Patent Abstract:
A fiber optic switch with a plurality of switches, each having one input and N outputs, the switches are arranged and oriented relative to each other so that the input of a switch is in line with the outputs of any adjacent switches of the plurality of switches, wherein each switch includes controllable mirror and has a solid state actuator to directly control the mirror, this facilitating selection of one of a plurality of outputs.

Full Description:
This appln is a 371 of PCT/US00/32719 filed Dec. 1, 2000 and claims the benefit of Prov. No. 60/168,291 filed Dec. 1, 1999 and claims benefit of Prov. No. 60/183,116 filed Feb. 17, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to fiber optic switches. 
     Typically, in the fabrication of dense N×N switches, two N×N switch cores or fabrics are required for redundancy. In each switch core, a signal emanating from an incoming fiber is split and return paths are recombined. Such switching may be implemented with individual switching mechanisms, which select desired paths. As overall switch core size (i.e., the value N) continues to increase, so too does the number of individual switching mechanisms that must be packaged in a single port unit. 
     SUMMARY OF THE INVENTION 
     In one aspect of the invention, a fiber optic switch assembly includes a first strip arrangement of deflecting mirrors and a second opposing strip arrangement of deflecting mirrors, the deflecting mirrors in the first and second strip arrangements being configured to operate together to form a plurality of switches. 
     Embodiments of the invention include one or more of the following features. 
     Ones of the deflecting mirrors in each strip each can receive an optical beam and provide the optical beam to a selected one of N of the deflecting mirrors in the opposing strip. 
     Among the advantages of the present invention are the following. The interleaving of 1×N switches provides for a very compact arrangement, thus reducing the overall packaging size of a switch assembly. Such a compact arrangement is of particular interest for fiber optical switching applications that require that many switches be packaged as a single unit. 
     Other features and advantages of the invention will be apparent from the following detailed description and from the claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an illustration of a switch configured to include four 1×2 switches. 
     FIG. 2A is a side view of the switch depicted in FIG.  1 . 
     FIG. 2B is a top view of the switch depicted in FIG.  1 . 
     FIGS. 3A and 3B are top and side views, respectively, of an exemplary mirror structure. 
     FIG. 4 is an illustration of a detector arrangement to optimize coupling for each switching path in the switch of FIGS.  1  and  2 A- 2 B. 
     FIG. 5 is an illustration of an alternative 1×2 switch arrangement that uses a latching switch element. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1, a switch  10  includes an arrangement of two arrays or strips  12   a ,  12   b  of mirrors  14   a ,  14   b ,  14   c ,  14   d ,  14   d ,  14   e  and  14   f , and  16   a ,  16   b ,  16   c ,  16   d ,  16   e  and  16   f , respectively. The mirrors  14 ,  16  as described herein are two-dimensional mirrors. Alternatively, the mirrors  14 ,  16  can be one-dimensional mirrors. The mirrors are grouped to form one input by N outputs (1×N) switches  18 , where N has a value of 2. The mirrors  14   a ,  14   d ,  16   c  and  16   f  serve as inputs and the other mirrors serve as outputs. The mirrors  14   a ,  16   a  and  16   b  form a first switch  18   a , the mirrors  16   c ,  14   b  and  14   c  form a second switch  18   b , the mirrors  14   d ,  16   d  and  16   e  form a third switch  18   c , and the mirrors  16   f ,  14   e  and  14   f  form a fourth switch  18   d . Light directed to the mirror  14   a  in the mirror strip  12   a  from a launching collimator (not shown) is directed by the mirror  14   a  towards either of the target mirrors  16   a  or  16   b  in the opposing mirror strip  12   b . Light falling on the mirror  16   c  in the mirror strip  12   b  is directed towards either the mirror  14   b  or the mirror  14   c  in the mirror strip  12   a . Likewise, the mirror  14   d  directs a light beam to a selected one of the target mirrors  16   c  and  16   d , and the mirror  16   f  directs a light beam to a selected one of the target mirrors  14   e  and  14   f . It can be seen from the figure that the switches  18   a  and  18   c  have one orientation and the switches  18   b  and  18   d  have a second orientation that is the opposite of the first orientation. For a compact arrangement of switches as shown, therefore, the switches having the first orientation are interleaved with the switches having the second orientation. That is, the inputs,  14   a ,  14   d ,  16   c  and  16   f  of the switches  18   a ,  18   c ,  18   b  and  18   d , respectively, are oriented for alignment with outputs of adjacent ones of the switches  18 . For example, the input  14   a  of the switch  18  is in line with the outputs  14   b  and  14   d  of adjacent switch  18   b , and, likewise, the input  16   c  of the switch  18   b  is in line with the outputs  16   a ,  16   b  of the switch  18   a , as well as the outputs  16   de  and  16   e  of the switch  18   c , also adjacent to the switch  18   b.    
     Since the target mirrors, e.g.,  14   e  and  14   f , are close together, the deflection angles for the mirror from which the beam is deflected (for the example of target mirrors  14   e ,  14   f , that mirror would be the mirror  16   f ) can be quite small and the driving voltages required for deflection are also very small. For example, if the distance from lens to lens is 50 mm (using a 1.5 mm focal length lens), and the mirror spacing is 1 mm, then the required mirror deflection is only a little more than half a degree. The deflection angle can be further reduced by orienting the beam launching collimator for each 1×2 switch such that the undeflected target position is half way between the two target mirrors, again reducing the angle that needs to be used. Only one deflection direction along the strip needs appreciable deflection. The other direction requires only a very small correction, if the mechanical alignment is done correctly. Of course, and as indicated above, the mirrors could be one-dimensional and therefore deflect in one direction only. 
     Referring to FIGS. 2A and 2B, an assembly for the switch  10  (of FIG.  1 ), switch assembly  20 , includes two assemblies  22  and  24 , which are tightly clamped together with pin  26 . Assembly  24  is a monolithic block which holds lenses  28   a ,  28   b  and fiber with fiber ferrules  30   a ,  30   b , which are adjusted against each other to produce maximum throw of the waist coming out of the fiber at the end of the ferrules  30   a ,  30   b . The assembly  22  holds the mirror strips  12   a  and  12   b  (that include associated substrates, e.g., silicon, ceramic, glass, etc.), which have connecting ribbons  32   a  and  32   b  for their leads. The assembly  20  further includes heaters  34  and a temperature sensor  36  to provide a stabilized thermal environment. The switch assembly  20  may be thermally isolated from its environment with an insulated jacket (not illustrated). 
     With reference to FIGS. 3A-3B, an exemplary mirror strip structure  40  for implementing the mirror strips  12   a ,  12   b  is shown in partial view. The mirror strip structure  40  includes micro-mirror structures  42  (which correspond to the mirrors  14 ,  16  in FIG.  1 ), each of the micro-mirror structures  42  including a mirror arrangement  44  disposed above and supported over a top surface of a reference member or substrate  46 . To illustrate the detail of the mirror structures  42 , only three are shown in the figure. It will be appreciated that there would be six micro-mirror structures  42  in each of the strips  12   a ,  12   b  in the switch  10  of FIG.  1 . As shown in FIG. 3A, each mirror arrangement  44  includes a mirror  48  coupled to mirror frame  50  by a first pair of torsion members  52   a ,  52   b . The mirror arrangement  44  further includes a second pair of torsion members  54   a ,  54   b , which couple the mirror frame  50  to strips  56 . 
     Referring to FIG. 3B, the substrate  46  includes a base portion  58 , a raised portion  60  on the base portion  58 , and sidewall portions  62  on either side of the base portion  58 . The substrate may be made of ceramic or other suitable materials. The strips  56  are located on top of the sidewalls  62 . As shown by the raised portion  60  (FIG.  3 A), the raised portion  60  is conical or quasi-conical in shape. 
     Electrodes  64  are disposed on the surface of the raised portion  60  to impart a rotational motion to the mirror  48  and the mirror frame  50  (shown in FIG.  3 A). The electrodes  64  control the inner rotation of the mirror arrangement around the torsion members  52   a ,  52   b  (“x-axis”), as well as control the outer rotation of the mirror arrangement around the torsion members  54   a ,  54   b  (“y-axis”). 
     Preferably, for large deflection angles and small driving voltages, the mirror structure includes the raised portion  60  as described and, although the raised portion  60  has been thus described as having a cone or cone-like form, it may take any shape or structure that allows the electrodes  64  to be positioned close to the mirror arrangement  44  and support rotational movement of the mirror arrangement in the x-y plane. It will be understood, however, that, although the raised portion may be desirable, any other electrode structure or structure for supporting electrodes can be used. For example, planar electrodes can be used. 
     Preferably, the mirror arrangement  14  and the electrodes  34  are so positioned relative to the cone  30  such that the cone  30  is centered approximately under the mirror  18 . Substrate areas beneath the mirror frame  20  need not be conical, but may be sloped on such an angle as required to allow the mirror arrangement  14  to rotate freely through its outer axis of rotation around torsion members  24   a ,  24   b . These substrate areas can be machined linearly in the substrate  16 , thus simplifying the fabrication of the substrate  16 . 
     As can be seen in FIG. 3B, a spacer  65  can be used between each of the strips  56  and the sidewall portions  62  of the substrate  46  below such strips  56 . The angles in the bottom of the substrate  12  are not critical. Typically, because the substrate  16  is made in sections of 4.5″×4.5″, the sections are all made together. The substrate material may be machined in vertical and horizontal directions to remove material under a desired angle. The cone or cone-like shape is ground on the top to complete the substrate structure or can be etched into the substrate surface. Alternatively, a mold may be made to cast the substrate material in a green state. In yet another alternative, the electrodes can be plated onto the substrate surface. 
     The mirror structure  42  can be fabricated using silicon-on-insulator fabrication techniques, with the mirror arrangement  44  being defined in the top (or device) silicon wafer. Other fabrication techniques may be used. 
     The embodiment of the mirror structure  42  illustrated in FIGS. 3A-3B and various associated fabrication techniques are described more fully in co-pending U.S. patent application Ser. No. 60/165,863, entitled “Improvements for an Optical N×N Switch”, filed on Nov. 16, 1999, incorporated herein by reference. 
     Other structures (such as mirror structures having different electrode structures, as mentioned above) may be used. For example, the mirror strips  12   a ,  12   b , and their associated mirror structures  14 ,  16 , respectively, may be constructed in accordance with the techniques described in U.S. Pat. Nos. 6,044,705 and 5,629,790, incorporated herein by reference. Other known two-dimensional micro-machined mirror structures may be used. 
     The deflection of mirrors  14 ,  16  can be driven by a closed loop system. If desired, angle deflection sensors may be used to control deflection, as described in the above-mentioned application and patents. The deflection may be electrostatic or magnetic or both, in either direction. For example, the axis having the relatively large deflection may be magnetic and the relatively smaller deflection axis could be electrostatic, since the latter requires only minor correction. Thus, even if the mirrors are spaced far apart from each other, there is little possibility of electrostatic instability. 
     Alternatively, the deflectors may be driven open loop, or an external alignment scheme may be used. For example, and referring to FIG. 4, a fiber  70  exiting the collimator  30   b  (from FIG. 2A) is bent, possibly around a mandrel  71 , and produces radiation which is collected and imaged on a detector  72  with a simple lens (e.g., plastic) or Fresnel lens  74 . By dithering the driving voltages or currents of the deflecting mirrors through very small angles and detecting with phase sensitive detection a maximum value for the transmitted power peak (using the detector  72 ), the mirrors  14 ,  16  can be locked into an optimum deflection position for transmission of light from one fiber to another. 
     Although the interleaving scheme is described above with reference to 1×2 switches, it is equally applicable to switches of any size 1×N, where N is a value of two or greater. Additionally, although the switch  10  is depicted as having four 1×N (where N=2) switches, the switch  10  could include more or less than the four 1×N switches that are shown. 
     The switches  18  have been thus described as having a single input and N outputs. Alternatively, the switches  18  may have N inputs and one output, or may be operated in two modes so that the mirrors serving as inputs and mirrors serving as outputs in one mode serve as outputs and inputs, respectively, in a second mode. For example, and again referring to FIG. 1, the switches  18  can be operated to use the mirrors  14   b - 14   c ,  14   e ,  14   f ,  16   a ,  16   b ,  16   d ,  16   e  as inputs and the mirrors  14   a ,  14   d ,  16   c  and  16   f  as outputs. Thus, each of the 1×2 switches could have two inputs and one output and thus select one of the input signals (that is, the optical beams) received at a corresponding one of the two input mirrors to be directed to the single output mirror. 
     Other embodiments of a 1×2 switch for use in a switch including a plurality of 1×2 switches, such as the switch  10 , are contemplated. For example, and referring to FIG. 5, a 1×2 switch can be implemented with a single latching switch element  82  arranged in a configuration with collimator and fiber assemblies (hereinafter, collimators)  84   a - 84   c , shown as switch  80 . The collimator  84   a  serves a launching collimator and the collimators  84   b  and  84   c  serve as exiting collimators. Each of the collimators  84  is coupled to one or the other of the mirror strips  12   a ,  12   b , and are preferably situated in “V” shaped grooves in the silicon substrate. The latching switch element  82  may be implemented with magnetic actuating and electrostatic clamping, as described in co-pending U.S. patent application Ser. No. 09/388,772, incorporated herein by reference. 
     The operation of the switch  80  is as follows. When the latching switch element  82  is not activated, the optical beam path is from the collimator  84   a  to the collimator  84   b . When the latching switch element  82  is activated (by electrostatic clamping) for positioning at a 45 degree angle as shown, a beam from the collimator  84   a  is directed not to the collimator  84   b  but instead to the collimator  84   c . Although the latching switch element  82  is clamped electrostatically in a particular position, minor adjustments in the position can still be made, as described in the above-referenced U.S. patent application Ser. No. 09/388,772. The mechanical location of the latching switch element  82  relative to the collimators  84  can vary, as the associated mirror may be tilted and adjusted appropriately in two directions when switching is performed. 
     OTHER EMBODIMENTS 
     It is to be understood that while the invention has been described in conjunction with the detailed description thereof, the foregoing description is intended to illustrate and not limit the scope of the invention, which is defined by the scope of the appended claims. Other embodiments are within the scope of the following claims.

Technology Classification (CPC): 6