Abstract:
An imaging lens unit has an imaging lens and an integral holder for a light source such as a LED. The imaging lens unit can include a body portion, with the imaging lens being formed as an integral part of the body portion, together with a light source support fixture also formed as an integral part of the body portion. The support fixture supports a light source in a desired spatial relationship with respect to the imaging lens, and may have an opening for insertion of the light source into the support fixture along an installation axis. The fixture may be configured to prevent removal of the light source along substantially all other axes. The light source support fixture can be configured to support and retain the light source without additional cooperating structure. The invention further includes a computer mouse having an imaging lens unit with an integral light source support.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
   This application is a continuation-in-part of the U.S. patent application titled “Multiple Channel Light Guide for Optically Tracking Pointing and Input Devices,” filed on Mar. 7, 2003 and having Ser. No. 10/382,867 now U.S. Pat. No. 7,009,598, and is also a continuation-in-part of the U.S. patent application titled “Computer Input Device with Multi-Purpose Light Guide,” filed on Mar. 7, 2003 and having Ser. No. 10/382,931. 

   FIELD OF THE INVENTION 
   This invention relates generally to optical components usable in optically-tracking pointing and input devices such as computer mice. More particularly, this invention relates to an imaging lens having an integral holder for supporting and positioning a light source. 
   BACKGROUND OF THE INVENTION 
   Computer input and other pointing devices, such as electronic mice, convert physical movement into movement of a cursor or other image across a computer screen. Previously, many such devices utilized mechanically driven encoder wheels and other moving components to detect direction and magnitude of motion, and to then convert that information into data for communication to a computer or other device. Optical surface tracking offers an improved method of motion detection. Instead of encoder wheels rotated by a ball rolling across a surface, an array of photo-sensitive elements generates an image of a desktop (or other supporting surface) portion when light from an associated illumination source (such as a light emitting diode) reflects from the desktop or other surface. Subsequent images are compared, and based on the correlation between images, the magnitude and direction of mouse motion may be determined. Exemplary optical tracking systems, and associated signal processing techniques, include those disclosed in commonly owned U.S. Pat. Nos. 6,172,354, 6,303,924 and 6,373,047. 
     FIG. 1A  schematically shows various components of an existing optical tracking system in a computer mouse  1   a . Mouse  1   a  (shown in phantom lines) moves across a surface  2   a  such as a desk top or a table. A region  3   a  of the bottom surface of mouse  1   a  is either transparent or open so that light may reach a portion of the surface  2   a  (the “target area” T) and be reflected back to an image sensor  7   a . A light source  4   a  inside of mouse  1   a , which is typically a LED, is selectively turned on and off so as to controllably illuminate the target area T. Light from LED  4   a  reflects from the target area and is collected and focused by a lens  5   a  through an aperture  6   a . Light passing through aperture  6   a  strikes a photo-sensing surface of an image sensor  7   a . Image sensor  7   a  then forms (sometimes in connection with other components) an image of the target area T (or a portion thereof). Typically, image sensor  7   a  is attached to a Printed Circuit Board (PCB)  8   a , only a portion of which is represented in  FIG. 1A . In alternative configurations, a light guide directs light from a LED to the target area. One such configuration is shown in  FIG. 1B , in which components  1   b – 8   b  are generally similar to components  1   a – 8   a  of  FIG. 1A . In the configuration of  FIG. 1B , however, light from LED  4   b  is transmitted to the target area T via light guide  9   b . Typically, light guide  9   b  is formed from light-transmissive material such as glass or plastic. The light from LED  4   b  enters light guide  9   b  and reflects from the internal surfaces of the material, and then exits from an exit face e to illuminate the target area. 
   Although an improvement over mechanically-tracking types of motion sensing systems, optically-tracking systems present a new set of challenges. The light source, lens, image sensor and other components must be properly positioned with respect to one another. Permissible tolerances for this positioning are generally closer than tolerances associated with assembly of mechanical tracking components. Mismatches between mating components can cause imaging errors which degrade overall system performance. It is therefore often desirable to minimize the number of components which must be assembled. There are also advantages in minimizing the number of structural components beyond reduction of tolerance stack-ups. For example, fewer components can lead to reduction in assembly costs. 
   Various structures for holding a lens and at least partially supporting a LED (or other light source) have been developed. Commonly-owned U.S. Pat. No. 6,421,045 describes a lens carrier having a lens formed within a well of an annular bearing surface. The carrier also has a LED rest formed on the underside of the carrier. However, the structure described by the U.S. Pat. No. 6,421,045 patent cooperates with another structure (or structures) to retain and properly align the LED. 
   SUMMARY OF THE INVENTION 
   The present invention addresses many of the challenges described above. In particular, the present invention provides an imaging lens unit having an imaging lens and an integral holder for a light source such as a LED. In one embodiment, the imaging lens unit includes a body portion, with the imaging lens being formed as an integral part of the body portion. A light source support fixture is also formed as an integral part of the body portion. The support fixture is configured to support a light source in a desired spatial relationship with respect to the imaging lens. The support fixture also has an opening for insertion of the light source into the support fixture along an installation axis; the fixture is further configured to prevent removal of the light source along substantially all other axes. In another embodiment, a light source support is configured to receive the light source and to support and retain the light source (without additional cooperating structure) in a desired spatial relationship with respect to the imaging lens. The invention further includes a computer mouse having an imaging lens unit with an integral light source support. Other features and advantages of the invention are described herein and in the accompanying drawings, or will be apparent to persons skilled in the art once provided with the following description and accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1A  is schematic drawing of components in an existing optically-tracking computer mouse. 
       FIG. 1B  is a schematic drawing of one existing arrangement for illuminating a target area. 
       FIG. 2  is an “exploded” view of a computer mouse incorporating an optical structure according to one embodiment of the invention. 
       FIG. 3  is a cross section taken along lines  3 — 3  of  FIG. 2 . 
       FIG. 4  is an inverted “exploded” partial view of the computer mouse of  FIG. 2 . 
       FIG. 5  is a top view of an optical structure according to one embodiment of the invention. 
       FIG. 6  is a cross section taken along lines  6 — 6  of  FIG. 5 . 
       FIG. 7  is a cross section of an optical structure shown in  FIG. 6  when assembled with other components. 
       FIG. 8  is a schematic drawing showing operation of a multi-channel light guide according to one embodiment of the invention. 
       FIG. 9  is a cross section of an optical structure according to another embodiment of the invention. 
       FIG. 10  is a cross section taken along lines  10 — 10  of  FIG. 9 . 
       FIG. 11  is a drawing schematically showing light patterns from the optical structure of  FIGS. 9 and 10 . 
       FIG. 12  is a cross section of an optical structure according to another embodiment of the invention. 
       FIG. 13  is a cross section taken along lines  13 — 13  of  FIG. 12 . 
       FIG. 14  is a drawing schematically showing light patterns from the optical structure of  FIGS. 12 and 13 . 
       FIGS. 15A–15F  are cross sections of a portion of an optical structure according to additional embodiments of the invention. 
       FIG. 16  is a rear perspective view of a computer mouse according to another embodiment of the invention. 
       FIG. 17  is an “exploded” view of a computer mouse incorporating an optical structure according to another embodiment of the invention. 
       FIG. 18  is a cross section taken along lines  18 — 18  of  FIG. 17 . 
       FIG. 19  is an inverted “exploded” partial view of the computer mouse of  FIG. 17 . 
       FIG. 20  is a top view of an optical structure according to another embodiment of the invention. 
       FIG. 21  is a cross section taken along lines  21 — 21  of  FIG. 20 . 
       FIG. 22  is another cross section similar to that of  FIG. 21 , but with various angles labeled. 
       FIG. 23  is a cross section of an optical structure shown in  FIG. 21  when assembled with other components. 
       FIG. 24  is a cross section of an optical structure according to a further embodiment of the invention. 
       FIG. 25  is a cross section of an optical structure according to yet another embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The invention is described using an optically-tracking computer mouse as an example of a device into which the invention may be incorporated. However, the invention is not limited to computer mice. 
     FIG. 2  is an “exploded” view of portions of a computer mouse  10  incorporating an optical structure  100  according to one preferred embodiment of the invention. Housing base  12  is configured to rest upon and move over a desk top or other tracking surface, as well as to support and contain other components. Housing base  12  may be molded from ABS (acrylonitrile butadiene styrene) or other suitable material. Formed in the interior of housing base  12  is an access/support structure  14 .  FIG. 3  is a cross section of access/support structure  14  taken along line  3 — 3  in  FIG. 2 . Access/support structure  14  includes walls  16  extending upward from the interior bottom surface  18  of housing base  12 . Access/support structure  14  includes a first well  20 . Located in the bottom of first well  20  is a transmission hole  22 . Located at the other end of access/support structure  14  is a second well  24 . Located in the center of second well  24  is a receiving hole  26 . Separating wells  20  and  24  is a baffle  28 . Mouse  10  also has an upper housing  70 , which may have one or more buttons  72 ,  74 , an opening for a scroll wheel  76 , and other mechanisms for receiving user input. Mouse  10  would typically include numerous other components such as a battery (if mouse  10  is wireless), various connectors, cabling, etc. So as not to obscure  FIG. 2  with unnecessary detail, these additional components are not shown, but would be understood as present by persons skilled in the art. 
   Optical structure  100  fits over access/support structure  14 . Located on one end of optical structure  100  and extending upward is LED support  102 . Also located on optical structure  100  and extending upward may be a positioning post  104  and spacer/shield wall  106 . As shown in  FIG. 2 , positioning post  104  cooperates with a hole in printed circuit board (PCB)  200  to position and stabilize optical structure  100  with respect to PCB  200 . Spacer/shield wall  106  may also be formed so as to position and stabilize optical structure  100  with respect to PCB  200 . In alternate embodiments, either or both of positioning post  104  and spacer/shield wall  106  may be absent. LED support  102  extends through an opening  202  in PCB  200 . Image sensor  204  is positioned adjacent to opening  202  on the underside of PCB  200 . When assembled, LED  210  is positioned vertically downward inside of LED support  102  (see  FIG. 7 ). Leads  212  from LED  210  are soldered to PCB connection points  214 . Different types of LEDs may be used in connection with the invention. In one preferred embodiment, a T1-¾ size LED producing light at approximately 630 nm is used. Such a LED is available from Agilent Technologies of Palo Alto, Calif. having part number HLMP-EG24-RU000. LEDs producing light at other wavelengths and having other or different features may also be used. Light sources other than LEDs could also be used. 
   As can be seen in  FIGS. 2 ,  4  and  7 , LED  210  is completely contained within LED support  102 . LED support  102  maintains LED  210  in a desired position without reliance upon other structural components. 
   Image sensor  204  contains multiple light sensitive elements and can be used to create electrical signals representing an image. In one preferred embodiment, image sensor  204  is an integrated circuit containing both the light sensitive elements and the circuitry for converting the received light into electrical signals. On such device is described in commonly-owned U.S. patent application Ser. No. 10/305,062, titled “Photo-Sensor Array for Motion Detection” and filed Nov. 27, 2002, incorporated by reference herein. Other image sensor integrated circuits are known in the art and are commercially available. One such sensor is available from Agilent Technologies and has part number ADNS-2620. Other image sensing components are described in the aforementioned U.S. Pat. Nos. 6,172,354, 6,303,924 and 6,373,047 (including documents referenced therein). In other embodiments, image sensor  204  may only contain light sensitive components, with the associated conversion circuitry located elsewhere. 
     FIG. 4  is similar to  FIG. 2 , but inverted so as to expose the underside of PCB  200  and optical structure  100 .  FIG. 4  shows LED  210  in place, and omits housing base  12 . Aperture plate  216  covers image sensor  204  (not shown in  FIG. 4 ) and has an aperture  220  formed therein. Light enters aperture  220  and strikes photo-sensitive regions of image sensor  204 . In other embodiments, aperture plate  216  could be situated on the underside of PCB  200  and image sensor  204  on the upper side of PCB  200 , with an opening in PCB  200  between image sensor  204  and aperture plate  216 . Aperture plate  216  may be integrated with image sensor  204  prior to attachment to PCB  200 , may be formed as an integral component of the image sensor, or may be attached as a separate piece to PCB  200 . Exposed on the underside of optical structure  100  are two light guide channels  110  and  112 , which are further described below. Also shown on the underside of optical structure  100  is imaging lens  114  (also described below). 
     FIGS. 5 and 6  show optical structure  100  in more detail.  FIG. 5  is a top view of optical structure  100 . LED support  102  is formed as a hollow cylinder, and has a vertical opening  116  on one side. Upon assembly, LED  210  is positioned inside the cylinder of LED support  102  and pointing vertically downward. Three vertical locating ridges  118  are formed inside of LED support  102  and serve to align LED  210 . In some embodiments, locating ridges  118  are sized such that a press fit would exist between the outer surface of LED  210  and ridges  118 . In particular, use of certain more flexible materials for optical structure  100  (such as, e.g., polycarbonate) would facilitate a press fit. If optical structure  100  is instead formed from a more brittle material (such as, e.g., polystyrene), ridges  188  could be sized to provide a clearance fit. Even in the case of a clearance fit, however, LED  210  would still be supported on all sides. LED  210  could only be removed by withdrawal along an axis substantially coincident with the axis along which LED  210  is inserted into the interior cavity of support  102 . In particular, the opening  116  between the rightmost two ridges  118  in  FIG. 5  is not sufficiently wide to allow LED  210  to pass through. 
   Formed in the bottom of LED support  102  is a collection lens  120 . Collection lens  120  collects light emitted by LED  210  and directs that light to the tracking surface target area via channels  110  and  112 . Also formed in optical structure  100  is an imaging lens  114 . Imaging lens  114  collects and focuses light reflected from a target area and directs that light through aperture  220  in aperture plate  216 . LED support  102  maintains LED  210  in a fixed position relative to imaging lens  114 . 
     FIG. 6  is a cross section of optical structure  100  taken along lines  6 — 6  of  FIG. 5 . Collection lens  120  and channels  110  and  112  form a light guide for directing light from LED  210  (when placed in support  102 ) to a target area. This light guide receives light from LED  210 , divides that light between two channels  110  and  112  having stepped front faces (as described below), and rejoins that light by directing it to the target area. Channels  110  and  112  are located on the underside of LED support  102 . Front channel  110  has a front face  124  and a rear face  126 . Rear face  126  forms a Total Internal Reflecting (TIR) surface. A portion of the light emitted by LED  210  and entering collection lens  120  is diverted to channel  110 . This diverted light is then reflected by the TIR surface and exits channel  110  through front face  124 . Rear channel  112  has a front face  130 , a rear face  132 , and a rear vertical face  134 . Rear face  132  also forms a TIR surface. A portion of the light from LED  210  entering collection lens  120  is diverted to channel  112 . This portion of the light is reflected by the TIR surface of rear face  132  and exits channel  112  through front face  130 . Front faces  124  and  130  form a stepped arrangement relative to one another. In other words, front faces  124  and  130  lie in generally parallel planes, but are offset by an amount g by which the rear channel  112  extends further downward than front channel  110 . Channels  110  and  112  are separated by a space bounded by the rear face  126  of front channel  110  and the front face  130  of rear channel  112 . This separation between the channels is filled with a material (air in this case) that is dissimilar to that of the channels. In a preferred embodiment, channels  110  and  112  have the following dimensions (referring to  FIG. 6 ): 
   
     
       
             
             
           
         
             
               TABLE 1 
             
             
                 
             
           
           
             
               a 1  (angle of front channel front face to horizontal) 
               88.0° 
             
             
               a 2  (angle of front channel rear face to horizontal) 
               52.5° 
             
             
               b 1  (angle of rear channel front face to horizontal) 
               88.0° 
             
             
               b 2  (angle of rear channel rear face to horizontal) 
               47.5° 
             
             
               c (distance from top of front channel rear face to collection 
               0.872 in. 
             
             
               lens centerline) 
             
             
               d (height of top of front channel rear face) 
               4.880 in. 
             
             
               e (height of top of rear channel rear face) 
               2.930 in. 
             
             
               f (distance from top of rear channel rear face to collection 
               3.402 in. 
             
             
               lens centerline) 
             
             
                 
             
           
        
       
     
   
   As seen in  FIGS. 4 and 6 , a vertical wall  138  surrounds the underside of optical structure  100 . Channels  110  and  112  are inside the perimeter of wall  138 , as is imaging lens  114 . Upon assembly, optical structure  100  fits over access/support structure  14 , with walls  138  of optical support structure  100  surrounding walls  16  of access/support structure  14 . 
   Optical structure  100  is preferably molded as an integral component. Possible materials for optical structure  100  include clear polystyrene available from BASF Corporation of Mount Olive, N.J., grade 148G KG21; clear polystyrene available from Nova Chemicals Corporation of Moon Township, Pa., grade PS1300; LEXAN polycarbonate resin available from GE Plastics of Fairfield, Conn., grade 121R, color 1111; and MAKROLON polycarbonate resin available from Bayer Polymers of Pittsburgh, Pa., grade 2405, color 1000. Other possible materials include acrylic, cyclic olefin copolymer, SAN styrene blend and NAS styrene blend. 
   Imaging lens  114  includes upper and lower convex lenses  114   a  and  114   b . The refractive power and other optical properties of imaging lens  114  may vary based upon distance from image sensor  204 , distance of image sensor  204  above the tracking surface, the specific design of image sensor  204 , and other configuration choices. The determination of imaging lens optical requirements is within the routine ability of a person skilled in the art once provided with the descriptions herein and various design parameters. Similarly, the preferred refractive power and other optical properties of collection lens  120  may vary based on parameters such as size of LED  210 , size of channels  110  and  112 , distances from a target area, and other configuration choices. The determination of collection lens optical requirements is likewise within the routine ability of a person skilled in the art once provided with the descriptions herein and the relevant design parameters. In one preferred embodiment, collection lens  120  causes light emanating from channels  110  and  112  to be slightly out of focus. In this manner, light is more evenly spread onto the target area of the tracking surface. 
     FIG. 7  is a cross section of optical structure  100 , access/support structure  14 , PCB  200 , image sensor  204  and LED  210  in an assembled condition. Channels  110  and  112  rest within and to the rear of first well  20  of access/support structure  14 . Baffle  28  (which also prevents or minimizes stray light from reaching imaging lens  114 ), together with a beveled edge  30  on transmission hole  22 , defines boundaries for an angled path for light from channels  110  and  112  to target area  34 . Light exiting from front faces  124  and  130  of channels  110  and  112  shines upon and illuminates target area  34 . The arrows showing target area  34  only approximate the location and extent of the target area for purposes of illustration. A portion of this light is then reflected upward from target area  34  through entrance hole  26  to imaging lens  114 . Imaging lens  114  then collects and focuses this reflected light and directs it into aperture  220  of aperture plate  216 . The light then passes through aperture  220  and reaches the photo-sensitive elements of image sensor  204 . 
   As can also be appreciated from  FIG. 7 , optical structure  100  provides a unitary structure that positions LED  210  with respect to imaging lens  114  without reliance upon other structures. 
     FIG. 8  schematically shows operation of optical structure  100  and advantages provided over other systems for directing illumination to a target surface. In  FIG. 8 , the arrows generally show the directions in which most of the light is directed through channels  110  and  112 . Because of scattering and other effects, however, there will also be light transmitted in other directions. Light from front channel  110  exits the front face  124  at a first angle α. Light exits the front face  130  of rear channel  112  at an angle β, which is shallower than angle α. There is a gap g between the lowest portion of channel  110  and the lowest portion of channel  112 . Light from rear channel  112  and front channel  110  simultaneously illuminates the target area T. By illuminating from two different angles, light is more evenly distributed across the target area, and non-uniform illumination is reduced. Light can be divided between channels  110  and  112  in any proportion. Preferably, a majority of the light from LED  210  is directed into channel  110 , and a smaller portion of light is directed into channel  112 . In one preferred embodiment, channels  110  and  112  are formed such that approximately 80% of the target area illumination comes from front channel  110 , and approximately 20% of the target area illumination comes from rear channel  112 . In that embodiment, light is directed to the target area from the front channel at an angle of approximately 70° from the vertical (or approximately 20° from the horizontal). Light is directed to the target area from the rear channel at approximately 80° from the vertical (or approximately 10° from the horizontal). In other embodiments, approximately 50%–90% of light reaching the target area comes from front channel  110 , and approximately 10%–40% of light reaching the target area comes from rear channel  112 . In yet other embodiments, approximately 70%–90% of light reaching the target area comes from front channel  110 , and approximately 10%–30% of light reaching the target area comes from rear channel  112 . In still other embodiments, light is directed to the target area from the front channel at an angle of approximately 50°–85° from the vertical (or approximately 5°–40° from the horizontal), and light is directed to the target area from the rear channel at approximately 50°–85° from the vertical (or approximately 50–40° from the horizontal), although at a shallower angle than light from the front channel. 
     FIGS. 9–14  show additional embodiments of an optical structure  100 ′ and  100 ″. Optical structure  100 ′ ( FIG. 9 ) is substantially similar to optical structure  100  except for the configurations of front faces  124 ′ and  130 ′ of channels  110 ′ and  112 ′. As shown in  FIG. 10 , a cross section taken along lines  10 — 10  of  FIG. 9 , the front faces  124 ′ and  130 ′ are not planar. Instead, each channel front face is faceted. In this manner, light can be more evenly distributed across the target area.  FIG. 11  schematically shows light shined on a target area by front faces  124 ′ and  130 ′. Each facet will generally direct most of its light to a portion of the target area, with those portions substantially overlapping. Because of scattering and other effects, however, some light is also transmitted in other directions and in regions outside of the general illumination patterns shown. As shown in  FIG. 11 , faceted front faces  124 ′ and  130 ′ do not shine all light in the same areas, but their illumination patterns do substantially overlap. To simplify  FIG. 11 , only three boxes are shown for the patterns caused by various facets, and not six boxes (one for each facet). Although channels  110 ′ and  112 ′ each has three facets, the number of facets can be varied. Optical structure  100 ″ ( FIG. 12 ) is also similar to optical structure  100  except for the shape of the front faces  124 ″ and  130 ″ of channels  110 ″ and  112 ″. In this embodiment, and as shown in  FIG. 13 , the front faces  124 ″ and  130 ″ are formed as curvilinear concave refractive surfaces. As shown in  FIG. 14 , front faces  124 ″ and  130 ″ are configured to spread light across the target area out of focus, i.e. over a larger spot size, thereby distributing light more evenly. The non-planar front face(s) of the channels could take other forms. For example, the front face of one or more of the channels could have a cross-section in a form such as is shown in one of  FIGS. 15A through 15F .  FIGS. 15A–15F  are cross sections of a single channel taken in a location similar to that of line  10 — 10  in  FIG. 9 , with the proportions slightly exaggerated for clarity of illustration.  FIGS. 15A–15C  are examples of other forms of a faceted front face.  FIG. 15D  is an example of a curvilinear convex front face.  FIG. 15E  is an example of a combination faceted-concave front face.  FIG. 15F  is an example of a combination faceted-convex front face. In some embodiments, one front face may be planar and the other non-planar (whether faceted, convex, concave, combination convex-faceted or combination concave-faceted). In still other embodiments, one front face may be one type of non-planar face and another front face may be another type of non-planar face. 
     FIG. 16  is a rear perspective view of a mouse  300  according to another embodiment of the invention. Mouse  300  is similar to mouse  10  of  FIGS. 3–7 , and includes an upper housing  370 , a housing base  312 , a scroll wheel  376  and buttons  372  and  374  (not shown in  FIG. 16 , but seen in  FIG. 17 ). Mouse  300  further includes an externally-visible light window  304 . Light window  304  may be transparent or translucent, and may also be color tinted. Window  304  is arranged so that light from an internal light source (as described more fully below) is visible to a mouse user when the lower housing  312  of mouse  300  rests upon a supporting surface. Window  304  could be located elsewhere on mouse  300 ; an example of a possible alternate location includes, but is not limited to, window  304 ′. In use, mouse  300  is connected to a computer (not shown) and provides signals to the computer to control a cursor or other screen image. Mouse  300  may communicate with and receive power from the computer via a wired connection (not shown), or may be wireless and receive power from a battery within mouse  1  (also not shown). 
     FIG. 17  is an “exploded” view of portions of computer mouse  300 . Except as set forth in more detail below, the features of mouse  300  shown in  FIGS. 17–23  are similar to the features of mouse  10  shown in  FIGS. 2–7 . For convenience, each feature in  FIGS. 17–23  has the same reference number as the analogous feature in  FIGS. 2–7 , except that 300 has been added (e.g., scroll wheel  376  in  FIG. 17  is analogous to scroll wheel  76  in  FIG. 2 ). Except where stated otherwise, the previous description of features of mouse  10  applies to the features of mouse  300 . As seen in  FIG. 17 , and unlike mouse  10 , walls  316  of access/support structure  314  are open at the end (see also  FIG. 18 , a cross-section of access/support structure  314  taken along lines  18 — 18  in  FIG. 17 ). The opening between walls  316  faces window  304 . In one embodiment, window  304  is a transparent or translucent insert attached to housing base  312 , housing base  312  being otherwise opaque. Window  304  fits into a cutout  345  in upper housing  370  when mouse  300  is assembled. In other embodiments, window  304  could be located entirely within upper housing  370 . Upper housing  370  may have one or more buttons  372 ,  374 , an opening for a scroll wheel  376 , and/or other mechanisms for receiving user input. Mouse  300  would typically include numerous other components such as a battery (if mouse  300  is wireless), various connectors, cabling, etc. So as not to obscure the drawings with unnecessary detail, these additional components are not shown, but would be understood as present by persons skilled in the art. 
   As with optical structure  100  of mouse  100 , optical structure  400  of mouse  300  fits over access/support structure  314 . As shown in  FIG. 19 , however, optical structure  400  differs from optical structure  100 . As seen in  FIG. 19  (which is similar to  FIG. 17  but inverted so as to expose the underside of PCB  500  and optical structure  400 ), light guide channels  410  and  412  face in opposite directions. Moreover, wall  438  is open at one end. 
     FIGS. 20 and 21  show optical structure  400  in more detail.  FIG. 20  is a top view of optical structure  400 , and is similar to  FIG. 5 .  FIG. 21  is a cross section of optical structure  400  taken along lines  21 — 21  of  FIG. 20 . Upon assembly, LED  510  is positioned inside the cylinder of LED support  402  and pointing vertically downward. Three vertical locating ridges  418  are formed inside of LED support  402  and serve to align LED  510 . Formed in the bottom of LED support  402  is a collection lens  420 . Collection lens  420  collects light emitted by LED  510  and directs that light to the tracking surface target area via channel  410  and to window  304  via channel  412 . Also formed in optical structure  400  is an imaging lens  414 . Imaging lens  414  collects and focuses light reflected from a target area and directs that light through aperture  511  in aperture plate  520 . 
   Light from LED  510  strikes the upper surface of collection lens  420  and is divided between channels  410  and  412 . The portion divided into channel  410  is used to illuminate a target area for imaging by image sensor  504 . Channel  410  has an exit face  424  and a reflecting face  426 . Reflecting face  426  forms a Total Internal Reflecting (TIR) surface. Light travels through channel  410  and strikes the TIR surface of reflecting face  426 . The light is then reflected by the TIR surface of reflecting face  426  and exits channel  410  through exit face  424 . Another portion of the light emitted by LED  510  and entering collection lens  420  is diverted to channel  412 . This diverted light is then reflected by a TIR surface of reflecting face  430  of channel  412 , and exits channel  412  through exit face  434 . Reflecting face  430  and exit face  434  may be separated by a horizontal face  432 . Light divided into channel  412  is used for illuminating window  304 . Channels  412  and  410  are separated by a space bounded by the reflecting face  426  of channel  410  and by reflecting face  430  of channel  412 . Upon assembly, the open end of optical structure  400  aligns with the opening between walls  316  of access/support structure  314  so as to allow light from exit face  434  to reach window  304 . Channels  410  and  412  rest between walls  316  and within well  320 . 
   Like optical structure  100  of  FIGS. 2–7 , optical structure  400  is preferably molded as an integral component. Possible materials for optical structure  400  include clear polystyrene available from BASF Corporation of Mount Olive, N.J., grade 148G KG21; clear polystyrene available from Nova Chemicals Corporation of Moon Township, Pa., grade PS1300; LEXAN polycarbonate resin available from GE Plastics of Fairfield, Conn., grade 121R, color 1111; and MAKROLON polycarbonate resin available from Bayer Polymers of Pittsburgh, Pa., grade 2405, color 1000. Other possible materials include acrylic, cyclic olefin copolymer, SAN styrene blend and NAS styrene blend. 
   Imaging lens  414  includes upper and lower convex lenses  414   a  and  414   b . The refractive power and other optical properties of imaging lens  414  may vary based upon distance from image sensor  504 , distance of image sensor  504  above the tracking surface, the specific design of image sensor  504 , and other configuration choices. The determination of imaging lens optical requirements is within the routine ability of a person skilled in the art once provided with the descriptions herein and various design parameters. Similarly, the preferred refractive power and other optical properties of collection lens  420  may vary based on parameters such as size of LED  510 , size of channels  410  and  412 , distances from a target area, desired output illumination through window  304 , and other configuration choices. The determination of collection lens optical requirements is likewise within the routine ability of a person skilled in the art once provided with the descriptions herein and the relevant design parameters. 
   In one embodiment, approximately 80% of light entering collecting lens  420  is directed to channel  410 , and approximately 20% of the light entering collecting lens  420  is directed to channel  412 . In that embodiment, angle α ( FIG. 22 ) is approximately 67.5°, angle β is approximately 52° and angle γ is approximately 90°(β+2)°. In other embodiments, approximately 70%–90% of light entering collecting lens  420  is directed to channel  410 , and approximately 10%–30% of light entering collecting lens  420  is directed to channel  412 . In another embodiment similar to that shown in  FIG. 17 , angle α is approximately 55°. Angle α may generally be between approximately 45° and 70°, depending on LED (or other light source) height, angle of face  434  with the vertical, distance to the window to be illuminated and height of the window. 
     FIG. 23  is a cross section of optical structure  400 , access/support structure  314 , PCB  500 , image sensor  504  and LED  510  in an assembled condition. Channels  412  and  410  rest between walls  316  of access/support structure  314 . Baffle  328 , together with a beveled edge  330  on transmission hole  322 , define boundaries for an angled path for light from channel  410  to target area T. The bracket above the “T” in  FIG. 23  only approximates the location and extent of the target area for purposes of illustration. Baffle  328  also prevents or minimizes stray light from reaching imaging lens  414 . Light exiting from exit face  424  of channel  410  shines upon and illuminates target area T. A portion of this light is then reflected upward from target area T through entrance hole  326  to imaging lens  414 . Imaging lens  414  then collects and focuses this reflected light and directs it into aperture  520  of aperture plate  516 . The light then passes through aperture  520  and reaches the photo-sensitive elements of image sensor  504 . Light exiting from exit face  434  of channel  412  shines upon window  304  and is visible to a user of mouse  300  while mouse  300  rests upon a supporting surface. 
   In the embodiments of  FIGS. 17–23 , light generally exits from faces  424  and  434  in directions that are approximately 180° apart in the horizontal plane (e.g., the plane of the bottom housing  318  in  FIG. 23 ). In other embodiments, light from exit faces  424  and  434  may be separated by other angles. For example, and referring to  FIG. 16 , alternate location  304 ′ could instead be located on (or toward) one of the sides of mouse  300 . Access/support structure  314  could be modified as necessary to allow direction of light to a window not directly behind optical structure  400 . Light from exit face  434  could also be directed upward or downward by modification of channel  412 . 
     FIGS. 24 and 25  show cross sections of optical structures according to alternate embodiments of the invention.  FIG. 24  is a cross section of an optical structure  600  taken along a lengthwise centerline, similar to the cross sections shown in  FIGS. 6 ,  7 ,  9 ,  12  and  21 – 23 . The LED support structure of optical structure  600  does not extend in a direction parallel to an optical axis of the imaging lens, as shown in prior embodiments. Instead, the support structure includes a cavity  617  formed in an end of optical structure  600 , and LED  810  is inserted into that cavity. Although a rim is shown around an end of LED  810 , an optical structure such as optical structure  600  could alternatively accept a LED without such a rim. In the embodiment of  FIG. 24 , the LED longitudinal axis P L  is perpendicular to an optical axis P O  of the imaging lens  614 . Formed at the end of cavity  617  is a collection lens  620 . Opposite collection lens  620  is an exit face  624 . Although exit face  624  is formed as a planar surface, face  624  could instead be a convex refractive surface or have other shapes. As shown by the bold arrow in  FIG. 24 , light from LED  810  is refracted from exit face  624  toward a tracking surface (e.g., desk top or other supporting surface of an optical mouse). Light is then reflected by surface roughness of the tracking surface at various angles (not shown) toward imaging lens  614 . Similar to prior embodiments, optical structure  600  may have one or more spacer/shield walls  606 , a positioning post (not shown) and one or more vertical walls  638 . The open region  621  within vertical walls  638  and under imaging lens  614  could cooperate with a modified access/support structure (not shown) formed on the interior of a computer mouse. 
     FIG. 25  is a cross section of an optical structure  700 , also taken along a lengthwise centerline similar to the cross sections shown in  FIGS. 6 ,  7 ,  9 ,  12  and  21 – 23 . Similar to optical structure  600  of  FIG. 24 , optical structure  700  does not position a LED such that the longitudinal axis of the LED is parallel to an optical axis of the imaging lens. Instead, an end of optical structure  700  is angled upward to form a LED support structure, with LED  810  resting within cavity  717 . An optical structure such as optical structure  700  could alternatively accept a LED without a rim. In the embodiment of  FIG. 25 , the LED longitudinal axis P L  is at an angle Φ to optical axis P O  of the imaging lens  714 . In one embodiment, Φ is approximately 60°. Formed at the end of cavity  717  is a collection lens  720 . Opposite collection lens  720  is an exit face  724 . Although exit face  724  is formed as a convex refractive surface, face  724  could instead be planar or have other shapes. As shown by the bold arrows in  FIG. 25 , light from LED  810  is directed from exit face  624  toward a tracking surface, and is then reflected by surface roughness at various angles (not shown) toward imaging lens  714 . Similar to prior embodiments, optical structure  700  may have one or more spacer/shield walls  706 , a positioning post (not shown) and one or more vertical walls  738 . The open region  721  within vertical walls  738  and under imaging lens  714  could cooperate with a modified access/support structure (not shown) formed on the interior of a computer mouse. 
   As can be appreciated from the above description, an integral lens and light holder according to the invention provides numerous advantages over the prior art. Instead of separate structures for mounting and aligning a LED and for focusing and directing reflected light, a single structure is provided. Because only a single structure is needed, overall costs are reduced. Moreover, reducing the number of pieces permits close tolerances to be more easily maintained during assembly. Although several examples of carrying out the invention have been described, those skilled in the art will appreciate that there are numerous variations and permutations of the above described examples that fall within the spirit and scope of the invention. As but one example, a unitary lens and light source holder according to the invention need not be used in conjunction with a corresponding support structure such as access/support structures  14  or  314 . Numerous other configurations are possible. As but one other example, more or less than two channels could be implemented. One, some or all of the additional channels could also have a non-planar front face. These and other modifications are within the scope of the invention, which is only limited by the attached claims.