Abstract:
An optical switch including a bistable component, a reflective component, the reflective component being operatively connected to the bistable component, a first electrothermal bent beam actuator, a first contacting component operatively connected to the first electrothermal bent beam actuator component, the first electrothermal bent beam actuator component and the first contacting component disposed such as to enable advancing the bistable component the reflective component from a first stable configuration to a second stable configuration, a second electrothermal bent beam actuator component and a second contacting component operatively connected to the second electrothermal bent beam actuator component, the second electrothermal bent beam actuator component and the second contacting component disposed such as to enable advancing the bistable component and the reflective component from the second stable configuration to the first stable configuration.

Description:
BACKGROUND 
     These teachings relate generally to MEMS optical switches. 
     Optical switches are devices that route optical signals along selected fibers of an optical network. Such switches constitute the fundamental building blocks of modern optical networks. Prior art optical switches are primarily based on mechanisms that perform mechanical movements, change waveguide coupling ratios, and perform polarization rotations. Mechanical relay based optical switches has large size. Considerable interest has been shown in MEMS technology for its small size. Among them, MEMS electrostatic rotating mirror based devices are one of most common approaches. However, their need for a high electrical field to generate sufficient actuation force results in the requirement of costly hermetic packaging. Furthermore, they are non-latched and switch states are lost when external electric power is lost. A bistable mechanism using electro-thermal actuation is also used for optical switches. However, those devices use an in-plane actuation for a vertical etched mirror, leading to costly fabrication and small depth mirror size. 
     Therefore, there is a need for an improved MEMS switch design that is small in size, ultra-stable, latching, low cost and easy to manufacture, scalable to multiple output ports. 
     BRIEF SUMMARY 
     One embodiment of the optical switch of these teaching includes a bistable component comprising one or more first beams and one or more second beams, a reflective component; the one or more first beams extending from a first support to a location on the reflective component, the one or more second beams extending from a second support to the location on the reflective component, the reflective component being operatively connected to the bistable component, a first electrothermal bent beam actuator component extending from a first electrode to a second electrode, a first contacting component operatively connected to the first electrothermal bent beam actuator component, the first electrothermal bent beam actuator component and the first contacting component disposed such as to enable advancing the bistable component the reflective component from a first stable configuration to a second stable configuration, a second electrothermal bent beam actuator component extending from a third electrode to a fourth electrode and a second contacting component operatively connected to the second electrothermal bent beam actuator component, the second electrothermal bent beam actuator component and the second contacting component disposed such as to enable advancing the bistable component and the reflective component from the second stable configuration to the first stable configuration. 
     Values other embodiments of the optical switch of these teachings are also disclosed. 
     Embodiments of the method of operation of the optical switch of these teachings and embodiments of methods for fabricating the optical switch of these teachings are also disclosed. 
     For a better understanding of the present teachings, together with other and further objects thereof, reference is made to the accompanying drawings and detailed description and its scope will be pointed out in the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic representation of one embodiment of the optical switch of these teachings; 
         FIGS. 1   a  and  1   b  are schematic representations of another embodiment of the optical switch of these teachings. 
         FIG. 2  is a graphical representation of displacement-force relationship in a bistable component in one embodiment of the optical switch of these teachings; 
         FIGS. 2   a  and  2   b  show an optical system utilizing embodiment of the optical switch of these teachings; 
         FIG. 3  is a schematic representation of yet another embodiment of the optical switch of these teachings; 
         FIGS. 4   a  and  4   b  are schematic representations of embodiment of one component of the optical switch of these teachings; and 
         FIGS. 5   a - 5   e  are graphic illustrations of an embodiment of a process for manufacturing devices of these teachings. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description is of the best currently contemplated modes of carrying out these teachings. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of these teachings, since the scope of these teachings is best defined by the appended claims. 
     In one embodiment, the present teachings overcome the above problems by providing an optical switch that uses one or more elements of micro-electro-mechanical system (MEMS) devices aligned with one or more fiber collimators to steer light beams from one or more input ports to one or more output ports. In that embodiment, a MEMS chip has an in-plane optical reflective component (such as, but not limited to, a mirror) suspended on a self-latching bistable mechanism, and two electrothermal actuator components. The actuators drive the bistable mechanism from its first stable position to its second stable position and from its second stable position to its first position. Thus, the suspended mirror directs the light beam in a plane that is perpendicular to the plane of the MEMS device to different output ports at different stable positions through either transmission or reflection of the light beam. 
     In one embodiment of the present teachings, the above and the optical switch includes a MEMS bistable mirror configuration comprising a frame having a planar surface, two MEMS actuators that drive the reflective mirror in the planar surface to its stable positions to steer light beam transmitting from sources of electromagnetic radiation such as, but not limited to, optical fibers. 
     In one embodiment, the reflective mirror surface is suspended by multiple identical paralleled bistable mechanisms, which constraint the motion of mirror in the plane of the mirror surface. 
     In one embodiment of the bistable mechanism formed by curved beam segments arranged symmetrical to the suspended mirror and anchored at an outer frame. 
     In one embodiment, each actuator component is formed by multiple electrothermal parallel V-beams with optimal displacement output. 
     In one embodiment, each set of actuators has one center or multiple contact surfaces along the bistable mechanism to push the mirror to different stable locations. When multiple contact surfaces are used, different contact surfaces may have different time sequence to contact. This can decrease the mechanical wear on each contact surface to increase contact cycle life. The off-center actuations can also increase travel distance of the mirror. 
     In one embodiment, the one or more contact surfaces have a flexible surface and a hard surface to form a self-contact when contact force applied. This can decrease contact force on each surface therefore increase contact life time. When different contact surfaces have different time sequences, the contact duration can be further enhanced. 
     In one embodiment, the mirror position can be detected through resistance change of the components of the bistable mechanism (silicon wire in one embodiment) due to a change in the strain of the bistable mechanism. At this first stable position, the bistable mechanism has substantially no strain while at the second stable position, strain is developed. 
     In one embodiment, the mirror position can be detected through capacitance change due to gaps between the contact surfaces changes at each stable position. 
     In one embodiment, the MEMS fabrication steps are simplified by using only a few steps with a minimum number of masks using silicon on insulator (SOI) wafers. 
       FIG. 1  illustrates a schematic view of an embodiment of a MEMS bistable optical switch chip. The MEMS bistable optical switch chip  1  includes a substrate  49  (embodiments in which the bistable optical switch chip is lifted from the substrate are also within the scope of these teachings) having a planar surface frame  16 , a reflective mirror  2  arranged on the planar surface  16 , a bistable mechanism  3  formed by two curved beams  4  and  5  and symmetrical to the center of the mirror  2 ; two electrothermal actuators  6  and  11 . The bistable mechanism  3  suspends the mirror  2  on the frame  16 . Multiple identical, paralleled bistable mechanisms  3  are used to restrict the motion of the mirror in the plane  16  along the symmetric axis of the bistable mechanism or Y axis. Typical displacement-force relationship of the bistable mechanism is shown in  FIG. 2 . The two stable positions are as labeled in the plot. Each stable position has a maximum break force as labeled in  FIG. 2 . 
     A number of possible embodiments of the bistable mechanism are within the scope of these teachings. Embodiments such as, but not limited to, those disclosed in U.S. Pat. No. 6,911,891, issued to Qui et al., which is incorporated by reference herein in its entirety for all purposes, and the embodiments disclosed in Jin Qiu; Lang, J. H.; Slocum, A. H., A curved-beam bistable mechanism. Journal of Micro-electromechanical Systems, April 2004, Vol. 13, Issue 2, pp. 137-146, Casals-Terre, J., Shkel, A., Dynamic Analysis Of A Snap-Action Micromechanism, 2005 IEEE Sensors, 2005, and Youngseok Oh, Synthesis of Multistable Equilibrium Compliant Mechanisms, Ph. D. Thesis, Univ. of Michigan, 2008, all of which are incorporated by reference herein in their entirety for all purposes, are within the scope of these teachings. 
     Electrothermal actuator  6  is used to switch the bistable mechanism from first stable position to second stable position, or the mirror  2  from the first stable position to the second stable position. Electrothermal actuator  11  is used to switch the bistable mechanism from second stable position to first stable position, or the mirror  2  from the second stable position to the first stable position. Actuator  6  has a multiple identical paralleled V-beam wire structure  54 , force and displacement translation beam  7 , and contact surfaces  8 ,  9  and  10  (the force and displacement translation beam  7 , and contact surfaces  8 ,  9  and  10  are one embodiment of a first contacting component and the force and displacement translation beam  12 , and contact surfaces  13 ,  14  and  15  are one embodiment of a second contacting component) to interact with bistable mechanism  3 . Note a single contact surface  9  can be used for actuation and is covered by this patent. The actuator  6  has two electrodes  37  and  38  are on the frame surface  16 . When a voltage different applied on electrodes, a driving electric current will apply to the wires (beams)  54  of the actuator  6 , the wires  54  and contact surfaces  8 ,  9  and  10  will move along Y-axis to close to the bistable mechanism  3  and mirror  2 . The contact forces at those contact surfaces will push the bistable mechanism  3  and mirror  2  to its second stable position. The multiple surfaces  8 ,  9  and  10  have different time sequence to engage with the bistable mechanism  3  and mirror  2  with  9  first and then  8  and  10 . This different time contact sequence can greatly reduce mechanical wear at each surface therefore increase switch cycle life. Off-center contact surface  8  and  10  can also increase the travel distance of the mirror  2 , and, therefore, increase mirror size. 
     In the embodiment shown in  FIG. 1 , the actuator  11  has multiple V-beam (also referred to as “bent beam”) wire (beam) structure  53 . When a current is applied the wires  53  through electrodes  41  and  42  which are on the surface  16 , the center of the wires  53  will move the contact surfaces  13 ,  14  and  15  close to the mirror  2  and bistable mechanism  3 . The contact forces will move the bistable mechanism  3  and the mirror  2  from the second stable position to the first stable position. The multiple contact surfaces  13 , 14  and  15  are used to decrease mechanical wear, increase contact duration and travel distance of the mirror  2  along Y-axis. 
     A variety of bent beam actuators are within the scope of these teachings. Actuators such as, but not limited to, those disclosed in U.S. Pat. No. 6,853,765, to K. Cochran, and in Long Que et al., Bent-Beam Electrothermal Actuators-Part I: Single Beam and Cascaded Devices, Journal of Microelectromechanical Systems, Vol. 10, NO. 2, June 2001, both of which are Incorporated by reference herein in their entirety for all purposes. Actuators that are not bimetallic actuators are within the scope of these teachings 
     With mirror size along Y-direction equal or less to the (largest) travel distance of the bistable mechanism along the Y direction (the distance travelled by the mirror in the direction substantially perpendicular to the contact surfaces), when light beams in the plane perpendicular to the plane  16  with light beam sizes equal or smaller to the mirror size, the mirror  2  can completely block the light beam and steer the light beam to different directions at one stable position while let the light beams continue propagate in the original direction without effect at the other stable position. Multiple light beams with such MEMS chips can be used to form a switch with multiple input ports and multiple output ports. 
     The stable positions of the mirror  2  can be detected by the intrinsic strain gage properties of the bistable mechanism  3 . At the first stable position, the bistable mechanism has substantially no strain while at second stable position, a large strain is developed. Therefore, by measuring the resistance change between the electrodes  39  and  40 , the positions of the mirror  2  can be detected. An another embodiment of the method to detect the mirror  2  positions is to detect the capacitance change at electrodes  37  and  39  or  39  and  41  due to the gap changes between the contact surfaces at different stable position. 
     In another embodiment, shown in  FIGS. 1   a  and  1   b , the bistable mechanism  3  is comprised of two curved beams ( 83 ,  84 ) and each bent beam actuator  6 ,  11  has one beam comprised of two parts ( 60 ,  65  for the first bent beam actuator  6 ,  75 ,  70  for the second bent beam actuator  11 ). In the embodiment shown in  FIGS. 1   a  and  1   b , the first contacting component  81  has a single contact surface  85  and the second contacting component  89  has a single contact surface  87 .  FIG. 1   a  shows the bistable component  3  in a first stable configuration and  FIG. 1   b  shows the bistable component  3  in the second stable configuration. 
     In yet another embodiment, shown in  FIG. 3 , the MEMS bistable optical switch  17  includes a substrate  50  (embodiments in which the bistable optical switch is lifted from the substrate are also within the scope of these teachings) having a planar surface frame  17 , a reflective mirror  18  arranged on the planar surface  17 , a bistable mechanism  19  suspending the mirror  18  to frame  17 . Multiple identical, paralleled bistable mechanisms  19  are used to restrict the motion of the mirror in the plane  16  along the symmetric axis of the bistable mechanism or Y axis. 
     Electrothermal actuator  22  is used to switch the mirror  18  from its first stable position to its second stable position. Electrothermal actuator  27  is used to switch the mirror  18  from its second stable position to its first stable position. Actuator  22  has contact surfaces  24 ,  25  and  26  to interact with bistable mechanism  19 . As shown in  FIG. 4   a , contact surface  25  has a flexible frame  33  and inside close-by hard surface  34 . When contact force is applied, the contact surface  25  will become self-contacting. This can decrease contact force on each surface therefore increase contact life time.  FIG. 4   b  shows the self-contacting off-center contact surface  26  design. Similarly, the flexible frame  35  will contact with the inside close-by hard surface  36  when contact force applied. Therefore, the contact force is decreased for each surface. Actuator  27 , which for switch the mirror  18  from its the second stable position to its first stable position, has contact surfaces self-contacting surface  29 ,  30  and  31  similarly as shown in  FIGS. 4   a  and  4   b.    
     In one embodiment the method of these teachings includes providing an optical switch as described herein above where the bistable component and the reflective opponent are in initial state, the initial state being the first stable configuration or the second stable configuration, applying a predetermined voltage across the actuating component, the actuating component being either the first or the second electrothermal bent beam actuator depending on the initial state. The predetermined voltage causes a current equal to or higher than a predetermined current to flow across the actuating component. The current flow in the actuating component causes the actuating component and the driving component, the driving component being the first or second contacting component, to advance the bistable component of the reflective component from the initial state to a second state, the second state being the other stable configuration. By moving the reflective component from one stable configuration to the other stable configuration, one or more optical beams are switched. 
     The above disclosed embodiment of the method of these teachings can also include measuring a resistance change in the bistable component in order to determine whether the bistable component is in the first stable configuration or in the second stable configuration. In another instance, the embodiment of the method includes measuring a change in the capacitance between the first electrothermal bent beam actuator and the bistable component or between the second electrothermal bent beam actuator and the bistable component. The above embodiments of the method of these teachings are not limited to configurations in which the bistable component is in the first stable configuration or in the second stable configuration. Methods that apply to either configuration are within the scope of these teachings. 
     When the first contacting component has a first number of contact surfaces and the second contacting components has a second number of contact surfaces, applying a predetermined voltage across the actuating component (first or second electrothermal bent beam actuator) causes each one of the contact surfaces, in either the first number of contact surfaces or the second number of contact surfaces, at a different time in a time sequence (also referred to as at one predetermined time from a number of predetermined times). 
       FIGS. 2   a  and  2   b  illustrate the operation of the optical switch in one embodiment of an optical system, these teachings not being limited to only that optical system. Referring to  FIGS. 2   a  and  2   b , the embodiment  100  shown therein includes an optical switch  1  such as disclosed hereinabove, a first optical system  101  and a second optical system  102  and optical beams  108 ,  109  propagating between optical system  101  an optical system  102 . Optical beams  104  and  105  input/exit the first optical system  101  and optical beams  106  and  107  exit/input the second optical system  102 . In the configuration shown in  FIG. 2   a , the two optical beams  108 ,  109  propagate unobstructed between the first optical system  101  and the second optical system  102 . When the optical switch is operated and the reflective component moves to the other stable configuration, as shown in  FIG. 2   b , the reflective component intersects the propagating beams  108 ,  109 . The propagating beams  108 ,  109  can be deflected to a location different from the other optical system. 
     In one embodiment, the MEMS fabrication steps are simplified by using silicon on insulator (SOI) wafers. MEMS fabrication steps comprise only 5 steps: patterning the front and back sides, front-side deep reactive ion etching (DRIE), back-side DRIE, release of the buried oxide layer (box) oxide, and front-and-back metal depositions. This processing has the advantage that every step has a defined stop by the wafer structure; therefore the process control monitoring is drastically simplified. Specifically, the front-side DRIE will be stopped at the buried oxide layer, the back-side DRIE will also be stopped at the buried oxide layer, the oxide release will have minimal etch rate on the Si material, and metal deposition step (preferred a dry processing step) will have minimal impact to the released spring. The process flow is shown in  FIGS. 5   a - 5   b . The process starts with  FIG. 5   a  the SOI wafer substrate, proceeding to  FIG. 5   b  device layer pattern, then  FIG. 5   c  BOX layer pattern to protect the device, then  FIG. 5   d  backside release etch and, lastly  FIG. 5   e  the remaining BOX is stripped away, resulting in a completed optical switch. 
     For the purposes of describing and defining the present teachings, it is noted that the term “substantially” is utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. The term “substantially” is also utilized herein to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue. 
     Although the invention has been described with respect to various embodiments, it should be realized these teachings are also capable of a wide variety of further and other embodiments within the spirit and scope of the appended claims.