Endoscopic detector system, use of a composite optical fiber, endoscopic system and method for examining a sample

Abstract

The invention relates to an endoscopic detector system (11) with an optical fiber assembly (1) comprising a multimode optical fiber (2) with an optical axis (3), a proximal end (4), and a distal end (5), as well as a focusing element (6) arranged at the distal end (5) of the multimode optical fiber (2). The endoscopic detector system (11) further comprises a detector unit (12) arranged at the proximal end (4) of the multimode optical fiber (2), which is configured to separately detect light emerging from the multimode optical fiber (2) at the proximal end (4) at one or more predetermined angles to the optical axis (3). The invention further relates to the use of a composite optical fiber (1) and an endoscopic system (19) comprising the endoscopic detector system (11) and an illumination device (20).Furthermore, the invention relates to a method for examining a sample (22) using an endoscopic system (19).

Description

Technical field

[0001] The invention relates to endoscopic examinations using a multimode optical fiber, in particular by means of holographic endoscopy. Specifically, the invention relates to an endoscopic detector system, the use of a composite optical fiber, an endoscopic system, and a method for examining a sample using an endoscopic system. Background of the invention

[0002] Holographic endoscopes, which utilize controlled light transmission through ultra-thin multimode optical fibers, are used, among other things, for minimally invasive observations in biomedical applications. This concept is based on the photonics of complex media, which exploits the empirical quantification of optical propagation through a random medium, enabling applications that are not possible with conventional endoscopes. Holographic endoscopy uses wavefront shaping technology (via spatial light modulators) to shape light propagating through otherwise randomized multimode optical fibers in such a way as to achieve a desired light intensity. For example, detailed images can be obtained from great depths within sensitive tissue structures, such as neurons.

[0003] US patent application US 2011 / 0137126 A1 describes an endoscope with a light source capable of generating coherent incident light and a plurality of optical imaging fibers arranged in a fiber bundle for receiving light at a proximal end of the fiber bundle and transmitting light to a distal end of the fiber bundle. The endoscope also includes a spatial light phase modulator located between the light source and the fiber bundle, arranged to receive the incident light from the light source and adjust the relative phase of the incident light entering each of the plurality of imaging optical fibers.

[0004] US patent application US 2019 / 0212761 A1 describes an optical probe with an optical source that generates an optical beam propagating from a proximal end to a distal end of an optical fiber, which transforms the spatial profile of the optical beam. An optical control device imparts a compensating spatial profile to the optical beam.

[0005] The German patent application DE 10 2023 109 837 A1, which is not considered in the assessment of inventive step, describes a lighting device with at least one wavefront manipulator which is configured to generate a sample beam, to pre-shape a wavefront of the light from a light source in such a way that the pre-shaped light can be focused essentially in an object area.

[0006] European patent application EP 3 130 950 A1 describes a beam deflection element and an optical component with a beam deflection element. Summary of the invention

[0007] The object of the invention is to propose an endoscopic detector system, the use of a composite optical fiber, an endoscopic system, and a method for examining a sample using an endoscopic system, all of which are further improved compared to known holographic endoscopes and, in particular, enable even better images, especially images with higher contrast, better axial resolution, faster imaging, and / or additional imaging capabilities when using pulsed laser light. This object is achieved by the subject matter of the independent claims. Further developments of the invention are described in the dependent claims and the following description.

[0008] The invention is described in the attached set of claims.

[0009] One aspect of the invention relates to an endoscopic detector system. The endoscopic detector system comprises an optical fiber assembly and a detector unit. The optical fiber assembly includes a multimode optical fiber and a focusing element.

[0010] A multimode optical fiber is understood to be an optical fiber or waveguide that has a fiber core with a diameter large enough to accommodate multiple light modes, in particular hundreds to hundreds of thousands of light modes. This naturally depends on the wavelength of the light used, with light typically in the visible spectrum, i.e., with wavelengths in the range of approximately 380 nm to 750 nm, and / or in the near-infrared range, with wavelengths in the range of approximately 750 nm to 1.5 µm. The terms optical fiber or waveguide can therefore be used synonymously with multimode optical fiber in the context of the present invention, provided the fiber core has a sufficiently large diameter.In particular, the multimode optical fiber is a step-index fiber, meaning that the fiber core has one refractive index and the cladding of the multimode optical fiber has a different refractive index. This refractive index changes in steps at the transition from the fiber core to the cladding, with the refractive index of the cladding being lower than that of the fiber core. It is also possible for the step-index fiber to have further layers, with the refractive index changing in steps between each layer.

[0011] The multimode optical fiber has an optical axis. Assuming a straight, unbent multimode optical fiber, the optical axis coincides with the axis of rotational symmetry of the multimode optical fiber. The optical axis therefore extends along the length of the multimode optical fiber, so that the multimode optical fiber appears circular in a cross-section perpendicular to the optical axis.

[0012] Furthermore, the multimode optical fiber has a proximal end and a distal end opposite the proximal end. The distal end of the multimode optical fiber can be inserted into or brought near a sample. The sample can be inorganic or organic, for example, an animal or a human.

[0013] The focusing element is located at the distal end of the multimode optical fiber. It can be configured to focus light coming from the multimode optical fiber and to convert light emitted from a point on the sample located at the focus of the focusing element into a collimated light beam and to feed this collimated light beam into the distal end of the multimode optical fiber.

[0014] The detector unit is located at the proximal end of the multimode optical fiber and is designed to separately detect light emerging from the fiber at one or more predetermined angles to the optical axis. This light may have been emitted from a point on the sample, collimated by the focusing element into a beam of light, and guided through the multimode optical fiber. To be collimated by the focusing element into a beam of light, the point on the sample must lie within a focal plane of the focusing element. The collimated beam of light then has an angle to the optical axis of the multimode optical fiber that depends on the distance of the point from the optical axis. The greater the distance of the point from the optical axis, the greater the angle of the collimated beam of light to the optical axis.An axial component of the k-vector of light is a propagation constant; that is, the axial component of the k-vector remains constant from the point of entry into the multimode optical fiber until its exit from the multimode optical fiber. This is particularly pronounced in step-index fibers. Since the axial component of the k-vector is related to the angle of the light to the optical axis, light entering the multimode optical fiber at a specific angle to its optical axis exits the fiber as a cone of light. The opening angle of this cone of light relative to the optical axis is equal to a specific angle, which in turn depends on the distance of the point on the sample emitting the light from the optical axis.If the detector unit only captures light exiting at a predetermined angle to the optical axis, then only light from points at the same distance from the optical axis as the point of the sample being examined is detected. Light from points at a different distance from the optical axis is not detected. This selective detection results in high contrast for the endoscopic detector system. The same applies if the detector unit only captures light exiting at several predetermined angles to the optical axis. In this case, only light from points at the same distance from the optical axis as several points of the sample being examined is detected.Provided that these multiple points are far enough apart and have different distances from the optical axis, a high contrast of the endoscopic detector system is also achieved, and the total examination time can be shortened by examining multiple points simultaneously.

[0015] In some embodiments, the optical fiber assembly further comprises a light-reflecting surface. This light-reflecting surface is located at the distal end of the multimode optical fiber and / or at the focusing element. The angle between the normal to the light-reflecting surface and the optical axis of the multimode optical fiber at the distal end is between 30° and 60°, particularly between 40° and 50°. The light-reflecting surface deflects light propagating along the optical axis in the multimode optical fiber in a direction radial to the optical axis. In particular, the light is deflected by 90° when the light-reflecting surface is inclined at 45° to the optical axis. Thus, areas of the sample located radially to the optical axis at the distal end of the multimode optical fiber can be examined.The above description of the angles to the optical axis also applies to this embodiment, whereby the angles are then to be understood in the multimode optical fiber and / or the optical axis is deflected at the light reflection surface.

[0016] The light-reflecting surface can be used, in particular, in conjunction with a light-transmitting surface. This light-transmitting surface can be essentially parallel to the optical axis; that is, the angle between the optical axis and the light-transmitting surface can be less than 15°, particularly less than 10°, and most especially less than 5°. The light-transmitting surface can be configured to transmit light radially to the optical axis. Thus, light can exit the multimode optical fiber through the light-transmitting surface, and light from outside the multimode optical fiber can enter the multimode optical fiber through the light-transmitting surface. This light-transmitting surface can be a flat surface or can be configured to form the focusing element.

[0017] The light-reflecting surface and / or the light-transmitting surface can be produced by polishing or milling the distal end of the multimode optical fiber and / or the focusing element, whereby the milling can be carried out in particular with a focused ion beam or by laser ablation. Furthermore, the light-transmitting surface can be provided with a coating, in particular with a dielectric coating, to increase the transmission coefficient. The light-reflecting surface can also be provided with a coating, in particular with a dielectric and / or a metallic coating, to increase the reflection coefficient.

[0018] In some embodiments, the focusing element is a gradient-index lens. The gradient-index lens is, in particular, a multimode optical fiber with a gradient profile of a quarter-pitch length or shorter. The gradient-index lens can be connected to the multimode optical fiber to form a composite optical fiber. This connection can be achieved, for example, by splicing. In particular, the outer diameter of the gradient-index lens can be chosen to be the same as the outer diameter of the multimode optical fiber, resulting in a particularly uniform composite optical fiber. If a light-reflecting surface is provided, it can be integrated into the gradient-index lens, especially at an end of the gradient-index lens opposite the end of the gradient-index lens connected to the multimode optical fiber.

[0019] Alternatively, the focusing element can be a spherical lens, a plano-convex lens, or a Fresnel lens. These lenses can be spliced, glued, printed, etched, or fused to the distal end of the multimode optical fiber.

[0020] In some embodiments, the detector unit comprises a detector array configured to selectively detect light in one or more annular regions corresponding to one or more predetermined angles. If light emerges from the multimode optical fiber as a cone of light at the predetermined angle, which, as described above, corresponds to the distance of the light-emitting point from the optical axis, it is detected by the detector array in the annular region. However, if light is emitted from a different point at a different distance from the optical axis, this light is emitted into an annular region with a different radius and is not detected by the detector array. This unwanted light is thus filtered out, thereby increasing the contrast of the detector system.

[0021] In some embodiments, the detector unit further comprises an additional focusing element facing the proximal end of the multimode optical fiber. This additional focusing element can be configured as a lens. The additional focusing element focuses the light exiting the multimode optical fiber at one or more predetermined angles onto one or more annular regions within a focal plane of the additional focusing element. This further increases the angular resolution of the detector unit and allows for a more compact detector arrangement.

[0022] In some embodiments, the detector arrangement includes a selection element for choosing one or more annular regions. If the detector unit includes the additional focusing element, the selection element is specifically located at the focus of this additional focusing element. Furthermore, the detector arrangement includes a detector element for detecting the light arriving in the selected one or more annular regions. The selection element can be an annular aperture. The annular aperture can be adaptable to different radii of the annular regions; for example, different annular apertures with different radii can be interchangeable.In this case, the detector element is located on the side of the selection element facing away from the proximal end of the multimode optical fiber and / or the additional focusing element, so that light transmitted through the aperture strikes the detector and is registered by it. Alternatively, the selection element can be an annular mirror that reflects only light arriving within a ring-shaped region. The detector is then located on the same side of the selection element as the proximal end of the multimode optical fiber and / or the additional focusing element. A variable annular mirror can, for example, be implemented as a micromirror array. These variants of the detector arrangement are particularly lightweight and cost-effective to manufacture.

[0023] Alternatively, the detector arrangement comprises a detector element configured for the selective detection of light in one or more ring-shaped regions. If the detector unit includes the additional focusing element, the detector element is specifically located at the focus of the additional focusing element. The detector element can, for example, have ring-shaped detector regions. Alternatively, the detector element can comprise a grid arrangement with individual pixels arranged in rows and columns, in which case only the pixels located on a ring-shaped region with a predefined radius are evaluated for the selective detection of light. This allows for the quick and easy examination of various ring-shaped regions.

[0024] Another aspect of the invention relates to a composite optical fiber. This composite optical fiber comprises a multimode optical fiber with an optical axis, a proximal end and a distal end, and a gradient-index lens connected to the distal end of the multimode optical fiber.

[0025] A multimode optical fiber is understood to be an optical fiber or waveguide that has a fiber core with a diameter large enough to accommodate multiple light modes, in particular hundreds to hundreds of thousands of light modes. This naturally depends on the wavelength of the light used, with light typically in the visible spectrum, i.e., with wavelengths in the range of approximately 380 nm to 750 nm, and / or in the near-infrared range, with wavelengths in the range of approximately 750 nm to 1.5 µm. The terms optical fiber or waveguide can therefore be used synonymously with multimode optical fiber in the context of the present invention, provided the fiber core has a sufficiently large diameter.In particular, the multimode optical fiber is a step-index fiber, meaning that the fiber core has one refractive index and the cladding of the multimode optical fiber has a different refractive index. This refractive index changes in steps at the transition from the fiber core to the cladding, with the refractive index of the cladding being lower than that of the fiber core. It is also possible for the step-index fiber to have further layers, with the refractive index changing in steps between each layer.

[0026] The optical axis of a multimode optical fiber coincides with the axis of rotational symmetry of the multimode optical fiber when the fiber is straight, i.e., not bent. The optical axis thus extends along the length of the fiber, so that the fiber appears circular in cross-section perpendicular to the optical axis. In the case of a bent multimode optical fiber, the optical axis is bent along with the fiber, corresponding to the bend.

[0027] The distal end of the multimode optical fiber is opposite the proximal end and can be inserted into and / or brought close to a sample. The sample can be inorganic or organic, for example, an animal or a human.

[0028] The gradient-index lens can be designed to focus light coming from the multimode optical fiber and to transform light emitted from a point on the sample that lies at the focus of the gradient-index lens into a collimated light beam and to feed this collimated light beam into the distal end of the multimode optical fiber.

[0029] The gradient-index lens can be, in particular, a multimode optical fiber with a gradient profile of a quarter-pitch length or shorter. It can be connected to the multimode optical fiber, for example, by splicing. Specifically, the outer diameter of the gradient-index lens can be chosen to be the same as the outer diameter of the multimode optical fiber, resulting in a particularly uniform composite optical fiber.

[0030] The composite optical fiber can be used in an endoscopic detector system according to the preceding description, so that a high resolution of the endoscopic detector system can be achieved with the help of the composite optical fiber.

[0031] In some embodiments, the gradient-index lens has a light-reflecting surface. This light-reflecting surface is located at an end of the gradient-index lens opposite the end of the gradient-index lens connected to the multimode optical fiber. The angle between the normal to the light-reflecting surface and the optical axis of the multimode optical fiber at the distal end is between 30° and 60°, particularly between 40° and 50°. The light-reflecting surface deflects light propagating along the optical axis in the multimode optical fiber in a direction radial to the optical axis. Specifically, the light is deflected by 90° when the light-reflecting surface is inclined at 45° to the optical axis. Therefore, areas of the sample located radially to the optical axis within the region of the gradient-index lens can be examined.

[0032] The light-reflecting surface can be used, in particular, in conjunction with a light-transmitting surface. This light-transmitting surface can be essentially parallel to the optical axis; that is, the angle between the optical axis and the light-transmitting surface can be less than 15°, particularly less than 10°, and most especially less than 5°. The light-transmitting surface can be configured to transmit light radially to the optical axis. Thus, light can both exit the composite optical fiber through the light-transmitting surface and light from outside the composite optical fiber can enter the composite optical fiber through the light-transmitting surface. This light-transmitting surface can, in particular, be a flat surface.

[0033] The light-reflecting surface and / or the light-transmitting surface can be produced by polishing or by milling the end of the gradient-index lens opposite the end of the gradient-index lens connected to the multimode optical fiber, whereby the milling can be carried out, in particular, with a focused ion beam. Furthermore, the light-transmitting surface can be provided with a coating, in particular a dielectric coating, to increase the transmission coefficient. The light-reflecting surface can also be provided with a coating, in particular a dielectric and / or a metallic coating, to increase the reflection coefficient.

[0034] Another aspect of the invention relates to an endoscopic system. The endoscopic system comprises a lighting device and the endoscopic detector system as described above.

[0035] The lighting device is designed to illuminate a sample or part of a sample. This sample can be inorganic or organic, for example, an animal or a human.

[0036] The endoscopic system achieves a high contrast due to the aforementioned endoscopic detector system.

[0037] In some embodiments, the illumination device is designed to illuminate a sheet of light. This sheet of light extends, in particular, perpendicular to the optical axis, may be generated by a laser, and intersects the sample. The fluorescence emitted by the sample is then detected by the endoscopic detector system. Using a transfer matrix of the optical fiber arrangement, it is then possible to deduce the presence of light points in the sample from the light detected by the endoscopic detector system. This is an inverse problem that can be solved, for example, using the maximum likelihood method.Since the present detector system can selectively detect points in the sample that are located on ring-shaped areas in the sample, noise coming from points outside these ring-shaped areas, which would otherwise affect the reconstruction algorithm, is suppressed, thus reducing numerical artifacts and improving the contrast of the obtained image.

[0038] Alternatively, the illumination system comprises a coherent light source and a light modulator. The coherent light source is, in particular, a laser. The coherent light source and the light modulator are configured such that the coherent light source emits coherent light, which is then pre-shaped by the light modulator and fed into the proximal end of the multimode optical fiber. The light modulation can be performed, in particular, as amplitude, phase, and / or polarization modulation. The light modulation is performed, in particular, such that one or a few points of the sample are illuminated. Thus, only this point or these points in the sample are illuminated, and stray light is suppressed by the endoscopic detector system, resulting in particularly good contrast and therefore particularly good image quality.If several points in the sample are to be illuminated, these points should be at different distances from the optical axis so that the light emitted from these points enters the multimode optical fiber at different angles and exits at correspondingly different angles, where it can then be differentiated by the detector unit. This enables the simultaneous illumination of multiple points, allowing for faster endoscopic image acquisition. The light modulation required for illuminating a specific point can be determined, for example, by establishing a transfer matrix that describes the transfer of coherent light from one end of the optical fiber array to the other.This can be achieved, for example, by determining the light transfer from a large number of known points emitting coherent light. Using the transfer matrix, the modulation of the coherent light required to illuminate one or more points in the sample is then determined.

[0039] Another aspect of the invention relates to a further endoscopic system. This endoscopic system comprises a lighting device and an optical fiber arrangement.

[0040] The lighting device comprises a pulsed light source, in particular a pulsed coherent light source, and most especially a pulsed laser. The lighting device also comprises a light modulator.

[0041] The optical fiber assembly comprises a multimode optical fiber and a focusing element.

[0042] A multimode optical fiber is understood to be an optical fiber or waveguide that has a fiber core with a diameter large enough to accommodate multiple light modes, in particular hundreds to hundreds of thousands of light modes. This naturally depends on the wavelength of the light used, with light typically in the visible spectrum, i.e., with wavelengths in the range of approximately 380 nm to 750 nm, and / or in the near-infrared range, with wavelengths in the range of approximately 750 nm to 1.5 µm. The terms optical fiber or waveguide can therefore be used synonymously with multimode optical fiber in the context of the present invention, provided the fiber core has a sufficiently large diameter.In particular, the multimode optical fiber is a step-index fiber, meaning that the fiber core has one refractive index and the cladding of the multimode optical fiber has a different refractive index. This refractive index changes in steps at the transition from the fiber core to the cladding, with the refractive index of the cladding being lower than that of the fiber core. It is also possible for the step-index fiber to have further layers, with the refractive index changing in steps between each layer.

[0043] The multimode optical fiber has an optical axis. Assuming a straight, unbent multimode optical fiber, the optical axis coincides with the axis of rotational symmetry of the multimode optical fiber. The optical axis therefore extends along the length of the multimode optical fiber, so that the multimode optical fiber appears circular in a cross-section perpendicular to the optical axis.

[0044] Furthermore, the multimode optical fiber has a proximal end and a distal end opposite the proximal end. The distal end of the multimode optical fiber, along with the focusing element, can be inserted into or brought close to a sample. The sample can be inorganic or organic, such as an animal or a human.

[0045] The focusing element is located at the distal end of the multimode optical fiber. It can be configured to focus light coming from the multimode optical fiber and to convert light emitted from a point on the sample located at the focus of the focusing element into a collimated light beam and to feed this collimated light beam into the distal end of the multimode optical fiber.

[0046] The light modulator is configured such that the pulsed light is injected into the proximal end of the multimode optical fiber at at least one predetermined angle to the optical axis. Since light injected into the multimode optical fiber at a specific angle propagates primarily within a single mode group, with each mode group comprising modes exhibiting similar propagation velocities, little or no intermodal dispersion occurs, thus preserving the light pulse. If the light is injected at more than one predetermined angle, the light pulses for the respective angles are preserved, and multiple points on a sample at varying distances from the optical axis can be illuminated simultaneously. Furthermore, if the multimode optical fiber is a step-index fiber, a circular polarization state of the coherent light is also maintained.Other microscopy techniques, such as fluorescence lifetime microscopy, STED (stimulated emission depletion) microscopy, or multiphoton microscopy, also benefit from the improved light pulses obtained in this way.

[0047] Furthermore, the lighting device may include apertures and / or lenses.

[0048] The endoscopic system may also include a detector. The detector can, for example, detect light emitted by the sample via fluorescence, entering the multimode optical fiber at the distal end, being guided by the multimode optical fiber, and exiting the multimode optical fiber at the proximal end. Alternatively, the detector can detect light emitted by the sample via fluorescence using another optical system. Examples of such a detector include a photodetector, a camera, a photon counter (especially a photomultiplier), a hybrid photodetector, and a single-photon avalanche diode.

[0049] Another aspect of the invention relates to a method for examining a sample using an endoscopic system according to the preceding description.

[0050] In this process, the sample is illuminated by means of the illumination device. This illumination can be direct, such as with the light sheet, or it can be provided via the fiber optic array, in particular using light pre-shaped by the light modulator.

[0051] Before illuminating the sample with the lighting device, it may be necessary to align the multimode optical fiber so that light emitted by the sample can enter the distal end of the fiber. This alignment can be performed manually or automatically, with the specific details depending on the sample.

[0052] In response to illumination, the sample emits light, for example, by fluorescence. This emitted light then enters the distal end of the multimode optical fiber via the focusing element, is propagated by the multimode optical fiber, and finally exits the multimode optical fiber. The light exiting at one or more predetermined angles to the optical axis is then detected. By selectively detecting light exiting at one or more predetermined angles from points on the sample at one or more corresponding distances from the optical axis, the contrast and quality of an image obtained by this method are improved.

[0053] For confocal microscopy, a transmission matrix for the multimode optical fiber with the focusing element can be determined. This can be achieved, for example, by determining the light transfer from a multitude of known points emitting coherent light. The light modulator is then controlled based on the transmission matrix such that the light illuminating the sample is focused at one or more points on the sample corresponding to one or more predetermined angles to the optical axis. This enables scanning of one or more points in the sample. If only one point is illuminated at a time, the image quality can be improved by suppressing light exiting the multimode optical fiber at angles other than the predetermined angle to the optical axis.However, if several points are illuminated simultaneously at different distances from the optical axis, the selective detection of light exiting the multimode optical fiber at the corresponding angles to the optical axis allows differentiation between the points, while simultaneously suppressing light exiting the multimode optical fiber at angles other than the predetermined angles to the optical axis improves image quality.

[0054] It is understood that a preferred embodiment can also be achieved from a combination of dependent claims with the respective independent claim.

[0055] For further clarification, the invention is described with reference to embodiments illustrated in the figures. These embodiments are to be understood as examples only, and not as limitations. Brief description of the characters

[0056] This shows: Fig. 1 a schematic longitudinal section through an embodiment of a composite optical fiber; Fig. 2 a schematic longitudinal section through another embodiment of a composite optical fiber; Fig. 3 a schematic longitudinal section through an embodiment of an endoscopic detector system; Fig. 4 a schematic longitudinal section through another embodiment of an endoscopic detector system; Fig. 5 a schematic longitudinal section through a further embodiment of an endoscopic detector system; Fig. 6 a schematic longitudinal section through an embodiment of an endoscopic system; Fig. 7 a schematic longitudinal section through another embodiment of an endoscopic system; Fig. 8 a schematic longitudinal section through a further embodiment of an endoscopic system; and Fig. 9 a schematic longitudinal section through a further embodiment of an endoscopic system. Detailed description of the invention

[0057] In the figures, identical reference symbols denote either identical elements or elements with equivalent functions. Elements that have already been described are not necessarily described again in subsequent figures.

[0058] Fig. Figure 1 shows a schematic longitudinal section through an embodiment of a composite optical fiber 1. The composite optical fiber 1 comprises a multimode optical fiber 2 with an optical axis 3, a proximal end 4 and a distal end 5, and a gradient-index lens 6 connected to the distal end 5.

[0059] A multimode optical fiber 2 is understood to be an optical fiber or waveguide that has a fiber core 7 whose diameter is large enough to accommodate multiple light modes, in particular hundreds to hundreds of thousands of light modes. This naturally depends on the wavelength of the light to be used, with light in the visible spectrum, i.e., with wavelengths in the range of approximately 380 nm to 750 nm, and / or in the near-infrared range, with wavelengths in the range of approximately 750 nm to 1.5 µm, typically being used. The terms optical fiber or waveguide can therefore also be used synonymously with multimode optical fiber 2 in the context of the present invention, provided that the fiber core 7 has a sufficiently large diameter.In particular, the multimode optical fiber 2 is a step-index fiber, meaning that the fiber core 7 has one refractive index and the cladding 8 of the multimode optical fiber 2 has a different refractive index, with this refractive index changing in steps at the transition from the fiber core 7 to the cladding 8, and with the refractive index of the cladding 8 being lower than the refractive index of the fiber core 7. It is also possible that the step-index fiber has further layers, with the refractive index changing in steps between each layer.

[0060] The optical axis 3 of the multimode optical fiber 2 coincides with the axis of rotational symmetry of the multimode optical fiber 2 when the multimode optical fiber 2 is straight, i.e., not bent. The optical axis 3 therefore extends along the longitudinal direction of the multimode optical fiber 2, so that the multimode optical fiber 2 appears circular in a cross-section perpendicular to the optical axis 3.

[0061] The distal end 5 of the multimode optical fiber 2 is opposite the proximal end 4 and, together with the gradient-index lens 6, can be inserted into and / or brought close to a sample. The sample can be inorganic or organic, for example, an animal or a human.

[0062] The gradient index lens 6 can be configured to focus light coming from the multimode optical fiber 2, and / or to transform light emitted from a point on the sample that lies in the focal plane of the gradient index lens 6 into a collimated light beam and to feed this collimated light beam into the distal end 5 of the multimode optical fiber 2.

[0063] The gradient-index lens 6 can, in particular, be a multimode optical fiber with a gradient profile of a quarter-pitch length or shorter. It can be connected to the multimode optical fiber 2, for example, by splicing or bonding. In particular, the outer diameter of the gradient-index lens 6 can be chosen to be the same as the outer diameter of the multimode optical fiber 2, so that a particularly uniform composite optical fiber 1 is obtained.

[0064] Fig. Figure 2 shows a schematic longitudinal section through another embodiment of a composite optical fiber 1. In comparison to the embodiment of the Fig. In this embodiment, the gradient-index lens 6 has a light-reflecting surface 9. This light-reflecting surface 9 is arranged at an end of the gradient-index lens 6 opposite the end of the gradient-index lens 6 that is connected to the multimode optical fiber 2. The angle between the normal to the light-reflecting surface 9 and the optical axis 3 of the multimode optical fiber 2 at the distal end 5 is between 30° and 60°, particularly between 40° and 50°. The light-reflecting surface 9 deflects light propagating along the optical axis 3 in the multimode optical fiber 2 in a direction radial to the optical axis 3. In particular, the light is deflected by 90° when the light-reflecting surface 9 is inclined at 45° to the optical axis. Therefore, areas of the sample can be examined that lie radially to the optical axis 3 in the region of the gradient index lens 6.

[0065] The light-reflecting surface 9 can be used, in particular, in conjunction with a light-transmitting surface 10. This light-transmitting surface 10 can be substantially parallel to the optical axis 3, i.e., an angle between the optical axis 3 and the light-transmitting surface 10 can be less than 15°, in particular less than 10°, and most particularly less than 5°. The light-transmitting surface 10 can be configured to transmit light radially to the optical axis 3. Thus, light can both exit the composite optical fiber 1 through the light-transmitting surface 10 and light from outside the composite optical fiber 1 can enter the composite optical fiber 1 through the light-transmitting surface 10. This light-transmitting surface 10 can, in particular, be a flat surface.

[0066] The light-reflecting surface 9 and / or the light-transmitting surface 10 can be produced by polishing or by milling the end of the gradient-index lens 6 opposite the end of the gradient-index lens 6 connected to the multimode optical fiber 2, the milling being carried out in particular with a focused ion beam. Furthermore, the light-transmitting surface 10 can be provided with a coating, in particular a dielectric coating, to increase the transmission coefficient. The light-reflecting surface 9 can also be provided with a coating, in particular a dielectric and / or a metallic coating, to increase the reflection coefficient.

[0067] Fig. Figure 3 shows a schematic longitudinal section through an embodiment of an endoscopic detector system 11. The endoscopic detector system 11 comprises an optical fiber arrangement 1, represented as a composite optical fiber 1 according to the preceding description, and a detector unit 12.

[0068] In general, the optical fiber assembly 1 can comprise a multimode optical fiber 2 and a focusing element 6. The focusing element 6 can alternatively be a spherical lens, a plano-convex lens, or a Fresnel lens instead of a gradient-index lens 6. These lenses can be spliced, glued, printed, etched, or fused to the distal end 5 of the multimode optical fiber 2.

[0069] The detector unit 12 is arranged at the proximal end 4 of the multimode optical fiber 2 and is configured to separately detect light exiting the multimode optical fiber 2 at the proximal end 4 at one or more predetermined angles to the optical axis 3. Light beam paths 13 emitted from a point 14 located offset from the optical axis 3 are shown as black lines. For comparison, light beam paths 13 emitted from a point 14 located on the optical axis 3 are also shown as gray lines. The light emitted from point 14 of the sample is transformed into a collimated light beam by the focusing element 6 and guided through the multimode optical fiber 2. In order to be transformed into a collimated light beam by the focusing element 6, point 14 of the sample must be located in a focal plane of the focusing element 6.The collimated light beam then has an angle to the optical axis 3 of the multimode optical fiber 2, which depends on the distance of point 14 from the optical axis 3. The greater the distance of point 14 from the optical axis 3, the greater the angle of the collimated light beam to the optical axis 3. An axial component of the k-vector of the light is a propagation constant, meaning that the axial component of the k-vector remains constant from the point of entry into the multimode optical fiber 2 to its point of exit. This is particularly pronounced in step-index fibers.Since the axial component of the k-vector is related to the angle of the light to the optical axis 3, light entering the multimode optical fiber 2 at a specific angle to the optical axis 3 exits the multimode optical fiber 2 as a light cone. The opening angle of the light cone to the optical axis 3 is equal to a specific angle, which in turn depends on the distance of the point 14 of the sample emitting the light to the optical axis 3. If only the light exiting at the predetermined angle to the optical axis 3 is detected by the detector unit 12, then only light from points 14 that are at the same distance from the optical axis 3 as the point 14 of the sample being examined is detected. Light from points 14 that have a different distance to the optical axis 3 is not detected. This selective detection results in high contrast for the endoscopic detector system 11.The same applies if only the light exiting at several predetermined angles to the optical axis 3 is detected by the detector unit 12. Then, only light from points 14 that are at the same distance from the optical axis 3 as several points 14 of the sample to be examined is detected. Provided that these several points 14 are sufficiently far apart and have different distances from the optical axis 3, a high contrast of the endoscopic detector system 11 is also achieved, and the overall examination time can be reduced by examining several points 14 simultaneously.

[0070] In the present embodiment, the detector unit 12 comprises a detector arrangement 15 configured to selectively detect light in one or more annular regions. The detector arrangement 15 includes a selection element 16 designed as an annular aperture for selecting the one or more annular regions. Furthermore, the detector arrangement 15 includes a detector element 17 for detecting the light arriving in the selected one or more annular regions. The annular aperture can be adapted to different radii of the annular regions; for example, different annular apertures with different radii can be interchangeable. In this case, the detector element 17 is arranged on the side of the selection element 16 facing away from the proximal end 4 of the multimode optical fiber 2, so that light transmitted through the aperture strikes the detector 17 and is registered by it.Alternatively, the selection element 16 can be an annular mirror that reflects only light arriving within an annular region. The detector 17 is then located on the same side of the selection element 16 as the proximal end 4 of the multimode optical fiber 2. A variable annular mirror can, for example, be implemented as a micromirror array.

[0071] Fig. Figure 4 shows a schematic longitudinal section through another embodiment of an endoscopic detector system 11. Compared to the one in Fig. In the embodiment shown in Figure 3, the detector unit 12 of this endoscopic detector system 11 further comprises an additional focusing element 18 directed towards the proximal end 4. This additional focusing element 18 is depicted as a lens. The additional focusing element 18 focuses the light exiting the multimode optical fiber 2 at one or more predetermined angles onto one or more annular areas in a focal plane of the additional focusing element 18, where the selection element 16 is also located. This further increases the angular resolution of the detector unit 12.

[0072] Fig. Figure 5 shows a schematic longitudinal section through a further embodiment of an endoscopic detector system 11. In comparison to the one in Fig. In the embodiment shown in Figure 4, the detector arrangement 15 of this endoscopic detector system 11 does not include a selection element 16. Instead, the detector element 17 is configured for the selective detection of light in one or more ring-shaped regions. The detector element 17 can, for example, have ring-shaped detector regions. Alternatively, the detector element 17 can comprise a grid arrangement with individual pixels arranged in rows and columns, whereby only the pixels located on a ring-shaped region with a predetermined radius are evaluated for the selective detection of light. This allows for the quick and easy examination of various ring-shaped regions.

[0073] Fig. Figure 6 shows a schematic longitudinal section through an embodiment of an endoscopic system 19. The endoscopic system 19 comprises the endoscopic detector system 11 according to one of the embodiments described above, as well as an illumination device 20, which here includes a coherent light source 21, for example, a laser. The illumination device 20 is designed to illuminate a sample 22 or a part of a sample. This sample 22 can be an inorganic or an organic sample, for example, an animal or a human being.

[0074] In the present embodiment, the illumination device 20 is configured to illuminate a sheet of light 23. This sheet of light 23 extends, in particular, perpendicular to the optical axis 3 and intersects the sample 22. The fluorescence emitted by the sample 22 is then detected by the endoscopic detector system 11. Using a transfer matrix of the optical fiber arrangement 1, it is then possible to deduce light points 14 in the sample 22 from the light detected by the endoscopic detector system 11. This is an inverse problem that can be solved, for example, using the maximum likelihood method. Since the present detector system 11 can selectively detect points 14 in the sample 22 that are located on annular regions within the sample 22, the contrast of the resulting image is improved.

[0075] Fig. Figure 7 shows a schematic longitudinal section through another embodiment of an endoscopic system 19. In comparison to the endoscopic system 19 of the embodiment from Fig. 6, the illumination device 20 comprises, in addition to the coherent light source 21, a light modulator 24 and a semi-transparent mirror 25. The coherent light source 21 is, in particular, a laser. The coherent light source 21 and the light modulator 24 are configured such that the coherent light source 21 emits coherent light, which is then pre-shaped by the light modulator 24 and fed into the proximal end 4 of the multimode optical fiber 2 via the semi-transparent mirror 25. The light modulation can be carried out, in particular, as amplitude, phase, and / or polarization modulation. The light modulation is carried out, in particular, such that one point 14 or a few points 14 of the sample 22 are illuminated.

[0076] Thus, only this or these points 14 in the sample 22 are illuminated, and stray light is suppressed by the endoscopic detector system 11, resulting in particularly good contrast and therefore particularly good image quality. If several points 14 in the sample 22 are illuminated, these points 14 are at different distances from the optical axis 3, so that the light emitted from these points 14 enters the multimode optical fiber 2 at different angles and exits the multimode optical fiber 2 at correspondingly different angles, where it can then be differentiated by the detector unit 12. This enables the simultaneous illumination of several points 14, allowing for faster endoscopic image acquisition.The light modulation required to illuminate a specific point 14 can be determined, for example, by establishing a transfer matrix that describes the transfer of coherent light from one end of the optical fiber array 1 to the other end. This can be achieved, for instance, by determining the light transfer from a multitude of known points emitting coherent light. Using the transfer matrix, the modulation of the coherent light required to illuminate the one or more points 14 in the sample 22 is then determined.

[0077] Fig. Figure 8 shows a schematic longitudinal section through a further embodiment of an endoscopic system 19. This endoscopic system 19 comprises a lighting device 20 and an optical fiber arrangement 1.

[0078] The illumination device 20 comprises a pulsed light source 21, in particular a pulsed coherent light source, and most especially a pulsed laser. Furthermore, the illumination device 20 comprises a light modulator 24 configured such that the pulsed light is injected into the proximal end 4 of the multimode optical fiber 2 at at least a predetermined angle to the optical axis 3. Since light injected into the multimode optical fiber 2 at a certain angle propagates mainly within a mode group, wherein a mode group comprises modes exhibiting a similar propagation speed, no or only minimal intermodal dispersion occurs, so that the light pulse is preserved.If the light is injected at more than one predetermined angle, the light pulses for the respective angles are retained, and several points 14 of the sample 22, which have different distances from the optical axis 3, can be illuminated simultaneously. Furthermore, if the multimode optical fiber 2 is a step-index fiber, a circular polarization state of the coherent light is also maintained. Other microscopy techniques, such as fluorescence lifetime microscopy, STED (stimulated emission depletion) microscopy, or multiphoton microscopy, also benefit from the improved light pulses obtained in this way.

[0079] The lighting device 20 can also include lenses 26 and / or apertures in addition to the light modulator 24.

[0080] For example, another optical system with a detector can be provided to detect the light emitted by sample 22 through fluorescence.

[0081] Fig. Figure 9 shows a schematic longitudinal section through yet another embodiment of an endoscopic system 19. In addition to the one shown in Fig. The endoscopic system 19 shown in Figure 8 comprises a semi-transparent mirror 25 and a detector 17. The detector 17 detects light emitted by the sample 22 via fluorescence, entering the multimode optical fiber 2 at its distal end 5 via the focusing element 6, being guided by the multimode optical fiber 2, exiting the multimode optical fiber 2 at its proximal end 4, and being deflected by the semi-transparent mirror 25. Examples of such a detector 17 are a photodetector, a camera, a photon counter, in particular a photomultiplier, a hybrid photodetector, and a single-photon avalanche diode.

Claims

[1] An endoscopic detector system (11) comprising an optical fiber arrangement (1) comprising a multimode optical fiber (2) having an optical axis (3), a proximal end (4) and a distal end (5); and a focusing element (6) arranged at the distal end (5) of the multimode optical fiber (2); and a detector unit (12) arranged at the proximal end (4) of the multimode optical fiber (2) and designed to separately detect light emerging from the multimode optical fiber (2) at the proximal end (4) at one or more predetermined angles to the optical axis (3), wherein the one or more predetermined angles are strictly greater than 0°. [2] The endoscopic detector system (11) according to claim 1, wherein the optical fiber arrangement (1) further comprises a light reflection surface (9) arranged at the distal end (5) of the multimode optical fiber (2) and / or at the focusing element (6), wherein an angle between the normal to the light reflection surface (9) and the optical axis (3) of the multimode optical fiber (2) at the distal end (5) is between 30° and 60°, in particular between 40° and 50°. [3] The endoscopic detector system (11) according to claim 1 or 2, wherein the focusing element (6) is a gradient index lens (6) which is connected in particular to the multimode optical fiber (2) to form a composite optical fiber (1). [4] The endoscopic detector system (11) according to claim 1 or 2, wherein the focusing element (6) is a spherical lens, a plano-convex lens, or a Fresnel lens. [5] The endoscopic detector system (11) according to any one of claims 1 to 4, wherein the detector unit (12) comprises a detector array (15) configured to selectively detect light in one or more annular regions corresponding to the one or more predetermined angles. [6] The endoscopic detector system (11) according to claim 5, wherein the detector unit (12) further comprises a further focusing element (18) facing the proximal end (4) of the multimode optical fiber (2). [7] The endoscopic detector system (11) according to claim 5 or 6, wherein the detector arrangement (15) comprises: a, in particular arranged in the focus of the further focusing element (18), Selection element (16) for selecting the one or more annular regions; and a detector element (17) for detecting the light arriving in the selected one or more annular regions. [8] The endoscopic detector system (11) according to claim 5 or 6, wherein the detector arrangement (15) comprises a detector element (17), arranged in particular in the focus of the further focusing element (18), which is designed to selectively detect light in the one or more annular regions. [9] A use of a composite optical fiber (1) which a multimode optical fiber (2) having an optical axis (3), a proximal end (4) and a distal end (5); and a gradient index lens (6) connected to the distal end (5) of the multimode optical fiber (2), for examining a sample (22), wherein the sample (22) is illuminated and light entering the distal end (5) of the multimode optical fiber (2), guided by the multimode optical fiber (2) and exiting the proximal end (4) of the multimode optical fiber (2) at one or more predetermined angles to the optical axis (3) is separately detected, wherein the one or more predetermined angles are strictly greater than 0°. [10] The use of the composite optical fiber (1) according to claim 9, wherein the gradient index lens (6) has a light reflection surface (9), wherein an angle between the normal to the light reflection surface (9) and the optical axis (3) of the multimode optical fiber (2) at the distal end (5) is between 30° and 60°, in particular between 40° and 50°. [11] An endoscopic system (19) comprising an illumination device (20) and the endoscopic detector system (11) according to one of claims 1 to 8. [12] The endoscopic system (19) according to claim 11, wherein the illumination device (20) is designed to illuminate a light sheet (23). [13] The endoscopic system (19) according to claim 11, wherein the illumination device (20) comprises a coherent light source (21) and a light modulator (24) configured such that the coherent light source (21) emits coherent light which is pre-shaped by the light modulator (24) and fed into the proximal end (4) of the multimode optical fiber (2). [14] A method for examining a sample (22) by means of an endoscopic system (19) according to one of claims 11 to 13, comprising: Illuminating the sample (22) by means of the illumination device (20); and Detecting the light entering the distal end (5) of the multimode optical fiber (2), guided by the multimode optical fiber (2) and exiting the proximal end (4) of the multimode optical fiber (2) at one or more predetermined angles to the optical axis (3), wherein the one or more predetermined angles are strictly greater than 0°.

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