Abstract:
An optical switching device comprising a plurality of mechanical optical switching structures having one to several movable optical fibers and one to several fixed optical fibers installed in a housing in which a refractive index matching oil is filled up and immerses the structures. Each of the structures has an electromagnetic actuator to reciprocate open ends of the movable optical fibers relatively to open ends of the fixed optical fibers and to connect/disconnect optical paths. Ends opposite to the open ends of the movable optical fibers and the fixed optical fibers are drawn out through ports located on the housing so that a certain number of optical fibers among the optical fibers drawn out serve as input optical fibers, while a certain number of optical fibers among the other optical fibers drawn out serve as output optical fibers, to constitute the optical switching device of m×n type, in which m is the number of input paths and n is the number of output paths, providing a small-sized optical switching device having variable numbers of input/output paths.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an optical switch, and in particular, to a mechanical optical switching device having multiple input optical fibers and multiple output optical fibers.  
         [0003]     2. Description of the Related Art  
         [0004]     As for an optical switch for switching an optical path, those for switching a traveling direction of light by electrically changing a refractive index or phase of an optical path, switching a traveling direction of light by mechanically displacing an optical path, and so on have been developed. The mechanical optical switch has been often used in an optical communication apparatus, optical transmission apparatus, or the like because it has a low coupling loss of light, is substantially independent of the wavelength of the propagating light, and have a self-latching property for maintaining, even after removal of electric power, the coupling state of light in a state before the removal.  
         [0005]     The mechanical optical switch comprises a movable optical fiber which can be elastically deformed and two fixed optical fibers, an open end of the movable optical fiber facing to open ends of the fixed optical fibers via an optical gap, and switches the optical path by displacing the open end of the movable optical fiber with respect to the open ends of the fixed optical fibers. In the mechanical optical switch, the movable optical fibers and the fixed optical fibers are usually used as input paths and output paths, respectively. A silicone based liquid or the like serving as a refractive index matching oil is placed between the open end of the movable optical fiber and those of the fixed optical fibers in order to prevent attenuation and scattering of light from occurring there. For that purpose, the whole mechanism of the optical switch is contained in an air-tight housing, and the housing is filled with the silicone based liquid or the like.  
         [0006]     The fixed optical fibers are held by a fixed holder (fixed block) at portions close to their open ends. The movable optical fiber is held by a movable holder (movable block) at a portion close to its open end. The movable optical fiber is held by another fixed holder at a point distant from the tip of the movable optical fiber, and the point constitutes a fulcrum.  
         [0007]     Since the open ends of the fixed optical fibers and the open end of the movable optical fiber are provided to face to each other, the fixed holder and the movable holder also face to each other. In order to displace the open end of the movable optical fiber with respect to the open ends of the fixed optical fibers, the movable holder is displaced with respect to the fixed holder. In order to keep such a movement within a certain route for avoiding misalignment when displacing the movable holder with respect to the fixed holder, guide pins are provided on one of the holders (for example, fixed holder) to protrude from the facing surface thereof and are inserted into guide channels provided on the facing surface of the other holder (for example, movable holder). Thus, when the movable holder is displaced, the guide pins move along the guide channels, and the movable holder is stopped when the guide pins reach the ends of the guide channels.  
         [0008]     An electromagnetic actuator is used to displace the movable holder or movable optical fiber with respect to the end of the fixed optical fiber, which is typically large in size. The movable holder or movable optical fiber is moved in the refractive index matching oil having viscosity, so that a significant magnitude of force is required. For that purpose, a large electromagnetic actuator is required. The housing of the optical switch is intended to contain the large electromagnetic actuator therein, so that it also becomes large in size. In addition, since the optical switch circuit includes a combination of many optical switches, if the individual optical switches are large, the optical switch circuit is also large.  
         [0009]     U.S. Pat. No. 6,169,826 (issued on Jan. 2, 2001) has been proposed to reduce the size of an electromagnetic actuator used in an optical switch. The structure thereof will be described below with reference to  FIGS. 10 and 11 .  
         [0010]     Referring to  FIGS. 10 and 11 , in an optical switch  800 , fixed optical fibers  824  and movable optical fibers  822  are positioned so as to have their respective open ends faced to each other in a housing  810 . The open ends of the movable optical fibers are moved relatively to the open ends of the fixed optical fibers to connect and/or disconnect optical paths. The fixed optical fibers are held by a fixed holder  832  made of soft magnetic ceramic at a portion close to the open ends thereof in the housing  810 . The movable optical fibers  822  are supported and fixed in the housing  810  by another fixed holder  836  at a distance from the open ends thereof and are held by a movable holder  834  made of soft magnetic ceramic at a portion close to the open ends thereof. When the movable holder  834  made of soft magnetic ceramic is reciprocated with respect to the fixed holder  832  made of soft magnetic ceramic, the open ends of the movable optical fibers held by the movable holder  834  made of soft magnetic ceramic are reciprocated with respect to the tips of the fixed optical fibers  824  along with the movable holder  834  to connect and/or disconnect the optical paths.  
         [0011]     An electromagnetic actuator  850  comprises an E-shaped yoke  852  having a back yoke (column yoke)  854  which is located on the side of the fixed optical fibers  824  from the fixed holder  832  made of soft magnetic ceramic in the housing, and first and second end legs  856  and  856 ′ of the E-shaped yoke  852  extend from the back yoke  854  to the side surfaces of the movable holder  834  made of soft magnetic ceramic. The first and second end legs  856  and  856 ′ have first and second pole pieces  858  and  858 ′, respectively, which face the side surfaces of the movable holder  634  made of soft magnetic ceramic. The movable holder  834  made of soft magnetic ceramic can reciprocate between the first and second pole pieces  858  and  858 ′. A center leg  862  protruding from the center of the back yoke  854  toward the movable holder  834  made of soft magnetic ceramic is constituted by a permanent magnet  864  and the fixed holder  832  made of soft magnetic ceramic. For example, the permanent magnet  864  may be a sintered neodymium-iron-boron permanent magnet.  
         [0012]     The permanent magnet  864  is magnetized in a direction from the fixed holder  832  made of soft magnetic ceramic to the back yoke  854  or in the direction opposite thereto. Part of the magnetic flux exiting from the permanent magnet  864  enters the first end leg  856  through the back yoke  854 . Then, it enters the movable holder  834  made of soft magnetic ceramic via the first pole piece  858 . Then, it passes through the fixed holder  832  made of soft magnetic ceramic to return to the permanent magnet  864 . In this way, the permanent magnet  864 , a first half of the back yoke  854 , the first end leg  856 , the first pole piece  858 , the movable holder  834  and the fixed holder  832  constitute a first magnetic path. The magnetic flux of the permanent magnet passing through the first magnetic path is denoted by reference symbol A in this drawing.  
         [0013]     Part of the magnetic flux exiting from the permanent magnet  864  enters the second end leg  856 ′ through the back yoke  854 . Then, it enters the movable holder  834  made of soft magnetic ceramic via the second pole piece  858 ′. Then, it passes through the fixed holder  832  made of soft magnetic ceramic to return to the permanent magnet  864 . In this way, the permanent magnet  864 , a second half of the back yoke  854 , the second end leg  856 ′, the second pole piece  858 ′, the movable holder  834  and the fixed holder  832  constitute a second magnetic path. The magnetic flux of the permanent magnet passing through the second magnetic path is denoted by reference symbol B in this drawing.  
         [0014]      FIG. 10  shows a state in which the movable holder  834  made of soft magnetic ceramic is attracted by the first pole piece  858 , and there is a wider gap between the movable holder and the second pole piece  858 ′. The optical switch  800  comprises four fixed optical fibers  824  (denoted by reference symbols f 1 , f 2 , f 3 , and f 4  from the left) and two movable optical fibers  822  (denoted by reference symbols m 1  and n 2  from the left). When the movable holder  834  made of soft magnetic ceramic is attracted by the first pole piece  858 , the fixed optical fiber f 1  and the movable optical fiber m 1  have their open ends face each other, and the fixed optical fiber f 3  and the movable optical fiber m 2  have their open ends face each other, thereby establishing optical paths between them respectively. On the other hand, when the movable holder  834  made of soft magnetic ceramic is attracted by the second pole piece  858 ′, optical paths are established between the fixed optical fiber f 2  and the movable optical fiber m 1 , and between the fixed optical fiber f 4  and the movable optical fiber m 2 . Displacing the movable holder  834  from the first pole pieces  858  to the second pole piece  858 ′ can switch the position of the movable optical fiber m 1  from the fixed optical fiber f 1  to f 2 , and the position of the movable optical fiber m 2  from the fixed optical fiber f 3  to f 4 .  
         [0015]     First and second coil members  872  and  872 ′ are wound around the first and second end legs  856  and  856 ′, respectively. When a current for canceling or decreasing the magnetic flux A is applied to the first coil member  872 , and a current having a direction intended to increase the magnetic flux B is applied to the second coil member  872 ′, the attraction between the movable holder  834  and the first pole piece  858  is vanished, and then the movable holder  834  is attracted to the second pole piece  858 ′ to move toward the second pole piece  858 ′. When the movable holder  834  is attracted by the second pole piece  858 ′, the optical paths are established in such a manner that the movable optical fiber m 1  is connected to the fixed optical fiber f 2  and the movable optical fiber m 2  is connected to the fixed optical fiber f 4 . If the current applied to the first and second coil members  872  and  872 ′ is stopped in this state, the state in which the movable holder  834  is attracted by the second pole piece  858 ′ is maintained by the permanent magnet  864 .  
         [0016]     If a current for canceling or decreasing the magnetic flux B is applied to the second coil member  872 ′, and a current for increasing the magnetic flux A is applied to the first coil member  872  when the movable holder  834  is attracted by the second pole piece  858 ′, the movable holder  834  leaves the second pole piece  858 ′ and moves toward the first pole piece  858 . Then, as shown in  FIG. 10 , the movable optical fiber m 1  is connected to the fixed optical fiber f 1 , and the movable optical fiber m 2  is connected to the fixed optical fiber f 3 . If the current applied to the coil members  872  and  872 ′ is stopped in this state, the connections are maintained.  
         [0017]     In case of the electromagnetic actuator according to the above-described US patent, downsizing is realized by utilizing the movable holder  834  and fixed holder  832  both made of soft magnetic ceramic as part of the magnetic circuit of the electromagnetic actuator  850 .  
         [0018]     Since the fixed holder  832  is utilized as part of the magnetic circuit, however, most parts of the electromagnetic actuator  850  are provided on the side of the fixed optical fiber  824  in the optical switch  800 . The length of the movable optical fiber  822  from its fulcrum to its open end is required to be enough for allowing a portion thereof from the fulcrum to the open end, in particular, to the point supported by the movable holder, to elastically pivot without undergoing an excessive force. For this reason, this portion of the movable optical fiber cannot be shortened.  
         [0019]     Therefore, the optical switch has a length more than the sum of the length from the fulcrum to the open end of the movable optical fiber and the length of the electromagnetic actuator. The electromagnetic actuator includes the coil members. If the length of the electromagnetic actuator is reduced, the length of the coil member should also be reduced. Therefore, in order to ensure the same level of ampere-turn, the coil is rolled up to increase the number of overlap accordingly. As a result, the coil has an increased diameter.  
         [0020]     The optical switch is provided on the bottom of a lower half  811  of the housing made of alumina ceramics or the like and is covered by the upper half  812  of the housing from the above, and a gap between the lower half and the upper half is sealed to provide the air-tight housing  810  as shown in  FIG. 11  in a perspective view. Refractive index matching oil is filled into the housing  810  through its inlet  817  which is closed thereafter so that the mechanical optical switching structures are completely immersed in the refractive index matching oil.  
         [0021]     The assignee of this invention proposed in U.S. patent application Ser. No. 09/993,649 (filed Nov. 27, 2001) an optical switch further smaller than that proposed in the US patent. The optical switch  900  will be described below, referring to  FIG. 12 .  
         [0022]     Fixed optical fibers  924  near their open ends are fixed by a fixed holder  932  attached to a base plate  915  near a housing side wall. Movable optical fibers  922  are fixed, at a distance from the open ends thereof, to the base plate  915  by another fixed holder  936  attached to the base plate  915 . The latter fixed holder  936  is arranged near another housing side wall having a slot  913  passing the movable optical fibers  922  therethrough. A movable holder  934  made of soft magnetic material is provided on the base plate  915  so as to face the fixed holder  932 , holds the movable optical fibers  922  near the open ends thereof, and reciprocates relatively to the fixed holder  932  on the base plate  915 , thereby connecting and/or disconnecting, or switching, the open ends of the fixed optical fibers and the open ends of the movable optical fibers. Providing a gap between the movable holder  934  of soft magnetic material and the base plate  915 , such as a glass plate, allows the movable holder  934  to move smoothly.  
         [0023]     In order to reciprocate the movable holder  934  made of soft magnetic material relatively to the fixed holder  932 , an electromagnetic actuator  950  is located in an area on the side of the movable optical fibers  922  from the open ends of the movable optical fibers in the housing  910 . That is, the electromagnetic actuator  950  is provided between the front end of the movable holder  934  near the fixed holder  932  and the rear end of the fixed holder  936  (that is, the end of the fixed holder  936  near the housing side wall on the side of the movable optical fiber).  
         [0024]     As shown in  FIG. 12 , the electromagnetic actuator  950  has an E-shaped yoke  952 , which has two end legs  956 ,  956 ′ and a center leg  962 . The E-shaped yoke  952  has a back yoke  954 , and the end leg  956  extends from one end of the back yoke  954  to a position where it faces one side surface of the movable holder  934  of soft magnetic material. The end leg  956 ′ extends from the other end of the back yoke  954  to a position where it faces the other side surface of the movable holder  934  of soft magnetic material. The end legs  956  and  956 ′ have pole pieces  958  and  958 ′, respectively, each of which faces a side surface of the movable holder  934 .  
         [0025]     The end leg  956  and the half of the back yoke  954  on the side of the end leg  956  may be collectively referred to as a first yoke. The end leg  956 ′ and the half of the back yoke  954  on the side of the end leg  956 ′ may be collectively referred to as a second yoke. The pole piece  958  attached to the end leg  956  may be referred to as a first pole piece, the pole piece  958 ′ attached to the end leg  956 ′ may be referred to as a second pole piece.  
         [0026]     The movable holder  934  has gaps between the first pole piece  958  and one side surface of the movable holder  934  and between the second pole piece  958 ′ and the other side surface of the movable holder  934 , respectively, so as to reciprocate between the first and second pole pieces  958  and  958 ′.  
         [0027]     A permanent magnet  964  and a soft magnetic material block  966  are provided on the center leg  962  attached to the back yoke  954  of the E-shaped yoke  952 , and the center leg  962  extends toward the movable holder  934 . The permanent magnet  964  is magnetized in a direction from the soft magnetic material block  966  to the back yoke  954 , or in the direction opposite thereto. The permanent magnet  964  may be a sintered neodymium-iron-boron permanent magnet. Part of the magnetic flux exiting from the permanent magnet  964  enters the end leg  956  through the back yoke  954 . Then, it enters the movable holder  934  made of soft magnetic material via the first pole piece  958 . Then, it passes through the soft magnetic material block  966  to return to the permanent magnet  964 . In this way, the permanent magnet  964 , the first half of the back yoke  954 , the end leg  956 , the first pole piece  958 , the movable holder  934  and the soft magnetic material block  966  constitute a first magnetic path. The magnetic flux of the permanent magnet passing through the first magnetic path is denoted by reference symbol A in the drawing.  
         [0028]     Part of the magnetic flux exiting from the permanent magnet  964  enters the end leg  956 ′ through the back yoke  954 . Then, it enters the movable holder  934  made of soft magnetic material via the second pole piece  958 ′. Then, it passes through the soft magnetic material block  966  to return to the permanent magnet  964 . In this way, the permanent magnet  964 , the second half of the back yoke  954 , the end leg  956 ′, the second pole piece  958 ′, the movable holder  934  and the soft magnetic material block  966  constitute a second magnetic path. The magnetic flux passing through the second magnetic path is denoted by reference symbol B in the drawing.  
         [0029]     A first coil member  972  and a second coil member  972 ′ are wound around the end legs  956  and  956 ′, respectively. The first and second coil members  972  and  972 ′ are connected in series in such a manner that when a DC voltage is applied between their respective terminals  976  and  976 ′, the two coil members  972  and  972 ′ generate magnetic fields of directions opposite to each other. When a current for canceling or decreasing the magnetic flux A is applied to the first coil member  972 , and a current having a direction intended to increase the magnetic flux B is applied to the second coil member  972 ′, the attraction between the movable holder  934  and the first pole piece  958  is vanished, and then the movable holder  934  is attracted to the second pole piece  958 ′ to move toward the second pole piece  958 ′. In the state in which the movable holder  934  is attracted by the second pole piece  958 ′, the optical paths are established in such a manner that the movable optical fiber m 1  is connected to the fixed optical fiber f 2  and the movable optical fiber m 2  is connected to the fixed optical fiber f 4 . If the current applied to the first and second coil members  972  and  972 ′ is stopped in this state, the state in which the movable holder  934  is attracted by the second pole piece  958 ′ is maintained by the permanent magnet  964 .  
         [0030]     If a current for canceling or decreasing the magnetic flux B is applied to the second coil member  972 ′, and a current for increasing the magnetic flux A is applied to the first coil member  972  when the movable holder  934  is attracted by the second pole piece  958 ′, the movable holder  934  leaves the second pole piece  958 ′ and moves toward the first pole piece  958 . Then, the movable optical fiber m 1  is connected to the fixed optical fiber f 1 , and the movable optical fiber m 2  is connected to the fixed optical fiber f 3 . If the current applied to the coil members is stopped in this state, the connections are maintained.  
         [0031]     The optical switches described in U.S. Pat. No. 6,169,826 and U.S. patent application Ser. No. 09/993,649 have electromagnetic actuators provided in an air-tight housing, which actuators move movable optical fibers at the input side to switch the optical paths. The movable optical fibers are immersed in a refractive index matching oil and, when moving the movable optical fibers, they receive viscous resistance of the refractive index matching oil. Since a large driving force is required for the reason that elastic resistance of the optical fiber becomes large when the number of movable optical fibers increases, a large-sized electromagnetic actuator is also required when the number of movable optical fibers increases. Hence, with respect to the optical switch, if expressed by a ratio of the number of input optical fibers and the number of output optical fibers, a ratio of the number of inputs and the number of outputs is 1:2 or 2:4, that is, those of a 1×2 type or a 2×4 type are used in large quantities.  
         [0032]     However, in order to switch the optical paths, the optical switch having the number of optical fibers which match the number of paths presently used is required and a 4×8 type or a larger type is also required. There are often cases where, in order to construct any m×n optical switches, the optical switches having a small number of input optical fibers and a small number of output optical fibers such as the 1×2 type, the 2×4 type are combined plurally in use. Such an example is disclosed in Japanese Patent Laid-Open No. 6-208065 (JP 6-208065 A). Illustrated there is a 1×8 type optical switch, which was fabricated by combining seven 1×2 type optical switches in three stages.  
         [0033]     When the 1×8 type optical switch is fabricated according to JP 6-208065 A by using a plurality of the 1×2 type optical switches disclosed in the above described U.S. Pat. No. 6,169,826 and U.S. patent application Ser. No. 09/993,649, it forms a combination shown in  FIG. 13  in a plane view. In the same drawing, reference numeral  800  denotes the 1×2 type optical switch, and an input signal enters the 1×2 type optical switch located at the first stage from the input optical fiber. The output of the 1×2 type optical switch of this first stage is connected to the input optical fibers of the two 1×2 type optical switches located at the second stage. Each of outputs of the 1×2 type optical switches of the second stage is connected to the input optical fibers of the four 1×2 type optical switches located at the third stage. Since the output optical fibers of the 1×2 type optical switches of the third stage are eight in total, it is obvious that the 1×8 type optical switch is constructed by the seven 1×2 type optical switches.  
         [0034]     Because of the requirement to downsize the optical switch circuits, efforts are made to downsize individual 1×2 optical switches. Nevertheless, the 1×8 type optical switch fabricated in this way by combining the seven 1×2 type optical switches are large in size.  
       SUMMARY OF THE INVENTION  
       [0035]     It is therefore an object of the invention to provide an optical switching device which is small-sized in whole, while the device comprises multiple mechanical optical switching structures having one to several input optical fibers and one to several output optical fibers.  
         [0036]     Another object of the invention is to provide an optical switching device with variable numbers of input/output optical fibers.  
         [0037]     A further object of the invention is to prevent an electromagnetic interference between electromagnetic actuators of a plurality of mechanical optical switching structures used in combination.  
         [0038]     An optical switching device according to the invention comprises an air-tight housing, a plurality of mechanical optical switching structures installed in the housing and a refractive index matching oil filled up in the housing to immerse the plurality of mechanical switching structures. In the device, each of the plurality of mechanical optical switching structures comprises one to eight fixed optical fibers having open ends, one to four movable optical fibers having open ends movable relatively to the open ends of the fixed optical fibers and an electromagnetic actuator which reciprocates the open ends of the movable optical fibers relatively to the fixed optical fiber open ends to connect/disconnect optical paths composed of the fixed and the movable optical fibers. Each of ends opposite to the open ends of the movable optical fibers and the fixed optical fibers are drawn out or extended through ports located on the housing. A certain number of optical fibers among the optical fibers drawn out serve as input optical fibers for the device, while a certain number of optical fibers among the optical fibers drawn out serve as output optical fibers for the device, constituting the optical switching device of m×n type, in which m is the number of input paths or input optical fibers and n is the number of output paths or output optical fibers.  
         [0039]     In the optical switching device of the invention, ends opposite to the open ends of one to several fixed optical fibers among the fixed optical fibers of a mechanical optical switching structure may be connected, in the housing, to ends opposite to the open ends of one to several movable optical fibers among the movable optical fibers of another mechanical optical switching structure or to ends opposite to the open ends of one to several fixed optical fibers among the fixed optical fibers of another mechanical optical switching structure. In the optical switching device of the invention, ends opposite to the open ends of one to several movable optical fibers among the movable optical fibers of a mechanical optical switching structure may be connected, in the housing, to ends opposite to the open ends of one to several movable optical fibers among the movable optical fibers of another mechanical optical switching structure. Furthermore, in the housing of the optical switching device, ends opposite to the open ends of one to several movable optical fibers among the movable optical fibers of a mechanical optical switching structure may be connected to ends opposite to the open ends of one to several fixed optical fibers among the fixed optical fibers of the same mechanical optical switching structure or to ends opposite to the open ends of one to several movable optical fibers among the movable optical fibers of the same mechanical optical switching structure. Ends opposite to the open ends of one to several fixed optical fibers among the fixed optical fibers of a mechanical optical switching structure may be connected, in the housing, to ends opposite to the open ends of one to several fixed optical fibers among the fixed optical fibers of the same mechanical optical switching structure. The connection between the ends of the optical fibers may be accomplished by splicing.  
         [0040]     In the optical switching device of the invention, ends opposite to the open ends of the movable and the fixed optical fibers in the housing except for those connected or spliced to one another at their ends are drawn out or extended through ports located on the housing side wall. Ends of one to several optical fibers among the optical fibers drawn out of the housing through the ports of the housing side wall may be connected to ends of one to several other optical fibers.  
         [0041]     Each of the mechanical optical switching structure used in the optical switching device of the invention has one to eight fixed optical fibers and one to four movable optical fibers. In order for each of the mechanical optical switching structures to work with a small electromagnetic actuator, it is desirable that the number of the movable optical fibers is reduced. Also, to make the mechanical optical switching structures as simple as possible, they are preferably a 1×2 type or a 2×4 type.  
         [0042]     It is preferable that the plurality of mechanical switching structures used in the optical switching device of the invention are arranged in parallel to each other in the housing and that each of the structures is in antiparallel to a neighboring structure. Alternatively, it is preferable that the neighboring mechanical switching structures used in the optical switching device of the invention are arranged in parallel to each other in the housing and that an electromagnetic shield is interposed between the electromagnetic actuators of the neighboring mechanical switching structures. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0043]      FIG. 1  is a plan view of an optical switching device of EXAMPLE 1 according to the invention, with an upper half of a housing removed;  
         [0044]      FIG. 2  is a perspective view of a mechanical optical switching structure used in EXAMPLE 1 of the invention;  
         [0045]      FIG. 3  is an exploded perspective view of a housing used in EXAMPLE 1 of the invention;  
         [0046]      FIG. 4  shows a perspective view of the optical switching device of EXAMPLE 1 of the invention;  
         [0047]      FIG. 5  is a plan view of an optical switching device of EXAMPLE 2 according to the invention, with an upper half of a housing removed;  
         [0048]      FIG. 6  is a plan view of an optical switching device of EXAMPLE 3 of the invention, with an upper half of a housing removed;  
         [0049]      FIG. 7  is a plan view of an optical switching device of EXAMPLE 4 of the invention, with an upper half of a housing removed;  
         [0050]      FIG. 8  is a plan view of an optical switching device of EXAMPLE 5 of the invention, with an upper half of a housing removed;  
         [0051]      FIG. 9  is a plan view of an optical switching device of EXAMPLE 6 of the invention, with an upper half of a housing removed;  
         [0052]      FIG. 10  is an exploded perspective view of an optical switch described in U.S. Pat. No. 6,169,826;  
         [0053]      FIG. 11  is a perspective view of the optical switch of  FIG. 10 ;  
         [0054]      FIG. 12  is an exploded perspective view of an optical switch described in a US patent application; and  
         [0055]      FIG. 13  is a plan view of a combination of optical switches described in a prior reference, JP 6-208065 A. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0056]     Optical switching devices according to EXAMPLES of the invention will be described with reference to the drawings.  
       EXAMPLE 1  
       [0057]     An optical switching device  100  according to EXAMPLE 1 of the invention is shown in  FIGS. 1 through 4 .  FIG. 1  shows the optical switching device  100  and is a plan view of a state of an upper half of an air-tight housing  110  removed,  FIG. 3  is an exploded perspective view of the housing  110 , and  FIG. 4  is a perspective view of the optical switching device  100 .  
         [0058]     As can be seen by these drawings, the optical switching device  100  has the housing  110  made of alumina ceramics or the like. The housing  110  is covered by an upper half  112  which is a lid on a lower half  111  having a bottom, and is sealed. A gap between the lower half  111  and the upper half  112  is bonded by butting portions of surrounding walls.  
         [0059]     A total of four sets of optical switching structures by summing two 1×2 type mechanical type optical switching structures  700  and two 2×4 type mechanical optical switching structures  700  are placed in parallel on the bottom of the housing  110 . A movable optical fiber of each mechanical optical switching structure  700  is drawn outside of the housing  110  through an opening opened at the left side wall or a groove  113 . A fixed optical fiber is drawn outside the housing  110  through the opening opened at the right side wall of the housing  110  or a groove  114 . The openings opened at the housing or the grooves  113 ,  114  are sealed by synthetic resin bond after passing the optical fibers. Cylindrical supports which surround each opening  113 ,  114  are attached on housing wall surfaces, and both the opening and the cylindrical support constitute a port  120 . Insertion of the bond into the port  120  allows the optical fibers passing there to be held. The movable optical fibers  722  of the four mechanical optical switching structures  700  drawn outside the housing from the housing port  120  constitute input optical fibers  122 . The fixed optical fibers  724  of the four mechanical optical switching structures  700  drawn outside the housing from the housing port  120  constitute output optical fibers  124 . The optical switching device  100  shown in the drawing has six input paths and 12 output paths, thereby constituting a 6×12 type.  
         [0060]     Here, the output optical fibers  124  can be used as the input paths, and the input optical fibers  122  can be used as the output paths. Alternatively, the two fixed optical fibers  724  of a mechanical optical switching structure  700   a  are connected to the two movable optical fibers of an optical switching structure  700   b , respectively outside of the housing, thereby making it possible to reduce both the number of input paths and the number of output paths by two each and, moreover, the two fixed optical fibers of an optical switching structure  700   c  are connected to the two movable optical fibers of an optical switching structure  700   d , respectively outside of the housing, thereby making it possible also to reduce both the number of input paths and the number of output paths by two each. In this way, it is possible to constitute the optical switching device of a 4×10 type or a 2×8 type.  
         [0061]     Alternatively, the two fixed optical fibers of the optical switching structure  700   a  are connected to two among the four fixed optical fibers of the optical switching structure  700   b , and the two fixed optical fibers of the optical switching structure  700   c  are connected to the remaining two among the four fixed optical fibers of the optical switching structure  700   b  so as to use the movable optical fibers of the optical switching structures  700   a ,  700   c , and  700   d  as the input paths, and the movable optical fiber of the optical switching structure  700   b  and the fixed optical fiber of the optical switching structure  700   d  as the output paths, thereby constituting this optical switching device as a 4×6 type.  
         [0062]     In the housing  110  of the optical switching device  100 , the fixed optical fibers of an optical switching structure can be connected to the movable optical fibers of another optical switching structure, and the fixed optical fibers of an optical switching structure can be connected to the fixed optical fibers of another optical switching structure, or the movable optical fibers of an optical switching structure can be connected to the movable optical fibers of another optical switching device. Alternatively, in the housing  110  of the optical switching device  110 , the fixed optical fibers of an optical switching structure can be connected to the movable optical fibers of the same optical switching structure, the fixed optical fibers of an optical switching structure can be connected to the fixed optical fibers of the same optical switching structure, or the movable optical fibers of an optical switching structure can be also connected to the movable optical fibers of the same optical switching structure. Further, in case of necessity, ends of some fixed optical fibers or some movable optical fibers may be let opened. In this way, the input paths and the output paths can be changed variously.  
         [0063]     The optical switching device  100  has four optical switching structures  700   a - d , which are provided in parallel arrangement on the bottom of the air-tight housing  110 , the housing  110  has refractive index matching oil filled  118  therein, and each optical switching structure is immersed in the refractive index matching oil  118 , and an open end gap between the movable optical fibers and the fixed optical fibers located at each optical switching structure is also filled with the refractive index matching oil. Each of the optical switching structures  700   a - d  has a structure as shown in  FIG. 2  in a perspective view, and they can have the same structure of the optical switch shown in  FIGS. 10 and 12 .  
         [0064]     The optical switching structures  700   a - d  have the open ends of the movable optical fibers  722  positioned so as to face to the open ends of the fixed optical fibers  724  in the electromagnetic actuators  750  provided on a base plate  715  made of glass and the like. Each base plate  715  of the optical switching structures  700   a - d  is bonded and fixed on a bottom of the lower half of the housing. The movable optical fiber open ends relatively move with respect to the open ends of the fixed optical fibers  724 , thereby connecting/disconnecting the optical paths. The fixed optical fibers are held on the base plate  715  by a fixed holder  732  near the open ends. The movable optical fibers  722  are supported by another fixed holder  736  fixed on the base plate at a distance from the open ends of the movable optical fibers  722 , and the movable optical fibers are held by a movable holder  734  comprising a soft magnetic material, for example, soft magnetic ceramics near the open ends. The movable holder  734  is reciprocated with respect to the fixed holder  732 , so that the movable optical fiber open ends held by the movable holder  734  are reciprocated together with the movable holder relatively to the tips of the fixed optical fibers  724 , thereby connecting/disconnecting the optical path.  
         [0065]     Since the electromagnetic actuator  750  may have the same structure as described with reference to  FIGS. 10 and 12 , there will be no need to describe in detail a structure and an operation thereof. Note, however, that the movable holder  734  is driven depending on the direction of the current let flow to a coil member  722 , thereby connecting/disconnecting the optical paths.  
         [0066]     In case of the optical switch shown in  FIGS. 10 and 12 , each optical switching structure is provided in the optical switch housings  810 ,  910 , while in case of the optical switching device  100  according to the invention, four of the optical switching structures  700   a - d  are provided in one set of the housing  110 . For this reason, there exists no housing wall between the optical switching structures, and the optical switching structures are provided in close vicinity to each other. In contrast to the case where four conventional optical switches are used, the optical switching device  100  according to the invention having the four optical switching structures is small in its occupied area.  
         [0067]     As shown in  FIG. 1 , when the four optical switching structures are arranged in parallel, the electromagnetic actuators  750  of adjacent optical switching structures are also located in close vicinity to each other and, therefore, it is necessary to set the distance between them at such a pitch so that no electromagnetic interference is caused between the electromagnetic actuators.  
       EXAMPLE 2  
       [0068]     An optical switching device  200  according to EXAMPLE 2 of the invention is shown in  FIG. 5  in a plan view of a state of the upper half of the housing  110  removed. This optical switching device  200  has a 1×2 type optical switching structure  700   a , a 2×4 type optical switching structure  700   b ′, a 1×2 type optical switching structure  700   c  and a 2×4 type optical switching structure  700   d ′ arranged in parallel in the optical switch housing  110 . The adjacent optical switching structures are in anti-parallel to each other. The optical fibers drawn outside of the housing from the port  120   a  located on the left side wall in the drawing are ten in total, and the optical fibers drawn outside of the housing from the port  120   a  located on the right side wall are eight in total. If the optical fibers extended outside from the left side port serve as input paths, and the optical fibers extended outside from the right side port as output paths, this optical switching device can constitute a 10×8 type.  
         [0069]     Since the adjacent optical switching structures are in anti-parallel to each other, that is, in the directions opposite to neighboring structures, as can be seen from the drawing, the position of the electromagnetic actuator located in each optical switching structure is apart from each other and does not abut against each other. For this reason, there is no risk of electromagnetic interference being caused between the electromagnetic actuators of the adjacent optical switching structures.  
         [0070]     As is evident from the comparison of  FIG. 5  with  FIG. 1 , the port  120   a  of the optical switching structure  200  is integrally formed by four ports. Since the port is metal-bonded and assembled on the position corresponding to the housing wall, when a plurality of ports are integrated as shown by this EXAMPLE, an assembling labor thereof can be saved.  
       EXAMPLE 3  
       [0071]     An optical switching device  300  according to EXAMPLE 3 of the invention is shown in  FIG. 6  in a plan view of a state of the upper half of the housing  110  removed. This optical switching device  300  has, similarly to EXAMPLE 1, four optical switching structures  700   a - d  arranged in parallel in the optical switch housing. Electromagnetic shield plates  130  are interposed among the electromagnetic actuators of the neighboring optical switching structures and the electromagnetic interference is prevented among them. As the electromagnetic shield plate  130 , nickel iron alloy having a thickness of 0.3 mm and single crystal of Mn-Zn ferrite having a thickness of 0.9 mm can be used. In the case where the electromagnetic shield plate made of single crystal of Mn-Zn ferrite is interposed between the electromagnetic actuators, even when the interval between the neighboring optical switching structures is 1 mm or less, there occurred no electromagnetic interference. In addition, employment of the electromagnetic shield plate made it possible to reduce the amount of refractive index matching oil to be filled in the housing.  
       EXAMPLES 4 AND 5  
       [0072]     An optical switching device  400  according to EXAMPLE 4 and an optical switching device  500  according to EXAMPLE 5 of the invention are shown respectively in  FIGS. 7 and 8  in a plan view of a state of the upper half of the housing  110  removed. Although the optical switching devices  400  and  500  are the same as the optical switching device  200  of EXAMPLE 2, in replacement of the optical switching structure  700   c  of the optical switching device  200 , the 2×4 type optical switching structure  700   c ′ is provided between the optical switching structures  700   b ′ and  700   d ′ and arranged in parallel to them.  
         [0073]     In the optical switching device  400 , two fixed optical fibers  724  of the 1×2 type optical switching structure  700   a  are connected to two movable optical fibers  722  of the 2×4 type optical switching structure  700   b ′, respectively. When movable optical fibers  722  of the 1×2 type optical switching structure  700   a  serve as input paths, four fixed optical fibers  724  of the 2×4 type optical switching structure  700   b ′ serve as output paths, so that the 1×4 type optical device is constituted at this portion. Four fixed optical fibers  724  of the 2×4 type optical switching structure  700   c ′ are connected to four fixed optical fibers  724  of the 2×4 type optical switching structure  700   d ′, respectively. When two movable optical fibers  722  of the 2×4 type optical switching structure  700   c ′ serve as input paths, two movable optical fibers  722  of the 2×4 type optical switching structure  700   d ′ serve as output paths, so that a 2×2 type optical switching device is constituted at this portion. The optical switching device  400  constitutes a 3×6 type as a whole.  
         [0074]     In the optical switching device  500 , two fixed optical fibers  724  of the 1×2 type optical switching structure  700   a  are connected to two movable optical fibers  722  of the 2×4 type optical switching structure  700   b ′, respectively. Two among four fixed optical fibers  724  of the 2×4 type optical switching structure  700   b ′ are connected to two movable optical fibers  722  of the 2×4 type optical switching structure  700   c ′, and the remaining two of the four fixed optical fibers  724  of the 2×4 type optical switching structure  700   b ′ are connected to the two movable optical fibers  722  of the 2×4 type optical switching structure  700   d ′. Fixed optical fibers  724  of the 2×4 type optical switching structures  700   c ′ and  700   d ′ constitute output paths of the optical switching device  500 , while a movable optical fiber  722  of the 1×2 type optical switching structure  700   a  constitutes input path. Hence, this optical switching device  500  constitutes a 1×8 type as a whole.  
       EXAMPLE 6  
       [0075]     An optical switching device  600  of still another example of the invention is shown in  FIG. 9  in a perspective view removing an upper half of the housing  110 . The optical switching device  600  has a 1×2 type optical switching structure  700   a ″, a 2×4 type optical switching structure  700   b ″, a 2×4 type optical switching structure  700   c ″ and a 2×4 type optical switching structure  700   d ″ in the housing  110 . A movable optical fiber of the 1×2 type optical switching structure  700   a ″ passes through a front wall of the housing  110  and come outside of the housing  110 , and fixed optical fibers of the 1×2 type optical switching structure  700   a ″ are connected to movable optical fibers of the 2×4 type optical switching structure  700   b ″ in the housing. Fixed optical fibers of the 2×4 type optical switching structure  700   b ″ pass through a rear wall of the housing  110  and come outside of the housing  110 . Two each of movable optical fibers of the 2×4 type optical switching structures  700   c ″ and  700   d ″ pass through the front wall of the housing  110  and are drawn outside of the housing  110 , and four each of fixed optical fibers thereof pass through the rear wall of the housing  110  and are drawn outside of the housing  110 . Two among the four fixed optical fibers of the 2×4 type optical switching structure  700   b ″ are connected to the two movable optical fibers of the 2×4 type optical switching structure  700   c ″ outside of the housing  110 , and the remaining two among the four fixed optical fibers of the 2×4 type optical switching structure  700   b ″ are connected to the two movable optical fibers of the 2×4 type optical switching structure  700   d ″ outside of the housing  110 . The movable optical fiber of the 1×2 type optical switching structure  700   a ″ serves as input path of the optical switching device  600 , and a total sum of eight of the fixed optical fibers of the 2×4 type optical switching structures  700   c ″ and  700   d ″ serve as output paths of the optical switching device  600 , so that the optical switching device  600  constitutes the 1×8 type. The optical switching device  600  of this EXAMPLE arranges the housing  110  and the connecting portions of the optical fibers in a fiber protection case  770  and fixes the housing and the optical fibers in the protection case, so that the optical switching device can be easily handled.