Abstract:
A method involves depositing on a surface of an optical substrate an optical layer made of a substance that has an index of refraction approximately equal to an index of refraction of the optical substrate, the optical substrate and the layer collectively defining a multi-section substrate in which the optical substrate and the optical layer serve as respective sections. According to a different aspect, an apparatus includes a multi-section substrate having a first section that is an optical substrate with a surface, and having a second section that is an optical layer provided on the surface and made of a substance having an index of refraction approximately equal to an index of refraction of the optical substrate.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates in general to optical components and, more particularly, to techniques for fabrication and/or repair of the substrate of an optical component. 
       BACKGROUND 
       [0002]    Optical components such as lenses, domes and windows are typically made from a larger blank, which is ground and/or polished down to the shape needed. Even after shaping, the part may sometimes be out of specification. As one example, the part may have a high-tolerance specification because it is intended for use in a high-precision device, such as a high-end microscope or an expensive camera. As another example, the part may be made from a material that is difficult to accurately grind and/or polish. 
         [0003]    When the part reaches a point during fabrication when it should in theory be completed, but is actually found to be out of specification, the part is reworked in order to try to bring it into compliance with the specification. The reworking removes more material. For particularly difficult parts, several rounds of reworking may be carried out. Each time the part is reworked, more material is removed, and the part becomes thinner. At some point, the part may become too thin to be used. 
         [0004]    A similar situation exists in the case of a part that was previously fabricated and then used for a period of time, such that an outside surface became scratched or otherwise physically damaged. A repair of the part can be attempted, involving removing coatings (if any),and then grinding and/or polishing the damaged surface. However, this thins the part. At some point, possibly after multiple attempts at repair, the part may become too thin. 
         [0005]    Where grinding and/or polishing of an optical part causes it to become too thin, the traditional approach has been to scrap the thin part, purchase a new blank, and begin the manufacturing process again from the very beginning. While this approach has been generally adequate for its intended purposes, it has not been satisfactory in all respects, especially in regard to optical components that are relatively expensive. The existing approach typically involves undesirable cost and delay, reflected not only in the cost of the new blank, but also in the cost of labor, material and equipment used in creating a part that ultimately ends up being discarded. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    A better understanding of the present invention will be realized from the detailed description that follows, taken in conjunction with the accompanying drawings, in which: 
           [0007]      FIG. 1  is diagrammatic sectional side view of an apparatus that is a conventional optical component, in particular a substrate that is a lens, shown at a selected stage during fabrication thereof. 
           [0008]      FIG. 2  is a diagrammatic sectional side view similar to  FIG. 1 , but showing that several successive reworking operations have removed material from one side of the lens, resulting in a new side surface. 
           [0009]      FIG. 3  is a diagrammatic sectional side view of the thin lens of  FIG. 2 , with the addition of a coating on a side surface thereof. 
           [0010]      FIG. 4  is diagrammatic sectional side view of a conventional coating apparatus that has therein the coated lens of  FIG. 3 , and another similar coated lens. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]      FIG. 1  is diagrammatic sectional side view of an apparatus that is a conventional optical component, in particular a substrate that is a lens  10 , shown at an selected stage during fabrication thereof. Although the optical component  10  in  FIG. 1  is a lens, it could alternatively be some other type of optical component, such as a window or a dome. The lens  10  has curved surfaces  13  and  14  on opposite sides thereof. The process of manufacturing the lens  10  begins with a blank that is shown diagrammatically at  21 . Although the blank  21  in  FIG. 1  has an initial shape that is generally rectangular, the blank could alternatively have some other initial shape. For example, the blank could have an initial shape that is closer to the shape of the desired lens  10 . 
         [0012]    Material of the blank  21  is removed by grinding and/or polishing, in order to obtain the lens  10  with the desired shape.  FIG. 1  represents a state of the lens  10  in which the fabrication of the lens should in theory be completed. However, when the lens is tested for accuracy at this point, it is sometimes determined that the lens does not meet one or more of its design specifications, for example because it is a high-tolerance part, or because it happens to be made of a material that is hard to accurately shape. Accordingly, when a lens reaches the point at which it should theoretically be completed but fails to meet one or more of its specifications, the lens is reworked, which has the effect of removing additional material. In some cases, there may be multiple cycles of reworking and retesting, involving the repeated removable of material. 
         [0013]    A similar situation can arise where a component was previously fabricated and then used for a period of time, and an outside surface has become scratched or otherwise physically damaged. A repair can then be attempted through grinding and/or polishing, which removes material and thins the part. There may be multiple cycles of reworking and retesting, involving the repeated removable of material. 
         [0014]      FIG. 2  is a diagrammatic sectional side view similar to  FIG. 1 , but showing that several successive reworking operations have removed an amount of material  31  from one side of the lens  10 , resulting in a new side surface  34 . At some point, multiple cycles of reworking may cause the lens  10  to become too thin for actual use in the intended application. When this occurs, the traditional course of action is to scrap the thin lens, select another blank  21  ( FIG. 1 ), and begin the entire fabrication process again from the beginning. 
         [0015]    To avoid the traditional approach of scrapping a part that has become too thin, one aspect of the invention involves adding material where material has been removed. In this regard,  FIG. 3  is a diagrammatic sectional side view of the thin lens  10  as shown in  FIG. 2 , with the addition of a coating  46  on the side surface  34  thereof. The material selected for the coating  46  is a material that has substantially the same index of refraction as the material of the lens  10 , in order to avoid optical interference effects that would ruin the optical properties of the resulting optical component defined by the lens  10  with the coating  46  thereon. Depending on the material of the lens  10 , it may be possible to make the coating  46  from the same material. However, even if the lens and coating are each made from the same material, in the sense that the materials are chemically equivalent, this does not automatically guarantee that the lens and coating will have the same index of refraction. For example, the lens and the coating will typically be formed by different processes, and the lens and coating may therefore have different crystalline structures, such as where the coating has a more amorphous crystalline structure. In some cases, a closer match in indexes of refraction may be obtained by making the coating  46  from a material different from the material of the lens  10 . 
         [0016]    Beyond matching the indexes of refraction of the lens  10  and coating  46 , it can also be advantageous to obtain a match in the hardnesses and/or coefficients of thermal expansion of the lens  10  and coating  46 . If the hardnesses are approximately the same, then the lens with the coating thereon can be ground or polished under the same conditions that would be used for the lens alone. In contrast, if the coating has a hardness that is significantly different from the hardness of the lens, the grinding and/or polishing conditions may need to be adjusted to accommodate the higher or lower hardness of the coating  46 . Matching the coefficients of thermal expansion has the advantage of reducing shear forces that can occur at the interface between the lens and coating in response to temperature changes. 
         [0017]    In a situation where the coating  46  is made from a material that is softer than the material of the lens  10 , the coating should be formed on the less-exposed surface of the lens. For example, if the lens will be mounted in a housing so that one surface is exposed to ambient conditions external to the housing, whereas the other surface will face the interior of the housing, the soft coating should be applied to the latter surface. 
         [0018]    In some cases, there may be an existing coating material with a refractive index that closely matches the refractive index of the lens substrate. But if a coating material with the requisite index of refraction is not readily available, it may be possible to alter the index of refraction of an existing coating material by modifying process conditions used during the coating process, for example by changing the temperature, changing ion assist parameters, or changing an oxygen flow rate (for oxides). Still another possibility is to mix two or more existing coating materials that have different indexes of refraction, in order to obtain a mixture of those materials that provides the requisite index of infraction. 
         [0019]      FIG. 4  is diagrammatic sectional side view of a conventional coating apparatus  110  that has therein the lens  10  with coating  46  ( FIG. 3 ), and also another similar lens  108  with a similar coating  109 . The coating apparatus  110  includes a housing  112  with a chamber  113  therein. During a typical coating operation, a vacuum is maintained in the chamber  113  by a not-illustrated vacuum pump. The housing  112  supports a primary axle  117  for rotation about a primary vertical axis  118 . A support part  119  is supported on the axle  117  within the chamber  113  for rotation with the axle about the axis  118 . In the disclosed embodiment, the support  119  is disk-shaped, but it could alternatively have any other suitable shape. 
         [0020]    The support part  119  rotatably supports two workpiece support members  121  and  122 . More specifically, two additional vertical axles  123  and  124  are rotatably supported on the support part  119 . These two additional axles are spaced circumferentially from each other about the primary axle  117 , and they each rotate about a respective additional vertical axis  126  or  127 . The two support members  121  and  122  are each fixedly supported on a respective one of the axles  123  and  124  for rotation therewith about the associated axis  126  or  127 . In the disclosed embodiment, the support members  121  and  122  are disk-shaped, but they could each alternatively have any other suitable shape. Although  FIG. 4  shows two workpiece support members  121  and  122  having respective axles  123  and  124 , it would alternatively be possible to have one or more additional workpiece support members with respective axles, where the axles for all workpiece support members are spaced circumferentially from each other about the primary axle  117 . 
         [0021]    A drive mechanism  131  such as an electric motor is coupled to the axle  117 , in order to effect rotation of the axle  117  and the support part  119 . A not-illustrated planetary gearing mechanism of a well-known type is provided and, in response to rotation of the support part  119  with respect to the housing  112 , effects rotation of the additional axles  123  and  124  with respect to the support part  119 . Thus, the workpiece support members  121  and  122  each undergo planetary movement about the primary axis  118  with respect to the housing  112 . Each of the workpiece support members  121  and  122  has fixed thereon a respective workpiece support fixture  136  or  137 . The workpiece support fixtures  136  and  137  are each a cylindrical sleeve with an annular piece of double-sided adhesive tape  138  or  139  on the inner surface thereof at the lower end. The tape  138  engages a peripheral edge of the lens  10  in order to fixedly but removably support that lens on the fixture  136 , and the tape  139  engages a peripheral edge of the lens  108  in order to fixedly but removably support that lens on the fixture  137 . 
         [0022]    Although the disclosed embodiment uses double-sided adhesive tape  138  and  139  to support the lenses  10  and  108 , it would alternatively be possible to support the lenses on the workpiece support members  121  and  122  in any other suitable manner. As one example, the fixtures  136  and  137  could each have at the lower end thereof a radially inwardly projecting annular flange that engages the peripheral edge of the surface on the underside of the corresponding lens  10  or  108 . 
         [0023]    The primary axle  117 , the support part  119 , the additional axles  123  and  124 , the workpiece support members  121  and  122 , and the workpiece support fixtures  136  and  137  collectively serve as a workpiece support mechanism. For simplicity and clarity,  FIG. 4  shows each of the workpiece support members  121  and  122  with just one workpiece support fixture  136  or  137  thereon. However, it would alternatively be possible for each of the workpiece support members  121  and  122  to have a plurality of workpiece support fixtures thereon. 
         [0024]    The apparatus  110  forms the respective coatings  46  and  109  on the lenses  10  and  108 . In this regard, the coating apparatus  110  includes a source  162  within the housing  112 , in a lower portion of the chamber  113 . The source  162  is spaced downwardly from the support part  119 . The source  162  and the drive mechanism  131  are both controlled by a control unit  164  of a known type. Although  FIG. 4  shows only a single source  162 , it would alternatively be possible to provide two or more sources in the apparatus  110 . In the disclosed embodiment, the source  162  is spaced radially from the primary axis  118 , and is positioned approximately below the path of travel of the workpiece support members  121  and  122 . However, it would alternatively be possible for the source  162  to be positioned at any of a variety of other locations within the housing  112 . 
         [0025]    The source  162  is a device of a type well known in the art, and is therefore described here only briefly. In the disclosed embodiment, the source  162  is a type of device commonly referred to as an electron beam evaporator. However, the source  162  could alternatively be any other suitable type of device. The source  162  contains one or more different materials that can be used to form the coatings  46  and  109 . The source  162  can evaporate only one such material in order to form the coatings  46  and  109 . Alternatively, the source  162  can carry out co-deposition by simultaneously evaporating a combination of two or more of the materials therein in order to form the coatings  46  and  109 . 
         [0026]    When the source  162  is evaporating one or more of the materials therein, a plume of the evaporated material(s) travels upwardly, as indicated diagrammatically by arrows  171 - 174 . The plume  171 - 174  has a dispersion angle  191 . The plume  171 - 174  from the source  162  coats the lower surfaces of the lenses  10  and  108  as the lenses pass above the source  162 , thereby forming the coatings  46  and  109 . 
         [0027]    Although the coating apparatus  110  shown in  FIG. 4  is an evaporation system that utilizes an electron beam evaporator  162  to form the coatings  46  and  109 , it would alternatively be possible to form the coatings  46  and  109  in any other suitable manner. For example, the uncoated lenses  10  and  108  could be placed in a conventional sputter apparatus, and the coatings  46  and  109  could be formed by carrying out sputtering using one or more sputter targets that emit one material or a combination of materials needed for the coatings  46  and  109 . 
         [0028]    Although selected embodiments have been illustrated and described in detail, it should be understood that a variety of substitutions and alterations are possible without departing from the spirit and scope of the present invention, as defined by the claims that follow.