Abstract:
An optical assembly includes a housing having an interior region, a first lens disposed within the interior region of the housing, a second lens disposed within the interior region of the housing, the second lens being spaced from the first lens, a spacer disposed within the interior region of the housing between the first lens and the second lens, the spacer being fabricated from glass material, and a retention assembly configured to engage the second lens when assembled to retain the first lens, the spacer and the second lens in place. The housing may include a port providing fluid communication from an exterior of the housing to the interior region of the housing. The optical assembly further may include a filler material disposed in a space defined by an exterior surface of the spacer and an interior surface of the housing via the port.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. provisional application No. 61/740,029 filed on Dec. 20, 2012 and titled “OPTICAL ASSEMBLY”, which is herein incorporated by reference in its entirety. 
     
    
     BACKGROUND OF THE DISCLOSURE 
       [0002]    A thermal lens systems require a thermal expansion of lens mounts to be counteracted by a change in optical properties of the lens, causing the lenses to remain in focus as the temperature of the lens system changes. Aluminum is commonly used as a lens mount material due to its low inherent cost (inexpensive material and processing costs). However, aluminum has one of the highest coefficient of thermal expansion (CTE) for metals (around 24 ppm/° C.). This high CTE frequently results in lens designs are difficult to correct optically. 
         [0003]    Glass spacers are also known in the art of lens mounts. Reference may be made to U.S. Pat. Nos. 5,100,218 and 6,185,040 for lens mounts using glass spacers. 
       SUMMARY OF THE DISCLOSURE 
       [0004]    One aspect of the present disclosure is directed to an optical assembly comprising a housing having an interior region, a first lens disposed within the interior region of the housing, a second lens disposed within the interior region of the housing, the second lens being spaced from the first lens, a spacer disposed within the interior region of the housing between the first lens and the second lens, the spacer being fabricated from glass material, and a retention assembly configured to engage the second lens when assembled to retain the first lens, the spacer and the second lens in place. 
         [0005]    Embodiments of the optical assembly further may include a flat portion provided on the first lens and the second lens to engage the spacer. The retention assembly may include an O-ring positioned to engage the second lens. The retention assembly further may include a retaining ring positioned to engage the O-ring. The housing may include a port providing fluid communication from an exterior of the housing to the interior region of the housing. The optical assembly further may include a filler material disposed in a space defined by an exterior surface of the spacer and an interior surface of the housing. The filler material may be disposed in the space through the port. The filler material may include an epoxy material. An interior surface of the housing may have a seat formed therein, and wherein the first lens is disposed within the interior region of the housing against the seat. 
         [0006]    Another aspect of the present disclosure is directed to an optical assembly comprising a housing having an interior region, the housing including a port providing fluid communication from an exterior of the housing to the interior region of the housing, a first lens disposed within the interior region of the housing, a second lens disposed within the interior region of the housing, the second lens being spaced from the first lens, a spacer disposed within the interior region of the housing between the first lens and the second lens, the spacer being fabricated from glass material, and a filler material disposed in a space defined by an exterior surface of the spacer and an interior surface of the housing. 
         [0007]    Embodiments of the optical assembly further may include disposing the filler material in the space through the port. The filler material may include an epoxy material. The optical assembly further may include a second spacer fabricated from a material other than glass material. In one embodiment, the second spacer may be fabricated from aluminum or an aluminum alloy. 
         [0008]    Yet another aspect of the disclosure is directed to a method of assembling an optical assembly. In one embodiment, the method comprises: positioning a first lens within a housing having an interior region; positioning a spacer fabricated from glass material within the interior region of the housing so that the spacer engages the first lens; positioning a second lens within the interior region of the housing so that the second lens engages the spacer; and securing the first lens, the spacer and the second lens with a retention assembly configured to engage the second lens when assembled lens when assembled to retain the first lens, the spacer and the second lens in place. 
         [0009]    Embodiments of the method further may include depositing a filler material in a space defined by an exterior surface of the spacer and an interior surface of the housing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    Various aspects of at least one embodiment are discussed below with reference to the accompanying figures, which are not intended to be drawn to scale. The figures are included to provide illustration and a further understanding of the various aspects and embodiments, and are incorporated in and constitute a part of this specification, but are not intended as a definition of the limits of the invention. Where technical features in the figures, detailed description or any claim are followed by references signs, the reference signs have been included for the sole purpose of increasing the intelligibility of the figures and description. In the figures, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every figure. In the figures: 
           [0011]      FIG. 1  is a cross sectional view of a mounting system incorporating a glass spacer according to an embodiment of the present disclosure; 
           [0012]      FIG. 2  is a cross sectional view of a lens assembly including a mounting system of another embodiment of the present disclosure; and 
           [0013]      FIG. 3  is a cross sectional view of a lens assembly including a mounting system of yet another embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0014]    Aspects and embodiments are directed to selectively choosing a lower CTE material for spacers between certain lenses, by which the optical design can be simplified. The present disclosure is directed to using low CTE glass piping (a low cost material) with standard plano glass processing to create inexpensive low CTE lens spacers for thermal optical systems. These spacers and this arrangement can result in substantial cost savings for optomechanics while delivering better repeatability and stability than aluminum and plastic spacers that are commonly used. 
         [0015]    It is to be appreciated that embodiments of the methods and apparatuses discussed herein are not limited in application to the details of construction and the arrangement of components set forth in the following description or illustrated in the accompanying drawings. The methods and apparatuses are capable of implementation in other embodiments and of being practiced or of being carried out in various ways. Examples of specific implementations are provided herein for illustrative purposes only and are not intended to be limiting. In particular, acts, elements and features discussed in connection with any one or more embodiments are not intended to be excluded from a similar role in any other embodiment. 
         [0016]    Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. Any references to embodiments or elements or acts of the systems and methods herein referred to in the singular may also embrace embodiments including a plurality of these elements, and any references in plural to any embodiment or element or act herein may also embrace embodiments including only a single element. The use herein of “including,” “comprising,” “having,” “containing,” “involving,” and variations thereof is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. References to “or” may be construed as inclusive so that any terms described using “or” may indicate any of a single, more than one, and all of the described terms. Any references to front and back, left and right, top and bottom, upper and lower, and vertical and horizontal are intended for convenience of description, not to limit the present systems and methods or their components to any one positional or spatial orientation. 
         [0017]    Standard glass tubing is typically produced by an extruding process, which results in a product that is inexpensive, but without the tight mechanical tolerances normally associated with optical systems. The parallelism of the cut faces, the inner and outer diameters, bending and ellipticity of the glass tubing are all examples of non-ideal characteristics that glass tubing exhibits, making it difficult to incorporate glass tubing as a mechanical spacer. These loose tolerances can be accommodated by the mechanical system that is the lens body. The use of an oversized metal housing in which the glass spacer resides, with generous flats on the lenses or cells that contact the face of the glass tubing, provides part of the solution in utilizing glass tubing as a spacer element. The addition of epoxy ports in the metal housing around the glass spacer can be used to bond in the space between the outer diameter of the glass tubing and the inner diameter of the metal housing limits lateral shifts of the glass spacer. Finally, the use of a compressed O-ring to “spring” load the lenses against glass spacer completes the mechanical system that accommodates the loose tolerances associated with glass tubing. 
         [0018]    The parallelism issue of the glass tubing, and setting the correct length can be accomplished via standard plano optics polishing, where the tube is bonded to a fixture and ground or polished on both ends to achieve the requisite length and end parallelism. 
         [0019]    The use of glass tubing as a low CTE mechanical spacer, with the mechanical details listed above to solve the loose tolerances that the glass tubing exhibits. Embodiments include: 
         [0020]    1) a mechanical spacer (mechanical element setting the distance between two optical elements) made of glass tubing or other low CTE material tubing; and 
         [0021]    2) a mechanical system that accommodates loose tolerances in the mechanical spacer in dimensions other than the length and parallelism of the faces controlling the tilt of the optical elements
       a. oversized outer housing accommodating tubing outer diameter (OD), ellipticity, tilt and bending tolerances,   b. compliant method of securing a loose fitting spacer within the housing: epoxy ports in outer housing, a compressible O-ring disposed between tubing and housing, flexures positioned between housing and spacer, etc.,   c. oversized mechanical seats on optical/mechanical elements in contact with faces of the spacer accommodating tubing OD, ellipticity, tilt and bending tolerances, and   d. a mechanical method of compressing an optical system (along the local optical axis) against spacer to accommodate CTE difference in housing and the spacer: compressed O-ring lens/mount, spring/flexure mounted optics, bonded optics with appropriate mechanical details to provide compression loading of the system when adhesive cures.       
 
         [0026]      FIG. 1  depicts an example mounting system, generally indicated at  10 , incorporating the details needed to utilize a glass spacer of embodiments of the present disclosure disposed along an optical axis A. Glass has a CTE of approximately 4-9 ppm/° C., which is significantly less than aluminum. In one embodiment, a low CTE borosilicate glass (e.g., PYREX® brand glass) having a CTE of 3.3 ppm//° C. may be employed. As shown, the mounting system  10  includes a cylindrical housing  12  having an outer surface  14  and an inner surface  16 . The inner surface  14  of the housing  12  includes a lens seat  18 , which is configured to retain a lens assembly, generally indicated at  20 , when inserting the lens assembly into an interior of the housing. In one embodiment, the lens assembly  20  includes a first lens  22 , a second lens  24 , a cylindrical glass spacer  26  positioned between the first lens and the second lens, and a retention assembly, generally indicated at  28 . The first lens  22  includes a flat portion  30  that engages an annular edge  32  of the glass spacer  26 . Similarly, the second lens  24  includes a flat portion  34  that engages an opposite annular edge  36  of the glass spacer  26 . The first lens  22 , glass spacer  26  and the second lens  24  are held in place by the retention assembly  28 , which in one embodiment includes a retaining ring  38  and an O-ring  40  disposed between the second lens and the retaining ring. As shown in  FIG. 1 , there is a gap  42  between the housing  12  and the glass spacer  26 . In one embodiment, this gap  42  is filled by a suitable material, e.g., epoxy, by a port  44  formed in the housing  12 . The epoxy holds the glass spacer  26  in place when the epoxy hardens. 
         [0027]    In one embodiment, which is illustrated in  FIG. 1 , the glass spacer  26  is sits directly on the flat portions  30 ,  34  of the respective first and second lenses  22 ,  24 . In another embodiment, the glass spacer  26  can also be used with the lenses mounted in cells, with the glass spacer being seated on surfaces of the cells instead of directly on the flat portions  30 ,  34  of the respective first and second lenses  22 ,  24 . In one embodiment, the glass spacer  26  has an inner diameter of 90 millimeter (mm) and an outer diameter of 100 mm. It should be understood that the mounting assembly  10  may be configured to secure lenses of varying shapes and sizes and still fall within the scope of the instant disclosure. 
         [0028]    As discussed above, the mounting system  10  includes a compression mechanism in the form of the retention assembly  28  along the optical axis A, which holds the first and second lenses  22 ,  24  and the glass spacer  26  tightly against each other, as an aluminum housing would expand faster over temperature than the low CTE glass spacer. This compression mechanism embodies the compressed O-ring  40  of the retention assembly  28  in  FIG. 1 . The retaining ring  38  compresses the O-ring  40  against the second or front lens  24 , which pushes on the glass spacer  26 , which in turn pushes on the first or back lens  22 , which, finally, sits on the mounting surface or seat  18  machined in the housing  12 . There are numerous variants of the mounting mechanism, which are lens dependent. The key information is the use of a compliant compressive mounting mechanism holding the lens assembly  20  tightly together over temperature. Other mechanisms and approaches that can accomplish this are spring loading, flexure mounting, and epoxy bonding with appropriate details to cause compression loading of the lenses during bonding. 
         [0029]    Another aspect of the mounting system  10  is the oversized gap  42  between the inner surface  16  of the housing  12  and an outer surface  46  the glass spacer  26 . Due to the loose tolerances on commodity glass tubing a tight fit (tighter than 0.1 mm) is not possible without the potential of the parts not fitting together. The oversized gap  42  allows the glass spacer  26  in all its variations of outer diameter, ellipticity, etc. to fit within the housing  12 . The provision of the glass spacer  26  positioned within the oversized housing  12  causes the glass spacer to rattle around during use, causing particle generation, potentially wearing of the accurately finished faces of the glass spacer, and possible breakage of the glass spacer. Compliant lateral support of the glass spacer  26  within the housing  12  addresses this issue. This lateral support can be achieved by the epoxy port holes  44  on the outer surface  14  of the housing  12 , and injecting epoxy after alignment is complete. Other mechanisms could alternatively be employed, including flexures between the housing  12  and glass spacer  26 , or O-ring(s) between the housing and the glass spacer. It could he possible to have the flexures built into the housing itself, causing the housing itself to be compliant. 
         [0030]    The elements sitting on the annular surfaces  32 ,  36  of the glass spacer  26 , which, in the embodiment shown in  FIG. 1  is the lenses themselves, may embody other spacers or cells holding the lenses. The elements contacting the glass spacer  26  require oversized mounting surfaces, shown as lens flats  30 ,  34  in  FIG. 1 , compared to typical optical systems. The larger mounting surfaces are required to accommodate the range of outer diameter, wall thickness and other tolerances of the glass spacer. 
         [0031]    Finally, the mounting surfaces of the glass spacer  26  need to be set to the correct separation and parallelism. This is part of the glass spacer  26  most probably needs to be done by a standard glass plano process, as the standard glass tubing tolerances are not typically sufficient to meet optical performance. The glass spacer  26  would have both of its faces ground, and perhaps polished, to achieve the required thickness and parallelism for the optical system. 
         [0032]      FIG. 2  illustrates a lens assembly, generally indicated at  50 , of an embodiment of the present disclosure. As shown, the lens assembly  50  includes an elongate, cylindrical housing  52  having an outer surface  54  and an inner surface  56 . The housing  52  is configured to support a plurality of lenses, e.g., lenses  58 ,  60 ,  62 ,  63 ,  64 ,  66 ,  73  within an interior of the housing along optical axis B. In one embodiment, a cylindrical glass spacer  68  is positioned between the lens  60  and lens  62 , and a first retention assembly  70  configured to secure lens  60 , and a second retention assembly  72  configured to secure lens  62 . As with spacer  26 , spacer  68  may be fabricated from a low CTE borosilicate glass. 
         [0033]    An end cap  74  and an O-ring  76  are provided to close an open end of the housing  52  near lens  58 . As shown in  FIG. 2 , there is a gap  78  between the housing  52  and the glass spacer  68  In one embodiment, this gap  78  is filled by a suitable material, e.g., epoxy, by a port  80  formed in the housing  52 . As with mounting system  10 , the epoxy holds the glass spacer  68  in place when the epoxy hardens. The oversized gap  78  allows the glass spacer  68  in all its variations of outer diameter, ellipticity, etc. to fit within the housing  52 . Compliant lateral support of the glass spacer  68  within the housing  52  is achieved by the epoxy port holes  80  on the outer surface  54  of the housing  52 , and injecting epoxy after alignment is complete. 
         [0034]      FIG. 3  illustrates a lens assembly, generally indicated at  90 , of another embodiment of the present disclosure. As shown, the lens assembly  90  includes an elongate, cylindrical housing  92  having an outer surface  94  and an inner surface  96 . The housing  92  is configured to support a plurality of lenses, e.g., lenses  98 ,  100  within an interior of the housing along optical axis C. In one embodiment, a cylindrical glass spacer  102  and an aluminum spacer  104  are positioned between the lens  98  and lens  100 , and a retention assembly generally indicated at  70  configured to secure lenses and spacers in place. As shown, the glass spacer  102  and the aluminum spacer  104  are positioned next to one another and coaxial along optical axis C. As with lens assembly  20 , lens  98  includes a flat portion that engages an annular edge of the glass spacer  102 . Similarly, lens  100  includes a flat portion that engages an annular edge of the aluminum spacer  104 . 
         [0035]    The retention assembly includes a retaining ring  108  and an O-ring  110 . As with spacers  26  and  68 , glass spacer  102  may be fabricated from a low CTE borosilicate glass. The aluminum spacer may  104  may be fabricated from aluminum or an aluminum alloy. As shown, there is a Gap  112  between the housing  92  and the glass spacer  102 . In one embodiment, this gap  112  may be filled by a suitable material, e.g., epoxy, by a port formed in the housing  52 . 
         [0036]    By providing the glass spacer  102  and the aluminum spacer  104 , the overall thermal effect of the spacer can be manipulated to achieve a desired CTE. For example, the provision of a 5 mm aluminum spacer positioned adjacent a 5 mm glass (Pyrex) spacer in the manner illustrated in  FIG. 3  provides an equivalent of a 10 mm spacer that has a CTE of 13.95 ppm/° C. In another example, the provision of a 2 mm aluminum spacer with 8 mm glass (Pyrex) spacer provides an equivalent of a 10 mm spacer that has a CTE of 7.56 ppm/° C. As described, by selecting the sizes (lengths and thicknesses) of the glass and aluminum spacers  102 ,  104 , the athermalization of an existing system may be manipulated by adjusting a ratio of the lengths of the two spacers, thereby providing a method of compensating for unexpected thermal behavior within the assembly  90 . 
         [0037]    Having described above several aspects of at least one embodiment, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure and are intended to be within the scope of the invention. Accordingly, the foregoing description and drawings are by way of example only.