Mounting arrangement for an optical element

Abstract

A mounting arrangement with a support platform (2) to which at least one optical element (3) is fixed, wherein the support platform (2) is connected to a base (8) at defined bearing points (5) via an elastically compliant and damping connection structure (6), wherein the connection structure (6) is designed to elastically accommodate thermal expansions of the support platform (2), characterized in that the at least one optical element (3) is located at a distinguished point (13) on the support platform (2), wherein this point (13) is positionally stable as a neutral point relative to the base (8) in the event of thermal deformation of the support platform (2), wherein the support platform (2) is connected to a heat sink or heat source (16) via a flexible, preferably ribbon-shaped heat transfer element (15), and wherein the support platform (2) is connected to the flexible heat transfer element (15) via an intermediate heat pump.

Description

[0001] The invention relates to a holding arrangement with a support platform to which at least one optical element is fixed, wherein the support platform is connected to a base at defined bearing points via an elastically compliant and damping connection structure, wherein the connection structure is designed to elastically accommodate thermal expansions of the support platform.

[0002] Optical systems require mounting concepts for the optical elements used (e.g., lenses, filters, prisms, etc.). For example, in laser systems, there is often a requirement to fix optical subsystems to a base (mounting surface) of the laser system, whereby one optical axis of the respective subsystem should be as stable as possible relative to the base.

[0003] For example, the direction of the output beam of a laser system is subject to certain fluctuations which can cause significant problems, e.g. when the beam has to be coupled into or out of a light-conducting fiber and / or when the beam is to hit a target at a greater distance with precision.

[0004] Beam direction fluctuations can have various causes. If the laser beam propagates through an optical subsystem attached to the laser system, this generally affects the beam guidance, with this effect depending strongly on how positionally stable the optical elements of the subsystem are relative to the base. For example, if...

[0005] If laser radiation is emitted from one end of a fiber optic cable in a coupling unit connected to the laser system and collimated by a lens, the position of the laser beam after the lens will exhibit an undesirable lateral movement corresponding to the angular fluctuations of the lens. A desirable design is one in which the fluctuations in the angular orientation of the laser beam represent only a small fraction of the beam divergence.

[0006] It is known that beam position fluctuations can be minimized by minimizing mechanical vibrations of the relevant optical elements through a stable setup and mechanical decoupling. Another known measure to prevent beam position fluctuations is to minimize thermal drift, for example, by shielding heated components such as laser diodes or electronic circuits from the optical elements that influence the beam position.

[0007] In practice, the known approaches often prove to be insufficient or too complex and therefore too expensive for certain applications.

[0008] DE 103 44 178 A1 discloses a holding and positioning device for an optical element, specifically a mirror. The device comprises a mounting ring for the optical element and three manipulator units with linear actuating elements. Each manipulator unit has a head and a foot, which are connected to each other via solid-state joints. This allows for axial adjustment and tilting of the optical element (about two independent axes) relative to a base.

[0009] DE 600 26 891 T2 discloses an extruded holding device, e.g. for an optical fiber. The fiber lies in a slot of a holding element. The latter is connected to a base via parallelogram-shaped lever elements and solid-state joints.

[0010] From DE 10 2010 022 934 A1, an optical assembly is known which comprises an optical element having an approximately rotationally symmetric cross-section perpendicular to an axis of symmetry. The optical assembly also comprises a socket for the optical element, with at least three retaining assemblies arranged on a circle around the axis of symmetry in the socket. These retaining assemblies fix the optical element in the socket by means of a positive and force-fit connection.

[0011] German patent DE 10 2018 200 956 A1 describes an optical element (concave mirror) for beam guidance. A counterweight system allows for changes to the mass distribution of the optical element's base body. This enables the gravitational compensation of what the document refers to as "passede deformations." Three counterweight elements are arranged on the base body for this purpose. Each element consists of two Peltier elements with an intermediate U-shaped tube filled with a liquid (water). The Peltier elements alter the mass distribution through evaporation and condensation of the liquid in one or the other leg of the U.

[0012] Against this background, the object of the invention is to provide a holding arrangement for optical elements that ensures improved beam position stability with the least possible effort.

[0013] The invention solves this problem in a holding arrangement of the type specified above by arranging the at least one optical element at a distinguished point on the support platform, wherein this point is positionally stable as a neutral point relative to the base in the event of thermal deformation of the support platform, wherein the support platform is connected to a heat sink or source via a flexible, preferably ribbon-shaped heat transfer element, and wherein the support platform is connected to the flexible heat transfer element via an intermediate heat pump.

[0014] The base essentially serves as the reference structure for the mounting. For example, the optical subsystem mounted on the support platform can be connected to a laser system via the base. Similarly, the base can be, for instance, a component of a housing or base frame for a laser system or other optical system.

[0015] The invention's approach is based on providing mechanical decoupling via an elastically compliant and / or damping connection structure, thus minimizing the effects of mechanical fluctuations on the optical elements fixed to the support platform. Simultaneously, thermal influences are minimized by positioning the at least one optical element relevant to the beam direction at the neutral point and / or on the neutral axis of the support platform. The neutral point is defined as one that remains positionally stable relative to the base even during thermal deformation of the support platform, e.g., due to thermal expansion during temperature fluctuations.

[0016] In one possible embodiment, the support platform forms an optical bench, with the beam passing through the neutral point via at least one optical element fixed to the support platform. This allows the desired beam stability to be achieved.

[0017] The support points are advantageously positioned in an arrangement that is statically suitable for the support task. In one design, the support points can, for example, be spaced apart from each other around the outer circumference of the support platform. In principle, however, any arrangement of the support points on the support platform is conceivable. The number of support points can also vary. The support provided by the support points serves to prevent any unwanted tilting movements. For example, three (or more) support points can be provided, which do not all lie on a common axis.

[0018] During thermal deformation, an elastic displacement occurs in the compliant connection structures. For the most diverse conceivable geometries of the support platform with various arrangements of the bearing points on the support platform, a neutral point or a neutral axis can be found that always remains stable during thermal deformation. According to the invention, the optical element critical for the beam position is positioned there.

[0019] In other words, the arrangement of the support points compensates for quasi-static movements resulting from changes in the isotropic ambient temperature field by absorbing these movements through the elastic compliance of the connecting structure. This compliance effectively allows for a "sacrificial movement" that ensures the optical element located at the neutral point remains stable and, consequently, that the beam position does not change despite temperature fluctuations (i.e., only within tolerable limits).

[0020] The support platform is connected to a heat sink or heat source via a flexible, preferably ribbon-shaped, heat transfer element. In some applications, it is necessary to temper the optical elements located on the support platform, i.e., to bring them to a specific operating temperature and maintain it there. According to the invention, the necessary heat conduction path is formed by the flexible heat transfer element, e.g., in the form of a flexible ribbon made of metal mesh. The advantage of the flexibility of the heat transfer element is that the thermal connection to the heat sink or heat source is mechanically independent; the mechanical decoupling provided by the connection structure is therefore not affected by the thermal connection. Furthermore, the flexible heat transfer element offers the advantage that the connected heat sink or heat source...The heat source can be freely positioned, especially at a greater distance from the support platform. When designing the heat transfer element, care should be taken to ensure the largest possible contact area with the support platform. Temperature control can be achieved by specifying the heat flow through the heat transfer element.

[0021] The support platform is connected to the flexible heat transfer element via an intermediate heat pump, preferably in the form of a Peltier element. Temperature control can be achieved by appropriately controlling the Peltier element, ideally in combination with a temperature sensor on the support platform. The Peltier element controls the heat flow from the heat source to the support platform and from the support platform to the heat sink. This allows the support platform and the optical elements mounted on it to be kept at a stable, predetermined temperature.

[0022] The inventive approach to beam position stabilization can be further supported by selecting a material for the support platform with thermally / mechanically invariant behavior, i.e., a material or material composition with the lowest possible thermal expansion.

[0023] In one possible configuration, the connecting structure includes thermal insulation designed to reduce or largely prevent heat flow between the support platform and the base. This thermal insulation minimizes the thermal impact on the support platform and the optical elements mounted on it.

[0024] In a practical embodiment, the connection structure can include a connecting element attached to the base, which is linked to the support platform via an elastic solid-state joint. An elastic solid-state joint, for example in the form of a plate joint, has the advantage that the displacement of the connecting element relative to the support platform is well-defined. A plate joint can, for example, be designed to be flexible along only one axis. By combining such joints at the various support points with targeted alignment of the respective displacement axes, the position of the neutral point or neutral axis on the support platform can be precisely defined according to the requirements.

[0025] In a particularly simple and therefore advantageous implementation, the connecting element can be a bolt screwed to the base, guided in a sleeve (e.g., a threaded sleeve) that is connected to the support platform via the elastic solid-state joint. Due to the reduced material cross-sections in the joint area, the solid-state joint also has the advantage of intrinsically reducing heat flow from the base to the support platform via the connection structure (thermal insulation).

[0026] The solid body joint can also be designed to provide sufficient damping for the desired mechanical decoupling.

[0027] In one possible configuration, at least one optical element is from the list: lens, optical grating, prism, beam splitter, filter, end of a light-conducting fiber, filter, laser diode, or a combination of these elements, to name just a few exemplary possibilities.

[0028] In an advantageous application, one end of a light-conducting fiber and a lens are fixed to the support platform, with the lens located at the neutral point. In this case, the holding arrangement supports the components of a fiber coupler for coupling light out of the fiber or coupling light into the fiber. The beam position stabilization achieved according to the invention ensures efficient and stable coupling out and coupling in.

[0029] An embodiment of the invention is explained in more detail below with reference to the figures. They show: Fig. 1a,b: schematic top view of a holding arrangement from above; Fig. 2: Schematic side view of the holding arrangement of the Fig. 1.

[0030] In the following figure description, the same reference symbols and terms are used for the same elements.

[0031] In the figures, the entire holding arrangement is designated by reference numeral 1. This includes a support platform 2, in the form of a ( in top view ( Fig. 1) polygonally shaped blocks. A focusing lens 3 and the end 4 of a light-conducting fiber are fixed to the support platform 2 as optical elements. The focusing lens 3 focuses a laser beam 7, coming from the left in the drawings, onto the fiber end 4 in order to couple the radiation into the light-conducting fiber. The support platform 2 is mounted at three bearing points 5, arranged in a triangular configuration around the outer circumference of the support platform 2, each via an elastically compliant and damping connection structure 6 with a base 8 ( Fig. 2) connected.

[0032] The connecting structures 6 each comprise a connecting element in the form of a screw bolt 9 connected to the base 8 ( Fig. 2), which is screwed into the base 8. The screw bolt 9 is guided in a sleeve 10, which is connected to the support platform 2 via a solid-state joint 11 designed as a plate joint. The plate joints each define a deflection axis 12. By combining the joints 11 at the three bearing points 5 with the illustrated orientation of the deflection axes 12, the position of a designated point 13 on the support platform 2 is predetermined ( Fig. 1) Due to thermal expansion caused by temperature fluctuations, an elastic displacement occurs along the axes 12. This thermal expansion is absorbed by the solid joints 11. In the geometry shown, the designated point 13 acts as a neutral point, which remains stable relative to the base 8 even under thermal deformation. The lens 3 is positioned at point 13 to ensure that its position, and thus the focus of the laser beam 7 on the fiber end 4, remains unchanged despite temperature fluctuations.

[0033] In the depicted geometry of the support points 5 in combination with the three solid hinges 11, the neutral point 13 results, as explained. In the case of a different geometry, where, for example, the deflection axes 12 do not intersect at a single point but run parallel to each other, an alternative neutral axis (not shown) can be realized.

[0034] The connecting structure 6 includes thermal insulation in the form of spacer sleeves 14 made of thermally insulating material, which are designed to minimize heat flow between support platform 2 and base 8.

[0035] As in Fig. As can be seen in Figure 2, the support platform 2 is only connected to the base 8 via the screw bolts 9 of the connecting structure 6 and the spacer sleeves 14 arranged between them. Otherwise, there is no material contact between the support platform 2 and the base 8.

[0036] The support platform 2 is connected to a heat sink or heat source 16 via a flexible, ribbon-shaped heat transfer element 15 ( Fig.2) The flexible heat transfer element 15 forms a heat conduction path to allow for the targeted temperature control of the support platform 2 with the optical element 3 attached to it. Due to the flexibility of the heat transfer element 14, the thermal connection to the heat sink or heat source 16 is mechanically independent. The mechanical decoupling provided by the compliant connection structure 6 is therefore not affected by the thermal connection. The support platform 2 is connected to the flexible heat transfer element 15 via an intermediate Peltier element 17. Temperature control can be achieved by controlling the Peltier element. The Peltier element 17 controls the heat flow from the heat source 16 to the support platform 2 and from the support platform 2 to the heat sink 16.

Claims

[1] Holding arrangement with a support platform (2) to which at least one optical element (3) is fixed, wherein the support platform (2) is connected to a base (8) at defined support points (5) via an elastically compliant and damping connection structure (6), wherein the connection structure (6) is designed to elastically accommodate thermal expansions of the support platform (2), characterized by , that the at least one optical element (3) is located at a distinguished point (13) on the support platform (2), wherein this point (13) is positionally stable as a neutral point relative to the base (8) in the event of thermal deformation of the support platform (2), wherein the support platform (2) is connected to a heat sink or source (16) via a flexible, preferably ribbon-shaped heat transfer element (15), and wherein the support platform (2) is connected to the flexible heat transfer element (15) via an intermediate heat pump. [2] Holding arrangement according to claim 1, wherein the bearing points (5) are spaced apart from each other on the support platform (2). [3] Holding arrangement according to claim 1 or 2, wherein the connecting structure (6) comprises a thermal insulation (14) designed to reduce heat flow between support platform (2) and base (8). [4] Holding arrangement according to one of claims 1 to 3, wherein the connecting structure (6) comprises a connecting element (9) connected to the base (8) which is connected to the support platform (2) via an elastic solid joint (11). [5] Holding arrangement according to claim 4, wherein the connecting member (9) is a bolt screwed to the base (8) which is guided in a sleeve (10) which is connected to the support platform (2) via the elastic solid body joint (11). [6] Holding arrangement according to one of claims 1 to 5, wherein the intermediate heat pump is designed as a Peltier element (17). [7] Holding arrangement according to one of claims 1 to 6, wherein the support platform (2) forms an optical bench, wherein an optical axis defined by the at least one optical element fixed on the support platform (2) passes through the neutral point. [8] Holding arrangement according to any one of claims 1 to 7, wherein the at least one optical element (3) is an element from the list: lens, optical grating, prism, beam splitter, filter, end of a light-conducting fiber, filter, laser diode. [9] Holding arrangement according to one of claims 1 to 8, wherein an end of a light-conducting fiber (4) and a lens (3) are fixed to the support platform (2), wherein the lens (3) is located at the neutral point (13). [10] Use of a holding arrangement according to any one of claims 1 to 9 for fixing optical elements in a laser system.

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