Method and device for lithography-based additive manufacturing of a structure
Patent Information
- Application Number
- PCT/EP2026/060831
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2025-04-15
- Filing Date
- 2026-04-15
- Publication Date
- 2026-10-22
Smart Images
Figure EP2026060831_22102026_PF_FP_ABST
Abstract
Description
[0001] Method and apparatus for lithography-based additive manufacturing of a structure
[0002] The present invention relates to a method for the lithography-based additive manufacturing of a structure, in particular an optical lens, at an axial end of an optical conductor, in which electromagnetic radiation emitted in a writing style by an irradiation device is focused by means of a focusing optics downstream of the irradiation device into a writing beam, which is successively directed to focal points within a material that can be solidified, preferably by means of multiphoton absorption, whereby a volume element of the material located at the focal point is solidified in each case.
[0003] The invention further relates to a device for lithography-based additive manufacturing of a structure, in particular an optical lens, at an axial end of an optical conductor.
[0004] Optical conductors are used, among other things, in communication technology, sensor technology (especially in the life sciences), and certain manufacturing technologies. Besides using special connectors to optically connect individual optical conductors or conductor bundles, or to couple light in or out of the conductors or conductor bundles, light can also be coupled in or out of individual conductors without a corresponding end piece. However, it is not always easy to position the incoming light beam at a suitable point for coupling to the axial end of the optical conductor and simultaneously at a suitable angle. At the same time, the light output at a desired point towards which the conductor is directed is insufficient when coupling light out from the axial end if the exiting light is not focused in some way.
[0005] Therefore, there are approaches to applying structures that act as optical lenses to the axial ends of optical waveguides, and the scientific community is increasingly focusing on lithography-based additive manufacturing processes, which can produce even very small structures with very high precision. Such processes are commonly referred to as 3D printing. In these processes and the corresponding devices, the 3D printers, a material that can be solidified by electromagnetic radiation is selectively solidified layer by layer by appropriate exposure, according to a model calculated as a three-dimensional body in layers, and in this way the finished structure is additively built up.
[0006] When constructing an optical lens at the axial end of an optical conductor using this method, the extremely small dimensions of such a conductor pose a particular challenge. With typical core thicknesses of optical conductors (waveguides) ranging from approximately 5 pm to 30 pm, it is especially difficult to reference the 3D printer to the center of the conductor's core or to the optical center of the core as a reference point in order to subsequently build the optical lens symmetrically with respect to this center. The center of the core is not always located at the geometric center of the respective axial end of an optical conductor, and the optical center is not always located at the center of the core, as both the optical conductor and the core can be deformed due to tolerances occurring during mass production, or an intentional asymmetry may be present.The optical center can therefore only be effectively determined by actually introducing a light beam and measuring the resulting light power or intensity at the other end, or by measuring the exiting light. A further challenge lies in achieving a desired angular alignment, particularly a perfectly aligned alignment, of the optical conductor relative to the optical axis of the focusing optics, in order to subsequently construct the structure according to this optical axis.
[0007] The present invention is disclosed herein with particular reference to an optical lens as a structure to be manufactured at the axial end of an optical waveguide; however, it is nevertheless within the scope of the invention to additively manufacture other structures instead of an optical lens, and in particular diffraction gratings, apertures and the like.
[0008] The present invention is therefore based on the objective of improving a method of the type mentioned at the outset in such a way that the referencing of the 3D printer to the optical center of the optical conductor and the angular alignment is simplified and can therefore be carried out quickly and reliably.
[0009] To solve this problem, the method according to the invention is characterized in that, in a measuring step preceding the writing process, electromagnetic radiation, which is preferably emitted by the irradiation device, is focused by the focusing optics into a measuring beam focused on the plane of the axial end and directed onto a finite number of measuring points distributed over the axial end, wherein the light power of the light guided through the optical conductor at each measuring point is measured and a reference point at the axial end of the optical conductor for the additive manufacturing of the structure is determined on the basis of the light powers measured at the measuring points.
[0010] By focusing the writing beam and the measuring beam using the same focusing optics, additional apparatus that would require calibration is no longer needed to determine the reference point at the axial end of the optical conductor. Using the same focusing optics for the additive manufacturing process of the structure allows production of the structure, particularly the lens, to begin immediately after determining the reference point, without having to reposition the apparatus and / or the optical conductor. The inventive method for determining the optical center of the optical waveguide is thus fully integrated into the 3D printing process and can therefore be highly automated.
[0011] Once the reference point at the axial end has been determined using the described measurement step, the subsequent scanning process can be carried out while referencing the focusing optics to the determined reference point. Referencing the focusing optics to the determined reference point can be achieved by relative displacement of the focusing optics to the optical conductor in a plane orthogonal to the optical axis of the focusing optics, thereby finding, for example, a relative position in which the optical axis of the focusing optics is directed towards the reference point at the axial end of the optical conductor. Alternatively, the focal point can be directed towards the reference point by appropriately controlling a deflection device, such as a galvanometer scanner, for the beam upstream of the focusing optics.
[0012] Within the scope of the present invention, it is preferred that a measurement point or a group of adjacent measurement points with higher luminous intensities than the luminous intensities of the surrounding measurement points is determined as the reference point. If the mode distribution of the light emitted at the other end of the optical waveguide results in a distribution of the measured luminous intensities at the measurement points similar to a Gaussian intensity distribution, the reference point can be determined as the maximum of this distribution. However, more complex mode distributions typically occur, leading to other luminous intensity distributions with a local minimum of the luminous intensity at the optical center. In this case, within the scope of the present invention, it is preferred that a measurement point or a group of adjacent measurement points with lower luminous intensities than the luminous intensities of the surrounding measurement points is determined as the reference point.The location of the measurement points defined in this way, or the group of adjacent measurement points defined in this way, can also be achieved by evaluating measurement points with regard to their light output in an iterative procedure.
[0013] Although, as mentioned above, the method according to the invention is not fundamentally intended to determine the geometric center of the optical waveguide or the geometric center of the core of the optical waveguide, it is nevertheless true that the determination of the reference point is fundamentally based on the light power distribution at the measuring points and that the reference point is usually located at least approximately in the center of the cross-section of the core.
[0014] Preferably, the procedure includes at least the following steps:
[0015] Aligning the optical axis of the focusing optics, which defines a z-direction of a Cartesian coordinate system, with the axial end,
[0016] Scanning the axial end in the x-directions and y-directions of the Cartesian coordinate system, which extend perpendicular to the z-direction, using the measuring beam focused on the plane of the axial end, so that a measured value of the luminous power of the light passed through the optical conductor during scanning is obtained for each measuring point; fitting a distribution function to the measured values of the luminous power.
[0017] Determining the reference point at the axial end from the distribution function,
[0018] Additive manufacturing of the structure by referencing the focusing optics to the determined reference point at the axial end using the writing beam to solidify the material.
[0019] In the first step of aligning the optical axis of the focusing optics with the axial end of the optical conductor, the optics are only roughly aligned with the axial end, so that in the subsequent scanning step, the optical conductor at the axial end is at least struck by the light used for scanning. If the optical conductor has a circular cross-sectional area, the axial end essentially consists of a more or less annular outer shell and a light-guiding core inside the shell. The objective of the present invention is to determine the optical center of the core as precisely as possible as a reference point in order to subsequently print the structure, such as an optical lens, with reference to the optical center.
[0020] The step of scanning the axial end in the x- and y-directions with a focused measuring beam (measuring light beam) and measuring the resulting light powers at the other end of the optical waveguide due to the x- and y-position of the respective measuring points leads to obtaining a set of measuring points with corresponding light intensity or light power measurement values, whereby the light power measured at a specific measuring point at the other end of the optical waveguide depends primarily on how accurately the measuring beam hits the optical center, that is, how accurately the measuring point in question corresponds to the optical center of the optical waveguide.The more precisely the measuring beam enters the optical center, the more completely the light is coupled into the conductor, and the more effective and complete the total internal reflection of the incident light occurs at the inner walls of the cladding. This results in either a higher light output at the other end of the optical fiber or, in the case of more complex mode distributions, a lower light output compared to measurement points surrounding the optical center than would be the case if the measuring beam were incident at a more peripheral area of the core or even next to the core in the cladding region of the conductor. Thus, depending on the position of the measurement points relative to the optical center, a light output distribution is obtained. This distribution allows, in the following steps, the optical center to be determined as a reference point and the focusing optics of the 3D printer to be referenced to it.
[0021] For this purpose, a distribution function is adapted to the measured values of the light power and in the next step the reference point at the axial end is determined from the distribution function.
[0022] In principle, the step of adjusting the distribution function to the luminous intensities measured at the measuring points can be performed directly from the entirety of the multivariate distributions in the x- and y-directions of the Cartesian coordinate system. However, according to a preferred embodiment, the present invention can also be characterized in that measured values along lines in the x-direction and along lines in the y-direction are summed separately, and that the reference point is determined as a coordinate pair with the two highest values of the sums obtained in the x-direction and in the y-direction. In this way, the coordinates of the reference point can be determined automatically.
[0023] In principle, the scanning step can also be replaced by an iterative optimization procedure to determine the reference point.
[0024] As mentioned above, the step of aligning the optical axis of the focusing optics serves only to roughly align the measuring beam to the axial end and not yet to precisely determine the optical center of the optical waveguide. Accordingly, in a preferred embodiment of the present invention, the step of aligning the optical axis of the focusing optics is performed using a camera directed through the focusing optics. The camera provides a conventional image of the axial end and, in conjunction with the focusing optics, can provide suitable magnification compared to the human eye. The position of the optical waveguide in the Z-direction can be determined by an autofocus routine on the surface of the fiber.
[0025] In the field of lithography-based additive manufacturing (3D printing) of components in the pm (micrometer) range, the focusing optics are generally a largely conventional microscopy lens, providing magnifications of approximately 5x to 100x. The images captured by the camera through the focusing optics can be modified using established techniques to adjust contrast or color, thereby improving the visualization of the core edges or the outer contour of the optical waveguide. This enables computer-aided edge detection, allowing the focusing optics to be automatically aligned with the axial end of the optical waveguide based on the detected edges.
[0026] For the fabrication of structures in the size range of a few micrometers (pm range), a printing process is preferably used within the scope of the present invention. In this process, the material to be solidified is present as a droplet on the axial end of the optical conductor, and the structure, such as an optical lens, is built up within the droplet by moving the focal point of the writing beam in the x, y, and z directions. Such a process utilizes the absorption of multiple photons to excite a molecule at the focal point by the material to be solidified, leading to specific solidification. This type of lithography process is therefore called multiphoton lithography. Outside the focal point, a sufficient number of photons are not absorbed within a reactive timeframe, so no solidification occurs.
[0027] The present invention is therefore preferably further developed in such a way that the solidifiable material is introduced between the focusing optics and the axial end, wetting the axial end, before the measuring step. In this way, the solidifiable material is already in the working field when the reference point is determined, so that the printing process can begin immediately after the reference point, and thus the optical center, has been determined.
[0028] Simultaneously, in this preferred embodiment of the present invention, the determination of the reference point and the referencing of the focusing optics are carried out through the same medium that is also present during the manufacture of the optical lens or during the manufacture of any other optical structure in the optical path, so that no different optical phenomena with regard to aperture, refractive index, and the like need to be taken into account between the phase of referencing the optics and the phase of printing the structure. In this way, a high precision of the method according to the invention is achieved.
[0029] In this same sense, a further improvement is achieved if the solidifiable material is introduced between the focusing optics and the axial end, wetting them, prior to the measurement step, as is the case in a preferred embodiment of the present invention. Furthermore, in this preferred embodiment of the present invention, a higher numerical aperture of the optics can be achieved when using immersion optics as the focusing optics, as is also the case in immersion microscopy. This leads to an improvement in spatial resolution and light throughput.
[0030] If the focusing optics are not to be contaminated with the material to be solidified, an alternative method can be used: Before the measurement step, the material to be solidified is introduced between the focusing optics and the axial end of the optical conductor, wetting a transparent plate, particularly a precision cover glass, positioned between the axial end and the focusing optics. In this way, the material to be solidified is held between the axial end of the optical conductor and the transparent plate, and the exposure of the material occurs through the transparent plate. The focusing optics remain clean. This preferred embodiment is particularly suitable in combination with focusing optics with cover glass correction and a precision cover glass 17015 µm thick.
[0031] The measuring beam differs from the writing beam used to solidify the material in terms of its light output and is therefore less intense, so that the measuring beam does not cause solidification by means of multiphoton absorption during the measuring step.
[0032] The present method preferably relates to a lithography-based additive manufacturing process based on multiphoton absorption, in which solidification of the material generally only occurs when a sufficiently strong dose of light acts on a focal point of the material. However, excessively long irradiation times can lead to non-specific polymerization reactions of the monomers in the material to be solidified, so it appears advantageous to limit the electromagnetic energy irradiated before the planned solidification of the material. For this reason, according to a preferred embodiment of the present invention, the measuring beam has at most half, preferably at most one-third, more preferably at most one-fifth, and particularly preferably at most one-tenth of the radiation energy of the writing beam. The radiation energy is typically measured using an optical power meter (e.g., a 3D optical power meter).measured by Thorlabs).
[0033] Preferably, according to the present invention, both the measuring beam and the writing beam are generated by the irradiation device. This ensures that the equipment required to carry out the proper procedure remains low and prevents any displacement of the apparatus after the focusing optics have been referenced to the reference point of the core of the optical conductor.
[0034] In addition to determining the x-coordinates and y-coordinates of the reference point at the axial end of the optical conductor, it is also essential for the quality of the structure manufactured using the methods according to the invention to determine the degree of tilt of the end region of the optical conductor facing the focusing optics, on which the structure, such as an optical lens, a diffraction grating, an aperture, or the like, is to be manufactured, with respect to the optical axis of the focusing optics or to the direction of travel of the focusing optics. If, in the case of a tilted optical conductor, only the reference point and thus the optical center of the optical waveguide is determined using the method according to the invention, and the structure is subsequently manufactured without taking the tilt into account, a structure, such as an optical lens, may be printed whose optical axis is oblique to the entrance or exit axis of the optical conductor.This naturally affects the quality of coupling light into or out of the optical conductor. Therefore, it is desirable to determine not only the coordinates in the x-direction and the y-direction, but also the degree of tilt within the scope of the present invention.
[0035] To determine the degree of tilt, the method according to the invention is preferably further developed in such a way that the measurement step for determining the optical center is repeated several times by varying the distance of the focusing optics from the axial end in the z-direction, so that a plurality of points of the optical center in different positions are obtained, and a local difference defines a tilt direction in which the optical conductor is tilted with respect to the optical axis of the focusing optics or to the direction of travel of the focusing optics. The measurement of the light power at the measuring points in the x- and y-planes described so far is carried out according to this preferred method.
[0036] The embodiment of the present invention thus involves several x- and y-planes differing in the z-direction. A direction can be determined in which the respective distribution in the respective variations is shifted in the z-direction, so that the tilt of the optical waveguide can be determined.
[0037] According to a preferred embodiment of the present invention, the writing process takes into account the tilt direction. This can mean that either the optical conductor or the focusing optics are readjusted with respect to the tilt, for example, to achieve an alignment of the optical axis of the focusing optics with the optical axis of the axial end of the optical conductor. Alternatively, the tilt can also be taken into account by adjusting the 3D layer model of the structure to be printed accordingly (e.g., rotated with respect to a reference coordinate system) and subsequently manufacturing the structure while maintaining the determined position and orientation of the optical conductor.
[0038] A further improvement in the optical performance of the structure produced on the axial end of the optical conductor using the inventive method can be achieved, according to a preferred embodiment of the present invention, by carrying out the inscription process in two stages, wherein in a second manufacturing stage a hardenable material different from that used in a first manufacturing stage is employed. In the second manufacturing stage, according to this preferred procedure, for example, a particularly scratch-resistant material or a material with a particularly low refractive index or low reflectance can be used.
[0039] According to a second aspect of the present invention, a device for lithography-based additive manufacturing of a structure, in particular an optical lens, at an axial end of an optical conductor is provided, comprising an irradiation device for emitting electromagnetic radiation, a holding device for holding the optical conductor, and a focusing optic for focusing a writing beam generated by the irradiation device into a material that can be solidified, preferably by means of multiphoton absorption, wherein the writing beam can be successively focused on focal points within the solidifiable material in a script-like manner, whereby a volume element of the material located at the focal point can be solidified at each point, wherein, according to the invention, a measuring device for measuring the luminous flux of light guided through the optical conductor is further provided.such that in a measuring step preceding the writing process, a measuring beam, which can be focused by the focusing optics onto the plane of the axial end and directed onto a finite number of measuring points distributed over the axial end, generates a measured value for each measuring point after passing through the optical conductor, and wherein the measuring device is connected to an evaluation device to which the measured values are supplied and which is configured to determine a reference point at the axial end of the optical conductor based on the light intensities measured at the measuring points.
[0040] Further developments of the device according to the invention relate to the implementation of preferred embodiments of the method described above, whereby reference is made to the above description of the method according to the invention with regard to the respective technical effects.
[0041] Preferably, the device further comprises a control unit which controls the irradiation device and the focusing optics and which is configured to scan the axial end in the x-directions and y-directions of a Cartesian coordinate system extending normal to the optical axis of the focusing optics (z-direction) by means of the measuring beam focused by the focusing optics onto the plane of the axial end, so that a measured value of the luminous flux of the light passed through the optical conductor during scanning is obtained for each measuring point, and the evaluation unit is configured to adapt a distribution function to the measured values of the luminous flux and to detect the reference point at the axial end, whereupon the control unit performs the additive manufacturing of the structure by referencing the focusing optics to the determined reference point at the axial end by means of the writing beam to solidify the material.
[0042] Preferably, the evaluation unit is set up to sum measured values along lines in the x-direction and along lines in the y-direction separately and to determine the reference point as a pair of coordinates with the two highest values of the sums obtained in the x-direction and in the y-direction.
[0043] Preferably, the measuring beam has at most half, preferably one third, more preferably at most one fifth and in particular preferably at most one tenth of the radiation energy of the writing beam.
[0044] Preferably, the irradiation device is configured to generate both the measuring beam and the writing beam. Preferably, the control device is configured to repeat the measuring step for determining the reference point several times by varying the distance of the focusing optics from the axial end in the z-direction, so that a plurality of reference points are obtained, and the evaluation device is configured to determine a tilt direction from a local difference of the reference points in which the optical conductor is tilted with respect to the optical axis of the focusing optics or to the travel direction of the focusing optics.
[0045] Preferably, the control device is set up to control the writing mechanism, taking into account the tilting direction.
[0046] The invention is explained in more detail below with reference to an embodiment illustrated in the drawing. Figure 1 shows a simplified representation of the apparatus for carrying out the method according to the invention, Figure 2 shows the result of the scanning and measuring step in a graphical representation, Figure 3 shows the result of the step of fitting a distribution function to a sum function of the light intensities measured at the measuring points in the x-direction and y-direction respectively, Figure 4 shows the results of the scanning and measuring step while varying the distance of the focusing optics from the axial end in the z-direction, and Figure 5 shows the diagrammatic evaluation of the data from Figure 4 for determining the tilt direction in which the optical conductor is tilted with respect to the optical axis of the focusing optics or to the direction of travel of the focusing optics.Figure 1 shows a longitudinal section of an optical conductor, or waveguide, designated by reference numeral 1. The optical conductor 1 essentially consists of a cladding 2 with a substantially annular cross-section and a core 3 located therein. Light, represented by the measuring beam (or measuring light beam) 4, which enters the core 3, is totally reflected due to the difference in refractive index between the core 3 and the cladding 2 and is thus directed to an end 5 of the conductor 1, where the light beam 4a guided through the conductor 1 strikes a photosensor 6. The photosensor 6 measures the light power in the conventional manner. The light beam 4 exits substantially along the optical axis 7 of the focusing optics 8, which defines a z-direction of a three-dimensional Cartesian coordinate system.The measuring beam 4 may be slightly deflected from the optical axis 7 in order to scan the axial end 1a of the conductor 1. The conductor 1 has an entry region 1b, which is defined such that a light beam that is first reflected only beyond this region is indistinguishable from a light beam entering the conductor 1 completely parallel with respect to the luminous flux to be measured at the end 5 of the conductor 1. The structure to be printed onto the axial end 1a of the conductor 1, in this case an optical lens, is designated by reference numeral 9 in Figure 1.
[0047] Scanning a large number of measuring points at the axial end 1a of the conductor 1 results in an intensity or luminous flux distribution of the light beam 4a on the photosensor 6, as shown in Figure 2. This distribution depends on the x- and y-position of the measuring point at the axial end 1a of the conductor 1. It can be seen that a measured value of the luminous flux of the beam 4a exiting the end 5 was obtained for each measuring point, with the measured values arranged in a checkerboard pattern according to the arrangement of the measuring points in the x- and y-directions. Depending on the position of the incident light, a different luminous flux is measured by the photosensor 6. As can be seen in Figure 2, a more or less centrally located incident light beam 4a on the core 3 does not necessarily result in a maximum luminous flux.This is due to the fact that light of a certain wavelength has a different number of guided modes in the optical waveguide, which can lead to distributions of light power that deviate from a Gaussian intensity distribution.
[0048] Summing the light powers measured in the x-direction and y-direction and fitting a distribution to this summation function yields the distributions shown in Figure 3, from which the position of the reference point at the axial end of the conductor 1 in the x-direction and y-direction can be read. The reference point essentially coincides with the optical center of the optical waveguide 1. Thus, a coordinate pair x and y is obtained to which the focusing optics 8 can be referenced for the additive manufacturing of the optical lens or another optical structure at the axial end 1a.
[0049] Figure 4 shows light power distributions and their adjusted distributions in the x-direction and y-direction. It can be seen that when varying the z-direction between a z-distance of -100 pm and +100 pm relative to z=0, where z=0 is the starting position, different light power distributions can be measured and represented. In the case shown in Figure 4, this is due to the fact that the entry area 1b of the conductor 1 is tilted relative to the optical axis 7 of the focusing optics 8, or rather to the direction of travel of the focusing optics 8. This tilt shifts the reference points determined in the respective planes, resulting in a different raster image depending on the distance in the z-direction.
[0050] Figure 5 shows diagrams of the distributions with respect to their width (row 1), their maximum values of the luminous flux distribution (row 2), and the position of the respective luminous flux centers (row 3). The diagrams in the left column represent the corresponding values in the x-directions, and those in the right column represent the values in the y-directions. It can be seen that, in this case, the width decreases in both the x- and y-directions after a reduction in the range from -100 pm to -50 pm (with respect to z=0) and then increases again until z=+100 pm (row 1). Similarly, the luminous flux initially increases in both the x- and y-directions in the aforementioned first range, before decreasing again (row 2). The position of the axial end α of the conductor can be determined from the axial profile of the width and flux distribution. Alternatively, a separate autofocus routine can be used for this.The position of the center of the light intensity in the x-direction (line 3, left) moves with increasing distance (-100pm < z.
[0051]
[0052] +100pm) but steadily from approximately 16.7pm to approximately 15.25pm. The position of the center of luminous intensity in the y-direction (row 3, right) shifts with increasing distance (-100pm).
[0053]
[0054] z
[0055] +100 pm) also continuously from approximately 11.9 pm to approximately 16 pm. From the pairs of values (x, y) of z = -100 pm and z = +100 pm, a vector can be formed that represents the direction of the tilt of the entry region 1b of the conductor 1a with respect to the optical axis 7. The linearity of the measured values is clearly visible in line 3, so that a definite direction of the tilt can indeed be measured in a striking manner using the method according to the invention. The optical lens 9 can subsequently be printed to adapt to the tilt in order to obtain a lens 9 arranged symmetrically on the axial end 1a of the conductor 1.
Claims
22 Patent claims:
1. A method for the lithography-based additive manufacturing of a structure, in particular an optical lens, at an axial end of an optical conductor, in which electromagnetic radiation emitted by an irradiation device is focused by means of a focusing optics arranged downstream of the irradiation device into a writing beam, which is successively directed to focal points within a material that can be solidified, preferably by means of multiphoton absorption, whereby a volume element of the material located at the focal point is solidified in each instance, characterized in that in a measuring step preceding the writing process, electromagnetic radiation, which is preferably emitted by the irradiation device, is focused by the focusing optics into a measuring beam focused on the plane of the axial end and directed onto a finite number of measuring points distributed over the axial end.wherein the luminous flux of the light guided through the optical conductor at the respective measuring points is measured and a reference point at the axial end of the optical conductor is determined for the additive manufacturing of the structure based on the luminous fluxes measured at the measuring points.
2. Method according to claim 1, characterized in that a measuring point or a group of adjacent measuring points with higher luminous intensities than the luminous intensities of the surrounding measuring points is determined as the reference point, or that a measuring point or a group of adjacent measuring points with lower luminous intensities than the luminous intensities of the surrounding measuring points is determined as the reference point.
3. The method of claim 1 or 2, the method comprising at least the following steps: Aligning the optical axis of the focusing optics, which defines a z-direction of a Cartesian coordinate system, with the axial end, Scanning the axial end in the x-directions and y-directions of the Cartesian coordinate system, which extend perpendicular to the z-direction, using the measuring beam focused on the plane of the axial end, so that a measured value of the luminous power of the light passed through the optical conductor during scanning is obtained for each measuring point; fitting a distribution function to the measured values of the luminous power. Determining the reference point at the axial end from the distribution function, Additive manufacturing of the structure by referencing the focusing optics to the determined reference point at the axial end using the writing beam to solidify the material.
4. Method according to claim 3, characterized in that measured values along lines in the x-direction and along lines in the y-direction are summed separately and that the reference point is determined as a pair of coordinates with the two highest values of the sums obtained when summing in the x-direction and in the y-direction.
5. Method according to claim 3 or 4, characterized in that the step of aligning the optical axis of the focusing optics is performed with a camera directed through the focusing optics.
6. Method according to any one of claims 1 to 5, characterized in that the solidifiable material is introduced between the focusing optics and the axial end before the measuring step, wetting the axial end.
7. Method according to one of claims 1 to 6, characterized in that the consolidable material is introduced between the focusing optics and the axial end in a wetting manner before the measuring step.
8. Method according to one of claims 1 to 6, characterized in that the consolidable material is introduced between the focusing optics and the axial end before the measuring step, wetting a transparent plate, in particular a precision cover glass, arranged between the axial end and the focusing optics.
9. Method according to one of claims 1 to 8, characterized in that the measuring beam has at most half, preferably at most one third, further preferably at most one fifth and in particular preferably at most one tenth of the radiation energy of the writing beam.
10. Method according to one of claims 1 to 9, characterized in that both the measuring beam and the writing beam are generated by the irradiation device.
11. Method according to one of claims 1 to 10, characterized in that the measuring step for determining the reference point is performed several times by varying the distance of the focusing optics from the axial end in the z-direction.25 is repeated, and a local difference between the reference points defines a tilting direction in which the optical guide is tilted with respect to the optical axis of the focusing optics or to the travel direction of the focusing optics.
12. Method according to claim 11, characterized in that the writing is carried out taking into account the tilting direction.
13. Method according to one of claims 1 to 12, characterized in that the writing process is carried out in two stages, wherein in a second manufacturing stage a consolidable material different from the consolidable material used in a first manufacturing stage is used.
14. Device for lithography-based additive manufacturing of a structure, in particular an optical lens, at an axial end of an optical conductor, particularly for carrying out the method according to one of claims 1 to 13, the device comprising an irradiation device for emitting electromagnetic radiation, a holding device for holding the optical conductor, and a focusing optic for focusing a writing beam generated by the irradiation device into a material that can be solidified, preferably by means of multiphoton absorption, wherein the writing beam can be successively focused on focal points within the solidifiable material in a writing manner, whereby a volume element of the material located at the focal point can be solidified at each point, characterized in that a measuring device for measuring the luminous power of light guided through the optical conductor is further provided, so that in a dem26 In a measuring step preceding the writing step, a measuring beam, which can be focused by the focusing optics onto the plane of the axial end and directed onto a finite number of measuring points distributed over the axial end, generates a measured value for each measuring point after passing through the optical conductor, and that the measuring device is connected to an evaluation device to which the measured values are supplied and which is designed to determine a reference point at the axial end of the optical conductor based on the light powers measured at the measuring points.
15. Device according to claim 14, further comprising a control device which controls the irradiation device and the focusing optics and which is configured to scan the axial end in the x-directions and y-directions of a Cartesian coordinate system extending normal to the optical axis of the focusing optics (z-direction) by means of the measuring beam focused by the focusing optics onto the plane of the axial end, so that a measured value of the luminous flux of the light passed through the optical conductor during scanning is obtained for each measuring point, and the evaluation device is configured to adapt a distribution function to the measured values of the luminous flux and to detect the reference point at the axial end, whereupon the control device performs the additive manufacturing of the structure by referring the focusing optics to the determined reference point at the axial end by means of the writing beam to solidify the material.
16. Device according to claim 15, characterized in that the evaluation unit is configured to summate measured values along lines in the x-direction and along lines in the y-direction separately and to determine the reference point 27 to be determined as a pair of coordinates with the two highest values of the sums obtained when summing in the x-direction and in the y-direction.
17. Device according to one of claims 14 to 16, characterized in that the measuring beam has at most half, preferably one third, more preferably at most one fifth and particularly preferably at most one tenth of the radiation energy of the writing beam.
18. Device according to one of claims 14 to 17, characterized in that both the measuring beam and the writing beam are generated by the irradiation device.
19. Device according to one of claims 14 to 18, characterized in that the control device is configured to repeat the measuring step for determining the reference point several times by varying the distance of the focusing optics from the axial end in the z-direction, so that a plurality of reference points are obtained, and the evaluation device is configured to determine from a local difference between the reference points a tilting direction in which the optical conductor is tilted with respect to the optical axis of the focusing optics or to the travel direction of the focusing optics.
20. Device according to claim 19, characterized in that the control device is configured to control the writing, taking into account the tilting direction.