Abstract:
The invention describes an optical deflection element for the refractive production of a spatially structured bundle of light beams fanned concentrically to an optical axis of the deflection element. The optical deflection element has a base body made of optically transparent material, and has a light input and output side. The light input side is configured such that a primary bundle of light beams can be coupled in the base body. The light output side has a cylindrically symmetrical contour, which defines a recess in the base body. The fanning of the primary bundle of light beams is achieved by refraction on rotationally symmetric interfaces, which are variably inclined relative to the optical axis. The invention further relates to an optical measuring device for the three-dimensional measurement of a cavity in an object and a method for producing a concentrically fanned, spatially structured bundle of light beams.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the US National Stage of International Application No. PCT/EP2008/050929, filed Jan. 28, 2008 and claims the benefit thereof. The International Application claims the benefits of German application No. 10 2007 005 388.8 filed Feb. 2, 2007, both of the applications are incorporated by reference herein in their entirety. 
     FIELD OF THE INVENTION 
     The present invention relates to an optical deflection element, which can be used to fan a primary homogenous light beam bundle in the shape of a cone surface. The present invention also relates to an optical measuring device for the three-dimensional measuring of a cavity formed in an object, said optical measuring device comprising the above-mentioned optical deflection element. The present invention also relates to a method for producing a concentrically fanned, spatially structured light beam bundle using the above-mentioned optical deflection element. 
     BACKGROUND OF THE INVENTION 
     The surface structure of at least approximately tubular inner surfaces of a cavity can be captured three-dimensionally by means of optical triangulation. In this process a spatially structured illumination pattern is projected onto the inner surface of the respective cavity to be captured and the scene is captured digitally by means of a camera system. By measuring the distortion of the illumination pattern projected onto the inner wall as a result of the surface shape, which can be done automatically using known image processing methods, it is possible to calculate a digital model, which maps the shape of the cavity. Deviations and/or distortions of the captured projected lines from the known, initially symmetrical circular shapes that were concentric to an optical axis are captured in this process. 
     Such a cavity measurement by means of optical triangulation can advantageously be used when measuring or profiling the human auditory canal. The anatomy of the auditory canal means that an optical measuring device must be provided, which cannot exceed a maximum diameter of 4 mm. This basic condition applies to the entire object-side optical system of such a measuring device, said optical system having to be inserted into the auditory canal. The object-side optical system here comprises at least a camera system and an optical element for producing the structured illumination. The camera system and the optical element are disposed concentrically to a common optical axis of the optical measuring device here. 
     It is known that diffractive optical elements can be used to produce structured illumination. In particular (binary) phase gratings, also known as so-called Dammann gratings, can distribute the incident intensity of a primary light beam bundle selectively and in some instances largely uniformly to specific orders of diffraction due to a particularly advantageous substructure. 
     A so-called circular Dammann grating for producing a structured illumination pattern from concentric rings is known from the publication “Changhe Zhou, Jia Jia, Liren Liu;  Circular Dammann Grating; Optics Letters , Vol. 28, No. 22, 2003, pages 2174-2176”. However this has the disadvantage that it is difficult to achieve larger deflection angles in relation to the optical axis of the circular phase grating. It is true that larger deflection angles would in principle be possible using extremely small phase grating structures in the region of 150 mm but such small phase grating structures are technologically extremely difficult to produce. To produce such fine gratings, etching processes are needed which require much finer structuring than the etching processes currently used with a best resolution of 400 nm. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to create an optical deflection element, which allows broad fanning of a primary light beam bundle and which can also be produced in a comparatively simple manner. 
     This object is achieved by the subject matter of the independent claims. Advantageous embodiments of the present invention are described in the dependent claims. 
     The first independent claim describes an optical deflection element for the refractive production of a spatially structured light beam bundle that is fanned concentrically to an optical axis of the deflection element. The optical deflection element has a base body, which is made at least partially of an optically transparent material and which has a light input side and a light output side. The light input side is configured such that a primary light beam bundle can be coupled into the base body. In relation to the optical axis of the deflection element the light output side has a cylindrically symmetrical contour, which defines a recess in the base body. 
     The described optical deflection element is based on the knowledge that it is possible to realize comparatively broad beam fanning in a simple manner by means of refraction at the corresponding optical interface due to a concave, i.e. inward curving, cylindrically symmetrically shaped contour on the output side. In this process the angle formed by the respective radial region of the contour with the optical axis determines the degree of spatial fanning according to Snellius&#39;s law of refraction. 
     The described optical deflection element can be produced with considerably less manufacturing outlay than known diffractive optical elements. In addition to conventional mechanical production methods, pressure methods are also suitable and these should be considered as suitable for economical mass production in particular. 
     According to one exemplary embodiment of the invention, the contour has a first annular section, which essentially has the shape of at least part of a first lateral surface of a cone pointing into the interior of the base body. The lateral lines of the first lateral surface form a first angle with the optical axis here. 
     If the contour essentially has the shape of a complete cone surface, the above-mentioned condition of a cylindrically symmetrical contour is automatically satisfied. If the contour has the shape of an incomplete cone surface, the above-mentioned condition of a cylindrically symmetrical contour is satisfied if the contour has the shape of the lateral surface of a truncated cone. 
     The term lateral lines here refers to those lines that run on the surface of the cone, which represents a rotational body, longitudinally in relation to its axis of rotation. The axis of rotation corresponds to the optical axis of the deflection element and/or base body here. The lateral lines are therefore the connecting lines between the actual or virtual tip of the cone or truncated cone and the peripheral points of the corresponding base circle. 
     The first angle described above between the lateral lines and the optical axis here is precisely half the size of the acceptance angle of the cone pointing into the interior of the base body. It is possible to determine the angular deflection and therefore the degree of fanning of the light cone exiting from the light exit surface by selecting the acceptance angle for the cone. 
     According to a further exemplary embodiment of the invention the contour has a second annular section, which is disposed outside the first annular section in a radial direction and which essentially has the shape of a second lateral surface of a truncated cone. The lateral lines of the second lateral surface here form a second angle with the optical axis, this second angle being different from the first angle. 
     The described annular sections thus represent different concentrically disposed, essentially conical facets. Each facet fans the primary light beam bundle as a function of the acceptance angle of the cone and the refractive index of the base body material with a specific acceptance angle in a cylindrically symmetrical manner. The light beam bundle exiting from the light exit surface therefore has two light structures with the shape of a cone surface, which have a different acceptance angle. In the case of a cylindrical cavity, which is oriented parallel and concentrically to the optical axis, it is thus possible to produce circular projection lines on the inner wall of the cylindrical cavity. 
     According to a further exemplary embodiment of the invention the contour has at least a third annular section, which is disposed outside the second annular section in a radial direction and which essentially has the shape of a third lateral surface of a truncated cone. The lateral lines of the third lateral surface form a third angle with the optical axis here, this third angle being different from the second angle. 
     The third angle is also preferably different from the first angle, so that all the light structures with the shape of a cone surface, which exit from the light exit surface, have a different acceptance angle. 
     It should be noted that the cylindrically symmetrical contour can also be divided into more than three annular sections. It is thus possible for the primary light beam bundle coupled in on the light input side in principle to be spatially structured to any degree of fineness, so that a plurality of light structures with the shape of a cone surface can be produced in a simple manner. 
     By using a number of light structures with the shape of a cone surface when measuring the human auditory canal it is possible to tailor the structure of the overall illumination pattern effectively to the expected shape of an auditory canal to be measured. The projection of a number of concentric rings at different angles to the optical axis onto the inner wall of the auditory canal should be considered to be particularly appropriate here. In order to achieve a sufficiently large triangulation angle in an optical measuring device, ensuring a local resolution of 50 μm in all spatial directions, as required for many applications, illumination angles in the region of 10° to 30° are required in relation to the optical axis. Such illumination angles can be achieved without any problem using the described optical deflection element. The triangulation angle is defined as usual by the angular distance between the beam path of the illumination light and the beam path of the measuring light captured by the camera. 
     According to a further exemplary embodiment of the invention the angular difference between the first angle and a right angle is greater than the angular difference between the second angle and a right angle. This means that the outer conical facets have a flatter inclination in relation to a cross-sectional plane oriented perpendicular to the optical axis than the inner conical facets. 
     The described configuration of the different conical facets with graduated angles of inclination has the advantage that the optical deflection element can be produced particularly simply. The configuration of the cylindrically symmetrical recess here can be achieved by two-stage machining, in which (a) a first conical recess with a small acceptance angle is assigned to the first annular section and (b) a second conical recess with a large acceptance angle is assigned to the second annular section. The sequence of the machining steps (a) and (b) is immaterial here. 
     It should be noted that a gradual increase in the described angular differences for the individual annular sections can also be realized in a corresponding manner from the outside inward, i.e. toward the optical axis, with more than three annular sections. 
     According to a further exemplary embodiment of the invention the angular difference between the first angle and a right angle is smaller than the angular difference between the second angle and a right angle. This means that the outer conical facets have a steeper inclination in relation to a cross-sectional plane to the optical axis than the inner conical facets. 
     The graduated angles of inclination described with this exemplary embodiment have the advantage that those light beams exiting from the light output side of the base body at the lateral surfaces of the outer annular section are refracted further away from the optical axis than those light beams exiting from the light output side of the base body at the lateral surfaces of annular sections further in. The beam paths of the individual light structures exiting from the light output side therefore do not cross, so the pattern of the individual beam paths is particularly clear. 
     According to a further exemplary embodiment of the invention the first annular section has the shape of at least part of a first lateral surface of a cone pointing into the interior of the base body, the second annular section has the shape of a second lateral surface of a truncated cone and/or the third annular section has the shape of a third lateral surface of a truncated cone. The described most exact cone-shaped or truncated cone-shaped recess possible has the advantage that the recess can be configured in the body in an effective and particularly simple manner. Depending on the size of the recess and/or the mechanical machinability of the optically transparent material it is possible to use different methods, such as mechanical turning, compression or hot-stamping to produce the optical deflection element. 
     According to a further exemplary embodiment of the invention the first annular section, the second annular section and/or the third annular section has a curved surface. The respective surfaces can have a concave or convex surface independently of one another. 
     The described curvature in the individual annular sections has the advantage that the light beams exiting from the different slightly curved conical facets can be focused individually. In this process a convex optical interface of a facet results in slight focusing of the corresponding light structure. If there is focusing of the light structure on a circular line even without a concave interface, a slightly concave optical interface of a facet results in focal displacement of the corresponding light structure backward, in other words to a point that is further away from the light output side of the optical deflection element than the above-mentioned circular line. 
     According to a further exemplary embodiment of the invention the base body has the outer shape of a cylinder, in particular a circular cylinder. The described optical deflection element can thus be made from a so-called rod lens. 
     The base body of the optical deflection element preferably consists at least partially of a material having a high refractive index. This applies in particular to a wavelength of approximately 405 nm. This has the advantage that coherent light from standard semiconductor laser diodes can be fanned particularly significantly. Light with this comparatively short wavelength in the optical spectrum also has a much smaller depth of penetration into the human skin than light with a longer wavelength. 
     According to a further exemplary embodiment of the invention the light input side has a convex curvature. In this context convex curvature means that the light input side also has a contour that curves out in relation to the base body. In the case of a conventional contour in the manner of a cone surface this means that the center of curvature of the corresponding cone surface is on the side of the base body in relation to the light input side. 
     Convex curvature has the advantage that the refraction of the primary light beam bundle entering the base body on the light input side means that the primary light beam bundle is focused as a function of the degree of curvature. The curvature of the light input side can be tailored to the respective application here. If the light structures are projected onto the inner wall of an at least approximately cylindrical cavity, focusing can be set so that the light structures represent sharp illumination lines that are as fine as possible on the inner wall of the cavity to be measured. 
     According to a further exemplary embodiment of the invention the light input side has a curved first annular section and at least a curved second annular section. The respective surfaces here can have a concave or convex surface independently of one another. 
     Like the individual curvature of the annular sections on the light output side described above, the individual curvature of the individual annular sections on the light input side has the advantage that the light beams exiting from the different conical facets can be focused individually. In this process a convex optical interface of a facet results in slight focusing of the corresponding light structure. If there is focusing of the light structure to a circular line even without a convex interface, a slightly concave optical interface of a facet results in focal displacement of the corresponding light structure backward, in other words to a point that is further away from the light output side of the optical deflection element than the above-mentioned circular line. 
     Compared with the individual curvature of the annular sections on the light output side, the individual curvature of the individual annular sections on the light input side can be produced much more simply by means of conventional machining methods, such as mechanical turning, compression or hot-stamping. This is because compared with the light output side the light input side has a much simpler topology or surface structure, so the corresponding curvatures can be configured more easily. 
     According to a further exemplary embodiment of the invention the base body has a through opening, which extends coaxially to the optical axis. 
     This makes it possible for an optical observation system or camera to be passed through the optical deflection element. This is particularly advantageous if the optical deflection element is used for an optical measuring instrument with a compact structure, which is used to measure the size and/or shape of the cavity by spatial measurement of illumination lines projected onto the inner wall of a cavity. 
     According to a further exemplary embodiment of the invention the through opening is a drilled core having the shape of a cylinder disposed concentrically to the optical axis. 
     The described drilled core has the advantage that the optical deflection element can be produced particularly simply and therefore in a cost-saving manner. 
     The second independent claim describes an optical measuring device for the three-dimensional measuring of a cavity configured in an object, in particular for the three-dimensional measuring of the auditory canal of a human or animal. The optical measuring device has (a) a light source, set up to transmit illumination light along an illumination beam path, (b) an optical deflection element of the type mentioned above, which structures the transmitted illumination light spatially in such a manner that at least one illumination line running around the optical axis of the deflection element is produced on the inner wall, the shape of said illumination line being a function of the size and shape of the cavity, and (c) a camera, which captures the at least one illumination line at a triangulation angle by way of a mapping beam path. 
     The above-mentioned optical measuring device is based on the knowledge that cylindrically symmetrically structured illumination, which is projected into the inner wall of the cavity to be measured, allows three-dimensional (3D) measurement of the cavity in a simple manner using a modified triangulation method. The shape of the at least one illumination line is captured by the camera here, said camera preferably recording a two-dimensional (2D) image of the projection ring or projection rings symmetrically to the optical axis. It is possible to measure the inner wall of the cavity based in 3D on the deviations and/or distortions of the captured illumination line from symmetrical circular shapes concentric to the optical axis. 
     Compared with three-dimensional distance sensors, with which only one measuring point is illuminated and the height position of the illuminated measuring point is captured, the described optical measuring device has the advantage that a number of measuring points are measured almost simultaneously (automatically), being disposed around the optical axis. This significantly increases the scan rate overall. 
     A number of illumination structures are preferably produced, each of the illumination structures produced having the shape of a cone surface. This allows the number of measuring points that can be captured simultaneously by means of a single camera image to be increased further. 
     In the case of a cylindrical cavity, which extends symmetrically around the optical axis of the optical measuring device, illumination rings result, which are configured or disposed concentrically to the optical axis. In the case of a cylindrical cavity, which extends around a cylindrical axis having a parallel offset in relation to the optical axis of the optical measuring device, distorted illumination lines result, which have an elliptic shape in relation to the optical axis. Adjacent illumination lines in a first wall region of the inner wall, which is further away from the optical axis than a second wall region, are further away from one another. This is because the conical fanning of the individual illumination structures means that adjacent illumination lines are further away from one another, the further they are away from the optical axis. It is thus evident that both the deviation of the 3D form of the illumination lines captured by the camera from a perfect circle and the distance between adjacent illumination lines provide information about the 3D contour of the cavity. 
     It should be noted specifically here that an illumination structure or an, in some instances deformed, illumination line already contains 3D information relating to the size and shape of the cavity to be measured. Nevertheless it is advantageous, in particular for reasons of measuring speed and spatial resolution, to structure the illumination light transmitted by the light source into a number of conically widened illumination structures. 
     The capturing of the illumination lines at a triangulation angle means that the beam path of the mapping light and the beam path of the illumination light, i.e. the respective acceptance angle of the conical illumination structure, form an angle that is not 0°. 
     This angle is referred to as the triangulation angle. The greater this triangulation angle, the greater the accuracy of the 3D position determination. 
     The described optical measuring device has the advantage that no moving parts and in particular no moving optical components are required within the measuring device for 3D measurement. This means that the optical measuring device can be produced at comparatively low cost and that the reliability of the measuring device is also very good in actual deployment conditions. 
     It should be noted that the entire measuring device can preferably be displaced along the optical axis to measure larger cavities. The partial images recorded during such a movement can be put together again using appropriate image processing methods. Such putting together is frequently referred to as stitching. 
     According to one exemplary embodiment of the invention the optical measuring device also has an evaluation unit, which is connected downstream of the camera and is set up so that it is possible to determine the size and shape of at least part of the cavity automatically by processing the image of the at least one illumination line captured by the camera. 
     The described evaluation unit thus advantageously allows automatic image evaluation of the 2D images captured by the camera, so that 3D data of the measured cavity can be supplied directly as the output variable of the optical measuring device for further data processing. 
     According to a further exemplary embodiment of the invention the optical measuring device also has an optical projection system, which is disposed in the illumination beam path. This has the advantage that it is possible to focus the illumination light, optionally in combination with a suitable curvature of the essentially conical facets of the light output side, so that the illumination lines are mapped as sharply as possible on the inner wall of the cavity to be measured and can therefore be captured as sharp structures by the camera. 
     The optimal selection of the focal length of this optical system is therefore a function of the fanning of the illumination beam striking the optical system, the optical path length of the illumination light between the optical system and the optical deflection element and the optical path length between the optical deflection element and the inner wall. The focal length of this optical system should therefore be a function not only of the design of the described optical measuring device but also of the approximate anticipated size of the cavity to be measured. 
     It should be noted that the convex curvature of the light input side of the base body described above in conjunction with an exemplary embodiment of the optical deflection system also has the same qualitative effect as the optical projection system described here. The same also applies to the curvatures of the essentially conical facets on the light output side. 
     According to a further exemplary embodiment of the invention the optical measuring device also has a beam splitter disposed at an oblique angle in the optical axis of the deflection element. This beam splitter deflects the illumination beam path in such a manner that either (a) an object-side section of the illumination beam path runs parallel to the optical axis or (b) an image-side section of the mapping beam path runs at an angle to the optical axis. 
     In this context an oblique angle means that the beam splitter is disposed at an angle not equal to 0° and not equal to 90° in relation to the optical axis. The beam splitter is preferably inclined at an angle of 45° to the optical axis, so that the illumination beam path or the mapping beam path has a 90° bend. 
     According to a further exemplary embodiment of the invention at least one section of the illumination beam path, in which the illumination light is passed parallel to the optical axis, is shaped around the mapping beam path running in the center of the optical axis. 
     The illumination beam path here can be disposed around the optical axis or mapping beam path with annular symmetry or concentrically to the optical axis in cross-section. This means that an illumination beam concentric to the optical axis strikes the optical deflection element, which is likewise configured symmetrically to the optical axis. The refractive optical deflection element having a drilled core described above is an appropriate optical deflection element for example. 
     It should be noted that the illumination beam path and the mapping beam path can also run coaxially to some degree. For the 3D measurement based on the triangulation principle it is sufficient if the illumination beam path and the mapping beam path are spatially separated on the object side, i.e. in proximity to the illumination lines to be measured, so that a triangulation angle is defined. An object-side branching of the illumination beam path and mapping beam path can be effected for example by appropriate beam splitters or by an optical waveguide, the object-side end of which is split into two spatially separate sub-ends. 
     According to a further exemplary embodiment of the invention the optical measuring device also has a light-conducting facility, which is disposed in the mapping beam path and which is set up to transmit a two-dimensional image of the illumination lines to the camera. 
     A mechanically relatively rigid rod lens arrangement, as used in endoscopes for example, can be used as the light-conducting facility. An endoscopic system based on a graded optical system can also be used as the light-conducting facility, the refractive index changing as a function of radius. It is thus possible to achieve curvature of the light beams within the light-conducting facility so that the camera can capture mapping beams from a wide angle range as a result. 
     A so-called Hopkins optical system can also be used as the light-conducting facility, this also being a mechanically largely rigid optical arrangement. A Hopkins optical system can be a type of glass tube for example, in which air lenses are inserted to give a particularly detailed view during endoscopic examinations. This advantage of the particularly detailed view also results with the described optical measuring device in a particularly high level of accuracy and reliability for the 3D measurement. 
     A so-called image waveguide, which comprises a number of individual optical waveguides or glass fibers, is also suitable as a light-conducting facility. An image waveguide has the advantage of flexibility, so that the optical measuring device can be realized with an at least partially flexible structure. This allows accurate cavity measurement even in curved cavities, into which a rigid measuring device cannot be inserted. 
     The third independent claim describes a method for producing a concentrically fanned, spatially structured light beam bundle. The method has the following steps: transmission of a primary light beam bundle to an optical deflection element as described above, so that the primary light beam bundle enters the base body of the optical deflection element on the light input side and exits from the base body as a secondary light beam bundle on the light output side. In this process the secondary light beam bundle has a light structure at least in the shape of a cone surface. 
     The above-mentioned method is based on the knowledge that use of the refractive optical deflection element described above allows broad fanning of the secondary light beam bundle to be realized particularly simply compared with the use of known diffractive optical deflection elements. Broad fanning means that the corresponding cone surfaces have a large acceptance angle. 
     If the light output side of the base body has a number of annular sections with differently inclined, essentially conical facets, the corresponding cone tips of the fanned light cones can coincide at an actual source point, which is on the optical axis. In this context an actual source point means that the illumination structures start at least approximately from one source point on the optical axis. 
     If the base body, as described above in a preferred exemplary embodiment, has a through opening or drilled core, the secondary light beam bundle exits from at least a circular section, which is disposed concentrically around the optical axis. In this instance too the corresponding cone tips can be seen as an actual source point of the secondary light beam bundle which is fanned in the shape of a cone surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantages and features of the present invention will emerge from the exemplary description which follows of currently preferred embodiments. The individual figures in the drawing accompanying this application should only be considered to be schematic and not to scale. 
         FIG. 1   a  shows a cross-sectional view of an optical measuring device according to one exemplary embodiment of the invention. 
         FIG. 1   b  shows a camera image with four images of illumination lines projected onto the inner wall of a cavity to be measured. 
         FIG. 1   c  shows a front view of the object-side end of the optical measuring device shown in  FIG. 1   a.    
         FIG. 2  shows the beam paths of the illumination light and mapping light configured at the object-side end of the optical measuring device shown in  FIG. 1   a , said beam paths determining the triangulation angle. 
         FIG. 3  shows a simulation of the refractive production of an individual light structure in the shape of a cone surface. 
         FIG. 4   a  shows a perspective view of an optical deflection element, having two conical facets. 
         FIG. 4   b  shows a structural diagram of the optical deflection element shown in  FIG. 4   a.    
         FIG. 4   c  shows a simulation of the refractive production of two light structures in the shape of a cone surface using the optical deflection element shown in  FIG. 4   a.    
         FIG. 5  shows a simulation of the refractive production of three light structures in the shape of a cone surface, which are produced by an optical deflection element with three conical facets. 
         FIG. 6  shows an optical deflection element, wherein the annular sections each have a convex curvature on the light output side. 
         FIG. 7  shows an optical deflection element, wherein the light input side has two curved annular sections, each with a convex curvature. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     It should be noted here that the reference characters for identical or corresponding components only differ in the first figure in the drawing. 
       FIG. 1   a  shows a cross-sectional view of an optical measuring device  100  according to one exemplary embodiment of the invention. The optical measuring device  100  has a cylindrically symmetrical shape in relation to an optical axis  117 . 
     The optical measuring device  100  has a light source  110 , which is a laser diode  110  according to the exemplary embodiment shown here. Of course other light sources can also be used, for example a light-emitting diode. The laser diode  110  emits monochromatic illumination light  111 , which strikes an optical projection system  112 , which widens the illumination beam  111 . The widened illumination beam  111  strikes a beam splitter  113 , which is oriented at an angle of 45° in relation to the optical axis  117 , so that at least some of the illumination light  111  is coupled into a hollow cylinder  115  as a function of the reflective capacity of the beam splitter  113 , said hollow cylinder  115  being disposed symmetrically in relation to the optical axis  117 . To prevent the illumination light  111  being coupled into the central part of the hollow cylinder  115 , an optical shading element  114  is disposed between the beam splitter  113  and the laser diode  110 . 
     The illumination light deflected by the beam splitter  113  is guided by the hollow cylinder  115  in an illumination beam path  116 . The illumination beam path  116  is configured as cylindrically symmetrical in relation to the optical axis  117 . At an object-side end of the optical measuring device  100  the illumination light strikes an optical deflection element  150 , which likewise has a cylindrically symmetrical shape and is disposed in a cylindrically symmetrically manner around the optical axis  117 . According to the exemplary embodiment shown here the optical deflection element  150  is an optically refractive element, which is described in more detail below with reference to  FIGS. 3 ,  4   a  and  4   b.    
     The optical deflection element  150  structures the illumination light spatially in such a manner that a number of illumination structures result concentric to the optical axis  117 , each having the shape of a cone surface  122  and being projected onto the inner wall of a cavity  125  to be measured. Only one illumination structure  122  is shown in  FIG. 1   a  for reasons of clarity. 
     It should be noted that the camera  145  and the laser diode  110  can also be swapped when using a corresponding beam splitter  113 . A transmission-selective glass plate for example can be used as a beam splitter, being metal-coated within a small elliptical region in the center such that the image in the center of the illumination beam path  116  is coupled out rather than the laser beam. 
     According to the exemplary embodiment shown here the cavity to be measured is an auditory canal  125  of a patient. The auditory canal  125  typically has a diameter d of approximately 4 mm. 
     It should however be pointed out that the measuring device  100  can also be used to measure other cavities. Thus for example the three-dimensional shape of drilled holes can be measured in an exact manner before precisely fitting rivets can be selected for a particularly reliable riveted connection, in aviation construction for example. 
     The projection of the illumination structure  122  onto the inner wall of the cavity  125  produces a closed illumination line  128 , the shape of which is a function of the size and shape of the cavity  125 . The sharpness of the illumination lines  128  here is a function of the focusing of the illumination structures  122  on the inner wall. The focal length of the optical projection system  112  can thus be adjusted so that sharp illumination lines  128  are produced on the inner wall of the cavity for an approximate anticipated size of the cavity to be measured. 
     The size and shape of the individual illumination lines  128  are captured by a camera  145 . This is done by way of a mapping light  130  from the illumination lines  128 . This mapping light  130  is converged by means of an optical mapping system  132 , which has a particularly short focal length. The optical mapping system  132  can also be referred to as a fish eye due to its extremely wide acceptance angle. 
     The mapping light  130  converged by the optical mapping system  132  is guided by means of a light-conducting facility  135  to the image-side end of the optical measuring device  100 . According to the exemplary embodiment shown here the light-conducting facility is a rod lens arrangement  135 , which is also used for example in endoscopic devices in medical engineering. The second optical mapping system can be configured as a single piece with the rod lens arrangement  135 , in that the corresponding end face interface of a corresponding rod lens facing the cavity has an extremely severe curvature. 
     The rod lens arrangement  135  has a number of individual rod lenses  135   a , which together produce a length  1  of approximately 50 mm. The rod length arrangement  135  can of course also be of any other length. The rod lens arrangement can also be a so-called Hopkins lens arrangement. 
     The rod lens arrangement  135  therefore defines a mapping beam path  136 , which extends along the optical axis  117  to the image-side end of the optical measuring device  100 . The mapping beam path  136  and the illumination beam path  116  are each disposed in a cylindrically symmetrical manner in relation to the optical axis  117 , with the illumination beam path  116  outside the mapping beam path  136 . 
     Of course the optical measuring device can also have a structure in which the mapping beam path runs outside the illumination beam path. In any case there must be a spatial separation of illumination light  122  and mapping light  130  at the latest at the object-side end of the measuring device  100 , so that the projected illumination lines  128  can be captured at a triangulation angle and the 3D contour of the cavity  125  can thus be determined. A triangulation angle is always present when the illumination, in other words here the production of the illumination lines  128 , takes place at a different angle from the observation, in other words here the mapping of the illumination lines  128  toward the camera  145 . 
     The mapping light  130  guided in the rod lens arrangement  135  strikes the beam splitter  113 . The beam splitter is penetrated by at least some of the mapping light  130  only with a certain parallel offset. This parallel offset is a function of the thickness, the refractive index and the angular position of the beam splitter  113  relative to the optical axis  117 . The remaining part of the mapping light  130  is reflected at the beam splitter and strikes the optical shading element  114  and/or the laser diode  110  as lost light. 
     The part of the mapping light  130  passing through the beam splitter strikes an optical mapping system  142  and is mapped by this onto the camera  145 . The camera  145  therefore records a camera image  148 , which shows images  149  of the illumination lines  128  as a function of the shape of the cavity  125 , these being distorted in particular in the peripheral region of the camera image  148 .  FIG. 1   b  shows an example of such a camera image  148 , in which a total of four images  149  of corresponding illumination lines  128  projected onto the inner wall of the cavity  125  can be seen. A quantitative analysis of this distortion carried out in an evaluation unit  146  downstream of the camera  145  allows the shape and size of the cavity  125  to be determined. 
       FIG. 1   c  shows a front view of the object-side end of the optical measuring device  100 . The optical mapping system  132 , which is enclosed by the optical deflection element  150  is clearly shown. 
       FIG. 2  shows a cross-sectional diagram of beam paths of the illumination light  222  and the mapping light  230  configured at the object-side end of the optical measuring device  100  now shown with the reference character  200 . A mean projection or illumination angle β results for a specific illumination line  228 , as shown in  FIG. 1   d , in relation to the optical axis  217 . 
     The optical deflection element  250  has a mean radial distance r from the optical axis  217 . A mapping angle α correspondingly results for the illumination line  228  shown in relation to the optical axis  217 . It is taken into account here that the mapping light  230  is converged by the optical mapping system  232  disposed in the center of the optical axis  217 . 
     The triangulation angle θ results from the difference between the two angles α and β (θ=α−β). As shown in  FIG. 1   d  this triangulation angle θ is of course also a function of the longitudinal distance Δ 1 . This longitudinal distance Δ 1  results from the distance parallel to the optical axis  217  between the deflection element  250  and the optical mapping system  232 . 
       FIG. 3  shows a simulation of the refractive production of an individual light structure  322  in the shape of a cone surface. A primary light beam bundle  311  passes through a light input side  360  into the base body  352  of the optical deflection element  350 . The light output side  370  opposite the light input side  360  has a conical facet  371 , so that a cone-shaped recess is configured in the base body. The light beam bundle penetrating the base body is widened to form the illumination structure  322  with the shape of a cone surface at the optical interface inclined correspondingly in relation to an optical axis  317  of the deflection element  350 . An illumination line  328  thus results on a cylindrical inner surface (not shown) of a cavity to be measured. 
       FIGS. 4   a  and  4   b  show an optical deflection element  450 , which has two conical facets, a first conical facet  471  configured in a first annular section and a second conical facet  472  configured in a second annular section.  FIG. 4   a  shows a perspective view of the optical deflection element  450 , while  FIG. 4   b  shows a structural diagram of the optical deflection element  450 . 
     The optical deflection element  450  has an essentially cylindrical base body  452 , in which a through opening  454  is configured. According to the exemplary embodiment shown here the base body  452  has a diameter of 3 mm and a length of 3.65 mm. The through opening  454  configured as a drilled hole has a diameter of 1.3 mm. The deflection element  450  can of course also be realized with different dimensions. 
     An end-face light input side  460  has a slight convex curvature  465  with a radius of curvature of 30 mm. This curvature  465  thus represents a slightly focusing optical interface for a primary light beam bundle entering on the light input side  460 . Like the entire base body  452  the convex shaped input interface has a rotationally symmetrical shape in relation to the optical axis  417 . 
     The light output side  470  opposite the light input side  460  has a concave contour, which is determined by the two conical facets  471  and  472 . As shown in  FIG. 4   b  the second conical facet  472  has a radial thickness of 0.51 mm in relation to the optical axis  417 . The optical interface of the second conical facet  472  is also inclined at an angle of 105° in relation to the optical axis  417 . The first conical facet  472  is inclined at an angle of 120.06° in relation to the optical axis  417 . Other dimensions and/or angles are of course possible here too. 
       FIG. 4   c  shows a simulation of the refractive production of two light structures in the shape of a cone surface using the optical deflection element  450 . A primary light beam bundle  411  strikes the base body  452  of the deflection element  450  parallel to the optical axis  417 . The through hole  454  shown in  FIGS. 4   a  and  4   b  is taken into account by a circular shading element  454   a  in the simulation. The shading element  454   a  is disposed concentrically to the optical axis  417 . 
     The concave curvature  465  of the light input side  460  is simulated by a converging lens  465   a , which is likewise disposed concentrically to the optical axis  417  directly behind the base body  452 . The two conical facets  471  and  472  bring about a cylindrically symmetrical branching of the primary light beam bundle  411  into a secondary light beam bundle  422 , which has a first light structure  422   a  in the shape of a cone surface and a second light structure  422   b  in the shape of a cone surface. 
       FIG. 5  shows a simulation of the refractive production of three light structures  522   a ,  522   b  and  522   c  in the shape of a cone surface, which are produced by an optical deflection element  550  with three conical facets. In the simulation shown a primary light beam bundle  511  strikes a base body  552  parallel to an optical axis  517 . A through hole is simulated by a circular shading element  554   a , which is disposed concentrically to the optical axis  517 . 
     Concave curvature of the light input side of the optical deflection element  550  is simulated by a converging lens  565   a , which is likewise disposed concentrically to the optical axis  517  and directly behind the base body  552 . The three conical facets bring about a cylindrically symmetrical branching of the primary light beam bundle  511  into a secondary light beam bundle  522 , which has the first light structure  522   a  in the shape of a cone surface, the second light structure  522   b  in the shape of a cone surface and the third light structure  522   c  in the shape of a cone surface. 
     It should be noted that only half of the simulations shown in  FIGS. 3 ,  4   c  and  5  are illustrated so that the resulting widened light cones can be shown more clearly. In the context of the corresponding simulations this halving of the diagram was achieved using a suitable rectangular shutter in the respective beam path. 
       FIG. 6  shows an optical deflection element  650  according to a further exemplary embodiment of the invention. Like the deflection elements described above the deflection element  650  has a base body  652  with a drilled core  654 , shaped with rotational symmetry in relation to an optical axis  617 . The light input side  660  has a flat interface. The light output side  670  has two annular sections shaped symmetrically in relation to the optical axis  617 , a first annular section  671  and a second annular section  672 . 
     It should be noted that the annular sections  671  and  672  each have a gentle curvature, which is shown in a greatly exaggerated manner in  FIG. 6 . The large radius of curvature means that the corresponding surface contours can be described as before as essentially conical facets. The curvature of the essentially conical facet  671  may be different from the curvature of the essentially conical facet  672 . It is thus possible to focus the light beams exiting from the different slightly curved conical facets individually. 
       FIG. 7  shows an optical deflection element  750  according to a particularly preferred exemplary embodiment of the invention. The deflection element  750  also has a base body  752  with a drilled core  754 , which is shaped with rotational symmetry in relation to an optical axis  717 . In contrast to the exemplary embodiment shown in  FIG. 6  the light input side  760  has a structured surface contour, which comprises two annular sections shaped symmetrically in relation to the optical axis  717 , a first annular section  761  and a second annular section  762 . The annular sections  771  and  772  on the light output side have no further curvature at the two conical facets. 
     The radii of the individual annular sections  761 ,  762 ,  771 ,  772  are tailored to one another such that when illumination strikes parallel to the optical axis  717 , the first annular section  761  is assigned to the first annular section  771  and the second annular section  762  is assigned to the second annular section  772 . Therefore the light beams exiting from the different conical facets  771  and  772  can be focused individually due to a corresponding curvature of the annular sections  761  and  762 . 
     It should be noted that the two exemplary embodiments shown in  FIG. 6  and  FIG. 7  can also be combined with one another so that the annular sections each have an individual curvature both on the light input side and on the light output side. 
     It should be noted that the embodiments described here only represent a limited selection of possible variants of the invention. It is thus possible to combine the features of individual embodiments in an appropriate manner so that the person skilled in the art will consider a plurality of different embodiment to be disclosed in an evident manner with the variants set out explicitly here.