Abstract:
A piezoelectric optical relay is disclosed in which a solid slug moves within a switching channel formed in relay housing. An optical path passing through the switching channel is blocked or unblocked by motion of the solid slug. Motion of the solid slug is controlled by at least two piezoelectric actuators within the switching channel. Motion of the solid slug is resisted by a liquid, such as a liquid metal, that wets between the solid slug and at least one fixed contact pad in the switching channel. The surface tension of the liquid provides a latching mechanism for the relay.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is related to the following co-pending U.S. patent applications, being identified by the below enumerated identifiers and arranged in alphanumerical order, which have the same ownership as the present application and to that extent are related to the present application and which are hereby incorporated by reference: 
     Application 10010448-1, titled “Piezoelectrically Actuated Liquid Metal Switch”, filed May 2, 2002 and identified by Ser. No. 10/137,691; 
     Application 10010529-1, “Bending Mode Latching Relay”, and having the same filing date as the present application; 
     Application 10010531-1, “High Frequency Bending Mode Latching Relay”, and having the same filing date as the present application; 
     Application 10010570-1, titled “Piezoelectrically Actuated Liquid Metal Switch”, filed May 2, 2002 and identified by Ser. No. 10/142,076; 
     Application 10010571-1, “High-frequency, Liquid Metal, Latching Relay with Face Contact”, and having the same filing date as the present application; 
     Application 10010572-1, “Liquid Metal, Latching Relay with Face Contact”, and having the same filing date as the present application; 
     Application 10010573-1, “Insertion Type Liquid Metal Latching Relay”, and having the same filing date as the present application; 
     Application 10010617-1, “High-frequency, Liquid Metal, Latching Relay Array”, and having the same filing date as the present application; 
     Application 10010618-1, “Insertion Type Liquid Metal Latching Relay Array”, and having the same filing date as the present application; 
     Application 10010634-1, “Liquid Metal Optical Relay”, and having the same filing date as the present application; 
     Application 10010640-1, titled “A Longitudinal Piezoelectric Optical Latching Relay”, filed Oct. 31, 2001 and identified by Ser. No. 09/999,590; 
     Application 10010643-1, “Shear Mode Liquid Metal Switch”, and having the same filing date as the present application; 
     Application 10010644-1, “Bending Mode Liquid Metal Switch”, and having the same filing date as the present application; 
     Application 10010656-1, titled “A Longitudinal Mode Optical Latching Relay”, and having the same filing date as the present application; 
     Application 10010663-1, “Method and Structure for a Pusher-Mode Piezoelectrically Actuated Liquid Metal Switch”, and having the same filing date as the present application; 
     Application 10010664-1, “Method and Structure for a Pusher-Mode Piezoelectrically Actuated Liquid Metal Optical Switch”, and having the same filing date as the present application; 
     Application 10010790-1, titled “Switch and Production Thereof”, filed Dec. 12, 2002 and identified by Ser. No. 10/317,597; 
     Application 10011055-1, “High Frequency Latching Relay with Bending Switch Bar”, and having the same filing date as the present application; 
     Application 10011056-1, “Latching Relay with Switch Bar”, and having the same filing date as the present application; 
     Application 10011064-1, “High Frequency Push-mode Latching Relay”, and having the same filing date as the present application; 
     Application 10011065-1, “Push-mode Latching Relay”, and having the same filing date as the present application; 
     Application 10011121-1, “Closed Loop Piezoelectric Pump”, and having the same filing date as the present application; 
     Application 10011329-1, titled “Solid Slug Longitudinal Piezoelectric Latching Relay”, filed May 2, 2002 and identified by Ser. No. 10/137,692; 
     Application 10011344-1, “Method and Structure for a Slug Pusher-Mode Piezoelectrically Actuated Liquid Metal Switch”, and having the same filing date as the present application; 
     Application 10011345-1, “Method and Structure for a Slug Assisted Longitudinal Piezoelectrically Actuated Liquid Metal Optical Switch”, and having the same filing date as the present application; 
     Application 10011397-1, “Method and Structure for a Slug Assisted Pusher-Mode Piezoelectrically Actuated Liquid Metal Optical Switch”, and having the same filing date as the present application; 
     Application 10011398-1, “Polymeric Liquid Metal Switch”, and having the same filing date as the present application; 
     Application 10011410-1, “Polymeric Liquid Metal Optical Switch”, and having the same filing date as the present application; 
     Application 10011436-1, “Longitudinal Electromagnetic Latching Optical Relay”, and having the same filing date as the present application; 
     Application 10011437-1, “Longitudinal Electromagnetic Latching Relay”, and having the same filing date as the present application; 
     Application 10011459-1, “Damped Longitudinal Mode Latching Relay”, and having the same filing date as the present application; 
     Application 10020013-1, titled “Switch and Method for Producing the Same”, filed Dec. 12, 2002 and identified by Ser. No. 10/317,963; 
     Application 10020027-1, titled “Piezoelectric Optical Relay”, filed Mar. 28, 2002 and identified by Ser. No. 10/109,309; 
     Application 10020071-1, titled “Electrically Isolated Liquid Metal Micro-Switches for Integrally Shielded Microcircuits”, filed Oct. 8, 2002 and identified by Ser. No. 10/266,872; 
     Application 10020073-1, titled “Piezoelectric Optical Demultiplexing Switch”, filed Apr. 10, 2002 and identified by Ser. No. 10/119,503; 
     Application 10020162-1, titled “Volume Adjustment Apparatus and Method for Use”, filed Dec. 12, 2002 and identified by Ser. No. 10/317,293; 
     Application 10020241-1, “Method and Apparatus for Maintaining a Liquid Metal Switch in a Ready-to-Switch Condition”, and having the same filing date as the present application; 
     Application 10020242-1, titled “A Longitudinal Mode Solid Slug Optical Latching Relay”, and having the same filing date as the present application; 
     Application 10020473-1, titled “Reflecting Wedge Optical Wavelength Multiplexer/Demultiplexer”, and having the same filing date as the present application; 
     Application 10020540-1, “Method and Structure for a Solid Slug Caterpillar Piezoelectric Relay”, and having the same filing date as the present application; 
     Application 10020541-1, titled “Method and Structure for a Solid Slug Caterpillar Piezoelectric Optical Relay”, and having the same filing date as the present application; 
     Application 10030438-1, “Inserting-finger Liquid Metal Relay”, and having the same filing date as the present application; 
     Application 10030440-1, “Wetting Finger Liquid Metal Latching Relay”, and having the same filing date as the present application; 
     Application 10030521-1, “Pressure Actuated Optical Latching Relay”, and having the same filing date as the present application; 
     Application 10030522-1, “Pressure Actuated Solid Slug Optical Latching Relay”, and having the same filing date as the present application; and 
     Application 10030546-1, “Method and Structure for a Slug Caterpillar Piezoelectric Reflective Optical Relay”, and having the same filing date as the present application. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to the field of optical switching relays, and in particular to a piezoelectrically actuated optical relay that latches by means of liquid surface tension. 
     BACKGROUND 
     Communications systems using optical signals require the use of optical switches and routers. An early approach to optical switching was to convert the optical signal to an electrical signal, use an electrical switch or router and then convert back to an optical signal. More recently, optical relays have been used in which an electrical control signal is used to control the switching or routing of an optical signal. Optical relays typically switch optical signals by using movable solid mirrors or by using the creation of vapor bubbles to alter the index of refraction inside a cavity. The moveable mirrors may use electrostatic latching mechanisms, whereas bubble switches do not latch. Piezoelectric latching relays either use residual charges in the piezoelectric material to latch, or actuate switch contacts containing a latching mechanism. 
     Liquid metal is also used in electrical relays. A liquid metal droplet can be moved by a variety of techniques, including electrostatic forces, variable geometry due to thermal expansion/contraction, and pressure gradients. When the dimension of interest shrinks, the surface tension of the liquid metal becomes the dominant force over other forces, such as body forces (inertia). Consequently, some micro-electromechanical (MEM) systems utilize liquid metal switching. 
     SUMMARY 
     The present invention relates to an optical switch in which a solid slug is moved within a channel and used to block or unblock an optical path passing through the channel. The solid slug is moved by piezoelectric elements. In accordance with certain embodiments, the slug is wetted by a liquid, such as liquid metal, that also adheres to wettable metal contact pads within the channel to provide a latching mechanism. Motion of the solid slug may be damped to prevent damage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features of the invention believed to be novel are set forth with particularity in the appended claims. The invention itself however, both as to organization and method of operation, together with objects and advantages thereof, may be best understood by reference to the following detailed description of the invention, which describes certain exemplary embodiments of the invention, taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is an end view of an optical relay in accordance with certain embodiments of the present invention. 
         FIG. 2  is a side view of an optical relay in accordance with certain embodiments of the present invention. 
         FIG. 3  is a sectional view through an optical relay in accordance with certain embodiments of the present invention. 
         FIG. 4  is a further sectional view through an optical relay in accordance with certain embodiments of the present invention. 
         FIG. 5  is a top view of an optical relay with the cap layer and vent layer removed in accordance with certain embodiments of the present invention. 
         FIG. 6  is a further sectional view through an optical relay in accordance with certain embodiments of the present invention. 
         FIG. 7  is a view of the underside of a cap layer of an optical relay in accordance with certain embodiments of the present invention. 
         FIG. 8  is a view of a vent layer of an optical relay in accordance with certain embodiments of the present invention. 
         FIG. 9  is a view of a circuit substrate of an optical relay in accordance with certain embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     While this invention is susceptible of embodiment in many different forms, there is shown in the drawings and will herein be described in detail one or more specific embodiments, with the understanding that the present disclosure is to be considered as exemplary of the principles of the invention and not intended to limit the invention to the specific embodiments shown and described. In the description below, like reference numerals are used to describe the same, similar or corresponding parts in the several views of the drawings. 
     The present invention relates to a piezoelectrically actuated optical relay that switches and latches by means of a wettable magnetic solid slug and a liquid. 
     In accordance with certain embodiments of the present invention, the relay uses piezoelectric elements to displace a solid magnetic slug. The slug blocks or unblocks an optical path, allowing the switching of optical signals. The solid slug is held in place by surface tension in a liquid, preferably a liquid metal such as mercury, that wets between the solid slug and at least one fixed contact pad on the relay housing. Magnetorestrictive actuators, such as Terfenol-D, that deform in the presence of a magnetic field may be used as an alternative to piezoelectric actuators. In the sequel, piezoelectric actuators and magnetorestrictive actuators will be collectively referred to as “piezoelectric actuators”. 
     In one embodiment, micro-machining techniques are used to manufacture the relay. An end view of an optical relay  100  is shown in FIG.  1 . In this embodiment, the body of the relay is made up of four layers and is amenable to manufacture by micro-machining. The lowest layer is a circuit substrate  108  that will be described in more detail below with reference to FIG.  9 . The next layer is a switching layer  106 . The switching of the optical signal occurs in a switching channel contained in this layer. The next layer is a vent layer  104  that contains pressure relief vents (vias) for relieving pressure variations in the switching channel. The cap layer  102  provides a pressure relief passage or channel that connects the pressure relief vents. In operation, an optical signal enters the relay through an optical fiber or waveguide  110  and, if not blocked in the relay, exits through optical fiber or waveguide  112 . The section  3 — 3  is shown in FIG.  3 . 
       FIG. 2  is a side view of the optical relay shown in FIG.  1 . Optical fibers  110  and  124  are positioned in alignment notches,  122  and  126  respectively, in the switching layer  106 . Each fiber is optically aligned with a corresponding fiber on the opposite side of the relay (as shown in FIG.  1 ). The optical fibers may be held in place by adhesive. 
     A view of a longitudinal, vertical cross-section through section  3 — 3  of the relay in  FIG. 1  is shown in  FIG. 3. A  switching channel  130  is formed in the switching layer  106 . A solid slug  132  is moveably positioned within the switching channel. A pressure relief channel  134  is coupled to the ends of the switching channel  130  by vent holes  135  and  136 . The pressure relief channel  134  allows pressure variations in the switching channel, due to movement of the solid slug  132 , to be equalized by allowing fluid to flow from one end of the switching channel to the other through the vent holes. Three contact pads  137 ,  138  and  140  are fixed to the circuit substrate  108  within the switching channel. These contact pads may be formed on the circuit substrate  108  by deposition or other micro-machining techniques. The contact pads are wettable by a liquid, such as a liquid metal. When the solid slug  132  is positioned as shown in  FIG. 3 , a liquid  142  wets the surface of the solid slug and the surface of the contact pads  137  and  138 . Surface tension holds the solid slug in this position. Additional liquid  144  wets the contact pad  140 . 
     Piezoelectric elements  50  and  54  are attached to the substrate of the switching layer  106 . Electrical connections (not shown) to the piezoelectric elements either pass along the top of the circuit substrate  108  to the edges of the relay or pass through holes or vias in the circuit substrate and connect to connection pads on the bottom of the relay. 
     When the solid slug occupies the position shown in  FIG. 3 , the optical path between waveguides  110  and  112  (in  FIG. 1 ) is open, while the optical path through waveguide  124  (in  FIG. 2 ) is blocked by the slug and the liquid. In order to change the switch-state of the relay, the piezoelectric element  50  is energized by applying an electric potential across the element. This causes the piezoelectric element  50  to expand and apply an impulsive force to the end of the solid slug  132 . The motion of the piezoelectric element is rapid and causes the imparted momentum of the solid slug to overcome the surface tension forces (from the liquid) that would hold it in contact with the contact pad or pads near the actuating piezoelectric element. The surface tension latch is broken and the solid slug moves to the left end of the switching channel, as shown in FIG.  4 . The solid slug  132  is then in wetted contact with the contact pads  138  and  140  and is latched in its new position. In this new position, the optical path between waveguides  110  and  112  (in  FIG. 1 ) is blocked by the slug and the liquid, while the optical path through waveguide  124  (in  FIG. 2 ) is open. 
     In order to prevent the brittle piezoelectric elements from breaking when the switching slug arrives at its new locations during switching, energy dissipative elements are used to lessen the impact forces. In a first embodiment of the invention, shown in FIG.  3  and  FIG. 4 , compliant, energy absorptive faces  52  and  56  are used on the piezoelectric elements  50  and  54 . Materials such as “Sorbothane” are effective at absorbing shock and vibration. In a second embodiment, energy absorptive faces  52  and  56  are absent and the switching channel is narrowed near the piezoelectric actuators so there is little clearance between the channel walls and the slug between the rest position of the piezoelectric actuator face and the vent opening. When the slug arrives, liquid metal is trapped between the slug and the actuator face and is squeezed through the opening surrounding the slug, thus providing damping. Various passage designs may be used to better control the flow of liquid metal and damping. Referring to  FIG. 3 , when the actuator  50  pushes the slug  132  to actuate it, the actuator face pushes the slug to the level of the vent opening  136 , relieving any vacuum between the actuator face and the end of the slug that would tend to hold the slug back. One advantage of the second embodiment is that there is minimal damping when the slug departs. 
     The switch-state may be changed back from the switch state shown in  FIG. 4  to the original state shown in  FIG. 3 , by energizing the piezoelectric element  54  to move the solid slug. Once the solid slug has returned to its original position it is again latched into position by surface tension in the liquid. 
       FIG. 5  is a top view of the relay with the solid slug, the cap layer  102  and the vent layer  104  removed. The optical waveguides  110 ,  112 ,  124  and  152  are glued into notches  122 ,  154 ,  126  and  156  respectively in the switching layer  106 . Waveguide  110  is optically aligned with waveguide  112  so that light may couple between the waveguides through the switching channel  130 . Similarly, waveguide  124  is optically aligned with waveguide  152  so that light may couple between the waveguides. Contact pads  140 ,  137  and  138  lie at the bottom of the switching channel  130 , and are deposited on top of the circuit substrate. Piezoelectric actuators  50  and  54  are attached to the switching layer  106  within the switching channel  130 . When the solid slug bridges the gap between the contact pads  140  and  138 , the optical path between the waveguides  110  and  112  is blocked. When the solid slug bridges the gap between the contact pads  137  and  138 , the optical path between the waveguides  124  and  152  is blocked. 
       FIG. 6  is a sectional view through the section  6 — 6  shown in FIG.  2 . Referring to  FIG. 6 , the optical waveguides  110  and  112  are positioned in glue-filled notches  122  and  154  respectively in the switching layer  106 . Waveguide  110  is optically aligned with waveguide  112  so that light may couple between the waveguides through the switching channel  130 . Contact pad  140  lies at the bottom of the switching channel  130 . In this embodiment, the pressure relief channel  134  is formed in the cap layer  102 . Alternatively, it could be formed in vent layer  104 . 
       FIG. 7  is a view of the underside of the cap layer  102  showing the pressure relief channel  134 . 
       FIG. 8  is a top view of the vent layer  104 . Vent holes  135  and  136  pass through the layer, coupling the vent passage to the switching channel in the layer below and to the pressure relief channel in the cap layer above. 
       FIG. 9  is a top view of the circuit substrate  108 . Three contact pads  137 ,  138  and  140  are formed on top of the substrate. The surfaces of the contact pads are wettable by the liquid in the switching channel. The contact pads are preferably constructed of a wettable metal. In an exemplary embodiment, electrical circuitry to allow connection to the piezoelectric actuator is formed on the circuit substrate. 
     The optical relay of the present invention can be made using micro-machining techniques for small size. The switching time is short, yielding switching rates of several kHz or higher. Heat generation is also low, since the only heat generators are the piezoelectric element and the passage of control currents through the conductors to the piezoelectric elements. 
     While the invention has been described in conjunction with specific embodiments, it is evident that many alternatives, modifications, permutations and variations will become apparent to those of ordinary skill in the art in light of the foregoing description. Accordingly, it is intended that the present invention embrace all such alternatives, modifications and variations as fall within the scope of the appended claims.