High-resolution digital holography system

Abstract

The invention relates to a system (1) for digital holographic imaging, comprising at least the following components: - a beam splitter (2), - a retroreflector array (3) comprising a plurality of retroreflector elements (30), - a reference mirror (4), wherein the system (1) is configured to superimpose the object light (100) reflected off the reference mirror (4) and off the retroreflector array (3) such that a plurality of interference patterns that can be assigned to the respective retroreflector elements (30) are produced, wherein the system (1) has a phase-adapting optical structural component (5) for predefined phase adaptation of the object light (100), characterized in that the phase-adapting optical structural component has an assigned angle-of-incidence / phase relation (1000) for each of a predefined plurality of incidence directions (e) of the object light (100), wherein the phase-adapting optical structural component (5) is configured to impress phases (Φ) on the object light (100) in accordance with the assigned angle-of-incidence / phase relation (1000) for each of said plurality of incidence directions such that the interference patterns comprise information with which a hologram correspondingly reconstructed from said interference patterns has an improved resolution with respect to a system (1) without the predefined phase adaptation.

Description

[0001] akm108wo

[0002] 1

[0003] High-resolution digital holography system

[0004] Description

[0005] The invention relates to a system for high-resolution digital holography.

[0006] Systems for digital holographic imaging are known from the state of the art.

[0007] For example, DE 102021114059 B3 discloses a compact system. With such a system, object light originating from an object can be collected. 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.

[0008] A retroreflector element includes, 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.

[0009] This results in 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, the superimposed object light then forms interference patterns attributable to the retroreflector elements, which can be recorded, for example, using a camera. Based on the recorded interference patterns, or...

[0010] Holograms can be defined by corresponding three-dimensional representations of an object.

[0011] However, these systems have disadvantages.

[0012] Firstly, the spatial resolution is physically limited by the optical apertures of the retroreflector elements, and in particular by the apertures of the lenses of the retroreflector elements. This means that the spatial resolution of a digital hologram is limited by the size of the apertures. However, using larger apertures brings other disadvantages, such as increased extinction of object light with a spectral akm108wo

[0013] 2

[0014] Widths greater than 3 nm. Furthermore, parabolic, nonlinear deviations in the interference pattern increasingly occur, which cannot be adequately captured in an algorithmic reconstruction, leading to a deterioration of hologram quality. This means that the specialist is limited in their choice of apertures. The smaller the aperture, the better the algorithmic reconstruction, but the lower the achievable spatial resolution. The larger the aperture, the narrower the bandwidth of the object light must be, although this can still lead to a deterioration of the reconstruction.

[0015] Another problem with state-of-the-art systems, separate from this, is the previously mentioned issue with broadband object light, e.g., in spectral ranges larger than 10 nm. 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. The more broadband the object light, the more these contributions become blurred, so that a satisfactory reconstruction no longer seems possible with broadband object light.

[0016] To solve this problem, the interference pattern would need to reveal information that allows a distinction between wavelength and spatial information. If this is not possible, the spatial information becomes increasingly blurred with a wider spectral range.

[0017] 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).

[0018] However, it is desirable to be able to generate spatial information from broader-bandwidth 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.

[0019] 3

[0020] Recordings, which can be extremely advantageous when capturing time-critical images, e.g., when the object being recorded is moving.

[0021] 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, 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, could be simultaneously captured and evaluated separately.

[0022] Especially when daylight or a light source consisting of multiple broadband colored light sources is to be used, it is essential to be able to utilize at least approximately 30 nm per color to maximize the use of light energy. 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 subbands, so that with three colors, a total of 18 subbands would need to be separated.

[0023] The object of the invention is to provide a system that enables increased spatial resolution in the reconstruction of a digital hologram.

[0024] Furthermore, it is desirable to be able to use broadband object light with a variety of subbands to generate the hologram.

[0025] The problem according to the invention is solved by a system according to claim 1.

[0026] Advantageous embodiments of the invention are specified in the dependent claims and are described below. akm108wo

[0027] 4

[0028] According to the invention, a system for digital holographic imaging is provided, which comprises at least the following components: a beam splitter, a retroreflector array comprising a plurality of retroreflector elements, a reference mirror, wherein the system, in particular the beam splitter, is configured to superimpose the object light reflected by the reference mirror and by the retroreflector array, so that interference patterns are created which can each be assigned to and are associated with one of the retroreflector elements, wherein the system has a phase-matching optical structural component for predefined phase matching of the object light.

[0029] According to the invention, the phase-matching optical structural component has an associated angle-of-incident phase relation for each of a predefined plurality of incident directions of the object light, wherein the phase-matching optical structural component is configured to imprint phases on the object light for each of these plurality of incident directions according to the associated angle-of-incident phase relation, so that the interference patterns contain information with which a hologram reconstructed from these interference patterns has a resolution that is improved, particularly in relation to a system without the predefined phase matching.

[0030] This allows a digital hologram with improved resolution, especially improved lateral resolution, to be generated by evaluating the multitude of interference patterns assigned to the retroreflector elements using this angle-of-incidence phase matching by the phase-matching optical structure component.

[0031] The improvement in resolution is particularly noticeable with respect to spatial directions, especially along lateral directions, i.e., perpendicular to the optical axis. akm108wo

[0032] 5

[0033] Phase matching allows at least some interference patterns to include higher spatial frequencies than would be possible in a system without the phase-matching optical structural component.

[0034] The higher spatial frequencies result in an increased spatial resolution in object space, i.e., in the reconstructed hologram.

[0035] The inventive concept of this invention is that, via the phase-matching optical structural component, predefined phases are imprinted on the object light 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 matching, the interference patterns do not include higher spatial frequencies, so an improvement in resolution is not possible.

[0036] The “lost” information about the low spatial frequencies can be extracted from interference patterns that include this part, i.e., that do not have an optical structural component or have a structural component with a weak angle-of-incidence-phase relation.

[0037] 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.

[0038] In the context of this specification, the term "imprinting phases" is understood to mean, in particular, a superposition of the object light, akm108wo

[0039] 6 the light originating from one side of the beam splitter on which the reference mirror is located, and the object light originating from one side of the beam splitter on which the retroreflector array is located, is designed by the phase-matching optical structure component in one or both optical arms such that induced phase differences in the interference pattern come into play, reflecting the intended angle-of-incident-phase relation.

[0040] 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.

[0041] 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.

[0042] Each subband can therefore be assigned a central wavelength, which, for example, lies in the middle of the spectral range encompassed by the subband.

[0043] 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.

[0044] The term “phase-adapting optical structural component” in the context of this specification refers in particular to one or more optical elements that work together to effect the angle-of-incident phase relation assigned to each of the predefined multitude of incident directions of the object light.

[0045] Preferably, the phase-matching optical structure component comprises a plurality of optical gratings. The optical gratings need not necessarily be identifiable as separate, individual components within the system, but can be integrated into one or more components of the structure. akm108wo

[0046] 7

[0047] In the context of this specification, the term "direction of incidence" refers specifically to the direction of propagation of the object light with respect to a plane perpendicular to the optical axis. The direction of incidence 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 direction of incidence thus extends, in particular, within this plane. Specifically, the vector denoting the direction of incidence always points towards the optical axis.

[0048] The system is now specifically designed to imprint phases for a predefined multitude of incidence directions, e.g., eight incidence directions, according to the incidence angle-phase relationship assigned to the incidence direction.

[0049] Furthermore, the phase-matching structural component can be designed such that one or more retroreflector elements impart no phase or only a constant phase according to the angle-of-incidence-phase relationship. These retroreflector elements therefore do not effect phase matching. Consequently, the interference patterns associated with these retroreflector elements do not include higher spatial frequencies and thus contain information about the lower spatial frequencies.

[0050] The eight directions of incidence can be oriented as follows, for example:

[0051] Where “+x” is a direction of incidence 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 akm108wo

[0052] 8 to the optical axis, ,,-x“ describes a direction of incidence opposite to the x-axis (and also points to the optical axis) and corresponds to an orientation of 0°.

[0053] , ,+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°).

[0054] ,,-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°).

[0055] In further advantageous embodiments, in which subband-specific phases can be imposed on the object light according to a subband phase relation, the following is further noted:

[0056] 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.

[0057] Similarly, the phase-adapting optical structural component 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.

[0058] 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.

[0059] 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. akm108wo

[0060] 9

[0061] It should be noted that while the beam splitter divides and recombines the beam path of the object light, and the phase-matching optical structural component can also be distributed across different sides of the beam splitter according to at least some embodiments, a clearly defined angle of incidence can still be determined in any case, for example by considering an optically conjugate image of one side (e.g., the reference mirror) and another side (e.g., the retroreflector array).

[0062] 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.

[0063] According to some advantageous embodiments, it may be advantageous if the phase-matching optical structural component for a subband and / or for one or more retroreflector elements has an angle-of-incidence-phase relation 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).

[0064] Similar to the angle-of-incidence-phase relation, the subband-phase relation describes and defines a connection between the wavelength, and in particular the wavelength of the subband or the central wavelength of the subband, the object light, and a phase imprinted on the subband. This relation can also be given by an essentially linear functional relationship. However, the relationships differ for different retroreflector elements.

[0065] In the context of this specification, the term retroreflector element refers specifically to an optical element designed to reflect incident light back onto itself. Specifically, the retroreflector element does not reflect the incident light according to Snell's law, but rather reflects the light back along the direction of incidence at essentially the same angle. akm108wo

[0066] 10

[0067] A retroreflector element can have a lens that is designed 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 light reflected from there.

[0068] As described in the following embodiments, a retroreflector element can include further optical elements and also parts of the phase-matching optical structure component.

[0069] According to some embodiments of the invention, each retroreflector element comprises a subband phase structure component which is configured to imprint phases on the object light according to the subband phase relation associated with the retroreflector element.

[0070] This 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 Bragg mirror system is designed for and reflects a specific subband, while the other Bragg mirrors in the Bragg mirror system are transparent to the other subbands.

[0071] This causes the object light to travel through a subband-specific optical path length within the retroreflector element, so that the retroreflector element imparts 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. In the case of subband-specific phase matching using the retroreflector elements, the reflecting element of the retroreflector can correspond to the Bragg mirrors within the retroreflector element.

[0072] According to some embodiments of the invention, at least some of the retroreflector elements differ with respect to the subband phase relation, so that based on akm108wo

[0073] By analyzing the different phases and subband phase relationships in the evaluation of the interference patterns assigned to the retroreflector elements, a subband-specific reconstruction of the digital hologram can be performed. This allows, in particular, the wavelength-dependent compression or stretching of the interference pattern described earlier to be compensated for by additional "re-sampling" measures.

[0074] Similarly, the signal components in the interference pattern can be assigned to the respective subbands. This is particularly advantageous in conjunction with phase matching with respect to the angle of incidence.

[0075] Each retroreflector element can be assigned an aperture. This aperture is essentially limited by the aperture of the lens.

[0076] The inventor realized the following during the invention process.

[0077] The phase-adaptive optical structural component makes it possible to imprint phases onto the incident light source according to the angle-of-incident phase relationship, depending on the angle of incidence. This angle-of-incident phase relationship can, for example, stipulate that the imprinted phase is greater the larger the angle of incidence of the light source, or conversely, that it is smaller the larger the angle of incidence. It is also possible to define a constant angle-of-incident phase relationship (i.e., a phase independent of the angle of incidence). The angle-of-incident phase relationship modifies the interference pattern attributable to a retroreflector element in a manner defined by the respective angle-of-incident phase relationship. This type of phase adjustment with respect to the angle of incidence (and the direction of incidence) allows this phase information to be used in hologram reconstruction to achieve increased spatial resolution.Therefore, in the context of this specification, the terms phase matching or phase coding are also used.

[0078] According to further embodiments, it was found that it is possible and advantageous to impose wavelength-dependent phases on the object light according to subband phase relations assigned to the retroreflector elements, which are different for at least some retroreflector elements. akm108wo

[0079] 12

[0080] In this way, the system can comprehensively process object light over a comparatively broad spectral range, since the adverse effects described at the beginning (indistinguishability of lateral spatial information in the interference pattern of an object point compared to wavelength-related compression or stretching of the interference pattern, resulting in a blurring of the spatial information) are algorithmically separable and thus compensated for due to the phase matching for the sub-bands, i.e., due to the coding for different wavelengths.

[0081] 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.

[0082] According to this embodiment of the invention, the system can therefore be used to determine a digital hologram with object light comprising a plurality of subbands, which, on the one hand, has an increased spatial resolution compared to prior art systems due to the phase adjustment of the object light via the angle of incidence phase relation(s), and, on the other hand, can be used to generate the digital hologram with spectral widths in the range of 30 nm, 50 nm and larger due to the wavelength-dependent phase adjustment of the object light via the subband phase relations.

[0083] This would not be possible without phase matching.

[0084] The respective angle-of-incidence phase relation(s) and subband phase relations can be determined once before using the system by appropriate test measurements.

[0085] In particular, it may be provided that the phase-adapting optical structural component has an angle-of-incidence-phase relationship corresponding to the akm108wo

[0086] 13

[0087] Object light imposes an angle-of-incidence-phase relationship regardless of the direction of incidence, where the phase with respect to the angle of incidence is constant, e.g. 0.

[0088] 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:

[0089] - a first page for collecting object light,

[0090] - a second side to which the collected object light is redirected at the beam splitter surface, in particular partially reflected,

[0091] - a third page that extends opposite the first page,

[0092] - a fourth side that extends opposite the second side, so that object light originating from the second and third sides propagates to the fourth side, and can form the interference patterns on the fourth side,

[0093] 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, wherein this adjacent side is the second or third side.

[0094] 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.

[0095] 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.

[0096] It is known 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). These four sides correspond, in particular, to sides of the beam splitter that are perpendicular to the optical axes of the beam splitter. akm108wo

[0097] 14

[0098] According to a further embodiment of the invention, the phase-adapting optical structural component has two or more associated angle-of-incident phase relations for each of the predefined plurality of directions of incidence of the object light, wherein the phase-adapting optical structural component is configured to assign exactly one of the two or more associated angle-of-incident phase relations to one or more retroreflector elements, in particular a group of retroreflector elements, and to assign the remaining two or more angle-of-incident phase relations to other retroreflector elements.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] If, for example, the phase-adapting optical structural component includes three angle-of-incidence phase relations per direction of incidence, further retroreflector elements are necessary that are exclusively assigned to this third angle-of-incidence phase relation.

[0103] According to a further embodiment of the invention, the one or more angle-of-incident phase relationship(s) assigned to the respective direction of incidence are identical for the predefined plurality of incidence directions. akm108wo

[0104] 15

[0105] Particularly in cases where the phase-matching optical structure component comprises a multitude of optical grating pairs, each assigned to a direction of incidence, the same optical grating pairs, i.e., in particular with the same grating constant and the same grating spacing, can be used, whereby the grating pairs differ with respect to their orientation, i.e., each is aligned along one of the multitude of directions of incidence.

[0106] This embodiment allows for simplified manufacturing of the phase-matching optical structural component and simplified evaluation of the interference patterns.

[0107] According to a further embodiment of the invention, the phase-adapting optical 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-angle-phase relation, so that each assigned grating pair imposes the phases on the object light according to the incidence-angle-phase relation, depending on the incidence direction.

[0108] In order to impose no phase or only a constant phase on the incident object light, the phase-adjusting optical structural 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.

[0109] The grid pairs make it easy to realize the angle-of-incidence-phase relationships for different directions of incidence.

[0110] In particular, the grating pairs are aligned along different directions perpendicular to the optical axis. These directions correspond to the directions of incidence of the incident light.

[0111] In particular, the grating pairs enclose different angles to each other in a plane perpendicular to the optical axis.

[0112] The grid pairs can be arranged along at least two or at least three, in particular along more than three, especially along four or more akm108wo

[0113] They can be oriented in 16 different directions. The grid pairs can also be oriented along six or eight different directions.

[0114] According to a further embodiment of the invention, the grid pairs each enclose a predefined angle of, for example, 45° or 90° to each other.

[0115] This allows each grating pair to be assigned an incidence direction, with respect to which it imposes the associated angle-of-incidence-phase relation on the incident light.

[0116] Optical gratings are understood to be structures or structured elements that cause diffraction of the object light and thereby produce various advantageous properties.

[0117] 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.

[0118] 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.

[0119] 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.

[0120] The grating pairs can include transmission gratings. Alternatively or additionally, gratings made of metamaterials ("meta-grates") can be used.

[0121] The grating pairs are each formed in such a way that they each form an optical double grating.

[0122] By orienting the grid pairs with respect to the predefined incidence directions, it can be achieved that the grid pairs are suitable for one of the predefined akm108wo

[0123] 17

[0124] Depending on the angle of incidence, incoming light imprints different phases according to the mechanisms described above.

[0125] 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.

[0126] 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.

[0127] 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.

[0128] 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.

[0129] 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.

[0130] 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.

[0131] 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.

[0132] 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.

[0133] This embodiment allows the formation of grating pairs with two transmission gratings. akm108wo

[0134] 18

[0135] According to a further embodiment of the invention, the phase-adapting optical structural component is configured to effect a subband-specific phase adaptation of the object light and to imprint phases according to the associated angle-of-incidence-phase relation on one subband, in particular exactly one subband of the object light, i.e., subband-specifically, on each of the multitude of incidence directions, and in particular not to imprint phases according to the associated angle-of-incidence-phase relation on the other subbands.

[0136] Furthermore, as previously described, the phase-adapting optical structural component for a subband of the object light can have an angle-of-incidence-phase relation that 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.

[0137] 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.

[0138] In addition to the angle-of-incidence phase relation, this embodiment encodes further phases according to the subband phase relation.

[0139] To better understand the functioning of the subband phase relation and its mode of operation, only the principle of the subband phase relation for the spectral separation of the object light with respect to the subbands is described below.

[0140] According to the subband-phase relationship, the invention provides that a plurality of retroreflector elements are each assigned different subband-phase relationships. This assignment can be achieved by means of specifically provided subband-phase structural components within the retroreflector elements.

[0141] Object light striking and reflected by the retroreflector element is imprinted with wavelength-dependent and thus subband-specific phases by the subband phase structure component (subband phase coding). These phases differ depending on the wavelength; furthermore, the phases akm108wo

[0142] 19. This also applies to different retroreflector elements. That is, the subband phase relationships for different retroreflector elements also differ from one another.

[0143] Consequently, the interference patterns assigned to the retroreflector elements reflect these subband phase relations.

[0144] Because the subband phase relations for each retroreflector element are known - through measurement and / or design - this information can be used when reconstructing the hologram via the interference patterns to separate the contributions of the individual subbands in the interference pattern.

[0145] That is, the number of different subband phase relationships determines the number of resolvable subbands.

[0146] This makes it possible to correct the wavelength-related compressions and stretches of the spatial information of an object in the interference pattern by first performing the spectral separation and then making the compressions and stretches (known to experts).

[0147] Furthermore, the possibility of spectral separation, as described in the embodiment, can be used to separate the contributions from the different directions of incidence.

[0148] This makes it possible to assign to a single retroreflector element the angle-phase relation associated with the respective angle of incidence for several or all directions of incidence (of the multitude of directions of incidence).

[0149] While, on the other hand, as many different subband phase relationships as there are subbands are required, the phase-matching optical structural component can advantageously be configured with respect to the angle-of-incidence phase relationship in such a way that it provides the same angle-of-incidence phase relationships for all retroreflector elements. This simplifies the manufacturing process and, in particular, allows parts of the phase-matching optical structural component—for example, a reflection grating—to be arranged on the side of the reference mirror as well. akm108wo

[0150] 20

[0151] According to a further embodiment of the invention, the number of different subband phase relations is equal to the multitude of incidence directions.

[0152] 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-incident-phase relation, depending on the direction of incidence.

[0153] In particular, the phase-adapting optical structure component comprises a multitude of optical gratings, wherein the optical gratings are each assigned to each other 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 multitude 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.

[0154] 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.

[0155] 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.

[0156] 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.

[0157] This embodiment implements the previously described subband phase coding mechanism. akm108wo

[0158] 21

[0159] In particular, multiple retroreflector elements can be assigned to a single subband phase relation. This increases the signal-to-noise ratio.

[0160] According to a further embodiment of the invention, some or each of the retroreflector elements has a Bragg mirror system which is configured to imprint the phases on the incident object light according to the subband phase relation assigned to the respective retroreflector element.

[0161] In particular, the subband phase structure component is formed in the form of various Bragg mirror systems.

[0162] The Bragg mirror system comprises a multitude of Bragg mirror layers 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 remaining transparent to other subbands.

[0163] This results in the object light traversing a subband-specific effective optical path length within the retroreflector element, so that the retroreflector element imparts 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 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. In the case of subband-specific phase matching via the retroreflector elements, the reflecting element of the retroreflector can correspond to the Bragg mirrors within the retroreflector element.

[0164] The Bragg mirror system is therefore arranged in a focal plane and takes on the role of the reflector element, i.e., the retroreflector mirror.

[0165] Different subband phase relationships can be achieved by varying the spacing of the Bragg mirrors in the respective Bragg mirror systems. akm108wo

[0166] 22

[0167] This embodiment is particularly advantageous because, by using different configurations of the Bragg mirror systems for different retroreflector elements, it is possible to ensure that at least some of the retroreflector elements differ with respect to their assigned subband phase relation, which is essential for further processing to separate the signal components in the interference patterns.

[0168] According to a further embodiment of the invention, some or each of the associated grating pairs comprises 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 with the associated second reflection grating forms the respective grating pair, in particular wherein the first reflection grating is encompassed by the Bragg mirror system.

[0169] It should be noted that the first reflection gratings encompassed by the retroreflector elements each form a virtual first grating by projecting the lens of the retroreflector element in front of said lens, i.e., on one side of the lens that faces the beam area. The conjugate images of these virtual first gratings on the reference arm side are referred to in the context of this specification as conjugate images of the first reflection gratings.

[0170] This embodiment allows the use of two reflection gratings as a grating pair. This is only possible due to the subband-specific phase coding, since the subband-specific phase coding allows all retroreflector elements to be assigned the angle-of-incident phase relationships from all directions of incidence, so that no local, in particular retroreflector element-specific, angle-of-incident phase relationship needs to be achieved, so that part or even the entire phase-matching optical structure component, with regard to the phase matching with respect to the angle of incidence, can also be located on the side of the reference mirror.

[0171] Since reflection gratings generally have a higher spectral resolution, this embodiment is particularly advantageous. akm108wo

[0172] 23

[0173] When using two reflection gratings, the first reflection grating must always be located on the side of the retroreflector array, and in particular in the retroreflector elements of the retroreflector array.

[0174] This embodiment provides in particular that the retroreflector elements, in addition to the subband phase structure components (e.g. Bragg mirror), also perform the function of the reflection grating.

[0175] The first reflection grating can essentially be divided among the retroreflector elements, so that each retroreflector element includes the first reflection grating.

[0176] The subband phase structure components can be designed accordingly.

[0177] In particular, if the subband phase structure components are designed as a Bragg mirror system with a large number of Bragg mirrors, these Bragg mirror systems can be set up to also perform the function of the second reflection grating.

[0178] Then the second reflection grating also includes one or more Bragg mirrors.

[0179] Provided that at least one transmission grating is used, the phase-matching optical structural component, with respect to phase matching with respect to the angle of incidence, can be located entirely on the side of the reference mirror.

[0180] In particular, according to this embodiment, the system comprises at least as many different groups of retroreflector elements as there are angle-of-incidence phase relationships. This ensures that the phase matching is reflected in at least one interference pattern.

[0181] According to a further embodiment of the invention, the system has different subband phase relations between 3 and 25, in particular between 3 and 9, and in particular between 3, 5, 9, 17, 25, or 49, wherein each subband phase relation is assigned to at least one or more retroreflector elements, in particular a group of retroreflector elements. akm108wo

[0182] 24

[0183] In particular, several angle-of-incidence-phase relations are assigned to a retroreflector element.

[0184] This design offers a multitude of advantages.

[0185] In the case of 9 subbands and 9 different subband phase relationships, it can be advantageous for the phase-adapting optical structure component to include an incidence angle-phase relationship for each of the 8 predefined incidence directions. Furthermore, the phase-adapting optical structure component can have an incidence angle-phase relationship independent of the incidence direction, which imposes a constant phase with respect to the incidence angle, e.g., 0, i.e., no phase.

[0186] The predefined directions of incidence can each be rotated by 45° relative to each other, as shown in the example in the preceding paragraphs.

[0187] In this way, the nine subbands can be used to resolve the phases for each direction of incidence according to the associated angle-of-incidence-phase relationship. The subband of the nine subbands that is subject to no phase change or only a constant phase change (i.e., is assigned the constant angle-of-incidence-phase relationship) generates the signal that would be generated in a conventional system and encompasses the low spatial frequencies along all directions.

[0188] According to the invention, the signals of the 9 sub-bands are generally present simultaneously in the respective interference patterns assigned to the retroreflector element.

[0189] To separate the signals in a subband-specific manner, the system therefore includes, for example, 9 or more subband phase relations that are assigned to different retroreflector elements of the retroreflector array.

[0190] The interference patterns contain information encoded via the Bragg mirror systems (phase-encoded), which allows the signals for each subband to be determined separately. This enables the use of broadband object light to generate a digital hologram, and simultaneously makes it possible to distinguish the different phase contributions of the various akm108wo.

[0191] 25

[0192] to algorithmically capture incidence angle-phase relationships and to evaluate this information to improve resolution.

[0193] In this example, the resolution of a digital hologram can be improved isotropically along the lateral directions (x,y).

[0194] In the case of a non-isotropic resolution improvement, e.g. only along one axis, for example along the x-axis, 3 subbands and 3 subband phase relations should be included in the system in order to be able to resolve one angle of incidence phase relation each for the two directions of incidence along and against the x-axis.

[0195] Of course, in all examples it is possible to encode more subband phase relations than angle-of-incidence phase relations, for example to be able to evaluate broadband object light.

[0196] According to a further embodiment of the invention, the number of subband phase relations of the system is equal to or greater than the number of subbands in the object light.

[0197] According to a further embodiment of the invention, the system comprises at least as many different subband phase relations as incidence angle phase relations. It should be noted that in this case, an incidence angle phase relation must also be considered which imposes no phase or only a constant phase on the object light, regardless of the direction of incidence.

[0198] A different approach is necessary if recording is to be done with fewer subband phase relations than angle-of-incidence phase relations.

[0199] One approach is disclosed in several of the following embodiments.

[0200] 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 of the phase-matching optical structure component. akm108wo

[0201] 26

[0202] This embodiment provides a system with which narrowband object light, in particular object light that comprises only one subband, can be processed.

[0203] In contrast to subband-specific coding, signal resolution is achieved by assigning the angle-of-incidence-phase relationships to different retroreflector elements of the retroreflector array. This means that the interference patterns assigned to the respective retroreflector elements exhibit a pre-known angle-of-incidence-phase relationship, particularly for exactly one incidence direction.

[0204] Furthermore, the phase-adapting optical structural component is specifically designed to imprint phases on one or more retroreflector elements according to an angle-of-incident-phase relation, regardless of the direction of incidence of the object light, whereby this angle-of-incident-phase relation provides for a phase that is independent of the angle of incidence, i.e., a constant phase or no phase at all.

[0205] The system can also be implemented as a mixed system and include a variety of subband phase relations, so that the system can also process broadband object light without the disadvantages of the prior art.

[0206] The retroreflector elements can also cause the different subband phase relationships.

[0207] In contrast to the additional subband-specific coding of phases in a retroreflector element, this system (and the phase-adapting optical structure component) assigns different retroreflector elements to each angle-of-incident phase relationship, so that signal separation with respect to the direction of incidence does not necessarily require subband phase matching. This means that the system, according to this embodiment, allows the generation of higher-resolution digital holograms even if the object light comprises fewer subbands (and correspondingly fewer subband phase relationships) than angle-of-incident phase relationships.

[0208] The system according to this embodiment can therefore be used to generate a high-resolution digital hologram that was or is recorded using narrowband object light. akm108wo

[0209] 27

[0210] According to a further embodiment of the invention, 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 phase-adapting optical structure component, wherein each group comprises a plurality of retroreflector elements.

[0211] In particular, each group of retroreflector elements on the retroreflector array forms a connected region, especially where each region is the same size and / or has the same shape.

[0212] This embodiment is advantageous because typical lateral offsets of the object light do not matter due to the phase-matching optical structure component.

[0213] Furthermore, the system can include another group of retroreflector elements that are assigned to an angle-of-incidence phase relation of the phase-matching optical structure component, which impose a constant or no phase on the incident object light regardless of the direction and angle of incidence.

[0214] This embodiment allows for an increased signal-to-noise ratio when evaluating the interference patterns grouped together.

[0215] According to a further embodiment of the invention, each group of retroreflector elements on the retroreflector array forms a contiguous area, in particular wherein each area is of the same size and / or has the same shape.

[0216] This embodiment allows for a simplified construction of the system, since the optical gratings of the phase-matching optical structure component can be manufactured in one piece.

[0217] According to a further embodiment of the invention, the system comprises an evaluation unit configured to reconstruct a hologram based on the interference patterns, which, compared to a system without the predefined phase matching, exhibits improved, in particular spatial, and especially lateral resolution. akm108wo

[0218] 28

[0219] On the detection side, the system can include a detector, such as a camera, designed to capture the interference patterns and generate digital data from the optical signals of these patterns for processing by the evaluation unit. The evaluation unit can include a computer that can receive the detector's data directly or via other components.

[0220] The evaluation unit can include a computer program designed to evaluate the altered interference patterns associated with the phases imprinted by the phase-matching optical structure component in order to generate a hologram with increased resolution.

[0221] In particular, the system can be designed to reproduce the reconstructed hologram via a display unit.

[0222] Mathern atisch-

[0223] The lateral resolution Ay oö; The digital hologram of the presented type, by means of self-interference, results from

[0224] Here, D denotes the lens diameter of the retroreflector element, f the focal length of the lens of the retroreflector element, and A the wavelength of the object light.

[0225] A large lens diameter, however, causes the wavefronts of the object light to no longer behave planarly across the aperture of a retroreflector element, negatively impacting the quality of the reconstructed image pixels. Furthermore, deviations from a monochromatic wavelength range lead to partial signal cancellation at the lens edge. Therefore, a compromise must be found between signal cancellation and resolution. This compromise is found for lens diameters in the range of 100 pm to 5 mm, with preferred ranges between 250 pm and 1 mm.

[0226] Combining several lens apertures of individual retroreflector elements leads to the result, due to the essentially identical information in the akm108wo

[0227] 29

[0228] The interference patterns associated with the retroreflector elements did not result in any increase in resolution.

[0229] One insight of the invention is based on the fact that an interference pattern can be assigned to each retroreflector element via interference, whereby the interference patterns can be transformed into an object by appropriate evaluation (Fourier transformation).

[0230] The minimum distance of an object point to a neighboring object point Ay oö; is calculated according to the equation:

[0231] G / .2 to a difference spatial frequency Av", which ultimately represents the resolution from object point to object point. The wavelength n describes the subband n and f is the focal length of a lens or converging lens which is arranged in front of the beam splitter and is designed to collect the object light.

[0232] The invention introduces phase relations in object space via the phase-encoding optical structure component, which can also be referred to as a phase ramp.

[0233] The effect of these relationships is explained below:

[0234] The difference in the phase progression A <p eines Interferenzmusters von zwei direkt benachbarten Objektpunkten, Ay 0ÖJ -, in one-dimensional form looks like this:

[0235] The first term describes the phase profile in the interference pattern, depending on the interference pattern coordinate y. H , which denote the location of the spatial frequencies in the interference pattern.

[0236] The second term defines the phase relation O, which is the difference between two directly adjacent object points Ay. 0ÖJ which is to be created and is described, for example, by a slope parameter q. akm108wo

[0237] 30

[0238] Using the phase relation and its slope, the interference pattern space can be expanded by additional spatial frequencies v H to be expanded.

[0239] Assuming that the interference pattern coordinate with the maximum spatial frequency lies at the edge of the interference pattern, and thus at y H = D / 2, then a phase relation in the form of c1- A could be used. n = D the spatial frequency point y H = 0 the spatial frequency This phase relationship allows for the assignment of spatial frequencies that were not included in the original interference pattern. As a result, the spatial frequencies appear "shifted" to higher frequencies due to this phase relation (because of the limited extent of the interference pattern on the detection side, lower spatial frequencies are "cut off" on the other side and are no longer included in the interference pattern). The extent of the interference pattern does not increase, but other, especially higher, spatial frequencies are then included in the interference pattern. Since the maximum spatial frequency in the interference pattern determines the resolution of the reconstructed digital hologram, such a phase relation enables an increase in resolution. If the slope q of the phase relation is chosen to be even larger, even higher spatial frequencies are included in the interference pattern, allowing for even higher resolutions.

[0240] Figures and examples

[0241] Further features and advantages of the invention are explained below with reference to the description of exemplary embodiments in the figures. These show:

[0242] Fig. 1 is a schematic representation of the invention principle;

[0243] Fig. 2 Incidence direction-dependent angle-of-incidence phase relationships for different subbands;

[0244] Fig. 3 shows a representation of the subband-specific phase coding in a retroreflector element; akm108wo

[0245] 31

[0246] Fig. 4 shows the effect of a grating pair as a phase-adapting optical structure component for realizing the angle-of-incidence-phase relation;

[0247] Fig. 5 shows a first embodiment of the phase-adapting structural component;

[0248] Fig. 6 shows a second embodiment of the phase-adapting structural component;

[0249] Fig. 7 shows a third embodiment of the phase-adapting structural component as a lattice triplet;

[0250] Fig. 8 shows a first embodiment of the system according to the invention;

[0251] Fig. 9 shows a second embodiment of the system according to the invention;

[0252] Fig. 10 shows a third embodiment of the system according to the invention;

[0253] Fig. 11 shows a schematic representation of a retroreflector element with a Bragg mirror system and first reflection gratings;

[0254] Fig. 12 Matching arrangement for subband phase coding; and

[0255] Fig. 13 shows different arrangements and designs of the system and, in particular, the phase-adapting optical structural component.

[0256] Figure 1A schematically depicts a retroreflector array 3 with three retroreflector elements 30, each of which is assigned an angle-of-incidence phase relation 1000 (shown as a diagram). As previously explained, this results in the interference pattern (Figure 1B) associated with each retroreflector element 30 comprising different spatial frequencies. Figure 1B shows the respective signal strength (y-axis) of the spatial frequencies for each position (x-axis) within the interference pattern.

[0257] 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 in the interference pattern. This can be seen in Fig. 1B in the central panel, which contains the so-called centroid 1001 in the middle (y H = 0) includes a high typical signal 1001 around low spatial frequencies (around 0 / mm). akm108wo

[0258] 32

[0259] 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 (labeled 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, so that spatial frequencies corresponding to a virtual total aperture of approximately D* = 2.6D are captured in the interference patterns.

[0260] The three interference patterns can now be combined along the x-axis to create a single interference pattern (not shown) that encompasses the spatial frequencies of all three patterns. This combined interference pattern can be used to reconstruct a digital hologram with increased resolution. In this (one-dimensional) case, a resolution improvement of almost three times would theoretically be possible.

[0261] An even higher resolution could be achieved by increasing the slope of the angle of incidence phase relations 1000 of the outer retroreflector elements 30, thereby further “shifting” the centroids 1001, in particular to such an extent that they are no longer included in the interference pattern.

[0262] To ensure improved hologram reconstruction, it is possible to add further retroreflector elements 30 with different angle-of-incidence phase relationships 1000. These are configured to successively introduce higher spatial frequencies into the interference patterns.

[0263] To extend the described scenario to the two-dimensional case, it is advantageous to define the angle-of-incident 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).

[0264] In the two-dimensional case, to ensure good 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. akm108wo

[0265] 33

[0266] It is noted that the Centroid 1001, as well as the other signals in the interference pattern, is in practical application the signal that is produced when the object light is averaged over all angles of incidence OF.

[0267] Fig. 2 shows schematically and by way of example how a subband-specific phase coding of the different directions of incidence can be carried out in a single retroreflector element 30.

[0268] In Figures 2A and 2B, the corresponding angle-of-incident-phase relationship 1000 is schematically represented as a diagram for an incidence direction e1 or e2 from the multitude of predefined incidence directions. The x-axis represents the angle of incidence α, and the y-axis corresponds to the applied phase. The example illustrates the situation for two subbands S1 and S2 of the object light. Figure 2A shows the situation for a first incidence direction e1 of the object light opposite the x-axis, while Figure 2B shows the situation for a second incidence direction e2 along the y-axis.

[0269] 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 for each of the subbands S1, S2 - in Fig. 2A the first grating pair 50-1 is assigned to the first subband S1 and in Fig. 2B the second grating pair 50-2 is assigned to the second subband S2 - it causes the angle-of-incidence phase relation 1000 assigned to the respective angle-of-incidence direction e1, e2 and thus imposes phases on the respective subband S1, S2 which are given by the angle-of-incidence phase relation 1000.

[0270] In Fig. 2A, 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 can be seen from the angle-of-incident phase diagram 1000 in Fig. 2A, which represents the angle-of-incident phase relation 1000 for the first incidence direction e1. The effect of the phases imposed on the subband S1 in the interference pattern assigned to this retroreflector element 30 is that the centroid 1001-1 of the first subband S1 in this example is shifted along the y-axis akm108wo

[0271] 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.

[0272] Figure 2B 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.

[0273] Fig. 3 schematically shows a situation similar to that shown in Fig. 2, 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.

[0274] In this case, the phase-adapting optical structural component 5 is designed to imprint phases on one of the eight subbands S, depending on the incidence direction, according to an essentially linear angle-of-incidence-phase relationship. This can be achieved, as described, by appropriately manufactured and arranged grating pairs 50. For the ninth subband, the phase-adapting optical structural component 5 only acts in such a way that it imprints no phases, regardless of the incidence direction; i.e., regardless of the incidence direction, the angle-of-incidence-phase relationship is constantly equal to 0.

[0275] The situation shown in Fig. 3 corresponds to a practical application in which the object light 100 typically arrives from all directions of incidence. In Fig. 3A, for the sake of clarity, only two grating pairs 50 are indicated, with the phase-matching optical structure component 5 comprising eight grating pairs, each designed for a subband S and oriented accordingly.

[0276] Fig. 3B shows a similar situation, where the lattice pairs 50 are each configured such that they have an angle-of-incidence-phase relation with a steeper akm108wo

[0277] 35

[0278] exhibit an angle-of-incidence phase relation such 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 are therefore shown hatched in Fig. 3B.

[0279] 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 only appears so for illustrative purposes.

[0280] A combination of the embodiments in Fig. 3A and 3B would be possible by a phase-adapting optical structural component 5, which assigns these different angle-of-incidence phase relations, with respect to the slope of the linear relation, to different retroreflector elements.

[0281] Furthermore, it would be possible to implement phase coding in a single retroreflector element by using even more grid pairs, introducing even more subband phase relations and correspondingly even more subbands, and thus also combining the explanations for Fig. 3A and 3B.

[0282] Figure 4 schematically illustrates the operation of a grating pair 50. The grating pair 50 comprises a first grating 51 and a second grating 52. Figure 4 schematically depicts two situations. In the first situation, a light beam 101 with a subband strikes the first grating 51 at an angle of incidence of OF = 0° (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 diffracts this light beam 101 according to its grating constant g, so that the light 101 propagates further at a deflection angle β. The diffracted light beam 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, thus compensating for the deflection angle β, and the light ray 101 is merely shifted relative to d1, but propagates further at the original angle of incidence OF. Importantly, however, the light ray 101 has to travel a longer optical path length through the grating pair 50, which leads to a phase shift compared to a light ray that would not propagate through the grating pair 50 (not shown). akm108wo.

[0283] 36

[0284] In the second situation, a light beam 102 with an angle of incidence QF > 0° strikes the first grating 51 and, according to the diffraction laws, is also diffracted by a deflection angle β to order 1 or -1, which is then compensated by the second grating 52 via order -1 or 1. The light beam exits the grating pair 50 with a larger offset d2 below the original angle of incidence OF. 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 implement a phase-matching optical structure component 5 using the 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.

[0285] 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.

[0286] The gratings can be so-called "thin gratings," which, however, present the difficulty 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.

[0287] 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.

[0288] 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 – enclosed by the retroreflector elements, and from a reflection grating on the side of the

[0289] Reference mirror - be formed. The grating spacing G in a

[0290] The reflection grating arrangement is then determined via the position of a conjugate image of an akm108wo

[0291] 37 of the reflection gratings are given in relation to the position of the other reflection grating along the optical axis.

[0292] To form the phase-adapted optical structure component 5 for different incidence directions e, a large number of differently oriented (with respect to the x- and y-axes) grating pairs 50 can be used. In the case of subband-specific coding, the grating pairs 50 can also be manufactured nested within each other (cf. Fig. 13).

[0293] Figure 5 shows an embodiment of the invention suitable for object light 100 with only one subband S. For this purpose, the phase-matching optical structure 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-incidence-phase relationship assigned to the retroreflector element 30, but only for object light from the respective direction of incidence. The optical axis in Figure 5 extends perpendicular to the image plane of Figure 5. Thus, object light incident on the retroreflector elements (Box C) occurs along the optical axis, optionally with a lateral component along one of the multiple directions of incidence. The phase-matching optical structure component comprises all grating pairs 50.

[0294] 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, and in particular is at 0.

[0295] The retroreflector elements 30 are indicated as circles in Figure 5. 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 incidence directions, 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. akm108wo

[0296] 38

[0297] 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. In the center of the retroreflector elements 30 is a retroreflector element 30 in which the 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.

[0298] Since the interference pattern, angle-phase relationship, and direction of incidence are known for each 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°, thus explicitly encoding 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, advantageously matching a square geometry of the beam splitter or the retroreflector array.

[0299] The embodiment shown in Figure 5 can be achieved by means of transmission gratings arranged in front of or within the retroreflector elements 30. These cause a beam offset, as explained in Figure 4. As a result, 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.

[0300] This problem is mitigated by a configuration as shown in Fig. 6.

[0301] In contrast to Fig. 5, individual grating pairs 50 extend over a plurality of retroreflector elements 30 (Fig. 6A), each grouped into a set of 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 set of nine (defined by the same grating pair), thus minimizing signal loss. In this case, the retroreflector array therefore comprises at least one module 30M (akm108wo).

[0302] 39 nine groups 30G of retroreflector elements 30, each comprising nine retroreflector elements 30.

[0303] Fig. 6B shows four modules 30M of a retroreflector array as shown in Fig. 6A, wherein these modules 30M have different angle-of-incidence phase relations, so that an additionally increased resolution can be achieved.

[0304] Figure 7 discloses an embodiment of associated gratings 51, 52, 53 encompassed by a grating triplet 50. This figure illustrates how a phase-matching optical structure component 5 can be configured to achieve two angle-of-incident phase relationships with respect to a predefined incidence direction by means of a triple grating 50, wherein the individual gratings 51, 52, 53 must diffract the object light 101, 102 in a subband-specific manner. The first grating 51 diffracts the object light 101, 102 from a first subband and a second subband equally. The second grating 52 of the triplet 50 refracts the light beam 101 of the first subband, so that the angle of incidence (0° in this example) is again obtained for this subband with an additional offset d1. For the second subband 102, the second grating 52 is transparent, and the beam 102 propagates towards the third grating 51 of the triplet.There, this subband 102 is selectively diffracted back, while light 101 of the first subband experiences no interaction. For the second subband, the angle of incidence (0° in this example) is again obtained with an additional offset d2. For an inclination of the beam by an angle of incidence, the phase is changed according to the principles described in Fig. 4. The same applies to the grating properties as already described.

[0305] This allows, for example, the subband-specific encodings, e.g. Figs. 2 to 3, to be combined with the embodiments from Figures 5 and 6.

[0306] Figure 8 shows an exemplary embodiment of the system according to the invention.

[0307] 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 entrance aperture of the system, on whose side a converging lens 7 akm108wo is located.

[0308] 40 is arranged, which collects object light 100 originating from an object 200 to be examined.

[0309] The object light 100, provided it originates from a focal plane of the converging lens 7, is collimated by the converging lens 7. Object light 100 that does not originate from the focal plane is accordingly convergent or divergent.

[0310] The object light 100 propagates from the lens 7 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.

[0311] 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.

[0312] 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.

[0313] In the example of Fig. 8, the retroreflector array 3 is arranged on the second side 22 of the beam splitter 2 and the reference mirror 4 is arranged on the third side 23 of the beam splitter 2.

[0314] 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. 8. This interchange of the sides of the retroreflector array and the reference mirror is possible for every embodiment of the system 1 and is hereby explicitly disclosed. akm108wo

[0315] 41

[0316] 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.

[0317] 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.

[0318] 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.

[0319] 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. Lambda-quarter 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.

[0320] 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.

[0321] Detector 8 can be a camera, specifically a digital monochrome camera. akm108wo

[0322] 42

[0323] The detector 8 can be 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.

[0324] The system shown in Fig. 8 comprises a phase-adapting optical structural component 5, which is designed in particular according to Figures 5 or 6.

[0325] For this purpose, most retroreflector elements 30 are each preceded by a grating pair 50, which imprints phases on 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, depending on the direction of incidence. This imprints additional information on 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.

[0326] The retroreflector elements 30 can each be provided separately with a grid pair 50 as shown in Fig. 5, or can be grouped together as described in Fig. 6, which have the same grid pair in front of them (not shown).

[0327] An actuator system 6 of system 1 is configured to adjust a distance and / or an angle of the retroreflector array 3 with respect 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.

[0328] Figures 9 and 10 show a system 1 according to the invention which additionally performs subband-specific phase coding on the object light, so that object light with a plurality of subbands can be processed.

[0329] This is made possible by separate phase coding and evaluation of the sub-bands.

[0330] In Fig. 9, each retroreflector element 30 comprises a Bragg mirror system 320 with a plurality of Bragg mirrors 32-1, 32-2, 32-3 which is configured to akm108wo

[0331] 43 wavelength-dependent, i.e., subband-specific, phases are to be imprinted onto the incident object light according to a subband phase relation encompassing 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.

[0332] As indicated in Fig. 9, the different subband phase relationships are achieved by varying the spacing of the Bragg mirror layers 32-1, 32-2, 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 enlarged in the optical axis direction – is shown in a separate box in Fig. 9.

[0333] 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. This condition is explained in more detail in Fig. 12. In this example, the reference mirror 4 is thus configured as a Bragg mirror system 40.

[0334] 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 akm108wo

[0335] 44

[0336] For each of these multiple directions of incidence of the object light, e.g. for eight directions of incidence, phases are assigned to a subband according to the associated angle-of-incidence-phase relation.

[0337] The orientation and nature of the grid pairs 50 have already been described in detail.

[0338] In the example shown in Fig. 10, a particularly high-quality variant of the invention is schematically illustrated. In this variant, which is also based on a subband-specific coding of the object light, the subband-specific angle-of-incident-phase relationships 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.

[0339] The grid pairs 50 are implemented as follows.

[0340] 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.

[0341] 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.

[0342] 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, which point 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 interact together with the second reflection gratings akm108wo

[0343] 45

[0344] 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.

[0345] It is noted that the first reflection gratings 51 R are still formed in a structure that also includes the respective Bragg mirror system 320 for subband phase coding of the retroreflector element 30. These integral structures are comparatively complex, but can be manufactured without difficulty.

[0346] This embodiment benefits from the advantageous properties of reflection gratings compared to transmission gratings.

[0347] Fig. 11 shows a schematic representation of a retroreflector element 30, which illustrates the function and integration of the first reflection grating 51 R.

[0348] 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 shown in Figures 10 and 11. Secondly, the Bragg mirror system 320 effects the subband-specific phase coding through the subband phase relation assigned to the Bragg mirror system 320.

[0349] The conjugate image 51K (Fig. 10) of 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. 10. akm108wo

[0350] 46

[0351] 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.

[0352] Figure 12A shows exemplary optical path lengths for three subbands S1, S2, S3 for a retroreflector element 30. Figure 12B shows exemplary 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.

[0353] 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 As n (n = 2,3) move on the order of + / - 1 wavelength. This distance together with the wavelength then results in a phase. <P n = 2 / n ■ As n In this embodiment, the phase coding is thus created according to the subband phase relation with a phase range (0 ... 2TT). Multiples of this can always be "mapped" to this phase range up to 2TT, 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.

[0354] Fig. 13 shows various configurations of the system 1 according to the invention by way of example. In Fig. 13A, the part of the phase-matching optical structure component 5, which is responsible for the angle-of-incident-phase relationship, is formed from transmission grating pairs 50, 51T, 52T, which are mounted on the sides of the akm108wo

[0355] 47

[0356] Reference mirror 4 are arranged. For further details on this example, refer to Fig. 9.

[0357] This variant must perform subband phase encoding in order to separate the subband information and thus achieve successful reconstruction of the hologram.

[0358] In Fig. 13B, unlike in Fig. 13A, the transmission grid pairs 50, 51T, 52T are arranged on the side of the retroreflector array 3.

[0359] In Fig. 13C, the grating pairs 50 each comprise a reflection grating 52R and a transmission grating 51T at a distance G in the third arm of the beam splitter 2. This variant also requires subband phase coding.

[0360] In Fig. 13D, the grating pairs 50 each comprise a reflection grating 52R and a transmission grating 51T. In this case, the transmission grating 51T is arranged in the second arm, and the reflection grating 52R forms the reference mirror 4. This configuration allows for a compact design and increased spectral resolution with respect to the subbands.

[0361] Fig. 13E shows a variant in which reflection gratings 51 R of the grating pairs 50 are formed in the retroreflector elements 30 of the retroreflector array 3 and the transmission gratings 52T of the grating pairs 50 are also arranged in front of the respective retroreflector elements of the retroreflector array 3.

[0362] This variant can be designed to be subband-specific or for monochrome versions.

[0363] Reference symbol list

[0364] 1 system

[0365] 2 beam splitters

[0366] 2a Beam splitter area

[0367] 21 first side of the steel divider

[0368] 22 second side of the steel divider

[0369] 23 third side of the steel divider

[0370] 24 fourth side of the steel divider akm108wo

[0371] 48

[0372] 3 Retroreflector array

[0373] 30 Retroreflector element

[0374] 31 Lens of the retroreflector element

[0375] 32 retroreflector mirrors

[0376] 32-1 Reflective layer

[0377] 32-2 Reflective layer

[0378] 32-3 Reflective layer

[0379] 320 layer system mirror / Bragg mirror system

[0380] 30G Retroreflector Element Group

[0381] 30M module

[0382] 4 reference mirrors

[0383] 40-layer system mirror / Bragg mirror system

[0384] 40-1 Reflective layer

[0385] 40-2 reflective layer

[0386] 40-3 reflective layer

[0387] 5 phase-adapting structural components

[0388] 50 grid pair / grid triplet

[0389] 50-1 first grid pair

[0390] 50-2 second grid pair

[0391] 51 first grid

[0392] 52 second grid

[0393] 53 third grid

[0394] 51 R first reflection grating

[0395] 52R second reflection grating

[0396] 52K conjugate image first reflection grating

[0397] 51V virtual image of the first reflection grating

[0398] 51T first transmission grid

[0399] 52T second transmission grid

[0400] 6 Actuator

[0401] 7 Converging lens

[0402] 8 Array Detector

[0403] 9 computers

[0404] 100 object light

[0405] 101 first light beam

[0406] 102 second light beam akm108wo

[0407] 200 objects

[0408] 1000 Angle of incidence-phase relationship

[0409] 1001 Centroid

[0410] 1001-1 Centroid first subband

[0411] 1001-2 Centroid second subband

[0412] OA optical axis

[0413] D Aperture of the retroreflector element

[0414] D* virtual total aperture

[0415] S Subband

[0416] 51 Subband

[0417] 52 Subband

[0418] 53 Subband e Direction of incidence e1 First direction of incidence e2 Second direction of incidence a / OF Angle of incidence ß Angle of deflection

[0419] Phase x,y,z directions of the associated Cartesian coordinate system

Claims

akm108wo 50 1. A system (1) for digital holographic imaging, comprising at least the following components: a beam splitter (2), a retroreflector array (3) comprising a plurality of retroreflector elements (30), a reference mirror (4), wherein the system (1) is configured to superimpose the object light (100) reflected by the reference mirror (4) and by the retroreflector array (3) so that interference patterns are created, each of which can be assigned to one of the retroreflector elements (30), wherein the system (1) has a phase-matching optical structure component (5) for predefined phase matching of the object light (100), characterized in that the phase-matching optical structure component has an assigned angle-of-incident-phase relation (1000) for each of a predefined plurality of incident directions (e) of the object light (100), wherein the phase-matching optical structure component (5) is configured tofor each of these multiple directions of incidence, phases are imprinted on the object light (100) according to the associated angle-of-incident-phase relation (1000), so that the interference patterns contain information with which a hologram reconstructed accordingly from these interference patterns has an improved resolution.

2. The system (1) according to one of the preceding claims, wherein the phase-matching optical structural component (5) has two or more assigned angle-of-incident phase relations (1000) for each of the predefined plurality of incidence directions (e) of the object light (100), wherein the phase-matching optical structural component (5) is configured to assign exactly one of the two or more assigned angle-of-incident phase relations (1000) to one or more retroreflector elements (30), akm108wo 51 in particular to assign to a group (30G) of retroreflector elements (30), and to assign the remaining of the two or more angle-of-incidence phase relations to other retroreflector elements (30).

3. The system (1) according to one of the preceding claims, wherein 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 (e).

4. The system (1) according to one of the preceding claims, wherein the phase-adapting optical structure component (5) comprises a plurality of optical gratings (51, 52), wherein the optical gratings are each assigned to one another in pairs and thus form a grating pair (50), wherein each assigned grating pair (50) is designed and arranged for one of the predefined plurality of incidence directions and an incidence angle-phase relation, such that each assigned grating pair (50) imposes the phases on the object light (100) according to the incidence angle-phase relation, depending on the incidence direction.

5. The system (1) according to claim 4, wherein at least some or each of the associated grating pairs (50) comprises at least one first transmission grating (51T).

6. The system (1) according to claim 4 or 5, wherein at least some or each of the associated grating pairs (50) has at least one first reflection grating (51 R), in particular wherein the respective first reflection grating (51 R) is encompassed by the retroreflector elements (30).

7. The system (1) according to claim 5 or 6, wherein at least some or each of the associated grating pairs (50) has at least one second transmission grating (52T).

8. The system (1) according to one of the preceding claims, wherein the phase-matching optical structure component (5) is configured to effect a subband-specific phase matching of the object light (100), akm108wo 52 the interference patterns assigned in the retroreflector elements (30) encode subband-specific information, wherein the phase-adapting optical structure component (5) is configured to impose phases according to the assigned angle-of-incidence-phase relation (1000) on each of these multiple directions of incidence (e), in particular exactly one subband (S), i.e. subband-specifically, and in particular not to impose phases according to the assigned angle-of-incidence-phase relation (1000) on the other subbands.

9. The system according to claims 4 and 8, wherein each associated grating pair (50) is also designed and arranged for a subband (S) such that each associated grating pair (50) imprints the subband-specific phases on the object light (100) according to the angle of incidence-phase relation, depending on the direction of incidence.

10. The system according to claim 8 or 9, wherein the retroreflector elements (30) have a subband phase relation assigned to the respective retroreflector element (30), such that the retroreflector elements (30) imprint phases on the object light (100) depending on the wavelength according to the assigned subband phase relation, the interference patterns assigned to the retroreflector elements (30) encode subband-specific information, wherein at least some of the assigned subband phase relations differ from one another, so that the interference patterns include subband information that enables a separation of contributions of the subbands to the interference pattern.

11. The system according to claim 10, wherein some or each of the retroreflector elements (30) comprise a Bragg mirror system (320) configured to imprint the phases according to the subband phase relation associated with the respective retroreflector element (30).

12. The system (1) according to any one of claims 8 to 11, insofar as it refers back to claim 6, wherein some or each of the associated grating pairs (50) comprises a second reflection grating (52R), wherein the second reflection grating (52R) akm108wo 53 is arranged on the side of the reference mirror (4), in particular wherein the associated grating pairs (50) are arranged such that the respective optically conjugate image of the first reflection grating (51 R) with the associated second reflection grating (52R) form the respective grating pair (50), in particular wherein the respective conjugate image (51 K) is the image of a first virtual grating (51 V), wherein the first virtual grating (51 ) is generated by an image of the first reflection grating (51 R) which is generated by the lenses (31) of the retroreflector elements (30) on a side facing the beam splitter surface (2a).

13. The system (1) according to any one of claims 9 to 11, wherein the system (1) has different subband phase relations between 3 and 25, in particular between 3 and 9, in particular 3, 5, 9, 17, 25, or 49, wherein each subband phase relation is assigned to at least one or more retroreflector elements (30), in particular a group of retroreflector elements (30).

14. The system (1) according to one of the preceding claims, characterized in that one or more retroreflector elements (30) are assigned to each direction of incidence, such that each retroreflector element (30) is assigned in particular exactly one angle-of-incidence-phase relation of the phase-adapting optical structure component (5).

15. The system (1) according to claim 14, wherein each direction of incidence is assigned a group (30G) of retroreflector elements, each of which is assigned one, in particular exactly one, angle of incidence-phase relation (1000) of the phase-matching optical structural component (5), wherein each group (30G) comprises a plurality of retroreflector elements (30).

16. The system (1) according to claim 14, wherein each group (30G) of retroreflector elements (30) on the retroreflector array (3) forms a contiguous area, in particular wherein each area is of the same size and / or has the same shape. akm108wo 54 17. The system (1) according to one of the preceding claims, characterized in that the system (1) comprises an evaluation unit (9) which is configured to reconstruct a hologram based on the interference patterns, which has improved resolution with respect to a system (1) without phase matching.

18. The system (1) according to one of the preceding claims, characterized in that the phase-matching optical structure component (5) comprises a plurality of optical grating pairs (50) each assigned to an incident direction, wherein the grating pairs (50) differ with respect to their orientation.

19. The system (1) according to claim 18, characterized in that the grid pairs (50) are each aligned along one of the plurality of incidence directions.

Images