Patent Publication Number: US-7715105-B2

Title: Acylindrical optical device

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application is a continuation-in-part of U.S. patent application Ser. No. 10/659,727 filed Sep. 10, 2003 now U.S. Pat. No. 7,116,486 granted Oct. 3,2006 for Acylindrical Optical Devices and Method of Manufacture, which patent is assigned to the same assignee as this application. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention generally relates to optical devices and methods for the manufacture of such optical devices and more particularly to optical devices with lens systems of a small diameter or cross section. 
   2. Description of Related Art 
   Endoscopes are examples of optical devices that utilize optical systems characterized by an assembly of a plurality of optical elements, such as lenses, that are serially disposed along an optical axis. In an endoscope, for example, a lens system comprising multiple lens elements at a distal end constitutes an objective; a lens system at the proximal end constitutes an eyepiece; and one or more groups of intermediate lens elements define one or more relay lens systems. 
   Endoscopes utilizing such systems generally have working channels and lumens. Some working channels are filled with fiber to enable an external light source to illuminate a field of view. Others allow a surgeon to move instruments along the length of the endoscope to perform some function at the distal end while simultaneously viewing the area being treated. Still other working channels allow a surgeon to dispense a therapeutic, diagnostic or other material at the distal end of the endoscope, again while simultaneously viewing the area being treated. 
   Endoscopes and other optical devices of this nature generally are formed with cylindrical lens elements extending along a centered optical axis. The lens elements generally have concave, planar or convex image forming surfaces that are transverse to the optical axis. Multiple lens elements may be adjoined in lens systems in order to achieve particular optical characteristics, all as known in the prior art. Such lens elements and lens systems are called centered, rotationally symmetrical lens elements and systems, respectively. 
   Medical personnel who use these optical devices now indicate a preference for optical devices that have smaller and smaller diameters or cross sections. In fact some optical devices are now produced with an outer diameter of 1 to 2 mm using traditional lens making methods. However products that achieve these goals are difficult and expensive to manufacture with traditional lens making methods. 
   Traditional lens making methods include grinding and polishing operations to produce approximately spherical or other shaped image forming surfaces at the entrance and exit faces that define the optical characteristics of that lens element. Then the lens element is rotated about its geometric axis that will generally lie on the optical axis. A geometric axis is defined as a straight line locus of the centers of curvature of the refracting surfaces. The outer lens boundary then can be made essentially circular, as by abrasive grinding, such that the result is essentially a right circular cylinder with imaging forming spherical end surfaces and a cylindrically centered axis, i.e., a centered, rotationally symmetrical lens element. Individual lens elements can then be adjoined along the coincident optical and geometric axes to form a lens system. 
   The ability to make smaller optical devices including those with lens systems that continue to exhibit centered rotationally symmetrical characteristics, becomes more difficult as the lens diameter reduces. First, the final diameter of the lens is controlled by the location of the grinding or edging tool with respect to the optical axis including any positional variation due to tolerances in the manufacturing equipment. In conventional lenses these tolerances do not constitute a significant portion of the overall lens diameter. However, to achieve an absolute tolerance as a constant percentage of very small diameters requires extreme accuracy and tools that operate with extremely close tolerances. Machines for providing such accuracies become increasingly expensive as tolerance requirements become more stringent. 
   Second, in these optical devices, a lens element generally has an axial length that is several times the diameter. At small diameters it becomes difficult to support the lens element so that its optical axis remains in a single position relative to a tool reference. Moreover, as the diameter decreases the lens element becomes, in effect, more brittle and thus extremely fragile. These factors lead to an increased potential for breakage during manufacture. 
   Thus about 1-2 mm tends to be a practical minimum diameter for any lens element manufactured by traditional lens manufacturing methods. Lens systems in most currently commercially available endoscopes have an outer diameter of approximately 1.7 mm or greater. Endoscopes with such readily available lens elements are too big to be used in many applications including (1) medical applications such as viewing fine vascular structure, (2) minimally invasive endoscopy such as neurological and neurosurgical applications and arthoscopy, ear, nose and throat (ENT) applications, (3) cardiac surgical applications, and (4) endoscope applications that can benefit from the use of stereoscopic endoscopes. 
   What is needed is a method for enabling the efficient manufacture of high quality lens elements and lens systems having cross sectional dimensions that can be as little as 1 mm or less. 
   SUMMARY 
   Therefore it is an object of this invention to provide a method of manufacturing lens systems having cross sectional dimensions that are less than 1 or 2 mm. 
   Another object of this invention is to provide a lens element with high centering accuracy and with cross sectional dimensions of less than approximately 1 mm. 
   Still another object of this invention is to provide a method for efficiently manufacturing a high quality lens or lens system from a conventional lens or lens system useful in optical devices with a reduced outer diameter to less than 1mm. 
   In accordance with one aspect of this invention, an optical device extends along an axis and comprises at least one lens element having polished image forming surfaces at each end thereof. At least three sawn planar surface faces extend between the image forming surfaces. Each sawn planar surface lies on a plane intersecting two planes coincident with the planes of adjacent sawn planar surfaces. As a result, the lens element has a polygonal cross-section. 
   In accordance with another aspect of this invention, an optical device includes a plurality of optical elements and a means for supporting the plurality of optical elements to form a lens system. At least one optical element comprises a lens element having a pair of spaced, polished image forming surfaces. At least three sawn planar surface faces extend between the image forming surfaces. Each sawn planar surface lies on a plane intersecting two planes coincident with the planes of adjacent sawn planar surfaces. Consequently, the lens element has a polygonal cross-section. 
   In accordance with another aspect of this invention, a plurality of final lens elements, each having polygonal cross-sections are formed from a plurality of initial lens elements in a supported array. The final lens elements are formed by sawing across the array thereby to remove portions of each of the initial lens elements and to form a plurality of sawn planar faces for each initial lens element. This produces an array of sawn lens elements, each having a polygonal cross-section. Final lens elements are produced by separating the sawn lens elements from the supported array. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The appended claims particularly point out and distinctly claim the subject matter of this invention. The various objects, advantages and novel features of this invention will be more fully apparent from a reading of the following detailed description in conjunction with the accompanying drawings in which like reference numerals refer to like parts, and in which: 
       FIG. 1  is a perspective view of an optical device constructed in accordance with this invention; 
       FIG. 2  is a cross-section of the optical device taken along lines  2 - 2  in  FIG. 1 ; 
       FIG. 3  is another perspective view to illustrate the construction of the optical device in  FIGS. 1 and 2 ; 
       FIG. 4  is a chart that depicts major steps in the manufacturing process for obtaining the optical device shown in  FIG. 1 ; 
       FIGS. 5A through 5I  are illustrative of certain steps in the manufacturing process shown in  FIG. 4 ; and 
       FIGS. 6A through 6I  are illustrative of the appearance of an optical device at various stages during the manufacturing process of  FIG. 4 ; 
       FIGS. 7A through 7C  are useful in understanding variations of the method and construction depicted in  FIGS. 1 through 6I ; 
       FIG. 8  is a chart that depicts major steps in an alternative manufacturing process for obtaining optical devices; 
       FIGS. 9A and 9B  are plan views of a lens element useful in the process of  FIG. 8 ; 
       FIG. 10  depicts an array of lens elements that is useful in the process of  FIG. 8 ; 
       FIGS. 11 through 14  depict the effects of sawing operations that occur in accordance with the process of  FIG. 8 ; 
       FIGS. 15A and 15B  are plan views of one embodiment of a final lens element produced by the process of  FIG. 8 ; 
       FIGS. 16A and 16B  are plan views of an alternative embodiment of a final lens element constructed in accordance with this invention; and 
       FIG. 17  is a cross-section of an optical device incorporating final lens elements as shown in  FIGS. 15A ,  15 B,  16 A and  16 B. 
   

   DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     FIGS. 1 through 3  depict a portion of an optical device  20 , such as an endoscope, constructed in accordance with this invention that lies along an axis  21 . In this embodiment, the optical device  20  includes a lens system  22  with adjoined lens elements  23 ,  24  and  25 . In this particular embodiment, each of the lens elements  23 ,  24  and  25  and the lens system  22  have centered rotational symmetry with respect to the axis  21  so the optical and geometric axes of the optical device are coincident. Although not shown, but as will be known to persons of ordinary skill in the art, the end surfaces of each lens element constitute image forming surfaces that are polished, generally spherical surfaces that produce an image of any object proximate the axis  21 . As manufacture and use of lens elements with such surfaces are known,  FIGS. 1 through 3  do not depict a specific spherical surface. A flat traverse surface is shown as a representation of an entire class of image forming surfaces. 
   A sheath  26  circumscribes the lens system  22  and defines an outer diameter d o . Referring specifically to  FIG. 2  and in accordance with this invention, the lens element  23 , like the lens elements  24  and  25 , has a polygonal shape in cross-section, in this particular embodiment a regular polygon cross-section and specifically a square cross-section. That is, in cross section the lens element  23 , and all the other lens elements in the lens system  22 , form a square bounded by four flat surfaces  30 ,  31 ,  32  and  33  that intersect at right angles and are equidistant from the axis  21 . Moreover, in  FIGS. 1 through 3  the axis  21  is representative of the optical axis and the geometric axis because these axes are coincident. 
   As the sheath  26  is circular and circumscribes the square lens element  23 , each face forms a chord that, with the sheath  26  defines an axially extending working channel with a cross section in the form of a segment. Such working channels are called “segmental working channels” in the following description. In  FIGS. 1 through 3  segmental working channel faces  30  through  33  define one boundary of each of segmental working channels  34 ,  35 ,  36  and  37 , respectively. At least one of these segmental working channels, such as the segmental working channel  36 , could be used to contain optical fibers  38  for transferring light from the proximal end of the optical device beyond the distal end to illuminate a field of view. The other segmental working channels could accommodate instruments or therapeutic or diagnostic material or both or other agents such as water and saline solution. 
   As will be apparent, one characteristic of this invention is that placing a lens system with a polygonal cross section in a circumscribing cylindrical sheath automatically produces the segmental working channels. It will also be apparent that the transverse cross sectional area of a segmental working channel increases as the number of faces decreases. 
   Optical devices such as shown in  FIGS. 1 through 3  can have a wide range of diameters. Lens assemblies in accordance with this invention have been constructed with outer sheath diameters, d o , of 1.2 mm. Optical devices with even smaller diameters are anticipated. 
   The method for making these lenses is described in  FIGS. 4 ,  5 A through  5 I and  6 A through  6 I. This particular method is described with respect to manufacturing a final lens system or systems in which the geometric and optical axes are coincident and in which a cross section normal to the axes is a square. Step  60  in  FIG. 4  represents the selection of one or more initial cylindrical lens elements characterized by having a centered rotational symmetry with coincident optical and geometric axes. If it is an objective to produce a three-piece initial lens assembly, process  60  represents the selection of optical elements  61 ,  62  and  63  as shown in  FIG. 5A  with the cross section shown in  FIG. 6A . The diameter should be at least as large as the diameter of a circle that will circumscribe the final lens system. These lens elements will have different end faces forming convex, concave, planar or other image forming surfaces in order to achieve the desired optical characteristics as previously described. 
   Referring to  FIG. 4 , if, as in this example, a decision is made at step  64  of  FIG. 4  as to whether a final lens system will contain multiple lens elements like the lens system shown in  FIG. 5B  with the geometric axis of the final lens system (hereinafter the “final geometric axis”) coincident with the optical axis  67 . Step  65  in  FIG. 4  sets up the formation of one or more initial lens assemblies.  FIG. 5B  shows a single initial lens assembly  66  formed by joining, typically by cementing, the initial lens elements  61  through  63  along an optical axis  67 . A cross-section  FIG. 6B  depicts the initial lens system  66  with its circular cross section and one initial lens element  62  that is centered on the optical axis  67 . 
   Once the initial lens assembly is formed, step  70  of  FIG. 4  represents the procedure of providing a support for each initial lens assembly, such as the initial lens assembly  66 . In accordance with one aspect of this invention, a tool  71  in  FIG. 5C  is formed with a plurality of parallel support slots  72 . The slot width is selected to provide a stable support for an initial lens system.  FIG. 5C  shows the single initial lens system  66  for clarity. It also will become apparent that multiple initial lens systems may be positioned in each support slot. It will be apparent that these multiple initial lens systems can be spaced along a single slot and have different initial lens elements. Generally it is merely necessary to assure that all the lens systems in a single support slot should be selected so they will have the same finished cross section. 
   In one particular embodiment, the tool  71  is formed of a float glass plate and the support slots  72  are formed by a dicing saw. Dicing saws are regularly used in the semiconductor industry and are constructed to have cutting tolerances consistent with an indexing accuracy cumulative error of 0.001 mm per 160 mm traversal or less. 
   As shown in  FIGS. 5C and 6C , a thermoplastic cement  73  fills the support slots, like the support slot  72  to capture each initial lens assembly, such as the initial lens system  66 , in the tool  71 . The initial lens system  66 , particularly the initial lens element  62 , now lies in the support slot  72  filled with the thermoplastic cement  73  and is rigidly fixed. This process positions the initial lens systems accurately for subsequent processing. 
   Step  74  in  FIG. 4  represents a process by which a portion of the initial lens system  66  is removed to form a sawn planar face  75  of  FIG. 6D  that is equally spaced from the desired final geometric axis that in this specific example is coincident with the optical axis  67 . In accordance with one aspect of this invention, the distance to the final geometric axis measured perpendicular to a face, such as the sawn face  75  of  FIG. 6D  is (d i /2)sin 45° where d i  represents the desired finished size of the lens system measured diagonally between opposite corners. As will be apparent, this distance is one-half of the width of a face. 
   As shown in  FIGS. 5D and 6D , a dicing saw  76 , positioned to form a vertical cut relative to the tool  71 , removes material from the lens assembly to define the sawn face  75  at some predetermined distance from the axis  67 . Commercially available dicing saws make such a cut so that the face  75  is at a fixed distance from the optical axis  67  with an accuracy of 0.001 mm per 160 mm of traversal or less. 
   If a decision were made to produce a lens with a single sawn face, step  77  would terminate further processing steps. Consequently the final lens system would have a single sawn surface as shown in  FIG. 6D . 
   However, in most applications of this invention it is desired to have a final lens system with multiple sawn surfaces so assuming a decision has been made to form such additional faces, step  77  of  FIG. 4  transfers control to step  80  that represents a procedure for properly supporting the lens systems for forming another sawn face. To produce a final lens system with a square cross section in a plane normal to the final geometric axis  67 , step  80  requires that the tool  71  be rotated 180° and realigned. As shown in  FIGS. 5E and 6E  the dicing saw  76  is positioned. It saws a face  81  that is parallel to the face  75  and equidistant from the geometric axis. 
   If additional surfaces are to be formed, step  80  in  FIG. 4  needs to rotate the lens systems by 90°, such as by removing them from the tool  71  and placing them in another tool  82  having wider support slots  83  as shown in  FIGS. 5F and 6F . A thermosetting material  84  then fills the support slots  83  to capture the lens system  66 . Now the faces  75  and  81  are horizontal and in  FIGS. 5F and 6F  the face  75  is above the face  81 . The lens system  66  obviously could be reversed such that the face  75  was in contact with the tool  82 . 
   Steps  77  and  80  in  FIG. 4  represent the procedures by which the lens systems are sawn in succession. In a cut as shown in  FIGS. 5G and 6G , the dicing saw produces a third sawn face  88  that is perpendicular to the sawn faces  75  and  81  and that is equidistant from the geometric axis  67 . Then the tool  82  can be rotated 180° and aligned as shown in  FIGS. 5H and 6H , so the dicing saw produces a fourth sawn face  90  parallel to the third sawn face  88 , perpendicular to the sawn faces  75  and  81  and equidistant from the geometric axis  67 . 
   When this processing has been completed, step  91  in  FIG. 4  represents the step of removing each final lens system from the tool  82 . Step  92  represents the procedure of supporting the final lens systems in a sheath  93  as shown in  FIGS. 5I and 6I  to complete the optical device. 
   As will now be apparent, the procedures and controls of  FIG. 4  merely provide a work path organization to depict the various major processes to produce lens elements and systems in accordance with this invention. It will also be apparent that this method of manufacture by successive sawing of an initial lens system produces a final lens system that has a very small diameter or cross section without the need for expensive grinding or other operations. This procedure allows a manufacturer to use large conventional, economical lens elements as a foundation for the very small lens assembles. With each sawing operation the lens assembly becomes smaller. However, sawing allows the lens assembly to be fully supported during all the operations. This compensates for any breakage due to an increasing brittle nature of the lens assembly as manufacture proceeds. Generally the controls of steps  60 ,  65 ,  70 ,  74 ,  80 ,  91  and  92  and decisions  64  and  77  all operate to produce a lens system having a plurality of axially extending flat sawn faces that lie in intersecting planes. 
   This process has been used successfully to manufacture centered, point symmetric lenses circumscribed by a sheath having an inner diameter of 0.6 mm and an outer diameter of 0.85 mm. Optical devices with such reduced diameter or even smaller diameters will be useful in a large number of applications heretofore unavailable for endoscopic diagnosis and therapy. 
   This invention has been described in terms of one specific embodiment in which each of the lens elements selected for the lens assemblies are characterized by centered, rotational symmetry about coincident optical and geometric axes and in which the final lens system exhibits point symmetry about coincident geometric and optical axes.  FIG. 7A  schematically depicts such a configuration in which optical axis  67  is coincident with the geometric axis of the initial lens assembly  66  and the final lens assembly  22 .  FIG. 7B  depicts a variation in which the optical and geometric axis  67  of the lens assembly  66  are parallel but spaced. Processing according to  FIG. 4  is modified so that the support of the lens systems positions them to produce sawn planar faces at predetermined positions from a geometric axis  95 A that is offset from the optical axis  67 . In this specific embodiment, the boundary of the resulting final lens system  22 B includes the optical axis  67 . Such an approach would be useful for producing lens systems characterized by having an eccentric pupil. 
   Similarly  FIG. 7C  depicts a final lens system  22 C with a geometric axis  95 B offset from the optical axis  67 . In this embodiment the optical axis  67  lies outside the boundaries of the final lens system  22 C. Such an approach would be useful for producing lens systems with unobstructive apertures (“eccentric pupil” systems) such as a confocal reflective microscope, a Schwarzchild arrangement microscopic or telescopic system. 
   Each of the foregoing embodiments is characterized by a geometric axis that is coincident with or parallel to the optical axis of an initial lens assembly. To achieve still other optical properties, the sawing operation might also be controlled to produce sawn faces parallel to a geometric axis that is oblique to the optical axis. 
   It is also possible to form lens elements having polished image forming surfaces at each end thereof and at least three sawn planar faces extending between the image forming surfaces in which the lens elements are formed in a more efficient manufacturing operation.  FIG. 8  schematically depicts a process  100 , including steps  101  through  107 , for forming such multiple final lens elements. 
   Step  101  represents the step of forming a supported array of initial lens elements. There are several processes for forming such a supported array. In one approach conventional grinding and polishing operations form a lens element, such as a plano-concave lens  110  shown in  FIGS. 9A and 9B  having a planar imaging forming surface  111  and a convex imaging forming surface  112 . In this specific example and as shown in  FIG. 10 , a support  113  and an aperture plate  114  are bonded together with an appropriate adhesive  115  as known in the art. The aperture plate has a plurality of equally spaced apertures  116  for defining a position for each lens element  110  in the array. That is, each lens element  110  will be located so its geometric axis is aligned with an aperture  116 . A transparent optical adhesive  117  coextensive with the planar image forming surface  111  of each of the initial lens elements  110  bonds each lens element  110  to the aperture plate  114  in the supported array. 
   Other procedures could be used to complete the function of step  101 . For example, the individual lens elements  110  in  FIGS. 9A ,  9 B and  10  could be replaced with an integral lens array. Such an array could be bonded to an aperture plate with properly positioned apertures, like the aperture plate  114  in  FIG. 10 . Alternatively, the array could be bonded directly to a support, like the support  113  in FIG.  10  or be formed to a self-supporting array. By whatever process, step  101  produces an array of initial lens elements having polished image forming surfaces at two ends thereof. 
   Referring again to  FIG. 8 , step  102  establishes the spacing and a total number “N” of sawn faces for the final lens element. “Y” indicates the total number of saw cuts that will occur during a single set. For example, if the final lens element is to have an even number of sawn faces that produce a regular polygonal cross section, Y=2. Specifically, if the lens elements shown in  FIG. 10  are to be formed into final lens elements having regular octagonal cross sections, N=8 and Y=2. If the final lens element is to have a triangular cross section, N=3 and Y=1. If the final lens element is to have a non-regular hexagonal cross section, N=6 and Y=1. 
   Referring now to step  103  in  FIG. 8  and assuming (1) each final lens element is to be taken from one of the initial lens elements  110  and (2) each final lens element is to have the cross section of a regular octagon, the method of  FIG. 8  and related apparatus produces four sets of parallel saw cuts through the initial lens elements  110  in sequence with a depth set to penetrate some or all of the aperture plate  114 . As known in the dicing saw art, the depth of a saw cut will be determined, usually empirically, in view of the required cut depth and the cutting blade stability characteristics. 
   More specifically,  FIG. 11  depicts a first set of saw cuts  121  through  126  for four initial lens elements  110 A through  110 D arranged in an array. Steps  103  through  106  in  FIG. 8  define a loop by which all the initial lens elements are sawn. During a first iteration of the loop, step  103  in  FIG. 8  separates each of the lens elements  110 A through  110 D in  FIG. 11  into an oblong center structure  130  having final sawn faces  131  and  132 . In this embodiment the final sawn faces  131  and  132  are parallel and equidistant from the center of the intermediate lens structure  130 . Portions across the saw cuts, such as saw cuts  121  and  122 , constitute residual sections  133 . 
   Referring again to  FIG. 8 , after the process of step  103  is complete, a determination is made if additional saw cuts are required according to N=N−Y. As previously described, for a lens element to have a regular octagonal cross section, initially N=8 and Y=2. So step  104  calculates a new value for N, i.e., N=N−Y=6. Therefore step  105  transfers control to step  106  to allow a change in the relative angular relationship between the array and the sawing axes. In the particular embodiment this change occurs by rotating the array by 90°. 
   Step  103  then produces another set of parallel saw cuts. More specifically as shown in  FIG. 12 , the 90° shift produces saw cuts  134  through  137 ,  140  and  141  across the array as it existed after the saw cuts shown in  FIG. 11 . After the saw cuts of  FIG. 12  have been completed, the center portion or modified intermediate lens element  130  has a square cross section. The prior residual portions  133  are cut and the ends of the portion  130  in  FIG. 11  external to the saw cuts of  FIG. 12  are shown as new residual portions  142 . 
   Referring again to  FIG. 8 , step  104  calculates N=N−Y, so N=4 and step  105  again maintains the loop. Step  106  changes the relative angular relationship of the array.  FIG. 13  particularly depicts the process of rotating the array by 45° after which a series of four saw cuts  143  through  146  are made in accordance with the process of step  103  in  FIG. 8 . Now the central portion  130  has six sides and the sections  133  and  142  have been further divided into smaller residual portions. 
   When the operation in  FIG. 13  is complete, step  104  calculates N=N−Y so N=2 and step  105  again transfers control to step  106 . Now the relative angular relationship is changed by rotating the array through 90° so that step  103  produces saw cuts  150  through  153  shown in  FIG. 14 . During this iteration steps  104  and  105  produce a value N=0, so the sawing operations are completed and have produced a cross section for the lens element  130  that is a regular octagon. Portions of the glass outside the sawn cuts form residual portions. 
   Step  107  separates the final lens elements  130  from the supported array. That is, in this embodiment step  107  separates the final lens elements  130  from the support  113  and/or aperture plate  114  of  FIG. 10 . The particular separation process will depend on the specific structure of the array, the supporting structure and the final lens element design. Assume, for example, that the final design requires only the lens elements  130  without any additional elements. If the lens elements are mounted as shown in  FIG. 10 , the adhesives are selected so that a solvent dissolves the adhesives  115 . If the lens elements were originally bonded to a support, like the support  113 , the solvent dissolves the bonding adhesive. With any of these approaches, the process produces a plurality of lens elements, each of which has the structure of the lens element  160  shown in  FIGS. 15A and 15B . 
   As shown in  FIGS. 15A and 15B , the lens element  160  is a regular polygon, namely a regular octagon. More specifically, the lens element  160  has a plurality of sawn planar surfaces.  FIG. 15A  depicts a line  161  that lies on the plane of the sawn surface  162 ; a line  163 , on the plane of the sawn surface  164 ; and a line  165 , on the plane of the sawn surface  166 . Portions of each of the lines  161 ,  163  and  165  that are coextensive with their respective sawn surfaces intersect only the line portions associated with the adjacent sawn surfaces. For example, the portion of the line  161  only intersects the portions of the lines  163  and  165 . Thus, as shown in  FIG. 15A , the lens element  160  satisfies the mathematical definition of a polygon. In addition, each face has a width dimension “w” in the cross section of  FIG. 15A  along each sawn face. For a regular polygon, all sawn faces will have the same width dimension. 
   During manufacture a lens element, such as the lens element  160 , may be chamfered, be produced with other irregularities at one or more of the vertices or be characterized by other structural, optically insignificant variations due to the vagaries of the manufacturing process or the desired final design of the lens. To the extent such a lens does not meet the mathematical definition of a polygon, it remains “polygonal.” In this disclosure “polygonal” is intended to cover all such lens element cross sections. Similarly, “octagonal” is used to describe the cross section of any lens element that is an octagon or has the general shape of an octagon. 
   If the final design requires each lens element  130  and corresponding portions of the aperture plate  114 , the adhesives are selected so that a solvent dissolves the adhesive  115 , but not the optical adhesive  117 .  FIGS. 16A and 16B  depict a resulting lens element  170 . Specifically, the lens element  170  includes an octagonal plano-convex lens  171 , like the lens  160  in  FIGS. 15A and 15B , that is attached to a portion  172  of an aperture plate, such as the aperture plate  114  in  FIG. 10 , by an intermediate portion  173  of the optical adhesive  117  shown in  FIG. 10 . The aperture plate portion  172  incorporates an aperture  174  that aligns with the optical axis of the lens element  171 . 
   Thus, it will be seen that a variety of separation and recovery processes can be used. In whatever way, step  107  provides the plurality of final lens elements having sawn surfaces and regular or irregular polygonal cross sections. 
   The process of  FIGS. 10 through 14  is particularly adapted for “short” or “stubby” lens elements. Longer lens elements may be subject to bending or other forces that deflect the lens element during manufacture. Such deflections could produce non-planar sawn faces or even cause the lens element to fracture. However, for such longer lens elements filling the individual saw cuts with a dissolvable adhesive or other material that is readily removed from the final lens element can overcome this problem. For example, after the saw cuts  121  through  126  are made in  FIG. 11 , those saw cuts are filled with such a material so that the entire structure remains rigid and the lens elements  130  are fully supported. Similarly, after the saw cuts  134  through  141  are made in  FIG. 12  those saw cuts are also filled. This is repeated after the saw cuts made in  FIG. 13 . As a result, any susceptibility to deflection or fracture can be resisted. An analogous process could be used with a self supported array for the manufacture of stubby lens elements. Therefore it will be apparent that the process of  FIG. 8  is adapted to incorporate variations that enable the process to produce lens elements having all the features of invention. 
     FIG. 17  depicts a well known optical configuration for transferring an image from an object, not shown, to optical fibers. This specific configuration utilizes an octagonal lens element  160  of  FIGS. 15A and 15B  arranged as a convex-plano lens and an octagonal lens element  170  of  FIGS. 16A and 16B  arranged as a plano-convex lens with the aperture plate portion  172  and aperture  174  and the intermediate optical adhesive  173 . A sheath  175  carries the lens elements with the planar image forming surface of the lens element  160  facing a plurality of optical fibers  176 . The lens element  170  is positioned in the sheath  175  distally of the lens element  160  and spaced therefrom according to the optical characteristics for the optical device, as known in the art. In an alternate configuration, the convex surfaces of the lens elements  160  and  170  make contact. In this configuration the aperture  174  in the aperture plate portion  172  and the lens elements  160  and  170  focus the image on the ends of the optical fibers  176 , as for example, in a flexible endoscope, for transfer to a viewing station. 
   This process, as depicted in  FIGS. 8 through 14 , enables the efficient manufacture of high quality lens elements and optical devices. Lens elements as shown in  FIGS. 15A through 16B  have been produced efficiently with a corner-to-corner dimension of about 0.75 mm and an overall length of about 0.60 mm. or less. 
   This invention has been described in terms of initial and final lens assemblies. Multiple lens assemblies can also be produced with each having different structures. Those different lens assemblies could form lens subassemblies such as objectives, eyepieces and relay lens assemblies for use in endoscopes with each optical device being held in a single sheath or individual sheath assemblies being positioned in an outer sheath. It will also become apparent that other sawing or equivalent techniques may be used or may come into existence that will provide even better tolerances than are currently available to enable the construction of even smaller lenses and numerous lens geometries and sizes. Still many other modifications can be made to the disclosed apparatus without departing from the invention. Therefore, it is the intent of the appended claims to cover all such variations and modifications as come within the true spirit and scope of this invention.