Abstract:
An optical switch actuator moving an optical element into or out of an optical pathway. The optical element is coupled to a movable shuttle and driven by a motor between two rest positions. The motor includes two stationary coils and a magnet. The shuttle is magnetically latched in the rest positions. The optical element&#39;s position at the extended rest position is controlled with a stop that contacts the shuttle to provide accuracy and precision about multiple axes. The material used to construct the actuator&#39;s components aids in repeatedly positioning the optical element with precision.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a Continuation-In-Part of Ser. No. 09/473,455, filed on Dec. 28, 1999. 
     
    
     
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
         [0002]    Not Applicable  
         BACKGROUND OF THE INVENTION  
         [0003]    1. Field of Invention  
           [0004]    This invention pertains to an actuator for a fiber optical device. More particularly, this invention pertains to an assembly that linearly moves an optical element into an optical path thereby altering the optical path.  
           [0005]    2. Description of the Related Art  
           [0006]    In fiber optic networks, light signals are transmitted along optical fibers to transfer information from one location to another. Optical switches are used to selectively couple light from an input fiber to an output fiber. Optical fibers typically have very small cross-sections and narrow acceptance angles within which light entering the fiber must fall to promote efficient propagation of the light along the fiber. As such, optical switches must transfer light with precise alignment.  
           [0007]    One type of electromechanical optical switch operates by moving a mirror while maintaining the optic fibers and optical pathway stationary. In response to electrical signals, a relay arm moves a mirror into and out of an optical pathway. The relay arm moves the mirror substantially parallel to its reflective surfaces. The travel of the relay arm along that axis is limited by stops that determine the position of the mirror. The relay arm is constrained at the stops by only a single contact point, thereby allowing inaccuracies in the radial position due to rotation of the arm. Examples of such switches include U.S. Pat. No. 5,133,030, issued to Lee on Jul. 21, 1992, entitled “Fiber Optic Switch Having a Curved Reflector,” and U.S. Pat. No. 4,057,719, issued to Lewis on Nov. 8, 1977, entitled “Fiber Optics Electro-Mechanical Light Switch.” 
           [0008]    One problem with such a switch is that the relay mechanism may not be able to provide the accuracy and precision in positioning the mirror that may be required by some optical switching networks. Accuracy is the ability to achieve a desired position with any given movement. Precision is the ability to repeatedly achieve the same position over a number of movements, regardless of where that position is located. Because the movement of the relay arm is constrained by only a single point of contact with the stopper, the switch may only be able to provide accurate alignment along a single axis (in the direction of the arm&#39;s movement). The use of a single contact point may result in position inaccuracies due to the freedom of the relay arm to rotate about additional axes. Furthermore, relay mechanisms are typically constructed of materials that may be susceptible to significant wear from component contact through repeated use. Such material wear may lead to problems with precise placement of the mirror over time, in addition to position inaccuracies.  
           [0009]    Another problem with electromechanical switches is that they use a large electromechanical actuator that may not permit the placement of mirrors in the packing density that may be required for multiple switch arrays.  
           [0010]    Other types of systems use electromagnetic actuators, for example, disk drive systems. These systems typically use actuators to position drive components over different regions of a disk. One problem with such electromagnetic actuators is that they require a control servo loop in order to operate. With a servo loop, the position component must be actively adjusted to maintain proper positioning. As such, actuators of this type are unable to repeatedly return components to the same position when actuated, without the use of an active control loop. This adds complexity to a system&#39;s design and, thereby, may undesirably increase its cost.  
         BRIEF SUMMARY OF THE INVENTION  
         [0011]    According to one embodiment of the present invention, an optical switch actuator is provided. The actuator includes an optical element, a shuttle, and a motor. The optical element, in one embodiment, includes a mirror. The shuttle moves longitudinally within a cylinder, which has a cylindrical stopper that contacts a flat on the shuttle, thereby precisely locating the optical element in the extended position. The shuttle is connected to the motor by a cable member. The motor includes two stationary cored coils with a magnet that moves between the two cores. The magnet is attracted to the core, thereby latching the shuttle in either of two positions.  
           [0012]    In one embodiment the shuttle, the cylinder sleeve it moves within, and the stopper are made of a close grained ceramic material that has low coefficient of thermal expansion, is not susceptible to cold metal bonding or welding, and exhibits little wear with repeated use. The motor has a bearing and a bearing bushing made of the same material.  
           [0013]    The stopper permits the optical element to have high repeatability by stopping the shuttle at a fixed point and inhibiting the shuttle from moving longitudinally and from moving about its longitudinal axis. The optical element is attached to the shuttle with an adhesive with a low coefficient of thermal expansion and contains micro-spheres, which allow the optical element to maintain alignment once positioned. 
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0014]    The above-mentioned features of the invention will become more clearly understood from the following detailed description of the invention read together with the drawings in which:  
         [0015]    [0015]FIG. 1 is a perspective view of an optical switch actuator;  
         [0016]    [0016]FIG. 2 is a cross-sectional view of the actuator;  
         [0017]    [0017]FIG. 3 is an exploded diagram showing the internal components of the actuator;  
         [0018]    [0018]FIG. 4 is a schematic diagram of the actuator;  
         [0019]    [0019]FIG. 5 is a cross-sectional view of the driven element of the motor;  
         [0020]    [0020]FIG. 6 is an exploded view of the stopper and shuttle cylinder; and  
         [0021]    [0021]FIG. 7 is a cross-sectional view of the stopper and shuttle cylinder. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]    An apparatus for moving an optical element  132  between an extended position and a retracted position is disclosed. The apparatus is an optical switch actuator  10  suitable for use in optical switches.  
         [0023]    [0023]FIG. 1 illustrates the actuator  10 , which has a cylindrical body  114  with electrical leads  142   a ,  142   b ,  142   c  at one end and an optical element  132  at the opposite end. The optical element  132  has illustrated in the extended position. In the retracted position, the optical element  132  is positioned closer to the end of the cylindrical body  114 . A motor inside the cylindrical body  114  drives a shuttle  112 , and the optical element  132 , between the two positions. In one embodiment, the optical element  132  is a mirror. In another embodiment, the optical element  132  is a filter. In one embodiment, a wavelength division multiplexed (WDM) switch made with an optical element  132  being a partially reflective filter. The use of optical elements, such as mirrors and filters, to propagate light between fiber collimators is well known in the art; according, a more detailed discussion of their operation is not provided. As shown in FIG. 1, the optical element  132  is attached to the shuttle  112 , which is constrained by a cover  104  and surrounded by a tube  108 .  
         [0024]    The electrical leads  142  are attached to a flange  116  located at one end of the cylindrical body  114 . The electrical leads  142  are connected to a motor, or driver, in the cylindrical body  114 . The motor, or driver, moves the shuttle  132  linearly between an extended position and a retracted position. In the extended position, the optical element  132  on the shuttle  132  interacts with an optical pathway and in the retracted position the optical element  132  is out of the optical pathway.  
         [0025]    Referring to FIG. 2, the motor includes a pair of electromagnets  214 ,  212  and  224 ,  222  and a plunger assembly  232 . A pair of electrical conductors  102   a ,  102   b  connect the upper winding  214  to two of the electrical leads  142   a ,  142   b  and a second pair of electrical conductors  104   a ,  104   b  connect the lower winding  224  to two of the electrical leads  142   b ,  142   c . In one embodiment, the electrical conductors  102   a ,  102   b  are lacquered to the cylindrical body  114 . The electrical conductors  102   a ,  102   b ,  104   a ,  104   b  are connected to the electrical leads  142  by wrapping and then soldering the conductors  102   a ,  102   b ,  104   a ,  104   b  to the appropriate lead  142 . The upper and lower designations are used only for convenience in referring to the orientation presented in the figures. Those skilled in the art will recognize that the actuator  10  can be used in any orientation without departing from the spirit and scope of the present invention.  
         [0026]    [0026]FIG. 2 shows the actuator  10  in cross-section. Inside the cylindrical body  114  is the motor assembly, which includes an upper coil  214  wrapped around a hollow upper core  212 , a lower coil  224  wrapped around a hollow lower core  222 , and a plunger, or plunger assembly,  232  that moves between the upper core  212  and the lower core  222 . The plunger assembly  232  is attached to a wire  206  connected to the shuttle  112 . The plunger assembly  232  moves inside a bearing bushing  234 .  
         [0027]    The shuttle  112  moves within a cylindrical sleeve  202  between the extended and the retracted position. At the extended position, the shuttle  112  contacts a stopper  204 , which prevents the shuttle  112  from moving further in longitudinal direction. The stopper  204  determines the accuracy with which the shuttle  112 , and thereby the optical element  132 , can be positioned. However, the wear of the shuttle  112  may affect the precision with which the optical element  132  can be repeatedly positioned.  
         [0028]    The shuttle  112 , the cylindrical sleeve  202 , and the stopper  204  are constructed from a hard material having a small grain size, for example, ceramic. Ceramic may be polished to higher degree than softer materials such as plastics. When a material is polished, the grain size of the material determines its surface roughness and, thus, its surface area of contact. As a result, when materials come into contact with each other, the area of contact is determined by the grain size of the contacting materials. Materials having a small grain size will have a greater number of grain particles in contact with each other over a given surface area. As such, a smaller grain size results in more contact between the surface of the shuttle  112  and the cylindrical sleeve  202 .  
         [0029]    In one embodiment, for example, the grain size is approximately in the range of 0.3 to 0.5 microns and the distance of travel of shuttle  112  is approximately 2 millimeters. When materials having this grain size come into contact with each other, the contact accuracy may be approximately 0.2 microns. Such a contact accuracy over a distance of approximately 2 mm results in an angular accuracy of approximately 0.0001 radians.  
         [0030]    The wear of the material results from the dislodging of surface grains, of which the size of the grains is one factor. The more grains that are dislodged, the greater the wear of the material. However, a large force is required to dislodge a grain of any given size. A surface material having a greater number of small gains will tend to have fewer gains dislodged than a material having a fewer number of larger grains. As such, due to the larger number of grain contacts with small grained surfaces, less discernable wear may result than with a material having a larger grain size.  
         [0031]    In another embodiment, other fine grained materials that reduce wear on shuttle  112  and cylindrical sleeve  202  are used, for example, zirconia, silicon carbide, silicon nitride, and aluminum oxide. In yet another embodiment, shuttle  112  and cylindrical sleeve  202  are constructed from a metal or plastic material. If a larger grained material, such as a metal, is desired to be used, the speed at which shuttle  112  is moved is slowed to prevent the generation of forces that may increase the wear on shuttle  112  and cylindrical sleeve  202 . However, the use of ceramics provides greater precision and switching speed than is attainable with larger grained materials. As such, the proper selection of the material for shuttle  112  and cylindrical sleeve  202  may aid in achieving a high precision and repeatability in the positioning of optical element  132 . Grain size, however, is only one of several factors that may contribute to the wear resistance of a material. Other factors that may contribute to the wear resistance of a material include, for example, coefficients of friction, modulus of rapture, tensile strength, compressive strength, and fracture toughness. The operation of such factors is well known in the art; accordingly, a more detailed discussion is not provided.  
         [0032]    Actuator  10  is not limited to only having components constructed from the materials described above. In an alternative embodiment, shuttle  112  and cylindrical sleeve  202  are coated with the materials described above. For example, shuttle  112  and cylindrical sleeve  202  are constructed of any rigid material and coated with a wear resistant ceramic such as titanium nitride or aluminum oxide. The coating is applied using techniques that are well known in the art, for example, chemical vapor deposition.  
         [0033]    An advantage, other than wear resistance, to using a ceramic material for the interface between the shuttle  112 , the cylindrical sleeve  202 , and the stopper  204  is that ceramic is not susceptible to cold-metal bonding or welding. Cold-metal bonding occurs when two components in contact are placed under pressure, the more extreme the pressure, the greater the chance of cold-metal bonding occurring. Without cold-metal bonding, less motor power is required to overcome inertia and start the plunger assembly  232  and the shuttle  112  moving.  
         [0034]    The cylindrical sleeve  202  is aligned with the plunger assembly  232  by the tube  108 . The tube  108  has a central bore that is concentric with the outside edge of its flange, which has the same diameter as the cylindrical body  114 . The tube  108  is secured to the body  114  and the cylindrical sleeve  202  is secured to the inside of the tube  108 . In one embodiment adhesive is used to secure the tube  108  to the body  114  and the sleeve  202  to the tube  108 . In another embodiment, the tube  108  is not used, and the cylindrical sleeve  202  is secured to the upper core  212 . In another embodiment, the upper core  212  has an alignment recess or groove into which the cylindrical sleeve  202  is secured, without the tube  108 , by an adhesive.  
         [0035]    [0035]FIG. 3 illustrates an exploded view of the internal components of the actuator  10 . The shuttle  112 , in one embodiment, is an MU ferrule that is machined to have a first surface  336  for mounting the optical element  132  and a second surface  334  and an incline surface  332  for interfacing with the cylindrical stopper  204 . The wire  206  extends from the bottom of the shuttle  112  to the top portion of the shuttle  112 . In one embodiment, the wire  206  is secured to the shuttle  112  by an adhesive applied to the wire  206  before it is drawn into the shuttle  112 .  
         [0036]    The optical element  132  is secured to the first surface  336  with an adhesive. The optical element  132  attachment to the shuttle  112 , along with the repeatability of the shuttle  112  location in the extended position, is critical. The precise alignment of the optical element  132  relative to the cylindrical body  114  is critical. Any misalignment can result in an attenuation of the optical signal or the loss of the signal. By matching the coefficient of thermal expansion of the individual components and adhesives, the components of the actuator  10  remain in alignment over a wide temperature range such that the optical path does not suffer degradation as the temperature varies. In one embodiment, the temperature range is from −40° to +85° Centigrade. In another embodiment, the transition point of the adhesive is outside the operating temperature range, which enhances the dimensional stability of the connection of the optical element  132  to the first surface  336 . In one embodiment, keeping the transition point outside the operating range is accomplished by using fillers. In still another embodiment, the adhesive has limited shrinkage, which can be accomplished with a filler. Further, the adhesive can be cured in place. In one embodiment the adhesive is cured by ultraviolet light.  
         [0037]    In one embodiment the adhesive is a quick curing adhesive blended with amorphous silica spheres of a selected diameter. The adhesive is compressed between the optical element  132  and the first surface  336 , with the spheres forming a monolayer, which results in dimensional stability when the adhesive is cured. In another embodiment the adhesive is Dymax OP66LS, which has a coefficient of thermal expansion similar to that of the shuttle  112  such that the optical element  132  remains in alignment as the temperature varies within the operating range of the actuator  10 .  
         [0038]    In addition to the adhesive, the repeatability of the optical element  132  location relative to the cylindrical body  114  is achieved by the stopper  204  contacting the incline surface  332 , which makes the shuttle  112  self-aligning. The stopper  204  is fixed in position by the cover  104  and the cylindrical sleeve  202 . The stopper  204  contacts the incline surface  332  of the shuttle  112  which stops the shuttle  112  from extending further. Also, the stopper  204 , by its length contacting the width of the incline surface  332 , prevents the shuttle  112  from rotating within the cylindrical sleeve  202  in the fully extended position. Therefore, the interaction of the stopper  204  and the incline surface  332  serve to ensure that the optical element  132  position is highly repeatable when in the extended position.  
         [0039]    [0039]FIG. 5 illustrates the plunger assembly  232  which is shown between the upper coil core  212  and the lower coil core  222  shown on FIG. 3. The plunger assembly  232  includes an upper armature  314  and a lower armature  320 . Sandwiched between the upper and lower armatures  314 ,  320  are a permanent magnet  318  and a bearing  316 . The bearing  316  is ring shaped and has an inside diameter greater than the outside diameter of the permanent magnet  318 . The bearing  316  has an outside diameter greater than that of the upper and lower armatures  314 ,  320  and slightly less than the inside diameter of the bearing bushing  234 . The outside edge of the bearing  316  slides along the inside surface of the bearing bushing  234 . Both the bearing  316  and the bearing bushing  234 , in one embodiment, are constructed from a hard material having a small grain size, for example, ceramic, as described above for the shuttle  112  and the cylindrical sleeve  202 .  
         [0040]    The plunger assembly  232  is held together by the central plunger  324 , which has the wire  206  in its center. The central plunger  324  fits in a central opening in the upper and lower armatures  314 ,  320 , permanent magnet  318 , the upper washer  312  and the lower washer  322 . In one embodiment, the central plunger  324  is sized for an interference fit with the central opening and is pressed into the openings, thereby securing the assembly  232 . In another embodiment, the central plunger  324  is secured in the openings by an adhesive. In still another embodiment, the central plunger  324  is positioned in the openings and pressure is applied to its exposed ends, causing the central plunger  324  to expand.  
         [0041]    The upper and lower washers  312 ,  322 , in one embodiment, are constructed of a resilient material, such as nylon or an elastomer. In another embodiment, the washers  312 ,  322  are non-metallic. Resilient washers  312 ,  322  act as shock absorbers; thereby aiding in the long life of the actuator  10  by avoiding slamming the shuttle  112  into the stopper  204 . The actuation pressure of the assembly  324  against the cores  212 ,  222 , if the contact surfaces are metalto-metal, can cold-weld the contact surface to each other. Resilient or non-metallic washers  312 ,  322  avoid cold-welding or sticking of the assembly  324  to the upper and lower cores  212 ,  222 .  
         [0042]    [0042]FIG. 4 illustrates the electrical schematic of the actuator  10 . In operation, a direct current voltage is momentarily applied to electrical leads  142   a ,  142   b , which energizes the upper coil  214  and causes the permanent magnet  318  to be attracted to the upper core  212 . The movement of the permanent magnet is shown by the arrow  412  on FIG. 4. The voltage pulse causes the permanent magnet  318 , and the plunger assembly  324 , to move toward the upper core  214  and when the permanent magnet  318  is near the upper core  214 , magnetic attraction latches the plunger assembly  324  in the extended position. The plunger assembly  324  is connected to the shuttle  112  via the wire  206 . The shuttle  112  is constrained from extending by the stopper  204 , which ensures that the shuttle  112  stops at the same point each time it is in the extended position. With the shuttle  112  constrained by the stopper  204  and the wire  206  being straight, the plunger assembly  324  does not make contact with the upper core  212 . However, as the plunger assembly  324  moves between its two positions, the wire  206  flexes. This flexing serves to minimize any shock transmitted to the optical element  132  from the plunger assembly  324 . In one embodiment, the wire is coated with a slick material, such as Teflon, so that, if the wire were to contact the inside surface of the upper core  212 , the wire will slide with minimum friction.  
         [0043]    A direct current voltage pulse applied to electrical leads  142   b ,  142   c  momentarily energizes the lower coil  224  and causes the permanent magnet  318  to be attracted to the lower core  222 . The magnetic force induced in the lower core  222  overcomes the magnetic attraction of the permanent magnet  318  to the upper core  212  and causes the plunger assembly  232  to move toward the lower core  222 . When the permanent magnet  318  approaches the lower core  222 , the magnetic attraction to the lower core  222  pulls the plunger assembly  324  toward the core  222  until the lower washer  322  contacts the lower core  222 . With the optical element  132  in the retracted position, the plunger assembly  324  is latched against the lower core  222  by the magnetic attraction of the permanent magnet  318  to the lower core  222 . In one embodiment, the plunger assembly  232  is in contact with the core  212 ,  222 . In another embodiment, there is an air gap between the plunger assembly  232  and the core  212 ,  222 . In still another embodiment, a gap is created by the use of non-ferromagnetic washers  312 ,  322 . The use of a gap reduces the power required for the coils  214 ,  224  to move the plunger assembly  232 .  
         [0044]    In another embodiment, a direct current pulse is applied to one coil  214  or  224  to attract the permanent magnet  318  and another pulse is applied to the other coil  224  or  214  to repulse the permanent magnet  318 . The polarity of the voltage applied to the coils  214 ,  224  is reversed to move the plunger assembly  232  in the opposite direction. This has the effect of having one coil  214  or  224  attracting the permanent magnet  318  and the other coil  224  or  214  pushing the permanent magnet  318 , thereby requiring less power to move the plunger assembly  232  between its two positions.  
         [0045]    Position indication of the plunger assembly  324 , and the optical element  132 , is achieved by measuring the inductance of each of the coils  214 ,  224 . The plunger assembly  324  has two possible positions corresponding to the optical element  132  being extended and retracted: with the optical element  132  extended, the assembly  324  is adjacent the upper core  212  and with the optical element  132  retracted, the assembly  324  is adjacent the lower core  222 . The coil that the permanent magnet  318  is closest will have a different inductance than the other coil. In one embodiment, the relative inductance is measured by connecting the coils to a circuit that responds to changes in inductance and that responds to a measured inductance above or below a predetermined threshold value.  
         [0046]    [0046]FIG. 6 illustrates the cylindrical sleeve  202 , the stopper  204 , and the cover  104 . FIG. 7 is a cross-sectional view of the same three components. The stopper  204  is a rod-shaped member that rests in a notch cut in the cylindrical sleeve  202  and is held in position by the cover  104 . In one embodiment, the stopper  204  is fixedly held in position when the cover  104  is attached to the cylindrical sleeve  202 . In another embodiment, the stopper  204  is loosely held in position and when the shuttle  112  is in the extended position, the incline surface  332  forces the stopper  204  upwards and away from the longitudinal axis of the cylindrical sleeve  202  until the stopper  204  is wedged between the cover  104 , the notch cut in the cylindrical sleeve  202 , and the incline surface  332 . The repeatability of the shuttle  112  in the extended position is assured by the stopper  204  contacting the cover  104  and the cylindrical sleeve  202  and by the incline surface  332  of the shuttle  112  contacting the stopper  204  and having the shuttle  112  rotate within the cylindrical sleeve  202  such that the incline surface  332  aligns with the stopper  204 . This alignment function eliminates the need for tight tolerance between the shuttle  112  and the cylindrical sleeve  202  and results in the shuttle  112  returning to the same extended position during repeated operations with little spatial deviation.  
         [0047]    The ends of the stopper  204  do not extend past the outside cylindrical surface of the cylindrical sleeve  202 . The cover  104  fits over the end of the cylindrical sleeve  202 . In one embodiment, the cover  104  is sized for an interference fit with the cylindrical sleeve  202  and the cover  104  is pressed onto the end of the cylindrical sleeve  202 , thereby securing the stopper  204  in a fixed position. In another embodiment, the cover  104  is secured in place with an adhesive.  
         [0048]    From the foregoing description, it will be recognized by those skilled in the art that an actuator  10  for linearly moving an optical element  132  has been provided. The actuator  10  has opposed coils  214 ,  224  that force a magnet  318  to move between two positions. The magnet  318  movement is translated to a shuttle  112  with the optical element  132 . The shuttle  112  engages a stopper  204  at the extended position, which causes the shuttle  112  to stop at a fixed point with high repeatability. The stopper  204  prevents the shuttle  112  from moving longitudinally along the longitudinal axis. The stopper  204  also prevents the shuttle  112  from rotating about the longitudinal axis. Polishing the inside of the sleeve  202  and the shuttle  112  allows for low friction motion of the shuttle  112 . Polishing the inside of the bearing bushing  234  and the outside surface of the bearing  316  allows for low friction motion of the plunger assembly  232 . The low thermal expansion of the ceramic materials, along with the low friction surfaces and the self-aligning shuttle  112 , results in high repeatability and easier alignment of the optical element  132  within an optical pathway.  
         [0049]    While the present invention has been illustrated by description of several embodiments and while the illustrative embodiments have been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and methods, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicant&#39;s general inventive concept.