Patent Application
20090279171
This invention relates in general to optical systems and, more particularly, to techniques for providing an adjustable optical delay.
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.
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.
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:
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.
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.
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.
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.
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.
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.
In addition to the linear motor 31 and the support 32, the apparatus 110 of
The apparatus 110 of
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
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
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.
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.
