Abstract:
An apparatus for manipulating a path of a beam includes a first wedge and a second wedge. The first wedge includes a first refractive surface and a second refractive surface. The second wedge includes a third refractive surface adjacent to the second refractive surface, and a reflective surface. The beam refracts at the first refractive surface, refracts at the second refractive surface, refracts at the third refractive surface, reflects from reflective surface, refracts at the third refractive surface, refracts at the second refractive surface, refracts at the first refractive surface. At least one of the first wedge and the second wedge can be rotated so that the beam exiting the apparatus can be oriented substantially orthogonal to the beam entering the apparatus.

Description:
DESCRIPTION OF RELATED ART 
     FIGS. 1A and 1B  illustrate a conventional beam manipulator  100  using matched prisms (wedges)  110  and  120 , which are sometimes referred to as a Risley prism set, to adjust the direction of a beam  130 . Beam  130 , which is incident on wedge  110 , refracts in accordance with Snell&#39;s Law at each of the four air-glass interfaces  111 ,  112 ,  121 , and  122  of the two wedges  110  and  120 . 
   In the configuration of  FIG. 1A , consecutive interfaces  112  and  121  are parallel to each other, and the angular deflection of beam  130  at interface  121  is equal and opposite to the angular deflection of beam  130  at interface  112 . Similarly, interfaces  111  and  122  are parallel to each other, and since interfaces  112  and  121  cause no net angular deflection, the angular deflection of beam  130  at interface  122  is equal and opposite to the angular deflection at interface  111 . Accordingly, in the configuration of  FIG. 1  A, system  100  causes no net angular deflection of beam  130 . 
   Wedges  110  and  120  can be rotated with respect to each other to change the relative angle between interfaces  112  and  121 .  FIG. 1B  illustrates a configuration of system  100  where wedge  120  has been rotated so that interfaces  112  and  121  make a maximum angle with each other. In the configuration of  FIG. 1B , refractions at interfaces  112 ,  121 , and  122  deflect beam  130  in the same direction, causing the largest angular deflection θmax that system  100  can achieve. Smaller rotations of wedge  120  relative to wedge  110  produce smaller angular deflections, so that system  100  can achieve any desired angular deflection of beam  130  between 0 and θmax. The relative orientations of wedges  110  and  120  can thus be set to provide the desired (polar) angular deflection. System  100  can be also rotated as a unit about its optical axis to adjust an azimuthal angle of the deflection. 
   SUMMARY 
   In one embodiment of the invention, an apparatus for manipulating a path of a beam includes a first wedge and a second wedge. The first wedge includes a first refractive surface and a second refractive surface. The second wedge includes a third refractive surface adjacent to the second refractive surface, and a reflective surface. The beam refracts at the first refractive surface, refracts at the second refractive surface, refracts at the third refractive surface, reflects from reflective surface, refracts at the third refractive surface, refracts at the second refractive surface, and refracts at the first refractive surface. At least one of the first wedge and the second wedge can be rotated so that the beam exiting the apparatus can be oriented substantially orthogonal to the beam entering the apparatus. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIGS. 1A and 1B  are cross-sectional views of a prior art Risley prism set. 
       FIG. 2  is a cross-sectional view of an adjustable turning mirror in one embodiment of the invention. 
       FIGS. 3 and 4  are perspective and exploded views of the adjustable turning mirror of  FIG. 2  in one embodiment of the invention. 
       FIG. 5  is a cross-sectional view of an optic holder for receiving a wedge in the adjustable turning mirror of  FIG. 2  in one embodiment of the invention. 
       FIG. 6  is a front view of an optical mount for receiving the optic holders in the adjustable turning mirror of  FIG. 2  in one embodiment of the invention. 
       FIG. 7  is a cross-sectional view of a configuration of the adjustable turning mirror of  FIG. 2  in one embodiment of the invention. 
       FIG. 8  is a map of the beam reflection achieved by adjusting the wedges of the adjustable turning mirror of  FIG. 2  in one embodiment of the invention. 
       FIG. 9  is another configuration of the adjustable turning mirror of  FIG. 2  in one embodiment of the invention. 
       FIG. 10  is a cross-sectional view of another adjustable turning mirror in one embodiment of the invention. 
       FIG. 11  is a cross-sectional view of a configuration of the adjustable turning mirror of  FIG. 10  in one embodiment of the invention. 
       FIG. 12  is a map of the beam reflection achieved by adjusting the wedges of the adjustable turning mirror of  FIG. 10  in one embodiment of the invention. 
     Use of the same reference symbols in different figures indicates similar or identical items. The figures are not drawn to scale and are for illustrative purposes only. 
   

   DETAILED DESCRIPTION 
   In accordance with the invention, a Risley prism set is modified to create an adjustable turning mirror. The outer surface of one wedge in the prism set is coated with a reflective material. Thus, a light beam is reflected back through the two wedges instead of passing through them. The reflection of the light beam can be controlled by rotating one or both of the wedges. The modified prism set has been named a “Risley prism mirror.” The Risley prism mirror can replace expensive turning mirrors using complicated adjustable mounts. 
     FIG. 2  shows a side view of an adjustable turning mirror  200  for reflecting a light beam in one embodiment of the invention. Mirror  200  includes prisms  210  and  220 , which are also commonly referred to as “wedges.” In one embodiment, wedges  210  and  220  are configured with parallel surfaces  212  and  224  furthest from each other and angled surfaces  214  and  222  adjacent to each other. 
   Mirror  200  is placed in the path of a light beam  230 , which impinges on refracting surface  212 . Surface  212  may have an antireflective coating. Beam  230  refracts at surface  212  and travels through wedge  210  toward refracting surface  214 . Surface  214  may have an antireflective coating. Beam  230  refracts again at surface  214  and then exits wedge  210 . 
   Beam  230  travels through the air and impinges on refracting surface  222 . Surface  222  may have an antireflective coating. Beam  230  refracts at surface  222  and travels through wedge  220  toward reflective surface  224 . In one embodiment, surface  224  has a reflective coating  226 . In another embodiment, a mirror  226  is glued to or mechanically held against wedge  220  (e.g., by a spring finger). Thus beam  230  reflects from surface  224  and travels back towards refracting surface  222 . Beam  230  refracts at surface  222  and then exits wedge  220 . 
   Beam  230  travels through the air and impinges on refracting surface  214 . Beam  230  refracts at surface  214  and travels through wedge  210  toward refracting surface  212 . Beam  230  refracts again at surface  212  and then exits wedge  210 . In one embodiment, wedges  210  and  220  are oriented so the output path of beam  230  is substantially orthogonal to the input path of beam  230  in order to create an adjustable 90° turning mirror. For example, wedges  210  and  220  are oriented so that beam  230  has an angle of incidence of approximately 45° to surface  212 . Alternatively, wedges  210  and  220  can be oriented to create an adjustable turning mirror having any turning angle between 0° up to 180°. Wedges  210  and  220  are then rotated to fine tune the beam reflection. 
   Matched wedge sets with different wedge angles can vary the magnitude of the reflected steering adjustment. Larger wedge angles typically provide a larger range of adjustment at the cost of coarser resolution. Similarly, better resolution can be achieved with finer wedges at the expense of a smaller adjustment range. 
     FIGS. 3 and 4  illustrate one configuration of mirror  200  in one embodiment of the invention. Wedges  210  and  220  are substantially circular and have substantially the same wedge angle (e.g., 1° physical wedge). The diameter of wedges  210  and  220  depends on the beam size and typically has a ratio of 5:1 with the wedge thickness. The prism material is typically BK7. The air gap between wedges  210  and  220  is minimized to reduce the overall size of mirror  200 . 
   Wedges  210  and  220  fit into respective optic holders  312  and  322 . Optic holders  312  and  322 , which are substantially identical to each other, fit into an opening  510  ( FIG. 4 ) in an optical mount  340  from opposing sides. Optic holders  312  and  322  are circular to permit rotation of one or both optic holders  312  and  322  in optical mount  340  when adjusting the beam reflection. 
     FIG. 5  is a cross-sectional view of optic holder  322  in one embodiment of the invention. Optic holder  322  is a cylinder  400  with an inner ledge  410  extending inward from the inner circumference of the cylinder, and an outer ledge  430  extending outward from the outer circumference of the cylinder. In one embodiment, ledges  410  and  430  are on the same end of cylinder  400 . Wedge  220  sits on and is glued to inner ledge  410  by a flexible adhesive  420 . The use of a flexible adhesive  420  minimizes the effects of temperature or stress-induced deformation in wedge  220  when optic holder  322  is clamped in place. The inner diameter of optic holder  322  is made larger than the diameter of wedge  220  so that wedge  220  would not contact the sides of optic holder  322  under expansion. Thus, misalignment caused by temperature changes, humidity changes, and stress-induced birefringence in wedge  220  is minimized. 
   When optic holder  322  is inserted into opening  510 , outer ledge  430  abuts the outer surface of optical mount  340  to limit the insertion depth of optic holder  322  into opening  510 . The insertion depth in turn determines the air gap between wedges  210  and  220 . Outer ledge  430  may include features such as ridges that facilitate the rotation of optic holder  322  within optical mount  340 . Optic holder  312  can be similarly constructed as optic holder  322 . 
     FIG. 6  illustrates optical mount  340  in one embodiment of the invention. Optical mount  340  is a clamp having opening  510  into which optic holders  312  and  322  are inserted from opposing sides. Opening  510 , instead of being circular, has scalloped or concave sections  520  so that only separated regions  530  around the perimeter of opening  510  contact optic holders  312  and  322 . A clamping screw  342  tightens prongs  346  and  348  of optical mount  340  to keep optic holders  312  and  322  at fixed positions. Loosening clamping screw  342  allows the rotation of optic holders  312  and  322  to align the beam for the desired reflection, and a removable clip  344  prevents optic holders  312  and  322  from falling out of optical mount  340  when clamping screw  342  is loose. In one embodiment, optical mount  340  and optic holders  312  and  322  are made of a stable material (e.g., 416 stainless steel) that has a thermal expansion similar to that of wedges  210  and  220 . 
     FIG. 7  illustrates the configuration of optic holders  312  and  322  when placed into optical mount  340  ( FIG. 6 ) in one embodiment of the invention. As the two glued faces are placed away from each other, wedges  210  and  220  expand symmetrically toward a centerline  702  in order to minimize beam pointing due to temperature and humidity changes. Note that the rotation axis  704  of optic holders  312  and  322  is parallel to the mirror normal  706 . 
     FIG. 8  illustrates a map  800  of beam reflection achieved by rotating wedges  210  and  220  in mirror  200  ( FIG. 2 ). A dashed outer perimeter  802  illustrates the maximum range of beam reflection that can be achieved with the wedge pair. Along perimeter  802 , solid inner perimeters  804  show a range of beam reflection that can be achieved when wedge  210  is rotated 360° while holding wedge  220  stationary. Locations  806  indicate 90° rotations of wedge  220 , and locations  808  indicate 90° rotations of wedge  210 . When combined, the rotation of wedges  210  and  220  can reflect the beam anywhere within outer perimeter  802 . 
     FIG. 9  illustrates another configuration of mirror  200  ( FIG. 2 ) in one embodiment of the invention. In this configuration, each of optic holders  912  and  922  has an inner ledge  410  and an outer ledge  430  at the opposite ends of cylinders  400 . Again, wedge  210  and  220  are glued to inner ledge  410 . Again wedges  210  and  220  are allowed to expand symmetrically toward centerline  702  in order to minimize distortion. In this configuration, two optical mounts  340  may be needed to hold optic holders  312  and  322  individually. 
     FIG. 10  shows a side view of an adjustable turning mirror  1000  for reflecting a light beam in one embodiment of the invention. Unlike mirror  200  ( FIG. 2 ), wedges  210  and  220  are configured with parallel surfaces  212  and  224  adjacent to each other and angled surfaces  214  and  222  furthest from each other. Furthermore, reflective coating  226  is now on surface  222 . 
     FIG. 11  illustrates one configuration of mirror  1000  ( FIG. 10 ) in one embodiment of the invention. Mirror  1000  includes optic holders  912  and  922  that are inserted into optical mount  340  ( FIG. 6 ) from opposite sides. In this configuration, the two glued faces of wedges  210  and  220  face one another so that wedges  210  and  220  expand symmetrically outward from centerline  702  in order to minimize beam pointing due to temperature and humidity changes. 
     FIG. 12  illustrates a map  1200  of beam reflection achieved by rotating wedges  210  and  220  in mirror  1000  ( FIG. 10 ). A dashed outer perimeter  1202  illustrates the maximum range of beam reflection that can be achieved with the wedge pair. Along perimeter  1202 , solid inner perimeters  1204  show a range of beam reflection that can be achieved when wedge  210  is rotated 360° while holding wedge  220  stationary. Locations  1206  indicate 90° rotations of wedge  220 , and locations  1208  indicate 90° rotations of wedge  210 . As map  1200  shows, there may be a dashed inner perimeter  1210  delineating a region where the reflected light beam cannot impinge. This is caused by an angled reflective surface  222  that rotates about axis  704  (i.e. the mirror normal  706  and optic holder axis  704  are not parallel). Thus, the rotation of wedges  210  and  220  can reflect the beam anywhere between outer perimeter  1202  and inner perimeter  1210 . 
   Various other adaptations and combinations of features of the embodiments disclosed are within the scope of the invention. For example, varying wedge angles and indices of refraction can be used to achieve the precision desired for the beam reflection. Furthermore, the wedges can be mechanically fastened to the optic holder. Numerous embodiments are encompassed by the following claims.