Abstract:
In an optical switch for connecting optically a first optical fiber supported on a stationary supporting block to a second optical fiber supported on a movable supporting block being movable relative to the stationary supporting block between a first position for the optical connection between the terminating ends of the first and second optical fibers and a second position for disconnecting the optical connection therebetween and being adjacent to the stationary supporting block, and a magnetic flux generator for generating a magnetic flux for moving the movable supporting block relative to the stationary supporting block, the movable supporting block includes a soft magnetic substance so that the magnetic flux passes through the movable supporting block.

Description:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT 
     The present invention relates to an optical switch by which an optical fiber is optically connected to another optical fiber selectively as required. 
     In a prior art optical switch disclosed in JP-A-6-208062, a magnetic member mounted on a movable optical fiber is magnetized by a coil surrounding the magnetic member to be urged toward either of permanent magnets arranged respective radial sides of the coil opposite to each other so that the movable optical fiber is displaced to be optically connected to either of stationary optical fibers selectively. 
     OBJECT AND SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an optical switch for connecting optically a first optical fiber to a second optical fiber selectively as required, in which switch a switching operation is securely performed while a size of the optical switch is kept small. 
     In an optical switch for connecting optically at least one first optical fiber to at least one second optical fiber selectively, comprising, a stationary supporting block for supporting thereon a terminating end of the first optical fiber (the terminating end may project slightly from the stationary supporting block or may be completely surrounded by the stationary supporting block), a movable supporting block for supporting thereon a terminating end of the second optical fiber (the terminating end may project slightly from the movable supporting block or may be completely surrounded by the movable supporting block), being movable relative to the stationary supporting block between a first position for the optical connection between the terminating ends of the first and second optical fibers and a second position for disconnecting the optical connection therebetween, and being adjacent to the stationary supporting block, and a magnetic flux generator for generating a magnetic flux for moving the movable supporting block relative to the stationary supporting block. 
     According to the present invention, since the movable supporting block guided to be adjacent to the stationary supporting block includes a soft magnetic (feeble magnetism) substance so that the magnetic flux passes through the movable supporting block, the movable supporting block supporting thereon the terminating end of the second optical fiber is driven by the magnetic flux relative to the stationary supporting block adjacently or close to the stationary supporting block. Therefore, the terminating end of the second optical fiber is securely driven and correctly positioned relative to the terminating end of the first optical fiber, and the magnetic flux is effectively utilized to drive the movable supporting block so that a size of the magnetic flux generator, that is, a size of the optical switch is minimized. 
     If the soft magnetic substance of the movable supporting block is a soft magnetic ceramic (ceramic of feeble magnetism), a difference in expansion and contraction caused by temperature variation between the movable supporting block and the second optical fiber is made small while preventing a deterioration of a magnetic characteristic of the movable supporting block. If the stationary supporting block includes a ceramic having at least one of soft (feeble) magnetism and ferromagnetism, a difference in expansion and contraction caused by temperature variation between the stationary supporting block and the first optical fiber is made small while preventing a deterioration of a magnetic characteristic of the stationary supporting block. It is preferable for a thermal expansion coefficient of the stationary supporting block to be substantially equal to that of the movable supporting block, for maintaining a positional relationship between the first and second optical fibers correctly against the temperature variation of the optical switch. If the stationary supporting block includes at least one of a ceramic and a glass so that a difference in thermal expansion coefficient between the stationary supporting block and the first optical fiber is kept small, a thermal stress of at least one of the stationary supporting block and the first optical fiber is restrained. If the movable supporting block includes at least one of a ceramic and a glass so that a difference in thermal expansion coefficient between the movable supporting block and the second optical fiber is kept small, a thermal stress of at least one of the movable supporting block and the second optical fiber is restrained. 
     If a permanent magnet generates another magnetic flux sufficient for maintaining the movable supporting block at a selected or desired either one of the first and second positions when the magnetic flux generator is prevented from generating the magnetic flux, a so-called latching or self-hold of the optical switch when being deenergized is obtained. If the another magnetic flux passes through the stationary supporting block, the another magnetic flux effectively supplied to the movable supporting block. If the another magnetic flux passes through both of the stationary supporting block and the movable supporting block, the another magnetic flux effectively utilized for the latching or self-hold of the optical switch or the movable supporting block. 
     If the magnetic flux generated by the magnetic flux generator passes through both of the stationary supporting block and the movable supporting block, the magnetic flux effectively supplied to the movable supporting block. It is preferable for improving the effective supply of the magnetic flux to the movable supporting block that the stationary supporting block includes at least one of a soft magnetic (feeble magnetism) substance and a ferromagnetic or ferromagnetism substance so that the magnetic flux passes through the stationary supporting block. If the stationary supporting block and the movable supporting block includes a common soft magnetic (feeble magnetism) substance, differences in thermal deformation (expansion and contraction) and magnetic characteristic between the stationary supporting block and the movable supporting block is made small. 
     If the magnetic flux generator includes a first magnetic flux generator and a second magnetic flux generator, a direction of the magnetic flux (magnetic pole direction) generated by the first magnetic flux generator is opposite to a direction of the magnetic flux (magnetic pole direction) generated by the permanent magnet in a magnetic circuit including the movable supporting block (facing to or arranged between first and second front yoke (or core) portions of soft magnetism (feeble magnetism) opposite or facing to each other), the first magnetic flux generator, the first front yoke portion and the permanent magnet while a direction of the magnetic flux (magnetic pole direction) generated by the second magnetic flux generator is equal to the direction of the magnetic flux (magnetic pole direction) generated by the permanent magnet in a magnetic circuit including the movable supporting block, the second magnetic flux generator, the second front yoke portion and the permanent magnet, so that the movable supporting block moves from the first position to the second position by being drawn toward the second front yoke portion, and the direction of the magnetic flux (magnetic pole direction) generated by the first magnetic flux generator is equal to the direction of the magnetic flux (magnetic pole direction) generated by the permanent magnet in the magnetic circuit including the movable supporting block, the first magnetic flux generator, the first front yoke portion and the permanent magnet while the direction of the magnetic flux (magnetic pole direction) generated by the second magnetic flux generator is opposite to the direction of the magnetic flux (magnetic pole direction) generated by the permanent magnet in the magnetic circuit including the movable supporting block, the second magnetic flux generator, the second front yoke portion and the permanent magnet, so that the movable supporting block moves from the second position to the first position by being drawn toward the first front yoke portion. 
     The switching operation is performed securely by changing respectively the directions of the magnetic fluxes generated by the first and second magnetic flux generators with keeping the directions of the magnetic fluxes opposite to each other in the permanent magnet while the latching or self-hold of the optical switch is released as required. 
     If the magnetic flux generator includes first and second magnetic flux generators connected electrically in series, and a direction of the magnetic flux through the permanent magnet generated by the first magnetic flux generator in a magnetic circuit including the first magnetic flux generator, the permanent magnet, the stationary supporting block and the movable supporting block is opposite to a direction of the magnetic flux through the permanent magnet generated by the second magnetic flux generator in a magnetic circuit including the second magnetic flux generator, the permanent magnet, the stationary supporting block and the movable supporting block, the switching operation is performed by changing a direction of an electric current applied to the first and second magnetic flux generators through a pair of electric terminals between which the first and second magnetic flux generators is energized in series. 
     If a magnetically permeable member is connected magnetically to the permanent magnet and includes front portions facing to respective sides of the movable supporting block and being opposite to each other, a magnetic circuit including the permanent magnet and the movable supporting block is obtained with a decreased magnetic resistance. If the permanent magnet is arranged between the stationary supporting block and the magnetic flux generator in a magnetic flux proceeding direction, the permanent magnet is commonly used for the latching or self-hold at the first position and the latching or self-hold at the second position. If the stationary supporting block is arranged between the movable supporting block and the permanent magnet in a magnetic flux proceeding direction, the permanent magnet is prevented from arranged between the stationary supporting block and the movable supporting block while the permanent magnet is commonly used for the latching or self-hold at the first position and the latching or self-hold at the second position. Therefore, a friction between the movable supporting block and the permanent magnet is prevented. 
     It is preferable for improving a machinability of the movable supporting block and restraining the thermal stress of the movable supporting block and/or the first optical fiber that the soft magnetic (feeble magnetism) substance is an oxide ferrite. It is preferable for the oxide ferrite to include iron, manganese and zinc. For further improving the machinability of the movable supporting block, it is effective for the feeble magnetism substance to be a single crystalline ferrite. 
     If at least one guide pin is prevented from having a magnetic permeability when the guide pin contacts the stationary supporting block of feeble magnetism or ferromagnetism and the movable supporting block to guide a mutual movement of the stationary supporting block and the movable supporting block between the first and second positions, the mutual movement is not restrained by the guide pin. 
     If a distance between the stationary supporting block of at least one of feeble magnetism and ferromagnetism and the movable supporting block of feeble magnetism is kept substantially constant so that a magnetic gap or resistance between the stationary supporting block and the movable supporting block in a magnetic circuit including the stationary supporting block (which may include the permanent magnet), the magnetic flux generator and the movable supporting block is kept substantially constant although a magnetic gap or resistance between the magnetic flux generator (or the front yoke portion of feeble magnetism) and the movable supporting block in the magnetic circuit is variable, the movable supporting block is securely driven relative to the stationary supporting block by a stable degree of the magnetic flux. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partially cross-sectional view showing an optical switch according to the present invention. 
     FIG.  2   a  is a cross-sectional view of a movable optical fiber movable holder taken along II a— II a  in FIG.  1 . 
     FIG.  2   b  is a cross-sectional view of a stationary optical fiber holder taken along II b— II b  in FIG.  1 . 
     FIG. 3 is a partially cross-sectional view showing the optical switch in a first position of the movable optical fiber movable holder. 
     FIG.  4   a  is a schematic view of an actuator of the optical switch including the movable optical fiber movable holder, the stationary optical fiber holder, a permanent magnet, a U-shaped yoke and electromagnetic coils surrounding respective side yoke portions, in the first position of the movable optical fiber holder. 
     FIG.  4   b  is a schematic view of the actuator as seen when the movable optical fiber holder is moving from the first position to a second position. 
     FIG.  4   c  is a schematic view of the actuator in the second position of the movable optical fiber holder. 
     FIG.  5   a  is a schematic view showing an optical fiber connection obtainable in the first position of the movable optical fiber holder. 
     FIG.  5   b  is a schematic view showing an optical fiber connection obtainable in the second position of the movable optical fiber holder. 
     FIG.  6   a  is a schematic view showing an electromagnetic coil to be divided into a pair of electromagnetic coils connected electrically in series as the claimed first and second magnetic flux generators. 
     FIG.  6   b  is a schematic view showing a magnetic flux flow for moving a movable optical fiber movable holder from a second position to a first position. 
     FIG.  6   c  is a schematic view showing a magnetic flux flow for moving the movable optical fiber movable holder from the first position to the second position. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     As shown in FIGS. 1 and 3, movable optical fibers  20   a  and  20   b  are supported on a movable optical fiber stationary holder  31  made of a soft magnetic (feeble magnetism) ceramic and a movable optical fiber movable holder  30  made of the soft magnetic ceramic. The soft magnetic ceramic used in this embodiment is a Manganese/Zinc ferrite with a saturation magnetic flux density of 4700 G (minimum value is 3000 G), a magnetic permeability of 1200 at 1 MHz, and a thermal expansion coefficient of 115×10−7/° C. 
     As shown in FIG.  2   a,  the movable optical fibers  20   a  and  20   b  are supported between V-shaped grooves of the movable optical fiber movable holder  30  and a pressing plate  30   a  fixed onto the movable optical fiber movable holder  30  and made of a glass or the soft magnetic ceramic whose thermal expansion coefficient is substantially equal to a thermal expansion coefficient of the movable optical fiber movable holder  30 . The V-shaped grooves are formed accurately through a dicing process. The movable optical fibers  20   a  and  20   b  are supported on the movable optical fiber stationary holder  31  in a manner similar to this V-shaped-grooves-and-pressing-plate supporting structure. The movable optical fiber stationary holder  31  fixed to a base plate  10  made of a ceramic or steel supports fixedly the movable optical fibers  20   a  and  20   b  at intermediate parts of the movable optical fibers  20   a  and  20   b,  and the movable optical fiber movable holder  30  movable relative to the base plate  10  in a hole  11  of the base plate  10  supports the movable optical fibers  20   a  and  20   b  at forward or terminating ends of the movable optical fibers  20   a  and  20   b.  When the base plate  10  is made of steel, non-magnetically permeable (for example, glass) plate is preferably arranged between the base plate  10  and the holders  30  and  31 . Alternatively, a magnetic clearance for restraining sufficiently a magnetic flux leakage from the holders  30  and  31  toward the base plate  10  may be arranged between the base plate  10  and the holders  30  and  31 . 
     A stationary optical fiber holder  32  faces to the movable optical fiber movable holder  30  in a direction (X axis direction) substantially parallel to longitudinal axes of the movable optical fibers  20   a  and  20   b  and stationary optical fibers  21   a,    21   b,    21   c  and  21   d  while the longitudinal axes are substantially parallel to each other at least on the stationary optical fiber holder  32  and the movable optical fiber movable holder  30 , and is fixed to the base plate  10  to support thereon the stationary optical fibers  21   a,    21   b,    21   c  and  21   d  at forward or terminating ends of the stationary optical fibers  21   a,    21   b ,  21   c  and  21   d,  in such a manner that each of the forward or terminating ends of the stationary optical fibers  21   a ,  21   b ,  21   c  and  21   d  can face to each of the forward or terminating ends of the movable optical fibers  20   a  and  20   b  in the direction. As shown in FIG.  2   b,  the stationary optical fibers  21   a ,  21   b ,  21   c  and  21   d  are supported between V-shaped grooves of the stationary optical fiber holder  32  and a pressing plate  32   a  fixed onto the stationary optical fiber holder  32  and made of a glass or the soft magnetic ceramic whose thermal expansion coefficient is substantially equal to a thermal expansion coefficient of the stationary optical fiber holder  32 . 
     Non-magnetic guide pins  40   a  and  40   b  made of a cemented carbide metal are also supported between the V-shaped grooves of the stationary optical fiber holder  32  and the pressing plate  32   a , and are movably fitted in respective positioning holes  41   a  and  41   b  formed by the movable optical fiber movable holder  30  and the pressing plate  30   a  to determine positional and attitudinal relationships between the movable optical fiber movable holder  30  and the stationary optical fiber holder  32  so that the movable optical fiber movable holder  30  moves in Y axis direction between a first position (the guide pins  40   a  and  40   b  contact first side walls of the positioning holes  41   a  and  41   b  ) at which the longitudinal axis of the movable optical fiber  20   a  is substantially identical to that of the stationary optical fiber  21   a  and the longitudinal axis of the movable optical fiber  20   b  is substantially identical to that of the stationary optical fiber  21   c  on the stationary optical fiber holder  32  and the movable optical fiber movable holder  30  and a second position (the guide pins  40   a  and  40   b  contact second side walls of the positioning holes  41   a  and  41   b  opposite to the first side walls) at which the longitudinal axis of the movable optical fiber  20   a  is substantially identical to that of the stationary optical fiber  21   b  and the longitudinal axis of the movable optical fiber  20   b  is substantially identical to that of the stationary optical fiber  21   d  on the stationary optical fiber holder  32  and the movable optical fiber movable holder  30 . Therefore, a transmission loss of light between the movable optical fibers  20   a  and  20   b  and the stationary optical fibers  21   a ,  21   b ,  21   c and  21   d  is limited to a significantly low degree. Longitudinal ends of the guide pins  40   a  and  40   b  contact longitudinal ends of the positioning holes  41   a  and  41   b  respectively so that a distance between the movable optical fiber movable holder  30  and the stationary optical fiber holder  32  in a longitudinal direction of the optical fibers is kept constant. 
     A U-shaped magnetic yoke includes a pair of front yoke portions  50   a  and  50   b  fixed onto the base plate  10  and including a soft magnetic (feeble magnetism) iron, a base yoke portion  50   e  fixed onto the base plate  10  and including the soft magnetic iron, and a pair of side yoke portions  50   c  and  50   d  including the soft magnetic iron and extending along respective longitudinal axes between the front yoke portions  50   a  and  50   b  and the base yoke portion  50   e . The movable optical fiber movable holder  30  is arranged between the front yoke portions  50   a  and  50   b . An electromagnetic coil  51   a  surrounds the longitudinal axis of the side yoke portion  50   c , and an electromagnetic coil  51   b  surrounds the longitudinal axis of the side yoke portion  50   d . The stationary optical fiber holder  32  is magnetically connected to the base yoke portion  50   e  through a permanent magnet  52  including a neodymium-iron-boron compound. As shown in FIG.  6   a,  a single coil winding may be divided by straightening an intermediate length thereof into the electromagnetic coils  51   a  and  51   b  connected electrically in series. 
     As shown in FIG.  4   a,  when the movable optical fiber movable holder  30  is at the first position, a magnetic flux generated by the permanent magnet  52  passes through the stationary optical fiber holder  32 , the movable optical fiber movable holder  30 , the front yoke portion  50   a , the side yoke portion  50   c  and the base yoke portion  50   e , and returns to the permanent magnet  52  so that the movable optical fiber movable holder  30  is drawn toward the front yoke portion  50   a  to be maintained at the first position even if the electromagnetic coil  51   a  does not accelerate the magnetic flux generated by the permanent magnet  52  or both of the electromagnetic coils  51   a  and  51   b  are not energized. 
     As shown in FIG.  4   c,  when the movable optical fiber movable holder  30  is at the second position, the magnetic flux generated by the permanent magnet  52  passes through the stationary optical fiber holder  32 , the movable optical fiber movable holder  30 , the front yoke portion  50   b,  the side yoke portion  50   d  and the base yoke portion  50   e,  and returns to the permanent magnet  52  so that the movable optical fiber movable holder  30  is drawn toward the front yoke portion  50   b  to be maintained at the second position even if the electromagnetic coil  51   b  does not accelerate the magnetic flux generated by the permanent magnet  52  or both of the electromagnetic coils  51   a  and  51   b  are not energized. 
     As shown in FIG.  4   b , when the movable optical fiber movable holder  30  is being moved from the first position to the second position, the magnetic flux generated by the permanent magnet  52  passes through the stationary optical fiber holder  32 , the movable optical fiber movable holder  30 , the front yoke portion  50   b,  the side yoke portion  50   d  and the base yoke portion  50   e,  is amplified, accelerated or increased by the electromagnetic coil  51   b  being energized while the electromagnetic coil  51   a  is energized to prevent or restrain the magnetic flux from passing through the side yoke portion  50   c  and the electromagnetic coil  51   a  or to weaken a magnetization of the front yoke portion  50   a  [that is, a magnetic pole direction (direction of magnetic flux or N-S polarity direction) of the permanent magnet  52  is equal to that of the electromagnetic coil  51   b  in a magnetic circuit including the permanent magnet  52 , the stationary optical fiber holder  32 , the movable optical fiber movable holder  30 , the front yoke portion  50   b , the side yoke portion  50   d  and the base yoke portion  50   e , and is against or opposite to that of the electromagnetic coil  51   a  in another magnetic circuit including the permanent magnet  52 , the stationary optical fiber holder  32 , the movable optical fiber movable holder  30 , the front yoke portion  50   a , the side yoke portion  50   c  and the base yoke portion  50   e],  and returns to the permanent magnet  52  so that the movable optical fiber movable holder  30  is moved toward the second position from the first position. When the directions of the magnetic fluxes (magnetic pole directions, that is, N-S polarity directions) of the electromagnetic coil  51   a  and  51   b  are inverted respectively relative to the above described directions of the magnetic fluxes (magnetic pole directions) thereof, the movable optical fiber movable holder  30  is moved from the second position to the first position. In this embodiment, the change between the first and second position is performed within 10 msec by energizing each of the electromagnetic coil  51   a  and  51   b  with an electric current of 50 mA. 
     As shown in FIGS.  6   b  and  6   c,  by changing a direction of an electric current to be applied to the electromagnetic coils  51   a  and  51   b  connected electrically in series, the movable optical fiber movable holder  30  is driven between the first and second position, because a direction of the magnetic flux through the permanent magnet  52  and the stationary optical fiber holder  32  generated by the electromagnetic coil  51   a  in a magnetic circuit including the electromagnetic coil  51   a , the movable optical fiber movable holder  30 , the permanent magnet  52  and the stationary optical fiber holder  32  is opposite to a direction of the magnetic flux through the permanent magnet  52  and the stationary optical fiber holder  32  generated by the electromagnetic coil  51   b  in a magnetic circuit including the electromagnetic coil  51   b , the movable optical fiber movable holder  30 , the permanent magnet  52  and the stationary optical fiber holder  32 . 
     The movable optical fiber movable holder  30  and the stationary optical fiber holder  32  may be formed any of various soft magnetic (feeble magnetism) ceramics which can be machined finely and have thermal expansion coefficients closer to the thermal expansion coefficient of the optical fibers in comparison with soft magnetic (feeble magnetism) metals. It is preferable for the thermal expansion coefficients of the movable optical fiber movable holder  30  and the stationary optical fiber holder  32  to be substantially equal to each other so that the stationary optical fibers  21   a ,  21   b ,  21   c  and  21   d  is prevented from shifting relative to the movable optical fibers  20   a  and  20   b  in accordance with temperature variation. When the thermal expansion coefficient of both the movable optical fiber movable holder  30  and the stationary optical fiber holder  32  is 115×10−7/° C., the transmission loss of light between the movable optical fibers  20   a  and  20   b  and the stationary optical fibers  21   a ,  21   b ,  21   c  and  21   d  is −0.5 dB in a temperature range between −20° C. and +80° C. 
     When the pressing plates are formed of the soft magnetic ceramic, the movable optical fiber movable holder  30  and/or the stationary optical fiber holder  32  may be formed of a glass or silicon of a non-magnetic material. The positioning holes  41   a  and  41   b  may be rectangular or trapezoidal, and may be formed by grooves formed on each of the pressing plate  30   a  and the movable optical fiber movable holder  30 . The movable optical fiber movable holder  30  and/or the stationary optical fiber holder  32  may be received by a tube shaped container as a substitute of the base plate  10 . The grooves for receiving the optical fibers and the guide pins may be formed through etching process. 
     As shown in FIGS.  5   a  and  5   b,  the optical switch of the present invention can perform a switching operation of an optical path  22  relative to an AMD (add drop multiplexer) element  60 . The AMD element  60  may be replaced by various optical signal receivers.