Abstract:
An optical structure routes radiation from an optical input to an optical output, the radiation being successively reflected by orthogonal first, second and third reflective surfaces of a linearly movable section, and departing the section in a departure direction substantially opposite its arrival direction. The section can move approximately parallel to the arrival direction with respect to at least one of the optical input and optical output. A different aspect involves: routing radiation from an optical input to an optical output, including reflecting this radiation successively from orthogonal first, second and third reflective surfaces of a section of the structure, the radiation departing the section in a departure direction substantially opposite its arrival direction; and supporting the section for approximately linear movement approximately parallel to the arrival direction with respect to at least one of the optical input and optical output.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates in general to optical systems and, more particularly, to techniques for providing an adjustable optical delay. 
       BACKGROUND 
       [0002]    In optical systems, it is sometimes desirable to have an optical delay that can be adjusted. One known approach is to fixedly mount two planar mirrors on a movable support, so that the mirrors form an angle of 90° with respect to each other. Radiation exiting an end of a first optical fiber is passed through a collimating lens, is then successively reflected by the two mirrors, is then passed through an imaging lens, and then enters an end of a second optical fiber. The support for the mirrors can be moved toward and away from the ends of the optical fibers, in order to increase or decrease the length of the optical path, thereby increasing or decreasing the amount of optical delay. In this pre-existing system, the mirrors must be extremely precisely aligned with respect to each other, with respect to the lenses, and with respect to the ends of the optical fibers. Further, the support for the mirrors must move in a manner that is extremely precise, in order to accurately maintain all of these alignments. 
         [0003]    Although systems of this type have been generally adequate for their intended purposes, they have not been satisfactory in all respects. For example, they are extremely sensitive to mirror alignment, and to any tilt or tip of the support for the mirrors. Consequently, in order to achieve the necessary precision, these systems tend to be relatively expensive. Moreover, over time, normal operational wear and tear can lead to play in the movement of the support, and/or misalignment of the mirrors, thereby necessitating either recalibration, and/or replacement of part or all of the structure that supports and moves the mirrors. 
     
    
     
       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 perspective view of an optical apparatus that provides an adjustable optical delay, and that embodies aspects of the invention. 
           [0006]      FIG. 2  is a diagrammatic perspective view of an apparatus that is an alternative embodiment of the apparatus of  FIG. 1 , and that embodies aspects of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0007]      FIG. 1  is diagrammatic perspective view of an optical apparatus  10  that provides an adjustable optical delay, and that embodies aspects of the invention. The apparatus  10  includes a base  16 . An optical input fiber  21  has a terminator  23  at one end, and an optical output fiber  22  has a terminator  24  at one end. The terminators  23  and  24  are spaced a short distance from each other, and are each fixedly secured to one end of the base  16  by not-illustrated brackets. 
         [0008]    A linear motor  31  of a known type is fixedly secured to the base  16 , near an end of the base remote from the terminators  23  and  24 . A support  32  is provided adjacent the linear motor  31 . The linear motor  31  can selectively effect linear movement of the support  32  in directions identified by a double-headed arrow  34 . 
         [0009]    A member  41  is fixedly secured on the support  32 , for movement with the support in the directions  34 . The member  41  has a recess in a side thereof facing the terminators  23  and  24 , the recess being defined by three reflective planar surfaces  42 ,  43  and  44 . Each of the surfaces  42 ,  43  and  44  is perpendicular to the other two. Thus, the three surfaces  42 - 44  collectively define a shape that is equivalent to one corner of a cube. 
         [0010]    A collimating lens  51  is fixedly supported on the base  16  by a not-illustrated bracket, at a location that is near the terminator  23 , and that is optically between the terminator  23  and the member  41 . Similarly, an imaging lens  52  is fixedly supported on the base  16  by a not-illustrated bracket, at a location that is near the terminator  24 , and that is optically between the terminator  24  and the member  41 . 
         [0011]    When radiation exits the input fiber  21  through the terminator  23 , it follows a path of travel  56 . This path of travel extends from the terminator  23  through the lens  51  to the member  41 , approximately parallel to the directions  34 . The lens  51  collimates radiation passing through it. When the radiation reaches the member  41 , it is successively reflected by the three surfaces  42 ,  43  and  44 . One of the inherent properties of this configuration of three orthogonal surfaces is that, after successive reflection by all three surfaces, the radiation will depart the member  41  in a direction that is parallel to and precisely opposite the direction in which it arrived. This will be the case even if the member  41  is misaligned with respect to the arriving radiation, provided the radiation is successively reflected by all three of the surfaces. Thus, the directions of linear movement  34  of the member  41  do not have to be precisely parallel to the directions in which radiation arrives at and departs from the member  41 . 
         [0012]    The radiation departing the member  41  continues along the path of travel  56 , and passes through the imaging lens  52 . The lens  52  takes this collimated radiation, and images it toward the terminator  24 . The radiation then enters the end of output fiber  22  through the terminator  24 . 
         [0013]    The linear motor  31  can be selectively activated in order to move the support  32  and the member  41  either away from or toward the terminators  23  and  24 , parallel to the directions  34 . As the member  41  is moved away from the terminators  23  and  24 , the length of the optical path of travel  56  is increased, with a corresponding increase in the optical delay imparted to radiation traveling along the path of travel. Conversely, when the support  32  and the member  41  are moved toward the terminators  23  and  24 , the length of the optical path of travel  56  is decreased, with a corresponding decrease in the optical delay imparted to radiation traveling along the path of travel. The amount of adjustability needed for the delay will determine the length of linear movement needed for the support  32  and the member  41 . It should be noted that the length of the optical path of travel increases or decreases by an amount that is twice the distance moved by the member  41 . As a result of this “folding” of the optical path of travel, the overall apparatus  10  is physically smaller than it otherwise would be. Also, by reducing the amount of movement needed from the member  41  in order to achieve a given change in the optical delay, the apparatus can be adjusted more quickly to effect that change in the delay. 
         [0014]      FIG. 2  is a diagrammatic perspective view of an apparatus  110  that is an alternative embodiment of the apparatus  10  of  FIG. 1 . Parts in  FIG. 2  that are identical to parts in  FIG. 1  are identified with the same reference numerals. The following discussion is directed primarily to differences between the two embodiments. 
         [0015]    In addition to the linear motor  31  and the support  32 , the apparatus  110  of  FIG. 2  also includes a further linear motor  131  and a further support  132 . The support  132  is positioned closer to the terminators  23  and  24  than the support  32 . The linear motor  131  can effect reciprocal linear movement of the support  132 , in directions  134  that are approximately parallel to the directions of movement  34  of the support  32 . 
         [0016]    The apparatus  110  of  FIG. 2  includes two members  136  and  146  that are each identical to the member  41 . The member  136  is fixedly mounted on the support  132 , and is oriented so that its recess faces away from the terminators  23  and  24 . The member  146  is fixedly mounted on the support  32 , at a location spaced a short distance laterally from the member  41 , with its recess facing toward the terminators  23  and  24 . 
         [0017]    In operation, radiation exiting the input fiber  22  through terminator  23  passes through the collimating lens  51 , travels to and is successively reflected by the three surfaces in the recess of the member  41 , then travels to and is successively reflected by the three surfaces in the recess of member  136 , then travels to and is successively reflected by the three surfaces in the recess of member  146 , then passes through the imaging lens  52 , and then enters the end of output fiber  22  through the terminator  24 . In order to increase the optical delay imparted to radiation traveling along the path of travel  56  in apparatus  110 , the linear motor  31  can be selectively used to move the members  41  and  146  away from the terminators  23  and  24 , and/or the linear motor  131  can be selectively used to move the member  136  toward the terminators  23  and  24 . Conversely, in order to decrease the optical delay imparted to radiation by the apparatus  110 , the linear motor  31  can be selectively used to move the members  41  and  146  toward the terminators  23  and  24 , and/or the linear motor  131  can be selectively used to move the member  136  away from the terminators  23  and  24 . As a result of this “folding” of the optical path of travel, the overall apparatus  110  is physically smaller than it otherwise would be. Also, by reducing the amount of movement needed from the members  41 ,  136  and  146  in order to achieve a desired change in the optical delay, and by providing multiple members  41 ,  136  and  141  that can be moved simultaneously, the apparatus can be adjusted more quickly to effect a desired change in the delay. Although  FIG. 1  shows one member  41 , and  FIG. 3  shows three members  41 ,  136  and  146 , it would alternatively be possible to provide two such members, or to provide four or more such members. 
         [0018]    As discussed above, the members  41 ,  136  and  146  each output radiation in a direction exactly opposite and parallel to the direction in which that radiation arrived, so long as the radiation reflects successively off all three of the surfaces in the recess of the member. Consequently, the directions of movement  34  and  134  of the supports  32  and  132  do not have to be precisely aligned with respect to each other, or with respect to the directions of travel of radiation arriving at these members. Moreover, in regard to the mounting of the members  41 ,  136  and  146  on the supports  32  and  132 , none of the members  41 ,  132  and  146  needs to be precisely aligned with respect to either of the directions of travel  34  and  134 , or with respect to the directions of travel of radiation arriving at these members. It is only necessary that there be sufficient alignment so that radiation traveling along the path of travel  56  will be successively reflected by all three surfaces on each of the members  41 ,  136  and  146 , in all operational positions of these members. Consequently, the apparatus  10  of  FIG. 1  and the apparatus  110  of  FIG. 2  do not require highly precise tolerances of the type that are essential in pre-existing systems. As a result, the apparatus  10  and the apparatus  110  are each cheaper than pre-existing systems, and less likely to go out of alignment over time due to factors such as temperature, or normal wear and tear. 
         [0019]    In the disclosed embodiments, the recesses in the members  41 ,  136  and  146  are each an “open” cube corner, in that there is no structure within the recess, and radiation is successively reflected by all three surfaces without passing through any other structure. This configuration has the benefit of avoiding changes to the phase/polarization of the radiation. Alternatively, however, it would be possible to replace any or all of the members  41 ,  136  and  146  with a prism having three exterior surfaces that are each coated so as to make the surface reflective within the prism. Radiation would enter the prism, be successively reflected within the prism by each of the three surfaces, and then exit the prism. The use of such prisms may be acceptable for applications where changes in phase/polarization are not of significant concern. 
         [0020]    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.