Abstract:
An optical switch ( 1 ) includes a cover ( 10 ), a base ( 20 ), two input ports ( 30,50 ), two output ports ( 40,60 ), a movable reflecting element ( 70 ), a fixed reflecting element ( 80 ), and a driving means ( 90 ). The movable reflecting element has a first mirror ( 71 ) and an opposite facing second mirror ( 72 ). The fixed reflecting element has a third mirror ( 81 ). The movable reflecting element is movable by the driving means from a first position, in which signals transmit from input to output ports without reflection from mirrors, to a second position, in which reflection from the mirrors effects a switching of the optical signals to different output ports. The presence of the fixed reflecting element automatically compensates for a distance between the first and second mirrors, allowing reflected signals to accurately align with respective output ports.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an optical switch for use in optical fiber communication and optical network technology, and particularly to an optical switch having a movable mirror to control the path of a light beam. 
     2. Description of Related Art 
     Optical signals are commonly transmitted in optical fibers, which provide efficient light channels through which the optical signals can pass. Recently, optical fibers have been used in various fields, including telecommunications, where light passing through an optical fiber is used to convey either digital or analog information. Efficient switching of optical signals between individual fibers is necessary in most optical processing systems or networks to achieve the desired routing of the signals. 
     A typical switch has one or more light input port(s) and at least two light output ports for performing switching or logical operations to optical signals in a light transmitting line/system or in an integrated optical circuit. Factors for assessing the capability of an optical switch include low insertion loss (IL&lt;1 db), good isolation performance (&gt;50 db), and fast switching speed (normally, tens of milliseconds). 
     Optical switches are divided into two types: a mechanical type and a non-mechanical type. In principle, the mechanical-type optical switches have a number of advantages over other forms of optical switches in applications where switching speed is not important. Mechanical-type optical switches offer lower insertion losses, low cross-talk, and insensitivity to wavelength of light. 
     Conventional mechanical-type optical switches come in two different designs: where the optical components move, and where the fibers move. Moving fiber switches involve the actual physical movement of one or more of the fibers to specific positions to accomplish the transmission of a beam of light from one fiber end to another under selected switching conditions. Moving optical component switches, on the other hand, include optical collimating lenses, which expand the beam of light from the fibers, and then, using moving prisms or mirrors, reswitch the expanded beam as required by the switching process. 
     The moving fiber switches have a stringent tolerance requirement for the amount and direction of fiber movement. The tolerance is typically a small portion of the fiber core diameter for two fibers to precisely collimate to reduce loss. The fibers themselves are quite thin and may be subject to breakage if not properly protected. On the other hand, reinforcing the fibers with stiff protective sheaths makes the fibers less flexible, increasing the force required to manipulate each fiber into alignment. Thus these moving fiber optical switches share a common problem of requiring high precision parts to obtain precise positioning control and low insertion loss. This results in high costs and complicates manufacture of the switches. Moreover, frequently moving fibers to and fro is apt to damage or even break the fibers. The switching speed of these moving fiber optical switches is also slow. 
     Conventional moving optical component switches have less stringent movement control tolerance requirements because of the collimating lenses. 
     One prior art moving optical component switch is illustrated in FIGS. 4,  5  and  6  and comprises a first and second light input ports  130 ,  150 , a first and second light output ports  140 ,  160 , and a movable reflecting element  170 . The movable reflecting element  170  has two reflecting surfaces  171 ,  172 , which are parallel to each other. The first reflecting surface  171  is movably arranged to reflect light from the first light input port  130  to the second light output port  160 , and the second reflecting surface  172  is movably arranged to reflect light from the second light input port  150  to the first light output port  140 . 
     The optical switch switches the light signals by moving the movable reflecting element  170  between two positions. In the first position, the movable reflecting element  170  is out of the path of the light beams and optical signals from the first input port  130  are transmitted to the first output port  140 , while optical signals from the second input port  150  are transmitted to the second output port  160 . 
     In the second position, the movable reflecting element  170  moves into the path of the light beams and the optical signals from the first input port  130  are reflected by the first reflecting surface  171  to the second output port  160 , while the optical signals from the second input port  150  are reflected by the second reflecting surface  172  to the first output port  140 . 
     If the first reflecting surface  171  and the second reflecting surface  172  were on the same plane, the optical switch would achieve low loss and precise collimation. However, the prior art device has the two reflecting surfaces or reflective films deposited on two opposite surfaces of a substrate having some thickness, so it is impossible for the first reflecting surface and the second reflecting surface to be on the same plane. Thus, as illustrated in FIG. 6, when the movable reflector moves into the path of the light beams, the optical signals from the second input port  150  and reflected from the second reflecting surface  172  may not exactly align with the first output port  140 , as should the optical signals from the first input port  130  to the second output port  160 . Consequently, a solution to the misalignment of the second light beam in this kind of optical switch is desired. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to eliminate the influence of a distance between two opposite reflecting surfaces of a movable two-sided reflecting element when such reflecting element is used to switch signals coming from a first and second input ports between first and second output ports in an optical switch. 
     An optical switch in accordance with one embodiment of the present invention comprises two input ports, two output ports and a switching element. The switching element includes a movable reflecting element and a fixed reflecting element. The movable reflecting element is a two-sided mirror and can move between a first position and a second position. The fixed reflecting element has at least one mirror, which is mounted parallel to the two-sided mirror. The first input port is aligned with the first output port, and the second input port is aligned with the second output port. When the movable reflecting element is out of the path of the light beams, the fixed reflecting element does not affect the path of the optical signals, and the optical signals from the first and second input ports are transmitted to the first and second output ports, respectively. When the movable reflecting element is moved into the path of the light beams, the fixed reflecting element functions to reflect the optical signals coming from the second input port so that they are reflected twice off the two-sided mirror, automatically accommodating the distance between the two reflecting surfaces of the moveable reflecting element and correctly aligning the reflected optical signals with the first output port. An efficient switching operation is thus achieved. 
     Other objects, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of an optical switch having a movable reflecting element in accordance with the present invention. 
     FIG. 2 is an essential optical paths diagram of the optical switch of FIG. 1 with the movable reflecting element in a first position. 
     FIG. 3 is similar to FIG. 2, but with the movable reflecting element in a second position. 
     FIG. 4 is an essential optical paths diagram of a conventional optical switch with a movable reflective element in a first position. 
     FIG. 5 is an essential optical paths diagram of the switch of FIG. 4 with the movable reflective element in a second position. 
     FIG. 6 is a partial, enlarged view of FIG. 5 with the movable reflective element in a second position. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in FIGS. 1-3, an optical switch  1  with a movable reflector in accordance with the present invention comprises a cover  10  and a base  20 , with the base  20  mounting a first input port  30 , a first output port  40 , a second input port  50 , a second output port  60 , a movable reflecting element  70 , a fixed reflecting element  80 , and a driving means  90 . 
     The first input port  30 , the first output port  40 , the second input port  50  and the second output port  60  are all similar to each other. The first input port  30  comprises a first input fiber  31 , a first input ferrule  32  and a first input optical collimating lens, which in the present embodiment is a quarter pitch first input GRIN lens  33 . The first input fiber  31  is received and retained in the first input ferrule  32 , and an end face (not labeled) of the first input ferrule  32  is fixed in close proximity to a corresponding face (not labeled) of the quarter pitch first input GRIN lens  33 . The arrangement of a first output fiber  41 , a first output ferrule  42 , and a quarter pitch first output GRIN lens  43  in the first output port  40  is the same as for the first input port  30 , as is the arrangement of a second input fiber  51 , a second input ferrule  52 , and a quarter pitch second input GRIN lens  53  in the second input port  50 , and as is a second output fiber  61 , a second output ferrule  62 , and a quarter pitch second output GRIN lens  63  in the second output port  60 . The first input GRIN lens  33  and the second input GRIN lens  53  are each used to collimate a light beam which is selectively directed to either the first output GRIN lens  43  or the second output GRIN lens  63 . 
     The movable reflecting element  70  includes a first mirror  71  and a second mirror  72  parallel to and directed opposite one another. The movable reflecting element  70  moves to and fro between a first position and a second position. The first mirror  71  is oriented to reflect signals coming from the first input port  30 , and the second mirror  72  is oriented to reflect signals coming from the second input port  50 , when the movable reflecting element  70  is in the second position. 
     The fixed reflecting element  80  includes a third mirror  81  which confronts and is parallel to the second mirror  72  when the movable reflecting element  70  is in the second position. The first mirror  71 , the second mirror  72  and the third mirror  81  are small enough that, when the movable reflecting element  70  is not in the second position, they have no influence on the light beams. 
     The driving means  90  is realized by a motor or a relay, and comprises a movable arm  91 . The movable arm  91  is attached to the movable reflecting element  70  and actuates it to move to and fro between the first and second positions. 
     The cover  10  and the base  20  define an interior space (not labeled) therebetween for accommodating the first input/output ports  30 , 40 , the second input/output ports  50 , 60 , the movable reflecting element  70 , the fixed reflecting element  80  and the driving means  90  therein. The cover  10  has four lead sections  11 , 12 , 13 , 14  for protecting the corresponding fibers  31 , 41 , 51 , 61  of the ports  30 , 40 , 50 , 60 . The base  20  further includes four holders  34 , 44 , 54 , 64  for mounting the ports  30 , 40 ,  50 , 60 , respectively, on the base  20 . Moreover, the fixed reflecting element  80  is also attached to the base  20 . 
     FIG. 2 shows the essential optical paths diagram of the optical switch  1  with the movable reflecting element  70  in the first position, out of the path of the light beams, before the driving means  90  moves the movable reflecting element  70 . The fixed reflecting element  80  is also out of the path of the light beams in this first position. Optical signals from the first input fiber  31  are collimated by the first input GRIN lens  33  and are transmitted as parallel light beams to the first output GRIN lens  43 , which collimates the parallel light beams and transmits them to the first output fiber  41  of the first output port  40 . At the same time, optical signals from the second input fiber  51  are collimated by the second input GRIN lens  53  and are transmitted as parallel light beams to the second output GRIN lens  63 , which collimates the parallel light beams and transmits them to the second output fiber  61  of the second output port  60 . 
     FIG. 3 shows the essential optical paths diagram of the optical switch  1  after the driving means  90  and movable arm  91  have moved the movable reflecting element  70  to the second position, into the path of the light beams. In this second position, optical signals from the first input fiber  31  of the first input port  30  are collimated by the first input GRIN lens  33  and are transmitted as parallel light beams to the first mirror  71  of the movable reflecting element  70 , which reflects the parallel light beams to the second output GRIN lens  63 . After being collimated by the second output GRIN lens  63 , the signals are received by the second output fiber  61  of the second output port  60 . The optical signals from the second input fiber  51  are collimated by the second input GRIN lens  53  and are transmitted as parallel light beams to the second mirror  72  of the movable reflecting element  70 , whereupon they are reflected to the third mirror  81  of the fixed reflecting element  80 , which reflects the light beams to the second mirror  72  again, which reflects the light beams to the first output GRIN lens  43 . After being collimated by the first output GRIN lens  43 , the signals are received by the first output fiber  41  of the first output port  40 . 
     By controlling the position of the movable reflecting element  70  using the driving means  90 , the path of the light beams through the optical switch  1  is controlled, and the light beams emitted from the input ports  30 , 50  can be selectively switched between the output ports  40 , 60 . Transmission of the optical signals through the optical switch  1  is efficient, having a low insertion loss and good isolation performance, since the arrangement of the mirrors  71 , 72 , 81  automatically compensates for the distance between the first mirror  71  and the second mirror  72 . Thus optical signals from the second input port  50  which are reflected from the second mirror  72  and the first mirror  81  are aligned with the first output port  40 , yielding good transmission performance. Note that if a first distance between the first mirror  71  and the second mirror  72 , and a second distance between the second mirror  72  and the third mirror  81 , are chosen correctly, then the distance that a first set of optical signals travels from the second input port  50  to the first output port  40  will be substantially the same as the distance that a second set of optical signals travels from the first input port  30  to the second output port  60 . Thus there should be no phase shift between the signals arriving at the second output port  60  and those arriving at the first output port  40 . With very high speed communications, this can provide an added advantage. 
     Manufacture of the optical switch of the present invention can be accomplished using the process described in the following steps: 
     1) arranging the movable reflecting element  70  in the path of the light beams and then adjusting and fixing the positions and orientations of the first input port  30  and the second output port  60  so that the optical signals from the first input port  30  propagate to the second output port  60  after being reflected by the first mirror  71  of the movable reflecting element  70 ; 
     2) moving the movable reflecting element  70  out of the path of the light beams and adjusting the positions and orientations of the first output port  40  and the second input port  50  so that the optical signals from the first input port  30  accurately transmit to the first output port  40 , and the optical signals from the second input port  50  accurately transmit to the second output port  60 . 
     3) moving the movable reflecting element  70  into the path of the light beams again in the prior position and adjusting the position and orientation of the fixed reflecting element  80  so that the optical signals from the second input port  50  propagating to the first output port  40  are reflected three times (two times by the second mirror  72  of the movable reflecting element  70  and one time by the third mirror  81  of the fixed reflecting element  80 ). 
     It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. For example, the fixed reflecting element  80  may be movable, and further, the fixed reflecting element  80  may be movable in tandem together with the movable reflecting element  70  so that both the reflecting elements  70 ,  80  move into and out of the path of the light beams at the same time.