Abstract:
A beam steering module comprised of a mirror stack array in close proximity to a collimator array controllably steers photons along two axis and in a direction substantially less than 90 degrees to the collimator orientation. Several configurations of the module are described using single and double axis mirror rotation and relay optics. Optical telecommunications switches are shown using modules coupled to each other along flat and curved surfaces, with and without use of fold mirror and enabling a plurality of configuration options including photodetector optical power monitoring schemes that require no external power taps.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a continuation-in-part of co-pending U.S. patent application Ser. No. 09/536,164 to Michael J. Daneman, Berhang Behin, and Satinderpall S. Pannu, filed Mar. 25, 2000 and entitled “Apparatus and method for 2-Dimensional Steered-Beam N×M Optical Switch Using Single-Axis Mirror Arrays and Relay Optics”, which is incorporated herein by reference. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates generally to fiber optic communications. More particularly, the invention relates to optical routing.  
         BACKGROUND ART  
         [0003]    Modern fiber optical communications systems direct optical signals over multiple fibers. Such systems require optical switches to direct light beams from any given fiber in an input fiber array to any given fiber in an output array. One class of optical switches uses an approach called beam steering. In beam steering, the light from the fiber is selectively deflected or steered by one or more movable optical element from the input fiber to the output fiber. Suitable optical elements include microelectromechanical system (MEMS) mirrors. MEMS mirrors are usually actuated by magnetic interaction, electrostatic, or piezoelectric interaction. Typically, two sets of moveable mirrors are used to steer the beam. Each fiber has a small “acceptance window”. The fiber only efficiently couples light that is incident within a narrow range of angles and positions. Although a single mirror will generally direct the beam from an input fiber to the correct output fiber, two mirrors ensure that the light beam enters the output fiber at the correct angle. If the beam makes too large an angle with the axis of the fiber, light from the beam will not couple properly to the fiber, i.e. there will be high losses.  
           [0004]    Optical switches using the steering-beam approach have been demonstrated in two primary implementations. The first uses linear arrays of mirrors with a single angular degree of freedom. Combining two such mirror arrays as shown in FIG. 1 allows an implementation of an N×N optical switch, where the number of input and output channels is equal to the number of mirrors in each array. The first array steers an optical beam from an input fiber to the appropriate mirror on the second array, which then steers the beam into the corresponding output fiber. This implementation uses simple single-axis mirrors; however, it is limited in its scalability since the optical path between fibers becomes unreasonably large for large port counts (e.g. &gt;32×32), increasing the loss of the switch.  
           [0005]    The second implementation depicted in FIG. 2 uses two sets of 2-dimensional mirror arrays, each mirror having two angular degrees of freedom. The input and output fibers are each also arranged in a 2-dimensional grid with the same dimension as the mirror arrays. The mirrors in the first mirror array steer the optical beams from the fibers onto the appropriate mirror in the second mirror array which then steers the beam into the corresponding fiber. This approach is considerably more scalable, since, due to its 2-dimensional layout, the size of the mirror and fiber arrays grows as the square root of the number of input/output ports, which is much slower than in the case of a 1-dimensional grid. Therefore, switches with much larger port count (&gt;2000×2000) are possible. However, this implementation requires the mirrors to rotate about two different axes. Such mirrors are considerably more difficult to design, fabricate, and control.  
           [0006]    Prior art beam steering approaches as shown in FIG. 1 typically deflect light ˜90 degrees to another deflector which deflects the light at an offset of 90 degrees such that input and output fiber arrays are substantially parallel. Such beam steering optical switches deflect photons from an input to the output mirror array where the deflected light from the input mirror array causes the beam to be substantially perpendicular to the input fiber array. These designs are not modular, are limited in the number of ports they can physically occupy, and are subject to a fixed geometry.  
           [0007]    Another disadvantage of existing optical switches is that they tend to be monolithic in design, i.e., the mirror arrays are fixed components of the switch that are neither removable nor interchangeable. As a result, a prior art switch cannot easily be reconfigured or repaired.  
           [0008]    There is a need, therefore, for a beam steering apparatus that overcomes the above disadvantages.  
         SUMMARY  
         [0009]    These disadvantages associated with the prior art may be overcome by a beam steering module. The steering module generally comprises first and second N×M arrays of single axis mirrors. The mirrors in the first array rotate about a particular axis while the mirrors in the second array rotate about an axis different from the first axis (. Relay optics may be disposed between the two arrays image the first mirror array onto the second mirror array such that the beam angle may be controlled with respect to both axes by adjusting the angle of the appropriate mirrors in the first and second mirror grids.  
           [0010]    Two steering modules may be combined to form a beam steering system. With two modules, it is possible to completely determine, at the plane of the output fiber grid, the position and angle of an optical beam emerging from any of the input fibers.  
           [0011]    Embodiments of the steering modules of the present invention may be used to selectively couple light from an input fiber in an N×N input fiber module array to any output fiber in an M×M output fiber module array, or from an input fiber to an output fiber in an N×N module array. The beam steering modules of the present invention may be used interchangeably to achieve full-duplex operation modules functioning as inputs and outputs. 
       
    
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0012]    [0012]FIG. 1 depicts a one-dimensional beam steering apparatus according to the prior art;  
         [0013]    [0013]FIG. 2 depicts an isometric view of a two-dimensional beam steering apparatus according to the prior art;  
         [0014]    [0014]FIG. 3 depicts a beam steering module according to a first embodiment of the present invention;  
         [0015]    FIGS.  4  depicts an isometric view of a beam steering apparatus according to a second embodiment of the present invention;  
         [0016]    [0016]FIG. 5 depicts a schematic diagram depicting a modular optical switch according to a first alternative version of a third embodiment of the invention;  
         [0017]    FIGS.  6 A- 6 B depicts a modular optical switch according to a second alternative version of the third embodiment of the invention;  
         [0018]    [0018]FIG. 7A depicts a schematic diagram of a modular optical switch employing stacked beam steering modules according to a third alternative version of the third embodiment of the invention;  
         [0019]    [0019]FIG. 7B depicts a schematic diagram of a modular optical switch employing offset stacked beam steering modules according to a fourth alternative version of the third embodiment of the invention;  
         [0020]    [0020]FIG. 7C depicts a schematic diagram of a modular optical switch employing beam steering modules distributed along a curve according to a fifth alternative version of the third embodiment of the invention;  
         [0021]    [0021]FIG. 7D depicts a schematic diagram of a modular optical switch employing offset beam steering modules distributed along a curve according to a sixth alternative version of the third embodiment of the invention;  
         [0022]    [0022]FIG. 7E depicts a schematic diagram of a modular optical switch employing stacked beam steering modules with a fold deflector according to a seventh alternative version of the third embodiment of the invention;  
         [0023]    [0023]FIG. 7F depicts a schematic diagram of a modular optical switch employing stacked beam steering modules with a curved fold deflector according to a eighth alternative version of the third embodiment of the invention;  
         [0024]    [0024]FIG. 7G depicts a schematic diagram of a modular optical switch employing a curved array of beam steering modules with a fold deflector according to a ninth alternative version of the third embodiment of the invention;  
         [0025]    [0025]FIG. 7H depicts a schematic diagram of a modular optical switch employing a curved array of beam steering modules with a curved fold deflector according to a tenth alternative version of the third embodiment of the invention;  
         [0026]    [0026]FIG. 8 depicts a schematic diagram of a first alternative version of an optical module according to a fourth embodiment of the invention;  
         [0027]    [0027]FIG. 9 depicts a schematic diagram of a second alternative version of an optical module according to the fourth embodiment of the invention;  
         [0028]    [0028]FIG. 10 depicts a cross-sectional schematic diagram of a third alternative version of an optical module according to the fourth embodiment of the invention.  
         [0029]    [0029]FIG. 11 depicts a cross-sectional schematic diagram of a fourth alternative version of an optical module according to the fourth embodiment of the invention;  
         [0030]    [0030]FIG. 12 depicts a cross-sectional schematic diagram of a fifth alternative version of an optical module according to the fourth embodiment of the invention;  
         [0031]    [0031]FIG. 13 depicts a cross-sectional schematic diagram of a sixth alternative version of an optical module according to the fourth embodiment of the invention;  
         [0032]    [0032]FIG. 14 depicts a cross-sectional schematic diagram of a seventh alternative version of an optical module according to the fourth embodiment of the invention;  
         [0033]    [0033]FIG. 15 depicts an isometric schematic diagram of a eighth alternative version of an optical module according to the fourth embodiment of the invention;  
         [0034]    [0034]FIG. 16 depicts an isometric schematic diagram of an optical switch employing two modules of the type shown in FIG. 15.  
         [0035]    [0035]FIG. 17 depicts a cross-sectional schematic diagram of an optical switch according to a first alternative version of a fifth embodiment of the present invention;  
         [0036]    [0036]FIG. 18 depicts a cross-sectional schematic diagram of an optical switch employing a fold deflector according to a second alternative version of a fifth embodiment of the present invention;  
         [0037]    [0037]FIG. 19 depicts a cross-sectional schematic diagram of an optical switch employing dual axis deflectors with a fold deflector according to a fourth alternative version of a fifth embodiment of the present invention;  
         [0038]    [0038]FIG. 20 depicts a simplified schematic diagram of an optical beam steering module according to an embodiment of the present invention;  
         [0039]    [0039]FIG. 21 depicts a simplified schematic diagram of an optical switch according to an embodiment of the present invention;  
         [0040]    [0040]FIG. 22 depicts a simplified isometric diagram of an optical switch according to an embodiment of the present invention; and  
         [0041]    [0041]FIG. 23 depicts a cross-sectional diagram of the optical switch of FIG. 23. 
     
    
     DETAILED DESCRIPTION  
       [0042]    Although the following detailed description contains many specifics for the purposes of illustration, anyone of ordinary skill in the art will appreciate that many variations and alterations to the following details are within the scope of the invention. Accordingly, the following preferred embodiment of the invention is set forth without any loss of generality to, and without imposing limitations upon, the claimed invention.  
         [0043]    The optical switch system according to embodiments of the present invention may switch light from any of a set of input fibers into any of a set of output fibers in a non-blocking fashion using beam steering modules.  
         [0044]    Steering modules can switch a plurality of paths independent of the current configuration of the switch. FIG. 3 depicts a steering module  10  according to a first embodiment of the present invention. Module  10  may generally comprise beam steering element  12  configured with at least one pair of deflective elements  14 . Photons may enter the module through a collimator  16  and coupled through a first deflective element  18  which may steer the photons along an axis to a second deflective element  20  which may also steer the photons along a second axis. FIG. 4 shows an alternate configuration having one fixed deflective element  22  coupled to a double-gimbaled deflector  24 . Both module configurations are capable of steering photons along two axis in a manner substantially parallel to the orientation of the input collimator.  
         [0045]    Generally, the deflective elements are individually addressable, created using MEMs fabrication methods and actuated using a variety of known actuation methods, including but not limited to, electrostatic and magnetic types.  
         [0046]    The present invention includes a third embodiment directed to a modular optical switch. By way of example, FIG. 5 schematically depicts a modular switch  500  according to first alternative version of the third embodiment. The switch  500  may generally comprise a first beam steering module  502  optically coupled to a second beam steering module  504 . First and second sets of optical fibers  501 ,  505  may be respectively coupled to the first and second modules  502 ,  504  e.g., via one or more I/O ports. The beam steering modules  502 ,  504  may respectively include one or more beam steering elements  506 ,  508 . The I/O ports may include individual or arrayed collimators to facilitate couple of optical signals between the fibers  501 ,  505  and the beam steering elements  506 ,  508 . The beam steering elements  506 ,  508  may deflect one or more optical signals  503  in two dimensions such that an optical signal may be selectively routed between any of the first fibers  501  to any of the second fibers  505 . The beam steering elements  506 ,  508  may be configured such that the modules  502 ,  504  are substantially horizontally opposed, e.g., with the I/O ports on the first module  502  substantially parallel to the I/O ports on the second module  504 .  
         [0047]    The first and second modules  502 ,  504  may be operated under the direction of a controller  510 . The controller may be coupled to the beam steering elements  506 ,  508  by electrical optical or mechanical linkage. The controller may be implemented in hardware, software, firmware or some combination of these. The controller  510  may provide control signals to the beam steering elements to allow selective coupling of the optical signals  503  between the first module  502  and the second module  503  or vice versa.  
         [0048]    The modules  502 ,  504  can co-operate interchangeably with each other, and with fixed or movable deflector elements, in several ways. First, the modules  502 ,  504  may be removably attached to a frame, housing or substrate such that may be replaced to facilitate repair or upgrade. Second, the modules  502 ,  504  may be of a standardized configuration, e.g. with standardized dimensions, numbers of I/O ports, to facilitate design of new optical switches and other beam steering devices. Third, the beam steering elements  506 ,  508  may be removably attached to the modules  502 ,  504  to facilitate repair or upgrade. Fourth, the beam steering elements may be of a standardized configuration to facilitate the design of new optical switches and other devices.  
         [0049]    Although, FIG. 5 depicts a switch having horizontally opposed modules, the invention is in no way limited to this configuration. By way of example, FIG. 6A depicts an optical switch  600  according to a second alternative version of the third embodiment. The optical switch  600  may generally include a first beam steering module  602  optically coupled to a second beam steering module  604  via a fold deflector  610 . First and second sets of optical fibers  601 ,  605  may be respectively coupled to the first and second modules  602 ,  604  e.g., via one or more I/O ports. The beam steering modules  602 ,  604  may respectively include one or more beam steering elements  606 ,  608  optically coupled to each other via the fold deflector  610 . The beam steering elements  606 ,  608  may deflect one or more optical signals  603  in two dimensions such that an optical signal may be selectively routed between any of the first fibers  601  to any of the second fibers  605  via the fold deflector  610 .  
         [0050]    The fold deflector  610  may be a reflective element, such as a flat or curved mirror. Alternatively, the fold deflector  610  may be a refractive element such as a prism or a diffractive element such as a grating. Furthermore, the fold deflector  610  may include some combination reflective, refractive and diffractive elements. The fold deflector  610  may allow flexibility in the spatial positioning of the modules  602 ,  604  within the switch  600 . Alternatively, as shown in FIG. 6B a fold deflector  624  may be used with a single module  622  to provide an optical switch  620 . Fold deflector  624  may be made of a partially transparent material to allow a small percentage of light to pass behind the mirror into a photodetector array, and the photodetector array may be connected to a switch control  510  for controllably operating the input and output beam steering elements in response to the power monitoring signals generated therefrom said photodetector array.  
         [0051]    One alternative method for controllably operating the input and output beam steering elements in response to power monitoring includes an array of photodetectors clusters situated around each collimator. This arrangement may track photons not coupled into an output collimator and provide beam steering telemetry to the switch control for calibrating the input and output beam steering elements for maximum coupling. A photodetector array can be designed with a mask that centers each cluster array at referential points at locations corresponding to each collimator. A cluster may be comprised of a plurality of photodetectors, CCD, three or four individually addressable detectors. When using individually addressable photodetectors, optical insertion losses can be minimized by drilling or etching holes in precise referential locations corresponding to the location of the collimators on the module to allow the light to pass through the center of the cluster into the collimator.  
         [0052]    Although FIG. 5 and FIG. 6 depict switches having only two modules, the present invention is in no way limited to these particular configurations. By way of example, FIG. 7A depicts an optical switch  700  according to a third alternative version of the third embodiment. The optical switch  700  may generally comprise a first stack  701  of N beam steering modules  702   1 ,  702   2  . . .  702   N , where N is an integer greater than or equal to 1. The modules in the first stack  701  may be optically coupled to a second stack  703  of M beam steering modules  704   1 ,  704   2  . . .  704   M , where N is an integer greater than or equal to 1. M and N may be the same or they may be different numbers. Note that if each of the modules is capable of a sufficiently large angle of deflection of optical signals  705  any module in the first stack may be coupled to any module in the second stack. Although one-dimensional stacks  701 ,  703  are depicted in FIG. 7A for the sake of clarity, the modules may alternatively be arranged in two-dimensional arrays.  
         [0053]    [0053]FIG. 7A depicts a modular switch in which the beam steering elements may scan to the left and right of a center rest position. An example of such a beam steering element could include an array of MEMs mirrors that operate by “push-pull” actuation. Alternatively, the beam steering elements may scan “one way,” i.e., only in a sector to the left, or only to the right, of an end rest position. In such a case it may be desirable to offset the alignment of the first and second stacks of modules. FIG. 7B depicts an optical switch  710  according to a fourth alternative version of the third embodiment wherein the beam steering modules are offset. The optical switch  710  may generally comprise a first stack  711  of N beam steering modules  712   1 ,  712   2  . . .  712   N , where N is an integer greater than or equal to 1. The modules in the first stack  711  may be optically coupled to a second stack  713  of M beam steering modules  714   1 ,  714   2  . . .  714   M . The modules in the second stack  713  may be in an offset alignment with respect to the modules in the first stack. The offset alignment may compensate higher density port count when steering optical signals  715  with “one way” scanning capability in the beam steering modules. Optical signals corresponding to the rest and maximum deflections are shown for modules at opposite ends of the two stacks. Note that if each of the modules is capable of a sufficiently large angle of deflection of the optical signals  715  any module in the first stack may be coupled to any module in the second stack. Although one-dimensional stacks  711 ,  713  are depicted in FIG. 7B for the sake of clarity, the modules may alternatively be arranged in two-dimensional arrays.  
         [0054]    The modular switches depicted in FIGS. 7A, 7B may have substantially linear stacks or planar arrays of modules. In some applications, if the number of modules N becomes sufficiently large modules at opposite ends of the stacks may not be able to “see” one another. In such applications it may be desirable to distribute the stacks along one or more curves. FIG. 7C depicts an optical switch  720  according to a fifth alternative version of the third embodiment wherein the beam steering modules in at least one stack are distributed along a curve. The optical switch  720  may generally comprise a first stack  721  of N beam steering modules  722   1 ,  722   2  . . .  722   N , distributed substantially along a curve  727  where N is an integer greater than or equal to 1. The modules in the first stack  721  may be optically coupled to a second stack  723  of M beam steering modules  724   1 ,  724   2  . . .  724   M . The modules in the second stack  723  may be distributed along a second curve  729 . The curved stacking of the modules can facilitate coupling between modules at extreme opposite ends of the stacks. By way of example, the curves  727 ,  729  may be in the shape of a segment of a circle, parabola, ellipse, hyperbola, cycloid, or any other suitable curved shape. Alternatively, one of the curves  727 ,  729  could be a segment of a straight line.  
         [0055]    Although one-dimensional curved stacks are depicted in FIG. 7C for the sake of clarity, the switch  720  may employ two-dimensional curved arrays of modules, e.g. distributed across a curved surface. By way of example, the shape of the curved surface may be cylindrical, spherical, paraboloidal, ellipsoidal, hyperboloidal or any other suitable curved three-dimensional shape. Alternatively, one of the arrays of modules could be arranged in a planar array.  
         [0056]    [0056]FIG. 7D depicts an optical switch  730  according to a sixth alternative version of the third embodiment wherein offset beam steering modules distributed along a curve. The optical switch  730  may generally comprise a first stack  731  of N beam steering modules  732   1 ,  732   2  . . .  732   N , distributed substantially along a curve  737 . The modules in the first stack  731  may be optically coupled to a second stack  733  of M beam steering modules  734   1 ,  734   2  . . .  734   M . N and M are integers greater than or equal to 1. The modules in the second stack  733  may be distributed along a second curve  739 . The first and second curves  737 ,  739  may be in an offset alignment with respect to each other to facilitate coupling between modules at extreme opposite ends of the stacks By way of example, the curves  737 ,  739  may be in any shape, and not limited to those described above with respect to FIG. 7C.  
         [0057]    Multiple beam steering modules may be incorporated into an optical switch with a fold deflector. FIG. 7E depicts a schematic diagram of a modular optical switch  740  employing multiple beam steering modules with a fold deflector according to a seventh alternative version of the third embodiment of the invention. By way of example, the switch  740  includes first and second arrays  741 ,  743  of N and M modules  742   1 - 742   N ,  744   1 - 744   M  respectively, where N and M are integers greater than or equal to 1. The modules in the arrays  741 , 743  may be optically coupled to each other via a fold deflector  746 . In the exemplary version depicted in FIG. 7E, the fold deflector  746  may be flat surface coated mirror. Alternatively the fold deflector  746  may be a refractive element, such as one or more prisms.  
         [0058]    The fold deflector may alternatively be curved. FIG. 7F depicts a schematic diagram of a modular optical switch  750  that combines stacked beam steering modules with a curved fold deflector according to a eighth alternative version of the third embodiment of the invention. By way of example, the switch  750  may include first and second arrays  751 ,  753  of N and M modules  752   1 - 752   N ,  754   1 - 754   M  respectively, where N and M are integers greater than or equal to 1. The modules in the arrays  751 ,  753  may be optically coupled to each other via a curved fold deflector  746 . In the exemplary version depicted in FIG. 7F, the fold deflector  756  is a curved surface coated mirror. Alternatively the fold deflector  756  may include a refractive element, such as one or more prisms.  
         [0059]    Fold deflectors may also be combined with modules displaced along a curve or spline. By way of example, FIG. 7G depicts a schematic diagram of a modular optical switch  760  that employs a curved array of beam steering modules with a fold deflector according to a ninth alternative version of the third embodiment of the invention. By way of example, the switch  760  may include first and second arrays  761 ,  763  of N and M modules  762   1 - 762   N ,  764   1 - 764   M  respectively, where N and M are integers greater than or equal to 1. The modules in the arrays  761 ,  763  are distributed along curves  767 ,  769  respectively. The curves  767 ,  769  may have any 2-dimensional or 3-diemensional curved shape, including those described above with respect to FIG. 7C. Alternatively, the modules  762   1 - 762   N ,  764   1 - 764   M  may be distributed along the same curved surface or different portions of the same curved surface. The modules in the arrays  761 ,  763  may be optically coupled to each other via a fold deflector  766 . In the exemplary version depicted in FIG. 7G, the fold deflector  766  is a flat mirror. Alternatively the fold deflector  766  may include a refractive element, such as one or more prisms.  
         [0060]    Fold deflector  766  may be made of a partially transparent material to allow a small percentage of light to pass behind the mirror into a photodetector array, and the photodetector array may be connected to a switch control  510  for controllably operating the input and output beam steering elements in response to the power monitoring signals generated therefrom said photodetector array.  
         [0061]    Multiple modules may be displaced along a curve or spline and alternatively be combined with a curved fold deflector. FIG. 7H depicts a schematic diagram of a modular optical switch  770  employing a curved array of beam steering modules with a curved fold deflector according to a tenth alternative version of the third embodiment of the invention. By way of example, the switch  770  may include first and second arrays  771 ,  773  of N and M modules  772   1 - 772   N ,  774   1 - 754   M  respectively, where N and M are integers greater than or equal to 1. The modules in the arrays  771 ,  773  may be distributed along curves  777 ,  779  respectively. Alternatively, the modules  772   1 - 772   N ,  774   1 - 774   M  may be distributed along the same curved surface or different portions of the same curved surface. The curves  777 ,  779  may have any 2-dimensional or 3-diemensional curved shape, including those described above with respect to FIG. 7C. The modules in the arrays  771 ,  773  may be optically coupled to each other via a fold deflector  776 . In the exemplary version depicted in FIG. 7H, the fold deflector  776  may be a flat surface coated mirror. Alternatively the fold deflector  776  may include a refractive element, such as one or more prisms.  
         [0062]    Fold deflector  776  may be made of a partially transparent material to allow a small percentage of light to pass behind the mirror into a photodetector array, and the photodetector array may be connected to a switch control  510  for controllably operating the input and output beam steering elements in response to the power monitoring signals generated therefrom said photodetector array.  
         [0063]    Many different architectures are possible for the beam steering modules depicted in FIGS.  5 - 7 H. According to a fourth embodiment of the invention a beam steering module may include one or more beam steering elements that deflect optical signals in two dimensions. Such modules can cooperate interchangeably with one or more optical components in an optical beam steering device such as an optical switch, adaptive optics, steered beam optical display, or disk drive. The beam steering elements may include a first deflector array optically coupled to a second deflector array, wherein the first and second deflector arrays co-operate to steer an optical signal in two dimensions.  
         [0064]    [0064]FIG. 8 depicts a schematic diagram of a first alternative version of an optical module  800  according to a first version of the fourth embodiment of the invention. By way of example, the module  800  may generally include one or more beam steering elements, e.g., a stack of N beam steering elements  801   1  . . .  801   N . Each beam steering element may include a first array of one or more deflectors optically coupled to a second array of one or more deflectors. In the embodiment depicted in FIG. 8 the arrays may extend perpendicular to the plane of the drawing. The Module  800  may be coupled to one or more optical fibers  810   1  . . .  810   N , e.g., via individual collimators or by a collimator array.  
         [0065]    In the exemplary embodiment depicted in FIG. 8, first array may be an L×M array of x-deflectors  802   11  . . .  802   LM  configured to deflect light with respect to one or more first axes  804 . The second array may be a L′×M′ array of y-deflectors  806   11  . . .  806   LM  configured to deflect optical signals  811  with respect to one or more second axes  808 . L, M, L′ and M′ are all integers greater than or equal to one. According to one variation L=L′ and M=M′, however this need not be the case. The x-deflectors  802   11  . . .  802   LM  may deflect the optical signals  811  from the fibers  810  to one or more of the y-deflectors  806   11  . . .  806   L′M′ . The y-deflectors  806   11  . . .  806   L′M′  may deflect the optical signals  811  from the x-deflectors  802   11  . . .  802   LM  toward some other optical component, such as another module or a fixed fold mirror in the case of an optical switch. In the exemplary embodiment depicted in FIG. 8 the optical signals  811  enter and exit the modules  801   i  along substantially parallel paths. For the purposes of the present application, substantially parallel means that in traversing the modules  801   i  the angle of deflection of the optical signals  811  is less than 90°. This is particularly advantageous where, for example it is desired to configure two or more modules in horizontal opposition.  
         [0066]    By way of example and without loss of generality, the deflectors  802   11  . . .  802   LM ,  806   11  . . .  806   L′M′  may be mirrors that rotate about axes  804 ,  808  as shown by the arrows  805 ,  809  respectively. The first and second axes  804 ,  808  may be perpendicular to each other and may be referred to as the x- and y- axes respectively. The invention is not limited to the specific configuration of the x- and y- axis shown in FIG. 8. For example, the relative positions of the x-deflectors and the y-deflectors may be interchanged.  
         [0067]    Where two sets of deflectors are configured to rotate separately about different axes it is often desirable to optically couple relay optics to the deflectors. The relay optics may be placed between the x-deflectors and the y-deflectors. Such relay optics may include one or more lenses  820   1  . . .  820   N  or any of the alternative relay optics described above with respect to FIG. 2. In the particular version of the fourth embodiment depicted in FIG. 8, the deflectors  802   11  . . .  802   LM , may be in a one to one correspondence with the deflectors  806   11  . . .  806   L′M′ . For the purposes of the present applications a one-to-one correspondence means that each x-deflector  802   11  . . .  802   LM  is optically coupled to a different one of the y-deflectors  806   11  . . .  806   LM .  
         [0068]    The present invention is not limited to modules having single axis deflectors. Modules may be based on dual axis deflectors. FIG. 9 depicts a schematic diagram of an optical module  900  that employs dual axis deflectors according to a second alternative version of the fourth embodiment of the invention. By way of example, the module  900  may generally include one or more beam steering elements, e.g., a stack of N beam steering elements  901   1  . . .  901   N . The module  900  may be coupled to one or more optical fibers  910   1  . . .  910   N , e.g., via collimators. Each beam steering element  901   i  may include an L×M array of dual axis deflectors  902   11  . . .  902   LM  optically coupled to an L′×M′ array of fixed deflectors  906   11  . . .  906   L′M′ . L, M, L′ and M′ are all integers greater than or equal to one. According to one variation L=L′ and M=M′, however this need not be the case. The deflectors  902   11  . . .  902   LM  may be mirrors that rotate about x-axes  804 , and y-axes  808  as shown by the arrows  905 ,  909  respectively. The first and second axes  904 ,  908  may be perpendicular to each other and may be referred to as the x- and y- axes respectively. The fixed  906   11  . . .  906   L′M′  deflectors do not rotate, and may be comprised of one continuous deflector. By way of example, and without loss of generality, beam steering element  901   N  is depicted as including a single continuous deflector  907  coupled to all of the deflectors in an array  909  of dual axis deflectors. Furthermore, the invention is not limited to the specific configuration of the fixed and dual axis deflectors shown in FIG. 9. For example, the relative positions of the fixed deflectors and the dual axis deflectors may be interchanged.  
         [0069]    The dual axis deflectors  902   11  . . .  902   LM  may deflect one or more optical signals  911  from the fibers  910  to one or more of the fixed deflectors  906   11  . . .  906   L′M′ . The fixed deflectors  906   11  . . .  906   L′M′  may deflect the optical signals  911  from the x-deflectors  902   11  . . .  902   LM  toward some other optical component, such as another module in the case of an optical switch. The optical signals  911  may enter and exit the modules  901   i  along substantially parallel paths.  
         [0070]    Many variations are possible on the optical switches described with above with respect to FIGS. 8 and 9. For example the beam steering elements may include double-sided deflectors. FIG. 10 depicts a cross-sectional schematic diagram of an optical module  1000  that employs double sided deflectors according to a third alternative version of the fourth embodiment of the invention. The module  1000  may generally comprise a stack of N of beam steering elements  1001  containing double-sided arrays  1002  of deflectors  1003 . The deflectors  1003  in the double-sided arrays  1002  may include appropriate combinations of single axis deflectors, dual axis deflectors, or fixed deflectors.  
         [0071]    [0071]FIG. 11 depicts a cross-sectional schematic diagram of an optical module  1100  according to a fourth alternative version of the fourth embodiment of the invention. In this version, the module  1100  may include the beam steering elements  1201  having an array  1102  of double-sided elements single-axis  1103  sandwiched between two opposing arrays  1104 ,  1106  of single-sided elements. In the alternative version shown in FIG. 11, each of the double-sided elements  1102  may include an x-deflector  1105  on one side and a y-deflector  1107  on the other side. The x-deflector  1105  on the double-sided element  1103  may face a single sided y-deflector  1108  in the array  1104 . The y-deflector  1107  on the double-sided element  1103  may face a single sided x-deflector  1110  in the array  1106 . The arrays  1102 ,  1104 ,  1106  may extend perpendicular to the plane of the drawing M deflectors deep. Although a 1×M array is depicted in FIG. 11, the beam steering elements may alternatively contain L×M arrays. N beam steering elements may be stacked in the module to produce an N×L×M beam steering module.  
         [0072]    Other configurations of double-sided deflector arrays are possible. FIG. 12 depicts a cross-sectional schematic diagram of an optical module  1200  according to a fifth alternative version of the fourth embodiment of the invention. In this version, the module  1200  may include beam steering elements  1201  having an array  1202  of double-sided dual-axis elements  1203  sandwiched between two opposing arrays  1204 ,  1206  of single-sided fixed deflector elements. In the alternative version shown in FIG. 12, each of the double-sided dual-axis elements  1203  may include a first gimbaled xy-deflector  1205  on one side and a second gimbaled xy-deflector  1207  on the other side. The gimbaled xy-deflectors  1205 ,  1207  may face single sided fixed deflectors  1208 ,  1210  in the arrays  1204 ,  1206 . The fixed deflector arrays  1204 ,  1206  may each contain a single continuous deflector or individual deflectors coupled to the gimbaled xy deflectors  1205 ,  1207  in a one-to-one correspondence. The arrays  1202 ,  1204 ,  1206  may extend perpendicular to the plane of the drawing M deflectors deep. Although a 1×M array is depicted in FIG. 12, the beam steering elements may alternatively contain L×M arrays. N beam steering elements may be stacked in the module to produce an N×L×M beam steering module.  
         [0073]    The configuration depicted in FIG. 12 may be reversed. FIG. 13 depicts a cross-sectional schematic diagram of an optical module  1300  according to a sixth alternative version of the fourth embodiment of the invention. In this version, the module  1300  may include beam steering elements  1301  having an array  1302  of double-sided fixed elements  1303  sandwiched between two opposing arrays  1304 ,  1306  of single-sided dual-axis deflector elements. In the alternative version shown in FIG. 13, each of the double-sided fixed elements  1303  may include a first fixed deflector  1305  on one side and a second gimbaled fixed deflector  1307  on the other side. The fixed deflectors  1305 ,  1307  may face single sided gimbaled dual-axis (xy) deflectors  1308 ,  1310  in the arrays  1304 ,  1306 . The fixed deflector array  1302  may contain a single continuous deflector or individual deflectors coupled to the gimbaled xy deflectors  1308 ,  1310  in a one-to-one correspondence. The arrays  1302 ,  1304 ,  1306  may extend perpendicular to the plane of the drawing M deflectors deep. Although a 1×M array is depicted in FIG. 13, the beam steering elements may alternatively contain L×M arrays. N beam steering elements may be stacked in the module to produce an N×L×M beam steering module.  
         [0074]    There are still other variations on the beam steering modules of the fourth embodiment of the invention. FIG. 14 depicts a cross-sectional schematic diagram of a beam steering module  1400  according to a seventh alternative version of the fourth embodiment of the invention. The beam steering module  1400  may generally include a frame  1401  with first beam steering element having arrays of deflectors  1402  mounted to a first side  1411  of the frame  1401  and a second beam steering element having arrays of deflectors  1404  mounted to a second side  1413  of the frame  1401  opposite the first side  1411 . The first and second beam steering elements may be oriented in a staggered configuration that allows optical signals to between the arrays of deflectors  1402 ,  1404 . The frame  1401  may include a first set of holes  1403  opposite the beam steering elements  1402  that transmit optical signals through the first side of the frame  1401 . The frame  1401  may include a second set of holes  1405  opposite the beam steering elements  1404  that transmit optical signals. The deflectors  1402 ,  1404  may be of any of the types discussed above. For example the deflectors  1402 ,  1404  may respectively be x-deflectors and y-deflectors or vice versa. Alternatively, the deflectors  1402 ,  1404  may respectively be gimbaled dual-axis (xy) deflectors and fixed deflectors or vice versa.  
         [0075]    [0075]FIG. 15 depicts an isometric schematic diagram of an optical module  1500  that may use linear arrays of deflectors according to an eighth alternative version of the fourth embodiment of the invention. In this version, the module  1500  may include beam steering elements  1501  having a 1×M double-sided array  1502  containing deflectors  1505 ,  1507  sandwiched between two opposing 1×M arrays  1504 ,  1506  of single-sided deflectors  1508 ,  1510 . The arrays  1502 ,  1504  may be coupled to optical fiber arrays  1520   A ,  1520   B  e.g. via lens arrays  1530   A ,  153   B .  
         [0076]    The deflectors  1505 ,  1507  may face single sided deflectors  1508 ,  1510  in the arrays  1504 ,  1506 . The deflectors  1505 ,  1507  may be optically coupled to the single-sided deflectors  1508 ,  1510  in a one-to-one correspondence. N beam steering elements  1501  may be stacked in the module to produce an N×M beam steering module  1500 . The deflectors  1503 ,  1505 ,  1508 ,  1510  may be of any of the types discussed above. For example the deflectors  1505 ,  1507  may respectively be x-deflectors and y-deflectors or vice versa. If so, the deflectors  1508 ,  1510  may respectively be y-deflectors and x-deflectors or vice versa. Alternatively, the deflectors  1505 ,  1507  may gimbaled dual-axis (xy) deflectors and the deflectors  1508 ,  1510  may be fixed deflectors or vice versa. Alternatively the double-sided deflectors  1503  may contain various mixed pairs of x-deflectors, y-deflectors, dual-axis deflectors and fixed deflectors with the single sided deflectors  1508 ,  1510  containing appropriate corresponding deflectors.  
         [0077]    Modules of the type depicted in FIG. 15 may be incorporated into an optical switch. FIG. 16 depicts an isometric schematic diagram of an optical switch employing two modules of the type shown in FIG. 15. The switch  1600  may generally include a first module  1601  and a second module  1651 . The first and second modules may contain, respectively, N×M double-sided arrays  1602 ,  1652  sandwiched between opposing 1×M single-sided deflector arrays  1604 ,  1606 ,  1654 ,  1656 . The arrays  1602 ,  1604 ,  1652   1654  may be coupled to optical fiber arrays  1620   A ,  1620   B ,  1670   A ,  1670   B  e.g. via lens arrays  1630   A ,  1630   B ,  1680   A ,  1680   B . The beam steering modules  1601 , 1651  may selectively couple optical signals between any one of the fibers in the fiber arrays  1620   A ,  1620   B  and any one of the fibers in the fiber arrays  1670   A ,  1670   B .  
         [0078]    Although much of the previous discussion had focused on modular switches, other embodiments of the application include switches that are non-modular. For example, according to a fifth embodiment of the invention, modular or non-modular beam deflectors may be combined with a curved distribution of I/O ports to increase port count in an beam steering optical switch. FIG. 17 depicts a cross-sectional schematic diagram of an optical switch  1700  according to a first alternative version of a fifth embodiment of the present invention. The switch  1700  generally comprises a first set of optical input/output (I/O) ports  1702  distributed across a first curve  1704 , a second set of optical I/O ports  1706  distributed across a second curve  1708 , and one or more sets of beam steering elements  1710 ,  1712  optically coupled between the first set of I/O ports and the set of I/O ports. First and second sets of optical fibers  1714 ,  1716  may be optically coupled respectively to the first and second sets of I/O ports  1702 ,  1706 . The beam steering elements each may contain one or more deflectors  1711 ,  1713 . By way of example and without loss of generality, the deflectors  1711 ,  1713  may be single axis deflectors, dual-axis deflectors, fixed deflectors, or some combination of any or all of these. In the case where single axis deflectors are used, the switch  1700  may include relay optics, e.g. as described elsewhere herein.  
         [0079]    The curved distribution of the I/O ports allows a greater number of ports to be coupled closer together, thereby increasing the port count for the optical switch  1700 . By way of example, the curves  1704 ,  1708  may be in the shape of a segment of a circle, parabola, ellipse, hyperbola, cycloid, or any other suitable curved shape. Alternatively, one of the curves  1704 ,  1708  could be a segment of a straight line. Although one-dimensional curved I/O port distributions are depicted in FIG. 1700 for the sake of clarity, the switch  1700  may employ two-dimensional curved arrays of I/O ports, e.g. ports distributed across a curved three-dimensional surface. By way of example, the shape of the curved surface may be cylindrical, spherical, paraboloidal, ellipsoidal, hyperboloidal or any other suitable curved three-dimensional shape. Alternatively, one of the arrays of I/O ports could be arranged in a planar array. Furthermore, although beam steering elements having planar arrays of deflectors are depicted in FIG. 17, the invention is in no way limited to this particular configuration. The beam steering elements may alternatively be curved arrays of deflectors. Furthermore, the deflectors may scan “one way” or “two way” as required by the specific application of the switch  1700 .  
         [0080]    [0080]FIG. 18 depicts a cross-sectional schematic diagram of an optical switch  1800  that may employ a fold deflector according to a second alternative version of the fifth embodiment of the present invention. The switch  1800  may generally comprise a first set of optical input/output (I/O) ports  1802  distributed across a first curve  1804 , a second set of optical I/O ports  1806  distributed across a second curve  1808 , and one or more sets of beam steering elements  1810 ,  1812  optically coupled between the first set of I/O ports and the set of I/O ports. First and second sets of optical fibers  1814 ,  1816  may be optically coupled respectively to the first and second sets of I/O ports  1802 ,  1806 . The beam steering elements may each contain one or more deflectors  1811 ,  1813 . The second set of I/O ports may be coupled to the beam steering elements  1810 ,  1812  via a fold deflector  1815 . The fold deflector may allow the first and second sets of I/O ports to be arranged on the same side of the beam steering elements. By way of example and without loss of generality, the deflectors  1811 ,  1813  may be single axis deflectors, dual-axis deflectors, fixed deflectors, or some combination of any or all of these. In the case where single axis deflectors are used, the switch  1800  may include relay optics, e.g. as described below. Although a planar fold deflector is depicted in FIG. 18, the fold deflector may alternatively be curved, in a manner analogous to that depicted in FIG. 7F. By way of example, the shape of the fold deflector  1815  may be cylindrical, spherical, paraboloidal, ellipsoidal, hyperboloidal or any other suitable curved three-dimensional shape. Such a curved fold deflector may be convex fold deflector  1815 B as shown in phantom or a concave fold deflector  1815 C as shown in phantom.  
         [0081]    There may be certain advantages in the particular case that an optical switch according the fifth embodiment of the invention includes dual-axis deflectors. FIG. 19 depicts a cross-sectional schematic diagram of an optical switch  1900  employing dual-axis deflectors according to a third alternative version of the fifth embodiment of the present invention. The switch  1900  may generally comprise a first set of optical input/output (I/O) ports  1902  distributed across a first curve  1904 , a second set of optical I/O ports  1806  distributed across a second curve  1908 , and one or more of beam steering elements  1910  containing dual-axis deflectors  1911  optically coupled between the first set of I/O ports and the set of I/O ports. First and second sets of optical fibers  1914 ,  1916  may be optically coupled respectively to the first and second sets of I/O ports  1902 ,  1906 . The dual-axis deflectors may be employed without relay optics.  
         [0082]    The above embodiments may use relay optics. An example of a beam steering module  100  using relay optics according to a first embodiment of the invention is depicted in FIG. 20. The steering module  100  generally comprise two 2-dimensional mirror arrays  110 ,  130  and relay optics  120  disposed along an optical path between the mirror arrays. The mirror arrays  110 ,  130  each typically comprise N×M arrays of single axis mirrors  112 ,  132 . Generally N and M are integers greater than one. In the special case of square arrays, N=M.  
         [0083]    In the present application, a single axis mirror refers to a moveable mirror configured to rotate about a single axis. Mirrors  112  and  132  rotate about axes  114 ,  134  that are different. Typically, mirrors  112  and mirrors  132  rotate about axes  114 ,  134  that are substantially orthogonal to each other. For example, mirrors  112  are configured to rotate about axes  114 , oriented in a substantially horizontal plane. Mirrors  132  are configured to rotate about axis  134  oriented in a substantially vertical plane.  
         [0084]    An input light beam  101  from a input fiber in a given row and column of an N×M input fiber array (not shown) impinges on a given mirror  112  in array  110 . Mirrors  112  and  132  deflect the light beam  101  towards a fiber in an N×M output fiber array (not shown). Those skilled in the art will recognize that because the propagation of light is reversible, the role of input and output fibers may be reversed.  
         [0085]    In an exemplary embodiment, relay optics  120  comprises a first focusing element  122  and a second focusing element  124  in a confocal configuration. For the purposes of this application the “focusing element” encompasses optical elements capable of focusing light. Such elements include refractive elements such as lenses, reflective elements such as mirrors, diffractive elements and micro-optical elements. Lenses include simple lenses and compound, i.e. multiple element lenses, graded refractive index (GRIN) lenses, ball lenses, and the like. Diffractive elements include Fresnel lenses and the like. In a confocal configuration, focusing elements  122  and  124  are characterized by the substantially same focal length f and separated from each other by a distance substantially equal to 2f. Furthermore, array  110  is located a distance f from focusing element  122  and array  130  is located a distance substantially equal to f away from focusing element  124 .  
         [0086]    Relay optics  120  image mirror array  110  onto mirror array  130 . The angle of beam  101  may be controlled with respect to both axes  114  and  134  by adjusting the angle of the appropriate mirrors in the arrays  110  and  130 . For example, beam  101  emerges from mirror array  110  at an angle φ with respect to the object plane of relay optics  120 . The object plane of relay optics  120  is typically located proximate mirror array  110 . The image plane of relay optics  120  is typically located proximate mirror array  130 . Relay optics  120  are configured to ensure that beam  101  impinges on the image plane of relay optics  120  at the same angle φ. In other words, light beam  101  enters and leaves relay optics  120  at the same angle. Furthermore, parallel light entering relay optics  120  leaves as parallel light. Alternatively the angle beam  101  makes with the image plane may be related to the angle beam  101  makes with the object plane by some other predetermined relationship.  
         [0087]    Steering module  100  may be used for beam steering in small port-count switches or if loss is not critical. Alternatively, module  100  may be used to switch beam  101  from input fibers in an N×M array to a grid or array of photodetectors. Mirrors in array  110  deflect light beam  101  to the row containing the desired output fiber or detector. Mirrors in array  130  deflect beam  101  to the desired column on that row.  
         [0088]    [0088]FIG. 21 depicts a steered beam switching system  200  according to a second embodiment of the invention. If port count becomes sufficiently on module  100 , large losses may occur due to light entering the fibers at two great an angle. To overcome this, the system  200  that utilizes two modules of the type shown in FIG. 21 to ensure that beam  101  enters the output fiber at the correct angle.  
         [0089]    The system  200  generally comprises a first module  210  coupled to an N×M input fiber array  202  and a second module  220  coupled to an output fiber array  204 . Modules  210  and  220  determine, at the plane of output fiber array  204 , the position and angle of an optical beam emerging from any of the input fibers in input fiber array  202 . Modules  210  and  220  have features in common with module  100  of FIG. 21. Module  210  comprises single axis mirror arrays  212 ,  214  and relay optics  216 . Mirrors in arrays  212  and  214  rotate about mutually orthogonal axes. Module  220  comprises single axis mirror arrays  222 ,  224  and relay optics  226 . Mirrors in arrays  222  and  224  rotate about mutually orthogonal axes.  
         [0090]    In the exemplary embodiment depicted in FIG. 22 mirrors in arrays  214  and  222  rotate about substantially parallel axes. A light beam  201  from a fiber  203  in input fiber array  202  couples to a corresponding mirror  213  in mirror array  212 . Mirror  215  steers light beam  201  to a mirror  215  in array  214 . Relay optics  216  preserve the angle that light beam  201  makes at with respect to an image plane of relay optics  216 . Mirror  215  deflects light beam  201  to a mirror  223  on array  222 . Mirror  223  steers light beam  201  to a mirror  225  in array  224 . Relay optics  226  preserve the angle that light beam  201  makes at with respect to an image plane of relay optics  226 . Mirror  225  deflects light beam  201  to a corresponding fiber  205  in output fiber array  204 .  
         [0091]    Those skilled in the art will recognize that by suitable manipulation of mirrors  213 ,  215 ,  223 , and  225  any fiber in input array  202  may be coupled to any fiber in output array  204 .  
         [0092]    An exemplary embodiment of an optical switch  2300  employing various features described above is depicted in FIGS. 22 and 23. The switch  2300  generally comprises a plurality of beam steering modules  2302  attached to a case  2301 . The modules are disposed along a curved upper surface of the housing  2301 . Each beam steering module  2302  includes beam steering elements made up of alternating stacked arrays x-axis and y-axis beam steering mirrors  2304   2308 . By way of example the beam steering mirrors  2304  may be single axis mirrors that alternately rotate about x and y axes. The beam steering mirrors  2304  may be electrically connected to a controller by ribbon cables  2305 , which are not considered part of the modules  2302 . Optical signals from optical fibers  2303  are coupled to the beam steering elements by N×M groups of collimators  2306  disposed in holes in housings  2307  mechanically coupled to modules and optically coupled to beam steering elements. For clarity, some of the housings are have been removed to expose the beam steering elements. The modules are optically coupled to each other via a fold mirror  2310 , which is fixed to the case  2301 .  
         [0093]    It will be clear to one skilled in the art that the above embodiment may be altered in many ways without departing from the scope of the invention. For example, although in the above embodiments, the mirrors are described as MEMS mirrors other mirrors such as bulk mirrors or large-area deformable mirrors may be used. Accordingly, the scope of the invention should be determined by the following claims and their legal equivalents.