Optical system for digital holography

Abstract

The invention relates to an optical system (1) comprising at least the following components: a first holographic arrangement (2) comprising a first diffractive element (3) formed by a first prism arrangement (4) having an at least quadrilateral base surface, the side surfaces of the first prism arrangement (4) having the following side surface areas: a first incident surface (31) for reference light (100), the invention relates to a first prism arrangement (4), comprising a first incident surface (31) for object light (200) extending along a first incident plane (310), a second incident surface (32) for object light (200) extending along a second incident plane (320), where the first and second incident surfaces (31, 32) form opposite side surface regions of the first prism arrangement (4), an exit surface (33) extending along an exit plane (330), the first diffractive element (3) has an exit surface (33) through which diffracted reference light (102) and diffracted object light (201) can exit from the first diffractive element (3), a prismatic surface (34) opposite the exit surface (33) and extending along a prismatic plane (340), an optically transmissive diffraction grating arrangement (36) arranged in the first diffractive element (3), the transmission diffraction grating arrangement (36) of the first diffractive element (3) comprises at least one first volumetric phase grating, and wherein the first holographic arrangement (2) has a first mirror (35) on the prism surface (34) side and extends along a diffraction plane (360) intersecting the first incidence plane (310) between the first incidence surface (31) and the exit surface (33), and wherein the transmission diffraction grating arrangement (36) of the first diffractive element (3) comprises at least one first volumetric phase grating, and wherein the first holographic arrangement (2) has a second mirror (35) on the prism surface (34) side, the first mirror (35) has a first mirror plane (350), the first mirror plane (350) enclosing an angle alpha with the diffraction plane (360), and the prism plane (340) enclosing an angle omega 2 with the diffraction plane (360), at least one of the angles alpha, omega 2 being different from 45 degrees.

Description

Technical Field

[0001] The invention relates to an optical system for digital holography, in particular to the field of minimally invasive medical treatment. Background Art

[0002] From the prior art, so-called GRISMs are known as optical components consisting of a combination of gratings and prisms (from English: GRating+pRISM). In a GRISM, the light of the central wavelength passes directly through the GRISM and the light is still spectrally separated. This makes it particularly easy to build spectral imaging devices.

[0003] In addition, various systems are known in the field of digital holography in which a coherent reference beam is superimposed on a coherent object beam, wherein the spatial structure of the object surface, at which the object light is reflected or backscattered before being superimposed on the reference beam, can be calculated from the superimposed interference pattern. To this end, such a system has a camera configured to record the interference pattern. A laser is usually used as a source of reference light and object light, the laser light of which is divided into a reference beam and an object beam by a beam splitter. This ensures the spatial and temporal coherence of the reference light and the object light. Systems of this type are preferably used for 3D endoscopic imaging procedures in the field of minimally invasive medicine. Summary of the invention

[0004] Based on known prior art, an improved system will be created to enable multispectral digital holography, especially in the field of minimally invasive medical technology.

[0005] This object is achieved by an optical system, which comprises at least the following components:

[0006] A first holographic arrangement comprising a first diffractive element formed by a first prism arrangement having a quadrilateral base surface, wherein a side surface of the first prism arrangement has the following side surface area:

[0007] a) a first entrance surface for the reference light, which is in particular planar and extends along a first entrance plane, wherein the first entrance surface may be part of the first end face, and

[0008] b) a second entrance surface for the object light, which is in particular planar and extends along a second entrance plane, wherein the first and second entrance surfaces form opposite side surface areas of the first prism arrangement, wherein the second entrance surface may be part of the second end face,

[0009] c) an exit surface, which is in particular planar and extends along the exit plane and through which the diffracted reference light and the diffracted object light can exit from the first diffractive element,

[0010] d) a prism surface, opposite to the exit surface,

[0011] e) an optical transmission diffraction grating arrangement, which is arranged in the first diffraction element and extends between the first incident surface and in particular the exit surface along a diffraction plane intersecting the first incident plane and the exit plane, in particular so that the transmission diffraction grating arrangement forms a prism with the first incident surface and the exit surface.

[0012] The invention also provides that the transmission diffraction grating arrangement of the first diffraction element comprises at least one first volume phase holographic grating, and the first holographic arrangement has a first mirror, in particular a planar one, which has a first mirror plane on the prism surface side of the first diffraction element, wherein the first mirror plane encloses an angle α with the diffraction plane and the prism surface encloses an angle ω with the diffraction plane 2 , where the angles α and ω 2 At least one or both of them are not equal to 45°, in particular deviate from 45° by more than ±0.2°, in particular wherein the angle α=45°±β and β>0°, in particular wherein the angle ω 2 =45°±ρ 2 And 2 >0°, in particular in order to achieve the greatest possible efficiency of the object and reference light in the first holographic arrangement.

[0013] Preferably, β and / or ρ 2 Greater than 0.2.

[0014] Preferably, β and / or ρ 2 Less than 20°.

[0015] According to the present invention, the angles β and ρ 2 It is particularly selected so that the reference light incident on the transmission diffraction grating arrangement at an angle of 45° is diffracted by the transmission diffraction grating arrangement in the direction of the prism surface and reflected by the first reflector, whereby, due to the incident angle of the reflected reference light on the transmission diffraction grating arrangement, the reflected reference light is diffracted again in the direction of the first incident surface to a smaller extent, in particular to a proportion that is at least 30% smaller than when the reference light was initially incident on the transmission diffraction grating arrangement from the first incident surface side, and the remaining part of the reflected reference light propagates through the transmission diffraction grating arrangement in the direction of the exit surface.

[0016] The terms "reference light" and "object light" are known in the prior art in connection with digital holography. The reference light is superimposed in a diffraction element with the object light returning (e.g. reflected or scattered) from the object, which object light in particular comes from the same coherent light source as the reference light, so that after further propagation an interference pattern appears near the exit surface on an array detector (e.g. a 2D sensor or a camera). In particular, this pattern contains complete wave information about the object light, so that the object can be calculated in a holographic manner from the interference pattern. In particular, depth information, i.e. 3D information about the object, can be generated in this way, in particular when a large number of wavelengths, e.g. in the form of spectral lines, are used for the reference light and the object light.

[0017] Therefore, the present invention can be combined particularly well with minimally invasive medical imaging instruments designed to generate 3D information from the instrument's field of view.Stereo optics are too large for minimally invasive applications, which makes digital holography of great utility in this area of ​​technology.

[0018] In the state according to the invention, it is provided in particular that the reference light enters the diffraction element through the first entrance surface, in particular in a collimated manner. There, it is diffracted by the transmission diffraction grating arrangement in the direction of the prism surface. The mirror reflects the diffracted reference light back in the direction of the transmission diffraction grating arrangement, but at an angle that can be calculated according to Snell's law; due to this angle, at least part of the reflected reference light is not diffracted by the transmission diffraction grating arrangement, but is transmitted and propagates in the direction of the exit surface. According to the invention, the object light enters the diffraction element through the second entrance surface and is diffracted by the transmission diffraction grating arrangement directly in the direction of the exit surface, where it is superimposed and in particular interferes with the reference light on the array detector or camera chip.

[0019] The present invention provides an optical system for digital holography which makes it possible to separate multiple wavelengths included in the reference light from a relatively large wavelength range on the exit surface side, in particular wherein the wavelengths are present in the form of spectrally spaced spectral lines, and which at the same time impresses due to an extremely compact and robust design.

[0020] In particular, the optical properties of a volume phase holographic grating are combined in a very advantageous manner with a first mirror which is advantageously tilted relative to the transmission diffraction grating arrangement, which makes it possible for the first time to resolve a bandwidth of wavelengths.

[0021] By means of the first mirror arranged according to the invention, subsequent image information obtained from the object light superimposed on the reference light at the exit surface can be shifted outside the typical interference DC range.

[0022] Furthermore, the first mirror ensures that the portion of the reference light reflected at the first mirror is only slightly attenuated or not at all by the transmission diffraction grating arrangement when passing through the first transmission diffraction grating arrangement. 2 If θ is equal to 0°, a large part of the reference light will be diffracted back to the first incidence surface by the transmission diffraction grating arrangement and will therefore not reach the exit surface.

[0023] The first reflector comprises a first reflector plane extending along a reflective layer of the first reflector, in particular wherein the first reflector consists of the reflective layer.

[0024] In the following, the angle of the first reflector relative to a surface or a plane always means the angle of the first reflector plane of the first reflector and the surface or the respective plane.

[0025] In the context of the present invention, the term "prism" particularly refers to a geometrical body, in particular a physical body, which has two opposing base surfaces which are connected to each other via side surface areas arranged at the edges of the base surfaces.

[0026] According to the invention, the substrate surface of the prismatic arrangement is at least quadrilateral, i.e. the substrate surface has a polygon, wherein the polygon has at least four corners. However, it is entirely possible and conceivable that the substrate surface comprises additional corners and therefore additional side surface areas which are designed for other purposes, e.g., are comprised by the prismatic arrangement.

[0027] Thus, a quadrangular prism has four side surface areas that delimit two quadrilateral base surfaces. Unless otherwise defined, these base surfaces have the same shape and size.

[0028] In the context of the present invention, the term "prismatic arrangement" particularly refers to a fixed arrangement of at least one prism or a plurality of prisms.

[0029] According to one embodiment of the invention, at least the quadrangular prism arrangement is integrally or monolithically formed.

[0030] The terms “integrally designed” or “integrally formed” are to be understood in the context of the present invention as being synonymous with “integrally”.

[0031] According to one embodiment of the invention, at least a four-prism arrangement is formed by a first and a second prism, wherein the two prisms are connected to each other along a diffraction plane via a transmission diffraction grating arrangement. The first of the two prisms particularly comprises a first incident surface, an exit surface. The second of the two prisms particularly comprises a second incident surface, a prism surface. In particular, the four-prism arrangement is formed by two separate prisms firmly connected to each other.

[0032] Generally, in any embodiment of the present invention, at least a four-prism arrangement may be implemented integrally, unless explicitly disclosed otherwise.Alternatively, at least a four-prism arrangement may be formed by various prisms connected to each other in a similar manner.

[0033] If no information is given about the composition and / or properties of the prism arrangement, this includes monolithic designs as well as embodiments in which the prism arrangement is formed, for example, from a plurality of individual prisms connected to one another.

[0034] In particular, at least all side surface areas of the quadrangular prism arrangement are planar.

[0035] According to one embodiment of the invention, the prismatic arrangement comprises a solid transparent body, which in particular comprises transparent glass or a polymer.

[0036] According to an embodiment of the invention, the prism arrangement, in particular the prism arrangement except for the transmission diffraction grating arrangement, consists of transparent glass and / or polymer.

[0037] According to an embodiment of the invention, the first reflector has a reflectivity between 10% and 100%, in particular greater than 70%.The reflectivity level may be as high as almost 100%, such as 95% or even 99%.

[0038] Since there is usually enough reference light available (compared to the object light), the reflectivity of the first mirror does not have to be particularly high.

[0039] In particular, the first reflector has a smoothness equal to or better than λ / 2.

[0040] According to a further embodiment of the invention the transmission diffraction grating arrangement is a substantially planar transmission diffraction grating arrangement.

[0041] Volume phase holographic (transmission) gratings (abbreviated VPH) are known in the prior art. Volume phase holographic gratings are in particular transmission gratings. Volume phase holographic gratings are, for example, composed of a dichromate / dichroic gelatin (DCG) film between two glass substrates, in particular wherein the glass substrate is formed by a first and a second prism, in particular wherein the gelatin is arranged between the side surface areas of the first and second prisms, which extend along the diffraction plane. Volume phase holographic gratings provide first order diffraction peak efficiency and uniform performance over a specified bandwidth.

[0042] As an alternative to gelatin, photopolymers can also be used, which form a volume phase holographic grating by appropriate exposure. In particular, after exposure, the photopolymer can be introduced between two glass substrates. Photopolymers have the advantage over gelatin of being non-viscous and therefore easier to handle. For both gelatin and photopolymers, the layer thickness of the volume phase holographic grating can be of the order of a few micrometers to about 100 μm.

[0043] Furthermore, it is also known that volume phase holographic gratings are introduced into glass and in particular do not include any gelatin.

[0044] Volume phase holographic gratings in PTR glass have the advantage over other volume phase holographic gratings made of gelatin or photopolymers that they are more thermally stable, since these are typical properties of glass. However, since the refractive index modulation in PTR glass is about an order of magnitude weaker than in gelatin and photopolymers, the active glass layer must be correspondingly thicker. However, this leads to limitations in the angular dispersion or spectral properties. This means that, depending on the requirements of the diffractive element, appropriate volume phase holographic grating materials and manufacturing methods can be selected.

[0045] In particular, the first holographic arrangement is configured and formed to be operated in a so-called "Littrow arrangement". The diffractive element and the first holographic arrangement are arranged in the system in such a way that the diffractive plane encloses an angle of 45° with the optical axis of the diffractive element and, therefore, the first mirror plane encloses an angle β with the optical axis and / or the prism surface encloses an angle ρ with the optical axis. 2 . Therefore, the reference light (initially propagating along the optical axis) entering the first diffraction element through the first incident surface is ideally diffracted by the transmission diffraction grating arrangement at a diffraction angle of 2·45°=90°, in particular, wherein the reference light incident on the transmission diffraction grating arrangement encloses an angle of 45° with the diffraction plane and the diffraction plane also encloses an angle of 45°. The diffracted reference light is then reflected by the first reflector, wherein the angle of the reflector plane α and / or the angle of the prism plane ω 2 The reference light contributing to the reflection is incident on the transmission diffraction grating arrangement at an angle other than 45° and therefore propagates through the transmission diffraction grating arrangement to a large extent without being diffracted.

[0046] This functionality is achieved, as claimed in the present invention, because the first reflector and / or prism surface is arranged at an angle other than 45° relative to the diffraction plane.

[0047] Thus, the system according to the invention can be used particularly advantageously in digital holography applications.

[0048] It should be noted that the Littrow arrangement, i.e. diffraction at 90°, is only possible for the central wavelength of the grating. Wavelengths that deviate from this wavelength diffract by different angular amounts according to the angular dispersion.

[0049] If the transmission diffraction grating is not arranged at an angle of 45° to the optical axis, or if the grating frequency does not completely satisfy the Littrow condition, the 90° diffraction of the central wavelength will also vary slightly.

[0050] According to a further embodiment of the invention, the at least one first volume phase hologram grating of the transmission diffraction grating arrangement is configured to be oriented around a central wavelength λ when operating in a Littrow arrangement. 0 The first bandwidth λ of the diffraction wavelength within the diffraction angle range of about 90°±Δθ 0 ±Δλ.

[0051] The optical axis of the first diffraction element can be directed to the diffraction plane from the first or second incident surface and intersect the diffraction plane at an angle of 45°. Unless otherwise explicitly required, it is assumed that in the state of the system according to the present invention, both the reference light and the object light are incident on the diffraction plane along the optical axis.

[0052] According to the invention, each surface, i.e. the first and second incident surfaces, the exit surface and the prismatic surface, can be assigned a plane extending along the respective surface. When referring to the angle between two surfaces, this also means the angle between the planes. Unless explicitly stated otherwise, the angle specification refers to the internal angle of the prism arrangement.

[0053] In particular, the first entrance surface is bounded on the one hand by an edge with the exit surface and on the other hand by an imaginary intersection line of the diffraction plane with the first entrance plane.

[0054] In particular, the exit surface is defined on the one hand by an edge with the first entrance surface and on the other hand by an imaginary intersection line of the diffraction plane with the exit plane and / or by an edge with the second entrance surface.

[0055] Furthermore, in the context of the present invention, directional specifications, orientations and positions are to be understood in particular for the optically deployed state of the system. It is obvious to a person skilled in the art that, for example, the direction of the optical axis can be changed by deflection mirrors in the system, wherein the direction is not changed in an optically functional sense, but only in a geometric sense. This understanding should also be used to interpret the claims.

[0056] According to one embodiment of the present invention, the diffraction plane of the first diffraction element and the first incident surface of the first diffraction element form an angle ω 1 , in particular, where the angle is 30°≤ω 1 ≤60°, in particular, where ω 1 =45°.

[0057] According to one embodiment of the present invention, the diffraction plane of the first diffraction element and the prism surface of the first diffraction element form an angle ω 2 , in particular, where the angle is 30°≤ω 2 ≤60°, in particular, where ω 2 =45° or ω 2 =45°±β, in particular, where ω2 is chosen such that the prism surface extends parallel to the mirror plane of the first mirror.

[0058] According to one embodiment of the present invention, the diffraction plane of the first diffraction element and the second incident surface of the first diffraction element form an angle ω 3 , in particular, where the angle is 30°≤ω 3 ≤60°, in particular, where ω 3 =45°.

[0059] According to one embodiment of the present invention, the diffraction plane of the first diffraction element and the exit surface of the first diffraction element form an angle ω 4 , in particular, where the angle is 30°≤ω 4 ≤60°, in particular, where ω 4 =45° or ω 4 =45°±β, in particular, where ω 4 is selected such that the exit face extends parallel to the mirror plane of the first reflector.

[0060] According to an embodiment of the invention, the first and second incident surfaces of the first diffractive element are aligned parallel to each other.

[0061] According to another embodiment of the present invention, the angle ω 1 and ω 3 =45°. In this configuration, since the incident surface is perpendicular to the optical axis of the diffraction element, it is possible to radiate the reference light and the object light perpendicularly to the first incident surface and the second incident surface.

[0062] According to an embodiment of the invention, the prism surface and the exit surface of the first diffractive element are aligned parallel to each other.

[0063] According to another embodiment of the invention, the system comprises a first optical array detector, such as a camera, wherein the first array detector is configured to detect light emerging from an exit surface of the first diffractive element.

[0064] In particular, the first array detector is arranged on the exit surface side of the first diffraction element of the first holographic arrangement.

[0065] Furthermore, it can be provided that the first array detector is arranged on the exit surface of the first diffraction element of the first holographic arrangement, in particular, the first array detector is connected to the exit surface of the first diffraction element so that there is at least no air gap between the exit surface and the array detector.

[0066] Alternatively, the first array detector may be spaced apart from the exit surface and may include an air gap between the exit surface and the array detector.

[0067] Furthermore, the first array detector may be configured to convert the detected light into an electrical signal which may be evaluated by an evaluation device of the system at least with respect to a two-dimensional intensity distribution of the detected light on the first array detector.

[0068] An array detector may provide a detection plane extending along an array of the array detector, for example along a pixel matrix of a camera.

[0069] According to another embodiment of the present invention, it is provided that the detection plane of the first array detector encloses an angle of ε=45°±η with the diffraction plane, wherein η>0°, in particular, wherein η=β, in particular, wherein the detection plane extends parallel to the first reflector. In addition, the exit plane can extend parallel to the detection plane or coplanar with the detection plane.

[0070] In particular, 0°<η<20°.

[0071] According to one embodiment of the present invention, it can be provided that the detection plane encloses an angle with the diffraction plane, so that the light reflected from the detection plane is incident on the diffraction plane under the Littrow geometry, so that the reflected light is completely or at least largely diffracted by the transmission diffraction grating arrangement in the direction of the second incident surface and can be emitted there. This avoids "ghost" signals on the array detector caused by multiply reflected light.

[0072] The above embodiment of the present invention has the beneficial effect that it can prevent the light reflected from the array detector from reaching the first reflector again and prevent the light from being reflected from there back to the array detector, where an unwanted signal is generated. By selecting the angle η, the light reflected from the array detector can be completely or largely diffracted by the first transmission diffraction grating arrangement in the direction of the second incident surface.

[0073] According to another embodiment of the invention, the substrate surface of the first prism arrangement forms a parallelogram, in particular, wherein the diffraction plane of the first diffractive element extends along a diagonal extending in the substrate surface between the first entrance surface and the exit surface of the first diffractive element, in particular, wherein

[0074] i) The first incident surface and the diffraction plane of the first diffraction element form an angle ω 1 =45°±ρ1, the prism surface and the diffraction plane of the first diffraction element form an angle ω 2 =45°, where ρ1>0°, in particular, where ρ 1 >0.2°, or

[0075] ii) The first incident surface and the diffraction plane of the first diffraction element form an angle ω 1=45°, the prism surface and the diffraction plane of the first diffraction element form an angle ω 2 =45°±ρ 2 , where ρ 2 >0°, in particular, where ρ 2 >0.2°, or

[0076] iii) The first incident surface and the diffraction plane of the first diffraction element form an angle ω 1 =45°±ρ1, the prism surface and the diffraction plane of the first diffraction element form an angle ω 2 =45°±ρ 2 , where ρ 1 >0° and ρ 2 >0°, in particular, where ρ 1 >0.2° and ρ 2 >0.2°, or

[0077] iv) The first incident surface and the diffraction plane of the first diffraction element form an angle ω 1 =45°, the prism surface and the diffraction plane of the first diffraction element form an angle ω 2 =45°, the substrate surface is a special parallelogram, i.e. a rectangle, preferably a square, in particular, wherein the diffraction plane of the first diffraction element extends along a diagonal extending between the first incident surface and the exit surface of the first diffraction element in the substrate surface.

[0078] Each of embodiments i) to iii) advantageously reduces potential interfering reflections arising when the reference light and / or the object light enters or leaves the prism arrangement.

[0079] In particular, for example, if the angle ρ is chosen 2 =β, then embodiments ii) and iii) allow the first reflector to be arranged directly on the prism surface.

[0080] Furthermore, in embodiments ii) and iii), the first array detector may also be arranged directly on the exit surface, as already mentioned above.

[0081] The advantages of the low reflection geometry and the advantages of the array detector mentioned previously with respect to back reflections of the array detector in the Littrow configuration are particularly evident because the angle between the detection plane and the diffraction plane encloses ε = 45° ± η, where η = β = ρ 2 , so that the detection plane extends parallel to the first reflector. In addition, the exit plane is substantially coplanar with the detection plane.

[0082] In particular, if at least the second incident surface is anti-reflective, the proportion of the reference light reflected back again at the second incident surface (which is reflected by the first array detector and diffracted via the transmission diffraction grating arrangement) can be neglected. Depending on the beam configuration, there can also be a tilt angle at the exit surface (e.g. embodiment iii) so that additional back reflection suppression is achieved.

[0083] Embodiments i) and iii) advantageously allow the use of the Brewster angle and (if necessary) a polarization rotation element (e.g., a λ / 2 wave plate) to simultaneously perform polarization selection and / or achieve a reduction in reflections. The reference light and the object light are then coupled into the first diffraction element at an angle (i.e., not equal to 90°) such that the reference light and the object light around the center wavelength are incident on the transmission diffraction grating arrangement at an angle of 45° (i.e., in a Littrow configuration).

[0084] According to embodiment iv), the base surface of the first prism arrangement is rectangular, in particular square.

[0085] Embodiment iv) provides a first diffraction element that is easy to manufacture. In this configuration, both the reference light and the object light can be irradiated perpendicularly to the respective incident surfaces, thereby being incident on the transmission diffraction grating arrangement in the Littrow configuration. In addition, the angle α of the first reflector and, if necessary, the angle of the array detector are easily adjustable.

[0086] According to a further embodiment of the invention the first mirror is arranged on a prismatic surface of the first holographic arrangement.

[0087] This embodiment of the invention comprises the possibility that the first reflector is formed as a reflective layer on the prism surface.The reflective layer can be produced on the prism surface by known methods.

[0088] This embodiment is a particularly robust and compact embodiment of the invention, since the first mirror is directly connected to the diffractive element, so no assembly or adjustment of the mirror is required. Implicitly, the prism surface then encloses an angle α with the diffraction plane.

[0089] According to another embodiment of the invention, the angle β is adjustable, or is adjusted via the first mirror.

[0090] According to another embodiment of the invention, the first reflector is tiltable about at least one axis, so that the angle β is adjustable or adjustable via the first reflector.

[0091] In this embodiment, the first reflector is designed in particular as a separate element, which is optionally designed such that the angle β is adjustable.

[0092] According to a further embodiment of the invention, the optical transmission diffraction grating arrangement comprises a second volume phase holographic grating, which in particular also extends along or on the diffraction plane, wherein the first volume phase holographic grating and the second volume phase holographic grating have maximum diffraction intensities at different central wavelengths, in particular for the first order of diffraction, at different central wavelengths, in particular wherein the central wavelength has a distance of at least the bandwidth of the first and second volume phase holographic gratings. In particular, this ensures an undisturbed spectral separation of the two central wavelengths at the exit surface.

[0093] Compared to a single volume phase holographic grating, this embodiment allows to provide the system with an extended spectral range, i.e. a plurality of different wavelengths, in particular spectral lines, can be spectrally separated at the exit surface via the first diffraction element, without the first diffraction element requiring more installation space. For example, the center wavelength of the first volume phase holographic grating and five spectral lines from the bandwidth of the volume phase holographic grating can be diffracted via the first volume phase holographic grating, and in addition to the center wavelength of the second volume phase holographic grating, another five spectral lines within the bandwidth of the second volume phase holographic grating can be diffracted via the second volume phase holographic grating.

[0094] According to one embodiment of the present invention, the first volume phase holographic grating has a central wavelength of, for example, 600 nm and a bandwidth of 10 nm.

[0095] According to one embodiment of the present invention, the second volume phase holographic grating has a central wavelength of, for example, 620 nm and a bandwidth of 10 nm.

[0096] According to both embodiments, the wavelength ranges of the first volume phase holographic grating and the second volume phase holographic grating do not overlap because the central wavelengths are separated from each other by 20 nm, which corresponds to the sum of the bandwidths of the first volume phase holographic grating and the second volume phase holographic grating. The greater the distance between the central wavelengths within the bandwidth, the less interaction is expected.

[0097] According to another embodiment of the invention, the transmission diffraction grating arrangement comprises more than two volume phase holographic gratings, in particular wherein the volume phase holographic gratings have different central wavelengths. The central wavelengths may be spectrally spaced apart according to the bandwidth, or may be spaced apart more according to the above principle.

[0098] According to one embodiment of the invention, the optical system has a second holographic arrangement, the second holographic arrangement comprising a second diffractive element formed by a second prism arrangement having an at least quadrilateral base surface, in particular, wherein the first and second holographic arrangements are arranged adjacent to each other along the optical axis of the first diffractive element, wherein the side surface of the second prism arrangement has the following side surface area:

[0099] f) a first entrance surface for the reference light, which is in particular planar and extends along a first entrance plane, wherein the first entrance surface may be part of the first end face, and

[0100] g) a second entrance surface for the object light, which is in particular planar and extends along a second entrance plane, wherein the first and second entrance surfaces form opposite side surface areas of the second prism arrangement, wherein the second entrance surface may be part of the second end face,

[0101] h) an exit surface, which extends along the exit plane and through which the diffracted reference light and the diffracted object light can exit from the second diffraction element,

[0102] i) a prismatic surface, opposite to the exit surface,

[0103] wherein the optical transmission diffraction grating arrangement is arranged in the second diffraction element, extending between a first entrance surface and, in particular, an exit surface of the second diffraction element along a diffraction plane intersecting the first entrance plane and the exit plane, in particular such that the transmission diffraction grating arrangement forms a triangular prism with the first entrance surface and the exit surface of the second diffraction element, in particular wherein the diffraction plane forms an imaginary side surface area of ​​the triangular prism,

[0104] wherein the transmission diffraction grating arrangement of the second diffraction element comprises at least one first volume phase holographic grating, and the second holographic arrangement has a second mirror, in particular a planar one, which has a second mirror plane on the prism surface side, wherein the second mirror plane encloses an angle α' with the diffraction plane, and the prism surface encloses an angle ω' with the diffraction plane 2 , where the angles α', ω' 2 At least one or two of them are not equal to 45°, in particular, the angle α'=45°±β', β'>0°, in particular, the angle ω' 2 =45°±ρ'2, ρ'2>0°, in particular in order to achieve the maximum possible efficiency of the object light and the reference light in the second holographic arrangement.

[0105] Preferably, β' and / or ρ' 2 Greater than 0.2°.

[0106] Preferably, β' and / or ρ' 2 Less than 20°.

[0107] According to this embodiment of the invention, the angles β' and ρ' 2It is particularly selected so that the reference light incident on the transmission diffraction grating arrangement at an angle of 45° is diffracted by the transmission diffraction grating arrangement in the direction of the prism surface of the second diffraction element and reflected by the second reflector, so that due to the incident angle of the reflected reference light on the transmission diffraction grating arrangement of the second diffraction element, the reflected reference light is diffracted again in the direction of the first incident surface of the second diffraction element to a smaller extent, in particular in a proportion that is at least 30% smaller than when the reference light initially incident on the transmission diffraction grating arrangement from the first incident surface side of the second diffraction element, and the remaining part of the reflected reference light propagates through the transmission diffraction grating arrangement in the direction of the exit surface of the second diffraction element.

[0108] In a state according to the invention, it is particularly provided that the reference light enters the diffraction element through the first entrance surface of the second diffraction element, in particular in a collimated manner. There, it is diffracted by the transmission diffraction grating arrangement in the direction of the prism surface of the second diffraction element. The second reflector reflects the diffracted reference light back in the direction of the transmission diffraction grating arrangement, but at an angle that can be calculated according to Snell's law; in this way, at least part of the reflected reference light is not diffracted by the transmission diffraction grating arrangement, but is transmitted and propagates in the direction of the exit surface of the second diffraction element. According to the invention, the object light enters the second diffraction element through the second entrance surface and is diffracted by the transmission diffraction grating arrangement directly in the direction of the exit surface, where the object light is superimposed and in particular interferes with the reference light on the second array detector.

[0109] In the case of the system according to the invention, it is provided in particular that the reference light is firstly radiated into the first holographic arrangement and the object light is firstly radiated into the second holographic arrangement.

[0110] According to this embodiment, a second holographic arrangement is disclosed, which has substantially the same features as the first holographic arrangement, in particular, wherein the central wavelengths of the transmission diffraction grating arrangements of the first and second holographic arrangements are different.

[0111] According to a further embodiment of the invention the first volume phase holographic grating of the second holographic arrangement has a different central wavelength than the first volume phase holographic grating and / or the second volume phase holographic grating of the first holographic arrangement.

[0112] In particular, the first and the second holographic arrangement are arranged relative to each other in such a way that the exit surfaces are aligned in parallel, in particular co-planar - i.e. lying in the same plane - with each other, so that, for example, a single array detector can be used to record the interference pattern on the exit surfaces of the two diffraction elements.

[0113] According to an alternative embodiment of the invention, the first and second holographic arrangements are arranged relative to each other so that the exit surfaces of the first and second diffractive elements are aligned parallel to each other, wherein the exit surface of the first diffractive element is arranged on the prism surface side of the second diffractive element, and the exit surface of the second diffractive element is arranged on the prism surface side of the first diffractive element. In particular, the first holographic arrangement is rotated 180° relative to the second holographic arrangement, in particular around the optical axis. In particular, the diffraction planes of the first and second diffractive elements are usually surrounded by an angle of 90°.

[0114] This provides an advantage that two separate array detectors can be used and there are fewer installation space issues for the array detectors.

[0115] According to another embodiment of the invention, the first and second holographic arrangements are arranged relative to each other such that a first incident surface of a second diffraction element of the second holographic arrangement is arranged opposite to, and in particular parallel to, a second incident surface of the first diffraction element of the first holographic arrangement, in particular, wherein the diffraction planes of the first and second diffraction elements are aligned optically parallel to each other.

[0116] It should be pointed out here again that the expressions “relative” and “parallel” are to be understood in an optically functional sense and not necessarily in a strictly geometrical sense.

[0117] According to an embodiment of the present invention, the second diffractive element comprises an optical axis, which extends between the first exit surface and the second exit surface and intersects the diffraction plane of the second diffractive element at an angle of 45°.

[0118] In particular, the first and second holographic arrangements are arranged and aligned along a common optical axis corresponding to the optical axis of the first diffractive element.

[0119] It should be noted that all features, advantages and embodiments associated with and disclosed in conjunction with the first holographic arrangement, the first diffraction element, the first reflector or other components are similarly applicable to possible embodiments of the second holographic arrangement and can be used to specify the second holographic arrangement in accordance with further details of the preceding paragraphs.

[0120] The second reflector comprises a second reflector plane extending along the reflective layer of the second reflector, in particular wherein the second reflector consists of the reflective layer.

[0121] In the following, the angle of the second reflector relative to a surface or a plane always means the angle of the second reflector plane of the second reflector and the surface or the respective plane.

[0122] According to the invention, each surface, i.e. the first and second incident surfaces, the exit surface and the prism surface of the second diffractive element, can be assigned a plane extending along the corresponding surface. When referring to the angle between two surfaces, this also means the angle between the planes. Unless otherwise explicitly stated, the angle specification refers to the internal angle of the second prism arrangement.

[0123] According to one embodiment of the present invention, the diffraction plane of the second diffraction element and the first incident surface of the second diffraction element form an angle ω' 1 , in particular, where the angle is 30°≤ω' 1 ≤60°, in particular, where ω' 1 =45°.

[0124] According to one embodiment of the present invention, the diffraction plane of the second diffraction element and the prism surface of the second diffraction element form an angle ω' 2 , in particular, where the angle is 30°≤ω' 2 ≤60°, in particular, where ω' 2 =45° or ω' 2 =45°±β, in particular, where ω' 2 is chosen such that the prism surface extends parallel to the mirror plane of the second mirror.

[0125] According to one embodiment of the present invention, the diffraction plane of the second diffraction element and the second incident surface of the second diffraction element form an angle ω' 3 , in particular, where the angle is 30°≤ω' 3 ≤60°, in particular, where ω' 3 =45°.

[0126] According to one embodiment of the present invention, the diffraction plane of the second diffraction element and the exit surface of the second diffraction element form an angle ω' 4 , in particular, where the angle is 30°≤ω' 4 ≤60°, in particular, where ω' 4 =45° or ω' 4 =45°±β, in particular, where ω' 4 is chosen such that the exit surface extends parallel to the mirror plane of the second mirror.

[0127] According to an embodiment of the invention, the first and second incident surfaces of the second diffractive element are aligned parallel to each other.

[0128] According to an embodiment of the invention, the prism surface and the exit surface of the second diffractive element are aligned parallel to each other.

[0129] According to another embodiment of the present invention, the angle ω' 1 and ω'3 In this configuration, since the incident surface is perpendicular to the optical axis of the second diffraction element, it is possible to irradiate the reference light and the object light perpendicularly to the first incident surface and the second incident surface.

[0130] According to one embodiment of the present invention, the first incident surface of the first diffractive element and the second incident surface of the second diffractive element are aligned parallel to each other.

[0131] According to one embodiment of the present invention, the angles β' and β have different sizes.

[0132] The different angles β′ and β can advantageously be adapted to the central wavelength and the bandwidth of the volume phase holographic grating in the first and second diffractive elements.

[0133] According to an alternative embodiment of the invention, the angles β' and β are identical.

[0134] According to another embodiment of the present invention, the angle ω' 1 and ω 1 are the same.

[0135] According to another embodiment of the present invention, the angle ω' 2 and ω 2 are the same.

[0136] According to another embodiment of the present invention, the angle ω' 3 and ω 3 are the same.

[0137] According to another embodiment of the present invention, the angle ω' 4 and ω 4 are the same.

[0138] According to a further embodiment of the invention, the first and the second diffractive element have the same geometry, in particular the same dimensions, ie are identical except for the optical properties of the transmission diffraction grating arrangement.

[0139] The first and / or second incident surface of the first and / or second diffractive element may be provided with an anti-reflection coating. Similarly, the exit surface and / or prism surface of the first and / or second diffractive element may be provided with an anti-reflection coating.

[0140] In a state according to the invention, it is particularly provided that the reference light enters the first diffraction element through the first entrance surface of the first diffraction element, in particular in a collimated manner. There, it is partially diffracted by the transmission diffraction grating arrangement in the direction of the prism surface of the first diffraction element. Another part of the reference light, which is not diffracted at the transmission diffraction grating arrangement of the first diffraction element due to its wavelength, propagates in the direction of the second diffraction element and is diffracted there by the transmission diffraction grating arrangement of the second diffraction element in the direction of the prism surface of the second diffraction element.

[0141] This applies in particular to the object light, which first enters through the second entrance surface of the second diffractive element and then partially propagates further in the direction of the first diffractive element. At the exit surfaces of the first and second diffractive elements or the array detector, the reference light is then correspondingly superimposed with the object light in a spectrally resolved manner.

[0142] According to another embodiment of the invention, the system comprises a second optical array detector, such as a camera, wherein the second array detector is configured to detect light emerging from an exit surface of the second diffractive element.

[0143] In particular, the second array detector is arranged on the exit surface side of the second diffraction element of the second holographic arrangement.

[0144] Furthermore, it can be provided that the second array detector is arranged on the exit surface of the second diffraction element of the second holographic arrangement, in particular, the second array detector is connected to the exit surface of the second diffraction element so that there is at least no air gap between the exit surface and the array detector.

[0145] Furthermore, the second array detector may be configured to convert the detected light into an electrical signal which may be evaluated by an evaluation device of the system (eg a computer) at least with respect to a two-dimensional intensity distribution of the detected light on the second array detector.

[0146] The second array detector may provide a detection plane extending along the array of the second array detector, for example along the pixel matrix of the camera.

[0147] According to another embodiment of the present invention, the detection plane of the second array detector is provided to enclose an angle of ε'=45°±η' with the diffraction plane, wherein η'>0°, in particular, wherein η'=β, in particular, wherein the detection plane extends parallel to the second reflector. In addition, the exit plane can extend parallel to the detection plane or coplanar with the detection plane.

[0148] In particular, 0°<η'<20°.

[0149] According to one embodiment of the present invention, it can be provided that the detection plane encloses an angle with the diffraction plane of the second diffraction element, so that the light reflected from the detection plane is incident on the diffraction plane under the Littrow geometry, so that the reflected light is completely or at least largely diffracted by the transmission diffraction grating of the second diffraction element arranged in the direction of the second incident surface of the second diffraction element and can be emitted there. This avoids "ghost" signals on the second array detector caused by multiply reflected light.

[0150] The above embodiment of the present invention has the beneficial effect that it can prevent the light reflected from the second array detector from reaching the second reflector again and prevent the light from being reflected from there back onto the second array detector, where an unwanted signal is generated. By selecting the angle η', the light reflected from the second array detector can be completely or largely diffracted by the first transmission diffraction grating arranged in the direction of the second incident surface of the second diffraction element.

[0151] According to another embodiment of the invention, the substrate surface of the second prism arrangement forms a parallelogram, in particular, wherein the diffraction plane of the second diffractive element extends along a diagonal extending in the substrate surface between the first entrance surface and the exit surface of the second diffractive element, in particular, wherein

[0152] i) The second incident surface and the diffraction plane of the second diffraction element form an angle ω' 1 =45°±ρ' 1 , the prism surface and the diffraction plane of the second diffraction element form an angle ω' 2 =45°, where ρ' 1 >0°, especially where ρ' 1 >0.2°, or

[0153] ii) The first incident surface and the diffraction plane of the second diffraction element form an angle ω' 1 =45°, the prism surface and the diffraction plane of the second diffraction element form an angle ω' 2 =45°±ρ' 2 , where ρ' 2 >0°, especially where ρ' 1 >0.2°, or

[0154] iii) The first incident surface and the diffraction plane of the second diffraction element form an angle ω' 1 =45°±ρ' 1 , the prism surface and the diffraction plane of the second diffraction element form an angle ω' 2 =45°±ρ' 2 , where ρ' 1 >0° and ρ' 2 >0°, specifically where ρ'1 >0.2° and ρ' 2 >0.2°, or

[0155] iv) The first incident surface and the diffraction plane of the second diffraction element form an angle ω' 1 =45°, the prism surface and the diffraction plane of the second diffraction element form an angle ω' 2 =45°, the substrate surface is a special parallelogram, i.e. a rectangle, preferably a square, in particular, wherein the diffraction plane of the second diffraction element extends along a diagonal extending between the first incident surface and the exit surface of the first diffraction element in the substrate surface.

[0156] Each of embodiments i) to iii) advantageously reduces potential interfering reflections generated when the reference light and / or the object light enters or leaves the second prism arrangement.

[0157] In particular, for example, if the angle ρ' is chosen 2 =β', then embodiments ii) and iii) allow the second reflector to be arranged directly on the prism surface of the second diffractive element.

[0158] Furthermore, in embodiments ii) and iii), the second array detector may also be arranged directly on the exit surface, as already mentioned above.

[0159] The advantages of the low reflection geometry and the advantages of the array detector mentioned previously with respect to back reflections of the array detector in the Littrow configuration are particularly evident because the angle between the detection plane and the diffraction plane is ε' = 45° ± η', where η' = β' = ρ' 2 , so that the detection plane extends parallel to the second reflector. In addition, the exit plane is substantially coplanar with the detection plane.

[0160] In particular, if at least the second incident surface is anti-reflective, the proportion of the reference light reflected back again at the second incident surface (which is reflected by the second array detector and diffracted via the transmission diffraction grating arrangement) can be neglected. Depending on the beam configuration, there can also be a tilt angle at the exit surface (e.g. embodiment iii) so that additional back reflection suppression is achieved.

[0161] Embodiments i) and iii) advantageously allow the use of the Brewster angle and (if necessary) a polarization rotation element (e.g., a λ / 2 wave plate) to simultaneously perform polarization selection and / or achieve a reduction in reflections. The reference light and the object light are then coupled into the first diffraction element at an angle (i.e., not equal to 90°) such that the reference light and the object light around the center wavelength are incident on the transmission diffraction grating arrangement at an angle of 45° (i.e., in a Littrow configuration).

[0162] According to embodiment iv), the base surface of the second prism arrangement is rectangular, in particular square.

[0163] Embodiment iv) provides a second diffraction element that is easy to manufacture. In this configuration, both the reference light and the object light can be illuminated perpendicular to the respective incident surfaces and thus incident on the transmission diffraction grating arrangement in the Littrow configuration. In addition, the angle α' of the second reflector and, if necessary, the angle ε' of the second array detector are easily adjustable.

[0164] According to a further embodiment of the invention, the second mirror is arranged on a prism surface of the second holographic arrangement.

[0165] This embodiment of the invention comprises the possibility that the second reflector is formed as a reflective layer on the prism surface.The reflective layer can be produced on the prism surface by known methods.

[0166] Furthermore, this embodiment is a particularly robust and compact embodiment of the invention, since the second reflector is directly connected to the second diffractive element, so that no assembly or adjustment of the reflector is required. Implicitly, the prism surface then encloses an angle ω' with the diffraction plane of the second diffractive element 2 =α'.

[0167] According to another embodiment of the present invention, the angle β' is adjustable, or is adjusted via a second reflector.

[0168] According to another embodiment of the invention, the second reflector is tiltable about at least one axis, so that the angle β' is adjustable or adjustable via the second reflector.

[0169] In this embodiment, the second reflector is designed in particular as a separate element which is optionally designed such that the angle β′ is adjustable.

[0170] According to another embodiment of the invention, the optical transmission diffraction grating arrangement of the second diffraction element comprises a second volume phase holographic grating, which in particular also extends along or on the diffraction plane, wherein the first volume phase holographic grating and the second volume phase holographic grating of the second diffraction element have maximum diffraction intensities at different central wavelengths, in particular for the first order of diffraction, at different central wavelengths, in particular wherein the central wavelength has a distance of at least the bandwidth of the first and second volume phase holographic gratings of the second diffraction element. In particular, this ensures a spectral separation of the central wavelengths at the exit surface of the second diffraction element.

[0171] Compared to a single volume phase holographic grating, this embodiment allows providing the system with an extended spectral range, ie a plurality of different wavelengths, in particular spectral lines, can be spectrally separated at the exit surface via the second diffraction element, without the second diffraction element requiring more installation space.

[0172] According to one embodiment of the present invention, the first volume phase holographic grating has a central wavelength of, for example, 940 nm and a bandwidth of 10 nm.

[0173] According to one embodiment of the present invention, the second volume phase holographic grating has a central wavelength of, for example, 960 nm and a bandwidth of 10 nm.

[0174] According to both embodiments, the wavelength ranges of the first volume phase holographic grating and the second volume phase holographic grating of the second diffractive element do not overlap, because the central wavelengths are separated from each other by 20 nm, which corresponds to the sum of the bandwidths of the first volume phase holographic grating and the second volume phase holographic grating. The larger the distance between the central wavelengths within the bandwidth, the less interaction is expected.

[0175] According to another embodiment of the present invention, the transmission diffraction grating arrangement of the second diffraction element comprises more than two volume phase holographic gratings, in particular wherein the volume phase holographic gratings have different central wavelengths. The central wavelengths may be spectrally spaced apart according to the bandwidth, or may be spaced apart more according to the above principle.

[0176] In combination with the first holographic arrangement, the second spectral range can be used for digital holography.

[0177] In particular, the transmission diffraction grating arrangements of the first and second diffraction elements are configured for different central wavelengths, ie the central wavelengths of the transmission diffraction grating arrangements are here also spectrally spaced apart according to a bandwidth or more, according to the above-mentioned principle.

[0178] According to another embodiment of the present invention, it is provided that the second incident surface of the first diffraction element is connected to the first incident surface of the second diffraction element, in particular adhesively bonded or welded, in particular wherein the first diffraction element is formed integrally with the first incident surface of the second diffraction element along its second incident surface.

[0179] This embodiment allows a compact, adjustment-free construction of the optical system, since at least the first and second diffractive elements have a rigid alignment and position relative to each other. If the first and second reflectors are also integrally formed with the diffractive elements, the robustness is increased. Furthermore, both the first and second array detectors can be connected to the respective diffractive elements.

[0180] Depending on the nature of the connection of the respective incident surfaces, the connected incident surfaces may have substantially imaginary properties (e.g., because they merge into each other). However, in particular, at least within the scope of interpretation and general understanding by those skilled in the art, the present invention itself is intended to include overall embodiments of the first and second diffractive elements.

[0181] According to another embodiment of the invention, the optical system has a collimating optical unit for the reference light on the side of the first incident surface of the first holographic arrangement, the collimating optical unit having an optical axis extending in the direction of the first incident surface of the first holographic arrangement, in particular, wherein the optical axis extends laterally, i.e., can be offset, and wherein the collimating optical unit is designed to collimate the laser light in the form of the reference light before the laser light enters through the first incident surface of the first diffraction element. In particular, the collimating optical unit is aligned with its optical axis so that the reference light collimated thereby propagates along the optical axis of the first diffraction element after entering the first diffraction element, so that the reference light is incident on the diffraction plane of the first diffraction element at an angle of 45°. The lateral offset can be designed in such a way that the collimated light, after reflection by the reference reflector, is again incident on the exit surface or the detector array centrally at its angle β relative to the optical axis.

[0182] The term "collimation" is to be interpreted in particular in such a way that the reference light has only a minimal wavefront curvature at least for one wavelength. At different wavelengths, the convergence or divergence of the light beam or wave field increases depending on the wavelength. These chromaticity-related deviations from the ideal collimation are also included in the term "collimation" in the context of the present invention. In addition, deviations due to adjustments and system tolerances are also to be understood under the term "collimation". In particular, the term "collimation" is also to be understood as a convergence and / or divergence of the light beam up to a divergence or convergence angle ξ, which within the scope of the present invention lies in the range of 0°<ξ≤2*β or 2*ρ. 2 and / or 0°<ξ≤2*β'or 2*ρ' 2 within the range.

[0183] According to another embodiment of the invention, the optical system comprises an objective for object light, the objective having an optical axis extending in the direction of a second incident surface of the first holographic arrangement and / or of the second holographic arrangement, wherein the objective is arranged in the optical system such that light propagating from the objective in the direction of the second incident surface of the first diffraction element and / or of the second diffraction element is collimated when the light is emitted in and / or near the focal plane of the objective in the direction of the objective, in particular reflected or scattered, wherein the light is object light.

[0184] In the context of the present description, the term "near" in relation to the focal plane or focus should in particular be understood as a tolerance indication, since deviations from an ideal optical arrangement of components or deviations from an ideal beam / wave path of light can easily be handled by the system according to the invention. In this context, the term "near" can for example be understood as a tolerance range relative to the focal length of the objective, so that for a nominal focal length f, a deviation range of ±f / 5 is defined by the term "near". A similar understanding can also be applied to other components of the system.

[0185] According to the law of imaging optics, light closer to or farther from the focal plane of the objective lens is divergent or convergent when incident on the second incident surface. However, depending on the degree of divergence / convergence, this light can also contribute to imaging in the digital holography method.

[0186] In particular, the objective lens is aligned with its optical axis so that object light originating from the focus of the objective lens propagates along the optical axis of the first or second diffraction element after entering the first or second diffraction element, so that the object light is incident on the diffraction plane of the first or second diffraction element at an angle of 45°.

[0187] An objective may consist of one or more lenses or lens elements.

[0188] It should also be noted that according to the present invention, in particular, only one objective is provided even if two holographic arrangements are included in the system. The objective is then closer to the second diffractive element and its second incident surface side.

[0189] According to another embodiment of the present invention, the system includes the following components:

[0190] a laser source configured to provide laser light having one or more central wavelengths, in particular wherein the laser source comprises one or more lasers, in particular wherein each laser is configured to emit laser light comprising at least one central wavelength, wherein each laser emits at least one, preferably a plurality of laser lines in a wavelength range around the central wavelength of the laser,

[0191] a first optical fiber, in particular a polarization maintaining single mode optical fiber, configured to guide the laser light of the laser source to the input aperture of the collimating optical unit, such that the collimating optical unit can guide the collimated laser light in the form of reference light to the first holographic arrangement,

[0192] a second optical fiber, in particular a polarization-maintaining single-mode optical fiber, configured to guide laser light from the laser source to an output aperture of the optical system, from which the object to be inspected is illuminated with the laser light in the form of object light.

[0193] This embodiment allows controlling the polarization of the reference light and the object light. In particular, the volume phase holographic grating diffracts s-polarized light significantly better than p-polarized light, in particular, so that the system is configured so that the reference light and the object light are particularly s-polarized after they leave the first and second optical fibers.

[0194] According to another embodiment of the present invention, the system comprises a fiber splitter, in particular a polarization-maintaining fiber splitter, which is configured to split laser light of a laser source and couple it into at least one first optical fiber and a second optical fiber, in particular wherein the fiber splitter and the at least one first optical fiber and the second optical fiber are included in an integrated optical component.

[0195] According to one embodiment of the present invention, the system has an imaging optical unit, which is designed to project object light, in particular object light emitted from the second optical fiber, in the form of an intensity pattern, in particular onto an object to be detected, wherein the intensity pattern consists of at least one illumination area, but preferably consists of a plurality of non-intersecting illumination areas, in particular wherein the illumination areas of the pattern are point-shaped or circular, in particular wherein the object light reflected by the object is detected by an objective lens.

[0196] This form of intensity patterning allows multiple object areas to be recorded and evaluated in parallel using multiple wavelengths.

[0197] By moving the pattern on the object so that the object is optically scanned and detected in the area, full inspection can be performed.

[0198] In this way, the surface of the object may be scanned using the intensity pattern, wherein depth information and lateral position information may be generated for each region via the first and / or second holographic arrangement so that 3D information may be generated from the object surface scanned using the object light.

[0199] According to a further embodiment of the invention, the system has a housing, in particular a waterproof housing, wherein the housing comprises the first and / or second holographic arrangement, the first collimating optical unit and the objective lens, in particular wherein the laser source is arranged outside the housing and is connected to the housing at least via a flexible fiber optic line.

[0200] In particular, the laser source may be arranged in or outside the housing and configured to couple reference light originating from the laser source and object light coherent therewith into at least one first optical fiber and a second optical fiber via a fiber splitter preferably in the housing.

[0201] Such an optical system with a laser source and a fiber splitter can be integrated in a relatively compact module, wherein at least one reference arm of the system, i.e. the part of the system guiding the reference light, in particular the first and / or the second holographic arrangement, can be part of the integrated module. Such a system requires only minimal space within the housing, making it suitable for minimally invasive medical applications.

[0202] According to another embodiment of the present invention, the system is configured to provide a laser comprising wavelengths from at least two wavelength ranges, wherein a first wavelength range of the two wavelength ranges is arranged around a central wavelength and comprises wavelengths in particular in the form of spectral lines, such as laser lines, outside the second wavelength range, wherein the second wavelength range is arranged around a different central wavelength comprising the two wavelength ranges and the wavelengths in particular in the form of spectral lines, wherein in particular the first and second wavelength ranges each comprise a spectral range of no more than 50 nm, in particular no more than 15 nm, in particular wherein the spectral lines of the wavelength ranges each have a line width of no more than 0.5 nm, in particular no more than 0.2 nm.

[0203] In particular, such a system thus has two volume phase holographic gratings, each of which is configured for one of the two central wavelengths, namely configured to diffract the central wavelength of the configured volume phase holographic grating and to keep the other central wavelength undiffracted.

[0204] Both volume phase holographic gratings may be arranged in the first diffraction element or in the second diffraction element. Alternatively, each of the two diffraction elements may comprise one of these volume phase holographic gratings.

[0205] Another aspect of the invention relates to a human or veterinary medical endoscopy system comprising an optical system according to the invention for generating a digital holographic image.

[0206] The endoscopic system can be configured to create a holographic video recording and display a 3D representation of the detected object on a display screen. BRIEF DESCRIPTION OF THE DRAWINGS

[0207] Other features and advantages of the present invention are explained below with reference to the accompanying drawings of exemplary embodiments. Angles and lengths may be exaggerated or underestimated in the drawings and are only used to illustrate the present invention. In particular, it is advantageous if each incident surface of the diffractive element is larger than its exit surface.

[0208] In the attached picture:

[0209] Figure 1 A schematic cross-sectional view showing a first general embodiment of a holographic arrangement of a system according to the invention;

[0210] Figure 2 a schematic cross-sectional view showing a second embodiment of a holographic arrangement of a system according to the invention;

[0211] Figure 3 shows a schematic cross-sectional view of a third embodiment of a holographic arrangement of a system according to the invention;

[0212] Figure 4a schematic cross-sectional view showing a fourth embodiment of a holographic arrangement of a system according to the invention;

[0213] Figure 5 shows a schematic cross-sectional view of an embodiment of a system with a holographic arrangement according to the invention;

[0214] Figure 6 A schematic cross-sectional view of an embodiment of a system according to the invention with two holographic arrangements is shown. DETAILED DESCRIPTION

[0215] exist Figure 1 In FIG. 1 , an exemplary general embodiment of a system 1 according to the invention is schematically shown in a 2D cross section.

[0216] The optical system 1 has a first holographic arrangement 2 which comprises a first diffractive element 3 , a first mirror 35 and a first array detector 37 .

[0217] The system 1 also has a collimating optical unit 5 and an objective lens 6 (see Figure 5 and 6 ) The laser source 8 of the system 1 is configured as (see Figure 5 and Figure 6 ) provides reference light 100 and object light 200 to system 1.

[0218] A variation of the system may comprise a second holographic arrangement 2' further comprising a second diffractive element 3', a second mirror 35 and a second array detector 37. Since the essential features of the first and second holographic arrangements 2, 2' are arranged in the same way and are functionally related in the same way, Figures 1 to 4 2 '. The corresponding reference numerals of the elements and components are also indicated for the second holographic arrangement 2'. The reference numerals of the second holographic arrangement 2' correspond to the reference numerals of the first holographic arrangement 2 plus a "'". In the following, the first holographic arrangement 2 is first described, wherein the same or at least analogously applies to the second holographic arrangement 2'.

[0219] The first holographic arrangement 2 comprises a solid (e.g. glass or polymer) prism arrangement 4, which forms a first diffractive element 3, having in this case a quadrilateral base surface, the edges of which are surrounded by side surfaces of the prism arrangement 4. The side surfaces comprise four side surface areas, namely a first and a second entrance surface 31, 32, each of which may be part of an end face of the first diffractive element 3, an exit surface 33 and a prism surface 34. The first and second entrance surfaces 31, 32 and the exit surface 33 are transparent, except for the prism surface 34, which may also be designed to be reflective.

[0220] Each surface of the prism arrangement 4 can be assigned a corresponding plane extending along the respective surface (as shown by the dashed line). Thus, the first incident plane 310 extends along the first incident surface 31, the second incident plane 320 extends along the second incident surface 32, the exit plane 330 extends along the exit surface 33, and the prism plane 340 extends along the prism surface 34.

[0221] The first prism arrangement 4 further comprises a transmission diffraction grating arrangement 36, which extends along a diffraction plane 360 ​​in the first diffraction element 3. The transmission diffraction grating arrangement 36 comprises at least a first volume phase holographic grating.

[0222] The first reflector plane 350 extends through the first reflector 35 along the reflective surface of the first reflector 35. The first reflector 35 is arranged on the prism surface 34 side.

[0223] Between the first and second incident surfaces 31 , 32 , an optical axis OA of the first diffractive element 3 may be defined, which intersects the diffraction plane 360 ​​at an angle of 45°.

[0224] The first holographic arrangement 2 is now configured such that the first mirror plane 350 encloses an angle α with the diffraction plane 360 ​​of the first diffraction element 3, and wherein the prism plane 340 encloses an angle ω with the diffraction plane 360 2 , where the angles α and ω 2 Any one or only one of them is selected so that the reference light 101 diffracted by the transmission diffraction grating arrangement 36 in the direction of the prism surface 34 is reflected by the first reflector 35, whereby, due to the incident angle of the reflected reference light 102 on the transmission diffraction grating arrangement 36, the reflected reference light 102 is diffracted again in the direction of the first incident surface 31, in particular, smaller than the incident angle of the reference light 100 initially incident on the transmission diffraction grating arrangement, in particular a ratio of less than 30%, and the remaining part of the reflected reference light 102 propagates through the transmission diffraction grating arrangement 36 in the direction of the exit surface 33.

[0225] From the Littrow configuration, that is, when the reference light 100 is irradiated into the diffraction element 3 and propagates in a collimated manner along the optical axis OA of the first diffraction element 3, when the angle α=45°±β, β≠0°, and / or when the angle ω 2 =45°±ρ 2 , ρ 2 ≠0°, this object can be achieved particularly well. In particular, the angle β and / or the angle ρ 2 has an absolute value in the range of 0.2° and 20°, in particular, in the range of 0.5° and 20°, such that α is in the range of 25° to 44.5° or 45.5° to 65° and / or such that ω 2In the range of 25° to 44.5° or 45.5° to 65°.

[0226] In order to achieve the desired effect, the first reflector 35 or the prism surface 34 forms an angle α or ω which is not equal to 45°. 2 However, if Figure 1 As shown, it is possible that both the first reflector 35 and the prism surface 34 are at angles other than 45° to the diffraction plane.

[0227] According to the present invention, it is particularly provided that the reference light 100 in the collimated state is incident on the transmission diffraction grating arrangement 36 at an angle of 45°. The collimation and propagation direction of the reference light in the diffraction element 3 can be controlled by the collimating optical unit 5 ( Figure 1 This is achieved by the position and orientation of (not shown).

[0228] According to the present invention, the reference light 100 may include at least one central wavelength 100-1, at which the transmission diffraction grating arrangement 36 diffracts the first order diffraction at 90° relative to the optical axis OA of the diffraction element 3 in the Littrow configuration, so that the diffracted reference light 102 of the wavelength 100-1 propagates at 45° away from the transmission diffraction grating arrangement 36. 2 With the angle α of the first reflector 35, the diffracted reference light 102 of the central wavelength 100-1 reflected by the reflector 35 is no longer incident on the transmission diffraction grating arrangement at an angle of 45°. If the angle x at which the reflected reference light 102 is incident on the transmission diffraction grating arrangement 36 is outside the bandwidth of the transmission diffraction grating arrangement 36, the reflected reference light 102 propagates through the transmission diffraction grating arrangement 36 without diffraction and is incident on the exit surface 33 of the first diffraction element 3, where it is detected by the first array detector 37 (e.g., a camera).

[0229] On the other side of the diffraction element 3, that is, on the second incident surface 32 side, the imaging optical unit 12 of the system 1 (see Figure 5 or 6) projecting laser light in the form of object light 200 onto the object 300 to be inspected (see Figure 5 or 6). The object light 200 is projected onto the object 300 in the form of an intensity pattern, wherein the intensity pattern (not shown) consists of a plurality of laterally offset and laterally non-overlapping light spots, i.e. a plurality of illuminated areas separated from each other by non-illuminated areas.

[0230] The object light 200 from the illuminated area of ​​the intensity pattern is reflected or scattered back by the object 300 in the direction of the holographic arrangement 2. In order to collect the object light 200, the system 1 has an objective 6. In an implementation according to the invention, the objective 6 is kept at a distance from the intensity pattern that approximately corresponds to the focal length of the objective 6. In this way, the object light 200 of the intensity pattern is collimated. Perfect collimation assumes the object area in the focus of the objective 6. Areas outside the focal plane, i.e. at different z-distances, will result in a slightly curved wave field. The mathematical considerations of such wave fields are known to a person skilled in the art, therefore, mainly images through the radiation vectors are used.

[0231] The collimated object light 200 is incident on the second incident surface 32 of the first diffractive element 3 (or on the second incident surface 32' of the second diffractive element 3' if the system has two diffractive elements 3, 3', see for example Figure 6 ), i.e. it is incident on the transmission diffraction grating arrangement 36, 36' in the diffraction element 3, 3' at an angle of about 45°, i.e. in a Littrow configuration. For this purpose, the objective lens 6 may have a specific position and orientation relative to the optical axis OA of the diffraction element 3, 3' depending on the configuration of the diffraction element 3, 3', for example, if the second incident surface 32, 32' of the diffraction element 3, 3' forms an angle other than 90° with the optical axis OA of the diffraction element 3, 3', the optical axis of the objective lens 6 may be arranged to form a certain angle with the optical axis OA of the diffraction element 3, 3', so that the collimated object light 200 propagates along the optical axis OA of the diffraction element 3, 3' after entering the diffraction element 3, 3', thereby ensuring the Littrow configuration. The transmission diffraction grating arrangement 36 then diffracts the object light 201 to the exit surface 33, where it is superimposed with the diffracted and reflected reference light 102 and may form an interference pattern detected by the first array detector 37. From this interference pattern, 3D information of the object 300 can be calculated in a known manner.

[0232] The first array detector 37 may be arranged along its detection plane 370 at an angle ε=45°±η and not equal to 45° relative to the diffraction plane 360. This may advantageously suppress reflections.

[0233] In a general variant of the holographic arrangement 2, 2' (e.g. Figure 1 As shown in FIG. 3 , the side surface area of ​​the first diffraction element 3 may enclose an angle other than 45° relative to the diffraction plane 360. This also has a beneficial effect on the interference reflection from the surface. In particular, Figure 1 The following angles are shown:

[0234] Angle ω 1 , which is surrounded by the first incident surface and the diffraction plane, where ω 1It can be in the range of 30° to 60°.

[0235] Angle ω 2 , which is surrounded by the prism surface and the diffraction plane. Angle ω 2 The optional angular deviation from 45° is determined by the angle ρ 2 describe.

[0236] Angle ω 3 , which is surrounded by the second incident surface and the diffraction plane, where ω 3 It can be in the range of 30° to 60°.

[0237] Angle ω 4 , which is surrounded by the exit surface and the diffraction plane, where ω 4 It can be in the range of 30° to 60°.

[0238] An angle α is enclosed by the first reflector and the diffraction plane. An optional angular deviation of the angle α from 45° is described by the angle β.

[0239] The angle ε, which is enclosed by the first array detector, more precisely the detection plane of the array detector and the diffraction plane. The optional angular deviation from 45° is described here by the angle η.

[0240] As already mentioned at the beginning, the angle markings, the indicated angular relations between the surfaces and the planes of the first holographic arrangement 2, and the mode of operation of the first holographic arrangement 2 (e.g. Littrow arrangement) can be transferred in an analogous manner to the second holographic arrangement 2'. This means, for example, that instead of the first diffraction element 3, there is a second diffraction element 3', instead of the first reflector 35, a second reflector 35' is part of the second holographic arrangement 2', and instead of the first array detector 37, a second array detector 37' is arranged on the side of the exit surface 33' of the second diffraction element 3'. To this end, in Figure 1 The corresponding angular names and reference numerals of the components of the second holographic arrangement 2' are also shown accordingly, for which the angles and the mode of operation are substantially the same as those of the first holographic arrangement 2. In detail, this means:

[0241] Angle ω' 1 It is surrounded by the first incident surface 31' or the incident plane 310' and the diffraction plane 360' of the second diffraction element 3', wherein ω' 1 It can be in the range of 30° to 60°.

[0242] Angle ω' 2 The angle ω is surrounded by the prism surface 34' and the diffraction plane 360' of the second diffraction element 3'. 2 The optional angular deviation from 45° is determined by the angle ρ' 2 describe.

[0243] Angle ω' 3 It is surrounded by the second incident surface 32' and the diffraction plane 360' of the second diffraction element 3', where ω' 3 It can be in the range of 30° to 60°.

[0244] Angle ω' 4 It is surrounded by the exit surface 31' and the diffraction plane 360' of the second diffraction element 3', where ω' 4 It can be in the range of 30° to 60°.

[0245] The angle α' is enclosed by the second reflector 35' and the diffraction plane 360' of the second diffractive element 3'. An optional angular deviation of the angle α' from 45° is described by the angle β'

[0246] An angle ε' is enclosed by the second array detector 37', more precisely by the detection plane 370' of the second array detector 37' and the diffraction plane 360' of the second diffraction element 3'. An optional angular deviation from 45° is described here by the angle η'.

[0247] However, it should be noted that if the second holographic arrangement 2' is included in the system 1, it is advantageous if the first incident surface 31' of the second diffractive element 3' extends parallel to the second incident surface 32 of the first diffractive element 3, so that the two incident surfaces 32, 31' can be connected to each other, in particular without forming an air gap, so that the diffraction planes of the transmission diffraction grating arrangements 36, 36' of the first and second diffractive elements 3, 3' are parallel to each other (see, for example, Figure 6 ) or enclose an angle of 90° to each other (not shown). In particular, in the embodiment with two holographic arrangements 2, 2', the first incident surface 31' of the second diffractive element 3' and the second incident surface 32 of the first diffractive element 3 each enclose an angle of 45° with the corresponding diffractive plane 360, 360', i.e. perpendicular to the respective optical axes OA of the diffractive elements 3, 3' (see Figure 6 ).

[0248] The following is also noted with respect to the laser light and the resulting reference light 100 and object light 200. The present invention particularly provides for laser light comprising a plurality of wavelengths. If a plurality of separate spectral lines 106 or 206 (e.g., reference light 100 or object light 200) are included in a wavelength range around the central wavelength 100-1, 100-2 or 200-1, 200-2, Figure 2 and 5), for example a laser line in a laser, is particularly advantageous. For example, the width of the spectral line ranges from at most 0.5 nm, preferably less than 0.1 nm. In contrast, a typical width of the wavelength range may be up to about 10 nm. The laser and the transmission diffraction grating arrangement 36, 36' of the system 1 are particularly coordinated with each other. Since the transmission diffraction grating arrangement 36, 36' comprises at least one volume phase holographic grating, the following can first be noted. The volume phase holographic grating has a bandwidth around a central wavelength (ideally the central wavelength of the laser) within which the volume phase holographic grating fully diffracts the incident light in a Littrow configuration, wherein the central wavelength is "perfectly" diffracted by 2*45°=90°.

[0249] Lasers with slightly different wavelengths around a central wavelength are called frequency comb lasers and can be produced, for example, using quantum dot technology. These are used, for example, for frequency multiplexing for broadband transmission in telecommunications. Alternatively, it is also conceivable that single-mode bar lasers with slightly different wavelengths are tightly integrated on a laser diode module and the output apertures are combined via a specially integrated optical chip to form a laser source module. Fiber splitters can also become part of such a module. Such a combination may already be conceivable on the laser diode chip itself, which would simplify the production process. For simplification, we can refer to a laser source with a central wavelength.

[0250] In order to obtain clear depth information about the phase of the individual wavelength signals for each object point or each illumination point, multiple wavelengths around the central wavelength are advantageous or even necessary. The lateral object information is generated from the holographic frequencies, for example by Fourier transformation. In combination, 3D objects can be identified in principle, which is known in principle to the person skilled in the art.

[0251] The advantageous properties of volume phase holographic gratings are described in more detail below:

[0252] When the reference light or object light is incident on a grating with a frequency f gr When the volume phase holographic grating is on a volume phase holographic grating, it has a central wavelength λ 0 The light is diffracted in the Littrow arrangement by exactly 90° (=2*45°) in the direction of the prism surface 34, 34' or the exit surface 33, 33', as already described. In the case of a slight change in wavelength (multiple lines in the laser wavelength range), the following angular separation Δθ results in this Littrow arrangement:

[0253]

[0254] At a central wavelength of 660 nm this is 3 mrad / nm, at a central wavelength of 1300 nm this is 1.5 mrad / nm. If the typical distance between two spectral lines is 200 pm, the angle changes by Δθ = 0.6 mrad. If the wavelength change is positive (λ 0 +Δλ), the diffraction angle increases to 90°+Δθ.

[0255] For the object light and the reference light, the volume phase hologram grating diffracts the reference light and the object light in opposite directions, thereby providing an angle twice that of equation (1), namely 2*Δθ.

[0256] The advantages of volume holography over planar gratings alone are their angular and spectral selectivity. Both of these properties are exploited in the manner already described.

[0257] Taking the above example into account, for a wavelength change of 200 μm, 2*0.6 mrad = 1.2 mrad would be estimated. With a typical resolution limit of 0.1 mrad per pixel on an array detector, this means that there is a shift of at least 10 pixels relative to the adjacent spectral line with the next higher / lower wavelength. When exiting in the direction of the array detector, the refractive index of the prism arrangement again increases the above angle by a factor n prism , as the beam is diffracted away from the vertical. Since the refractive index is typically between 1.5–1.9, a corresponding increase can be expected.

[0258] From these considerations, it is clear that in the proposed prism arrangement, the transmission diffraction grating arrangement with a volume phase holographic grating in the Littrow configuration already has particularly advantageous properties for spectral separation of a large number of spectral lines. It should be noted that the angular separation treated in equation (1) comes only from the dispersion of the volume phase holographic grating, and not from the angles α or ω 2 .

[0259] Angle α or Angle ω 2 The reference light diffracted and reflected at the first reflector is incident on the transmission diffraction grating arrangement at an angle at which the reference light is substantially no longer diffracted (in particular >70%) but propagates further in the direction of the exit surface, thereby providing a sufficiently high intensity reference light at the exit surface to form an interference pattern with the object light. The corresponding beam path is Figure 1 The same considerations apply to the second holographic arrangement of the system.

[0260] For the following considerations, for illustration purposes, it is assumed that the first reflector 35 is arranged on the prism surface 34, so that the angles α and ω 2 are the same.

[0261] In this case, the reference light of the central wavelength λ is irradiated in the Littrow configuration and reflected by the first mirror 0 , is incident on the diffraction plane at an angle of 45°±2β, and therefore has an angle of 2β relative to the diffracted object light. The reflected reference light has a wave shift ratio λ 0 ±Δλ is the corresponding wave shift ratio λ of the diffracted object light 0 ±Δλ has an angle of 2Δθ+2β. Different angles 2Δθ result in corresponding holographic frequencies on the camera chip, which can be assigned to multiple wavelengths via Fourier transformation. The number of these wavelengths can be as few as two or as many as several dozen. Since modern camera chips can have several thousand pixels per dimension, there are still enough spatial frequencies (angles) free to be able to assign lateral image points in the object via Fourier transformation, as is known to those skilled in the art. If the array detector is separated from the exit surface of the diffractive element by an air gap, the angle is increased again by the multiples of the refractive index of the prism arrangement, as described above.

[0262] The tilt angle β can be obtained from a 0 The dispersion relation type of the volume phase holographic grating, the refractive index n (~1.5) of the grating and the thickness D of the volume phase holographic grating are roughly deduced:

[0263]

[0264] Among them, δ FWHM The incident angle, at which the intensity of the diffracted light is still only about 50%. According to the definition of FWHM ("full width at half maximum"), with the thickness of the volume phase holographic grating D = 10 μm, the wavelength λ 0 = 660nm, refractive index n = 1.5, so the angle δ FWHM / 2≈50mrad. Therefore, the reference light reflected by the first reflector (incident on the diffraction plane at an angle of 2β) satisfies the condition, that is, δ FWHM / 2≈2β≈50mrad, so half of the reference beam propagates undiffracted through the transmission diffraction grating arrangement, while the other half is diffracted back in the direction of the first incident surface. However, since the reference beam in a hologram is always significantly stronger than the object beam, the attenuation of the reference beam by a factor of 2 does not represent a limitation.

[0265] Therefore, the use of a volume phase holographic grating has the further advantage that the object light within the FWHM is largely diffracted in the direction of the exit surface. This can also be achieved by a "classical" grating, but the reflected reference light will be largely diffracted in the direction of the first incident surface, and interference formation can only be achieved at the exit surface if the signal intensity is weak. Therefore, in this case, the diffraction efficiency of the diffraction grating will have to be reduced (for example, to 50%), which in turn will lead to an attenuation of the diffracted object light in the direction of the exit surface.

[0266] Another advantage of volume phase holographic gratings is that two volume phase holographic gratings with different central wavelengths can be constructed, one arranged inside the other, or alternatively, two relatively thin volume phase holographic grating structures are arranged one above the other.

[0267] exist Figures 2 to 6 Detailed Description of the Preferred Embodiments Some particularly advantageous embodiments of the optical system 1 are explained by way of example. The same reference signs denote the same elements, components or features.

[0268] exist Figure 2 In FIG. 2 , an advantageous embodiment of a first or second holographic arrangement 2 , 2 ″ according to the invention is shown.

[0269] With reference to the introduced angular relationships and reference numerals, the angle ω of the diffractive element 1 ,ω 3 ,ω 4 (or, if it is the second diffractive element, the angle ω' 1 ,ω' 3 ,ω' 4 ) is 45°.

[0270] In addition, the angle ω 2 and β(or ω' 2 β and β') are identical, and the first or second reflector 35, 35' is formed in the form of a reflective layer on the prism surface 34, 34' of the diffractive element 3, 3'. This has the advantage of producing a robust and compact optical system 1. In addition, such a configuration of the first and second holographic arrangements 2, 2' enables a tandem arrangement to be realized in the optical system according to the invention (see Figure 6 ), wherein the first and second diffractive elements 3, 3' with respective entrance surfaces 32, 31' can be arranged adjacent to each other without an air gap.

[0271] The first or second array detector 37, 37' is also fixed directly on the exit surface 33, 33' of the diffraction element 3, 3', so that no air gap is generated here either.

[0272] In particular, Figure 2The prism arrangement 4, 4' in the embodiment may be formed as a whole or by two triangular prisms connected to each other along a diffraction plane 360, 360' via a transmission diffraction grating arrangement 36, 36'.

[0273] exist Figure 2 In the figure, the optical path of the reference light in the diffraction element 3 or 3' is shown as an example of reference light, which includes two further spectral lines 106 around the central wavelength, which form, for example, edge values ​​of the wavelength range around the central wavelength of the laser 100, 200 and a volume phase holographic grating adapted thereto. Starting from the reference light 100, the spectral lines are diffracted by the transmission diffraction grating arrangement 36 or 36', smaller or larger than the central wavelength. Therefore, the beam of the spectral line 106, after being diffracted by the transmission diffraction grating arrangement 36, 36', encloses an angle other than 45° with the diffraction plane. Due to the angular position α, α' of the mirrors 35, 35', the reflected spectral lines diverge further from the beam 102 around the central wavelength 102 and are incident on the exit surface 33, 33' at laterally different positions.

[0274] The same applies to the object light 200 diffracted by the transmission diffraction grating arrangement 36, 36'. The spectral lines 206 of the laser light here also result in a dispersive separation of the object light 200 to form spectral lines 206 which are diffracted to different degrees by the transmission diffraction grating arrangement 36, 36'.

[0275] Figure 3 A variant of the first or second holographic arrangement 2, 2' of the optical system 1 is shown, wherein the prism arrangement 4, 4' has a substrate surface in the form of a parallelogram, wherein the first and second entrance surfaces 31, 32 (or 31', 32') each enclose an angle ω of 45° with the diffraction plane 360, 360' 1 ,ω 3 (or ω' 1 ,ω' 3 ), that is, in particular perpendicular to the optical axis OA of the diffractive element 3, 3', the exit surface 33, 33' and the prism surface 34, 34' also extend in parallel, so that the angle ω 2 and ω 4 (or ω' 2 and ω' 4 ) are equal to and less than 45°. Likewise, in this exemplary embodiment, the reflectors 35, 35' are arranged directly (ie, without forming a gap) on the prism surfaces 34, 34', so that the angle α is equal to the angle ω 2 (and hence β = ρ 2 ) or the angle α' is equal to the angle ω' 2 (and hence β' = ρ' 2). The reflectors 35, 35' may also be designed as reflective layers which are vapor deposited onto the prism surfaces 34, 34' using, for example, a suitable method.

[0276] Furthermore, the array detectors 37, 37' are arranged directly on the exit surfaces 33, 33' so that the angles ε and ω 4 (or ε' and ω' 4 ) is the same. This leads to the following angular relationship:

[0277] α=ω 2 =ω 4 =ε<45°or α'=ω' 2 =ω' 4 =ε'<45°or,

[0278] α=ω 2 =ω 4 =ε>45°or α'=ω' 2 =ω' 4 =ε'>45°.

[0279] This embodiment is characterized by a simple geometric structure, which simultaneously improves the suppression of interference signals (ghosting) on ​​the array detectors 37, 37', because, as shown by the dotted arrows 103 and 104, due to the special angular relationship of the surfaces of the holographic arrangement 2, 2', the light that may be reflected by the array detector 37, 37' is incident on the transmission diffraction grating arrangement 36, 36' again at an angle of 45° and - with high diffraction efficiency - is diffracted again in the direction of the first incident surface 31, 31' and is thus guided out of the diffraction element 3, 3'.

[0280] and Figure 3 similar, Figure 4 An extended variant of the first or second holographic device 2, 2" is shown. The prism arrangement 4, 4' also has a parallelogram as its base surface, wherein Figure 3 In contrast, the angle ω between the first and second incident surfaces 1 and ω 3 (or ω' 1 and ω' 3 ) is not equal to 45°. This ensures that the entrance surfaces 31, 32 (or 31', 32') do not extend perpendicularly to the optical axis OA of the diffractive element 3, 3', which shows an advantageous deflection of possible back reflections on these surfaces (see arrow 105).

[0281] It should be noted that this geometry can also be used in a system 1 comprising two holographic arrangements 2, 2' arranged in series by arranging the first entrance surface 31' of the second diffractive element 3' on the second entrance surface 32 of the first diffractive element 3 without an air gap.

[0282] Figure 5 An optical system 1 according to an exemplary embodiment of the invention is shown, wherein, in addition to the holographic arrangements 2 , 2 ′ from the previous figures, further components of the system 1 are now schematically shown.

[0283] first, Figure 5 The system in includes a laser source 8 (dashed box) having only one laser 81, which is designed to provide laser light around a central wavelength and may have additional spectral lines within the wavelength range. Laser sources or lasers suitable for this purpose have been described as examples in the previous paragraphs. In addition, the laser source 8 can be configured to emit polarized laser light of a specific polarization. The laser light is then separated into a reference light 100 and an object light 200 by a beam splitter. The separation ratio may not be equal to 50:50, wherein preferably, a larger proportion of the laser light, such as 70% or 90%, is allocated to the object light.

[0284] The beam splitter may be integrated in a fiber splitter 13, which is configured to couple the reference light 100 into the first polarization-maintaining fiber 10 and to couple the object light 200 into the second polarization-maintaining single-mode fiber 11. The first optical fiber 9 is arranged with one end in the focus of the collimating optical unit 5 of the optical system 1 or at least in the focal plane of the collimating optical unit, so that the reference light 100 is coupled out of the optical fiber 9, and if necessary, the wavefront of the reference light is collimated by the collimating optical unit 5 through a corresponding coupling lens or aperture 10. The collimating optical unit 5 has an optical axis at Figure 5 In the example of FIG. 3 , the optical axis extends colinearly with the optical axis OA of the first diffraction element 3. If the first incident surface 31 forms an angle not equal to 45° with the diffraction plane 360, the optical axis of the collimating optical unit 5 is aligned accordingly so that the reference light propagates along the optical axis OA of the diffraction element 3 after entering the diffraction element 3. In this example, the optical axis of the collimating optical unit 5 is shifted to be parallel to the optical axis of the first diffraction element 3, so that the reference light enters the diffraction element 3 in a region closer to the reflector and is therefore superimposed on the corresponding beams 201, 206 of the object light at the array detector 37. The further propagation process in the first holographic arrangement 2 has been discussed in detail and will not be repeated here.

[0285] The object light 200 propagates along the second optical fiber 11 after the optical fiber splitter 13 and is emitted by the imaging optical unit 12 at the end of the second optical fiber 11 in such a way that an intensity pattern is projected onto the object 300 to be detected.

[0286] The intensity pattern has at least one illuminated point on the object 300, but preferably has a plurality of points that are laterally separated from each other by non-illuminated areas of the pattern.

[0287] The object light 200 from the pattern reflected by the object 300 is captured by the objective 6 of the system 1 and, if it originates from the focal plane of the objective 6, is collimated and directed in the direction of the second entrance surface 32. The object light 200 enters the diffractive element 3 and is diffracted in the direction of the exit surface 33, where it is superimposed with the reference light 102. This superposition is recorded by the first array detector 37 and transmitted to the computer 400 for further processing, for example in the form of digital data. The computer 400 can reconstruct the wave field of the object light and thus can generate a 3D representation of the illuminated area of ​​the object.

[0288] The laterally offset points in the intensity pattern has the consequence that each point on the first array detector 37 can be analyzed individually despite the spectral separation that occurs on the array detector 37. In order to obtain complete information about the object, the object is scanned using the intensity pattern so that each part of the object has ideally been illuminated at least once by a light point and detected by the first array detector 37.

[0289] like Figure 2 As shown in FIG. 1 , the beam paths of the spectral lines 106 and 206 of the wavelength range around the central wavelength from the reference beam 102 and the object beam 201 are also Figure 5 , which is advantageously determined by the dispersion properties of the transmission diffraction grating arrangement 36 or the volume phase holographic grating.

[0290] Figure 5 The holographic arrangement shown may be replaced by another previously disclosed holographic arrangement 2 without affecting the system 1 , wherein the position and orientation of the collimating optical unit 5 and / or the objective lens 6 may need to be adjusted accordingly so that the system 1 exhibits a Littrow configuration.

[0291] Figure 6 Shows Figure 5 An embodiment of a system 1, with Figure 5 Compared to the system in , it includes first and second holographic arrangements 2, 2'. The first holographic device 2 includes a first volume phase holographic grating 36 configured to a first central wavelength 100-1, 200-1, and the second holographic device 2' includes a volume phase holographic grating 36' configured to a second central wavelength 100-2, 200-2. This means that the volume phase holographic grating 36 of the first diffraction element 3 diffracts the reference and object light around the first central wavelength 100-1, 200-1 in a Littrow configuration and allows the light around the second central wavelength 100-2 to pass without diffraction, while the volume phase holographic grating 36' of the second diffraction element 3' diffracts the reference and object light around the second central wavelength 100-2, 200-2 in a Littrow configuration and allows the light around the first central wavelength 200-1 to pass without diffraction. This allows the expansion of the spectral range for digital holography.

[0292] It should be noted that Figure 6 , for the sake of clarity, the beam paths of the spectral lines 106 and 206 around the respective central wavelengths 100-1, 100-2, 200-1, 200-2 are not shown.

[0293] In order to provide laser light with two central wavelengths, the laser source 8 comprises two lasers 81, 82, wherein the first laser 81 is configured to emit laser light around a first central wavelength 100-1, 200-1 (and in particular, further spectral lines in a wavelength range around the first central wavelength), and wherein the second laser 82 is configured to emit laser light around a second central wavelength 100-2, 200-2 (and in particular, further spectral lines in a wavelength range around the second central wavelength). Figure 5 As already described in the previous section, the light of the two lasers 81, 82 is coupled into the first and second polarization maintaining optical fibers 9, 11 via the optical fiber splitter 13. If the bandwidth of the optical fibers 9, 11 is not sufficient for single-mode transmission of the two central wavelengths, it is also possible to use separate optical fibers for each central wavelength, which can be combined at their ends by a beam splitter, or arranged slightly laterally offset before they are projected onto the object 300 by the imaging optical unit 12, or collimated by the collimating optical unit 5.

[0294] exist Figure 6 In the example of , the first and second diffractive elements 3, 3' are arranged in series, and the second incident surface 32 of the first diffractive element 3 is connected to the first incident surface 31' of the second diffractive element 3' without an air gap, so as to avoid in particular the jump of the refractive index at the transition between the diffractive elements 3, 3'. For this purpose, the two incident surfaces 31', 32 extend parallel to each other. Depending on the requirements, the first and second reflectors 35, 35' enclose the same or different angles α, α' with the corresponding diffractive planes 360, 360'.

[0295] Each diffractive element 3, 3' comprises its respective array detector 37, 37' which may have an optical filter (not shown) connected upstream thereof to block stray light or reflections from wavelength ranges other than the intended wavelength range.

[0296] The signals recorded by the first and second array detectors 37, 37' at the respective exit surfaces 33, 33' are fed to the same computer 400 which can calculate a 3D representation of the object from this information.

[0297] The system 1 according to the invention enables digital holography to be realized in a compact and robust manner, for example in the field of minimally invasive medicine. In particular, the system is configured and adapted to be included in an endoscope.

[0298] Reference numerals list

[0299] 1. Optical system

[0300] 2First holographic layout

[0301] 2' Second holographic arrangement

[0302] 3. The first diffraction element

[0303] 3' Second diffraction element

[0304] 4. First prism arrangement

[0305] 4' Second prism arrangement

[0306] 5Collimation optical unit

[0307] 6 Objective lens

[0308] 8 Laser source

[0309] 81,82 Laser

[0310] 9First Fiber

[0311] 10 Input Aperture

[0312] 11 Second optical fiber

[0313] 12 Imaging optical units

[0314] 31,31' first incident surface

[0315] 32,32' Second incident surface

[0316] 33,33' exit surface

[0317] 34,34' prism surface

[0318] 35 First Reflector

[0319] 36,36' Volume Phase Holographic Grating

[0320] 37 First array detector

[0321] 37' Second array detector

[0322] Optical axis of OA diffraction element

[0323] ω1 Angle between 310 and 360

[0324] ω'1 Angle between 310' and 360'

[0325] ω2 Angle between 340 and 360

[0326] ω'2 Angle between 340' and 360'

[0327] ω3 Angle between 320 and 360

[0328] ω'3 Angle between 320' and 360'

[0329] ω4 Angle between 330 and 360

[0330] ω'4 Angle between 330' and 360'

[0331] Angle between 350 and 360

[0332] Angle between α'350' and 360'

[0333] Angle between ε370 and 360

[0334] Angle between '370' and 360'

[0335] Angles between χ102 and 360

[0336] 100 Reference light

[0337] 101 Diffracted Reference Light

[0338] 102 Reflected reference light

[0339] 103-105 Light reflection of reference light

[0340] 106 Spectral lines around the central wavelength of the reference light

[0341] 100-1 The first central wavelength of the reference light

[0342] 100-2 The second central wavelength of the reference light

[0343] 200 Object Light

[0344] 201 Diffracted Object Light

[0345] 206 Spectral lines around the central wavelength of the object light

[0346] 200-1 The first central wavelength of the object light

[0347] 200-2 The second central wavelength of the object light

[0348] 300 objects

[0349] 400 Computer

Claims

1. An optical system (1), comprising at least the following components: A first holographic arrangement (2) comprising a first diffractive element (3) formed by a first prism arrangement (4) having at least a quadrilateral base surface, wherein The side surface of the first prism arrangement (4) has the following side surface area: a) a first incident surface (31) for the reference light (100) extending along a first incident plane (310), b) a second entrance surface (32) for the object light (200) extending along a second entrance plane (320), wherein the first and second entrance surfaces (31, 32) form opposite side surface areas of the first prism arrangement (4) c) an exit surface (33) extending along an exit plane (330) and through which the diffracted reference light (102) and the diffracted object light (201) can exit from the second diffraction element (3), d) a prism surface (34) opposite to the exit surface (33) and extending along a prism plane (340), e) an optical transmission diffraction grating arrangement (36) which is arranged in the first diffraction element (3) and extends along a diffraction plane (360) which intersects the first incident plane (310) between the first incident surface (31) and the exit surface (33), Characterized in that the transmission diffraction grating arrangement (36) of the first diffraction element (3) includes at least a first volume phase holographic grating, and the first holographic arrangement (2) has a first reflector (35), the first reflector has a first reflector plane (350) on the side of the prism surface (34), wherein the first reflector plane (350) forms an angle α with the diffraction plane (360), and the prism plane (340) forms an angle ω2 with the diffraction plane (360), wherein at least one of the angles α, ω2 is different from 45°.

2. The optical system (1) according to claim 1, characterized in that The system (1) comprises a first array detector (37), wherein the first array detector (37) is configured to detect light emitted from the exit surface (33) of the first diffraction element (3), in particular, wherein the first array detector (37) is arranged on the exit surface (33) of the first diffraction element (3).

3. The optical system (1) according to any one of the preceding claims, characterized in that The base surface of the first prism arrangement (4) is a parallelogram, and in particular a rectangle, such as a square.

4. The optical system (1) according to any one of the preceding claims, characterized in that The first reflector (37) is arranged or formed on the prism surface (33) of the first diffractive element (3).

5. The optical system (1) according to any one of the preceding claims, characterized in that The optical transmission diffraction grating arrangement (36) of the first holographic arrangement comprises a second volume phase holographic grating, wherein the first volume phase holographic grating and the second volume phase holographic grating have different central wavelengths.

6. The optical system (1) according to any of the preceding claims, comprising a second holographic arrangement (2') with a second diffractive element (3'), the second holographic arrangement being formed by a second prism arrangement (4') with at least a quadrilateral base surface, wherein the first holographic arrangement (2) and the second holographic arrangement (2, 2') are arranged adjacent to each other along an optical axis (OA) of the first diffractive element (3), and the side surface of the second prism arrangement (4') has the following side surface area: f) a first incident surface (31') for the reference light (100) extending along a first incident plane (310'), g) a second incident surface (32') for the object light (200) extending along a second incident plane (320'), wherein The first and second entrance surfaces (31', 32') form opposite side surface areas of the second prism arrangement (4'), h) an exit surface (33') extending along an exit plane (330') and through which the diffracted reference light (102) and the diffracted object light (201) can exit from the second diffraction element (3'), i) a prism surface (33') opposite to the exit surface (33) and extending along a prism plane (330'), j) an optical transmission diffraction grating arrangement (36') which is arranged in the second diffractive element (3') and extends along a diffraction plane (360') which intersects the first incident plane (310') between the first incident surface (31') and an exit surface (33') of the second diffractive element (3'), Characterized in that the transmission diffraction grating arrangement (36') of the second diffraction element (3') comprises at least a first volume phase holographic grating, and the second holographic arrangement (2') has a second reflector (35'), the second reflector having a second reflector plane (350') on the side of the prism plane (340'), wherein the second reflector plane (350') forms an angle α' with the diffraction plane (360'), and the prism plane (340') forms an angle ω'2 with the diffraction plane (360'), wherein at least one of the angles α', ω'2 is different from 45°, in particular deviates from 45° by more than ±0.2°.

7. The optical system (1) according to claim 6, characterized in that The second incident surface (32) of the first diffraction element (3) is connected to the first incident surface (31') of the second diffraction element (3'), in particular adhesively bonded or welded, in particular wherein the first diffraction element (3) is integrally formed with the first incident surface (31') of the second diffraction element (3') along its second incident surface (32).

8. The optical system (1) according to any one of the preceding claims, wherein: The optical system (1) has a collimating optical unit (5) for reference light (100) on the side of the first incident surface (31) of the first diffraction element (3), the collimating optical unit having an optical axis extending in the direction of the first incident surface (31) of the first diffraction element (3), and wherein the collimating optical unit (5) is configured to collimate the reference light (100) before it enters through the first incident surface (31) of the first diffraction element (3).

9. The optical system (1) according to any one of the preceding claims, wherein: The optical system (2) comprises an objective lens (6) for object light (200), wherein the objective lens (6) is arranged in the optical system (1) so that when the object light (200) is radiated in the direction of the objective lens (6) within and / or near the focal plane of the objective lens (6), the object light (200) propagating from the objective lens (6) in the direction of the second incident surface (32, 32') of the first and / or second diffractive element (3, 3') is collimated.

10. The optical system (1) according to any one of the preceding claims, characterized in that The optical system (1) comprises the following components: a laser source (8) configured to provide laser light having one or more central wavelengths, in particular wherein the laser source (8) comprises one or more lasers (81, 82), at least one first optical fiber (9), in particular a polarization maintaining single mode optical fiber, configured to guide the laser light of the laser source (8) to the input aperture (10) of the collimating optical unit (5), so that the collimating optical unit (5) guides the collimated laser light in the form of reference light (100) to the first holographic arrangement (2), - at least one second optical fiber (11), in particular a polarization-maintaining single-mode optical fiber, configured to guide the laser light of the laser source (8) to an output aperture (12) of the optical system (1), from which the object (300) to be detected is illuminated with the laser light in the form of object light (200).

11. The optical system (1) according to claim 10, characterized in that The optical system (1) comprises a fiber splitter (13), in particular a polarization-maintaining fiber splitter, which is designed to split the laser light of the laser source (8) and couple it into the first and second optical fibers (9, 11), in particular wherein the fiber splitter (13) and the first and second optical fibers (9, 11) are included in an integrated optical component.

12. The optical system (1) according to any one of the preceding claims, characterized in that The optical system (1) has an imaging optical unit (12), which is designed to project object light (200), in particular object light (100) emitted from at least one second optical fiber (11), onto an object (300) to be detected in the form of an intensity pattern, wherein the intensity pattern consists of at least one illumination area, but preferably consists of a plurality of non-intersecting illumination areas, in particular wherein the illumination area of ​​the intensity pattern is point-shaped or circular, in particular wherein the object light (200) reflected by the object (300) is detected by the objective lens (6).

13. The optical system (1) according to any one of the preceding claims, characterized in that The optical system (1) is designed to provide laser light comprising wavelengths from at least two wavelength ranges, wherein a first wavelength range is arranged around a first central wavelength (100-1, 200-1) and comprises wavelengths in the form of spectral lines, in particular, outside a second wavelength range, wherein the second wavelength range is arranged around a second central wavelength (100-2, 200-2) and comprises wavelengths in the form of spectral lines, wherein in particular the first wavelength range and the second wavelength range each comprise a spectral range of not more than 50 nm, in particular not more than 15 nm, in particular wherein the spectral lines of the wavelength ranges each have a line width of not more than 0.5 nm.

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