of the hologram to achieve improved resolution. Without this phase adjustment, the interference patterns do not include higher spatial frequencies, so an improvement in resolution is not possible.

[0099] The “lost” information about the low spatial frequencies can be extracted from interference patterns that include this part, i.e., no optical structural component or a structural component with a weak angle-of-incidence-phase relation.

[0100] To achieve an isotropic resolution improvement, the interference patterns should include higher spatial frequencies along all directions; that is, some interference patterns should include higher spatial frequencies along a first direction, while other interference patterns should include higher spatial frequencies along a second spatial direction, and so on, so that for an isotropically distributed multitude of spatial directions, at least one interference pattern in each direction contains the information about the enhanced spatial frequencies along that direction.

[0101] In the context of this specification, the term incidence angle-phase structure component refers in particular to one or more optical elements that work together to produce the incidence angle-phase relation assigned to each of the predefined multitude of incidence directions of the object light.

[0102] Preferably, the incidence-angle-phase structural component comprises a plurality of optical gratings. The optical gratings do not necessarily have to be identifiable as separate individual components within the system, but can be implemented collectively in one or more components of the structural component.

[0103] In the context of this specification, the term "incident direction" refers specifically to the direction of propagation of the object light with respect to a plane perpendicular to the optical axis. The incident direction can be described by a two-dimensional vector. This vector essentially corresponds to a projection of the propagation direction vector of the object light along the optical axis onto a plane perpendicular to it. Without loss of generality, it can be assumed that this plane extends along an x- and y-direction of a Cartesian coordinate system, and that the optical axis lies along a z-axis on this plane. The vector denoting the incident direction thus extends, in particular, within this plane. Specifically, the vector denoting the incident direction always points towards the optical axis.

[0104] The system is now specifically designed to impose phases for a predefined multitude of incidence directions, e.g., eight incidence directions, according to the angle-of-incidence-phase relationship assigned to the incidence direction.

[0105] Furthermore, the incidence angle-phase structural component can be designed such that one or more retroreflector elements impart no phase or only a constant phase according to the incidence angle-phase relation. These retroreflector elements therefore do not cause any phase matching with respect to the incidence angle. The interference patterns associated with these retroreflector elements therefore do not include higher spatial frequencies and thus contain information about the lower spatial frequencies.

[0106] The eight directions of incidence can be oriented as follows, for example: Einfallsrichtung #1 #2 #3 #4 #5 #6 #7 #8 Richtung +X -x +y -y +x,+y -x,-y +x,-y -X,+y Orientierung 180° 0° 270° 90° 225° 45° 135° 315°

[0107] Where “+x” indicates an incidence direction along the x-axis (pointing in the direction of the optical axis) and defines an orientation of 180° with respect to a plane perpendicular to the optical axis. “-x” describes an incidence direction opposite to the x-axis (and also pointing towards the optical axis) and corresponds to an orientation of 0°.

[0108] “+x,-y” describes, for example, a direction of incidence along the diagonal along the x-axis and opposite to the y-axis, i.e., a direction of incidence along the diagonal in the second quadrant of the coordinate system (orientation 135°).

[0109] “-x,-y”, on the other hand, describes a direction of incidence along the diagonal opposite to the x-axis and opposite to the y-axis, i.e., a direction of incidence along the diagonal in the first quadrant of the coordinate system (orientation 45°).

[0110] In embodiments where, in addition to the angle-of-incidence phase relations, subband-specific phases are also imposed on the object light according to a subband phase relation, the following is noted.

[0111] The system is then specifically designed to impose phases on a predefined multitude of incidence directions, e.g., eight, on each subband, in particular exactly one subband, of the object light, i.e., subband-specific, according to the angle-of-incidence-phase relation assigned to the incidence direction, and in particular not to impose any phase on the other subbands of the object light according to the angle-of-incidence-phase relation assigned to the incidence direction.

[0112] Similarly, the system can be configured to impose incidence-direction-independent phases on a subband according to an incidence angle-phase relation, e.g., where the incidence angle-phase relation imposes a phase constant with respect to the incidence angle, i.e., for example, 0. This subband then contains information about the low spatial frequencies.

[0113] The term angle of incidence in the context of this specification refers in particular to an angle of incidence of the object light with respect to the optical axis, especially with respect to the phase-matching optical structural component, e.g. with respect to a normal vector of the structural component.

[0114] The angle of incidence can be defined, for example, as the angle between an optical axis of the system or structural component and a direction of propagation of the object light.

[0115] It should be noted that while the beam splitter divides and recombines the beam path of the object light, and at least according to some embodiments the angle-of-incident phase structure component and / or the subband phase structure component can be distributed across different sides of the beam splitter, a clearly defined angle of incidence can nevertheless be determined in any case, e.g., by considering an optically conjugate image of one side (e.g., the reference mirror) and another side (e.g., the retroreflector array).

[0116] The angle-of-incident phase relation describes and defines a relationship between the angle of incidence of the object light and the phase imprinted on the object light, or at least on a subband of the object light, for this angle of incidence. This relationship is advantageously uniquely given by a continuous function. In particular, there is an essentially linear relationship between the angle of incidence and the phase.

[0117] According to some advantageous embodiments, it may be advantageous if the system has an angle-of-incidence-phase relation for a subband and / or for one or more retroreflector elements, in which the phase is set independently of the angle of incidence, and in particular is constant with respect to the angle of incidence (neutral element).

[0118] According to a further embodiment of the invention, the incidence angle-phase structure component has two or more associated incidence angle-phase relations for the predefined plurality of incidence directions of the object light, wherein the incidence angle-phase structure component is configured to assign exactly one of the two or more associated incidence angle-phase relations to one or more retroreflector elements, in particular a group of retroreflector elements, and to assign the remaining of the two or more incidence angle-phase relations to other retroreflector elements.

[0119] This embodiment describes, in particular, the possibility of imprinting two or more angle-of-incident phase relationships on the object light for each of the incidence directions. For example, a first and a second angle-of-incident phase relationship. These can differ, for example, in the steepness of the angle-of-incident phase relationship. In particular, with approximately linear angle-of-incident phase relationships, the angle-of-incident phase relationships for the same incidence direction can differ with respect to their slope.

[0120] For this to work, some of the retroreflector elements of the retroreflector array must be exclusively assigned to the first angle-of-incidence-phase relation, while other retroreflector elements are exclusively assigned to the second angle-of-incidence-phase relation. This can be achieved by a suitably designed phase-matching optical structural component.

[0121] This embodiment enables the reconstruction of a digital hologram that, on the one hand, has a high signal-to-noise ratio and, on the other hand, includes an even higher spatial resolution.

[0122] If, for example, the angle-of-incidence-phase structural component includes three angle-of-incidence-phase relations per direction of incidence, additional retroreflector elements are necessary that are exclusively assigned to this third angle-of-incidence-phase relation.

[0123] According to a further embodiment of the invention, the one or more angle-of-incidence phase relation(s) assigned to the respective direction of incidence are the same for the predefined plurality of directions of incidence.

[0124] According to a further embodiment of the invention, the incidence-phase structure component comprises a plurality of optical gratings, wherein the optical gratings are each assigned to one another in pairs and thus form a grating pair, wherein each assigned grating pair is designed and arranged for one of the predefined plurality of incidence directions and an incidence-phase relation, so that each assigned grating pair imposes the phases on the object light according to the incidence-phase relation, depending on the incidence direction.

[0125] According to a further embodiment of the invention, the associated grating pairs each have a first reflection grating, which is each encompassed by a retroreflector element, in particular by the Bragg mirror system of the retroreflector element.

[0126] According to a further embodiment of the invention, the grating pairs each comprise a second reflection grating, wherein the second reflection grating is arranged on the side of the reference mirror, in particular wherein the associated grating pairs are arranged such that the respective optically conjugated image of the first reflection grating with the associated second reflection grating forms the respective grating pair, in particular wherein the respective conjugated image is the image of a first virtual grating, wherein the first virtual grating is generated by an image of the first reflection grating produced by the lenses of the retroreflector elements on a side facing the beam splitter surface.

[0127] According to a further embodiment of the invention, one or more retroreflector elements are assigned to each direction of incidence, such that each retroreflector element is assigned in particular exactly one angle-of-incidence-phase relation, in particular wherein each direction of incidence is assigned a group of retroreflector elements, each of which is assigned one, in particular exactly one, angle-of-incidence-phase relation of the angle-of-incidence-phase structural component, wherein each group comprises a plurality of retroreflector elements.

[0128] In order to impose no phase or only a constant phase on incident object light, the angle-of-incident phase structure component can, at least with respect to some retroreflector elements, comprise only a corresponding optical element, e.g. a glass plate, instead of a grating pair.

[0129] The grid pairs make it easy to realize the angle-of-incidence-phase relationships for different directions of incidence.

[0130] Optical gratings are understood to be structures or structured elements that cause diffraction of the object light and thereby produce various advantageous properties.

[0131] The steepness of the angle of incidence-phase relation (i.e., the change in phase with a changing angle of incidence) can be precisely defined on the one hand by adjusting a distance, G, of the gratings of a grating pair and on the other hand by the grating spacing, g, of the respective grating.

[0132] An inclination of the grating pair at a tilt angle relative to the optical axis can also be used to determine the steepness of the angle-of-incident-phase relation.

[0133] The grating pair causes a lateral displacement of an incident light beam due to a deflection angle from the angle of incidence caused by the respective grating. This results in a phase shift, as the optical path of the light is slightly lengthened. This phase shift correlates directly with the angle of incidence of the object light, depending on the parameters of the grating pair.

[0134] The grating pairs can include transmission gratings. Alternatively or additionally, gratings made of metamaterials ("meta-grates") can be used.

[0135] The grating pairs are each formed in such a way that they each form an optical double grating.

[0136] By orienting the grating pairs with respect to the predefined incidence directions, it can be achieved that the grating pairs imprint different phases on the incident light for one of the predefined incidence directions, according to the mechanisms described above, depending on the angle of incidence.

[0137] According to a further embodiment of the invention, at least some or each of the associated grid pairs each have at least one first transmission grid.

[0138] The first transmission grating forms a grating pair, in particular with a second optical grating, e.g. a second transmission grating or a reflection grating.

[0139] This embodiment is flexible in its application and easy to implement. In particular, the various grating pairs can be structurally nested and thus realized in a compact optical component.

[0140] According to a further embodiment of the invention, at least some or each of the associated grating pairs each have at least one first reflection grating, which is each encompassed by the retroreflector elements.

[0141] Reflection gratings have a higher spectral resolution compared to transmission gratings, which has a beneficial effect on the performance of the system according to the invention, as subband cross-talk is reduced.

[0142] In particular, the first reflection grating comprises one or more Bragg mirrors. These Bragg mirrors can form the Bragg mirror system, which can be specifically configured to imprint subband-specific phases onto the object light.

[0143] The first reflection grating of each grating pair can essentially be divided between the retroreflector elements, such that each retroreflector element includes the first reflection grating.

[0144] According to a further embodiment of the invention, at least some or each of the associated grid pairs each have at least one second transmission grid.

[0145] This embodiment allows the formation of grating pairs with two transmission gratings.

[0146] According to a further embodiment of the invention, the incidence angle-phase structure component and the subband phase structure component are arranged in such a way that they effect a subband-specific phase adjustment of the object light and, for each of the plurality of incidence directions, imprint phases according to the assigned incidence angle-phase relation on one subband, in particular exactly one subband of the object light, i.e., subband-specifically, and in particular do not imprint phases according to the assigned incidence angle-phase relation on the other subbands.

[0147] Furthermore, as previously described, the system can have an angle-of-incidence phase relation for a subband of the object light, which imposes an angle-of-incidence phase relation on the object light for this subband regardless of the direction of incidence, where the phase with respect to the angle of incidence is constant, e.g. 0.

[0148] This embodiment is particularly advantageous because, on the one hand, it makes it possible to use object light with a large number of sub-bands without the disadvantages described above coming into play, and on the other hand, it provides for an extremely compact design and implementation of the invention.

[0149] In addition to the angle-of-incidence phase relation, this embodiment encodes further phases according to the subband phase relation.

[0150] According to a further embodiment of the invention, the number of different subband phase relations is equal to the multitude of incidence directions.

[0151] According to a further embodiment of the invention, each associated grating pair is also designed and arranged for a subband, so that each associated grating pair imprints the subband-specific phases on the object light according to the angle of incidence-phase relation, depending on the direction of incidence.

[0152] In particular, the system, especially characterized by the incidence angle-phase structure component and the subband phase structure component, comprises a plurality of optical gratings, wherein the optical gratings are each assigned to one another in pairs and thus each form a grating pair, wherein each assigned grating pair is designed and arranged for a subband and for one of the predefined plurality of incidence directions and an incidence angle-phase relation, such that each assigned grating pair imposes the subband-specific phases on the object light according to the incidence angle-phase relation, depending on the incidence direction.

[0153] This embodiment provides that each of the grid pairs is designed for one subband and is “invisible” to the other subbands in the sense that it does not cause any phase change to the other subbands.

[0154] According to a further embodiment of the invention, the retroreflector elements have a subband phase relation assigned to the respective retroreflector element, so that the retroreflector elements imprint phases on the object light depending on the wavelength according to the assigned subband phase relation, wherein at least some of the assigned subband phase relations differ from one another, so that the interference patterns include subband information with which a separation of contributions of the subbands to the interference pattern is made possible.

[0155] In particular, the number of different subband phase relations is equal to or greater than the number of angle-of-incidence phase relations, and therefore, in particular, greater than the number of predefined incidence directions.

[0156] According to a further embodiment of the invention, the system comprises an evaluation unit which is configured to reconstruct a hologram based on the interference patterns.

[0157] According to a further embodiment of the invention, the evaluation unit is configured to reconstruct a chromatically corrected hologram based on the interference patterns.

[0158] According to a further embodiment of the invention, the evaluation unit is configured to reconstruct a hologram with improved resolution based on the interference patterns.

[0159] A second aspect of the invention relates to a method for zoom imaging with a digital holographic imaging system comprising a magnifying optic arranged at an input aperture, in particular with a system according to the first aspect of the invention, wherein the method comprises at least the following steps: - In particular, simultaneous capture of interference patterns on one detection side of the system, - Evaluation of the interference patterns, whereby the evaluation is carried out in such a way that along an optical axis of the system, e.g. in a volume area predefined by the magnifying optics, an at least two-dimensional image is reconstructed, which corresponds to an image of an associated focal plane that can be positioned via the evaluation.

[0160] The method according to the invention makes it possible to reconstruct images from the object space with a system for digital holographic imaging which has a magnification optic, whose associated focal plane can be positioned displaceably along the optical axis by means of appropriate evaluation.

[0161] The term "focal plane" corresponds in particular to a plane or surface in object space in which an object located therein can be sharply imaged by an optic operating in spatial space. In the context of the invention, therefore, the term "associated focal plane" is used, since the system is not necessarily set to a focal plane, as it is not a spatially operating imaging system, but rather a digital holographic system that operates in the frequency space conjugate to spatial space.

[0162] The term "capturing a recording" refers specifically to the digital capture of a recording. Digital capture can be achieved, for example, by reading data from a memory device containing information about the captured interference patterns. Furthermore, the term can also encompass the process of capturing the recording itself.

[0163] The method thus allows for the reconstruction of a large number of images, each with different assigned focal planes, meaning they are "sharply" imaged at different distances from the system.

[0164] This allows an assigned focal plane to be selected, especially after a recording with the digital holographic system, so that an object at a certain distance from the system can always be sharply imaged, particularly without the need for a change in the focal length of the magnifying optics.

[0165] Design features, characteristics, and definitions relating to the first aspect of the system can be applied analogously to the method according to the second aspect, and vice versa.

[0166] In particular, embodiments relating to optics and / or magnification optics can become part of the magnification optics of the method.

[0167] According to a further embodiment of the second aspect, the evaluation is carried out in such a way that the assigned focal plane is shifted along the optical axis between at least a first and a second position and for each position of the assigned focal plane an at least two-dimensional image is reconstructed, which corresponds to an image from the assigned focal plane.

[0168] This embodiment allows two or more sharp images to be generated from different assigned focal planes.

[0169] In particular, a large number of images can be generated, corresponding to a large number of assigned focal planes.

[0170] According to another embodiment of the second aspect, an image composition is generated from the two or more reconstructed images from different assigned focal planes, which includes the two or more images.

[0171] The image composition is characterized in particular by a high depth of field, which cannot be achieved with conventional zoom systems in just one shot.

[0172] According to a third aspect, a computer program is comprehensively disclosed as computer program code which, when executed on a computer, performs the procedure according to the second aspect.

[0173] In particular, the executing computer can be connected to the system in order to control the system and process recording data from the system using the computer program.

[0174] The computer program can be stored on a non-transient data storage device.

[0175] The processed data can be displayed on a screen.

[0176] Further features and advantages of the invention are explained below with reference to the description of exemplary embodiments in the figures. These show: Fig. 1 a first embodiment of the invention with a magnifying optic consisting of 2 convex lenses; Fig. 2 a second embodiment of the invention with a magnifying optic having a concave lens; Fig. 3 an illustration of the principle of angle of incidence phase coding; Fig. 4 incidence-direction-dependent angle-of-incidence-phase relations for different sub-bands; Fig. 5 a representation of the subband-specific phase coding in a retroreflector element; Fig. 6 the effect of a grating pair as a phase-adapting optical structure component to realize the angle-of-incidence-phase relation; Fig. 7 a first embodiment of the angle-of-incidence phase structural component; Fig. 8 a second embodiment of the angle-of-incidence phase structural component; Fig. 9 a first embodiment of the system according to the invention with an angle-of-incidence phase structural component; Fig. 10 a second embodiment of the system according to the invention comprising an angle-of-incidence phase structural component and a subband phase structural component; Fig. 11 a third embodiment of the system according to the invention with a structural component that combines the functions of the angle-of-incidence phase structural component and the subband phase structural component; Fig. 12 a schematic representation of a retroreflector element with Bragg mirror system and first reflection gratings; and Fig. 13 Matching arrangement for subband phase coding.

[0177] In Fig. Figure 1 shows an exemplary embodiment of the system according to the invention.

[0178] System 1 comprises a beam splitter 2, here in the form of a beam splitter cube. The beam splitter cube 2 has four sides. A first side 21 is assigned to an input aperture E of the system, on whose side an optic 7 is arranged, which collects object light 100 originating from an object 200 to be examined.

[0179] The optics comprise a magnifying optic 70, which in this example consists of a first convex lens 71 and a second convex lens 72.

[0180] The optics 7 may include further optical components (not shown), such as filters or corrective lenses, which, however, do not primarily contribute to an angular magnification of the object light. The angular magnification is achieved by the magnifying optics and its components.

[0181] In general, the first lens 71 can also be designed as a first lens system consisting of a multitude of lenses.

[0182] The second lens 72 can also be designed as a second lens system consisting of a multitude of lenses.

[0183] The first lens 71 has a first focal length f1, the second lens has a second focal length f2.

[0184] The first and second lenses are arranged at a distance along the optical axis OA that corresponds to the sum of the first and second focal lengths f1 and f2. Thus, these lenses form a telecentric system.

[0185] The first and second lenses are fixed at this distance without any displacement mechanism, thus forming a rigid lens system without moving components.

[0186] The magnifying optics are designed to increase the angle at which object light strikes the optics 7. In particular, the (angular) magnification assigned to the optics or the magnifying optics is in the range of more than three, especially more than five or ten. The magnification can also be more than 50 or 100.

[0187] The object light 100, provided it originates from a focal plane of the optic 7, is collimated by the optic 7 and directed onto the entrance aperture. Object light 100 that does not originate from the focal plane is convergent or divergent accordingly. Since the object 200 is very far away compared to a lens aperture of the lens 71, in particular more than 100x to 1000x farther away than the lens aperture, any convergences of the wavefronts of the object light 100 that may occur are very small, only a few mrad or less. Therefore, it can essentially be assumed that the object light 100 striking the optic 7 of system 1 is collimated.

[0188] The object light 100 propagates from the optics 7, which causes the angular magnification, via the entrance aperture E to a beam splitter surface 2a of the beam splitter 2. The beam splitter surface 2a is oriented such that it reflects a portion of the object light 100 originating from the first side 21 of the beam splitter 2 towards a second side 22 of the beam splitter 2 and transmits another portion of the object light 100 along a third side 23 of the beam splitter 2. The second side 22 extends adjacent to the first side 21 on the beam splitter cube. The third side 23 is arranged opposite the first side 21 and extends adjacent to the second side 22.

[0189] Opposite the second side 22, a fourth side 24 of the beam splitter 2 extends. Each side of the beam splitter 2 defines a plane. The planes assigned to the adjacent sides extend at an angle of 90° to each other.

[0190] The beam splitter surface 2a forms a 45° angle with these planes. Each side, together with the beam splitter surface 2a, defines an associated arm that designates a beam path between the beam splitter surface and the respective side.

[0191] In the example of the Fig. 1 On the second side 22 of the beam splitter 2 the retroreflector array 3 is arranged and on the third side 23 of the beam splitter 2 the reference mirror 4 is arranged.

[0192] Alternatively, the retroreflector array 3 can be arranged on the third side 23 and the reference mirror 4 can be arranged on the second side 22. This variant is not shown separately, as it is otherwise completely identical to Fig. 1. This exchange of the sides of the retroreflector array and the reference mirror is possible for every embodiment of system 1 and is hereby explicitly disclosed.

[0193] The retroreflector array 3 comprises a plurality of retroreflector elements 30, each retroreflector element 30 comprising a lens 31 and an associated retroreflector mirror 32. In particular, the retroreflector mirrors 32 are arranged in a focal plane of the associated lens 31.

[0194] Each retroreflector element 30 is configured so that incident object light 100 is reflected back on the axis of incidence, thus object light is reflected along the same direction at the same angle as it hits the retroreflector element.

[0195] The beam path for object light 100, which essentially travels along the optical axis OA via the first side 21 onto the beam splitter 2, causes the object light 100 to be reflected on the second side 22 via the retroreflector array 3 towards the fourth side 4. Simultaneously, the object light 100 is also reflected on the third side 23 via the reference mirror 4 towards the fourth side 24.

[0196] To minimize losses during passage through the beam splitter surface 2a, the object light 100 can undergo corresponding polarization reversals on the second and third sides, and the beam splitter surface can be designed to be polarization-dependent. This is known to those skilled in the art. Quarter-wave plates at appropriate locations in the beam path can effect these polarization reversals. However, for the sake of simplicity, corresponding polarization elements are not shown, as they are not essential to the invention.

[0197] On page 24, the object light 100 from the second and third arms of the beam splitter 2 overlaps, resulting in interference. This interference comprises a multitude of interference patterns (not shown), particularly those with lateral offsets, which can be assigned to a respective retroreflector element 30 of the retroreflector array 3. The interference patterns are detected by a detector 8 on page 24 and recorded as data.

[0198] The detector 8 can be a camera, in particular a digital monochrome camera.

[0199] The detector 8 is connected to a computer 9, to which the data is transferred. The computer 9 is or includes an evaluation unit that is configured to reconstruct a hologram of the object 200 under investigation from the interference patterns.

[0200] The computer can also be connected to various components of the system in such a way that the computer can communicate with these components and, in particular, control these components.

[0201] In particular, the computer 9 is equipped to carry out the method according to the invention, for example by executing the computer program according to the invention.

[0202] For this purpose, an image of interference patterns is captured on a detection side of system 1.

[0203] The recording can be captured by sending appropriate control commands from the computer to detector 8 and transferred to the computer.

[0204] Alternatively, the computer can also read the recording from a data storage device of the system.

[0205] By evaluating the interference patterns, an at least two-dimensional image is determined from the recording along an optical axis of the system, which corresponds to an image of an assigned focal plane that can be positioned via the evaluation.

[0206] The image therefore corresponds to a focal plane or a focal surface in object space.

[0207] The computer program can be trained to receive information about the position of the focal plane, for example via a user interface or by reading a data storage device containing this information.

[0208] This allows a large number of images to be generated by repeatedly evaluating the recording for different positions of the focal plane, which depict these focal planes sharply, i.e., with focus on the focal plane.

[0209] The multiple images can be used to create a composite image that, by combining them, depicts a multitude of focal planes in focus, resulting in a greater depth of field compared to the individual images. The composite image can be two- or three-dimensional.

[0210] Additionally or alternatively, one or more of the images can be displayed on a screen.

[0211] In particular, the evaluation can be carried out in such a way that the assigned focal plane is shifted along the optical axis between at least a first and a second position and an at least two-dimensional image is determined for each position of the assigned focal plane.

[0212] Provided the system includes the subband phase structure component, the computer or computer program can further be configured to consider and process the information about the subbands in the evaluation, so that the image is corrected for the respective subband / and / or where a large number of color channels are generated during the reconstruction of the subband information, so that the image includes color channel information, e.g. RGB information, in particular where the image is a color image.

[0213] Provided the system includes an angle-of-incidence phase structure component, the computer or computer program can still be configured to generate an image with increased spatial resolution.

[0214] It is also possible to combine information about the subband phase relation and the angle of incidence phase relation, so that a subband-corrected, resolution-enhanced image is generated, whose associated focal plane of the object space can be variably determined.

[0215] An actuator system 6 of system 1 is configured to adjust the distance and / or angle of the retroreflector array 3 with respect to the optical axis. It can also be used to introduce additional sequential phase steps to reduce or eliminate the twin-image problem known in the field.

[0216] In the example in Fig. The first and second lenses are both convex lenses and therefore have a positive focal length. The angular magnification m is calculated accordingly: m=f1f2, where f1 corresponds to the focal length of the first lens and f2 corresponds to the focal length of the first lens.

[0217] To make the magnifying optic 70 more compact, a so-called Galilean optic can be used, in which the second lens 72 is a concave lens with an associated negative focal length. The angular magnification then results from m=f1|f2|, where the first focal length is greater than the magnitude of the second focal length.

[0218] In Fig. Figure 2 shows an example of a system according to the invention, which is equipped with a Galilean optic 70.

[0219] Identical reference symbols refer to the same components and are not described again.

[0220] Since the distance between the first and second lenses 71, 72 is smaller in a Galilean optic than in a corresponding conventional (positive focal length) optic due to the negative focal length of the second lens, the magnifying optic 70 requires slightly less installation space.

[0221] It should also be explicitly noted here that both the first 71 and / or the second lens 72 can consist of a lens system, each comprising a multitude of lenses, with the second lens system in this case having a negative focal length.

[0222] Typical dimensions of the components of the system 1 according to the invention are shown below: With an aperture D of 1 mm of the retroreflector elements and a wavelength λ of the object light of 500 nm, the following results from the relationship Δβ=λ2D The system has an angular resolution of approximately 0.25 mrad.

[0223] A retroreflector element 30 with a larger aperture presents the challenge that the wavefronts no longer behave planarly across the aperture, which negatively affects the quality of the reconstructed pixels. Typically, an optimum diameter lies between a few millimeters at the upper edge and 100 µm at the lower edge. In particular, the range from D = 1 mm down to 250 µm is especially favored.

[0224] The system according to the invention allows the optical resolution to be significantly increased for a zoom range. For this purpose, the system 1 comprises an optic 7 with a magnifying optic 70. This optic 7 "translates" incident light waves by a factor of m (at the expense of a more restricted image field / zoom). In a typical zoom arrangement as in Fig. 2. Object light 200 is focused from a distance onto a (virtual) focal point with focal length f1 by the first convex lens 71. The wavefronts of object light 100, which strikes the system from a large distance, e.g., from more than 10 m, can generally be assumed to be planar. At the focal point of the first lens 71, or of the first lens system, the second concave lens 72 with the negative focal length f2 is arranged, which converts the focused object light 200 back into collimated light at the focal point of the first lens. The angular magnification factor (without sign) is given by m = .

[0225] For a first focal length of f1 = 50 mm, f2 = -2 mm, the angular magnification is m = 25, and thus the angular resolution of the system increases from Δß = 0.25 mrad to Δα=Δβm=10 μrad increased.

[0226] With this angular resolution, objects at a distance of, for example, z = 100 m can be detected with a lateral resolution Δx of Δx = Δα · z = 1 mm.

[0227] For example, with 512 object points, this would correspond to an image field of approximately 0.5 m.

[0228] A certain technical challenge lies in keeping the focal length f2 of the second lens 72 short while simultaneously ensuring that the entrance aperture E of system 1 – typically a few millimeters – is still filled with light. Therefore, the second lens 72 can also be designed as a lens system, i.e., as a lens system with lenses with a corresponding resulting focal length f2. The focal length of the first lens 71 in this example, f1 = 50 mm, is significantly shorter than that of a typical 800 mm zoom lens. This design is therefore very compact.

[0229] A further advantage of the system according to the invention is the fact that the first lens 71 / the first lens system in combination with the second lens / the second lens system 72 exhibits wavefront aberrations, which, however, can be compensated for by the described self-interference method using the beam splitter 2. In a "classic" zoom camera, the zoom lens must be optically corrected as perfectly as possible; otherwise, the image quality will be poor. This explains its size and weight, as up to 24 lenses can be used.

[0230] A further advantage of the system 1 according to the invention is that the system 1 can dispense with mechanical focusing, since the position of the focal plane is controlled algorithmically during the subsequent evaluation of the interference patterns. This allows, on the one hand, very rapid changes in the distance of an object 200 to be sharply detected and, almost more importantly, changes in the object depth within the image field to all be focused instantly.

[0231] The following describes embodiments relating to a further improvement in resolution by means of an angle-of-incidence phase structure component.

[0232] In Fig. Figure 3A schematically depicts a retroreflector array 3 with three retroreflector elements 30, where each retroreflector element 30 is assigned an angle-of-incidence phase relation 1000 (shown as a diagram). This causes the interference pattern assigned to the respective retroreflector element 30 ( Fig. 3B) includes different spatial frequencies. In Fig. 3B shows the respective signal strength (y-axis) of the spatial frequencies for the respective position (x-axis) in an interference pattern.

[0233] The angle-of-incidence-phase relation 1000 of the central retroreflector element 30 has a slope of zero, and therefore no change occurs in the spatial frequencies encompassed by the interference pattern. This is in Fig. 3B can be seen in the middle panel, which is the so-called centroid 1001 in the middle (y H = 0) includes a high typical signal 1001 around low spatial frequencies (around 0 / mm).

[0234] The centroid 1001 is "shifted" along the x-axis in the interference pattern for the two outer retroreflector elements 30, which have an incidence angle-phase relation 1000 with positive and negative slopes, respectively. This results in high spatial frequencies (denoted by Box B) being included in the respective interference patterns, frequencies that were previously not part of the interference pattern or were not included in the interference pattern of the central retroreflector element 30. The slopes, more precisely, the incidence angle-phase relations 1000, cause a shift of approximately ±0.8*D in this example, where D corresponds to the aperture of a retroreflector element 30, so that spatial frequencies corresponding to a virtual total aperture of approximately D* = 2.6D are captured in the interference patterns.

[0235] The three interference patterns can now be combined along the x-axis (e.g., by so-called "stitching"), resulting in an interference pattern (not shown) that encompasses the spatial frequencies of all three interference patterns. With this composite interference pattern, a digital hologram with increased resolution can be reconstructed, since the composite interference pattern includes higher spatial frequencies than the interference pattern of the central retroreflector element 30. In this (one-dimensional) case, a resolution improvement of almost three times would theoretically be possible.

[0236] An even higher resolution could be achieved by having the angle-of-incidence phase relations 1000 of the outer retroreflector elements 30 have a greater slope, and thus “shifting” the centroids 1001 even further, in particular to the point that they are no longer included in the interference pattern.

[0237] To ensure improved hologram reconstruction, it is possible to add further retroreflector elements 30 with different angle-of-incidence phase relationships 1000. These are designed to successively introduce higher spatial frequencies into the interference patterns.

[0238] To extend the described scenario to the two-dimensional case, it is advantageous to define the angle-of-incidence-phase relations 1000 for a multitude of incidence directions. In the one-dimensional case, there are only two incidence directions (along or against the x-axis; x, -x).

[0239] In the two-dimensional case, to ensure accurate reconstruction, eight directions of incidence should be defined. These are defined along and opposite the x- and y-axes, as well as along and opposite the diagonal.

[0240] It is noted that the centroid 1001, as well as the other signals in the interference pattern in practical application, is the signal that arises when the object light is reflected across all angles of incidence α. F averaged from the direction of incidence.

[0241] In Fig. Figure 4 shows schematically and exemplarily how a subband-specific phase coding of the different directions of incidence can be carried out in a single retroreflector element 30.

[0242] In Fig. 4A and Fig. 4B schematically depicts the corresponding angle-of-incident-phase relationship 1000 for an incidence direction e1 or e2 from the multitude of predefined incidence directions, where the x-axis represents the angle of incidence α and the y-axis corresponds to the applied phase Φ. The example illustrates the situation for two subbands S1 and S2, a first subband S1 and a second subband S2, of the object light 100. Fig. 4A shows the situation for a first direction of incidence e1 of the object light opposite the x-axis, while in Fig. Figure 4B shows the situation for a second direction of incidence e2 along the y-axis.

[0243] The schematically represented retroreflector element 30 is associated with two grating pairs 50, a first grating pair 50-1 and a second grating pair 50-2, wherein each grating pair 50 is configured such that it is responsible for one of the subbands S1, S2 - in Fig. 4A is the first grid pair 50-1, the first subband S1, and in Fig. 2B is the second grating pair 50-2 assigned to the second subband S2 - the incidence angle-phase relation 1000 assigned to the respective incidence direction e1, e2 causes and thus imposes phases on the respective subband S1, S2 which is given via the incidence angle-phase relation 1000.

[0244] In Fig. 4A The first grating pair 50-1, which is assigned to the first subband S1, acts on the first subband S1 with a linear angle-of-incident-phase relation 1000 when the object light 1000 is incident opposite to the x-axis along the first incidence direction e1. For the second subband S2, the phase does not change with the angle of incidence, as shown in the angle-of-incident-phase diagram 1000 in Fig. Figure 4A shows the angle-of-incidence phase relation 1000 for the first incidence direction e1. The effect of the phases imprinted on subband S1 in the interference pattern assigned to this retroreflector element 30 is that the centroid 1001-1 of the first subband S1 appears shifted along the y-axis in this example. The centroid 1001-2 of the second subband S2, however, remains unchanged, since no phase change occurs due to either of the grating pairs 50-1, 50-2. The centroid 1001-2 of the second subband S2 is represented by the hatched circle that appears in the center of the schematic representation of retroreflector element 30.

[0245] In Fig. Figure 4B shows the situation for the same retroreflector element 30 in which the object light 100 is incident from the second direction e2. In this case, the second grating pair 50-2 has a phase-matching effect on the second subband S2, while neither of the grating pairs 50-1, 50-2 has a phase-changing effect on the first subband S1. As a result, the centroid 1001-2 of the second subband S2 is shifted from the center of the interference pattern, in this example along the x-axis. The centroid 1001-1 of the first subband S1 remains unchanged.

[0246] In Fig. 5 is schematically a similar situation to that in Fig. 4 shown, except that here the positions of the centroids 1001 of nine different sub-bands S of the object light 1000 are shown simultaneously for all directions of incidence e.

[0247] The incidence angle-phase structural component and the subband phase structural component are here formed in a single structural component 5, which performs both functions. In this case, the structural component 5 is designed to imprint phases on one of the eight subbands S for eight of the nine subbands S, depending on the incidence direction, according to an essentially linear incidence angle-phase relationship. This can be achieved, as described, by appropriately manufactured and arranged grid pairs 50. For the ninth subband of the nine subbands, the structural component 5 only acts in such a way that it does not imprint any phases, regardless of the incidence direction; i.e., regardless of the incidence direction, the incidence angle-phase relationship is constantly equal to 0.

[0248] The in Fig. The situation depicted in section 5 corresponds to a practical application where the object light typically comes from all directions of incidence. Fig. For the sake of clarity, only two grid pairs 50 are indicated in 5A, with the structural component 5 comprising eight grid pairs, each designed for a subband S and oriented accordingly.

[0249] In Fig. Figure 5B shows a similar situation, where the grating pairs 50 are each configured to have an incidence angle-phase relation with a steeper incidence angle-phase relation, so that even higher spatial frequencies are included in the associated interference pattern, whereby the associated (shifted) centroids 1001 are then no longer included in the interference pattern, and therefore in Fig. 5B are shown hatched.

[0250] It is noted that a coincidence between the position and area of ​​the retroreflector element 3 and the interference pattern (the latter not shown) is not necessary and appears only for illustrative purposes.

[0251] A combination of the designs in Fig. 5A and Fig. 5B would be possible through a structural component 5 that assigns these different angle-of-incidence phase relations, with respect to the slope of the linear relation, to different retroreflector elements.

[0252] Furthermore, it would be possible to implement phase encoding in a single retroreflector element by using even more grating pairs, introducing even more subband phase relations, and correspondingly even more subbands, thus also extending the explanations regarding Fig. 5A and Fig. to unite 5B.

[0253] In Fig. Figure 6 schematically illustrates the operation of a lattice pair 50. The lattice pair 50 comprises a first lattice 51 and a second lattice 52. In Fig. Figure 6 schematically depicts two situations. In the first situation, a light beam 101 with a subband strikes the light at an angle of incidence of α.F =0° onto the first grating 51 (the dashed lines correspond to straight lines along the optical axis with respect to which the angle of incidence can be measured). The first grating 51 diffractes this light ray 101 according to its grating constant g, so that the light 101 propagates further at a deflection angle β. The diffracted light ray 101 then strikes the second grating 52, which is arranged parallel to the first grating 51 at a distance G and has the same grating constant g as the first grating 51. This causes the light ray 101 to be diffracted again, so that the deflection angle β is compensated and the light ray 101 is only displaced relative to d1 but at the original angle of incidence α. Ffurther propagated. However, it is important to note that the light beam 101 has to travel a longer optical path length through the grating pair 50, which leads to a phase shift compared to a light beam that would not propagate through the grating pair 50 (not shown).

[0254] In the second situation, a light ray 102 strikes with an angle of incidence α. F The light beam is directed at >0° onto the first grating 51 and, according to the diffraction laws, is also diffracted by a deflection angle β into order 1 or -1, which is then compensated by the second grating 52 via order -1 or 1. The light beam emerges with a larger offset d2 below the original angle of incidence α. Ffrom the grating pair 50. This light beam 102 also experiences an increase in the optical path length, such that the phase increases essentially linearly with the angle of incidence α (e.g., compared to the first situation). This makes it possible to realize an angle-of-incident phase structural component using grating pairs 50, which imposes phases on the incident light 100 according to a predefined angle-of-incident phase relationship. The specific relationship is realized, for example, by the grating constant g of the grating pair 50, by the grating spacing G, and also by an inclination (not shown) of the grating pair 50 with respect to the optical axis.

[0255] The deflection angle β should preferably be in the range of 3° to 30°. Large deflection angles result in a large offset, which can have a negative impact on the system design.

[0256] The gratings can be so-called "thin gratings," which, however, present the problem of allowing diffraction to higher orders. This can be avoided, for example, with holographic gratings. Metamaterials also offer a way to avoid diffraction to higher orders.

[0257] The selectivity of the subbands in transmission gratings can be solved, for example, by metamaterials, since these can be "activated" in a very narrowband wavelength-selective (subband-selective) way, while they are not "active" for other wavelengths, i.e., they act like a glass pane.

[0258] Depending on the embodiment, the grating pair 50 can be formed from two associated transmission gratings. In other embodiments, the grating pair 50 can also be formed from two associated reflection gratings – that is, from a reflection grating on the side of the retroreflector array – encompassed by the retroreflector elements – and a reflection grating on the side of the reference mirror. The grating spacing G in a reflection grating arrangement is then given by the position of a conjugate image of one of the reflection gratings relative to the position of the other reflection grating along the optical axis.

[0259] To form the incidence angle-phase structural component for different incidence directions e, a large number of differently oriented (with respect to the x- and y-axes) lattice pairs 50 can be used. In the case of subband-specific coding (with a subband phase structural component or a structural component 5 that combines both functions), the lattice pairs 50 can also be nested within each other.

[0260] In Fig. Figure 7 shows an embodiment of the invention suitable for object light 100 with only one subband S. For this purpose, the angle-of-incident phase structural component is designed such that it assigns at least one retroreflector element 30 to each of eight directions of incidence e (along and opposite the x- and y-axes as well as along and opposite the diagonal) of the object light 100. This retroreflector element imposes phases on the object light 100 according to the angle-of-incident phase relationship assigned to the retroreflector element 30, but only for object light from the respective direction of incidence. The optical axis in Fig. 7 extends perpendicular to the image plane of the Fig. 7. Object light thus occurs along the optical axis, possibly with a lateral component along one of the many incidence directions (shown as arrows in Box C), onto the retroreflector elements 30. The incidence angle-phase structural component comprises all grating pairs 50.

[0261] Object light 100 from other directions of incidence is not subjected to a variable phase, which corresponds to an angle-of-incidence-phase relationship that is constant, in particular at 0.

[0262] The retroreflector elements 30 are in Fig. The 7 are indicated as circles. The orientation of the associated grating pairs 50 is indicated by the dashed lines. The gratings 50 are arranged rotated 45° relative to each other, so that for the eight directions of incidence, indicated as arrows in box C, a corresponding angle-of-incidence-phase relationship is encoded, which can be assigned to the respective retroreflector element 30 (and thus to the interference pattern). The specific position of the retroreflector elements 30 in the depicted group of 9 is not important and can be interchanged with other retroreflector elements 30 in the group of 9.

[0263] The centroidal shifts in the interference pattern resulting from the grating constant g of the grating pairs 50 are indicated by the small black circle 1001, which is shifted from the center of the retroreflector element 30. At the center of the retroreflector elements 30 is a retroreflector element 30 in which a phase-matching optical structure component 5 imparts no phase or only a constant phase to the object light 100. This component does not require a grating pair 50 but can consist of an unstructured glass plate.

[0264] Since the angle-phase relationship and the associated direction of incidence are known for each interference pattern assigned to the respective retroreflector element 30, this information can be used from the eight outer or all nine retroreflector elements 30 to reconstruct a hologram exhibiting a substantially isotropic resolution improvement. It is possible to align the grating pairs 50 in smaller angular increments, e.g., 15°, 22.5°, or 30°, and thus to explicitly encode more than eight directions of incidence. The hologram reconstruction would then be more uniform, but the required number of retroreflector elements would also increase. The present embodiment allows the formation of groups of nine, which can be implemented in square arrangements, thus advantageously matching a square geometry of the beam splitter or the retroreflector array.

[0265] The in Fig. The embodiment shown in 7 can be achieved by means of transmission grids arranged in front of or within the retroreflector elements 30. These produce a result as shown in Fig. 6 explained the beam offset. This means that object light 100 striking a retroreflector element 30 can fall out of the aperture of the retroreflector element due to the aforementioned offset, which is an undesirable effect.

[0266] This problem is mitigated by a method such as in Fig. 8 configuration shown.

[0267] Unlike Fig. 7 individual grating pairs 50 extend over a multitude of retroreflector elements 30 ( Fig. 8A), each grouped into a 30G group, each group contains nine retroreflector elements 30 arranged in rows of three. This allows offset object light 100 to enter the aperture of the adjacent retroreflector element of the same 30G group (defined by the same grating pair), thus minimizing signal loss. In this case, the retroreflector array therefore comprises at least one 30M module, consisting of nine 30G groups of retroreflector elements 30, each group containing nine retroreflector elements 30.

[0268] In Fig. 8B are four, like in Fig. 8A shows modules 30M of a retroreflector array, where these modules 30M have different angle-of-incidence phase relations, so that an additionally increased resolution can be achieved.

[0269] The in Fig. The system shown in section 8 essentially corresponds to the system from Fig. 1 or Fig. 2, wherein the system additionally comprises an angle-of-incidence phase structure component, which in particular according to the Fig. 7 or Fig. 8 is designed.

[0270] The in Fig. 1 and Fig. The two elements and components already described will not be repeated here; instead, reference is made to the explanations regarding... Fig. 1 referred.

[0271] In contrast to Fig. 1. A grating pair 50 (corresponding in this example to the angle-of-incident structural component) is positioned in front of most retroreflector elements 30. Depending on the direction of incidence, this grating pair imprints phases onto the object light 100, which in particular comprises only a single subband, according to the angle-of-incident phase relation assigned to the respective grating pair 50. This imprints additional information onto the reflected object light, which is reflected in the interference patterns in a predefined manner and can thus be used to reconstruct a resolution-enhanced hologram.

[0272] We can supply the retroreflector elements 30 in Fig. 7 each be separately provided with a grid pair 50, or as in Fig. 8 described are grouped together, which have the same grid pair in front of them (not shown).

[0273] An actuator system 6 of system 1 is configured to adjust the distance and / or angle of the retroreflector array 3 relative to the grating pairs 50. It can also be used to introduce additional sequential phase steps to reduce or eliminate the twin-image problem known in the field.

[0274] The magnifying optics 70 of system 1 in Fig. 9, has a second lens system 72, which is shaped as an objective. However, the optics 7 and the structural component are independent components and can be readily interchanged between the embodiments.

[0275] In Fig. 10 and Fig. 11 is a system 1 according to the invention which additionally performs subband-specific phase coding on the object light. This allows object light with a plurality of subbands to be processed.

[0276] This is made possible by separate phase coding and evaluation of the sub-bands.

[0277] In Fig. Each retroreflector element 30 comprises a Bragg mirror system 320 with a plurality of Bragg mirrors 32-1, 32-2, 32-3, configured to imprint wavelength-dependent, i.e., subband-specific, phases onto the incident object light according to a subband phase relation encompassed by the respective Bragg mirror system 320. Depending on the number of subbands in the object light, the various Bragg mirror systems 320 should be configured to imprint subband-specific phases from different subband phase relations onto the object light, whereby the number of different subband phase relations should be equal to or greater than the number of subbands to be resolved. The subband phase relations should be sufficiently distinct to imprint unambiguous phase relationships between the subbands, so that the subbands can be separated based on the different phase relationships during hologram reconstruction.

[0278] As in Fig. As indicated in Figure 10, the different subband phase relationships are achieved by the different spacing of the Bragg mirror layers 32-1, 32-2, and 32-3 encompassed by the Bragg mirror system 320. The Bragg mirrors reflect the object light in a subband-specific manner and are transparent to the other subbands. An example of a Bragg mirror system 320—greatly magnified in the optical axis direction—is shown in a separate box in Figure 10. Fig. 10 shown.

[0279] To compensate for manufacturing-related spacing of the Bragg mirrors and the associated optical path lengths, which distort the intended subband phase relationships in the Bragg mirror system 320 alone, a Bragg mirror system 40 can also be arranged on the reference mirror 4 side. This system imprints phases onto the object light according to a subband phase relationship that compensates for the manufacturing-related spacing of the Bragg mirror layers, so that only the intended subband phase relationship is effective. This arrangement also ensures that the requirement known to those skilled in the art as the "matching" condition is met. In this example, the reference mirror 4 is therefore configured as a Bragg mirror system 40.

[0280] In order to imprint phases of the angle-of-incident phase relations onto the object light 100, in this example a plurality of optical grating pairs 50 are arranged on the side of the reference mirror 4 or on the side of the retroreflector array 3 (not shown) (only one of the grating pairs is indicated in the figure), each of which has an angle-of-incident phase relation, wherein the grating pairs 50 are arranged and oriented such that for a predefined plurality of incidence directions of the object light, e.g. for eight incidence directions, phases according to the assigned angle-of-incident phase relation are imprinted on a subband for each of these plurality of incidence directions.

[0281] The orientation and nature of the grid pairs 50 have already been described in detail.

[0282] In the example of Fig. Figure 11 schematically illustrates a particularly high-quality variant of the invention. In this variant, which is also based on a subband-specific coding of the object light, the subband-specific angle-of-incident-phase relations are generated by pairs of reflection gratings, each with a first and a second reflection grating placed in the second and third arms, instead of transmission grating pairs.

[0283] The grid pairs 50 are implemented as follows.

[0284] The first reflection grating 51R of each grating pair is enclosed in the retroreflector elements 30 of the retroreflector array 3 and forms the retroreflector mirror of the respective retroreflector element 30. The second reflection grating 52R of each grating pair 50 forms the reference mirror 4.

[0285] That is, the first reflection gratings 51R of the grating pairs 50 are formed in a structural element that combines the function of all first reflection gratings in a retroreflector element. The same applies to the second reflection gratings 52R, which are combined in the reference arm in a structural element that combines the function of all second reflection gratings in a retroreflector element. In particular, the different orientations and subband specificities of the respective reflection gratings are formed in these integral structural elements.

[0286] By imaging the first reflection gratings 51R formed in the retroreflector elements, virtual first reflection gratings 51V are created on the side of the lenses 31 of the retroreflector elements 30, pointing towards the beam splitter surface 2a. Conjugate images 51K in the third arm, i.e., in the arm of the reference mirror (which in this embodiment is formed by or encompasses the second reflection gratings), can be assigned to these virtual images 51V. The conjugate images 51K now act together with the second reflection gratings 52R as grating pairs. The conjugate images 51K of the reflection gratings 51R can be assigned a distance to the “real” reflection grating 52R (reference mirror) arranged in the third arm, so that the assigned grating pairs 50 are formed, which have a grating spacing G that can be determined by the distance of the conjugate images 51K of the first reflection gratings 51R and the second reflection gratings 52R.

[0287] It is noted that the first reflection gratings 51R are still formed in a structure that also includes the respective Bragg mirror system 320 for subband phase coding of the retroreflector element 30. Although these integral structures are comparatively complex, they can be readily manufactured.

[0288] This embodiment benefits from the advantageous properties of reflection gratings compared to transmission gratings.

[0289] In Fig. Figure 12 shows a schematic representation of a retroreflector element 30, which illustrates the function and integration of the first reflection grating 51R.

[0290] The incident object light 100 is focused onto the focal plane according to the focal length of the lens 31 of the retroreflector element 30. A Bragg mirror system 320 is arranged there, possessing the properties of the first reflection gratings 51R. The corresponding curvature of the Bragg mirror system 320, 51R ensures that the incident object light 100 is reflected back exactly in the direction of incidence. The Bragg mirror system 320, with the Bragg mirrors 32-1, 32-2, 32-3 encompassing the Bragg gratings, now accomplishes two things. Firstly, it imprints phases on the object light 100 according to the subband-specific angle-of-incident-phase relationship, depending on the direction of incidence, thus fulfilling the function of the first reflection gratings 51R, whose corresponding virtual image 51V is also represented in Fig. 11 and Fig. 12 is shown. On the other hand, the Bragg mirror system 320 effects the subband-specific phase coding through the subband phase relation assigned to the Bragg mirror system 320.

[0291] The conjugate image 51K ( Fig. 11) This virtual image 51V of the first reflection gratings 51R, together with the second reflection gratings 52R, causes the formation of the associated grating pairs 50, see Fig. 11.

[0292] The curved Bragg mirror system 320 can also be structured from dielectric materials, so that the above function can be structured planarly, e.g., as a holographic layer stack or meta-layer stack. The microlens of the retroreflector element can also be fabricated as a metastructure, so that the retroreflector element can, in principle, be manufactured as a planar structure.

[0293] In Fig. Figure 13A shows exemplary optical path lengths for three subbands S1, S2, S3 for a retroreflector element 30. Fig. Figure 13B shows, as an example, the optical path lengths for the same subbands S1, S2, S3 at the reference mirror 40, which, like the retroreflector element 30, is designed as a layered mirror, i.e., as a Bragg mirror system. Each layer of the layered mirror 32-1, 32-2, 32-3 (and 40-1, 40-2, 40-3) of the layered mirror 320, 40 acts as a wavelength-selective filter, reflecting the first subband S1 but transmitting the second and third subbands S2, S3. The second subband S2 is reflected by a second layer 32-2, 40-2 at a first optical distance from the first layer 32-1, 40-1, and the third subband S3 is transmitted. The third subband S3 is reflected by a third layer 32-3, 40-3, which has a second optical distance to the second layer 32-2, 40-2.

[0294] The diagram shows nearly identical layer system mirrors in the reference arm (comprising reference mirror 40) and in the object arm (comprising the retroreflector mirror; a layer system mirror 320 of a retroreflector element is shown). In the object arm, greatly exaggerated distances between the individual layers are depicted. These additional path lengths Δs n (n = 2,3) move on the order of + / - ½ wavelength. This distance together with the wavelength then results in a phase Φ. n = 2π / λ · Δs n In this embodiment, the phase coding is thus created according to the subband phase relation with a phase range (0 ... 2π). Multiples of this can always be "mapped" to this phase range up to 2π, which is generally known to those skilled in the art. It is also clear that this represents a significant simplification of the actual reflection situation in a layer stack. Reference symbol list 1 system 2 beam splitters 2a Beam splitter area 21 first side of the steel divider 22 second side of the steel divider 23 third side of the steel divider 24 fourth side of the steel divider 3 Retroreflector array 30 Retroreflector element 31 Lens of the retroreflector element 32 retroreflector mirrors 32-1 Reflective layer 32-2 Reflective layer 32-3 Reflective layer 320 layer system mirror / Bragg mirror system 30G Retroreflector Element Group 30M module 4 reference mirrors 40-layer system mirror / Bragg mirror system 40-1 Reflective layer 40-2 reflective layer 40-3 reflective layer 5 phase-adapting structural components 50 grid pair / grid triplet 50-1 first grid pair 50-2 second grid pair 51 first grid 52 second grid 53 third grid 51R first reflection grating 52R second reflection grating 52K conjugate image first reflection grating 51V virtual image of the first reflection grating 51T first transmission grid 52T second transmission grid 6 Actuator 7 Optics 70 Magnifying Optics 71 first lens system / first lens 72 second lens system / second lens 8 Array detector 9 computers 100 object light 101 first light beam 102 second light beam 200 objects 1000 Angle of incidence-phase relationship 1001 Centroid 1001-1 Centroid first subband 1001-2 Centroid second subband OA optical axis D Aperture of the retroreflector element D* virtual total aperture E Entrance aperture S Subband S1 Subband S2 Subband S3 Subband e direction of incidence e1 first direction of incidence e2 second direction of incidence f1 Focal length of the first lens system f2 Focal length of the second lens system α / α F angle of incidence β Deflection angle Φ Phase x, y, z directions of the associated Cartesian coordinate system QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 102021114059 B3

[0003]

Claims

[1] A system (1) for digital holographic imaging, comprising at least the following components: - a beam splitter (2) with an inlet aperture (E), - a retroreflector array (3) comprising a large number of retroreflector elements (30), - a reference mirror (4), wherein the system (1) is configured to receive object light (100) via the input aperture (E) and to superimpose object light (100) reflected from the reference mirror (4) and from the retroreflector array (3) so that interference patterns are created which can each be assigned to one of the retroreflector elements (30), wherein the system (1) has an optic (7) on the side of the entrance aperture (E) which includes a magnifying optic (70). [2] The system (1) according to claim 1, wherein the magnifying optics (70) comprises a first lens system (71) with a first focal length and a second lens system (72) with a second focal length, wherein the first focal length is greater than the second focal length in absolute value. [3] The system (1) according to claim 2, wherein the first and the second lens system (71, 72) are arranged as a telecentric system. [4] The system (1) according to claim 2 or 3, wherein the first lens system (71) comprises exactly one first lens. [5] The system (1) according to any one of claims 2 to 4, wherein the first and / or the second lens system (71, 72) comprises or is / are configured as a metalinson or holographic lens. [6] The system (1) according to one of the preceding claims, wherein the optics (7), in particular the magnifying optics (70), have a fixed focal length ratio and / or wherein the optics, (7), in particular the magnifying optics (70), do not have any movable optics or focal length-adjustable optics. [7] The system (1) according to one of the preceding claims, wherein the system (1) comprises a subband phase structure component configured to imprint wavelength-dependent phases onto the object light (100) incident on the retroreflector array (3) according to a subband phase relation assigned to the retroreflector element (30), wherein the subband phase relations are different for at least some of the retroreflector elements (30) such that information is encoded in the interference patterns which allows the interference patterns to be evaluated in a subband-specific manner. [8] The system (1) according to claim 7, wherein each of the at least some retroreflector elements (30) comprises a Bragg mirror system (320) which is configured to imprint object light phases according to the subband phase relation associated with the retroreflector element (30), wherein the Bragg mirror systems (320) are part of the subband phase structure component. [9] A method for zoom imaging with a digital holographic imaging system comprising a magnifying optic (70) arranged at an input aperture of the system, in particular with a system (1) according to one of the preceding claims, wherein the method comprises at least the following steps: - Capturing an image of interference patterns on a detection side of the system, - Evaluation of the interference patterns, whereby the evaluation is carried out in such a way that at least a two-dimensional image is determined along an optical axis of the system, which corresponds to an image of an associated focal plane that can be positioned via the evaluation. [10] The method according to claim 9, wherein the evaluation is carried out such that the associated focal plane is shifted along the optical axis between at least a first and a second position and an at least two-dimensional image is determined for each position of the associated focal plane. [11] A computer program comprising computer program code which, when executed on a computer, performs the method according to one of claims 9 or 10.

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