Patent Publication Number: US-2004057654-A1

Title: Devices and methods for switching transmission of light from one fiber to another

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
     [0001] This application claims priority from U.S.A. Provisional Application No. 60/261,351 filed on Jan. 12, 2001, and international application number PCT/US02/00231, filed Jan. 4, 2002, which are hereby incorporated by reference. 
    
    
     
       BACKGROUND OF THE INVENTION  
       [0002] 1. Field of the Invention  
       [0003] The present invention is related to the field of fiber optics communications, and more specifically to devices and methods for switching transmission of light from one optical fiber to another.  
       [0004] 2. Description of the Related Art  
       [0005] Light signals are transmitted through optical fibers. These are very thin, and made in very large lengths (e.g. of the order of 1 km or longer).  
       [0006] Often electrical signals are converted to light signals, then transmitted through fibers, and then reconverted to electrical signals. Fibers are thus widely use for wired communications over long distances, such as for telephone lines, etc.  
       [0007] It is often desirable to have an optical fiber switch device. That device can receive light from one fiber (often called the feeding fiber), and couple it to a receiving fiber. Or it can couple the received light selectively to one of many receiving fibers. This prevents the need of reconverting a light signal to an electrical signal for switching between channels, and then converting it back to a light signal for continuing transmission.  
       [0008] Optical fiber switch devices are implemented in a number of ways in the prior art. A first such way is described herein as FIG. 1 and FIG. 2. It has been reproduced from an article titled: Mechanical Optical-Fibre Switch, Electronics Letters Vol. 12, Jul. 22 1976.  
       [0009] Referring to FIG. 1, prior art switch  100  is provided in a glass tube  110  that defines an enclosure  115 . A feeding fiber  120  enters enclosure  115 , and couples light into either one of receiving fiber  132  or receiving fiber  134 . Enclosure  115  may be sealed, and filled with propyl alcohol to keep the ends of fibers  120 ,  132 ,  134  clean.  
       [0010] Referring to FIG. 2, a cross section of tube  110  is shown, at a plane where receiving fibers  132 ,  134  have their inputs. Tube  110  internally has a square cross section, and receiving fibers  132 ,  134  are at corners of the square, in corresponding grooves. Feeding fiber  120  can be more reliably aligned with either one of receiving fibers  132 ,  134 , by being driven to the same groove.  
       [0011] Returning to FIG. 1, feeding fiber  120  has a ferromagnetic sleeve  140 , made from nickel. This way the output end of fiber  110  can be driven to either groove by applying magnetic forces. These may be established by electromagnets (not shown).  
       [0012] Other implementations (not shown separately) use a reed switch to switch the device on and off, by deflecting or not the output end of the feeding fiber from an aligned position. A conventional reed runs along the entire length of the portion of the feeding fiber that is within tube  110  of the prior art. The magnetic field runs parallel to the conventional reeds, and in fact, it magnetizes them.  
       [0013] A consistent problem in the prior art is that large magnetic fields are needed to accomplish switching in devices such as that of FIG. 1. That is because the electromagnets for establishing the field are best placed outside the portion encapsulated by the glass tube, and therefore at a large distance from the fiber that is to be steered by applying the magnetic field. Due to the large distance, these electromagnets require a lot of electrical current to activate, more than is justified for a mere switch.  
       [0014] The problem has not been addressed satisfactorily in the prior art.  
       [0015] First, in the prior art of FIG. 1 the problem does not seem addressed at all. In fact, the disclosure of the reference does not seem fully implemented. The reference even concludes with a statement that the authors intend to proceed with development along the lines indicated in the disclosure. The reference seems to treat the actual process of switching as an abstraction, without addressing the large size of the requisite magnetic fields. In fact, sleeve  140  seems shorter than subsequent, actual implementations.  
       [0016] Second, in the aforementioned implementations of reed switches, a large reed is used, which is at least as long as the whole output end of the output fiber. This was done for better magnetic coupling. Still, such switches require a lot of current.  
       [0017] Third, referring to FIG. 3, another device in the prior art actually solves this problem, but by increasing mechanical complexity and thus also cost. The solution of FIG. 3 of the present document is taught in U.S. Pat. No. 4,415,229.  
       [0018] In FIG. 3, a device  300  receives a feeding fiber  317  (near the top) goes through a guiding sphere  320 . Sphere  320  can be rotated to various orientations, for aligning the free end of feeding fiber  317  with the receiving end of any one of receiving fibers  310 . Sphere  320  is steered to these various orientations by electromagnets  326  attracting selectively a disc  319  fitted about sphere  320 .  
       [0019] All this is done so that magnetic fields need not be applied over large distances. Indeed, sphere  320  is placed in a socket, and helps form an enclosure  330  that contains the free ends of feeding fiber  317  and receiving fibers  310 . This way disc  319  is wholly outside enclosure  330 , which permits it to be located closely to electromagnets  326 .  
       [0020] The drawback here is a very complex structure with mechanical parts moving against each other. This makes it expensive, and of a shorter useful life.  
       [0021] It is desirable to have an inexpensive, durable fiber-to-fiber switch.  
       BRIEF SUMMARY OF THE INVENTION  
       [0022] The present invention overcomes these problems and limitations of the prior art.  
       [0023] Generally, the present invention provides devices and methods for switching transmission of light from one fiber to another. A steerable fiber terminates in a capsule, as do one or more cooperating fibers. For switching, the steerable fiber is moved to exchange light selectively with one of the cooperating fibers.  
       [0024] The end of the steerable fiber includes an armature that moves in response to applied magnetic fields. At least one magnetic field is generated, and a pair of pole pieces transfers it to a location inside the capsule that is close to the armature.  
       [0025] The invention offers the advantage that the generated magnetic field need not be large, thus conserving electric current. Indeed, the pole pieces terminate in a short distance between them, to generate relatively large field strength. A switch is thus created that is economical to operate.  
       [0026] In addition, by further terminating close to the armature, the strength of the generated magnetic field need not be large in the first place. Furthermore, the armature itself need not be large, and maybe manufactured economically near the end of the steerable fiber as a sphere. A switch is thus simple, and further economical to manufacture.  
       [0027] The invention will become more readily apparent from the following Detailed Description, which proceeds with reference to the drawings, in which: 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0028]FIG. 1 is a diagram of a fiber-to-fiber switching device in the prior art.  
     [0029]FIG. 2 is a cross sectional diagram of a tube of the device of FIG. 1.  
     [0030]FIG. 3 is a diagram of another fiber-to-fiber switching device in the prior art.  
     [0031]FIG. 4A is a perspective view of a fiber-to-fiber switching device made according to an embodiment of the present invention.  
     [0032]FIG. 4B is a top view of salient parts of the device of FIG. 4A, showing one of its attainable switching states.  
     [0033]FIG. 4C is a top view of salient parts of the device of FIG. 4A, showing another one of its attainable switching states.  
     [0034]FIG. 5A is a perspective view of a fiber-to-fiber switching device made according to another embodiment of the present invention.  
     [0035]FIG. 5B is a top view of salient parts of the device of FIG. 5A, showing one of its attainable switching states.  
     [0036]FIG. 5C is a top view of salient parts of the device of FIG. 5A, showing another one of its attainable switching states.  
     [0037]FIG. 6A is a perspective view of a fiber-to-fiber switching device made according to yet another embodiment of the present invention.  
     [0038]FIG. 6B is a top view of salient parts of the device of FIG. 6A, showing it at a rest state.  
     [0039]FIG. 6C is a top view of salient parts of the device of FIG. 6A, showing it at a first one of its attainable switching states.  
     [0040]FIG. 6D is a top view of salient parts of the device of FIG. 6A, showing it at a second one of its attainable switching states.  
     [0041]FIG. 7 is a flowchart illustrating a method according to an embodiment of the present invention.  
     [0042]FIG. 8 is a plan view of parts of a switch, for describing technical implementation details of the invention.  
     [0043]FIG. 9 is a detailed view of a steerable optical fiber in the device of FIG. 8.  
     [0044]FIG. 10 is a schematic view of an arrangement of pole pieces operating to move a single steerable fiber along different directions for placing in horizontally disposed grooves.  
     [0045]FIG. 11 is a plan view of an arrangement where feeding fibers share a common armature according to an embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)  
     [0046] As has been mentioned, the present invention provides devices and methods for switching transmission of light from one fiber to another. A steerable fiber terminates in a capsule, as do one or more cooperating fibers. For switching, the steerable fiber is moved to exchange light selectively with one of the cooperating fibers. The invention is now described in more detail.  
     [0047] Referring now to FIG. 4A, a fiber-to-fiber switch  400  is shown. Switch  400  includes a capsule made from a bottom half  404  and a top half  406 . In FIG. 4A, top half  406  is shown separated and raised from bottom half  404  to better illustrate other important components of switch  400 .  
     [0048] Top half  406  normally closes down on bottom half  404 , to make the switch rugged. When the two halves are closed, an interior  408  of the capsule may optionally be filled with an index matching fluid, to improve coupling of light between the fibers.  
     [0049] Switch  400  also includes a first electromagnet  410  for selectively generating a first magnetic field. First electromagnet  410  includes at least a coil  412  and a wire  414  wrapped around coil  412 .  
     [0050] First electromagnet  410  is operated by electrical power source such as battery  416 , and a switch  418  for controlling when electrical current flows around coil  412 . Switch  418  may be electronic, and be switched ON and OFF by an electronic switching signal.  
     [0051] First electromagnet  410  is outside the capsule, although that is not necessary. First electromagnet  410  may equivalently be implemented within the capsule.  
     [0052] Switch  400  moreover includes a first pair of pole pieces  420 . Pole pieces  420  transfer the first generated magnetic field from the tips of coil  412  to a first transferred field location  424  inside the capsule near the tips of pole pieces  420 . Pole pieces  420  are preferably made from a material that conducts well a magnetic field.  
     [0053] At least the tips of pole pieces  420  are in part inside the capsule. If first electromagnet  410  is wholly within the capsule, then pole pieces  420  may also be wholly within the capsule.  
     [0054] In the preferred embodiment, coil  412  of first electromagnet  410  is outside the capsule. Pole pieces  420  then transfer the first generated magnetic field through a wall of the capsule.  
     [0055] Pole pieces  420  are preferably thin, so as to interfere only minimally with a lip of top half  406 , as it closes with bottom half  404  to form the capsule. The two halves may be sealed together using a foamy material between them, which accommodates a small thickness of pole pieces  420 . Alternately, one of the two halves (here top half  406 ) may have recesses  421  at the lip, for accommodating pole pieces  420 .  
     [0056] Switch  400  additionally includes a steerable fiber  430 , having an end  432  in the capsule. End  432  is also known as the output end of steerable fiber  430 .  
     [0057] A large portion of steerable fiber  430  is outside the capsule, including a remote end of fiber  430 . This large portion, along with the remote end are not shown, as unimportant to switch  400 . End  432  in the capsule is steerable, as will be explained below.  
     [0058] Fiber  430  is generally mounted on the bottom half  404  of the capsule. Mounting may be to a pedestal, which may in turn be mounted on the bottom half  404 . Alternately, mounting may be to a wall or lip of bottom half  404 .  
     [0059] Switch  400  further includes an armature  435  attached to steerable fiber  430  near end  432 . Armature  435  may be a standalone magnet, by being made from material which is inherently magnetized, or has been made to acquire magnetism. Alternately, armature  435  may be made from soft magnetic material, which responds to magnetic field, but does not retain magnetism.  
     [0060] It is highly preferred that the first transferred field location  424  is designed to be close to armature  435 . This way armature  435  is responsive to the transferred first magnetic field by being magnetically biased with respect to the first transferred field location  424 . If armature  435  has no magnetism, then being magnetically biased means being attracted towards the first transferred field location  424 . On the other hand, if armature  435  has magnetism, then being magnetically biased means being attracted towards or repelled from the first transferred field location  424 , depending on the orientation of its North-South field, and the orientation of the transferred magnetic field.  
     [0061] Switch  400  further includes at least one cooperating fiber  440 , having an end  442  in the capsule. In addition, switch  400  further includes a second cooperating fiber  450 , having an end  452  in the capsule. Including second cooperating fiber  450  is highly preferred, but not necessary for practicing the invention.  
     [0062] Light may be exchanged between steerable fiber  430  and either one of cooperating fibers  440 ,  450 . If steerable fiber  430  is the feeding fiber, i.e. the fiber that brings the light in switch  400 , then switch  400  is a 1×2 switch. If cooperating fibers  440 ,  450  are the feeding fibers, then switch  400  is a 2×1 switch. Not including second cooperating fiber  450  would simply render device  400  an ON/OFF switch between fibers  430 ,  440 .  
     [0063] Referring now also to FIG. 4B, and FIG. 4C, the operation of switch  400  is described.  
     [0064] In FIG. 4A, FIG. 4B, switch  418  is open, and the first magnetic field is not generated. Accordingly, armature  435  is not biased, and end  432  of steerable fiber  430  is at a rest position.  
     [0065] In FIG. 4C, switch  418  is closed, and the first magnetic field is generated. Accordingly, armature  435  is biased, and end  432  of steerable fiber  430  is moved from the rest position to a first position, where end  432  is aligned with end  442 . There it can exchange light substantially efficiently with end  442  of first cooperating fiber  440 .  
     [0066] In the drawings, it the biased armature  435  is shown contacting pole pieces  420 , although that is not necessary for practicing the invention. Alternate arrangements can be made by different relative positions of stops  457 ,  467  that control the travel of end  432 .  
     [0067] Since switch  400  includes second cooperating fiber  450 , another arrangement is advantageously made. When end  432  of steerable fiber  430  is in the rest position of no alignment with fiber  440 , it can exchange light substantially efficiently with end  452  of second cooperating fiber  450 .  
     [0068] The advantage in this arrangement is that a single action of turning switch  418  ON or OFF can connect fiber  430  with either fiber  440  or fiber  450 .  
     [0069] Another feature of the invention is that ends  442 ,  452  are not parallel to each other, contrary to what prior art teaches. In fact, they define a nonzero angle θ between them. More particularly, end  442  of first cooperating fiber  440  is at a first exchanging direction, when exchanging light with steerable fiber  430 , and end  452  of second cooperating fiber  450  is at a second exchanging direction when exchanging light with steerable fiber  430 . The first exchanging direction is at a nonzero angle θ from the second exchanging direction.  
     [0070] This feature permits better coupling by bending fibers  440 ,  450  less than that of the prior art, e.g. as seen in fibers  132 ,  134  of FIG. 1. It also permits exchanging light between  440 ,  450  and fiber  430  with less loss.  
     [0071] One more feature of the invention is that end  432  of steerable fiber  430  may be separately optionally prebiased with respect to the rest position. This is what enables switching coupling between two fibers with a single action.  
     [0072] In the case of switch  400 , steerable fiber  430  is mounted such that end  432  is bent when at the first position. This way, steerable fiber  430  is prebiased by an internal fiber tensile force, which tends to keep the fiber straight. That force therefore resists bending, and tends to return steerable fiber  430  to the rest position. From the rest position, steerable fiber  430  may couple light with second cooperating fiber  450 .  
     [0073] The invention thus takes advantage of one of the properties of optical fibers made from quartz. Such fibers have no “memory” of being bent, and always return to their shape. This way the switch does not lose efficiency after some time.  
     [0074] In other words, steerable fiber  430  is always bent, but less in the rest position (coupling with fiber  450 ) than in the first position (coupling with fiber  440 ). This is represented by steerable fiber  430  being shown mounted at an angle to a wall of bottom half  404  of the capsule.  
     [0075] In the case of switch  400 , a stop  457  may present a groove for end  432  to be pushed in, by the internal fiber tensile force. End  452  of second cooperating fiber  450  may also be in the same groove, to better secure alignment. Stop  457  is advantageously mounted in bottom half  404  of the capsule.  
     [0076] Equally, when switch  418  is closed (as in FIG. 4C), another stop  467  may provide a meeting place for fiber ends  432 ,  442 . Stop  467  is not shown in FIG. 4A, so as not to obscure salient features.  
     [0077] Referring now to FIG. 5A, a fiber-to-fiber switch  500  is shown, made according to another embodiment of the invention. It will be recognized that switch  500  includes many elements similar to those of switch  400 , whose detailed description will therefore not be repeated in detail.  
     [0078] Switch  500  includes a capsule made from a bottom half  504  and a top half  506 . They are intended to be closed together, thus defining an interior  508  of the capsule.  
     [0079] Switch  500  includes a first electromagnet  510  similar to electromagnet  410 . First electromagnet  510  may be implemented inside or outside the capsule, similarly to electromagnet  410 . First electromagnet  510  is controlled by a switch  518 , similar to switch  418 .  
     [0080] Switch  500  moreover includes a first pair of pole pieces  520 , similar to first pair of pole pieces  420 . As per the above, first pair of pole pieces  520  may go through a wall of the capsule.  
     [0081] Switch  500  also includes a first fixed magnet  522 , which is made from a permanent magnet. Magnet  522  is called fixed because of its close cooperating relationship with pole pieces  520 . Indeed, first fixed magnet  522  generates the first magnetic field in cooperation with first electromagnet  510 . In other words, the fields cooperate. The field of first fixed magnet  522  is transferred by first pair of pole pieces  520  to a location inside the capsule, along with the field from the coil, when generated.  
     [0082] Switch  500  additionally includes a steerable fiber  530 , having an end  532  in the capsule. Steerable fiber  530  is similar to steerable fiber  430 .  
     [0083] Switch  500  further includes an armature  535 , similar to armature  435 , and attached to steerable fiber  530  near end  532 .  
     [0084] Switch  500  moreover includes at least one cooperating fiber  540 , having an end  542  in the capsule, and a second cooperating fiber  550 , having an end  552  in the capsule.  
     [0085] Referring now also to FIG. 5B, and FIG. 5C, the operation of switch  500  is described.  
     [0086] In FIG. 5A, FIG. 5B, switch  518  is open, and the first magnetic field is not generated. Accordingly, armature  535  is not biased from the pole pieces  520 , and end  532  of steerable fiber  530  is at a rest position.  
     [0087] A feature of switch  500  is that end  532  of steerable fiber  530  is separately prebiased with respect to the rest position. A permanent prebiassing magnet  560  generates a separate prebiasing field, to prebias armature  535 . This makes for secure coupling, so that end  532  is aligned with end  552  of second cooperating fiber  550 . There end  532  can exchange light substantially efficiently with end  552 .  
     [0088] Magnet  560  is mounted in the capsule in any suitable way. Its strength is ideally enough to maintain steerable fiber  530  at the rest position, where there is coupling. This way, no electric current is needed to maintain a magnetic field, and better savings are realized.  
     [0089] Alternately, magnet  560  is mounted outside the interior  508  of the capsule. Pole pieces may or may not be provided to transfer its field to a location close to armature  535 .  
     [0090] In FIG. 5C, switch  518  is closed, and the first magnetic field is generated, overcoming the prebiasing field of permanent prebiassing magnet  560 . Accordingly, armature  535  is biased, and end  532  of steerable fiber  530  is moved to a first position. There end  532  is aligned with end  542  of first cooperating fiber  540 , and can exchange light substantially efficiently with it.  
     [0091] Permanent prebiassing magnet  560  makes it so that a single action of turning switch  518  ON or OFF can connect fiber  530  with either fiber  540  or fiber  550 . This way, steerable fiber  530  need not be bent by its mode of mounting, and may be mounted such that it is perpendicular to a side wall of bottom half  504  of the capsule.  
     [0092] For both positions, appropriate stops  557 ,  567  with grooves may provide meeting places for fiber end  532  to meet with fiber ends  542 ,  552 .  
     [0093] Referring now to FIG. 6A, a fiber-to-fiber switch  600  is shown made according to a third embodiment of the invention. It will be recognized that switch  600  includes many elements similar to those of switch  400 , whose detailed description will therefore not be repeated.  
     [0094] Switch  600  includes a capsule made from a bottom half  604  and a top half  606 . Top half  606  normally closes down on bottom half  604 , thus defining an interior  608  of the capsule.  
     [0095] Switch  600  also includes a first electromagnet  610  for selectively generating a first magnetic field. First electromagnet  610  is controlled by a switch  618 .  
     [0096] First electromagnet  610  is outside the capsule, although that is not necessary. First electromagnet  610  may equivalently be implemented to be within the capsule.  
     [0097] A first pair of pole pieces  619  transfer the first generated magnetic field from first electromagnet  610  to a first transferred field location inside the capsule. Pole pieces  619  are at least in part inside the capsule. In fact, they may go through a wall of the capsule.  
     [0098] Switch  600  moreover includes a second electromagnet  620 , for selectively generating a second magnetic field. Second electromagnet  620  is controlled by a switch  628 .  
     [0099] Second electromagnet  620  is outside the capsule, although that is not necessary. Second electromagnet  620  may equivalently be implemented to be within the capsule.  
     [0100] A second pair of pole pieces  629  transfer the second generated magnetic field from second electromagnet  620  to a second transferred field location inside the capsule. Pole pieces  629  are at least in part inside the capsule. In fact, they may go through a wall of the capsule. Pole pieces  629  are similar to pole pieces  619 .  
     [0101] Switch  600  additionally includes a steerable fiber  630 , similar to steerable fiber  430 . An armature  635 , similar to armature  435 , is attached to steerable fiber  630 .  
     [0102] Switch  600  further includes at least a first cooperating fiber  640  and a second cooperating fiber  660 . Light may be exchanged between steerable fiber  630  and either one of cooperating fibers  640 ,  660 .  
     [0103] A feature of switch  600  is that the end of steerable fiber  630  is not prebiased. It has a rest position between cooperating fibers  640 ,  660 . Biasing is needed for steerable fiber  630  to become aligned with either one of cooperating fibers  640 ,  660 .  
     [0104] When at the rest position, a tip of the end of steerable fiber  630  does not contact the capsule. In fact, armature  635  is cantilevered on steerable fiber  630  without contacting the capsule. This is especially possible from the little appreciated property of fused silica fibers that they never lose their shape, even in the face of persistent bending.  
     [0105] Referring now also to FIG. 6B, FIG. 6C, and FIG. 6D, the operation of switch  600  is described.  
     [0106] In FIG. 6A, FIG. 6B, switches  618 ,  628  are open. Neither the first nor the second magnetic field are generated. Accordingly, armature  635  is not biased, and the end of steerable fiber  630  is at the rest position.  
     [0107] In FIG. 6C, switch  618  is closed, and switch  628  is open. Accordingly, the first magnetic field is generated, but not the second. This biases armature  635 , and the end of steerable fiber  630  is moved to a first position of alignment with fiber  640 , where they can exchange light.  
     [0108] In FIG. 6D, switch  618  is open, and switch  628  is closed. Accordingly, the second magnetic field is generated, but not the first. This biases armature  635 , and the end of steerable fiber  630  is moved to a second position of alignment with fiber  660 , where they can exchange light.  
     [0109] As before, in both cases suitable stops confine the travel of the free end of steerable fiber  630 , so that coupling is achieved. These stops are not shown in FIG. 6A, so as not to obscure salient features.  
     [0110] Referring now to FIG. 7, a flowchart  700  is used to illustrate a method according to an embodiment of the invention. Elements of the method of flowchart  700  may also be practiced by devices  400 ,  500  and  600  described above.  
     [0111] According to a box  710 , light is received from an end of a steerable fiber. This would be the remote end from the switch, the end not shown in FIG.S  4 A,  5 A,  6 A. Such light may be received on a continuous basis, and be either always on, or be switching ON and OFF to transmit digital signals.  
     [0112] According to a next box  720 , the received light is output from the other end of the steerable fiber, in other words the end that is inside a capsule.  
     [0113] According to an optional next box  725 , the received light is coupled into a second cooperating fiber, upon exiting from the steerable fiber. That is in the case, for example, of where in device  400  fiber  450  is indeed provided.  
     [0114] According to a next box  730 , a first magnetic field is generated, and transferred to the capsule interior. Transferring is advantageously performed by pole pieces. The steerable fiber is steered to a first position, responsive to the transferred magnetic field. It is enough if only the end of the steerable fiber is thus moved.  
     [0115] According to a next box  740 , the received light is coupled into a first cooperating fiber. This is a result of moving the steerable fiber to the first position. If, at box  725  the received light was being coupled into a second cooperating fiber, that is discontinued.  
     [0116] According to a next box  750 , generation of the first magnetic field is discontinued. This could be for switching a switch for another signal. Accordingly, biasing from the first magnetic field is also discontinued.  
     [0117] According to an optional next box  755 , the steerable fiber is permitted to move to a rest position, as a result of discontinuing biasing from the first magnetic field. This will discontinue coupling light into first cooperating fiber, since the steerable fiber moves away from the first position. When at the rest position, the fiber may couple the received light into the second cooperating fiber.  
     [0118] According to a next box  760 , a second magnetic field is generated, and transferred to the capsule interior. Transferring is advantageously performed by pole pieces. The steerable fiber is thus steered to a second position, responsive to the transferred magnetic field. It is enough if only the end of the steerable fiber is thus moved.  
     [0119] According to a next box  770 , the received light is coupled into another cooperating fiber, as a result of being in the second position.  
     [0120] In addition, the method described above is for a 1×2 switch. The process equivalently reversed for 2×1 switch.  
     [0121] Referring now to FIG. 8, parts of a switch  800  are shown. These parts may also be used in devices  400 ,  500 ,  600 .  
     [0122] Switch  800  may be established in a bottom half  804  of a capsule. A top half (not shown) may be added later.  
     [0123] An optical bench  812  may be placed in bottom half  804 . Pedestals  814 ,  816 ,  818  are provided on bench  812 .  
     [0124] A steerable fiber  830  is provided in a pedestal  814 . Its output end terminates inside the capsule, and has an armature  835 . Armature  835  may be biased by magnetic field transferred into the capsule by pole pieces (not shown).  
     [0125] Two cooperating fibers  840 ,  860  are mounted on pedestal  816 , at a nonzero angle θ. This angle is actually very small, about a few degrees. It is shown large, to better emphasize the aspect.  
     [0126] Fibers  830 ,  840 ,  860  are thus mounted on the pedestals, and designed for end-to end coupling. The end of fiber  830  is brought very close to that of fiber  860  (solid line). In the other switching position, the end of fiber  830  is brought very close to that of fiber  840  (dashed line).  
     [0127] A bench  818  supports structure needed to ensure secure the coupling. This structure may include properly positioned grooves, etc.  
     [0128] Bench  812  may be made from fused silica. This results in the same temperature expansion coefficient as the fibers. As temperature changes, so does the distance between the pedestals, but not the distance between the fibers. Accordingly, the fiber ends may be brought very close, for better coupling.  
     [0129] Referring now to FIG. 9, a detail of steering fiber  830 , made according to the invention.  
     [0130] Longitudinal optical fiber  830  is suitable for waveguiding light. Fiber  830  has an output end  832 . It may be made from fused silica, as is known for fibers.  
     [0131] Fiber  830  includes a substantially spherically shaped armature  835 , attached near output end  832 . Armature  835  is made from a material responsive to a magnetic field, for selectively steering output end  832 . Preferably, armature  835  is spherically shaped.  
     [0132] Armature  835  need not be a magnet. It may be made by forming a drop of liquid glue around the fiber, suspending metal particles in the drop, and then curing the glue. Alternately, armature  835  is a standalone magnet. For purposes of this document standalone magnet means either a permanent magnet, or a magnet made from material that has been subsequently magnetized.  
     [0133] A switch made according to the invention has shown very promising results. In a test of longevity, a 1-by-2 switch passed 500 million switching cycles without a problem and was still running smoothly.  
     [0134] Referring now to FIG. 10, an alternate design is shown according to the invention. A switch  1000  includes a pedestal  1018 , similar to pedestal  818 . Pedestal  818  has two grooves  1022 , which are horizontally disposed.  
     [0135] A fiber  1030  is to be placed into grooves  1022 , to make contact with other cooperating fibers (not shown). Fiber  1030  has an armature  1035 , made similarly to armature  835 , and is moved by magnetic fields.  
     [0136] A permanent prebiasing magnet  1040  exerts a field on armature  1035 . This way, permanent prebiasing magnet  1040  maintains steerable fiber  1030  in whichever one of grooves  1022  it was last placed, without applying any current.  
     [0137] A first pair of pole pieces  1050  are designed to transfer a selectively generated vertical magnetic field, so as to overcome the field of permanent prebiasing magnet  1040 . This way, they can lift steerable fiber  1030  out of groove  1022  by its armature  1035 , along a vertical direction  1054 . When the vertical magnetic field is no longer generated, permanent prebiasing magnet  1040  prevails, and moves armature  1035  downwards, along vertical direction  1054 . An appropriate stop (not shown) may be used to prevent overtravel of steerable fiber  1030  and its armature  1035 .  
     [0138] A second pair of pole pieces  1060  and a third pair of pole pieces  1070  are designed to transfer selectively generated horizontal magnetic fields. This way, they can shift steerable fiber  1030  by its armature  1035  along a horizontal direction  1074 . They would do this preferably when steerable fiber  1030  has been lifted out of the one of grooves  1022  that it was placed in, for being aligned with the other. Lifting would take place along vertical direction  1054 , as described above. Again, appropriate stops (not shown) may be used to prevent overtravel of steerable fiber  1030  and its armature  1035 .  
     [0139] Switch  1000  may be optimized in a number of ways. For example, one of pairs of pole pieces  1060 ,  1070  may be substituted by a permanent magnet. For another example, three grooves  1022  may be used instead of two.  
     [0140] In other improvements, a single armature may be used for two fibers.  
     [0141] Referring to FIG. 11, a steerable fiber  1132  and an auxiliary steerable fiber  1134  share a common armature  1135 . They are to be coupled in various combinations with at least one of cooperating fibers  1142 ,  1144 ,  1146 . Coupling is over a pedestal  1118 , having groves  1122 .  
     [0142] Pairs of pole pieces  1160  and  1170  are designed to transfer selectively generated horizontal magnetic fields. This way, they can shift the pair of steerable fiber  1132  and auxiliary steerable fiber  1134  by their shared armature  1135 , and guide it to the right pair of groves  1122 .  
     [0143] A person skilled in the art will be able to practice the present invention in view of the description present in this document, which is to be taken as a whole. Numerous details have been set forth in order to provide a more thorough understanding of the invention. In other instances, well-known features have not been described in detail in order not to obscure unnecessarily the invention.  
     [0144] While the invention has been disclosed in its preferred form, the specific embodiments as disclosed and illustrated herein are not to be considered in a limiting sense. Indeed, it should be readily apparent to those skilled in the art in view of the present description that the invention may be modified in numerous ways. The inventor regards the subject matter of the invention to include all combinations and subcombinations of the various elements, features, functions and/or properties disclosed herein. For example, a switch may be made with combinations of elements from switches  400 ,  500 ,  600 . Plus, switch  600  can have a second fixed magnet to generate the second magnetic field in cooperation with the second electromagnet, and so on.  
     [0145] The following claims define certain combinations and subcombinations, which are regarded as novel and non-obvious. Additional claims for other combinations and subcombinations of features, functions, elements and/or properties may be presented in this or a related document.