Optical System for Digital Holography

Abstract

The present invention relates to an optical system (1) comprising at least the following components: a first holographic arrangement (2) comprising a first diffraction element (3) formed by a first prism arrangement (4) having at least a quadrangular bottom surface, wherein the outer surface of the first prism arrangement (4) has the following outer surface regions: a first incident surface (31) for reference light (100) extending along a first incident plane (310), and a second incident surface (32) for object light (200) extending along a second incident plane (320), the first and second incident surfaces (31, 32) forming opposing outer surface regions of the first prism arrangement (4); an exit surface (33) extending along an exit plane (330) through which diffracted reference light (102) and diffracted object light (201) can exit the first diffraction element (3); a prism surface (34) opposing the exit surface (33) and extending along a prism plane (340); and a light-transmissive diffraction grating arrangement (36) disposed in the first diffraction element (3) and extending along a diffraction plane (360) intersecting the first incident plane (310) between the first incident surface (31) and the exit surface (33), wherein the transmissive diffraction grating arrangement (36) of the first diffraction element (3) comprises at least one first volume phase hologram grating, and the first holographic arrangement (2) on the side of the prism surface (34) has a first mirror (35) having a first mirror plane (350), wherein the first mirror plane (350) encloses an angle α with the diffraction plane (360), and the prism plane (340) encloses an angle ω2 with the diffraction plane (360), wherein at least one of the angles α, ω2 is different from 45°.

Description

Technical Field

[0001] The present invention relates to an optical system for digital holography, particularly for use in the field of minimally invasive medicine.

[0002] In the prior art, a so-called grism (GRISM) is known as an optical component, which consists of a combination of an optical grating and a prism (GRating + pRISM). In a grism, light of the central wavelength propagates straight through the grism and further splits the light into a spectrum. This enables the construction of a spectral imaging device in a particularly simple way.

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

Summary of the Invention

Problems to be Solved by the Invention

[0004] Based on the known state of the art, an improved system enabling multispectral digital holography is to be constructed, particularly in the field of minimally invasive medical technology.

Means for Solving the Problems

[0005] This problem is solved by at least the following components: A first holographic arrangement comprising a first diffractive element formed by a first prism arrangement having a quadrangular base achieved by an optical system comprising, wherein the outer surface of the first prism arrangement has the following outer surface regions: a) a first, in particular planar, entrance surface for reference light, extending along a first entrance plane, said entrance surface being part of a first end face and the first entrance surface being able to be part of a first end face, said entrance surface; b) a second, in particular planar, entrance surface for object light, extending along a second entrance plane, the first entrance surface and the second entrance surface forming opposite outer surface regions of the first prism arrangement, the second entrance surface being able to be part of a second end face, said entrance surface; c) an exit surface, in particular planar, which extends along an exit plane and through which diffracted reference light and diffracted object light can emerge from the first diffractive element, said exit surface; d) a prism surface opposite the exit surface; e) an optically transmissive diffraction grating arrangement arranged within the first diffractive element, which, in particular such that the transmissive diffraction grating arrangement forms a triangular prism with the first entrance surface and the exit surface, extends along a diffraction plane intersecting the first entrance plane and the exit plane between the first entrance surface and in particular the exit surface, said optically transmissive diffraction grating arrangement having. DETAILED DESCRIPTION OF THE INVENTION

[0006] The present invention further provides that the transmissive diffraction grating arrangement of the first diffractive element comprises at least one first volume phase hologram grating, and that the first holographic arrangement has a first, in particular planar, mirror on the side of the prism surface of the first diffractive element, the first mirror plane enclosing an angle α with the diffraction plane, the prism surface enclosing an angle ω2 with the diffraction plane, at least one or both of the angles α, ω2 being not equal to 45°, in particular deviating by more than ±0.2° from 45°, in particular the angle α = 45° ± β with β > 0°, in particular the angle ω2 = 45° ± ρ2 with ρ2 > 0°.

[0007] Preferably, β and / or ρ2 are greater than 0.2.

[0008] Preferably, β and / or ρ2 are less than 20°.

[0009] According to the present invention, the angles β and ρ2 are selected such that, in particular, the reference light impinging at an angle of 45° on the transmissive diffraction grating arrangement is diffracted by the transmissive diffraction grating arrangement towards the prism surface and reflected by the first mirror, whereby the reflected reference light is diffracted again towards the first entrance surface from the side of the first entrance surface by virtue of the angle of incidence of the reflected reference light on the transmissive diffraction grating arrangement to a lesser extent, in particular at least 30% less, than the reference light which first impinged on the transmissive diffraction grating arrangement from the side of the first entrance surface, and the remaining part of the reflected reference light propagates through the transmissive diffraction grating arrangement towards the exit surface.

[0010] The terms "reference light" and "object light" are known in connection with state-of-the-art digital holography. The reference light is superposed in the diffractive element with the object light returning from the object (e.g. reflected or scattered), which in particular originates from the same coherent light source as the reference light and, after further propagation, gives rise to an interference pattern near the exit surface on an array detector such as a 2D sensor or camera. In particular, since this pattern contains complete wave information regarding the object light, the object can be calculated from the interference pattern in the form of a hologram. In particular, depth information regarding the object, i.e. 3D information, can be generated when a number of wavelengths in the form of spectral lines, for example, are used for the reference light and the object light.

[0011] Thus, the present invention can be particularly well combined in connection with minimally invasive medical imaging devices designed to generate 3D information from the field of view of the device. Since stereoscopic optical systems are too large for minimally invasive use, digital holography is very beneficial in this technical field.

[0012] In the state of the present invention, in particular, it is provided that the reference light is incident on the diffraction element through the first incident surface, in particular in a collimated manner. There, the reference light is diffracted by the transmission diffraction grating arrangement towards 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 from Snell's law, at least a part of the reflected reference light is not diffracted by the transmission diffraction grating arrangement and is transmitted and propagated in the direction of the exit surface. According to the present invention, the object light is incident on the diffraction element through the second incident surface and is directly diffracted towards the exit surface by the transmission diffraction grating arrangement, where it is superimposed on, in particular interferes with, the reference light on the array detector or camera chip.

[0013] The present invention enables separating a plurality of wavelengths included in the reference light, which are in the form of spectrally spaced spectral lines in particular, from a relatively wide wavelength range on the side of the exit surface, and at the same time provides an optical system for digital holography that is excellent due to a very compact and robust design.

[0014] In particular, the optical properties of the volume phase hologram diffraction grating are combined in a very advantageous way with a first mirror that is advantageously tilted with respect to the transmission diffraction grating arrangement, thereby making it possible for the first time to resolve the wavelength bandwidth.

[0015] By means of the first mirror arranged according to the present invention, the subsequent image information obtained from the object light superimposed on the reference light at the exit surface can be shifted, typically outside the interference DC range.

[0016] Furthermore, the first mirror achieves that only a slight attenuation or no attenuation at all occurs to the reference light reflected by the first mirror when a part of it passes through the first transmission diffraction grating arrangement by the transmission diffraction grating arrangement. When the angles β and ρ2 are equal to 0°, a very large part of the reference light will be diffracted by the transmission diffraction grating arrangement towards the first incident surface and will not reach the exit surface.

[0017] The first mirror includes a first mirror plane extending along the reflective layer of the first mirror, and in particular here the first mirror consists of the reflective layer.

[0018] Hereinafter, the angle of the first mirror with a surface or a plane means the angle between the first mirror plane of the first mirror and the surface or the corresponding plane.

[0019] The term "prism" in the context of the present invention refers in particular to a geometric, in particular physical, body having two opposing bottom surfaces connected to each other by outer surface regions of the outer surfaces arranged at the edges of the bottom surface.

[0020] According to the present invention, the bottom surface of the prism arrangement is at least quadrilateral, i.e., the bottom surface has a polygon, and the polygon has at least four corners. However, it is readily possible and conceivable that the bottom surface includes additional corners and thus additional outer surface regions designed for other purposes are provided, for example, by the prism arrangement.

[0021] Thus, a quadrilateral prism has four outer surface regions delimiting two quadrilateral bottom surfaces. Unless otherwise defined, these bottom surfaces have the same shape and size.

[0022] The term "prism arrangement" in the context of the present invention refers in particular to a fixed arrangement of at least one prism or several prisms.

[0023] According to one embodiment of the present invention, at least the square prism arrangement is integrally or monolithically formed.

[0024] The terms "integrally designed" or "integrally formed" should be understood as synonymous with "monolithic" in the context of the present invention.

[0025] According to one embodiment of the present invention, at least the square prism arrangement is formed by the first and second triangular prisms, where the two triangular prisms are connected to each other along the diffraction plane via a transmission-diffraction grating arrangement. The first of the two triangular prisms includes, in particular, a first incident surface and an exit surface. The second of the two triangular prisms includes, in particular, a second incident surface and a prism surface. In particular, the square prism arrangement is formed by two separate triangular prisms rigidly connected to each other.

[0026] Generally, at least the square prism arrangement can be implemented monolithically in any embodiment of the present invention (unless otherwise explicitly disclosed). Alternatively, at least the square prism arrangement can be formed in a similar manner by various prisms connected to each other.

[0027] If no information regarding the composition and / or properties of the prism arrangement is given, both the monolithic design and embodiments in which the prism arrangement is formed, for example, by a number of separate interconnected prisms, are included.

[0028] In particular, all outer surface regions of at least the square prism arrangement are planar.

[0029] According to one embodiment of the present invention, the prism arrangement comprises a solid transparent body, in particular comprising a transparent glass or polymer.

[0030] According to one embodiment of the present invention, the prism arrangement consists of a transparent glass and / or polymer, in particular excluding the transmission diffraction grating arrangement.

[0031] According to one embodiment of the present invention, the first mirror has a reflectivity of 10% to 100%, in particular a reflectivity exceeding 70%. The reflectivity can be close to 100%, for example 95% or even 99%.

[0032] Normally, since sufficient reference light is available (compared to the object light), it is not necessary to make the reflectivity of the first mirror particularly high.

[0033] In particular, the first mirror has a smoothness of λ / 2 or more.

[0034] According to another embodiment of the present invention, the transmissive diffraction grating arrangement is essentially a planar transmissive diffraction grating arrangement.

[0035] Volume Phase Holographic (transmissive) gratings (abbreviated as VPH) are known from the prior art. The volume phase holographic grating is particularly a transmissive grating. The volume phase holographic grating consists of a film of dichromated / dichroic gelatin (DCG) between two glass substrates, where in particular the glass substrates are formed by first and second triangular prisms, and in particular the gelatin is arranged between the outer surface regions of the first and second triangular prisms extending along the diffraction plane. The volume phase holographic grating provides high first-order diffraction peak efficiency and consistent performance with a specific bandwidth.

[0036] As an alternative to gelatin, a photopolymer can also be used, which is formed into a volume phase holographic grating by appropriate exposure. In particular, the photopolymer can be introduced between two glass substrates after exposure. The photopolymer has the advantage of being easy to handle because it has less viscosity than gelatin. For both gelatin and photopolymer, the layer thickness of the volume phase holographic grating can be on the order of several micrometers to about 100 μm.

[0037] Furthermore, volume phase holographic gratings introduced into glass and particularly not containing gelatin are also known.

[0038] The volume phase hologram grating of PTR glass has the advantage of high thermal stability, which is a typical property of glass, compared to other volume phase hologram gratings made of gelatin or photopolymer. However, since the refractive index modulation of PTR glass is about one order of magnitude weaker than that of gelatin and photopolymer, the active glass layer needs to be made thicker accordingly. However, this restricts the angular dispersion or spectral characteristics. That is, an appropriate volume phase hologram grating material and manufacturing method can be selected according to the requirements of the diffraction element.

[0039] In particular, the first holographic arrangement is configured and formed to operate in a so-called "retro arrangement". The diffraction element, and thus the first holographic arrangement, is arranged in the system such that the diffraction plane encloses an angle of 45° with the optical axis of the diffraction element, and thus the first mirror plane encloses an angle β with the optical axis, and / or the prism surface encloses an angle ρ2. As a result, the reference light incident on the first diffraction element through the first incident surface first propagates along the optical axis, but is ideally diffracted by the transmission diffraction grating arrangement, and the diffraction angle is 2 * ×45° = 90°. In particular, the reference light colliding with the transmission diffraction grating arrangement is at an angle of 45° with the diffraction plane and is diffracted, and the diffracted reference light is also at an angle of 45° with the diffraction plane. The diffracted reference light is then reflected by the first mirror, where the angle α of the mirror plane and / or the angle ω2 of the prism plane contribute to the fact that the reflected reference light collides with the transmission diffraction grating arrangement at an angle exceeding 45°, and thus most of it propagates without being diffracted by the transmission diffraction grating arrangement.

[0040] This function can be achieved by arranging the first mirror and / or the prism surface at an angle exceeding 45° with respect to the diffraction plane, as claimed in the present invention.

[0041] In this way, the system of the present invention can be particularly advantageously used in digital holography applications.

[0042] It should be noted that the Littrow configuration, i.e., 90° diffraction, is only possible for the central wavelength of the optical grating. Wavelengths deviating from this are diffracted by different angular amounts depending on the angular dispersion.

[0043] If the transmission diffraction grating arrangement is not exactly at an angle of 45° with respect to the optical axis, or if the grating frequency does not exactly match the Littrow condition, the 90° diffraction of the central wavelength may also be somewhat different.

[0044] According to a further embodiment of the present invention, at least one first volume phase hologram grating of the transmission diffraction grating arrangement, when operating in the Littrow configuration, is configured to diffract a first bandwidth λ0 ± Δλ of wavelengths around the central wavelength λ0 in a diffraction angle range of approximately 90° ± Δθ.

[0045] The optical axis of the first diffractive element points from the first or second incident surface to the diffraction plane and can intersect the diffraction plane at an angle of 45°. Unless otherwise explicitly required, in the context of the system of the present invention, the reference light and the object light are assumed to impinge on the diffraction plane along the optical axis respectively.

[0046] According to the present invention, a plane extending along each surface, i.e., the first and second incident surfaces, the exit surface, and the prism surface, can be assigned. When referring to the angle between two surfaces, the angle between the planes is also referred to. Unless otherwise specified, the angle specification refers to the interior angle of the prism arrangement.

[0047] In particular, the first incident surface is bounded on one hand by the end having the exit surface and on the other hand by the virtual intersection line between the diffraction plane and the first incident surface.

[0048] In particular, the exit surface is bounded on one hand by the end having the first incident surface and on the other hand by the virtual intersection line between the diffraction plane and the exit plane, and / or by the end having the second incident surface.

[0049] Furthermore, the direction designations, orientations, and positions in the context of the present invention should be understood particularly with respect to the state of an optically developed system. For example, it is obvious to those skilled in the art that the direction of the optical axis can be changed by a deflection mirror within the system, and in terms of the optical function, no change in direction occurs, and it is only performed in terms of geometry. This understanding also needs to be used for interpreting the claims.

[0050] According to an embodiment of the present invention, the diffraction plane of the diffraction element encloses an angle ω1 with the first incident surface of the diffraction element, where in particular the angle is 30° ≤ ω1 ≤ 60°, and in particular ω1 = 45°.

[0051] According to an embodiment of the present invention, the diffraction plane of the first diffraction element encloses an angle ω2 with the prism surface of the first diffraction element, where in particular the angle is 30° ≤ ω2 ≤ 60°, and in particular ω2 = 45° or ω2 = 45° ± β, and in particular ω2 is selected such that the prism surface extends parallel to the mirror plane of the first mirror.

[0052] According to an embodiment of the present invention, the diffraction plane of the first diffraction element encloses an angle ω3 with the second incident surface of the first diffraction element, where in particular the angle is 30° ≤ ω3 ≤ 60°, and in particular ω3 = 45°.

[0053] According to an embodiment of the present invention, the diffraction plane of the first diffraction element encloses an angle ω4 with the exit surface of the first diffraction element, where in particular the angle is 30° ≤ ω4 ≤ 60°, and in particular ω4 = 45° or ω4 = 45° ± β, and in particular ω4 is selected such that the exit surface extends parallel to the mirror plane of the first mirror.

[0054] According to an embodiment of the present invention, the first and second incident surfaces of the first diffraction element are aligned parallel to each other.

[0055] According to another embodiment of the present invention, the angles ω1 and ω3 are equal to 45°. In this configuration, in particular, since the incident surface is perpendicular to the optical axis of the diffraction element, it is possible to irradiate the reference light and the object light perpendicularly to the first and second incident surfaces.

[0056] According to an embodiment of the present invention, the prism surface and the exit surface of the first diffractive element are aligned parallel to each other.

[0057] According to another embodiment of the present invention, the system comprises a first optical array detector such as a camera, and the first array detector is configured to detect light emitted from the exit surface of the first diffractive element.

[0058] In particular, the first array detector is arranged on the side of the exit surface of the first diffractive element in the first holographic arrangement.

[0059] Furthermore, the first array detector is arranged on the exit surface of the first diffractive element in the first holographic arrangement, and in particular the first array detector is connected to the exit surface of the first diffractive element, so that there is at least no air gap between the exit surface and the array detector.

[0060] Alternatively, the first array detector can be separated from the exit surface, and an air gap can be provided between the exit surface and the array detector.

[0061] Furthermore, the first array detector can be configured to convert the detected light into an electrical signal that can be evaluated by an evaluation device of the system, at least with respect to the two-dimensional intensity distribution of the detected light on the first array detector.

[0062] The array detector can provide a detection plane that extends along the array of the array detector, for example along the pixel matrix of a camera.

[0063] According to a further embodiment of the present invention, the detection plane of the first array detector encloses an angle ε = 45° ± η (η > 0) with the diffraction plane, in particular η = β, and in particular the detection plane is provided to run parallel to the first mirror. Furthermore, the exit surface can run parallel or in the same plane with respect to the detection plane.

[0064] In particular, 0° < η < 20°.

[0065] According to an embodiment of the present invention, the detection plane can be provided to surround the diffraction plane at such an angle that the light reflected from the detection plane collides with the diffraction plane in a retro shape, and as a result, the reflected light can be diffracted completely or at least mostly by the transmission diffraction grating arrangement toward the second incident surface and can exit therefrom. Thereby, the "ghost" signal of the array detector caused by the multiply reflected light can be avoided.

[0066] The above embodiment of the present invention has the advantage that the light reflected from the array detector and returning can be prevented from reaching the first mirror again, being reflected back to the array detector again, and generating an unwanted signal there. By selecting the angle η, the light reflected by the array detector can be diffracted completely or mostly toward the second incident surface by the first transmission diffraction grating arrangement.

[0067] According to a further embodiment of the present invention, it is provided that the bottom surface of the first prism arrangement forms a parallelogram, and in particular here, the diffraction plane of the first diffraction element extends along the diagonal extending to the bottom surface between the first incident surface and the exit surface of the first diffraction element, and in particular here i) the first incident surface surrounds the diffraction plane of the first diffraction element at an angle ω1 = 45° ± ρ1, and the prism surface surrounds the diffraction plane of the first diffraction element at an angle ω2 = 45°, where ρ1 > 0°, in particular ρ1 > 0.2°, or ii) the first incident surface surrounds the diffraction plane of the first diffraction element at an angle ω1 = 45°, and the prism surface surrounds the diffraction plane of the first diffraction element at an angle ω2 = 45° ± ρ2, where ρ2 > 0°, in particular ρ2 > 0.2°, or iii) the first incident surface surrounds the diffraction plane of the first diffraction element at an angle ω1 = 45° ± ρ1, and the prism surface surrounds the diffraction plane of the first diffraction element at an angle ω2 = 45° ± ρ2, where ρ1 > 0° and ρ2 > 0°, in particular ρ1 > 0.2°, ρ2 > 0.2°, or iv) The first incident surface encloses an angle ω1 = 45° with the diffraction plane of the first diffraction element, and the prism surface encloses an angle ω2 = 45° with the diffraction plane of the first diffraction element. The bottom surface is a specific parallelogram, i.e., a rectangle, preferably a square. Here, in particular, the diffraction plane of the first diffraction element extends along the diagonal extending on the bottom surface between the first incident surface and the exit surface of the first diffraction element.

[0068] i) to iii) Each of the embodiments advantageously reduces potential interference reflections that occur when the reference light and / or the object light is incident on or exits from the prism arrangement.

[0069] In particular, embodiments ii) and iii) enable the first mirror to be placed directly on the prism surface when, for example, the angle ρ2 = β is selected.

[0070] Furthermore, in embodiments ii) and iii), the first array detector can also be placed directly on the exit surface as already described above.

[0071] The aforementioned advantages of the array detector regarding the retroreflection from the array detector of the retro configuration and the advantages of the low-reflection geometry are particularly evident because the angle between the detection plane and the diffraction plane encloses ε = 45° ± η (η = β = ρ2), whereby the detection plane extends parallel to the first mirror. Furthermore, the exit plane is essentially in the same plane as the detection plane.

[0072] In particular, when at least the second incident surface is antireflective, the portion of the reference light retroreflected again at the second incident surface (which is reflected by the first array detector and diffracted through the transmissive diffraction grating arrangement) can be ignored. Depending on the configuration of the light rays, there may also be an inclination angle at the exit surface (e.g., in embodiment iii), whereby additional retroreflection suppression is achieved.

[0073] Embodiments i) and iii) advantageously allow for polarization selection and / or achieving reduction of reflection by using the Brewster angle and, if necessary, a polarization rotation element such as a λ / 2 plate simultaneously. Thus, the reference light and the object light around the central wavelength need to impinge on the first diffraction element at an angle (i.e., not equal to 90°) such that they impinge on the transmission diffraction grating arrangement at an angle of 45° with respect to the transmission diffraction grating arrangement, i.e., in a retro configuration.

[0074] According to embodiment iv), the bottom surface of the first prism arrangement is rectangular, in particular square.

[0075] 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 perpendicular to the incident surface respectively, and thus impinge on the transmission diffraction grating arrangement in a retro configuration. Furthermore, the angle α of the first mirror and, if necessary, the angle of the array detector can be easily adjusted.

[0076] According to another embodiment of the present invention, the first mirror is arranged on the prism surface of the first holographic arrangement.

[0077] This embodiment of the present invention includes the possibility that the first mirror is formed as a reflective layer on the prism surface. The reflective layer can be created on the prism surface by known methods.

[0078] This embodiment is a particularly robust and compact embodiment of the present invention because the first mirror is directly connected to the diffraction element, and thus mirror assembly or adjustment is not required. Implicitly, the prism surface encloses an angle α with the diffraction plane.

[0079] According to another embodiment of the present invention, the angle β is adjustable or adjusted via the first mirror.

[0080] According to another embodiment of the present invention, the first mirror can be tilted around at least one axis, and as a result, the angle β is adjustable or adjusted via the first mirror.

[0081] In connection with this embodiment, the first mirror is designed as a separate element that is arbitrarily designed such that the angle β is particularly adjustable.

[0082] According to a further embodiment of the invention, the light-transmissive diffraction grating arrangement comprises a second volume phase hologram grating that extends particularly along or on the diffraction plane, and the first and second volume phase hologram gratings have maximum diffraction intensities at different central wavelengths, particularly with respect to first-order diffraction, and in particular these central wavelengths are at a distance of at least the bandwidth of the first and second volume phase hologram gratings. In particular, it is ensured that a non-disturbed spectral separation of the two central wavelengths at the exit surface is guaranteed.

[0083] This embodiment enables an increased spectral range to be used in the system compared to a single volume phase hologram grating, i.e., a plurality of different wavelengths, particularly spectral lines, can be spectrally separated at the exit surface via the first diffraction element, and the first diffraction element does not require more installation space. For example, five spectral lines from the central wavelength and the bandwidth of the first volume phase hologram grating can be diffracted via the first volume phase hologram grating, and in addition to the central wavelength of the second volume phase hologram grating, a further five spectral lines within the bandwidth of the second volume phase hologram grating can be diffracted via the second volume phase hologram grating.

[0084] According to an embodiment of the invention, the first volume phase hologram grating has, for example, a central wavelength of 600 nm and a bandwidth of 10 nm.

[0085] According to an embodiment of the invention, the second volume phase hologram grating has, for example, a central wavelength of 620 nm and a bandwidth of 10 nm.

[0086] According to these two embodiments, the wavelength ranges of the first and second volume phase hologram gratings are separated from each other by 20 nm, where the central wavelength corresponds to the sum of the bandwidths of the first and second volume phase hologram gratings, so they do not overlap. It is expected that the greater the distance between the central wavelengths within the bandwidth, the less the interaction.

[0087] According to another embodiment of the present invention, the transmission diffraction grating arrangement comprises two or more volume phase hologram gratings, in particular the volume phase hologram gratings have different central wavelengths. According to the above principle, the central wavelengths can be spaced apart according to the bandwidth or more spectrally.

[0088] According to one embodiment of the present invention, the optical system has a second holographic arrangement comprising a second diffractive element formed by a second prism arrangement having at least a quadrangular bottom surface. In particular, the first and second holographic arrangements are arranged side by side along the optical axis of the first diffractive element, and the outer surface of the second prism arrangement has the following outer surface regions: f) a first, in particular planar, incident surface for the reference light, extending along the first incident plane, said incident surface being part of the first end face and the first incident surface being part of the first end face; g) a second, in particular planar, incident surface for the object light, extending along the second incident plane, the first incident surface and the second incident surface forming opposite outer surface regions of the second prism arrangement, and the second incident surface being part of the second end face; h) an exit surface extending along the exit plane through which the diffracted reference light and the diffracted object light can exit the second diffractive element; i) a prism surface facing the exit surface. Here, the light transmission diffraction grating arrangement is arranged in the second diffractive element, which extends along a diffraction plane intersecting the first incident plane and the exit plane between the first incident surface and in particular the exit surface of the second diffractive element, in particular such that the light transmission diffraction grating arrangement forms a triangular prism having the first incident surface and the exit surface of the second diffractive element, in particular where the diffraction plane forms a virtual outer surface region of the triangular prism. Here, the transmissive diffraction grating arrangement of the second diffraction element includes at least one first volume phase hologram grating, and the second holographic arrangement has a second, in particular planar, mirror with a second mirror plane on the side of the prism surface. The second mirror plane encloses an angle α' with the diffraction plane, and the prism surface encloses an angle ω'2 with the diffraction plane. At least one or both of the angles α', ω'2 are not equal to 45°, in particular the angle α' = 45° ± β' with β' > 0°, and in particular the angle ω'2 = 45° ± ρ'2 with ρ'2 > 0°. In particular, this is to achieve the maximum possible efficiency of the object light and the reference light in the second holographic arrangement.

[0089] Preferably, β' and / or ρ'2 is greater than 0.2°.

[0090] Preferably, β' and / or ρ'2 is less than 20°.

[0091] According to this embodiment of the invention, the reference light that impinges on the transmissive diffraction grating arrangement at an angle of 45° is diffracted by the transmissive diffraction grating arrangement in the direction of the prism surface of the second diffraction element, and due to the angle at which the reflected reference light impinges on the transmissive diffraction grating arrangement of the second diffraction element, it is diffracted again towards the first incident surface of the second diffraction element to a lesser extent, in particular at least 30% less, than the reference light that first impinged on the transmissive diffraction grating arrangement from the side of the first incident surface of the second diffraction grating. The remaining proportion of the reflected reference light is reflected by the second mirror so as to propagate through the transmissive diffraction grating arrangement towards the exit surface of the second diffraction element. The angles β' and ρ'2 are particularly selected in this way.

[0092] In the context of the present invention, in particular, it is provided that the reference light is incident on the diffraction element through the first incident surface of the second diffraction element, and in particular, it is incident in a collimated manner. Thus, the reference light is diffracted by the transmission diffraction grating arrangement towards the prism surface of the second diffraction element. The second mirror reflects the diffracted reference light backwards in the direction of the transmission diffraction grating arrangement, at an angle that can be calculated from Snell's law: in this way, at least a part of the reflected reference light is not diffracted by the transmission diffraction grating arrangement and is transmitted and propagated towards the exit surface of the second diffraction element. According to the present invention, the object light is incident on the second diffraction element through the second incident surface and is directly diffracted towards the exit surface by the transmission diffraction grating arrangement, where it is superimposed on, and in particular interferes with, the reference light on the second array detector.

[0093] In the context of the system according to the present invention, in particular, it is provided that the reference light is first irradiated onto the first holographic arrangement and the object light is first irradiated onto the second holographic arrangement.

[0094] According to this embodiment, a second holographic arrangement is disclosed that has substantially the same characteristics as the first holographic arrangement, and in particular, here the central wavelengths of the transmission diffraction grating arrangements of the first and second holographic arrangements are different.

[0095] According to a further embodiment of the present invention, the first volume phase hologram grating of the second holographic arrangement has a central wavelength different from that of the first and / or second volume phase hologram gratings of the first holographic arrangement.

[0096] In particular, the first and second holographic arrangements are arranged relative to each other such that their exit surfaces are parallel, and in particular, aligned with each other on the same plane (i.e., on the same flat surface), so that, for example, a single array detector can be used to record the interference pattern of the exit surfaces of both diffraction elements.

[0097] According to an alternative embodiment of the present invention, the first and second holographic arrangements are arranged relative to each other such that the exit surfaces of the first and second diffractive elements are aligned parallel to each other, where the exit surface of the first diffractive element is arranged on the side of the prism surface of the second diffractive element, and the exit surface of the second diffractive element is arranged on the side of the prism surface of the first diffractive element. In particular, the first holographic arrangement is rotated 180° about the optical axis, in particular, with respect to the second holographic arrangement. In particular, the diffraction planes of the first diffractive element and the second diffractive element typically enclose an angle of 90°.

[0098] This allows the use of two independent array detectors, providing the advantage of reducing the installation space problem related to the array detector.

[0099] According to a further embodiment of the present invention, the first and second holographic arrangements are arranged relative to each other such that the first entrance surface of the second diffractive element of the second holographic arrangement is arranged opposite, in particular parallel to, the second entrance surface of the first diffractive element of the first holographic arrangement, and in particular the diffraction planes of the first and second diffractive elements are optically parallel and aligned with each other.

[0100] It must be pointed out again that the expressions "opposite" and "parallel" should be understood in an optically functional sense and not necessarily in a strict geometric sense.

[0101] According to an embodiment of the present invention, the second diffractive element includes an optical axis that 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°.

[0102] 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.

[0103] All features, advantages and embodiments related to the first holographic arrangement, the first diffractive element, the first mirror or other components disclosed in relation thereto are applicable by analogy to possible embodiments of the second holographic arrangement, and it should be noted that for the purpose of further specifying the second holographic arrangement accordingly, they can be used for further details from the previous paragraph.

[0104] The second mirror comprises a second mirror plane extending along the reflective layer of the second mirror, in particular here the second mirror consists of the reflective layer.

[0105] Hereinafter, the angle of the second mirror with respect to the surface or plane always means the angle between the second mirror plane of the second mirror and the surface or the corresponding plane.

[0106] According to the invention, a plane extending along each surface of the second diffractive element, namely the first and second incident surfaces, the exit surface and the prism surface, can be assigned to each surface. When referring to the angle between two surfaces, the angle between the planes is also meant. Unless otherwise specified, the angle designation refers to the interior angle of the second prism arrangement.

[0107] According to an embodiment of the invention, the diffraction plane of the second diffractive element encloses an angle ω'1 with the first incident surface of the second diffractive element, in particular the angle is 30° ≤ ω'1 ≤ 60°, in particular ω'1 = 45°.

[0108] According to an embodiment of the invention, the diffraction plane of the second diffractive element encloses an angle ω'2 with the prism surface of the second diffractive element, in particular the angle is 30° ≤ ω'2 ≤ 60°, in particular ω'2 = 45° or ω'2 = 45° ± β', in particular ω'2 is selected such that the prism surface extends parallel to the mirror plane of the second mirror.

[0109] According to an embodiment of the invention, the diffraction plane of the second diffractive element encloses an angle ω'3 with the second incident surface of the second diffractive element, in particular the angle is 30° ≤ ω'3 ≤ 60°, in particular ω'3 = 45°.

[0110] According to an embodiment of the present invention, the diffraction plane of the second diffraction element encloses an angle ω'4 with the exit surface of the second diffraction element, and in particular, the angle is 30° ≤ ω'4 ≤ 60°, and in particular, ω'4 = 45° or ω'4 = 45° ± β', and in particular, ω'4 is selected such that the exit plane extends parallel to the mirror plane of the second mirror.

[0111] According to an embodiment of the present invention, the first and second incident surfaces of the second diffraction element are aligned parallel to each other.

[0112] According to an embodiment of the present invention, the prism surface and the exit surface of the second diffraction element are aligned parallel to each other.

[0113] According to another embodiment of the present invention, the angles ω'1 and ω'3 are equal to 45°. In this configuration, it is particularly possible to irradiate the reference light and the object light perpendicularly to the first and second incident surfaces because the incident surfaces are perpendicular to the optical axis of the second diffraction element.

[0114] According to an embodiment of the present invention, the first incident surface of the first diffraction element and the second incident surface of the second diffraction element are aligned parallel to each other.

[0115] According to an embodiment of the present invention, the angles β' and β are of different magnitudes.

[0116] The different angles of β' and β can be advantageously adjusted according to the central wavelength and bandwidth of the volume phase hologram gratings of the first and second diffraction elements.

[0117] According to another embodiment of the present invention, the angle β' is the same as β.

[0118] According to a further embodiment of the present invention, the angle ω'1 is the same as ω1.

[0119] According to a further embodiment of the present invention, the angle ω'2 is the same as ω2.

[0120] According to a further embodiment of the present invention, the angles ω'3 and ω3 are the same.

[0121] According to a further embodiment of the present invention, the angles ω'4 and ω4 are the same.

[0122] According to a further embodiment of the present invention, the first and second diffraction elements have the same shape and a specific size, that is, they are identical except for the optical characteristics of the transmissive diffraction grating arrangement.

[0123] An antireflection coating may be applied to the first and / or second incident surfaces of the first and / or second diffraction elements. Similarly, an antireflection coating may be applied to the exit surface and / or prism surface of the first and / or second diffraction elements.

[0124] In the state of the present invention, in particular, it is provided that the reference light is incident on the first diffraction element through the first incident surface of the first diffraction element, and is incident in a particularly collimated manner. There, due to the transmissive diffraction grating arrangement, it is partially diffracted towards the prism surface of the first diffraction element. Another part of the reference light is not diffracted by the transmissive diffraction grating arrangement of the first diffraction element due to its wavelength, but propagates in the direction of the second diffraction element, where it is diffracted towards the prism surface of the second diffraction element by the transmissive diffraction grating arrangement of the second diffraction element.

[0125] The same also applies particularly to the object light, which first enters from the second incident surface of the second diffraction element and then further propagates partially in the direction of the first diffraction element. At the exit surface of the first and second diffraction elements or the array detector, the reference light is then appropriately superimposed on the object light in a spectrally decomposed manner.

[0126] According to a further embodiment of the present invention, the system comprises a second light array detector such as a camera, and the second array detector is configured to detect the light emerging from the exit surface of the second diffraction element.

[0127] In particular, the second array detector is arranged on the side of the exit surface of the second diffraction element of the second holographic arrangement.

[0128] Furthermore, it is possible to provide that the second array detector is arranged directly on the exit surface of the second diffraction element of the second holographic arrangement while avoiding the formation of an air gap, in particular here 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.

[0129] Furthermore, the second array detector can be configured to convert the detection light into an electrical signal that can be evaluated by an evaluation device of a system such as a computer, at least with respect to the two-dimensional intensity distribution of the detection light on the second array detector.

[0130] The second array detector can provide a detection plane that extends along the array of the second array detector, for example along the pixel matrix of a camera.

[0131] According to a further embodiment of the invention, it is provided that the detection plane of the second array detector encloses an angle of ε’ = 45° ± η’ (η’ > 0°) with the diffraction plane, in particular here η’ = β’, and in particular the detection plane extends parallel to the second mirror. Furthermore, the exit plane runs parallel or in the same plane as the detection plane.

[0132] In particular, 0° < η’ < 20°.

[0133] According to one embodiment of the invention, it is possible to provide that the detection plane encloses such an angle with the diffraction plane of the second diffraction element that the light reflected from the detection plane impinges on the diffraction plane in a retro shape, so that the reflected light is completely or at least mostly diffracted by the transmission diffraction grating arrangement of the second holographic arrangement in the direction of the second entrance surface of the second diffraction element and exits therefrom. Thereby, "ghost" signals in the second array detector caused by multiple reflections are avoided.

[0134] The above embodiment of the present invention has the advantage that the light retroreflected from the second array detector reaches the second mirror again, is retroreflected from there to the second array detector again, and can prevent the generation of unnecessary signals there. By selecting the angle η', the light reflected by the second array detector can be diffracted completely or mostly toward the second incident surface of the second diffractive element by the first transmission grating arrangement.

[0135] According to a further embodiment of the present invention, it is provided that the bottom surface of the second prism arrangement forms a parallelogram, in particular here the diffraction plane of the second diffractive element extends along the diagonal extending to the bottom surface between the first incident surface and the exit surface of the second diffractive element, in particular here i) the first incident surface encloses an angle ω’1 = 45° ± ρ’1 with the diffraction plane of the second diffractive element, and the prism surface encloses an angle ω’2 = 45° with the diffraction plane of the second diffractive element, where ρ’1 > 0°, in particular ρ’1 > 0.2°, or ii) the first incident surface encloses an angle ω’1 = 45° with the diffraction plane of the second diffractive element, and the prism surface encloses ω’2 ± ρ’2 with the diffraction plane of the second diffractive element, where ρ’2 > 0°, in particular ρ’2 > 0.2°, or iii) the first incident surface includes an angle ω’1 = 45° ± ρ’1 with the diffraction plane of the second diffractive element, and the prism surface encloses an angle ω’2 = 45° ± ρ’2 with the diffraction plane of the second diffractive element, where ρ’1 > 0° and ρ’2 > 0°, in particular here ρ’1 > 0.2° and ρ’2 > 0.2°, or iv) the first incident surface encloses an angle ω’1 = 45° with the diffraction plane of the second diffractive element, the prism surface encloses an angle ω’2 = 45° with the diffraction plane of the second diffractive element, and the bottom surface is a particular parallelogram, i.e., a rectangle, preferably a square, in particular, the diffraction plane of the second diffractive element extends along the diagonal extending to the bottom surface between the first incident surface and the exit surface of the second diffractive element.

[0136] Each of the embodiments (i) to (iii) advantageously reduces the interference reflection that may occur when the reference light and / or the object light enters or exits the second prism arrangement.

[0137] In particular, embodiments ii) and iii) enable, for example, the second mirror to be placed directly on the prism surface of the second diffractive element when the angle ρ'2 = β' is selected.

[0138] Furthermore, in embodiments ii) and iii), the second array detector can also be placed directly on the exit surface, as already described above.

[0139] The angle between the detection plane and the diffraction plane is ε' = 45° ± η' with η' = β' = ρ'2, so that the detection plane extends parallel to the second mirror. Thus, the above-mentioned advantages for the array detector regarding the retro-reflection from the array detector in a retro-configuration and the advantages of the low-reflection geometry are particularly clear. Furthermore, the exit surface is essentially in the same plane as the detection plane.

[0140] In particular, when at least the second entrance surface is anti-reflective, the portion of the reference light retro-reflected at the second entrance surface (the portion reflected by the second array detector and diffracted through the transmission diffraction grating arrangement) can be ignored. Depending on the configuration of the light rays, there may also be an inclination angle at the exit surface (for example, in embodiment iii), thereby achieving additional retro-reflection suppression.

[0141] Embodiments i) and iii) advantageously enable polarization selection and / or reduction of reflection to be carried out by simultaneously using the Brewster angle and, if necessary, a polarization rotation element such as a λ / 2 plate. Thus, the reference light and the object light impinge on the first diffractive element at an angle (i.e., not equal to 90°) such that the reference light and the object light around the central wavelength impinge on the transmission diffraction grating arrangement at an angle of 45°, i.e., in a retro-configuration, and collide.

[0142] According to embodiment (iv), the bottom surface of the second prism arrangement is rectangular, in particular square.

[0143] Embodiment iv) provides a second diffractive element that is easy to manufacture. In this configuration, both the reference light and the object light can be irradiated perpendicular to their respective incident surfaces, and thus can impinge on a transmissive diffraction grating arrangement in a retro configuration. Further, the angle α' of the second mirror and, if necessary, the angle ε' of the second array detector can be easily adjusted.

[0144] According to a further embodiment of the invention, the second mirror is arranged on the prism surface of the second holographic arrangement.

[0145] This embodiment of the invention includes the possibility that the second mirror is formed as a reflective layer on the prism surface. The reflective layer can be created on the prism surface by known methods.

[0146] The second mirror is directly connected to the second diffractive element, and thus no mirror assembly or adjustment is required, so this embodiment enables a particularly robust and compact embodiment of the invention. Implicitly, the prism surface encloses an angle ω'2 = α' with the diffraction plane of the second diffractive element.

[0147] According to another embodiment of the invention, the angle β' is adjustable or adjusted via the second mirror.

[0148] According to another embodiment of the invention, the second mirror is tiltable by at least one axis, whereby the angle β' is adjustable or adjusted via the second mirror.

[0149] In connection with this embodiment, the second mirror is designed in particular as a separate element that is arbitrarily designed so that the angle β' can be adjusted.

[0150] According to a further embodiment of the present invention, the light transmission diffraction grating arrangement of the second diffraction element comprises a second volume phase hologram grating, which also extends particularly along or on the diffraction plane, and the first and second volume phase hologram gratings of the second diffraction element have maximum diffraction intensities at different central wavelengths, particularly for first-order diffraction, and in particular here these central wavelengths have a distance at least equal to the bandwidths of the first and second volume phase hologram gratings of the second diffraction element. In particular, it can be ensured that the spectral separation of these central wavelengths at the exit surface of the second diffraction element is guaranteed.

[0151] Compared with a single volume phase hologram grating, this embodiment enables an expansion of the spectral range used by the system, i.e., a plurality of different wavelengths, particularly spectral lines, and it is possible to perform spectral separation at the exit surface via the second diffraction element without the second diffraction element requiring more space.

[0152] For example, according to an embodiment of the present invention, the first volume phase hologram grating of the second diffraction element has a central wavelength of 940 nm and a bandwidth of 10 nm.

[0153] According to an embodiment of the present invention, the second volume phase hologram grating of the second diffraction element has, for example, a central wavelength of 960 nm and a bandwidth of 10 nm.

[0154] According to these two embodiments, the central wavelengths are separated from each other by 20 nm, which corresponds to the sum of the bandwidths of the first and second volume phase hologram gratings of the second diffraction element, so the wavelength ranges of the first and second volume phase hologram gratings do not overlap. The greater the distance between the central wavelengths within the bandwidth, the less interaction is expected.

[0155] According to a further embodiment of the present invention, the transmission diffraction grating arrangement of the second diffraction element comprises two or more volume phase hologram gratings, and in particular these volume phase hologram gratings have different central wavelengths. According to the above principle, these central wavelengths can be spectrally spaced by more than the bandwidth.

[0156] In combination with the first holographic arrangement, a second spectral range can be used for digital holography.

[0157] In particular, the transmission diffraction grating arrangements of the first diffraction element and the second diffraction element are configured for different central wavelengths, that is, here too, the central wavelengths of these transmission diffraction grating arrangements need to be spaced apart by more than the bandwidth according to the above principle.

[0158] According to a further embodiment of the invention, the second incident surface of the first diffraction element is connected to the first incident surface of the second diffraction element, in particular adhesively or welded, in particular here the first diffraction element is integrally formed with the first incident surface of the second diffraction element along its second incident surface.

[0159] This embodiment enables a compact and adjustment-free construction of the optical system because at least the first diffraction element and the second diffraction element have a strict arrangement and alignment with each other. The robustness is improved when the first and second mirrors are also designed integrally with the diffraction elements. Furthermore, both the first and second array detectors can be connected to their respective diffraction elements.

[0160] Depending on the type of connection of the respective incident surfaces, the connected incident surfaces may have an essentially virtual nature (for example because they are fused together). However, in particular, in the sense of the present invention itself, it is intended that a monolithic design of the first and second diffraction elements is included, at least within the scope of the interpretation and general understanding of those skilled in the art.

[0161] According to a further embodiment of the invention, the optical system has a collimation optical unit for the reference light on the side of the first incident surface of the first holographic arrangement, which has an optical axis running in the direction of the first incident surface of the first holographic arrangement, in particular the optical axis runs transversely, i.e. is offsettable, and the collimation optical unit is designed to collimate the laser light in the form of reference light before it enters through the first incident surface of the first diffractive element. In particular, the collimation optical unit is aligned with respect to its optical axis such that the reference light collimated thereby propagates along the optical axis of the first diffractive element after entering the first diffractive element and thereby impinges on the diffraction plane of the first diffractive element at an angle of 45°. The transverse offset can be designed such that the collimated light impinges centrally again on the exit surface or the detector array at an angle β with respect to the optical axis after being reflected by the reference mirror.

[0162] The term "collimate (collimation)" should in particular be interpreted such that the reference light has a minimum wavefront curvature for at least one wavelength. At different wavelengths, the convergence or divergence of the light rays or wave field increases as a function of the wavelength. Deviations induced chromatically from ideal collimation are also encompassed by the term "collimate" in the context of the present invention. Furthermore, deviations due to further adjustment and system tolerances need to be understood under the term "collimate". In particular, the term "collimate" means that in the context of the present invention 0° < ξ ≤ 2 * β or 2 * ρ2 and / or 0° < ξ ≤ 2 * β’ or 2 * It should also be understood as the convergence and / or divergence of light rays up to a divergence or convergence angle ξ in the range of ρ’2.

[0163] According to a further embodiment of the present invention, the optical system comprises an objective lens for object light having an optical axis extending in the direction of the second incident surface of the first and / or second holographic arrangement, wherein the objective lens is arranged in the optical system such that light propagating from the objective lens towards the second incident surface of the first and / or second diffractive element is collimated in the focal plane of the objective lens and / or near the focal plane towards the objective lens when the light is radiated, in particular reflected or scattered, in particular where said light is object light.

[0164] The term "near" with respect to the focal plane or focus (focus or focal point) in the context of this specification should be understood in particular as a tolerance specification, because deviations from the ideal optical arrangement of the components or from the ideal ray / wave curve of the light can be easily handled by the system of the present invention. In this context, the term "near" can be understood, for example, as a tolerance range with respect to the focal length of the objective lens. Thus, at the nominal focal length f, a deviation range of ±f / 5 is defined by the term "near". A similar understanding applies to the other components of the system.

[0165] According to the laws of imaging optics, light near or far from the focal plane of the objective lens diverges or converges when it impinges on the second incident surface. However, depending on the degree of divergence / convergence, this light may also contribute to imaging by means of digital holography.

[0166] In particular, the objective lens is aligned with the optical axis such that object light emitted from the focal point of the objective lens propagates along the optical axis of the first or second diffractive element after entering the first or second diffractive element and thereby impinges on the diffraction plane of the first or second diffractive element at an angle of 45°.

[0167] The objective lens can consist of one or more lenses or lens elements.

[0168] Also, according to the present invention, it should be noted that even when two holographic arrangements are provided in the system, only one objective lens is provided. Therefore, the objective lens is disposed at a position close to the side of the second diffractive element and its second incident surface.

[0169] According to another embodiment of the present invention, the system comprises the following components: - A laser light source designed to provide laser light having one or more central wavelengths, in particular the laser light source includes one or more lasers, and in particular each laser is configured to emit laser light including at least one central wavelength, and each laser emits at least one, preferably a plurality of laser lines in a wavelength range around the central wavelength of the laser, said laser light source, - A first optical fiber, in particular a polarization-maintaining single-mode fiber, configured to guide the laser light from the laser light source to the input aperture of the collimation optical unit, whereby the collimation optical unit can guide the collimated laser light in the form of reference light to the first holographic arrangement, said first optical fiber, - A second optical fiber, in particular a polarization-maintaining single-mode fiber, configured to guide the laser light from the laser light source to the output aperture of the collimation optical unit, whereby the detected object is irradiated with laser light in the form of object light, said second optical fiber.

[0170] This embodiment enables control of the polarization of the reference light and the object light. In particular, the volume phase hologram grating diffracts s-polarized light significantly more than p-polarized light, whereby the system is specifically configured such that the reference light and the object light are particularly s-polarized after exiting the first and second optical fibers.

[0171] According to a further embodiment of the invention, the system comprises a fiber splitter, in particular a polarization-maintaining fiber splitter, configured to split the laser light of the laser source and couple it to at least one first and second optical fiber, in particular where the fiber splitter and the at least one first and second optical fiber are comprised in an integrated optical element.

[0172] According to one embodiment of the present invention, the system has an imaging optical system designed to project the object light, in particular the object light emerging from the second fiber, in particular in the form of an intensity pattern, in particular onto an object to be detected, where the intensity pattern consists of at least one illuminated area, preferably consisting of a multiplicity of discretely illuminated areas, in particular the illuminated areas of the pattern are point-shaped or circular, and where the object light, in particular reflected by the object, is detected by the objective lens.

[0173] This type of intensity pattern allows multiple object regions to be recorded and evaluated in parallel using multiple wavelengths.

[0174] Complete detection can be performed by moving the pattern over the object so that the object is optically scanned and detected area by area.

[0175] In this way, the surface of the object can be scanned with an intensity pattern, thereby generating depth and lateral position information for each region via the first and / or second holographic arrangements, and consequently the object surface can be scanned with the object beam to generate 3D information.

[0176] According to a further embodiment of the invention, the system has a housing, in particular a watertight housing, which comprises the first and / or second holographic arrangement, the first collimation optical unit and the objective lens, in particular the laser light source being arranged outside the housing and connected to the housing via at least a flexible fiber optic line.

[0177] In particular, the laser light source may be arranged either inside or outside the housing and is configured to couple the reference light and the coherent object light generated from the laser light source into at least one first and second fiber via a fiber splitter, preferably inside the housing.

[0178] Such an optical system with a laser light source and a fiber splitter can be integrated into a relatively compact module, where at least one reference arm of the system, i.e., a part of the system through which the reference light is guided, and in particular the first and / or second holographic arrangements can form part of the integrated module. Such a system is suitable for minimally invasive medical applications as it requires minimal installation space within the housing.

[0179] According to a further embodiment of the invention, the system is configured to provide laser light comprising wavelengths from at least two wavelength ranges, wherein a first wavelength range of the two wavelength ranges is arranged around a central wavelength, in particular in the form of spectral lines, for example, in the form of a laser line outside the second wavelength range, the second wavelength range is arranged around a different central wavelength, this central wavelength being provided with two wavelength ranges and wavelengths, in particular in the form of spectral lines, and in particular the first and second wavelength ranges each have a spectral range of 50 nm or less, in particular 15 nm or less, and in particular the spectral lines of the wavelength ranges each have a line width of 0.5 nm or less, in particular 0.2 nm or less.

[0180] In particular, such a system has two volume phase hologram gratings, each of which is configured for one of the two central wavelengths, i.e., the volume phase hologram grating is configured to diffract one central wavelength while leaving the other central wavelength undiffracted.

[0181] The two volume phase hologram gratings can both be arranged on the first diffractive element or the second diffractive element. Alternatively, each of the two diffractive elements can comprise one of these volume phase hologram gratings.

[0182] Another aspect of the present invention relates to a human or veterinary medical endoscope system comprising an optical system according to the present invention for generating a digital holographic image.

[0183] The endoscope system can be configured to create a holographic video record and display a 3D representation of the detected object on a screen.

[0184] Description of the Drawings Further features and advantages of the present invention will be described below with reference to the description of the figures of the exemplary embodiments. The angles and lengths may be exaggerated or presented conservatively in the figures and may only serve to illustrate the invention. This is particularly advantageous when each incident surface of the diffractive element is larger than its exit surface.

Brief Description of the Drawings

[0185]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

[0186] In FIG. 1, an exemplary general embodiment of a system 1 according to the present invention is schematically shown as a 2D cross-section.

[0187] The optical system 1 has a first holographic arrangement 2, and the first holographic arrangement 2 includes a first diffractive element 3, a first mirror 35, and a first array detector 37.

[0188] The system 1 further has a collimation optical unit 5 and an objective lens 6 (see FIGS. 5 and 6). The laser light source 8 of the system 1 (see FIGS. 5 and 6) is configured to supply the reference light 100 and the object light 200 of the system 1.

[0189] A modified version of the system can include a second holographic arrangement 2', and thus the second holographic arrangement 2' includes 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 and functionally connected in the same way, the corresponding reference signs of the elements and components are also shown for the second holographic arrangement 2' in FIGS. 1 to 4. The reference signs of the second holographic arrangement 2' correspond to the reference characters with a "'" added to those of the first holographic arrangement 2. In the following text, the first holographic arrangement 2 is described first, and thereby the same or at least similar things apply to the second holographic arrangement 2'.

[0190] The first holographic arrangement 2 includes a prism arrangement 4 of a solid (e.g., glass or polymer), and the prism arrangement 4 forms the first diffractive element 3. In this case, it has a rectangular bottom surface, and its ends are surrounded by the outer surfaces of the prism arrangement 4. The outer surfaces include four outer surface regions, namely the first and second incident surfaces 31, 32 (which can each be part of the end face of the first diffractive element 3), an exit surface 33, and a prism surface 34. The first and second incident surfaces 31, 32 and the exit surface 33 are transparent, except for the prism surface 34 which can also be designed to be reflective.

[0191] Each face of the prism arrangement 4 can be assigned a corresponding plane (each shown as a dotted line) that extends along the respective face. Thus, the first incident plane 310 extends along the first incident face 31, the second incident plane 320 extends along the second incident face 32, the exit plane 330 extends along the exit face 33, and the prism plane 340 extends along the prism face 34.

[0192] The first prism arrangement 4 further includes a transmissive diffraction grating arrangement 36 that extends along the diffraction plane 360 in the first diffraction element 3. The transmissive diffraction grating arrangement 36 includes at least a first volume phase hologram grating.

[0193] The first mirror plane 350 extends along the reflective surface of the first mirror 35 through the first mirror 35. The first mirror 35 is disposed on the side of the prism face 34.

[0194] Between the first and second incident faces 31, 32, the optical axis OA of the first diffraction element 3 can be defined, which intersects the diffraction plane 360 at an angle of 45°.

[0195] The first holographic arrangement 2 is configured such that the first mirror plane 350 encloses an angle α with the diffraction plane 360 of the first diffraction element 3, and the prism plane 340 encloses an angle ω2 with the diffraction plane 360, where the reference light 101 diffracted in the direction of the prism face 34 by the transmissive diffraction grating arrangement 36 is reflected by the first mirror 35, and the reflected reference light 102 is diffracted again towards the first incident face 31 at a ratio less than, in particular less than 30%, of the reference light 100 that first impinges on the transmissive diffraction grating arrangement 36, specifically due to the angle of incidence of the reflected reference light 102 on the transmissive diffraction grating arrangement 36, and the remaining ratio of the reflected reference light 102 propagates through the transmissive diffraction grating arrangement 36 in the direction of the exit face 33, and either both or only one of these angles α, ω2 is selected.

[0196] Based on the Littrow configuration, i.e., when the collimated reference light 100 radiated to the diffraction element 3 propagates along the optical axis OA of the first diffraction element 3, this goal is particularly well achieved when the angle is α = 45° ± β, β ≠ 0°, and / or the angle ω2 = 45° ± ρ2, ρ2 ≠ 0°. In particular, the angle β and / or the angle ρ2 must have an absolute value in the range of 0.2° to 20°, particularly in the range of 0.5° to 20°, so that α is in the range of 25° to 44.5° or 45.5° to 65°, and / or ω2 is in the range of 25° to 44.5° and 45.5° to 65°.

[0197] To achieve the desired effect, it is sufficient if either the first mirror 35 or the prism surface 34 forms an angle α or ω2 that is not equal to 45°. However, as shown in FIG. 1, both the first mirror 35 and the prism surface 34 can surround an angle other than 45° with the diffraction plane.

[0198] According to the present invention, in particular, it is provided that the collimated reference light 100 collides with the transmissive 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 achieved by the position and direction of the collimation optical unit 5 (not shown in FIG. 1).

[0199] According to the present invention, the reference light 100 can include at least a central wavelength 100-1, and at the central wavelength 100-1, the transmission diffraction grating arrangement 36 diffracts a first-order diffraction of 90° with respect to the optical axis OA of the diffraction element 3 in the retro configuration, whereby the diffracted reference light 102 of this wavelength 100-1 propagates away from the transmission diffraction grating arrangement 36 at 45°. Depending on the angle ω2 of the prism surface 34 and the angle α of the first mirror 35, the diffracted reference light 102 of the central wavelength 100-1 reflected by the mirror 35 no longer collides with the transmission diffraction grating arrangement at an angle of 45°. When the angle χ at which the reflected reference light 102 collides with 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 being diffracted and collides with the exit surface 33 of the first diffraction element 3, where it is detected by the first array detector 37, for example a camera.

[0200] On the other side of the diffraction element 3, i.e., on the side of the second entrance surface 32, laser light in the form of object light 200 is projected onto an object 300 (see FIGS. 5 or 6) detected by the imaging optical unit 12 (see FIGS. 5 or 6) of the system 1. The object light 200 is projected onto the object 300 in the form of an intensity pattern, where the intensity pattern (not shown) consists of a number of laterally offset and non-overlapping spots in the lateral direction, i.e., a number of illuminated regions separated from each other by non-illuminated regions.

[0201] The object light 200 from the illuminated regions of the intensity pattern is reflected or backscattered by the object 300 in the direction of the holographic arrangement 2. To collect the object light 200, the system 1 has an objective lens 6. In the operation according to the present invention, the objective lens 6 is held at a distance approximately corresponding to the focal length of the objective lens 6 from the intensity pattern. In this way, the object light 200 of the intensity pattern is collimated. For complete collimation, the object region is estimated at the focus of the objective lens 6. In regions outside the focal plane, i.e., regions with different z distances, a slightly curved wave field is generated. Mathematical considerations of such wave fields are well known to those skilled in the art. Therefore, an image via a radiation vector is mainly used.

[0202] The collimated object light 200 impinges on the second incident surface 32 of the first diffractive element 3 (or, if the system has two diffractive elements 3, 3', on the second incident surface 32' of the second diffractive element 3', see, for example, FIG. 6) at an angle of approximately 45° with respect to the transmission diffraction grating arrangements 36, 36' of the diffractive elements 3, 3', i.e., in a retro configuration, so as to collide. For this purpose, depending on the configuration of the diffractive elements 3, 3', the objective lens 6 can have a specific position and orientation with respect to the optical axis OA of the diffractive elements 3, 3': for example, if the second incident surfaces 32, 32' of the diffractive elements 3, 3' form an angle other than 90° with the optical axis OA of the diffractive elements 3, 3', the optical axis of the objective lens 6 can be angled with respect to the optical axis OA of the diffractive elements 3, 3', such that after the collimated object light 200 enters the diffractive elements 3, 3', it propagates along the optical axis OA of the diffractive elements 3, 3', thereby ensuring a retro configuration. The transmission diffraction grating arrangement 36 then diffracts the object light 201 towards the exit surface 33, where it is superposed with the diffracted and reflected reference light 102 to form an interference pattern that can be detected by the first array detector 37. The 3D information of the object 300 can be calculated from the interference pattern by known methods.

[0203] The first array detector 37 can be arranged along its detection plane 370 at an angle ε = 45° ± η not equal to 45° with respect to the diffraction plane 360. This enables suppression of reflections in an advantageous manner.

[0204] In a general variant of the holographic arrangement 2, 2' (as shown, for example, in FIG. 1), the outer surface region of the first diffractive element 3 can enclose an angle other than 45° with respect to the diffraction plane 360. This can also have a beneficial effect in terms of interference reflections from the surface. In particular, the following angles are shown in FIG. 1: Angle ω1. This is enclosed by the first incident surface and the diffraction plane, and ω1 can be in the range of 30° to 60°. Angle ω2. This is enclosed by the prism surface and the diffraction plane. Any angular deviation from 45° of angle ω2 is described by angle ρ2. Angle ω3. This is enclosed by the second incident surface and the diffraction plane, and ω3 can be in the range of 30° to 60°. Angle ω4. This is enclosed by the exit surface and the diffraction plane, and ω4 can be in the range of 30° to 60°. Angle α. This is enclosed by the first mirror and the diffraction plane. Any angular deviation from 45° of angle α is described by angle β. Angle ε. This is enclosed by the first array detector, more precisely, the detection plane of the array detector and the diffraction plane. Any angular deviation from 45° is described here by angle η.

[0205] As already described at the beginning, the specification of the angles, the indicated angular relationships between the surfaces and planes of the first holographic arrangement 2, and the mode of operation of the first holographic arrangement 2 (e.g., the retro arrangement) can be transferred in a similar manner to the second holographic arrangement 2'. This means that, for example, instead of the first diffraction element 3, there is a second diffraction element 3', instead of the first mirror 35, a second mirror 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'. For this reason, the corresponding angle specifications and reference symbols of the components of the second holographic arrangement 2' are also appropriately shown in FIG. 1, and for which, the same essentially applies to the first holographic arrangement 2 with respect to its angles and mode of operation. Specifically, this means the following: Angle ω'1 is enclosed by the first incident surface 31' or the incident plane 310' of the second diffraction element 3' and the diffraction plane 360', and ω'1 can be in the range of 30° to 60°. Angle ω'2 is enclosed by the prism surface 34' of the second diffraction element 3' and the diffraction plane 360'. Any angular deviation from 45° of angle ω'2 is described by ρ'2. The angle ω’3 is enclosed by the second incident surface 32’ of the second diffraction element 3’ and the diffraction plane 360’, and ω’3 can be in the range of 30° to 60°. The angle ω’4 is enclosed by the exit surface 33’ of the second diffraction element 3’ and the diffraction plane 360’, and ω’4 can be in the range of 30° to 60°. The angle α’ is enclosed by the second mirror 35’ of the second diffraction element 3’ and the diffraction plane 360’. Any angular deviation from 45° of the angle α’ is described by β’. The angle ε’ is enclosed by the second array detector 37’ of the second diffraction element 3’, more precisely, by the detection plane 370’ of the second array detector 37’ and the diffraction plane 360’. Any angular deviation from 45° is described by the angle η’.

[0206] However, when the second holographic arrangement 2’ is provided in the system 1, it is advantageous for the first incident surface 31’ of the second diffraction element 3’ to extend parallel to the second incident surface 32 of the first diffraction element 3, whereby the two incident surfaces 32, 31’ can be connected to each other, in particular without forming an air gap, whereby the diffraction planes of the transmission diffraction grating arrangements 36, 36’ of the first and second diffraction elements 3, 3’ either run parallel to each other (see, for example, FIG. 6) or enclose an angle of 90° with respect to each other (not shown). In particular, in one embodiment having two holographic arrangements 2, 2’, the first incident surface 31’ of the second diffraction element 3’ and the second incident surface 32 of the first diffraction element 3 are each provided to form an angle of 45° with their respective diffraction planes 360, 360’, that is, to be perpendicular to the respective optical axes OA of the diffraction elements 3, 3’ (see FIG. 6).

[0207] The following also describes the laser light and the resulting reference light 100 and object light 200. In particular, the present invention provides that the laser light includes a plurality of wavelengths. It is particularly advantageous when a number of distinct spectral lines 106 or 206 (see, for example, FIGS. 2 and 5), such as laser lines in the laser light, are included in the wavelength range around the central wavelengths 100-1, 100-2 or 200-1, 200-2. For example, the range of the width of the spectral line is at most 0.5 nm, preferably less than 0.1 nm. On the other hand, the wavelength range can have a general width of at most about 10 nm. The laser light and the transmissive diffraction grating arrangements 36, 36' of the system 1 are particularly adjusted relative to each other. Since the transmissive diffraction grating arrangements 36, 36' comprise at least one volume phase hologram grating, the following can first be noted. The volume phase hologram grating has a bandwidth around one central wavelength, ideally the central wavelength of the laser light, and diffracts the incident light to a sufficient extent in the retro configuration within the bandwidth. Here the central wavelength is 2 * is "completely" diffracted at 45° = 90°.

[0208] Lasers having slightly different wavelengths around the central wavelength are known as frequency comb lasers and can be generated, for example, using quantum dot technology. These are used, for example, for frequency multiplexing in broadband transmission in telecommunication. Alternatively, it is also conceivable to closely integrate a single-mode stripe laser having slightly different wavelengths on a laser diode module and combine the output apertures to form a laser light source module via a specially integrated optical chip. A fiber splitter can also be part of such a module. Such a combination may already be considered in the laser diode chip itself, which would simplify the manufacturing process. Briefly, a laser light source having a central wavelength can be mentioned.

[0209] Multiple wavelengths around the central wavelength are advantageous or even necessary to obtain clear depth information regarding the phase of the individual wavelength signals for each object point or each illumination spot. Lateral object information is generated from the hologram frequency, for example by Fourier transform. In combination, a 3D object is in principle recognized, which is in principle known to the person skilled in the art.

[0210] In the following, the advantageous properties of the volume phase hologram grating will be described in detail.

[0211] When the reference light or object light having the diffraction grating frequency f gr impinges on the volume phase hologram grating, the light of the central wavelength λ0 is, as already explained, in the retro arrangement, exactly at 90° (= 2 * 45°) diffracted in the direction of the prism surfaces 34, 34' or the exit surfaces 33, 33'. With slightly different wavelengths (multiple lines in the wavelength range of the laser light), the following angular separation Δθ is obtained in this retro arrangement:

Equation

[0212] For a central wavelength of 660 nm, this is 3 mrad / nm, and for 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 only Δθ = 0.6 mrad. When the wavelength change is positive (λ0 + Δλ), the diffraction angle increases to 90° + Δθ.

[0213] In the case of the object light and the reference light, the volume phase hologram grating diffracts the reference light and the object light in opposite directions. That is, it results in twice the angle, i.e., 2 * Δθ with respect to Equation (1).

[0214] The advantage of the volume hologram over a purely planar diffraction grating lies in the selectivity in terms of angle and spectrum. Both characteristics are used in the manner already described.

[0215] Therefore, considering the above example, for a wavelength change of 200 pm, 2 * 0.6 mrad = 1.2 mrad would be estimated. With a typical resolution limit of 0.1 mrad per pixel of the array detector, this means that there is an offset of at least 10 pixels for adjacent spectral lines having the next higher / lower wavelength. The refractive index of the prism arrangement increases the above angle again by a factor n when the light beam is diffracted away from the vertical line and exits towards the array detector. Since the refractive index is usually in the range of 1.5 - 1.9, a corresponding increase is expected. Prisma

[0216] From these, it becomes clear that the transmission diffraction grating arrangement using the volume phase hologram grating of the retro - configuration in the proposed prism arrangement already has particularly advantageous characteristics for the spectral separation of a large number of spectral lines. It should be noted that the angular division described by Equation (1) comes only from the dispersion of the volume phase hologram grating and not from the angle α or ω2.

[0217] The angle α or the angle ω2 causes the reference light reflected and diffracted by the first mirror to collide at an angle in the transmission diffraction grating arrangement, at which angle most of the reference light (especially > 70%) is no longer diffracted and propagates further in the direction of the exit surface, thus bringing about a reference light with a sufficiently high intensity at the exit surface to form an interference pattern with the object light. The corresponding light path is schematically shown in FIG. 1. The same idea also applies to the second holographic arrangement of this system.

[0218] In the following discussion, for the sake of explanation, it is assumed that the first mirror 35 is arranged on the prism surface 34, and thus the angles α and ω2 are the same.

[0219] ​In this case, the reference light with a central wavelength λ0, which is irradiated on the retro configuration and reflected by the first mirror, collides with the diffraction plane at an angle of 45° ± 2β. Therefore, it has an angle of 2β with respect to the diffracted object light. The wavelength shift portion λ0 ± Δλ of the reflected reference light has an angle of 2Δθ + 2β compared to the corresponding wavelength shift portion λ0 ± Δλ of the diffracted object light. The different angle 2Δθ causes a corresponding hologram frequency on the camera chip, which can be assigned to multiple wavelengths by Fourier transform. The number of these wavelengths can be at least two, but can also be in the dozens. Since the latest camera chips can have thousands of pixels per dimension, there still exists a sufficient spatial frequency (angle) for those skilled in the art to freely assign the lateral pixels within the object via the Fourier transform that is known to them. When the array detector is separated from the exit surface of the diffraction element through an air gap, the angle increases again by the refractive index coefficient of the prism arrangement, as already explained above.

[0220] The tilt angle β can be approximately derived as follows from the type of dispersion relation of the volume phase hologram grating having the central wavelength λ0, the refractive index n (about 1.5) of the grating, and the thickness D of the volume phase hologram grating:

Equation

[0221] The use of a volume phase hologram grating has the further advantage that the object beam within the FWHM is strongly diffracted towards the exit surface. This can also be achieved with a "classical" diffraction grating, but the reflected reference beam is strongly diffracted in the direction of the first incident surface and is only available for interference formation at the exit surface with weak signal intensity. Therefore, in this case, it is necessary to reduce the diffraction efficiency of the diffraction grating (e.g., by 50%), which will then result in attenuation of the diffracted object beam towards the exit surface.

[0222] Another advantage of the volume phase hologram grating is that it is possible to create two volume phase hologram gratings with different central wavelengths arranged relative to each other, or to stack and arrange two of these relatively thin volume phase hologram grating structures on top of each other.

[0223] In FIGS. 2 to 6, some particularly advantageous embodiments of the optical system 1 are illustratively shown. The same reference signs denote the same elements, components, or functions.

[0224] FIG. 2 shows an advantageous embodiment of the first or second holographic arrangement 2, 2' according to the invention.

[0225] Referring to the introduced angular relationships and reference signs, the angles ω1, ω3, ω4 of the diffraction element (or, in the case of the second diffraction element, the angles ω'1, ω'3, ω'4) are 45°.

[0226] Furthermore, the angles ω2 and β (or ω’2 and β’) are identical, and the first or second mirrors 35, 35’ are formed in the form of a reflective layer on the prism surfaces 34, 34’ of the diffraction elements 3, 3’. This has the advantage of creating a robust and compact optical system 1. Furthermore, this configuration of the first and second holographic arrangements 2, 2’ enables a continuous arrangement in the optical system according to the invention (see Fig. 6), where the first and second diffraction elements 3, 3’ having the incident surfaces 32, 31’ respectively can be arranged adjacent to each other without an air gap.

[0227] The first or second array detectors 37, 37’ are also directly fixed to the exit surfaces 33, 33’ of the diffraction elements 3, 3’, so that there is also no air gap here.

[0228] In particular, the prism arrangements 4, 4’ in Fig. 2 may be formed as one piece, or may be formed from two triangular prisms connected to each other along the diffraction planes 360, 360’ via transmissive diffraction grating arrangements 36, 36’.

[0229] Fig. 2 shows the optical path of the reference light in the diffraction element 3 or 3’ as an example of the reference light. The reference light includes two further spectral lines 106 around the central wavelength, whereby, for example, the boundary values of the wavelength range around the central wavelength of the laser lights 100, 200, and a volume phase hologram grating adapted thereto are formed. Starting from the reference light 100, the spectral lines are diffracted smaller or larger than the central wavelength by the transmissive diffraction grating arrangements 36 or 36’. Therefore, the light rays of the spectral lines 106 enclose an angle other than 45° with the diffraction plane after being diffracted by the transmissive diffraction grating arrangements 36, 36’. Due to the angular positions α, α’ of the mirrors 35, 35’, the reflected spectral lines diverge further from the light ray 102 around the light ray of the central wavelength 102 and impinge on the exit surfaces 33, 33’ at different lateral positions.

[0230] The same applies to the object light 200, which is diffracted by the transmission diffraction grating arrangements 36, 36'. The spectral lines 206 of the laser light also result in a dispersion decomposition of the object light 200 into spectral lines 206 that are diffracted to different extents by the transmission diffraction grating arrangements 36, 36'.

[0231] FIG. 3 shows a modified form of the first or second holographic arrangement 2, 2' of the optical system 1, where the prism arrangements 4, 4' have a bottom surface in the form of a parallelogram, and where the first and second incident surfaces 31, 32 (or 31', 32') enclose the diffraction planes 360, 360 at angles ω1, ω3 (or ω'1, ω'3) of 45° respectively, that is, perpendicular in particular to the optical axis OA of the diffraction elements 3, 3'. The exit surfaces 33, 33' and the prism surfaces 34, 34' also extend parallel, so that the angles ω2 and ω4 (or ω'2 and ω'4) are identical and less than 45°. Similarly, in this exemplary embodiment, the mirrors 35, 35' are arranged directly on the prism surfaces 34, 34' (i.e., without forming a gap), so that the angle α is equal to the angle ω2 (therefore β = ρ2), or the angle α' is equal to the angle ω'2 (therefore β' = ρ'2). The mirrors 35, 35' can be designed, for example, as a reflective layer vapor-deposited on the prism surfaces 34, 34' using a suitable method.

[0232] Also, the array detectors 37, 37' are arranged directly on the exit surfaces 33, 33', so that the angles ε and ω4 (or ε' and ω'4) are also identical. As a result, the following angular relationships are obtained: α = ω2 = ω4 = ε < 45° or α' = ω'2 = ω'4 = ε' < 45° or α = ω2 = ω4 = ε > 45° or α' = ω'2 = ω'4 = ε' > 45°

[0233] This embodiment is characterized by a simple shape that simultaneously improves the suppression of interference signals (ghosts) on the array detectors 37, 37'. This is because, as indicated by the dotted arrows 103 and 104, light that may be reflected by the array detectors 37, 37' due to the specific angular relationship of the surfaces of the holographic arrangements 2, 2' collides again at an angle of 45° with respect to the transmission diffraction grating arrangements 36, 36', diffracts again in the direction of the first incident surfaces 31, 31' with high diffraction efficiency, and is guided out of the diffraction elements 3, 3'.

[0234] Similar to FIG. 3, FIG. 4 shows an extended variant of the first or second holographic arrangement 2, 2'. Here too, the prism arrangements 4, 4' have a parallelogram as the base, and in contrast to FIG. 3, the angles between the first and second incident surfaces ω1 and ω3 (or ω'1 and ω'3) are not equal to 45°. This ensures that the incident surfaces 31, 32 (or 31', 32') do not extend perpendicular to the optical axis OA of the diffraction elements 3, 3', which shows an advantageous deflection of potential retroreflections at these surfaces (see arrow 105).

[0235] It should be noted that this shape can also be used in a system 1 comprising two holographic arrangements 2, 2' arranged in series by arranging the first incident surface 31' of the second diffraction element 3' without an air gap on the second incident surface 32 of the first diffraction element 3.

[0236] FIG. 5 shows an optical system 1 according to an embodiment of the invention. Here, in addition to the holographic arrangements 2, 2' of the previous figures, further components of the system 1 are also schematically represented.

[0237] First, the system of FIG. 5 comprises a laser light source 8 (dotted box) having only one laser 81, which provides laser light around the central wavelength and is designed to have additional spectral lines within the wavelength range in some cases. A laser light source or laser suitable for this purpose has already been disclosed as an example in the previous paragraph. The laser light source 8 can also be configured to emit polarized laser light with a specific polarization. Then, the laser light is split by a beam splitter into a reference light 100 and an object light 200. The splitting ratio can be made unequal to 50:50, and preferably a larger proportion, for example 70% or 90% of the laser light, is assigned to the object light.

[0238] The beam splitter can be integrated into a fiber splitter 13 configured to connect the reference light 100 to a first polarization-maintaining single-mode fiber 10 and the object light 200 to a second polarization-maintaining single-mode fiber 11. Since one end of the first fiber 9 is arranged at the focus or at least in the focal plane of the collimation optical unit 5 of the optical system 1, the reference light 100 is separated from the fiber 9 by a corresponding decoupling lens or aperture 10 if necessary, and the wavefront of the reference light is collimated by the collimation optical unit 5. The collimation optical unit 5 has an optical axis, which in the example of FIG. 5 extends on the same straight line as the optical axis OA of the first diffraction element 3. If the first incident surface 31 forms an angle unequal to 45° with the diffraction plane 360, the optical axis of the collimation optical unit 5 should be 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 collimation optical unit 5 is shifted 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 mirror and thus overlaps with the corresponding light rays 201, 206 of the object light at the array detector 37. The further propagation process in the first holographic arrangement 2 has already been discussed in detail and will not be repeated here.

[0239] The object light 200 propagates along the second optical fiber 11 after the fiber splitter 13 and is emitted by the imaging optical unit 12 at the end of the second fiber 11 so that the intensity pattern is projected onto the object 300 to be measured.

[0240] The intensity pattern has at least one illumination spot on the object 300, but preferably has a plurality of spots that are laterally separated from each other by non-illuminated regions of the pattern.

[0241] The object light 200 from the pattern reflected by the object 300 is captured by the objective lens 6 of the system 1 and, when it comes from the focal plane of the objective lens 6, is collimated and guided towards the second entrance surface 32. There, the object light 200 enters the diffraction element 3, is diffracted towards the exit surface 33, where it is superimposed with the reference light 102. This superposition is recorded by the first array detector 37 and transferred to the computer 400, for example in the form of digital data, for further processing. On the computer 400, the wave field of the object light can be reconstructed, thereby generating a 3D representation of the illuminated region of the object.

[0242] These laterally offset spots in the intensity pattern result in each spot on the first array detector 37 still being individually analyzable, regardless of the spectral splitting at the first array detector 37. In order to obtain complete information about the object, the object needs to be scanned using the intensity pattern, so that ideally each part of the object is illuminated by a spot at least once and detected by the first array detector 37.

[0243] As already shown in FIG. 2, FIG. 5 also shows the optical paths of the spectral lines 106 and 206 from the wavelength range around the central wavelengths of the reference light ray 102 and the object light ray 201, which is advantageously determined by the dispersion characteristics of the transmission diffraction grating arrangement 36 and the volume phase hologram grating.

[0244] The holographic arrangement shown in FIG. 5 can be replaced by another previously disclosed holographic arrangement 2 without affecting system 1, whereby it is necessary to appropriately adjust the position and orientation of the collimation optical unit 5 and / or the objective lens 6 so that system 1 assumes a retro configuration.

[0245] FIG. 6 shows an embodiment of system 1 of FIG. 5, which, in contrast to the system of FIG. 5, comprises first and second holographic arrangements 2, 2'. The first holographic arrangement 2' comprises a first volume phase hologram grating 36 configured for a first central wavelength 100-1, 200-1, and the second holographic arrangement 2' comprises a volume phase hologram grating 36' configured for a second central wavelength 100-2, 200-2. This means that the volume phase hologram grating 36 of the first diffractive element 3 diffracts the reference light and the object light around the first central wavelength 100-1, 200-1 in the retro configuration and allows the light around the second central wavelength 100-2 to pass through without diffraction, while the volume phase hologram grating 36' of the second diffractive element 3' diffracts the reference light and the object light around the second central wavelength 100-2, 200-2 in the retro configuration and allows the light around the first central wavelength 200-1 to pass through without diffraction. This enables an expansion of the spectral range available for digital holography.

[0246] Note in FIG. 6 that, for reasons of clarity, the optical paths of the spectral lines 106 and 206 are not shown around their respective central wavelengths 100-1, 100-2, 200-1, 200-2.

[0247] To supply laser light having two center wavelengths, the laser light source 8 includes two lasers 81 and 82. Here, the first laser 81 is configured to emit laser light around the first center wavelengths 100-1 and 200-1 (and in particular further spectral lines in the wavelength range around the first center wavelength), and the second laser 82 is configured to emit laser light around the second center wavelengths 100-2 and 200-2 (and in particular further spectral lines in the wavelength range around the second center wavelength). The light of the two lasers 81 and 82 is coupled to the first and second polarization-maintaining fibers 9 and 11 by a fiber splitter 13 as already described in FIG. 5. If the bandwidths of the fibers 9 and 11 are not sufficient to transmit both center wavelengths in single mode, separate fibers can also be used for each center wavelength, which may be coupled at their ends via a beam splitter, or may be arranged slightly laterally offset before being projected onto the object 300 via the imaging optical unit 12 or before being collimated via the collimation optical unit 5.

[0248] In the example of FIG. 6, the first diffractive element and the second diffractive element 3 and 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, thereby particularly avoiding a refractive index jump at the transition between the diffractive elements 3 and 3'. For this purpose, the two incident surfaces 31' and 32 run parallel to each other. Depending on the requirements, the first and second mirrors 35 and 35' enclose angles α and α', respectively, that are the same as or different from the respective diffractive planes 360 and 360'.

[0249] Each diffractive element 3 and 3' is provided with its own array detector 37 and 37', respectively, and may have an optical filter (not shown) connected upstream to block stray light or reflections from wavelength ranges other than the intended ones.

[0250] The signals recorded at the respective exit surfaces 33, 33’ by the first and second array detectors 37, 37’ are supplied to the same computer 400, which can calculate a 3D representation of the object from the information.

[0251] The system 1 according to the invention enables digital holography in a compact and robust manner, for example in the field of minimally invasive medicine. This system is in particular configured to be provided in and is suitable for an endoscope.

[0252] List of reference symbols 1 Optical system 2 First holographic arrangement 2’ Second holographic arrangement 3 First diffraction element 3’ Second diffraction element 4 First prism arrangement 4’ Second prism arrangement 5 Collimation optical unit 6 Objective lens 8 Laser light source 81, 82 Lasers 9 First optical fiber 10 Input aperture 11 Second optical fiber 12 Imaging optical unit 31, 31’ First entrance surface 32, 32’ Second entrance surface 33, 33’ Exit surface 34, 34’ Prism surface 35 First mirror 36, 36’ Transmission diffraction grating arrangement 37 First array detector 37’ Second array detector OA Optical axis of the diffraction element Angle between ω1310 and 360 Angle between ω’1310’ and 360’ Angle between ω2340 and 360 Angle between ω’2340’ and 360’ The angle between ω 3320 and 360 The angle between ω’ 3320’ and 360’ The angle between ω 4330 and 360 The angle between ω’ 4330’ and 360’ The angle between α 350 and 360 The angle between α’ 350’ and 360’ The angle between ε 370 and 360 The angle between ε’ 370’ and 360’ The angle between χ 102 and 360 100 Reference light 101 Diffracted reference light 102 Reflected reference light 103 - 105 Reflection of the reference light 106 Spectral lines around the central wavelength of the reference light 100 - 1 The first central wavelength of the reference light 100 - 2 The second central wavelength of the reference light 200 Object light 201 Diffracted object light 206 Spectral lines around the central wavelength of the object light 200 - 1 The first central wavelength of the object light 200 - 2 The second central wavelength of the object light 300 Object 400 Computer

Claims

1. At least the following components: A first holographic arrangement (2) comprising a first diffractive element (3) formed by at least a first prism arrangement (4) having at least a quadrangular base An optical system (1) comprising: Here, the outer surface of the first prism arrangement (4) has the following outer surface regions: a) A first entrance surface (31) for reference light (100) extending along a first entrance plane (310); b) A second entrance surface (32) for object light (200) extending along a second entrance plane (320), where the first entrance surface and the second entrance surface (31, 32) form opposing outer surface regions of the first prism arrangement (4), said second entrance surface (32); c) An exit surface (33) extending along an exit plane (330) through which diffracted reference light (102) and diffracted object light (201) can exit the first diffractive element (3), said exit surface (33); d) A prism surface (34) opposing the exit surface (33) and extending along a prism plane (340); e) An optically transmissive diffraction grating arrangement (36) disposed in the first diffractive element (3) and extending along a diffraction plane (360) that intersects the first entrance plane (310) between the first entrance surface (31) and the exit surface (33); And having: The optical system (1) is characterized in that the transmissive diffraction grating arrangement (36) of the first diffractive element (3) comprises at least a first volume phase hologram grating, and the first holographic arrangement (2) has a first mirror (35) having a first mirror plane (350) on the side of the prism surface (34), where the first mirror plane (350) encloses an angle α with the diffraction plane (360), and the prism plane (340) encloses an angle ω ２ with the diffraction plane (360), the angles α, ω ２ at least one of which is different from 45°, Said optical system (1).

2. The system (1) is characterized by comprising a first array detector (37), where the first array detector (37) is configured to detect light emerging from the exit surface (33) of the first diffraction element (3), and in particular, the first array detector (37) is arranged on the exit surface (33) of the first diffraction element (3). The optical system (1) according to claim 1.

3. The bottom surface of the first prism arrangement (4) is a parallelogram, and in particular, a rectangle such as a quadrilateral. The optical system (1) according to claim 1 or 2.

4. The first mirror (37) is arranged or formed on the prism surface (33) of the first diffraction element (3). The optical system (1) according to any one of claims 1 to 3.

5. The light transmission diffraction grating arrangement (36) of the first holographic arrangement comprises a second volume phase hologram grating, where the first and second volume phase hologram gratings have different central wavelengths. The optical system (1) according to any one of claims 1 to 4.

6. The optical system (1) comprises a second holographic arrangement (2') having a second diffraction element (3'), which is formed by a second prism arrangement (4') having at least a quadrilateral bottom surface. Here, the first and second holographic arrangements (2, 2') are arranged adjacent to each other along the optical axis (OA) of the first diffraction element (3), and the outer surface of the second prism arrangement (4') has the following outer surface regions: f) a first incident surface (31') for the reference light (100) extending along the first incident plane (310'); g) a second incident surface (32') for the object light (200) extending along the second incident plane (320'), where the first incident surface and the second incident surface (31', 32') form opposite outer surface regions of the second prism arrangement (4'). The second incident surface (32'). (h) an exit surface (33'), extending along an exit plane (330'), through which diffracted reference light (102) and diffracted object light (201) can emerge from the second diffractive element (3'), said exit surface (33'), (i) a prism surface (33'), opposite the exit surface (33'), extending along the prism plane (330'), (j) an optically transmissive diffraction grating arrangement (36'), disposed in the second diffractive element (3') and extending along a diffraction plane (360') that intersects the first incidence plane (310') between the first incidence surface (31') and the exit surface (33') of the second diffractive element (3') and having The optical system (1) is characterized in that the transmissive diffraction grating arrangement (36') of the second diffractive element (3') comprises at least a first volume phase hologram grating, and the second holographic arrangement (2') has a second mirror (35') having a second mirror plane (350') on the side of the prism plane (340'), where the second mirror plane (350') encloses an angle α' with the diffraction plane (360'), and the prism plane (340') encloses an angle ω ２ ' with the diffraction plane (360'), and at least one of the angles α', ω ２ ' is different from 45°, in particular deviating from 45° by more than ±0.2°, the optical system (1) according to any one of claims 1 to 5.

7. The second incidence surface (32) of the first diffractive element (3) is connected to the first incidence surface (31') of the second diffractive element (3'), in particular by adhesion or welding, in particular where the first diffractive element (3) is integrally formed with the first incidence surface (31') of the second diffractive element (3') along the second incidence surface (32), the optical system (1) according to claim 6.

8. The optical system (1) has a collimation optical unit (5) for the reference light (100) on the side of the first incident surface (31) of the first diffraction element (3). The reference light (100) has an optical axis running in the direction of the first incident surface (31) of the first diffraction element (3), and the collimation 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). The optical system (1) according to any one of claims 1 to 7.

9. The optical system (2) includes an objective lens (6) for the object light (200). When the object light (200) radiates in and / or near the focal plane of the objective lens (6) toward the objective lens (6), the objective lens (6) is arranged in the optical system (1) such that the object light (200) propagating from the objective lens (6) toward the second incident surfaces (32, 32') of the first and / or second diffraction elements (3, 3') is collimated. The optical system (1) according to any one of claims 1 to 8.

10. The optical system (1) has the following components: - A laser light source (8) configured to provide laser light having one or more center wavelengths, in particular comprising one or more lasers (81, 82), the laser light source (8); - At least one first optical fiber (9), in particular a polarization-maintaining single-mode fiber, configured to guide the laser light of the laser light source (8) to the input aperture (10) of the collimation optical unit (5), thereby enabling the collimation optical unit (5) to guide the collimated laser light in the form of the reference light (100) to the first holographic arrangement (2). The at least one first optical fiber (9); at least one second optical fiber (11), in particular a polarization-maintaining single-mode fiber, configured to guide the laser light of the laser source (8) to an output aperture (12) of the optical system (1), from where an object to be detected (300) is illuminated with the laser light in the form of an object beam (200); An optical system (1) according to any one of the preceding claims, characterized in that it comprises:

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

12. The optical system (1) according to any one of claims 1 to 11, characterized in that it has an imaging optical unit (12) designed to project the object light (200), in particular the object light (100) emerging from at least one second fiber (11), in the form of an intensity pattern onto an object (300) to be detected, where the intensity pattern consists of at least one illuminated area, but preferably consists of a number of separated illuminated areas, in particular the illuminated areas of the intensity pattern are point-like or circular, and where the object light (200), in particular reflected by the object (300), is detected by an objective lens (6).

13. The optical system (1) is characterized in that it is designed to provide laser light containing wavelengths from at least two wavelength ranges, where the first wavelength range is arranged around a first central wavelength (100-1, 200-1) and in particular contains wavelengths in the form of spectral lines outside the second wavelength range, the second wavelength range is arranged around a second central wavelength (100-2, 200-2) and in particular contains wavelengths in the form of spectral lines, in particular the first and second wavelength ranges each contain a spectral range of 50 nm or less, in particular 15 nm or less, and in particular the spectral lines of the wavelength ranges each have a line width of 0.5 nm or less, the optical system (1) according to any one of claims 1 to 12.

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