Abstract:
A method and apparatus involve: using beam influencing structure to cause a converging beam of radiation to propagate along a first portion of a path of travel; supporting an optical part so that the path of travel extends through the optical part, the converging beam arriving at the optical part along the first portion of the path of travel, and the path of travel having a second portion along which the converging beam travels away from the optical part; and selectively tilting the optical part about a pivot axis lying in an imaginary plane extending transversely to the first portion of the path of travel, pivotal movement of the optical part about the pivot axis causing a change in the orientation of the second portion of the path of travel with respect to the first portion thereof.

Description:
FIELD OF THE INVENTION 
     This invention relates in general to techniques for influencing a beam of radiation and, more particularly, to techniques for positioning a beam of radiation. 
     BACKGROUND 
     In optical systems, it is sometimes necessary to accurately position a focused beam of radiation with respect to a relatively small target, such as the core of an optical fiber. The traditional approach has been to effect relative movement between the target and the optical system that generates the focused beam. This typically requires a mechanism that can effect the relative movement with a level of precision and accuracy that is greater than the required adjustment between the beam and target. These movement mechanisms can be relatively expensive, and can also exhibit instability. Consequently, although pre-existing techniques for positioning a focused beam in relation to a target have been generally adequate for their intended purposes, they have not been satisfactory in all respects. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A better understanding of the present invention will be realized from the detailed description that follows, taken in conjunction with the accompanying drawing, in which: 
         FIG. 1  is diagrammatic perspective view of an apparatus that embodies aspects of the invention, and that includes an optical fiber and a beam positioning section. 
         FIG. 2  is a diagrammatic top view of an optical plate that is part of the beam positioning section in  FIG. 1 , and shows an exemplary operational movement of the optical plate. 
         FIG. 3  is a diagrammatic top view similar to  FIG. 2 , but showing a different operational movement of the optical plate. 
         FIG. 4  is a diagrammatic perspective view similar to  FIG. 1 , but showing an apparatus that is an alternative embodiment of the apparatus of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is diagrammatic perspective view of an apparatus  10  that embodies aspects of the invention, and that includes an optical fiber  12  and a beam positioning section  13 . The optical fiber  12  is a conventional part, and has a core  16  surrounded by a sleevelike cladding  17 . The beam positioning section  13  includes a stationary lens  21 . The lens  21  takes a beam of collimated radiation  26 , and converts it to focused radiation that is directed approximately toward the core  16  of the fiber  12 . 
     An optical plate  41  is supported between the lens  21  and the optical fiber  12 , and the focused beam  27  passes through the plate  41 . In the disclosed embodiment, the plate  41  is made of glass, but it could alternatively be made of any other suitable optical material. The plate has planar side surfaces  42  and  43  on opposite sides thereof. The surfaces  42  and  43  extend parallel to each other, and transversely to the direction of travel of the beam  27 . A not-illustrated anti-reflective coating of a known type is provided on the surface  42  and/or on the surface  43 , but this coating could optionally be omitted. In the embodiment of  FIG. 1 , the plate  41  has a shape that is approximately a square. However, the plate  41  could alternatively have a variety of other shapes. The square plate  41  has four corners, three of which are indicated by reference numerals  46 ,  47  and  48 . 
     An actuator  51  has a housing  52 , and an elongate rod  53  that is supported for lengthwise movement with respect to the housing  52 . The rod  53  extends approximately parallel to the direction of travel of the focused beam  27 . The housing  52  has a not-illustrated electric motor therein. The motor has a not-illustrated worm thread that engages a further worm thread provided on the rod  53 . In response to operation of the motor, the worm threads cooperate to selectively effect lengthwise movement of the rod  53  with respect to the housing  52 . A pivot joint  56  couples the outer end of the rod  53  to the corner  46  of the plate  41 . The pivot joint  56  permits the rod  53  to pivot freely in any direction about a pivot point located within the pivot joint  56 . The pivot joint  56  can, for example, be a universal joint or a gimbal mechanism. At the end of the housing  52  remote from the rod  53 , a similar pivot joint  57  pivotally couples the housing  52  to a stationary part  58 . 
     Another actuator  61  is identical to the actuator  51 . The actuator  61  has a housing  62 , and a rod  63  that can move in a lengthwise direction with respect to the housing  62 . The rod  63  extends approximately parallel to the direction of travel of the focused beam  27 . The outer end of the rod  63  is pivotally coupled to the corner  47  of the plate  41  by a pivot joint  66 . At the opposite end of the actuator  61 , a pivot joint  67  pivotally couples the housing  62  to a stationary part  68 . 
     A further actuator  71  is also identical to the actuator  51 . The actuator  71  has a housing  72 , and a rod  73  that can move in a lengthwise direction with respect to the housing  72 . The rod  73  extends approximately parallel to the direction of travel of the focused beam  27 . The outer end of the rod  73  is pivotally coupled to the corner  47  of the plate  41  by a pivot joint  76 . At the opposite end of the actuator  71 , a pivot joint  77  pivotally couples the housing  72  to a stationary part  78 . 
     It would be possible to provide three manually operable switches that each electrically control a respective one of the actuators  51 ,  61  and  71 . But in the embodiment of  FIG. 1 , a control circuit  81  is provided, and is electrically coupled to each of the actuators  51 ,  61  and  71 . A manual input device  82  is operatively coupled to the control circuit  81 . The manual input device  82  may, for example, be a device of the type commonly known as a “joystick”. By operating the manual input device  82 , an operator can cause the control circuit  81  to effect appropriate movement of one or more of the actuators  51 ,  61  and  71 . 
     In this regard, if the control circuit  81  causes the actuator  51  to extend the rod  53  by an amount “X”, and causes each of the actuators  61  and  71  to retract the associated rods  63  or  73  by the same amount X, then the plate  41  will pivot about a pivot axis  83  located halfway between the pivot joints  56  and  66 . Similarly, if the control circuit  81  causes the actuator  71  to extend the rod  73  by an amount X, and causes the actuators  51  and  61  to each retract the associated rod  53  or  63  by the same amount X, then the plate  41  will pivot about a pivot axis  84  located halfway between the pivot joints  66  and  73 . The pivot axes  83  and  84  each lie in a not-illustrated imaginary plane that is disposed between and extends parallel to the side surfaces  42  and  43  of the plate  41 . 
       FIG. 2  is a diagrammatic top view of the optical plate  41  of  FIG. 1 . With reference to  FIG. 2 , assume that the actuator  71  ( FIG. 1 ) moves the right side of the plate  41  in one direction by the amount X, and that the actuators  51  and  61  each move the left side of the plate in the opposite direction by the same amount X. The plate will pivot about the vertical axis  84  from the position shown in solid lines to the position shown in broken lines. In particular, the plate  41  will pivot about the pivot axis  84  through an angle  87  (θ). 
       FIG. 3  is a diagrammatic top view similar to  FIG. 2 , but showing a different operational movement. As shown in  FIG. 3 , if the actuator  71  moves the right side of plate  41  by the distance X, while the actuators  51  and  61  do not move the left side of the plate, then the plate will pivot about a pivot axis  88  located at the left side of the plate. In particular, the plate will pivot through an angle  89  (θ/2) that is half the angle  87 . 
     Although is it possible to use the actuators  51 ,  61  and  71  to move the plate  41  in the manner shown in  FIG. 3 , there are advantages to instead using the actuators in the manner shown in  FIG. 2 . First, in order to change the orientation of the plate by a particular angle, the approach of  FIG. 2  permits the positional adjustment to be completed in half the time needed to complete the same positional adjustment using the technique of  FIG. 3 . Further, for actuators with a given range of linear movement, the range of pivotal adjustment of the plate is twice as large as would be the case if an equivalent actuator is used to implement the technique of  FIG. 3 . Third, the space required to achieve a given pivotal adjustment using the technique of  FIG. 2  is approximately half the space required to achieve the same positional adjustment using the technique of  FIG. 3 . 
     Referring again to  FIG. 1 , it will be recognized that, by first effecting a pivotal movement of the plate  41  about the axis  83 , and then effecting a further pivotal movement of the plate about the axis  84 , the plate can be moved to any desired pivotal position. On the other hand, in order to effect the same overall movement, the control circuit  81  could simultaneously cause each of the actuators  51 ,  61  and  71  to move from a current position to a final position. This permits the plate  41  to reach its final position more quickly. 
     After passing through the lens  21 , the focused radiation  27  propagates to the plate  41  along a path of travel  91 . After passing through the plate  41 , the radiation propagates along a path of travel  92 . When the surfaces  42  and  43  of the plate happen to be perpendicular to the path of travel  91 , the path of travel  92  will be parallel to and co-extensive with the path of travel  91 . In other words, the path of travel  91  and the path of travel  92  will lie along the same straight line. However, when the plate  41  has been pivoted to any other operational position, where the surfaces  42  and  43  form an angle with respect to the path of travel  91 , the direction of travel of the focused radiation will be altered slightly as it passes through the plate  41 . In that case, the path of travel  92  will form a small angle with respect to the path of travel  91 . By using the actuators  51 ,  61  and  71  to pivot the plate  41  to an appropriate position, the path of travel  92  can be positioned very precisely, for example so that the focused radiation  27  is precisely centered on the core  16  of the fiber  12 . 
     For a given amount of pivotal movement of the plate  41 , the corresponding deviation of the path of movement  92  will depend on the thickness of the plate, and the index of refraction of the material of the plate. Even so, a small amount of movement of the beam requires a greater amount of pivotal movement of the plate  41 . Consequently, the actuators  51 ,  61  and  71  can be relatively inexpensive devices of moderate precision, yet the path of movement  92  of the focused beam can be positioned with excellent precision, accuracy and stability. 
     In the embodiment of  FIG. 1 , the plate  41  is disposed in a converging beam  27 . Consequently, the plate will inherently tend to introduce aberrations into the focused beam, most notably a spherical aberration. In the embodiment of  FIG. 1 , the lens  21  is specifically designed so that, in addition to converting the collimated beam  26  into the focused beam  27 , it also compensates for any spherical or other aberrations introduced by the plate  41 . Persons skilled in the art of lens design know how to configure the lens  21  to compensate for aberrations introduced by the plate  41 . 
       FIG. 4  is a diagrammatic perspective view similar to  FIG. 1 , but showing an apparatus  110  that is an alternative embodiment of the apparatus  10  of  FIG. 1 . The embodiment of  FIG. 4  is effectively identical to the embodiment of  FIG. 1 , except for differences that are discussed below. Parts in  FIG. 4  that are equivalent to parts in  FIG. 1  are identified with the same reference numerals. The embodiment of  FIG. 4  includes a manual input device and a control circuit similar to those shown at  82  and  81  in  FIG. 1 , but these parts have been omitted from  FIG. 4  for clarity. 
     The apparatus  110  of  FIG. 4  has a beam positioning section  113  that differs somewhat from the beam positioning section  13  in  FIG. 1 . One difference is that the square plate  41  of  FIG. 1  is replaced with a similar plate  141  having the shape of an equilateral triangle. Although the plate  141  is shown with a triangular shape for simplicity and clarity, it could alternatively have a variety of other shapes. The plate  141  has planar, parallel side surfaces  142  and  143  on opposite thereof, and is made of glass or some other suitable optical material. The plate  141  has three corners  146 ,  147  and  148 , and the pivot joints  56 ,  66 , and  76  are each coupled to a respective one of these corners  146 ,  147  and  148 . 
     An expansion spring  186  has one end coupled to a stationary part  187 , and its other end coupled to a midpoint of the edge of plate  141  extending between corners  146  and  147 . Similarly, an expansion spring  188  has one end coupled to a stationary part  189 , and its other end coupled to a midpoint of the edge of plate  141  extending between corners  147  and  148 . A third expansion spring  193  has one end coupled to a stationary part  194 , and its other end coupled to a midpoint of the edge of plate  141  extending between corners  146  and  148 . The expansion springs  186 ,  188  and  193  each extend in a direction approximately parallel to the direction of travel  91 . The springs  186 ,  188  and  193  each exert a resilient biasing force on the plate  41  in all operational positions of the plate, each such biasing force acting in a direction approximately parallel to the path of travel  91 . Although the springs  186 ,  188  and  193  in the embodiment of  FIG. 4  are expansions springs, it would alternatively be possible to use compression springs, or any other suitable biasing structure. 
     If actuator  51  is not moved, if actuator  61  is retracted (or extended) by an amount X, and if actuator  71  is extended (or retracted) by the same amount X, the plate  141  will pivot about the vertical axis  84 . Alternatively, if the actuator  51  is extended (or retracted) by an amount X, and if the actuators  61  and  71  are both retracted (or extended) by the same amount X, the plate  141  will pivot about the axis  83 . Thus, by using the actuators  51 ,  61  and  71  to appropriately tilt the plate  141 , the direction of travel  92  can be adjusted relative to the direction of travel  91 , in order to accurately micro-position the focused beam  27  with respect to the core  16  of the optical fiber  12 . 
     By first tilting the plate  141  about the axis  83 , and then tilting the plate about the axis  84 , the plate can be moved to any desired position, in order to give the path of travel  92  any desired orientation with respect to the path of travel  91 . But as a practical matter, the not-illustrated control circuit can simultaneously move each of the actuators from its initial position to its final position, thereby causing the plate to more quickly move from its initial position to its final position. 
     In the embodiment of  FIG. 4 , the three corners  146 ,  147  and  148  of the plate  141  are each an equal distance from the other two corners. Stated differently, the three actuators  51 ,  61  and  71  apply forces to the plate at respective points that are each spaced an equal distance from the other two. Further, the three springs  186 ,  188  and  193  each act on the plate at a location halfway between a respective pair of the actuators. The arrangement of actuators and springs is thus symmetric, and the forces of the springs are shared evenly by the actuators. Consequently, the embodiment of  FIG. 4  is stable, and well balanced. 
     Although the embodiments of  FIGS. 1 and 4  each permit a focused beam to be accurately positioned with respect to an optical fiber  12 , it would alternatively be possible to replace the optical fiber  12  with any other component with respect to which a beam needs to be accurately positioned. 
     Although selected embodiments have been illustrated and described in detail, it should be understood that a variety of substitutions and alterations are possible without departing from the spirit and scope of the present invention, as defined by the claims that follow.