Abstract:
A method and apparatus involve: supporting an optical part for movement in relation to a first path of travel of radiation; moving the part successively to first and second positions in which radiation arriving along the first path of travel passes respectively through first and second sections of the part that provide respective different levels of refraction, the first and second sections causing radiation to thereafter travel along respective second and third paths of travel; and receiving at an output first and second portions of radiation respectively propagating along the second and third paths of travel, the first and second portions containing different amounts of optical energy.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates in general to optical systems and, more particularly, to techniques for optical power transfer control in optical systems. 
       BACKGROUND 
       [0002]    In optical systems, there is often a need to regulate optical power. In one existing approach, a beam of radiation is expanded, collimated, and then routed through a variable density filter. The radiation exiting the filter is then collected and refocused to the output. The filter can be moved with respect to the beam. The position of the filter in relation to the beam determines the power transfer from the input to the output, which is a function of the density of the portion of the filter through which the beam is currently passing. 
         [0003]    Although systems of this type has been generally adequate for their intended purposes, they have not be satisfactory in all respects. For example, a variable density filter is a relatively expensive component. In addition, a variable density filter will absorb some portion of the energy of the beam passing through it. The amount of energy absorbed depends on the density of the portion of the filter through which the beam is currently passing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]    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: 
           [0005]      FIG. 1  is diagrammatic fragmentary view of an optical apparatus that provides optical power transfer control, and that embodies aspects of the invention. 
           [0006]      FIG. 2  is a diagrammatic side view of selected structure from the embodiment of  FIG. 1 , including a disk, a motor shaft and an axis of rotation. 
           [0007]      FIG. 3  is a diagrammatic fragmentary view of the apparatus of  FIG. 1 , but showing the disk in a different operational position. 
           [0008]      FIG. 4  is a diagrammatic view showing the end of an optical output fiber depicted in  FIG. 1 , and showing how a beam of radiation moves in relation to the output fiber as the disk is rotated, the plane of  FIG. 4  being coincident with the plane of an end surface of the output fiber. 
           [0009]      FIG. 5  is a diagram showing the energy distribution that is present within a beam of radiation at the plane of the end surface of the output fiber. 
           [0010]      FIG. 6  is diagrammatic fragmentary view of an optical apparatus that is an alternative embodiment of the optical apparatus of  FIG. 1 , that provides optical power transfer control, and that embodies aspects of the invention. 
           [0011]      FIG. 7  is a diagrammatic fragmentary view of the apparatus of  FIG. 6 , but showing a different operational position. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]      FIG. 1  is diagrammatic fragmentary view of an optical apparatus  10  that provides optical power transfer control, and that embodies aspects of the invention.  FIG. 1  is not completely to scale, for example in that some angles and distances have been exaggerated for clarity. The apparatus  10  includes two optical fibers  12  and  13  of a known type. The optical fiber  12  is an input fiber, and the optical fiber  13  is an output fiber. The apparatus  10  also includes two optical lenses  16  and  17  of a known type. The lens  16  is a collimating lens, and the lens  17  is an imaging lens. Further, the apparatus  10  includes a motor  21  having a shaft  23  that can rotate about an axis of rotation  24 . The motor  21  is controlled by a control circuit  22 . In the embodiment of  FIG. 1 , the motor  21  is a stepper motor, but it could alternatively be any other suitable type of motor. Although the embodiment of  FIG. 1  uses the motor  21  to rotate the shaft  23 , it would alternatively be possible to rotate the shaft  23  manually, or using any other suitable structure. 
         [0013]    A circular optical disk  26  is fixedly mounted on the shaft  23  of the motor  21 , in a manner so that the axis of the circular disk  26  is coincident with the rotational axis  24  of the motor shaft  23 .  FIG. 2  is a diagrammatic side view of the disk  26 , the motor shaft  23  and the axis  24 . The disk  26  has two planar side surfaces  31  and  32  on opposite sides thereof. The surfaces  31  and  32  form an angle  33  (σ) with respect to each other. Thus, in the side view of  FIG. 1 , the disk  26  has a wedged-shaped appearance. 
         [0014]    In the rotational position of the disk  26  that is shown in  FIGS. 1 and 2 , the thickest portion of the disk is at the very top (at  45  in  FIG. 2 ), and the thinnest portion is at the very bottom (at  46  in  FIG. 2 ). In  FIG. 2 , reference numeral  44  designates an imaginary line that is perpendicular to and intersects the axis of rotation  24 , and that passes through the thickest portion  45  and the thinnest portion  46  of the disk. As the disk  26  rotates, the imaginary line  44  rotates with the disk. 
         [0015]    Incoming radiation exits the input fiber  12  and then travels to the collimating lens  16 . The lens  16  collimates the radiation from the input fiber  12 . The collimated radiation then travels from the lens  16  along a path of travel  51  to the disk  26 . Radiation propagating along the path of travel  51  impinges on the side surface  31  of the disk  26  at an initial angle of incidence  53  (θ 0 ) in relation to a line  49  perpendicular to the side surface  31 . This radiation enters the disk  26  through the side surface  31 , and then exits through the side surface  32 . As this radiation is passing through the disk  26 , it is refracted or redirected in a manner so that, after exiting the disk, it travels along a path of travel  52  that forms an angle  54  (δ) with respect to the path of travel  51 . Using Snell&#39;s law equations (applied in a two-dimensional sense), the relationship between the angles  33  (σ) and  54  (δ) is given by equation (1) below. 
         [0000]    
       
         
           
             
               
                 
                   δ 
                   = 
                   
                     
                       
                         sin 
                         
                           - 
                           1 
                         
                       
                        
                       
                         ( 
                         
                           
                             
                               n 
                               disk 
                             
                             
                               n 
                               air 
                             
                           
                           * 
                           sin 
                            
                           
                             { 
                             
                               
                                 
                                   sin 
                                   
                                     - 
                                     1 
                                   
                                 
                                  
                                 
                                   [ 
                                   
                                     
                                       
                                         n 
                                         air 
                                       
                                       
                                         n 
                                         disk 
                                       
                                     
                                     * 
                                     
                                       sin 
                                        
                                       
                                         ( 
                                         
                                           θ 
                                           0 
                                         
                                         ) 
                                       
                                     
                                   
                                   ] 
                                 
                               
                               - 
                               σ 
                             
                             } 
                           
                         
                         ) 
                       
                     
                     - 
                     
                       
                         sin 
                         
                           - 
                           1 
                         
                       
                        
                       
                         ( 
                         
                           
                             
                               n 
                               disk 
                             
                             
                               n 
                               air 
                             
                           
                           * 
                           sin 
                            
                           
                             { 
                             
                               
                                 sin 
                                 
                                   - 
                                   1 
                                 
                               
                                
                               
                                 [ 
                                 
                                   
                                     
                                       n 
                                       air 
                                     
                                     
                                       n 
                                       disk 
                                     
                                   
                                   * 
                                   
                                     sin 
                                      
                                     
                                       ( 
                                       
                                         θ 
                                         0 
                                       
                                       ) 
                                     
                                   
                                 
                                 ] 
                               
                             
                             } 
                           
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where n air  is the index of refraction of air, and n disk  is the index of refraction of the disk  26 . For any rotational position of the disk  26 , equation (1) gives the deviation angle  54  (δ) as measured within a not-illustrated imaginary plane that contains line  51  and is parallel to line  44 . Within this imaginary plane, the deviation from line  51  to line  52  will always occur in a direction toward the thickest portion of the disk (as viewed within that not-illustrated imaginary plane). 
         [0016]    After exiting the disk  26 , the beam of collimated radiation propagates along the path of travel  52  to the imaging lens  17 . The imaging lens  17  focuses this beam, and directs it approximately toward the output fiber  13 . Depending on the position of the disk  26 , this focused beam may or may not strike the end of the output fiber  13 , as discussed in more detail later. When the beam reaches a plane  61  that is coincident with the end of the output fiber  13 , the beam has a diameter or spot size given by equation (2) below. 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       Spot 
                        
                       
                           
                       
                        
                       Size 
                     
                     = 
                     
                       
                         4 
                          
                         
                           μ 
                           2 
                         
                          
                         λ 
                          
                         
                             
                         
                          
                         f 
                       
                       
                         π 
                          
                         
                             
                         
                          
                         D 
                       
                     
                   
                   , 
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where λ is wavelength, f is focal length of the lens  17 , D is the diameter of the beam at lens  17 , and μ 2  is a beam mode parameter. 
         [0017]    As the disk  26  is rotated in relation to the other structure shown in  FIG. 1 , there will be a progressive change in the thickness of the portion of the disk that refracts the radiation arriving from the lens  16 . In this regard,  FIG. 3  is a diagrammatic fragmentary view that is identical to  FIG. 1 , except that the disk  26  is shown in a different operational position. In particular, in  FIG. 3 , the disk  26  has been rotated 180° from the position shown in  FIG. 1 . The portion of the disk  26  influencing radiation from the lens  16  in  FIG. 3  is significantly thinner than the portion of the disk influencing radiation in  FIG. 1 . Consequently, the deviation angle  54  (δ) between the path of travel  51  and the path of travel  52  is smaller in  FIG. 3  than in  FIG. 1 . As a result, the beam of radiation leaving the disk  26  along the path of travel  52  will impinge on the imaging lens  17  at a different location than the beam of radiation in  FIG. 1 . This in turn shifts the position of the focused beam traveling away from the lens  17  toward the output fiber  13 . Thus, for example, it will be noted in  FIG. 1  that the focused beam from the lens  17  strikes the end of the fiber  13 , whereas in  FIG. 3  the focused beam from the lens  17  misses the end of the output fiber  13 . This is discussed in more detail below, with reference to  FIG. 4 . 
         [0018]      FIG. 4  is a diagrammatic view in which the plane of the drawing is coincident with the plane  61  ( FIG. 1 ).  FIG. 4  shows the end of the output fiber  13 , and shows how the beam of radiation moves in relation to the output fiber as the disk  26  rotates. With reference to  FIG. 4 , the output fiber  13  has a typical configuration, including a cylindrical core  71  that is surrounded by a cylindrical sleeve  72  of cladding material. The broken-line circle  76  represents the location of the beam of radiation when the disk  26  is in the position shown in  FIG. 1 . The broken-line circle  77  represents the location of the beam of radiation when the disk  26  is in the position shown in  FIG. 3 . As the disk  26  is rotated, the beam moves along a circular path or travel  76 . 
         [0019]      FIG. 5  is a diagram showing the energy distribution that is present in the beam of radiation at the plane  61 . In particular, the energy in the beam has an approximately Gaussian distribution  87  across a diameter  86  of the beam  76 . That is, the energy is strongest at the center of the beam, and drops off progressively in all radial directions from the center of the beam toward the edges of the beam. Thus, with reference to  FIGS. 4 and 5 , when the beam is in the position shown at  76  in  FIG. 4 , the central portion of the beam is centered on the core  71  of the output fiber  13 , and the output fiber  13  will be receiving a relatively high amount of energy from the beam. 
         [0020]    If the disk  26  is then rotated, causing the beam to move away from the position  76  in either direction along the path of travel  79 , then the central portion of the beam will move away from the core  71 , and the core  71  will receive progressively less energy as the beam moves progressively farther from the position  76  toward the position  77  along the path of travel  79 . When the beam is in the position  77 , the core  71  of the fiber  13  will be receiving little or no energy from the beam. Thus, the coupling efficiency between the input fiber  12  and the output fiber  13  can be continuously varied by rotating the disk  26 . 
         [0021]      FIG. 6  is diagrammatic fragmentary view of an optical apparatus  110  that is an alternative embodiment of the optical apparatus  10  of  FIG. 1 , that provides optical power transfer control, and that embodies aspects of the invention.  FIG. 7  is a diagrammatic fragmentary view that is identical to  FIG. 6 , except that the disk  26  is shown in a different operational position. The apparatus  110  of  FIGS. 5 and 6  is identical to the apparatus  10  of  FIGS. 1-3 , except for the differences discussed below. 
         [0022]    In the apparatus  110  of  FIGS. 6-7 , the disk  26  is oriented so that the side surface  31  thereon is perpendicular to the axis of rotation of the shaft  23  of the motor  21 . In addition, the fiber  12  and the lens  16  are positioned so that the path of travel  51  is always perpendicular to the side surface  31  of the disk  26 , in all rotational positions of the disk. In the apparatus  10  of  FIG. 1 , the initial angle of incidence  53  (θ 0 ) will vary. In contrast, in the apparatus  110  of  FIGS. 6 and 7 , the initial angle of incidence will always be 0°, because the path of travel  51  is always perpendicular to the surface  31 . Substituting zero for θ 0  in equation (1) above, equation (1) simplifies down to equation (2) below: 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       
                         δ 
                         = 
                           
                          
                         
                           
                             
                               sin 
                               
                                 - 
                                 1 
                               
                             
                              
                             
                               ( 
                               
                                 
                                   
                                     n 
                                     disk 
                                   
                                   
                                     n 
                                     air 
                                   
                                 
                                 * 
                                 sin 
                                  
                                 
                                   { 
                                   
                                     
                                       
                                         sin 
                                         
                                           - 
                                           1 
                                         
                                       
                                        
                                       
                                         [ 
                                         
                                           
                                             
                                               n 
                                               air 
                                             
                                             
                                               n 
                                               disk 
                                             
                                           
                                           * 
                                           
                                             sin 
                                              
                                             
                                               ( 
                                               0 
                                               ) 
                                             
                                           
                                         
                                         ] 
                                       
                                     
                                     - 
                                     σ 
                                   
                                   } 
                                 
                               
                               ) 
                             
                           
                           - 
                         
                       
                     
                   
                   
                     
                       
                           
                          
                         
                           
                             sin 
                             
                               - 
                               1 
                             
                           
                            
                           
                             ( 
                             
                               
                                 
                                   n 
                                   disk 
                                 
                                 
                                   n 
                                   air 
                                 
                               
                               * 
                               sin 
                                
                               
                                 { 
                                 
                                   
                                     sin 
                                     
                                       - 
                                       1 
                                     
                                   
                                    
                                   
                                     [ 
                                     
                                       
                                         
                                           n 
                                           air 
                                         
                                         
                                           n 
                                           disk 
                                         
                                       
                                       * 
                                       
                                         sin 
                                          
                                         
                                           ( 
                                           0 
                                           ) 
                                         
                                       
                                     
                                     ] 
                                   
                                 
                                 } 
                               
                             
                             ) 
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                           
                          
                         
                           - 
                           
                             
                               sin 
                               
                                 - 
                                 1 
                               
                             
                              
                             
                               ( 
                               
                                 
                                   
                                     n 
                                     disk 
                                   
                                   
                                     n 
                                     air 
                                   
                                 
                                 * 
                                 sin 
                                  
                                 
                                   { 
                                   σ 
                                   } 
                                 
                               
                               ) 
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
         [0023]    The optical disk  26  in the disclosed embodiments is significantly cheaper than a variable density filter of a type used to carry out optical power transfer in pre-existing systems. Moreover, such a pre-existing filter absorbs energy from the radiation passing through it, whereas the disk  26  does not. 
         [0024]    In the disclosed embodiments, the disk  26  is rotated by the rotating shaft  23  of the motor  21 , under control of the control circuit  22 . However, it would alternatively be possible to omit the motor  21  and the control circuit  22 , and to manually adjust the position of the disk  26 . As still another alternative, it would be possible to replace the motor  22  with a not-illustrated linear motor, and to replace the disk  26  with a not-illustrated optical strip that is disposed in the converging beam rather than the collimated beam, the strip having a thickness that increases progressively in a direction lengthwise of the strip. 
         [0025]    Although a selected embodiment has 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.