Patent Publication Number: US-2005123235-A1

Title: Optical switch allowing multi-channelization in which plural optical path changing elements are arranged with ease and high-accuracy, and facilitating heating of optical path changing elements

Description:
This application claims benefit of Japanese Application No. 2003-408334 filed in Japan on Dec. 5, 2003, the contents of which are incorporated by this reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an optical switch for switching among optical paths, used in optical communications or the like.  
      2. Description of the Related Art  
      Hitherto, the optical switch used for optical communications or the like has been incorporated into a device that enters light for optical communications emitted from one or a plurality of input optical fibers into desired output optical fibers by switching among a plurality of optical paths using optical path switching elements (see Japanese Unexamined Patent Application Publication No. 2001-174724 for example).  
       FIG. 12  is a construction view of the above-described conventional optical switch.  FIG. 13  is plan view showing an example of mirror arrays in a micro electro-mechanical system (MEMS) used for the conventional optical switch.  
      As shown in  FIG. 12 , an optical switch  200  comprises input optical fiber arrays  212 , an input lens array  214 , a first MEMS mirror array  218 , a second MEMS mirror array  222 , an output lens array  226 , and output optical fiber arrays  228 . Here, for the sake of simplifying explanation, the input optical fiber arrays  212  and the output optical fiber arrays  228  are represented by four input optical fiber arrays  212   a  to  212   d  and four output optical fiber arrays  228   a  to  228   d , respectively.  
      As shown in  FIG. 13 , a mirror array  410  constituting the first MEMS mirror array  218  or the second MEMS mirror array  222  is formed by arranging, in an array form, inclined mirrors  412  that are each mounted on a spring  414 , on a base  416 . Also, the inclined mirrors  412  are adapted to be controlled by respective electrodes (not shown).  
      Here, a brief description is made on the operation of the optical switch  200  having the first MEMS mirror array  218  and the second MEMS mirror array  222  each having the mirror array  410  as described above.  
      The optical switch  200  receives an optical signal  208  via the plurality of input optical fiber arrays  212 . The input optical fiber arrays  212  send the optical signal  208  to the input lens array  214  serving as collimating lenses. The input lens array  214  produces pencil beams  216   a  to  216   d  out of the optical signal  208 . Here, the pencil beams  216   a  to  216   d  are produced out of the signal conveyed by the input optical fiber arrays  212   a  to  212   d.    
      The first MEMS mirror array  218  receives the beam  216 . The first MEMS mirror array  218  reflects in accordance with the inclination angle of each mirror element, and is selectively directed to a specified mirror element in the second MEMS mirror array  222 . For example, the pencil beam  216   a  produces beams from a reflected beam  220   a  to a reflected beam  220   a ′. Likewise, the pencil beam  216   d  produces beams from a reflected beam  220   d  to a reflected beam  220   d ′. These beams are received by the mirror elements of the second MEMS mirror array  222 , and are directed as beams  224  to the output lens array  226 . The output optical fiber arrays  228  receive light converged by the output lens array  226 , and transmit it as an optical signal  229 .  
      In the optical switch  200 , each output fiber is mapped, in a one-to-one relationship, to a respective one of the mirrors in the output mirror array. This requires single mode fibers. This is because the numerical aperture necessary for input beams and output beams to coaxially match to the axis of the optical fiber in order to restrict the power loss to a low value, is small.  
      As described above, the optical switch  200  has the input lens array  214 , which receives an optical signal from the plurality of input optical fiber arrays  212 . The input lens array  214  comprises a plurality of lens elements, and each of the lens elements directs an optical signal to the MEMS mirror arrays  218  and  222 . In other words, light is converged. These mirror arrays each have a plurality of mirror elements, and each of the elements inclines about one or a plurality of rotational axes when a control signal is applied to a desired mirror element.  
      Thus, the optical signal can be directed to various output optical fiber arrays  228  along various paths. As shown in  FIG. 13 , each of the MEMS mirror arrays  218  and  222  is configured so that a plurality of movable mirrors that are two-dimensionally arranged on a main surface by semiconductor process are integrally formed.  
     SUMMARY OF THE INVENTION  
      According to the present invention, there is provided an optical switch including a first plate having first mounting surfaces and first abutting surfaces that are provided on a first side, a second plate having second mounting surfaces and second abutting surfaces that are provided on a second side, each of the second mounting surfaces abutting against a respective one of the first mounting surfaces and each of the second abutting surfaces abutting against a respective one of the first abutting surfaces to fix the first plate and the second plate, and a plurality of optical path selecting elements mounted on the first plate and the second plate.  
      Other features and advantages of the present invention will become sufficiently apparent in the following description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  to  FIG. 11  relate to an embodiment of the present invention.  
       FIG. 1  is a perspective view showing the external appearance of an optical switch according to an embodiment of the present invention;  
       FIG. 2  is a perspective view of the top surface of the galvo plate in  FIG. 1 ;  
       FIG. 3  is a perspective view of the bottom surface of the galvo plate in  FIG. 1 ;  
       FIG. 4  is a top view of the optical switch in  FIG. 1 ;  
       FIG. 5  is an exploded development view of the optical switch in  FIG. 1 ;  
       FIG. 6  is a sectional view taken along a line A-A in  FIG. 4 ;  
       FIG. 7  is a sectional view taken along a line B-B in  FIG. 4 ;  
       FIG. 8  is a diagram explaining optical paths of the optical switch in  FIG. 1 ;  
       FIG. 9  is a perspective view showing the external appearance of the galvano-mirror in  FIG. 1 ;  
       FIG. 10  is an exploded development view of the galvano-mirror in  FIG. 9 ;  
       FIG. 11  is an exploded development view of the optical deflector in  FIG. 10 ;  
       FIG. 12  is a construction view of a conventional optical switch; and  
       FIG. 13  is plan view showing an example of mirror arrays of micro electromechanical system (MEMS) used for the conventional optical switch. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     Embodiment  
       FIG. 1  shows an example of an optical switch  1  in which sixteen galvano-mirrors  9 , each serving as an optical path selecting element, is fixed to each one of four galvo plates  7 A,  7 B,  8 A, and  8 B, and in which thirty-two input channels and thirty-two output channels are formed by arranging the aforementioned four galvo plates  7 A,  7 B,  8 A, and  8 B in two-stage and a substantially truncated chevron configuration. In  FIG. 1 , thirty-two galvano-mirrors fixed to each of the galvo plates  8 A and  8 B are omitted from illustration.  
      Hereinafter, detailed construction of the optical switch  1  according to the embodiment of the present invention will be described with reference to FIGS.  1  to  11 .  
      As shown in  FIGS. 2 and 3 , the galvo-plate  7 A has mounting surfaces  7 A-a provided on the bottom surfaces at its both ends, and also mounting surfaces  7 A-b provided on the top surfaces at its both ends. Twelve abutting sections  7 A-c are provided between the mounting surfaces  7 A-a at the both ends, and also similar twelve abutting sections  7 A-d are provided between the mounting surfaces  7 A-b at the both ends. The mounting surfaces  7 A-a at the both ends and the bottom surfaces of the twelve abutting sections  7 A-c are mutually flush. Likewise, the mounting surfaces  7 A-b at the both ends and the top surfaces of the twelve abutting sections  7 A-d are mutually flush.  
      Here, because the four galvo plates  7 A,  7 B,  8 A, and  8 B have the same shape, the explanation of the galvo plates  8 A and  8 B is omitted from explanation.  
      As shown in FIGS.  4  to  7 , out of sixteen galvano-mirrors  9  each serving as an optical path changing element, twelve galvano-mirrors  9 B exclusive of four galvano-mirrors  9 A, are fixed to the four galvo plates  7 A,  7 B,  8 A, and  8 B with the front and back of each of the galvano-mirrors fastened by two screws  18  (see  FIG. 7 ). The front side (mirror  14  side) of the galvano-mirror  9 A is fixed to the galvo plate  7 A by a screw  18  using one of two holes formed at the front and back of the housing  113  of the galvano-mirror  9 A. On the other hand, the back side of the galvano-mirror  9 A is not fixed by a screw  18 , and it is to be fixed to the base plate  2  when the galvano-mirror  9 A is fixed at a later time (see  FIG. 6 ).  
      The galvano-mirror  9  has a mirror  14 . The mirror  14  is configured to be inclinable about an X-axis and Y-axis, which are two axes orthogonally intersecting each other and parallel to the reflecting surface of the mirror  14 . The detailed construction of the galvano-mirror  9  is described later.  
      Then, four galvo plates  7 A,  7 B,  8 A, and  8 B on each of which sixteen galvano-mirrors are fixed, are fixed to the base plate  2 .  
      Two positioning pins  15  are pressed into the mounting sections  2   a  of the base plate  2 , and the holes at the both ends of the galvo plate  7 B are fitted to the positioning pins  15 , whereby the mounting surfaces  7 B-a on the bottom surfaces at the both ends of the galvo plate  7 B are caused to abut against the mounting sections  2   a  and assembled thereto.  
      Next, four galvano-mirrors  9 B are fixed to the galvo plate  7 B by fixing four studs  17  to screw holes  2   c  formed in four posts provided to the base plate  2  through the holes  113   b  in the back sides of the galvano-mirrors  9 B, of which back sides have not been fixed by the screws  18 , and also the galvo plate  7 B is fixed to the base plate  2 . At this time, the bottom surfaces of the abutting sections  7 B-c provided on the bottom surface of the galvo plate  7 B also abut against the mounting sections  2   a.    
      Then, the galvo plate  7 A is assembled onto the galvo plate  7 B. The mounting surfaces  7 A-a on the bottom surfaces at the both ends of the galvo plate  7 A are caused to abut against the mounting surfaces  7 A-b on the top surfaces at the both ends of the galvo plate  7 B. Simultaneously, the bottom surfaces of the abutting sections  7 A-c are caused to abut against the top surfaces of the  7 B-d. The galvo plate  7 A is also fitted to and positioned by the positioning pins  15  and assembled to the galvo plate  7 B. Then, the galvo plates  7 A and  7 B are simultaneously fixed to the base plate  2  by two screws  16 .  
      Thereafter, four galvano-mirrors  9 B are fixed to the galvo plate  7 A by fixing four screws  19  to screw holes  17   a  formed in the top surface of each of the four studs  17  through the holes  113   b  in the back sides of the four galvano-mirrors  9 A, of which back sides have not been fixed by the screw  18 , and the holes of the galvo plate  7 A, and also the galvo plate  7 A is fixed to the base plate  2 . At this time, the upper end of each of the studs  17  is not in contact with the rear surface of the galvo plate  7 A with a little space therebetween.  
      As described above, the galvo plates  7 A and  7 B, on each of which sixteen galvano-mirrors  9  are fixed, are fixed to the base plate  2  in a two-stage manner. Similarly, the galvo plates  8 A and  8 B, on each of which sixteen galvano-mirrors  9  are fixed, are fixed to the base plate  2  in a two-stage manner.  
      To the collimating plates  3 A that are fixed to the base plate  2 , sixteen collimating lenses  6  and sixteen end faces of the input optical fibers  4  are fixed on the upper and lower sides of the collimating plates  3 A, respectively. Thereby, light beams emitted from the input optical fibers  4  are collimated by the respective collimating lenses  6 , and respectively head toward the mirrors  14  opposed to the galvano-mirrors  9 .  
      Sixteen collimating lenses  6  and sixteen end faces of the output optical fibers  5  are fixed to collimating plates  3 B on their upper and lower sides, respectively. Thereby, light beams reflected from the mirrors  14  of the galvano-mirrors  9  enter the respective collimating lenses  6 , and after having been converged, enter the respective output optical fibers  5  to propagate therethrough.  
      Now, the optical path of the optical switch  1  will be described with reference to  FIG. 8 . Here, the description is made with respect to a single optical path for the sake of convenience.  
      Light emitted from an optical fiber  4 - 17  for input is made parallel light by a collimating lens  6 - 17 , and the incident light  20  is entered into a corresponding mirror  14 - 17 . The reflected light  20  from the mirror  14 - 17  is entered into a corresponding mirror  14 - 49 , then entered into a collimating lens  6 - 49 , and entered into an optical fiber  5 - 17  for output to propagate through the optical fiber  5 - 17 .  
      Here, an explanation is made on the case where light emitted from the optical fiber  4 - 17  is outputted by switching an optical fiber from the optical fiber  4 - 17  to an optical fiber  5 - 2 . Light emitted from an optical fiber  4 - 17  for input is made parallel light by a collimating lens  6 - 17 , and the incident light  20  is entered into a corresponding mirror  14 - 17 . At this time, the reflected light is rotated in a horizontal plane by rotating the mirror  14 - 17  by α1 about the Y-axis, which is a vertical direction, and further it is rotated in the vertical direction by rotating the mirror  14 - 17  by β1 about the horizontal axis. Thereby, the path of the reflected light  20 ′ from the mirror  14 - 17  can be switched so that the reflected light  20 ′ heads toward a mirror  14 - 34  instead of mirror  14 - 49 . Furthermore, by rotating the mirror  14 - 34  itself by α2 about the Y-axis and by β2 about the X-axis, the reflected light  20 ′ is entered into the collimating lens  6 - 34 , and then entered into the optical fiber  5 - 2  for output to propagate through the optical fiber  5 - 2 .  
      In this manner, the path of light entered from thirty-two optical fibers  4  on the input side can be switched by selecting an arbitrary optical fiber  5  from among the thirty-two optical fibers  5  on the output side. Thus the optical switch  1  is configured.  
      The galvano-mirror  9  is now explained with reference to FIGS.  9  to  11 .  
      The galvano-mirror  9  according to this embodiment includes an optical deflector  111  having a mirror  14 , flexible printed circuit (FPC)  112 , housing  113 , semiconductor laser  114 , polarizing beam splitter (PBS)  115 , ¼ wavelength plate  116 , converging lens  117 , semiconductor position sensitive detector (PSD)  118 , and spacer  119 .  
      The deflector  111  has a coil holder  121  serving as a movable section, and a magnet holder  122  serving as a fixing section. In the coil holder  121  and magnet holder  122 , the both ends of four springs  123  made of beryllium copper are held by insert molding their end portions on the movable section side and their end portions on the fixing section side, respectively, into the coil holder  121  and the magnet holder  122 .  
      Thus, at their both ends, the four springs  123  are fixed by the coil holder  121  and the magnet holder  122 , and support the coil holder  121  with respect to the magnet holder  122  so as to be inclinable about the rotational axes X and Y.  
      Each of the mirrors  14  is fixed to a mounting section  121   a  located in the central portion on the surface side of the coil holder  121 , by positioning and adhering its peripheral portion. The reflecting surface  14   a  of the mirror  14 , on the front side, is coated with gold or a dielectric multilayer that exhibits a high reflectance with respect to light with a wavelength of light for optical communications, e.g., light with a wavelength of 1.3 to 1.6 μm.  
      A mirror  125  constituting an inclination sensor for the mirror  14  is fixed to the central portion on the rear surface side of the coil holder  121 , by positioning and adhering its peripheral portion.  
      A first coil  127  and second coil  128  are adhered and fixed to the coil holder  121  after positioning, on the surface side and rear surface side of the coil holder  121 , respectively, with the mirror  14  and mirror  125  between the first and second coils.  
      In a spatial portion between the two mirrors  14  and  125 , the central portion of an arm  129 , serving as a first support member, formed by bending, for example, a stainless steel plate with a thickness of 0.1 mm is located, and the central portion is adhered and fixed to the magnet holder  121  by arranging the both end portions  129   a  of the arm  129  to surround the outer periphery of the mirror  125 . In the central portion of the arm  129 , there is provided a cone-shaped projection with a hole  129   b  formed in the center so as to be located apart by, e.g., 0.2 mm from the rear surface of the mirror  14 , and after a damping agent such as silicone rubber has been injected between the projection  129   b  and the mirror  14 , it is cured, thereby forming a pivot (not shown).  
      To the magnet holder  122 , two magnets  132  for the first coil  127  and two magnets  135  for the second coil  128  are fixed, upon adhering yokes  133  and  134  to their respective rear surfaces.  
      The optical deflector  111  is fitted to two holes formed in the mounting surface  113   a  of the housing  113 , and adhered to the mounting surface  113   a  after positioning.  
      In order to detect the inclination angle of the mirror  14  from that of the mirror  125 , the semiconductor laser  114 , PBS  115 , ¼ wavelength plate  116 , converging lens  117 , and PSD  118  are mounted to the housing  113 . The semiconductor laser  114  is mounted to an opening  113   b  of the housing  113 ; the PBS  115  has its one surface adhered to a pedestal of the housing  113 ; the ¼ wavelength plate  116  is joined to the PBS  115 ; the converging lens  117  is fixed to an opening  113   c  formed in the mounting surface  113   a  of the optical deflector  111  of the housing  113 , and the PSD  118  is adhered to the housing  113 .  
      The PSD  118  is a two-dimensional position sensitive detector that outputs the bidirectional light quantity central position of light projected onto its light-receiving section  118   a , and its examples include S5990-01 and S7848-01 produced by Hamamatsu Photonics Corp.  
      The FPC  112  includes a circuit for converting the output current of the PSD  118  into the output voltage, and a drive circuit  151  for the first coil  127  and the second coil  128 . Here, the drive circuit  151  is fixed by causing its surface to abut against aluminum-made spacer  119  fixed on the top surface of the PBS  115  of the housing  113 . Thereby, the spacer  119  and the housing  113  are caused to serve also as heat-dissipating members for the drive circuit.  
      In the galvano-mirror  9  with such configurations, once a current has been applied to the first coil  127  through two of four springs  123 , the movable section generates a torque about the rotational axis Y due to a magnetic field received from the magnets  132 , and thereby the four springs  123  undergo deflective deformation, so that the movable section comes to incline about the rotational axis Y.  
      Also, once a current has been applied to the second coil  128  through the other two out of the four springs  123 , the movable section generates a torque about the rotational axis X due to a magnetic field received from the magnets  135 , and thereby the four springs  123  undergo deflective deformation, so that the movable section comes to incline about the rotational axis X.  
      On the other hand, light from the semiconductor laser  114  enters the PBS  115  as P-polarized light, and after having passed through its polarization plane  115   a , enters the rear surface (reflecting surface) of the mirror  125  through the ¼ wavelength plate  116  and the converging lens  117 . The light reflected from the mirror  125  enters the PBS  115  through the converging lens  117  and the ¼ wavelength plate  116 .  
      Here, since the light that enters the PBS  115  after having been reflected from the mirror  125 , passes through the ¼ wavelength plate  116  twice in total in the forward and return paths, the polarization plane of the PBS  115  rotates 90 degrees, so that the light becomes S-polarized light. As a result, the light is reflected from the polarization plane  115   a  of the PBS  115 , and enters the light-receiving surface  118   a  of the PSD  118 .  
      When inclining the mirror  14 , and hence, the mirror  125  about the rotational axis Y by applying a current to the first coil  127 , the above-described light having entered the light-receiving surface  118   a  of the PSD  118  laterally moves on the light-receiving surface  118   a . Also, when inclining the mirror  14  about the rotational axis X by applying a current to the second coil  128 , the above-described light vertically moves on the light-receiving surface  118   a . Therefore, the bidirectional inclinations of the mirror  14  can be detected based on the output of the PSD  118 .  
      The above-described arrangements of the galvano-mirror  9  allows the mirror  14  to be supported and driven so as to be inclinable about the two axes, and provide an inclination sensor for sensing the inclinations of the mirror  14  about the two axes. By inclining the mirror  14  to change and control the direction of the reflection of light from the optical fiber  4  using these support and drive mechanism for the mirror  14  and inclination sensor, it is possible to switch among the output optical fibers as described above.  
      The described configurations of the present invention produce the following effects.  
      Since the galvo plate  7 B is caused to abut against the base plate  2  on its mounting sections  7 B-a at the both ends, and in addition, the abutting sections  7 B-c formed at portions near galvano-mirrors  9  are also caused to abut against the base plate  2 , heat transfer from the galvo-plate  7 B to the base plate  2  is improved, and heat of the galvano-mirrors  9 , particularly heat in their drive circuit  151  and laser  114 , can be dissipated to the base plate  2 . Furthermore, since abutting sections  7 B-c are provided at respective portions near the sixteen galvano-mirrors  9 , the heat dissipation characteristics of the respective galvano-mirrors  9  can be improved, thereby allowing the reduction in temperature rise of the laser  114 .  
      The two-tiered galvo plates  7 A and  7 B are caused to abut against each other on the mounting surfaces at their both ends, and in addition, the abutting sections  7 B-d and  8 A-c that are facing each other and disposed adjacent to the respective galvano-mirrors  9  between the galvo plates  7 A and  7 B, are also caused to mutually abut against. As a result, heat generated in the galvano-mirrors  9  in the galvo plate  7 A on the upper side can be dissipated to the base plate  2  through the abutting sections  7 B-d and  8 A-c as well as through the mounting sections  7 A-a and  7 B-b at the both ends, and via the galvo plate  7 B on the lower side.  
      The upper end of each of the studs  17  is not in contact with the rear surface of the galvo plate  7 A with a little space therebetween, and therefore, when the galvo plate  7 A is fixed to the base plate  2 , there is no possibility that the galvo plate is deformed by errors in the height position of the studs  17 .  
      As described above, the mounting surfaces  7 A-a at the both ends of the galvo plate  7 A and the bottom surfaces of the twelve abutting sections  7 A-c thereof are mutually flush, and the mounting surfaces  7 A-b at the both ends and the top surfaces of the twelve abutting sections  7 A-d thereof are also mutually flush. Therefore, when machining the mounting surfaces  7 A-a at the both ends of the galvo plate  7 A and the bottom surfaces of the twelve abutting sections  7 A-c thereof, and the mounting surfaces  7 A-b at the both ends of the galvo plate  7 A and the top surfaces of the twelve abutting sections  7 A-d thereof, they can be each machined to high flatness. This allows the contact conditions between the galvo plate B and the base plate  2 , and those between the galvo plates A and B to become superior, thereby improving the thermal conduction therebetween.  
      Since a plurality of galvano-mirrors are provided to a single galvo plate, and an optical switch is formed by using the plurality of galvano-mirrors, galvano-mirrors produced for every optical switch can be easily gathered, thereby allowing an multi-channelized optical switch to be easily formed.  
      Interposing a conductive member having good conductivity, such as thermal interface silicone rubber, between the abutting sections between the galvo plate  7 B and the base plate  2 , and between the abutting sections between the galvo plates  7 A and  7 B, would provide excellent heat dissipation characteristic.  
      The optical path changing element is not limited to the inclinable mirror described above but may include other optical elements, such as lenses, prisms, and the like that performs the required functions. Also, the construction of the galvano-mirror is not restricted to that described above but may include other constructions.  
      The configuration of the galvo plate is not limited to the two-stage type described above but may include other configurations. Also, the driving system is not restricted to coils and magnets as described above but may include other driving methods, such as electrostatic drive, drive by an piezoelectric element, and the like. Furthermore, the supporting means is not limited to the beryllium copper spring described above but may include other things, such as silicone spring, link, and the like that perform the required functions.  
      In this invention, it is obvious that widely different embodiments of this invention may be made on the basis thereon without departing from spirit and scope thereof. This invention is not limited to the specific embodiments thereof except as defined in the appended claims.