WO2016170043A1

WO2016170043A1 - Method for the shaping and/or shape correction of at least one optical element

Info

Publication number: WO2016170043A1
Application number: PCT/EP2016/058877
Authority: WO
Inventors: Matthias GOY; Claudia Reinlein; Nina LEONHARD; Michael APPELFELDER
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e. V.; Friedrich-Schiller-Universität Jena
Priority date: 2015-04-22
Filing date: 2016-04-21
Publication date: 2016-10-27
Also published as: DE102015106184A1; DE102015106184B4

Abstract

The invention relates to a method for the shaping and/or shape correction of at least one optical element, comprising the following steps: measuring the shape of an optical functional surface (6) and the thickness of the optical element (5) and determining the deviation from a target shape, producing a holding structure for the optical element, wherein the holding structure is formed by an assembly of a plurality of holding elements (3), and connecting the optical element (5) to the holding structure, wherein the shape of the optical functional surface is changed toward the target shape as the weight force of the optical element (5) acts on the assembly of the holding elements (3).

Description

description

Method for shaping and / or shape correction of at least one optical element

The invention relates to a method for shaping and / or shape correction of at least one optical element.

This patent application claims the priority of German Patent Application DE 102015106184.8, the disclosure of which is hereby incorporated by reference.

Optical elements such as mirrors or grids are usually held in a socket in optical systems. Optical elements whose area is large compared to their thickness typically have a low flexural rigidity, which makes grasping difficult. Forces introduced by grasping, gravitation or thermal effects (at high radiation energy or temperature change) can lead to a deformation of the optical functional surface of the optical element. These effects can be both static and dynamic. Furthermore, an optical element may already have production-related and in particular unintentional deviations from a target shape of the optical functional surface prior to installation in a socket.

The deformations of an optical element that occur during installation in a socket, in the production, by the gravitational force and / or by the operating conditions can lead to an impairment of the optical system, for example to optical aberrations and / or a shift of the focus. An object to be solved is therefore to specify a method by which the shape error of the optical functional surface of an optical element can be corrected and / or the shape of the optical functional surface can be adjusted in a targeted manner.

This task is achieved by a molding process

and / or shape correction of at least one optical element according to the independent claim. Advantageous embodiments and further developments of the invention are

Subject of the dependent claims.

According to at least one embodiment of the method for

Shaping and / or shape correction of an optical element is in the form of an optical element in a first step

Functional surface of the optical element measured and the

Deviation from a target shape. Furthermore, the thickness of the optical element is advantageously measured. The measurement of the shape and the thickness takes place in particular

spatially resolved, so that from the measurement data computer-aided, a three-dimensional model of the optical element can be created.

The optical element can be measured in particular by optical or tactile measuring methods with regard to its shape. Under optical measuring methods, e.g.

Interfometry, confocal technology or laser profilometry understood, tactile measurement methods may be Tastschnittmessungen or probing individual points

(Coordinate metrology). Preferably, both the

Front of the optical element, which is the optical

Function surface includes, as well as the back of the optical element, which the optical functional surface

opposite, measured in terms of their shape. Farther the thickness of the optical element is measured, wherein also optical or tactile measuring methods can be used.

Below the optical functional area is here and in the

Below understood the surface of the optical element, which is provided in operation for interaction with electromagnetic radiation, in particular light. The optical element may in particular be a mirror, wherein the

optical functional surface is the mirror surface. Alternatively, the optical element may for example be a grating, wherein the optical functional surface is the grating.

In particular, the dimension of the thickness of the optical element is perpendicular to a main plane of the optical element

Function surface or along the optical axis to

understand. The thickness of the optical element may in particular comprise the thickness of a substrate on which the optical functional surface is formed. For example, the optical functional surface by a reflective

Coating can be formed, which is applied to a mirror substrate. Alternatively, for example, the optical functional surface may be a grating disposed on a grating substrate. Furthermore, in one embodiment, the optical element may comprise one or more active components which are used to change the shape and / or position of the

optical element are provided in operation. Under the thickness of the optical element is in this case the

Total thickness of the area between the optical

Function surface and provided for a socket of the optical element socket structure understood, ie the thickness including a substrate of the optical functional surface and including optionally existing active Elements attached to the substrate, for example.

According to at least one embodiment, in the method in a further step, a socket structure for the optical element is produced, wherein the socket structure is formed by an arrangement of a plurality of socket elements. The socket elements preferably differ at least partially in their height and / or their rigidity. The frame structure formed from the arrangement of the socket elements on the one hand has the function to fix the optical element in a predetermined position for an application.

For example, the socket elements are connected on one side to the optical element, for example with a mirror substrate of the optical element or with active elements attached to the optical element. On an opposite side, for example, the socket elements are connected to a carrier substrate, which in the intended application acts as a support for the optical element. Furthermore, in the method described herein, the socket structure has the function of defining and / or correcting the shape of the optical functional surface of the optical element. According to at least one embodiment, in a further method step, the optical element with the

Connection structure associated with the shape of the optical functional surface under the action of gravity and / or an additional force in the same effective direction perpendicular to the optical functional surface of the optical element to the arrangement of the socket elements in the direction of the target shape. In this way, advantageous in the measurement of the shape of the optical functional surface and / or the thickness of the deformations detected or optical element

Thickness deviations at least partially or preferably even completely compensated, so that the optical element

within a predetermined tolerance range reaches the desired target form.

According to at least one embodiment is in

Process step of measuring the shape of the optical

Functional surface and the thickness of the optical element from the measurement data computer-aided three-dimensional model of the optical element created. The computer-aided model of the optical element advantageously forms the

Basis for a simulation calculation, with which in particular the arrangement and the heights and / or the rigidity of the socket elements are optimized in the socket structure. The positions, the heights and / or the stiffnesses of the socket elements of the socket structure are advantageously determined in such a way that deformations of the optical functional surface of the optical element caused by gravitation and / or by additional applied forces occur after connection to the socket structure of the particular

Counteract deviation from the target shape. The target shape can be in horizontal when joining with the frame structure

Installation position or in vertical mounting position can be achieved. For this purpose, an FEM simulation (finite element method) is advantageously used.

In an advantageous embodiment, the

Sockets on different heights. The

different heights of the socket elements can for

Example compensate for a production-related undesirable variation of the thickness of a substrate of the optical element. Furthermore, it is possible that by different heights the socket elements targeted a desired shape of the

optical functional surface is generated by the action of the weight of the optical element and / or an additional force in the same effective direction. In other words, the optical element deforms under the action of

Weight force on the socket elements such that it receives the desired target shape only in the frame structure.

It can be provided, for example, that the optical element in the production with a planar optical

Functional surface is manufactured, which only under

Effect of the weight of the optical element on a frame structure whose socket elements have a predetermined height distribution, in one for the application

provided curved shape is brought. For example, the socket elements can be radially symmetric

Have height distribution to selectively generate a predetermined radially symmetrically curved optical functional surface. Advantageously, for example, the optical

Functional surface after production, a comparatively easy to produce shape, for example, a flat or spherically curved shape, having the shape produced under the action of gravity on the

Socket elements in a different form,

for example, a curved or in particular aspherically curved shape, is transferred. Due to the height distribution of the socket elements can in particular comparatively

difficult to produce shapes of the optical functional surface, for example, aspherically curved surfaces, by the action of the weight of the optical element and / or an additional force in the same direction of effect on the

Setting elements are set specifically. In particular, in this way advantageous forms of optical Function surface can be generated, which is characterized by a

Surface processing of the substrate material of the optical element only comparatively difficult to produce. Alternatively, or in addition to different heights, the socket elements may have different stiffnesses

exhibit. Different stiffness of the

In particular, socket elements can bring about a predetermined height distribution under the influence of the weight of the optical element. The different stiffnesses of the socket elements can by

different materials and / or different

Cross-sectional shapes of the socket elements can be achieved.

Suitable materials for the socket elements are

For example, polymers as lower-grade materials

Rigidity and metals or ceramics as materials with comparatively high rigidity.

In one embodiment of the method, the target shape of the optical functional surface is a flat surface, wherein the

Deviation of the measured shape of the optical functional surface of the flat surface by the connection of the optical element is completely or partially compensated with the socket structure. In this embodiment, the

Distribution of heights and / or stiffness of the

Socket elements such that in the measurement

detected deviations from the flat surface by the action of the weight of the optical element and / or an additional force in the same direction of action on the socket elements are fully or partially compensated.

For example, the socket elements have a lower height at positions at which the optical functional surface deviates upward from the predetermined flat surface and / or a lower rigidity. Accordingly, the socket elements have a greater height and / or a greater rigidity at positions at which the optical functional surface deviates downward from the predetermined flat surface.

In a further embodiment of the method is the

Target shape of the optical functional surface, a curved surface, which is adapted to image electromagnetic radiation into a focus, and wherein a position of the focus by connecting the optical element with the

Frame structure is changed. In particular, a deviation of the focal point determined from the measurement of the surface shape of the optical functional surface from a desired value can be completely or partially corrected in this way.

In a further embodiment of the method is the

Target shape of the optical functional surface a curved surface, wherein an optical aberration of the measured optical functional surface is compensated in whole or in part by the connection of the optical element with the socket structure. By a suitable arrangement and height distribution of the socket elements can in particular by a deviation of the measured shape of the optical functional surface of a

Target shape-related optical aberrations, such as coma or astigmatism, be wholly or partially corrected.

The method described herein is particularly well suited for optical elements whose width is substantially greater than the thickness. Such optical elements are characterized by a low bending stiffness, so that by the action of their own weight a comparatively large deformation is possible. In this case, the width of the optical element is to be understood as meaning the extent in a direction parallel to the optical functional area, irrespective of the installation position in the intended application. For example, in the case of a circular mirror, the width is the mirror diameter. The ratio of the width b of the optical element to its thickness is particularly preferably b / d> 20. The width b of the optical element is preferably more than 100 mm, particularly preferably more than 1000 mm.

According to an advantageous embodiment, at least a part of the socket elements are at one of the optical

Function surface facing away from the back of the optical element mounted. In particular, the optical element can be arranged such that the weight force acts substantially perpendicular to the optical functional surface.

Alternatively or additionally, at least a part of

Socket elements on an outer edge of the optical

Elements, in particular in a direction parallel to the optical functional surface, be arranged. This is

For example, it makes sense if the optical element is arranged in the intended application such that the weight acts parallel to the optical functional surface.

It is also possible that a plurality of sub-elements of the optical element are connected to each other by the socket elements. For example, the several

Subelements are each individual mirror elements of a mirror array. In one embodiment, the optical element may comprise one or more active components which are provided for changing the shape and / or position of the optical element during operation. The active components may in particular comprise piezoelectric materials such as PZT (lead zirconate titanate), PMN (lead magnesium niobate) or PVDF (polyvinylidene fluoride), which change their shape by application of an electric field and thus a

Induce deformation of the substrate of the optical element. The optical element, for example, an active

controlled deformable mirror or an actively controlled grid. In addition to the mentioned electrical

Aktuationsprinzipien also mechanical drives such as micrometer screws can be used.

The invention will be described below with reference to

Embodiments in connection with the figures 1 to 7 explained in more detail. Show it:

Figure 1 is a schematic representation of a cross section through an optical element before connecting to a

Making structure,

Figure 2 is a schematic representation of two different arrangements of the socket elements,

Figure 3 is a schematic representation of various possible forms of the socket elements, and Figures 4 to 7 are each a schematic representation of a cross section through an optical element after connecting to a socket structure. Identical or equivalent elements are provided in the figures with the same reference numerals. The illustrated

Components as well as the proportions of the components among each other are not to be regarded as true to scale. The optical element 5 shown schematically in cross section in FIG. 1 has a mirror substrate 1 which supports the optical functional surface 6. The mirror substrate 1 may contain, for example, a glass, a metal, a ceramic or a polymer. To form the optical

Function surface 6, the mirror substrate 1 may be provided for example with a reflective coating. Furthermore, the optical element 5 in the illustrated here

Embodiment with the back of the mirror substrate 1 firmly connected active elements 2 on. The firm connection between the mirror substrate 1 and the active elements 2 can be, for example, by gluing, soldering, welding, direct bonding, silicate bonding or by melting

Manufacturing process done. The active elements 2 may in particular comprise piezoelectric materials such as PZT, PMN or PVDF, which change their shape by applying an electric field and thus a

Induce deformation of the mirror substrate 1. Thus, in the illustrated embodiment, the optical element 5 is a mirror deformable by the active elements 2.

The method described here can alternatively also be applied to other active or passive optical elements for example passive (not deformable)

Mirrors, active or passive gratings, or optical crystals such as laser crystals. In the case of an active optical element, the at least one active element 2 may consist of two or more layered materials having different thermal properties

Have expansion coefficients and can be thermally activated. In the method, the shape of the optical element 5 is measured. In particular, the shape of the optical functional surface 6 formed by the front side of the optical

Elements 5 measured. Furthermore, the shape of the rear side of the optical element 5 is advantageously measured, which in the embodiment of Figure 1 by the fixed with the

Rear side of the mirror substrate 1 connected active elements 2 is formed. Furthermore, the thickness of the optical

Elements 5 measured in a spatially resolved manner. For measuring the shape and thickness of the optical element are preferably optical

Measuring methods such as interferometry,

Konfokaltechnik or laser profilometry used.

Alternatively, tactile measuring methods such as stylus measurements or the probing of individual points

(Coordinate metrology) are used.

From the measurement data of the shape and thickness of the optical element 5, a computer-aided model of the optical element 5 is advantageously created. In particular, deviations of the optical functional surface 6 from one of the measured data can occur

Target shape or variations of the thickness of the mirror substrate 1 and / or connected to the mirror substrate 1 active elements 2 are determined. The method described here has the goal of deformations and / or thickness variations of the be compensated by a suitable socket structure such that the optical function is not affected by the connection of the optical element 5 with the frame structure caused by the production of the optical element 5 deformations and / or thickness variations. For this purpose, a socket structure is provided, which is formed by an arrangement of a plurality of socket elements 3. The socket elements 3 of the socket structure can be either rigid or flexible.

To calculate and optimize the arrangement of

Socket elements 3 is preferably a FEM simulation using the created from the measurement data

Three-dimensional model of the optical element 5

used. Known or systematic measurement errors caused by holding the optical element during the measurement

occur and are included in the generation of the three-dimensional model, are beneficial before the

Simulation corrected by calculation. The heights, the rigidity and the arrangement of the socket elements 3 in the

Frame structure are adjusted in an optimization so that the gravitational deformations of the optical functional surface 6 of the optical element 5 when placed on the frame structure the existing deformations

counteract.

The production of the socket elements 3 of the socket structure can be done by molding, by additive methods (3D printing, laser sintering, laser melting) or by separating methods (milling, turning, sawing). For example, the preparation of the socket elements 3 by molding of

silver-filled silicone in polyurethane tubing. After curing the silicone in the tubes will be sawed these into, for example, about 4 mm long pieces. Thereafter, the silicone cylinders can be removed.

The socket elements 3 thus produced are in the

optimized arrangement with a carrier substrate 4 below

Application of a suitable joining method. This can e.g. by gluing, soldering or bonding. The

Processing of the so joined socket elements 3 in terms of optimized height can then in a milling, turning,

Grinding or polishing process or by laser ablation or chemically ablative processes or combinations thereof. Likewise, the socket elements can work out from a previously applied / joined layer by the processes mentioned. The separate production of individual

Socket elements would be omitted.

In Figure 2, two embodiments of the arrangement of the socket elements 3 are shown side by side. The arrangement of the socket elements 3 depends in particular on the installation conditions, the installation position and / or the thermal load. It can e.g. be rotationally symmetric with different radial / azimuthal orders (shown on the left) or align with a grid (shown on the right). The number of socket elements 3 may depend, for example, on the number of active elements 2 of the optical element 5 or be a multiple of it. As an alternative to the arrangements shown by way of example in FIG. 2, it is also possible for the arrangement of the socket elements 3 to have a polar symmetry or to be asymmetrical.

In Figure 3, various possible forms of the socket elements 3 are exemplified. The shape of the individual

For example, socket elements may be cylindrical (a), cuboid (b), prismatic (c), tubular (d),

be frusto-conical (s), truncated pyramidal (f), conical (g) or pyramidal (h). Alternatively, however, other shapes are conceivable, the socket elements 3 may for example have a spiral shape, a T-shape, a double-T shape or any free-form.

The selection of the shape of the socket elements 3 in particular allows adjustment of the rigidity of

For example, is at a

cylindrical socket member 3 along the cylinder axis before a greater stiffness than in the lateral directions and against rotation. Depending on the application, a desired rigidity of the socket structure can be adjusted either by varying the shape or material of the socket elements 3, by the distribution of the socket elements 3, or by a combination of these parameters.

As material for the socket elements 3 are preferably polymers, metals or ceramics or mixed forms of these (for example composite materials such as silver-filled silicone)

used. Polymers can be easily produced by molding, have a high elasticity and can be easily reworked. The use of socket elements 3 with high elasticity is particularly in optical

Elements 5 advantageous, which, as in the embodiment shown in Figure 1 active elements 2 on the frame structure facing the rear side have to allow a deformation even after joining. As an elastic material for the socket elements 3, in particular a silicone can be used, for example

Elastic modulus in the range of 5 MPa to 20 MPa. If the application requires mountings 3 of greater rigidity, metals or metals are preferred

Ceramics used. The moduli of elasticity of metals or ceramics may in particular be more than 100 GPa. Metals and ceramics have compared to polymers

Advantage that they allow higher manufacturing accuracy. In addition, the use of polymers in vacuum applications is often critical. Metals or ceramics are considered

Full body very stiff, but reworkable with very high accuracy. At high thermal loads of the optical element in the operating state is also the

thermal conductivity of the material of the socket elements to be considered. The socket elements are in this case also able to dissipate the heat absorbed by the optical element.

The processing of the frame structure for adjusting the height of the individual socket elements 3 or the processing of the shape of the socket elements 3 can be about each erosive

Material processing procedures take place. For example, machining with a geometrically determined cutting edge can take place by turning or ultra-precision turning, adjusting turning, milling or fly-cutting, pushing or planing. Alternatively, the machining can be done by grinding, polishing, over

Impression technologies, laser ablation, chemical ablation processes, or combinations of these.

After editing the frame structure is in the

Method joined the optical element 5 with the socket elements 3. This can be done by gluing, soldering or bonding. If the weight of the optical element 5 is insufficient to achieve the required deformation, an additional force can also be applied to the joints. The following figures 4 to 7 each show

Embodiments of optical elements 5 after the

Process step of joining with the frame structure.

In the exemplary embodiment of FIG. 4, the optical element 5 has a planar optical functional surface 6 and, in the horizontal installation position, is connected to a carrier substrate 4 by socket elements 3. At the back of the

Mirror substrate 1 of the optical element 5 are active

Elements 2 attached, which have different thicknesses. The heights of the socket elements 3 of the socket structure are set such that they compensate for the production-related variations in the thickness of the active elements 2. In this way it is achieved that the optical functional surface 6 after joining with the socket structure the desired level

Target shape has. In contrast, at the

Use of a frame structure in which the heights of the socket elements 3 would not be adapted specifically to the thickness variation of the active elements 2, possibly

Deformations of the optical functional surface 6 occur in the finished optical element 5, which could affect the function in the application. In the embodiment of Figure 5, the optical

Element 5 on a curved optical functional surface 6. In this embodiment, it is possible that the curved shape of the optical functional surface 6 is defined and / or corrected by the height distribution of the socket elements 3.

For example, the optical element 1 before joining with the frame structure have a planar optical functional surface 6, which only under the influence of the weight of the optical element 5 and / or an additional force in the same direction of action is placed on the socket elements 3 in the curved target shape. In this way, the shape of the optical functional surface 6, the

exploited gravitational deformation of the optical element in the socket structure. This facilitates the

Production costs of the mostly by polishing process

produced mirror substrate 1 drastically, since this can be produced with a flat surface. The shaping of the optical functional surface by the influence of

Weight force on the socket elements 3 is advantageously possible in particular in optical elements 5, in which the ratio of the width to the thickness is at least 20: 1, and the comparatively large diameter of more than 100 mm or even more than 1000 mm.

In the embodiment of Figure 5, it is alternatively also possible that the optical functional surface 6 already has a curved surface prior to joining with the socket structure. In this case, by a suitable

Height distribution of the socket elements 3, for example, a measured deviation of the curved shape of the optical

Function surface 6 are corrected by the target shape.

For example, the focus position of a curved

Mirror by a suitable height distribution of

Socket elements 3 can be corrected later. Alternatively, optical aberrations of the optical element 5 can optionally be corrected by a suitable height distribution of the socket elements 3. FIG. 6 shows a further exemplary embodiment of a

optical element 5 with a planar optical

Function surface 6 shown, with the socket elements 3 in a vertical mounting position with a carrier substrate 4th connected is. In this embodiment, the

Socket structure on both socket elements 3, which are arranged on one of the optical functional surface 6 opposite back of the optical element 5, as well as at least one socket element 3, that with the outer edge of the

Mirror substrate 1 is connected. In this way, both forces perpendicular to the optical functional surface 6 as well as parallel to the optical functional surface 6 on the optical element 5 can be exercised by the socket elements 3 and targeted for shaping and / or

Shape correction can be used. At the same time, a shift of the optical element parallel to the optical functional surface can thereby be reduced. This is

especially advantageous when the optical element is in vertical mounting position.

In the further embodiment shown in Figure 7, the optical element 5 is a mirror array, the

a plurality of sub-elements 5a, 5b in the form of individual

Mirror elements, each by active elements 2

are deformable, is formed. The multiple mirror elements 5a, 5b of the mirror array are connected by the socket elements 3 of a socket structure on the one hand with the carrier substrate 4 and on the other also with each other. Like the

Previous embodiments can by the action of the weight of the mirror elements 5a, 5b on the

Frame structure a shaping and / or shape correction of the optical functional surfaces 6 done. The invention is not limited by the description with reference to the embodiments. Rather, the includes

Invention every new feature as well as every combination of

Characteristics, which in particular any combination of features in The patent claims, even if this feature or this combination itself is not explicitly in the

Claims or embodiments is given.

Claims

Method for shaping and / or shape correction

at least one optical element (5),

comprising the steps:

- Measuring the shape of an optical functional surface (6) and the thickness of the optical element (5) and

Determination of the deviation from a target shape,

- Making a socket structure for the optical

Element, wherein the frame structure by a

Arrangement of a plurality of socket elements (3) is formed,

- Connecting the optical element (5) with the

Frame structure, wherein the shape of the optical functional surface under the action of the weight of the optical element (5) on the arrangement of the

Socket elements (3) in the direction of the target shape

changed.

Method according to claim 1,

where from measurement data of the shape of the optical

Functional surface (6) and the thickness of the optical element (5) computer-aided three-dimensional model of the optical element (5) is created.

Method according to claim 2,

wherein, using the three-dimensional model, a simulation calculation is performed to calculate the

Arrangement, the heights and / or the rigidity of

To determine socket elements (3) such that

gravitational deformations of the optical

Functional surface of the optical element (3) after connecting to the socket structure of the particular Counteract deviation from the target shape.

Method according to one of the preceding claims, wherein the socket elements (3) have different heights.

Method according to one of the preceding claims, wherein the socket elements (3) different

Have stiffness.

Method according to one of the preceding claims, wherein the target shape of the optical functional surface (6) is a flat surface, and wherein the deviation of the measured shape of the optical functional surface (6) from the flat surface by connecting the optical element (5) with the socket structure completely or partially compensated.

Method according to one of claims 1 to 5,

wherein the target shape of the optical functional surface (6) is a curved surface capable of imaging electromagnetic radiation into focus, and a position of the focus is changed by connecting the optical element (5) to the socket structure.

Method according to one of claims 1 to 5,

wherein the optical functional surface (6) has a curved

Surface is for beam shaping

Electromagnetic radiation is provided, and wobe an optical aberration of the measured optical functional surface (6) by connecting the optical element (5) with the socket structure entirely or partially compensated.

9. The method according to any one of the preceding claims,

wherein the optical element (5) has a width b and a thickness d, and the ratio b / d is greater than 20.

10. The method according to any one of the preceding claims,

wherein a width b of the optical element (5) is more than 100 mm.

11. The method according to any one of the preceding claims,

wherein at least a part of the socket elements (3) on one of the optical functional surface (6) facing away from the back of the optical element (5) is mounted.

12. The method according to any one of the preceding claims,

wherein at least a part of the socket members (3) is attached to an outer edge of the optical element (5).

13. The method according to any one of the preceding claims,

wherein a plurality of sub-elements (5a, 5b) of the optical

Elements (5) through the socket elements (3) are interconnected.

14. The method according to any one of the preceding claims,

between the optical element (5) and the

Socket elements (3) one or more active

Components (2) are arranged.