Abstract:
Apparatus with an optical bench and at least one optical element, which is attached on the optical bench, whereby the optical bench comprises a layer structure with an extruded honeycomb plate from light alloy, paper or char-fiber-reinforced plastic. A first cover layer is glued to the honeycomb plate and comprises a first glass-like plate, which is surface-treated on that side which faces away from the honeycomb plate. A second cover layer glued to the lower surface of the light alloy honeycomb plate and comprises a second glass-like plate. The optical bench has suspensions, which glued to one or more parts of the layer structure for force introduction into the layer structure. The optical element is fixed by cold welding or glueing on the surface-treated side of the first glass-like plate.

Description:
[0001]     The present invention concerns a stable, light optical bench and its use in space.  
         [0002]     Optical setups require a precise mounting platform for the placement of single optical elements, such as for instance filters, prisms, mirrors, lenses, and so forth. Typically, an optical bench serves as mounting platform for such elements.  
         [0003]     Neither the floor space nor the weight play an important role for many applications and the corresponding materials and setups may be chosen. In more modern applications often massive glass or glass-ceramic plates are being deployed.  
         [0004]     More and more often, however, optical setups are being moved or employed in moving systems. In this case the size and weight of the optical bench can play an important role. The weight is a decisive factor in setups that have to be accelerated or decelerated.  
         [0005]     Today, such applications rely often on glass or glass-ceramic plates, whereby cutouts for the reduction of the weight are formed by means of milling, for example. It is an advantage of this approach that the knowledge collected in connection with apparatus based on such glass or glass-ceramic plates can be used further on. It is a disadvantage of this approach that the mass reduction due to the cutouts Is not sufficient for many applications. Moreover, the making of the cutouts is costly and may lead to waste in the production. The loss of stability is regarded to be a further disadvantage. In particular in case of setups that are dynamically loaded, or if being employed in an environment with strongly fluctuating temperatures, such as in space for instance, the cutouts cause inhomogeneities that may for example give rise to tensions. Particularly disadvantageous is the carving out of Zerodur-plates by means of milling, since during this handling step the part tend to burst due to internal tensions.  
         [0006]     The deployment of optical setups in space is mentioned as example for applications that are particularly critical. These setups have to be able to be transported into space and there to be permanently and reliably deployed. Especially at launch of the carrier rocket that shall bring the setup into space, the costs are determined based on the weight, since per kilogram of mass to be transported an enormous amount of energy has to be made available.  
         [0007]     Besides of the weight there are other factors for moving optical systems or optical systems that are being moved, that are important. Criteria, the adherence to which is of fundamental importance, are the (torsion-) stiffness, roughness, planarity, temperature stability, shock resistance, etc.  
         [0008]     It is an object of the invention to provide an apparatus that avoids or reduces the disadvantages of known apparatus.  
         [0009]     It is thus an object of the present invention to provide an optical bench that is lighter than conventional setups and that at the same time fulfils the essential criteria, which are, depending on the application and place of deployment, imposed on the system.  
         [0010]     Furthermore, it is an object of the invention to provide an optical bench that can be deployed extra terrestrically.  
         [0011]     According to the present invention this objective is achieved by the features of the claim  1  for the apparatus and by the features of the claim  10  for the use.  
         [0012]     Advantageous embodiments of the apparatus are defined by the claims  2  through  9 . An advantageous use is defined by the dependent claim  11 . 
     
    
       [0013]     Further characteristics and advantages of the invention will in the following be described in detail by means of the description and by making reference to the drawings. It shows:  
         [0014]      FIG. 1 a  first optical bench, according to the present invention, in a schematical representation;  
         [0015]      FIG. 2  the first optical bench, according to the present invention, in a schematical, exploded view;  
         [0016]      FIG. 3  further details of the first optical bench, according to the present invention, in a schematical representation;  
         [0017]      FIG. 4 a  second optical bench, according to the present invention, in a schematical partial representation;  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]     The principle of the present invention is being described in connection with a first embodiment. In  FIG. 1 , this first embodiment is shown by means of a first schematic view and in  FIG. 2  as schematically exploded view.  
         [0019]     A view of an optical bench  10  is shown that has, according to the invention, a layered structure. The layered structure comprises a honeycomb plate  12  with a flat upper and lower side. This honeycomb plate preferably comprises light metal (aluminum), paper (preferably Nomex® Aramid Paper), or carbon fiber enforced plastic (CFK). Preferably, the honeycomb plate is extruded. A first cover layer  11  is glued onto the honeycomb plate  12 . It comprises a first glass-type plate, which is surface-treated on the side which is facing away from the honeycomb plate  12 . In the example illustrated, the visible surface is surface-treated. A second cover layer  13  is glued onto the lower side of the honeycomb plate  12 . It comprises a second glass-type plate which may possibly also be surface-treated. In addition, the optical bench  10  comprises suspensions  14  which are glued to one or more elements for guiding forces into the layered structure. The suspensions  14  are placed like inserts into cutouts, as can be seen in  FIG. 2 .  
         [0020]     In a preferred embodiment, the suspensions are essentially only glued to the lower side of the upper cover layer  11  and the upper side of the lower cover layer  13 . In this case mainly the uppers sides O and the lower sides U of the suspensions  14  are connected with the cover layers  11 ,  13 . the respective glue connections are mainly loaded in parallel to theirs flat dimensions in the x-y plane (shear load). The guiding of forces thus occurs via large shear planes, the area dimension of which is defined by the upper and lower faces of the suspensions  14 .  
         [0021]     Preferably, the suspensions  14  comprise holes, that can receive pins, screws  17 . 1  or axis, as shown in  FIG. 3 . It is preferred to glue these connections. In this case the holes serve for provisional screwing, respectively for the injection of glue. Depending on the application it is sufficient to use screwing only.  
         [0022]     The honeycomb structure of the honeycomb plate  12  is recognizable in  FIG. 2 . The honeycomb plate comprises a large number of single honeycomb-shaped cells that are being made from thin aluminum foils that are being extruded accordingly. The honeycomb plate  12  has flat upper und lower sides which extend perpendicular to the sidewalls and which lie in the x-y plane.  
         [0023]     In the example shown the optical bench has a hexagon shape (if viewed from above or below) with six straight edges. It may, however, be realized in any other desired shape. The required optical stability defines the ratio between thickness D and largest length L. According to the invention this ratio is between 1/20 and 1/5. If the ratio between thickness D and largest length L is chosen taking into account these value, sufficient stability at low weight can be guaranteed for most optical applications.  
         [0024]     In the embodiments shown, the upper and the lower cover layers  11 ,  13  each only comprise one glass-type plate and a glue layer each, which is not visible in the  FIGS. 1 and 2 . The glass-typ plates hence are glued right onto the honeycomb plate  12 .  
         [0025]     In  FIG. 3 a  preferred suspension, according to the present invention, of the optical bench  10  is shown. There are three so-called bipods  17  provided which together serve as 3-point suspension.  
         [0026]     The bipods, as their name indicates, have two shanks  17 . 4  which terminate in foot plates  17 . 5 . For fixing the bipods  17  on a frame or mounting platform holes may be provided in the foot plates  17 . 5 . The bipods may also rest on another optical bench. In the area where the two shanks  17 . 4  meet a mounting plate  17 . 3  may be provided which in the example as shown comprises two through holes. A shim  17 . 2  may be applied and screws  17 . 1  may be screwed through the holes in the mounting plate  17 . 3  into the holes of the suspension  14 . With such a suspension of the optical bench  10 , in particular if glued in addition, a light and very stable 3-point bearing results. An optical element  16  is shown in  FIG. 1  that is fixed on the surface-treated glass-type plate  11 . The optical element  16  shown involves a reference cube. The 3-point suspension described is particularly well suited for use on a satellite.  
         [0027]     The following optical elements, beneath others, can be fixed on the glass-type plate  11 : prisms, lenses, mirrors, spacers, lambda-quarter or lambda-half wave plates, filters, lasers, etalons, optical detectors, etc. Resonators, light sources, interferrometers, transmitters, receivers, cameras and other optical systems can be realized with such optical elements.  
         [0028]     A further embodiment of an optical bench  20  is shown in  FIG. 4  in the form of a partial view. In the embodiment shown, the upper cover layer  21  and the lower cover layer  23  of the optical bench  20  comprise a glass-type plate  21 . 1  and  23 . 1 , a glue layer  21 . 3  and  23 . 3  each, and a fiber enforced layer  21 . 2  and  23 . 2  each. The glass-type plates  21 . 1  and  23 . 1  are in this case not glued directly onto the honeycomb plate  22 , but separated from the honeycomb plate  22  by the fiber enforced layers (e.g., CFK)  21 . 2  and  23 . 2  and the glue layers  21 . 3  and  23 . 3 . This has the advantage that, if necessary, the stiffness per unit of weight can be further increased significantly. A suspension  24  is shown, the upper surface O (in hatched representation) of which is glued to the lower side of the glue layer  21 . 3  and its lower surface U (not shown) is glued to the upper side of the glue layer  23 . 3 . The suspension  24  shows a hole  26  on the front side presented in gray which can receive a pin, a screw or an axis. Due to this a suspension similar to the one shown in  FIG. 3  can be employed.  
         [0029]     According to the present invention at least one optical element is fixed on the surface-treated side of the first glass-type plate by means of contacting or glueing. No optical element is shown in the  FIGS. 1 and 2  since in these Figures only the setup of the optical bench  10  is shown as a first embodiment. In  FIG. 3  one optical element is illustrated as example.  
         [0030]     During optical contacting the optical element is “exploded on”. A mechanical bond develops due to adhesion forces between the optical element and the surface-treated, glass-type plate. Preferably, the surface of the glass-type plate and one side of the optical element to be fixed are polished so even that both adhere to each other because of atomic adhesion. It is important that the connection is so well that the element cannot break loose. In a special optional embodiment the connection is at least in a certain wavelength range transparent to avoid losses. Preferably, the exploding on is carried out in a clean room. Especially preferred is a clean room of class 100 or better.  
         [0031]     The optical elements are, according to the present invention, either fixed by means of optical contacting, as described in the last section, or they are fixed by means of silicate glue (hydro-catalytic bonding). Both methods have in common that the connection practically occurs directly. In case of optical contacting the thickness is zero, in case of silicate glueing a few through 100 nanometers. Naturally, the parts can also be glued the normal way with glue thickness of some micrometers.  
         [0032]     Preferably, each of the glass-type plates has a thickness between 0.5 and about 5 millimeters. Especially preferred is a plate thickness of about 2.5 to 3.5 millimeters.  
         [0033]     The honeycombs of the honeycomb structure preferably have a cell size from 2 to 8 millimeters and a hexagonally arranged construction.  
         [0034]     It is an advantage of the invention that the mass as compared to conventional setups can be reduced by up to 60% and more without disregarding the most important criteria of the optical bench.  
         [0035]     Preferably, the glass-type plates are Zerodur (Schott Glass Technologies; Duryea, Pa.), ULE (Corning Inc.; Corning, N.Y.), or quarz glass (fused silica). Zerodur is a ceramic glass with an extremely small expansion coefficient and ULE is a titanium silicate with extremely small expansion coefficient. Especially preferred is a symmetrical setup that on the upper and lower side comprises an identical glass-type plate. Thermal tensions can be reduced due to this. Any deviation from the symmetrical layered setup can lead to tensions like in a bi-metal. This, however, does not exclude that the two cover plate have different thicknesses.  
         [0036]     An optical bench according to the invention allows a much better guiding of forces. Due to this the field of use is much larger. Dynamical loads can be better absorbed due to the special way how the forces are guided without causing damage to the optical bench or its elements. Temperature fluctuations can be better absorbed without causing problems.  
         [0037]     During the production no time- and cost consuming treatment of glass plates or glass-ceramic plates has to be carried out. More or less, conventionally available plates can be used. Due to this the total costs can be reduced and the waste can be kept small.  
         [0038]     It is an advantage of the invention that simple glass-type plates can be used that are more stable since they do not have any cutouts.  
         [0039]     Preferably the cover layers are connected to the honeycomb structure in a vacuum. Well suited for the deployment in space are honeycomb plates with walls comprising holes thus enabling a pressure relief. Preferred are honeycomb plates with perforated walls.  
         [0040]     It is an advantage of the invention that the cover layer can be adapted to the actual application. According to the invention accuracies if the range of nanometers can be achieved. Preferably the roughness of a surface-treated glass-type plate amounts to less than 10 nanometers and preferably less than 5 nanometers. The flatness across the whole dimension is between 10 and 200 nanometers and preferably between 20 and 50 nanometers.  
         [0041]     The honeycomb structure  12  has the advantage that it is relatively soft in the x-y plane. Due to the fact that the upper side as well as the lower side is glued with the respective cover layers  11  and  13 , respectively, no remarkable thermal movements occur in the x-y plane. In z-direction, however, the layered structure may work freely. At increasing temperatures the honeycomb structure expands in equal parts up and down. Since the two cover layers are independent from another the whole layered structure may work in z-direction.  
         [0042]     The honeycomb structure is built from light metal walls and has a high thermal conductivity. Temperature gradients are evened out quickly without local tensions to occur that could cause a tensioning of the cover layers. Especially preferred are aluminum honeycomb structures since aluminum is highly conductive.  
         [0043]     During the assembly of the optical bench  10  according to the invention the layers of the layered structure are glued to each other first. In doing so preferably an epoxy glueing film is employed that hardens at increased temperatures. The glueing film is applied onto the honeycomb structure and the cover layers are applied. Then the hardening of the glueing film is initiated by heating, for instance in an oven. Only after the hardening the suspensions  14  are provided on the upper and lower sides (O, U) with a suited glue and put into the cutouts  15 . Due to this step-wise assembly tensions can be excluded.  
         [0044]     In further steps the optical elements are optically contacted or glued on. Prior to this the surfaces of the glass-type plate are treated, for instance to remove grease remainders. The optical elements are being optically contacted or glued on in a clean room, as already mentioned.  
         [0045]     Preferably the optical bench and its suspension is realized so that it is suited for transportation into space that typically is done by means of a rocket and is connected with high static loads and vibrations. Finally, the optical elements have to be fixed on the optical bench so that the large temperature differences and the steep temperature gradients caused by these temperature differences have no negative influence on the total system.  
         [0046]     Preferably the optical bench with the optical elements is employed as part of an optical telescope that is designed for the communication between satellites (intersatellite communication) or for the communication between a terrestric appliance and a satellite. The optical bench may also be part of a spectrometer.