Abstract:
An optical relay is disclosed in which a liquid metal droplet is moved within a switching channel formed in relay housing. An optical path passing through the switching channel is blocked or unblocked by motion of the liquid metal droplet that coalesces with one of two additional liquid metal droplets. Motion of the liquid metal droplets is controlled by heaters that control the pressure of an actuation gas in the switching channel. The liquid metal droplets are held in place by surface tension acting on wettable contact pads within the switching channel. The surface tension of the liquid provides a latching mechanism for the relay. The pressure of the actuation gas is increased by direct heating of the gas or by heating a phase-change liquid to cause it to evaporate.

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”, having the same filing date as the present application and identified by Ser. No. 10/413,068; 
   Application 10010531-1, “High Frequency Bending Mode Latching Relay”, having the same filing date as the present application and identified by Ser. No. 10/412,912; 
   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”, having the same filing date as the present application and identified by Ser. No. 10/412,991; 
   Application 10010572-1, “Liquid Metal, Latching Relay with Face Contact”, having the same filing date as the present application and identified by Ser. No. 10/413,195; 
   Application 10010573-1, “Insertion Type Liquid Metal Latching Relay”, and having the same filing date as the present application and identified by Ser. No. 10/412,824; 
   Application 10010617-1, “High-frequency, Liquid Metal, Latching Relay Array”, having the same filing date as the present application and identified by Ser. No. 10/413,278; 
   Application 10010618-1, “Insertion Type Liquid Metal Latching Relay Array”, having the same filing date as the present application and identified by Ser. No. 10/412,880; 
   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”, having the same filing date as the present application and identified by Ser. No. 10/413,314; 
   Application 10010644-1, “Bending Mode Liquid Metal Switch”, having the same filing date as the present application and identified by Ser. No. 10/413,328; 
   Application 10010656-1, titled “A Longitudinal Mode Optical Latching Relay”, having the same filing date as the present application and identified by Ser. No. 10/413,215; 
   Application 10010663-1, “Method and Structure for a Pusher-Mode Piezoelectrically Actuated Liquid Metal Switch”, having the same filing date as the present application and identified by Ser. No. 10/413,098; 
   Application 10010664-1, “Method and Structure for a Pusher-Mode Piezoelectrically Actuated Liquid Metal Optical Switch”, having the same filing date as the present application and identified by Ser. No. 104/412,895; 
   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”, having the same filing date as the present application and identified by Ser. No. 10/413,237; 
   Application 10011056-1, “Latching Relay with Switch Bar”, having the same filing date as the present application and identified by Ser. No. 10/413,099; 
   Application 10011064-1, “High Frequency Push-mode Latching Relay”, having the same filing date as the present application and identified by Ser. No. 10/413,100; 
   Application 10011065-1, “Push-mode Latching Relay”, having the same filing date as the present application and identified by Ser. No. 10/413,067; 
   Application 10011121-1, “Closed Loop Piezoelectric Pump”, having the same filing date as the present application and identified by Ser. No. 10/412,857; 
   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”, having the same filing date as the present application and identified by Ser. No. 10/412,869; 
   Application 10011345-1, “Method and Structure for a Slug Assisted Longitudinal Piezoelectrically Actuated Liquid Metal Optical Switch”, having the same filing date as the present application and identified by Ser. No. 10/412,916; 
   Application 10011397-1, “Method and Structure for a Slug Assisted Pusher-Mode Piezoelectrically Actuated Liquid Metal Optical Switch”, having the same filing date as the present application and identified by Ser. No. 10/413,070; 
   Application 10011398-1, “Polymeric Liquid Metal Switch”, having the same filing date as the present application and identified by Ser. No. 10/413,094; 
   Application 10011410-1, “Polymeric Liquid Metal Optical Switch”, having the same filing date as the present application and identified by Ser. No. 10/412,859; 
   Application 10011436-1, “Longitudinal Electromagnetic Latching Optical Relay”, having the same filing date as the present application and identified by Ser. No. 10/412,868; 
   Application 10011437-1, “Longitudinal Electromagnetic Latching Relay”, having the same filing date as the present application and identified by Ser. No. 10/412,329; 
   Application 10011458-1, “Damped Longitudinal Mode Optical Latching Relay”, having the same filing date as the present application and identified by Ser. No. 10/412,894; 
   Application 10011459-1, “Damped Longitudinal Mode Latching Relay”, having the same filing date as the present application and identified by Ser. No. 10/412,914; 
   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 10020231-1, titled “Ceramic Channel Plate for a Switch”, filed Dec. 12, 2000 and identified by Ser. No. 10/317,960; 
   Application 10020241-1, “Method and Apparatus for Maintaining a Liquid Metal Switch in a Ready-to-Switch Condition”, having the same filing date as the present application and identified by Ser. No. 10/413,002; 
   Application 10020242-1, titled “A Longitudinal Mode Solid Slug Optical Latching Relay”, having the same filing date as the present application and identified by Ser. No. 10/412,858; 
   Application 10020473-1, titled “Reflecting Wedge Optical Wavelength Multiplexer/Demultiplexer”, having the same filing date as the present application and identified by Ser. No. 10/413,270; 
   Application 10020540-1, “Method and Structure for a Solid Slug Caterpillar Piezoelectric Relay”, having the same filing date as the present application and identified by Ser. No. 10/413,088; 
   Application 10020541-1, titled “Method and Structure for a Solid Slug Caterpillar Piezoelectric Optical Relay”, having the same filing date as the present application and identified by Ser. No. 10/413,196; 
   Application 10020698-1, “Laser Cut Channel Plate for a Switch”, filed Dec. 12, 2002 and identified by Ser. No. 10/317,932; 
   Application 10030438-1, “Inserting-finger Liquid Metal Relay”, having the same filing date as the present application and identified by Ser. No. 10/413,187; 
   Application 10030440-1, “Wetting Finger Liquid Metal Latching Relay”, having the same filing date as the present application and identified by Ser. No. 10/413,058; 
   Application 10030521-1, “Pressure Actuated Optical Latching Relay”, having the same filing date as the present application and identified by Ser. No. 10/412,874; 
   Application 10030522-1, “Pressure Actuated Solid Slug Optical Latching Relay”, having the same filing date as the present application and identified by Ser. No. 10/413,162; and 
   Application 10030546-1, “Method and Structure for a Slug Caterpillar Piezoelectric Reflective Optical Relay”, having the same filing date as the present application and identified by Ser. No. 10/412,910. 

   FIELD OF THE INVENTION 
   The invention relates to the field of optical switching relays, and in particular to an optical relay that is actuated by gas pressurization and latches by means of liquid surface tension. 
   BACKGROUND OF THE INVENTION 
   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 dominant force over other forces, such as body forces (inertia). Consequently, some micro-electro-mechanical (MEM) systems utilize liquid metal switching. 
   SUMMARY OF THE INVENTION 
   The present invention relates to an optical switch in which a liquid metal droplet is moved within a channel and used to block or unblock an optical path passing through the channel. The liquid metal droplet is moved by the pressurization of gas in a heater chamber that results in a pressure change in the channel. The liquid metal droplet adheres to wettable metal contact pads within the channel to provide a latching mechanism. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The novel features believed characteristic of the invention are set forth in the claims. The invention itself, however, as well as the preferred mode of use, and further objects and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawing(s), wherein: 
       FIG. 1  is an end view of an optical relay of the present invention. 
       FIG. 2  is a sectional view of optical relay of the present invention. 
       FIG. 3  is a top view of an optical relay of the present invention with the top cap layer removed. 
       FIG. 4  is a further top view of an optical relay of the present invention with the top cap layer removed. 
       FIG. 5  is top view of a chamber layer of an optical relay of the present invention. 
       FIG. 6  is sectional view through a chamber layer of an optical relay of the present invention. 
       FIG. 7  is bottom view of a circuit layer of an optical relay of the present invention. 
       FIG. 8  is sectional view through a circuit layer of an optical relay of the present invention. 
       FIG. 9  is top view of a switching layer of an optical relay of the present invention. 
       FIG. 10  is side view of a switching layer of an optical relay of the present invention. 
       FIG. 11  is bottom view of a top cap layer of an optical relay 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 optical relay that is actuated by gas pressurization and latches by means of a liquid metal droplet moving within a switching channel. In the preferred embodiment, the relay uses heating element to induce pressure changes in an actuation gas that in turn displaces the liquid metal. The liquid metal blocks or unblocks an optical path, allowing the switching of optical signals. The liquid metal, which may be mercury or an alloy that contains gallium, wets at least one fixed contact pad on the relay housing and is held in place by surface tension. 
   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 six layers and is amenable to manufacture by micro-machining. The lowest layer is a bottom cap layer  102 . The next layer is a chamber layer  104  that incorporates heater chambers and, optionally, a phase-change liquid. The next layer is a circuit layer  106  containing ducts (vias) that couple the heater chambers to the switching channel. The circuit layer also supports heater resistors and the associated electrical circuitry. Switching of the optical signal occurs in the switching channel contained in the switching layer  108 . 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 final layer is a top cap layer  114 . 
     FIG. 2  is a cross-sectional of the relay in FIG.  1 . The lowest layer is a bottom cap layer  102 . The next layer is the chamber layer  104  that incorporates the heater chamber  116 , the heater resistor  122  and, optionally, a phase-change liquid  118 . In operation, the heater resistor  122  increases the pressure in an actuation gas contained on the heater chamber  116 . In a first embodiment of the invention, the pressure increase is created by direct heating of the gas in the chamber. In a second embodiment, the pressure increase is created by heating a liquid  118  so that it changes from a liquid phase to a gas phase. The volume increase associated with the phase change produces a pressure increase in the actuation gas. One advantage of this approach is that heat is more efficiently passed from the heater resistor to a liquid than from the heater resistor to a gas. In addition, the phase transition can be very rapid and results in a large pressure change. This leads to more rapid switching and reduces energy losses into the substrate. The phase change is reversible, so that the vapor condenses on the heater resistor as it cools. The phase-change liquid may be an inert organic liquid such as a low viscosity 3M Flourinert. Alternatively, the phase-change liquid may be a liquid metal. A restrictive pressure relief passage between the heater chambers may be included to allow the pressure to equalize slowly across the changes to prevent the liquid metal in the switching channel from being drawn back as the heater cools. The next layer is the circuit layer  106  containing a duct  126  that couples the heater chamber  116  to the switching channel  128  (contained in the switching layer  108 ). 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 optical waveguide  110  is embedded in a notch  130  in the switching layer  108 . The optical waveguide  112  is embedded in a notch  132  in the switching layer  108 . Wettable contact pads  134  are fixed to the inside of the switching channel  128 . The contact pads may be made of seal belt metal. Each pad made be made in four pieces: a lower pad attached to the top of the circuit layer, two side pads attached to the sides of the switching channel in the switching layer, and a top pad attached to the lower surface of the top cap layer. The liquid metal used for switching is held in contact with these pads by surface tension. The final layer is a top cap layer  114 , which provides a cap for the switching channel. 
   A view of the optical relay with the top cap layer removed is shown in FIG.  3 . The switching layer  108  is positioned above the circuit layer  106 . An optical waveguide  110 , embedded in a notch  130  in the switching layer  108 , is optically aligned with the optical waveguide  112  (embedded in a notch  132 ). For light to couple between the waveguides  110  and  112  it must pass through the transparent actuation gas in the switching channel  128 . Optical waveguide  140 , embedded in a notch  142  in the switching layer  108 , is optically aligned with the optical waveguide  144  (embedded in a notch  146 ). A central droplet of liquid metal  148  is positioned within the switching channel  128  and is held in wetted contact with the contact pad  154 . In the preferred embodiment, the liquid metal is mercury or an alloy containing gallium. The central liquid metal droplet  148  may be moved to coalesce with one of the further liquid metal droplets  150  and  152 . The liquid metal droplets  150  and  154  are in wetted contact with contact pads  134  and  156 , respectively. The total volume of liquid metal is chosen so that only two volumes may coalesce at one time. The contact pads may be made of seal belt metal, for example. Each belt is made up of four elements, two attached to the switching layer  108 , one attached to the top of circuit layer  106  and one attached to the underside of the top cap layer  114 . Surface tension in the liquid metal droplets resists motion of the liquid. When the liquid metal droplets  148  and  152  are coalesced, as shown in  FIG. 3 , there is no gap between the droplets through which light can pass, so the optical path between the waveguides  140  and  144  is blocked. However, light may pass through the gap between liquid metal droplets  148  and  150 , so the optical path between waveguides  110  and  112  is open. The section  2 — 2  is shown in  FIG. 2 , and is described above. 
   Motion of the liquid droplets is controlled by a transparent, inert, electrically non-conducting actuation gas that fills the interior of the relay surrounding the liquid metal droplets. The actuation gas moves into or out of the switching channel  128  through vias or ducts positioned between the contact pads. The central droplet of liquid metal  148  can be separated from droplet  152  by increasing the pressure of the actuation gas on the left side of the central contact pads ( 154 ,  148 ). The resulting pressure difference across the central liquid metal droplet  148  moves it to the right, as shown in  FIG. 4 , where it coalesces with the droplet  150 . When the pressure in the actuation gas is equalized, the central droplet  148  remains coalesced with the droplet  150  because of surface tension in the liquid metal. Surface tension also holds the coalesced droplets to the contact pads  134  and  154 . The optical path between waveguides  140  and  144  is now opened, whereas the optical path between waveguides  110  and  112  is blocked by the liquid metal. 
     FIG. 5  is a top view of the chamber layer  104  of the relay. Two heater chambers  116  and  160  are formed in the layer. The chambers are completed by the bottom cap layer below and by the circuit layer above. Optionally, a pressure relief duct  120  couples the heater chambers and allows for slow pressure equalization between the chambers. Gas flow through the duct is restricted so as not to impair switching. 
     FIG. 6  is a sectional view through the section  6 — 6  of the chamber layer  104  shown in FIG.  5 . The heater chamber  116  is formed as a cavity in the layer. 
     FIG. 7  is a bottom view of the circuit layer  106  of the relay. Vias or ducts  126  and  158  allow passage of actuation gas from the heater chambers to pass through the circuit layer to the switching channel. The lowermost portions of the wettable contact pads  134 ,  154  and  156  (depicted by broken lines) are formed on or attached to the upper surface of the layer and are combined with other portions of the pads in the switching channel and on the top cap layer. Heater resistors  122  and  162  are formed on the circuit layer. After assembly, the heater resistors are positioned in the heater chambers. Electrical contact pads  124  facilitate connection of control signals to the heater resistors  122 . Electrical traces (not shown) formed on the circuit layer connect the electrical contact pads  124  to the heater resistors. 
     FIG. 8  is a sectional view through the section  8 — 8  of the circuit layer  106  shown in FIG.  7 . The gas duct  158  passes through the layer. The wettable contact pad  154  is attached to the top surface of the layer  106 . The heater resistor  162  and the electrical contact pad  124  are attached to the underside of the layer. Optionally, a phase-change liquid  164  wets the surface of the heater resistor  162 . This liquid may be added after or during assembly of the relay. 
     FIG. 9  is a top view of the switching layer  108  of the relay. Optical waveguide  110 , embedded in a notch  130  in the switching layer  108 , is optically aligned with the optical waveguide  112  (embedded in a notch  132 ). Optical waveguide  140 , embedded in a notch  142  in the switching layer  108 , is optically aligned with the optical waveguide  144  (embedded in a notch  146 ). Portions of the wettable contact pads  134 ,  154  and  156  are fixed to the inside of the switching channel  128 . 
   A side view of the switching layer  108  is shown in FIG.  10 . The optical waveguides  110  and  140  are imbedded in triangular notches  130  and  142  in the top surface of the layer. The use of notches allows for accurate optical alignment of the waveguides during assembly of the relay. 
     FIG. 11  is a bottom view of the top cap layer  114  of the relay. The topmost portions of the wettable contact pads  134 ,  154  and  156  are formed or attached to the lower surface of the layer and combined with other portions in the switching channel and the circuit layer. 
   The optical relay of the present invention can be made using micro-machining techniques for small size. 
   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.