Patent Publication Number: US-2009226132-A1

Title: Plasmon gate

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is related to and claims the benefit of the earliest available effective filing date(s) from the following listed application(s) (the “Related Applications”) (e.g., claims earliest available priority dates for other than provisional patent applications or claims benefits under 35 USC § 119(e) for provisional patent applications, for any and all parent, grandparent, great-grandparent, etc. applications of the Related Application(s)). 
     RELATED APPLICATIONS 
     For purposes of the USPTO extra-statutory requirements, the present application constitutes a continuation-in-part of U.S. patent application Ser. No. 11/471,288, entitled Plasmon Switch, naming Roderick A. Hyde, Edward K. Y. Jung; Nathan P. Myhrvold, John Brian Pendry, Clarence T. Tegreene, and Lowell L. Wood, Jr. as inventors, filed 19 Jun. 2006, which is currently co-pending, or is an application of which a currently co-pending application is entitled to the benefit of the filing date. 
    
    
     The United States Patent Office (USPTO) has published a notice to the effect that the USPTO&#39;s computer programs require that patent applicants reference both a serial number and indicate whether an application is a continuation or continuation-in-part. Stephen G. Kunin, Benefit of Prior-Filed Application, USPTO Official Gazette Mar. 18, 2003, available at http://www.uspto.gov/web/offices/com/sol/og/2003/week11/patbene.htm. The present Applicant Entity (hereinafter “Applicant”) has provided above a specific reference to the application(s) from which priority is being claimed as recited by statute. Applicant understands that the statute is unambiguous in its specific reference language and does not require either a serial number or any characterization, such as “continuation” or “continuation-in-part,” for claiming priority to U.S. patent applications. Notwithstanding the foregoing, Applicant understands that the USPTO&#39;s computer programs have certain data entry requirements, and hence Applicant is designating the present application as a continuation-in-part of its parent applications as set forth above, but expressly points out that such designations are not to be construed in any way as any type of commentary and/or admission as to whether or not the present application contains any new matter in addition to the matter of its parent application(s). 
     All subject matter of the Related Applications and of any and all parent, grandparent, great-grandparent, etc. applications of the Related Applications is incorporated herein by reference to the extent such subject matter is not inconsistent herewith. 
     SUMMARY 
     In one embodiment, a method of controlling energy propagation comprises guiding energy at a first plasmon frequency along a first path, blocking the guided energy at the first plasmon frequency from propagating along the first path responsive to a first signal at a first time, blocking the guided energy at the first plasmon frequency from propagating along the first path responsive to a second signal, different from the first signal, at a second time, and receiving an output that is a function of the first signal and the second signal. 
     In another embodiment, a plasmon gate comprises a first plasmon guide extending from an input location to an output location, a first plasmon switch interposed at a first central location intermediate the input location and output location and responsive to a first signal, and a second plasmon switch interposed at a second central location intermediate the input location and output location and responsive to a second signal, wherein the first switch and the second switch are arranged to control plasmon propagation to the output location. 
     In another embodiment, a method comprises inputting a plasmon signal, selectively controlling the plasmon signal with a plurality of control signals, and outputting a plasmon signal having a distribution that is a function of the plurality of control signals. 
     In another embodiment, an apparatus comprises a plasmon input receptive to a first plasmon signal, a first control input receptive to a first control signal, a second control input receptive to a second control signal, and a plasmon output configured to output a second plasmon signal as a function of the first plasmon signal, the first control signal and the second control signal. 
     The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a schematic of a plasmon at a boundary. 
         FIG. 2  is a schematic of an array of particles. 
         FIG. 3  is a schematic of a first path intersecting a second path. 
         FIG. 4  is a schematic of a first path intersecting a second path. 
         FIG. 5  is a schematic of a top cross-sectional view of a plasmon logic element. 
         FIG. 6  is a schematic of a top cross-sectional view of a plasmon logic element including an array of particles. 
         FIG. 7  is a schematic of a system including a plasmon logic element. 
         FIG. 8  is a schematic of a top cross-sectional view of a plasmon logic element. 
         FIG. 9  is a schematic of a top cross-sectional view of a plasmon logic element. 
         FIG. 10  is a schematic of a plasmon logic element configured on a fiber. 
         FIG. 11  is a schematic of a first embodiment of a plasmon gate. 
         FIG. 12  is a table corresponding to  FIG. 11 . 
         FIG. 13  is a schematic of a second embodiment of a plasmon gate. 
         FIG. 14  is a table corresponding to  FIG. 13 . 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here. 
     Surface plasmons may exist on a boundary between two materials when the real parts of their dielectric constants ∈ and ∈′ have different signs, for example between a metal and a dielectric.  FIG. 1  shows a plasmon  102  at a boundary  104  of a material  106  having a negative real dielectric constant, such as a metal. The material or structure  108  forming the boundary  104  with the material  106  may be: air, vacuum, or its equivalent; a substantially homogeneous dielectric material; or a different material or structure. The boundary  104 , although shown as being substantially continuous and planar, may have a different shape. The plasmon  102 , although shown as including substantially exponential functions with a field maximum at the boundary  104 , may include only approximately exponential functions, may be described by a different function, and/or may have a field maximum someplace other than the boundary. Further, although the plasmon  102  is shown at a certain location on the boundary  104  for illustrative purposes, the spatial distribution of the plasmon  102  may be anything. Plasmons are described in C. Kittel, “INTRODUCTION TO SOLID STATE PHYSICS”, Wiley, 2004, which is incorporated herein by reference. 
     In some embodiments the material thickness  110  may be smaller than the plasmon wavelength, as described in Alexandra Boltasseva, Thomas Nikolajsen, Krisjan Leosson, Kasper Kjaer, Morten S. Larsen, and Sergey I. Bozhevolnyi, “INTEGRATED OPTICAL COMPONENTS UTILIZING LONG-RANGE SURFACE PLASMON POLARITONS”, Journal of Lightwave Technology, January, 2005, Volume 23, Number 1, which is incorporated herein by reference. Further, Boltasseva describes how a metal may be embedded in a dielectric to allow propagation of long-range surface plasmon polaritons, where the parameters of the metal [including thickness  110  and width (not shown)] may control the propagation of the plasmon. 
     Particles  202  may be configured to support and guide surface plasmons, where the particles  202  shown in  FIG. 2  are silver spheres. Particles supporting plasmons are described in M. Salerno, J. R. Krenn, B. Lamprecht, G. Schider, H. Ditlbacher, N. Félidj, A. Leitner, and F. R. Aussenegg, “PLASMON POLARITONS IN METAL NANOSTRUCTURES: THE OPTOELECTRONIC ROUTE TO NANOTECHNOLOGY”, Opto-Electronics Review, 2002, Volume 10, Number 3, pages 217-222, which is incorporated herein by reference. Creation of plasmons on a particle in an electromagnetic field is described in P. G. Kik, A. L. Martin, S. A. Maier, and H. A. Atwater, “METAL NANOPARTICLE ARRAYS FOR NEAR FIELD OPTICAL LITHOGRAPHY”, Proceedings of SPIE, 4810, 2002 which is incorporated herein by reference.  FIG. 2  shows electromagnetic energy  206  incident on a chain of particles  202 , where the particles  202  are coated with a nonlinear material  204 , and the electromagnetic energy  206  couples to plasmons  102  on the particles  202 . The plasmons  102  are shown having a finite extent in  FIG. 2  for clarity and one skilled in the art will recognize that the spatial distribution of the plasmons  102  may fall off according to a power law away from the particles  202  and/or may have a different distribution than that shown in  FIG. 2 . Particles  202  may be configured on a substrate (not shown), as described in Stefan A. Maier, Paul E. Barclay, Thomas J. Johnson, Michelle D. Friedman, and Oskar Painter, “LOW-LOSS FIBER ACCESSIBLE PLASMON WAVEGUIDE FOR PLANAR ENERGY GUIDING AND SENSING”, Applied Physics Letters, May 17, 2004, Volume 84, Number 20, Pages 3990-3992, which is incorporated herein by reference. 
     Particles  202  may be coated with nonlinear material  204 , as described in N.-C. Panoiu and R. M. Osgood, Jr., “SUBWAVELENGTH NONLINEAR PLASMONIC NANOWIRE”, Nano Letters, Nov. 10, 2004, Volume 4, Number 12, Pages 2427-2430, which is incorporated herein by reference. In  FIG. 2  all of the particles  202  are coated with a nonlinear material  204 , however, in some embodiments only one particle may be coated with nonlinear material  204 , or a different number of particles  202  may be coated with nonlinear material  204 . Further, although  FIG. 2  shows the particles  202  completely coated with nonlinear material  204 , one or more particles  202  may only be partially coated with nonlinear material  204 . 
     Although the particles  202  in  FIG. 2  are shown as being substantially spherical, the particles may have a different shape that is configured to support plasmons. Further, although the particles  202  are shown as being substantially the same size, the particles  202  may vary in size, by design or by a randomized process of manufacturing the particles  202 . Moreover, the particles need not be homogenous or even solid. Also, although the particles  202  are described as silver particles, particles  202  that support plasmons may comprise a different metal or a different material. Although the particles  202  are illustrated as having a spacing between particles  208  that is substantially constant, the spacing may vary and may be different from that shown in  FIG. 2 , and in some embodiments, the particles  202  may be touching or very nearly so. 
       FIG. 3  shows a top cross-sectional view of a first embodiment including a first path  302  for guiding energy at a first plasmon frequency, a second path  304  for guiding energy at a second plasmon frequency, where the first path  302  and the second path  304  form an intersection region  306  including a nonlinear material or other material configured to saturate in response to a plasmon that forms a first portion of the first path  302 . The paths  302 ,  304  are boundaries  104  as described with respect to  FIG. 1 . An input coupling structure  310  is configured to convert incoming electromagnetic energy  312  into a plasmon  102  (shown in  FIG. 1 ) that propagates along the first path  302 , and an output coupling structure  314  is configured to convert a plasmon  102  propagating along the first path  302  into outgoing electromagnetic energy  316 . Similarly, a second input coupling structure  318  is configured to convert incoming electromagnetic energy  320  into a plasmon  102  (shown in  FIG. 1 ) that propagates along the second path  304 , and a second output coupling structure  322  is configured to convert a plasmon  102  propagating along the second path  304  into outgoing electromagnetic energy  324 . Electromagnetic energy  320  converted into a plasmon  102  propagating along the second path  304  can saturate the intersection region  306  and thus inhibit the propagation of a plasmon  102  through the intersection region  306  along the first path  302 . 
     Although the embodiment in  FIG. 3  is described such that the intersection region  306 , when saturated, inhibits propagation of a plasmon  102  through the intersection region  306 , in another embodiment the intersection region  306  may be configured to allow propagation of a plasmon  102  when it is saturated and inhibit or restrict propagation of a plasmon  102  when it is not saturated. 
     Some methods for coupling electromagnetic energy to a plasmon (and vice versa) that may be incorporated in an input and/or output coupling structure  310  and/or  314  are described in W. L. Barnes, A. Dereux, and T. W. Ebbesen, “SURFACE PLASMON SUBWAVELENGTH OPTICS”, Nature, Volume 424, Aug. 14, 2003, 824-830, which is incorporated herein by reference. These methods include and are not limited to prism coupling, scattering from a topological defect on the surface on which the plasmon is to be generated, and periodic corrugation in the surface on which the plasmon is to be generated. 
     In some approaches the input and output coupling structures  310 ,  314 ,  318 ,  322  may be integral to the first and second paths  302 ,  304 , while in other approaches, the first and second paths  302 ,  304  may be arranged primarily for guiding and separate structures may form the input and output coupling structures  310 ,  314 ,  318 ,  322 . 
       FIG. 4  shows a top cross-sectional view of another embodiment including a first path  302  for guiding energy at a first plasmon frequency, a second path  304  for guiding energy at a second plasmon frequency, where the first path  302  and the second path  304  form an intersection region  306  that forms a first portion of the first path  302 . In this case, particles  402  having a first size form the first path  302 , particles  404  having a second size form the second path  304 , and an elliptical particle  406  forms the intersection region  306 . The particle  406  forming the intersection region  306  is configured to resonate at both the first plasmon frequency and the second plasmon frequency. In this case the intersection region  306  includes a single elliptical particle  406  configured to resonate at two frequencies, however, other assemblies may resonate at two or more frequencies, including triangular particles, assemblies of two or more particles, or a different configuration. Further, other embodiments allow the first path  302  to guide energy at a first plasmon frequency and the second path  304  to guide energy at a second plasmon frequency, for example, by varying the size, shape, material, and/or other parameters of the particles  402 ,  404 . 
     Incoming electromagnetic energy  412  is converted into a plasmon  102  (shown on particles  202  in  FIG. 2 ) that propagates along the first path  302 . Plasmons  102  that pass through the intersection region  306  are then converted into outgoing electromagnetic energy  416 . Similarly, incoming electromagnetic energy  420  is converted into a plasmon  102  that propagates along the second path  304 . Plasmons  102  that pass through the intersection region  306  are then converted into outgoing electromagnetic energy  424 . Electromagnetic energy  420  converted into a plasmon  102  propagating along the second path  304  can saturate the elliptical particle  406 . The saturated elliptical particle  406  does not support propagation of plasmon energy, and thus inhibits propagation of the plasmon  102  through the intersection region  306  along the first path  302 . 
     The embodiment in  FIG. 4  is shown having paths  302 ,  304  with different size particles  402 ,  404 , however in some embodiments the paths  302 ,  304  may have substantially the same size particles  402 ,  404 . Further, although the embodiment is described such that plasmon propagation along the second path  304  blocks plasmon propagation along the first path  302 , the reverse may be the case, where plasmon propagation along the first path  302  blocks plasmon propagation along the second path  304 . 
     The embodiment in  FIG. 4  is further described such that plasmons propagating along one path and saturating the particle  406  forming the intersection region  306  block plasmons from propagating along a different path. However, in some embodiments plasmons propagating along one path may block only a portion of the plasmon energy propagating along a different path such that the amount of plasmon energy propagating on one path determines the amount of plasmon energy that may propagate on the other path. In such an approach, the relationship between the amount of plasmon energy along the second path  304  and the amount of plasmon energy that propagates along the first path  302  is not necessarily binary. That is, the amount of plasmon energy that passes the elliptical particle  406  can be an analog function of the amount of plasmon energy arriving at the elliptical particle  406  along the second path  304 . 
       FIG. 5  shows a top cross-sectional view of an embodiment of a plasmon logic element  500  including a first plasmon guide  502  extending from an input location  504  to an output location  506  and a first electromagnetically nonlinear structure  508  interposed at a first central location  510  (analogous to the intersection region  306  that forms a first portion of the first path  302 ) intermediate to the input location  504  and output location  506 , where the first nonlinear structure  508  is responsive to electromagnetic energy  512  to control plasmon propagation past the first central location  510 . An energy guiding structure  514  is configured to guide the electromagnetic energy  512  to the first central location  510 . An input coupling structure  310  is configured to convert incoming electromagnetic energy  312  into a plasmon  102  (shown in  FIG. 1 ) that propagates along the first plasmon guide  502 , and an output coupling structure  314  is configured to convert a plasmon  102  propagating along the first plasmon guide  502  into outgoing electromagnetic energy  316 . 
     In the embodiment shown in  FIG. 5 , the energy guiding structure  514  is an optical fiber configured to direct energy substantially in the optical frequency range to the first central location  510 . In other embodiments, the type of energy guiding structure  514  may be determined by the frequency response of the first nonlinear structure  508 . For example, the energy guiding structure may include an integrated optical waveguide, a set of particles, a carbon nanotube structure, a dielectric-dielectric interface, or any other appropriate structure that can guide the energy. In one embodiment, the energy guiding structure  514  may be configured to carry electromagnetic energy in the form of a plasmon  102 . In another embodiment, the energy guiding structure  514  can be removed and electromagnetic energy  512  can be directed toward the first nonlinear structure  508  through freespace or another transmissive medium. Or, electromagnetic energy  512  can emitted substantially adjacent to the first nonlinear structure, with a light emissive or plasmon emissive structure, such as a laser or another known form of locally emitting energy at the appropriate frequency. 
       FIG. 6  shows a top cross-sectional view of another embodiment of a plasmon logic element  500  including a first plasmon guide  502  extending from an input location  504  to an output location  506  and a first electromagnetically nonlinear structure  508  interposed at a first central location  510  intermediate to the input location  504  and output location  506 , where the first nonlinear structure  508  is responsive to electromagnetic energy  512  to control plasmon propagation past the first central location. In the embodiment shown in  FIG. 6 , the first plasmon guide  502  includes an array of particles  202  and the electromagnetically nonlinear structure  508  is a metallic particle coated with nonlinear material as described with respect to  FIG. 2 . However, in other embodiments the electromagnetically nonlinear structure  508  may be a different structure configured to support plasmons and to saturate under certain conditions. 
     Although the embodiment in  FIG. 6  shows only one particle  508  including nonlinear material, more than one particle in the guide  502  may include a nonlinear material, as described with respect to  FIG. 2 . Further, other variations may include those described with respect to  FIG. 2 . In an embodiment where more than one particle in the guide  502  includes a nonlinear material, electromagnetic energy  512  incident on the guide  502  can select the first central location  510  on the guide  502  where plasmon propagation is controlled. Or, a second particle  202  in the guide  502  coated with a nonlinear material may function as a second electromagnetically nonlinear structure at a second central location (not shown), where plasmon propagation along the guide  502  may be controlled at both the first central location and the second central location. 
       FIG. 7  shows a system including an embodiment similar to that in  FIG. 3 , where the system includes an energy generator  702  configured to produce energy. The input coupling structure  310  is configured to couple the energy from the energy generator  702  to a plasmon  102  (shown in  FIG. 1 ). In one embodiment, the energy generator  702  may be a device configured to produce electromagnetic energy, such as a laser, and the input coupling structure  310  may include a converter configured to convert energy to a plasmon  102 . Although the energy generator  702  is shown separate from the first path  302 , in some embodiments the first path  302  may include the energy generator  702 . Sources of electromagnetic radiation that may be included in the first path  302  are known to those skilled in the art, and may include a microcavity semiconductor laser such as that described in U.S. Pat. No. 5,825,799, entitled MICROCAVITY SEMICONDUCTOR LASER, to Seng-Tiong Ho, Daniel Yen Chu, Jian-Ping Zhang, and Shengli Wu, which is incorporated herein by reference. 
       FIG. 7  further includes the output coupling structure  314 , where the output coupling structure  314  may include a converter configured to convert a plasmon  102  into a different form of energy such as electromagnetic energy, and/or a region arranged to output the energy.  FIG. 7  further includes a detector  704 , where the detector  704  may include a device configured to detect electromagnetic energy, such as a photodetector or other detector, or the detector  704  may be configured to detect a different kind of energy, depending on the type of energy output from the output coupling structure  314 . Although  FIG. 7  includes an input coupling structure  310  and an output coupling structure  314 , in some embodiments these may not be included, for example, where the energy generator  702  is within the first path  302 , the input coupling structure  310  may not be included. 
       FIG. 7  further includes a second energy generator  706 , a second input coupling structure  318 , a second output coupling structure  322 , and a second detector  708 . The second input coupling structure  318  is configured to couple the energy from the second energy generator  706  to a plasmon  102 . In one embodiment, the second energy generator  706  may be a device configured to produce electromagnetic energy, such as a laser, and the second input coupling structure  318  may include a converter configured to convert energy to a plasmon  102 . Although the second energy generator  706  is shown separate from the second path  304 , in some embodiments the second path  304  may include the energy generator. 
     The second output coupling structure  322  may include a converter configured to convert a plasmon  102  into a different form of energy such as electromagnetic energy, and/or a region arranged to output the energy. The second detector  708  is configured to receive energy from the second output coupling structure  322  and may include a device configured to detect electromagnetic energy, such as a photodetector or other detector, or the second detector  708  may be configured to detect a different kind of energy, depending on the type of energy output from the second output coupling structure  322 . Although  FIG. 7  includes a second input coupling structure  318  and a second output coupling structure  322 , in some embodiments these may not be included, for example, where the second energy generator  706  is within the second path  304 , the second input coupling structure  318  may not be included. 
       FIG. 7  further includes a processor  710  operably connected to the energy generator  702 , the detector  704 , the second energy generator  706 , and the second detector  708 . The processor  710  may be connected directly to the elements  702 ,  704 ,  706 ,  708 , and/or there may be intermediate devices. Further, there may be more than one processor  710 . Although the processor  710  is shown only in  FIG. 7 , any of the embodiments may include a processor  710 , where the processor  710  may be operably coupled to elements of the system, where the elements are not limited to those described above. 
     Although the processor of  FIG. 7  is described with reference to  FIG. 3 , the corresponding structures, methods, systems, and apparatuses can be used in conjunction with any of the embodiments. Moreover, although the embodiment of  FIG. 7  illustrates a single processors and a single generation, the structures, methods, systems, and apparatuses herein may include one or more energy generators  702 ,  706  and/or detectors  704 ,  708 , and/or processor(s)  710 . A processor may include electrical circuitry and/or other apparatuses for processing signals. 
       FIG. 8  shows a top cross-sectional view of an embodiment similar to that of  FIG. 5 , further including a second electromagnetically nonlinear structure  802  interposed at a second central location  804  intermediate to the input location  504  and output location  506 . Although the embodiment shown in  FIG. 8  does not include the energy guiding structure  514 , in other embodiments it may include an energy guiding structure  514  configured to guide energy to the first central location  510 , and/or it may include a second energy guiding structure (not shown) configured to guide energy to the second central location  804 . 
     As described with respect to  FIG. 5 , the input coupling structure  310  is configured to convert incoming electromagnetic energy  312  into a plasmon  102  (shown in  FIG. 1 ), and the output coupling structure  314  is configured to convert a plasmon  102  into outgoing electromagnetic energy  316 . In the embodiment shown in  FIG. 8 , the first and second central locations  510 ,  804  both include an electromagnetically nonlinear structure configured to saturate when electromagnetic energy  512  or  806  is incident on it. Thus a plasmon  102  may propagate along the first plasmon guide  502  through the first and second central locations  510 ,  804  when electromagnetic energy  512 ,  806  is not incident on the first and second central locations  510 ,  804 , and when electromagnetic energy  512  or  806  is incident on one of the first and second central locations  510 ,  804 , the plasmon  102  may not propagate through the first and/or second central locations  510 ,  804 . Thus electromagnetic energy  512  or  806  incident on either the first or second central location  510  or  806  can inhibit electromagnetic energy  316  from being detected by the detector  704 . Although the embodiment shown in  FIG. 8  includes two electromagnetically nonlinear structures  508  and  802 , the system may be configured with any number of these. Further, although the first and second central locations  510 ,  804  are shown as small, rectilinear portions of the first plasmon guide  502 , they may be shaped differently depending upon the design considerations. 
       FIG. 9  shows a top cross-sectional view of another embodiment similar to that in  FIG. 5 , further including a second electromagnetically nonlinear structure  802  and a second output location  902  located on one branch of a ‘Y’ shaped structure, wherein the second electromagnetically nonlinear structure  802  is interposed at a second central location  904  intermediate to the input location  504  and the second output location  902 . 
     The input coupling structure  310  is configured to convert incoming electromagnetic energy  312  into a plasmon  102  (shown in  FIG. 1 ), and the output coupling structures  314 ,  906  are each configured to convert a plasmon  102  into outgoing electromagnetic energy  316 ,  908 . 
     In the embodiment shown in  FIG. 9 , the first and second central locations  510 ,  904  both include an electromagnetically nonlinear structure  508 ,  802  configured to saturate when electromagnetic energy  512  or  910  is incident on it. Thus a plasmon  102  may propagate along the first plasmon guide  502  through the first and second central locations  510 ,  904  when electromagnetic energy  512 ,  910  is not incident on the first and second central locations  510 ,  904 . When electromagnetic energy  512  is incident on the first central location  510  the plasmon  102  may not propagate through the first central location  510 , and thus electromagnetic energy  512  incident on the first central location  510  can inhibit electromagnetic energy  316  from being detected by the detector  704 . Similarly, when electromagnetic energy  910  is incident on the second central location  904  the plasmon  102  may not propagate through the second central location  904 , and thus electromagnetic energy  910  incident on the second central location  904  can inhibit electromagnetic energy  908  from being detected by the detector  912 . Or, when electromagnetic energy  512 ,  910  is incident on both the first central location and the second central location  510  and  904  the plasmon  102  may not propagate through either the first or second central locations  510  or  904 , and thus electromagnetic energy  512 ,  910  incident on the first and second central locations  510  and  904  can inhibit electromagnetic energy  316  and  908  from being detected by the detectors  704  and  912 . 
     Although the embodiment shown in  FIG. 9  includes two electromagnetically nonlinear structures  508  and  802 , the system may be configured with any number of these. Further, although the first and second central locations  510 ,  904  are shown as small, rectilinear portions of the first plasmon guide  502 , they may be configured in a different shape. 
     In the embodiment shown in  FIG. 10 , an electromagnetically nonlinear structure  508  is configured on a fiber  1002  having an outer conductive layer  1004 , where the fiber  1002  forms a first plasmon guide  502  extending from an input location  504  to an output location  506 , and where the first electromagnetically nonlinear structure  508  is interposed at a first central location  510  intermediate to the input location  504  and output location  506 . The first electromagnetically nonlinear structure  508  is fabricated on the conductive layer  1004 , where the first nonlinear structure  508  is responsive to electromagnetic energy  512  to control plasmon propagation past the first central location  510 . 
     Electromagnetic energy  312  is coupled into and propagates in the fiber  1002  and couples to an evanescent wave in the conductive layer  1004 , which couples to a plasmon  102  (shown in  FIG. 1 ) on an outer surface  1006  of the conductive layer  1004 . The conductive layer  1004  may include a high conductivity metal such as silver, gold, or copper, or it may be another type of metal or conductive material. Metal-coated fibers are known to those skilled in the art and various methods exist for coating a fiber with metal, including vacuum evaporation and sputtering. 
     Although the fiber  1002  in  FIG. 10  has a substantially circular cross-section  1008  that remains substantially constant along the length  1010  of the fiber  1002 , the fiber  1002  may have any shape, including but not limited to irregular cross-sections  1008  and/or cross-sections  1008  that vary along the length  1010 . 
     A first embodiment of a plasmon gate  1100 , shown in  FIG. 11  (and similar to the embodiment shown in  FIG. 8 ), comprises a first plasmon guide  502  extending from an input location  504  to an output location  506 , a first plasmon switch  1102  interposed at a first central location  510  intermediate the input location  504  and output location  506  and responsive to a first signal  1106 , and a second plasmon switch  1104  interposed at a second central location  804  intermediate the input location  504  and output location  506  and responsive to a second signal  1108 , wherein the first switch  1102  and the second switch  1104  are arranged to control plasmon propagation to the output location  506 . The input coupling structure  310  is configured to convert incoming electromagnetic energy  312  into a plasmon  102  (shown in  FIG. 1 ), and the output coupling structure  314  is configured to convert a plasmon  102  into outgoing electromagnetic energy  316 . 
     A table  1200  (truth table) shown in  FIG. 12  further illustrates the operation of the plasmon gate  1100 . In the example shown in  FIG. 11 , when the first signal  1106  is incident on the first plasmon switch  1102 , a plasmon  102  is inhibited from passing through the switch  1102 , representing a ‘0’ in the table  1200 . When the first signal  1106  is not incident on the first plasmon switch  1102 , a plasmon  102  may propagate through the switch  1102 , representing a ‘1’ in the table  1200 . 
     Similarly, when the second signal  1108  is incident on the second plasmon switch  1104 , a plasmon  102  is inhibited from passing through the switch  1104 , representing a ‘0’ in the table  1200 , and when the second signal  1108  is not incident on the second plasmon switch  1104 , a plasmon  102  may propagate through the switch  1104 , representing a ‘1’ in the table  1200 . 
     Thus a plasmon  102  may propagate along the first plasmon guide  502  through the first and second plasmon switches  1102 ,  1104  when a signal  1106 ,  1108  is not incident on the switches  1102 ,  1104 , allowing electromagnetic energy  316  to be detected by the detector  704 , represented by a ‘1’ in the ‘OUT’ column of the table  1200 . When a signal  1106  or  1108  is incident on one of the first and second plasmon switches  1102 ,  1104 , the plasmon  102  may not propagate through the first and/or second plasmon switch  1102 ,  1104 . Thus a signal  1106  or  1108  incident on either the first or second plasmon switch can inhibit electromagnetic energy  316  from being detected by the detector  704 , represented by a ‘0’ in the ‘OUT’ column of the table  1200 . 
     In a second embodiment of a plasmon gate  1300 , shown in  FIG. 13 , the first plasmon guide  502  extends from an input location  504  to an output location  506  and is arranged to route plasmon energy into a first branch  1302  and a second branch  1304  at a first intersection location  1306 . The first branch  1302  includes the first plasmon switch  1102  responsive to a first signal  1106  at a first central location  510  and the second branch  1304  includes the second plasmon switch  1104  responsive to a second signal  1108  at a second central location  804 , wherein the first switch  1102  and the second switch  1104  are arranged to control plasmon propagation to the output location  506 . The first plasmon guide  502  is arranged to join plasmon energy from the first branch  1302  and the second branch  1304  at a second intersection location  1308 . The input coupling structure  310  is configured to convert incoming electromagnetic energy  312  into a plasmon  102  (shown in  FIG. 1 ), and the output coupling structure  314  is configured to convert a plasmon  102  into outgoing electromagnetic energy  316 . Although  FIG. 13  is shown having two branches  1302 ,  1304  and two plasmon switches  1102 ,  1104 , other embodiments may include three or more branches and/or three or more switches, where each switch may be on a different branch or two or more switches may be on a single branch. 
     A table  1400  (truth table) shown in  FIG. 14  further illustrates the operation of the plasmon gate  1300 . When the first signal  1106  is incident on the first plasmon switch  1102 , a plasmon  102  is inhibited from passing through the switch  1102 , representing a ‘0’ in the table  1400 . When the first signal  1106  is not incident on the first plasmon switch  1102 , a plasmon  102  may propagate through the switch  1102 , representing a ‘1’ in the table  1200 . 
     Similarly, when the second signal  1108  is incident on the second plasmon switch  1104 , a plasmon  102  is inhibited from passing through the switch  1104 , representing a ‘0’ in the table  1200 , and when the second signal  1108  is not incident on the second plasmon switch  1104 , a plasmon  102  may propagate through the switch  1104 , representing a ‘1’ in the table  1400 . 
     Thus, a plasmon  102  may propagate along the first plasmon guide  502  through the first and second plasmon switches  1102 ,  1104  when a signal  1106 ,  1108  is not incident on the switches  1102 ,  1104 , allowing electromagnetic energy  316  to be detected by the detector  704 , represented by a ‘1’ in the ‘OUT’ column of the table  1400 . When a signal  1106  or  1108  is incident on one of the first and second plasmon switches  1102 ,  1104 , the plasmon  102  may propagate through the other plasmon switch  1102 ,  1104 . For example, when a signal  1106  is incident on the first plasmon switch  1102 , a plasmon  102  may not propagate through the first plasmon switch  1102 , but it may propagate through the second plasmon switch  1104 , allowing electromagnetic energy  316  to be detected by the detector  704 , represented by a ‘1’ in the ‘OUT’ column of the table  1400 . A signal  1106  or  1108  incident on both the first or second plasmon switch can inhibit electromagnetic energy  316  from being detected by the detector  704 , represented by a ‘0’ in the ‘OUT’ column of the table  1400 . 
     With regard to the embodiments shown in  FIGS. 11 and 13 , the input coupling structure  310  is shown as being receptive to electromagnetic energy  312 , however in other embodiments the input coupling structure  310  may be receptive to a different kind of energy, for example, plasmon energy. Similarly, the output coupling structure  314  is shown as being configured to output electromagnetic energy  316 , but in other embodiments the output coupling structure  314  may be configured to output a different kind of energy, for example, plasmon energy and/or electromagnetic energy. 
     The first signal  1106  and/or the second signal  1108  in  FIGS. 11 and 13  may include electromagnetic energy, plasmon energy, and/or a different form of energy, depending on the switches  1102 ,  1104 . The first and/or second plasmon switch  1102 ,  1104  may include an electromagnetically nonlinear structure, as described, for example, with respect to  FIG. 3 . The first plasmon guide  502  may be arranged substantially in a single plane or it may be configured in a non-planar arrangement. 
     Although the embodiments shown in  FIGS. 11 and 13  do not include an energy guiding structure  514 , other embodiments may include one or more energy guiding structures  514  configured to guide energy including the first and/or second signal  1106 ,  1108  to the first and/or second plasmon switch  1102 ,  1104 . 
     Although  FIGS. 11 and 13  show substantially linear guides, in other embodiments the first plasmon guide  502  may include at least one particle supportive of plasmon energy, as shown in  FIGS. 2 ,  4  and  6 . 
     Although the configuration of the gates  1100  and  1300  represented by tables  1200  and  1400  include switches  1102 ,  1104  that are represented by a ‘0’ when a signal  1106  or  1108  is incident on them and by a ‘1’ when a signal  1106  or  1108  is not incident on them, the switches may be configured such that a signal  1106  or  1108  incident on them is represented by a ‘1’ and a signal  1106  or  1108  not incident on them is represented by a ‘0’, and one skilled in the art may select and configure switches to produce a gate having a desired functional dependence. Further, although the tables  1200  and  1400  represent functions that are substantially constant in time, in other embodiments gates  1100 ,  1300  may be configured such that they are represented by functions that vary as a function of time. For example, in one embodiment, the switches  1102 ,  1104  may be configured to be responsive to a time-varying signal (not shown) such as a time-varying electromagnetic signal, electric or magnetic field, mechanical stress or strain, or a different time-varying stimulus, where the time-varying signal changes the properties of the switch as a function of time. 
     Although the embodiments shown in  FIGS. 11 and 13  each include two plasmon switches  1102 ,  1104 , other embodiments may have different numbers of switches. Further, although the first and second central locations  510 ,  804  are shown as small, rectilinear portions of the first plasmon guide  502 , they may be shaped differently depending upon the design considerations. 
     In one embodiment a method of controlling energy propagation comprises guiding energy at a first plasmon frequency along a first path (or first plasmon guide  502 ), blocking the guided energy at the first plasmon frequency from propagating along the first path  502  responsive to a first signal  1106  at a first time, blocking the guided energy at the first plasmon frequency from propagating along the first path  502  responsive to a second signal  1108 , different from the first signal  1106 , at a second time, and receiving an output (for example, the outgoing electromagnetic energy  316 ) that is a function of the first signal  1106  and the second signal  1108 . The second time may follow the first time, may be substantially the same as the first time, or may precede the first time. The embodiment may further comprise guiding energy at a second plasmon frequency along the first path  502 . 
     The method may further comprise, at a first location (or first intersection location  1306 ) on the first path  502 , directing a first portion of the energy at the first plasmon frequency into a first branch  1302 , directing a second portion of the energy at the first plasmon frequency into a second branch  1304 , and/or combining the first portion of the energy at the first plasmon frequency from the first branch  1302  and the second portion of the energy at the first plasmon frequency from the second branch  1304  at a second location (or second intersection location  1308 ) on the first path. The method may further comprise applying the first signal  1106  to the first branch  1302  and/or applying the second signal  1108  to the second branch  1304 . 
     The method may further comprise coupling electromagnetic energy to the first path  502 , generating the electromagnetic energy, coupling plasmon energy to the first path  502 , generating the plasmon, and/or generating a plasmon along the first path. The method may further comprise generating the first and/or second signal  1106 ,  1108 , and/or guiding the first and/or second signal  1106 ,  1108 . The method may further comprise detecting, storing, and/or sending the output  316 . 
     Blocking the guided energy at the first plasmon frequency from propagating along the first path  502  responsive to a first signal  1106  may include saturating a first portion of the first path (or first central location  510 ) with the first signal  1106  and, similarly, blocking the guided energy at the first plasmon frequency from propagating along the first path  502  responsive to a second signal  1108  may include saturating a second portion of the first path (or second central location  804 ) with the second signal  1108 . 
     In one embodiment, a method comprises inputting a plasmon signal, selectively controlling the plasmon signal with a plurality of control signals (a first signal  1106  and a second signal  1108 ), and outputting a plasmon signal having a distribution that is a function of the plurality of control signals. The distribution may be a spatial distribution, a temporal distribution, or a different kind of distribution. It may be a function of the input plasmon signal, where the function may be substantially described by a table such as those in  FIGS. 12 and 14  and/or may vary in time. The method may comprise generating at least one of the plurality of control signals  1106 ,  1108 , where at least one of the plurality of control signals  1106 ,  1108  may include plasmon energy and/or at least one of the plurality of control signals may include electromagnetic energy. 
     In one embodiment, an apparatus such as the plasmon gate  1100  comprises a plasmon input (or input location  504 ) receptive to a first plasmon signal, a first control input (or first plasmon switch  1102 ) receptive to a first control signal (the first signal  1106 ), a second control input (or second plasmon switch  1104 ) receptive to a second control signal (the second signal  1108 ), and a plasmon output (or output location  506 ) configured to output a second plasmon signal as a function of the first plasmon signal, the first control signal  1106  and the second control signal  1108 . The embodiment may further comprise a third control input receptive to a third control signal, not shown. The first control input  1102  may be further receptive to a third control signal, also not shown. The function of the first plasmon signal, the first control signal  1106  and the second control signal  1108  is substantially described by a table such as the tables  1200  and  1400  in  FIGS. 12 and 14 , where the table may describe an OR gate, an AND gate, or a different kind of gate. 
     Although the embodiments described in  FIGS. 1-14  are generally described such that saturation of a region and/or energy incident on a nonlinear material inhibits propagation of a plasmon  102  through the region and/or material, in other embodiments saturation of a region and/or energy incident on a nonlinear material may be configured to allow propagation of a plasmon  102 , and no saturation of a region and/or energy not incident on a nonlinear material may be configured to inhibit and/or restrict propagation of a plasmon  102 . 
     In this disclosure, references to “optical” elements, components, processes or other aspects, as well as references to “light” may also relate in this disclosure to so-called “near-visible” light such as that in the near infrared, infra-red, far infrared and the near and far ultra-violet spectrums. Moreover, many principles herein may be extended to many spectra of electromagnetic radiation where the processing, components, or other factors do not preclude operation at such frequencies, including frequencies that may be outside ranges typically considered to be optical frequencies. 
     Although  FIGS. 1-14  show structures configured to transport energy over relatively short distances, in some embodiments structures may be configured to transport energy over very long distances of even thousands of kilometers or more. For example, referring to  FIG. 10 , an optical fiber may be configured to carry electromagnetic energy over a substantially large distance, and metal deposited on the fiber may convert energy from electromagnetic energy propagating in the fiber to plasmon energy propagating on the metal. 
     Applications of plasmons and logic systems including plasmons are wide ranging. For example, there may be situations, such as in optical fiber systems where all-optical switching is desired, where electromagnetic energy is converted to plasmons to do the switching and then converted back to electromagnetic energy. 
     Although the term “plasmon” is used to describe a state propagating at the boundary between two materials whose real parts of their dielectric constants and E′ have different signs, one skilled in the art may recognize that other terms may exist for this state, including, but not limited to, “surface plasmon” and/or “surface plasmon polariton”. 
     The foregoing detailed description has set forth various embodiments of the devices and/or processes via the use of block diagrams, flowcharts, and/or examples. Insofar as such block diagrams, flowcharts, and/or examples contain one or more functions and/or operations, it will be understood by those within the art that each function and/or operation within such block diagrams, flowcharts, or examples can be implemented, individually and/or collectively, by a wide range of hardware, software, firmware, or virtually any combination thereof. In one embodiment, several portions of the subject matter described herein may be implemented via Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), digital signal processors (DSPs), or other integrated formats. However, those skilled in the art will recognize that some aspects of the embodiments disclosed herein, in whole or in part, can be equivalently implemented in integrated circuits, as one or more computer programs running on one or more computers (e.g., as one or more programs running on one or more computer systems), as one or more programs running on one or more processors (e.g., as one or more programs running on one or more microprocessors), as firmware, or as virtually any combination thereof, and that designing the circuitry and/or writing the code for the software and or firmware would be well within the skill of one of skill in the art in light of this disclosure. In addition, those skilled in the art will appreciate that the mechanisms of the subject matter described herein are capable of being distributed as a program product in a variety of forms, and that an illustrative embodiment of the subject matter described herein applies regardless of the particular type of signal bearing medium used to actually carry out the distribution. Examples of a signal bearing medium include, but are not limited to, the following: a recordable type medium such as a floppy disk, a hard disk drive, a Compact Disc (CD), a Digital Video Disk (DVD), a digital tape, a computer memory, etc.; and a transmission type medium such as a digital and/or an analog communication medium (e.g., a fiber optic cable, a waveguide, a wired communications link, a wireless communication link, etc.). 
     In a general sense, those skilled in the art will recognize that the various embodiments described herein can be implemented, individually and/or collectively, by various types of electromechanical systems having a wide range of electrical components such as hardware, software, firmware, or virtually any combination thereof; and a wide range of components that may impart mechanical force or motion such as rigid bodies, spring or torsional bodies, hydraulics, and electro-magnetically actuated devices, or virtually any combination thereof. Consequently, as used herein “electromechanical system” includes, but is not limited to, electrical circuitry operably coupled with a transducer (e.g., an actuator, a motor, a piezoelectric crystal, etc.), electrical circuitry having at least one discrete electrical circuit, electrical circuitry having at least one integrated circuit, electrical circuitry having at least one application specific integrated circuit, electrical circuitry forming a general purpose computing device configured by a computer program (e.g., a, general purpose computer configured by a computer program which at least partially carries out processes and/or devices described herein, or a microprocessor configured by a computer program which at least partially carries out processes and/or devices described herein), electrical circuitry forming a memory device (e.g., forms of random access memory), electrical circuitry forming a communications device (e.g., a modem, communications switch, or optical-electrical equipment), and any non-electrical analog thereto, such as optical or other analogs. Those skilled in the art will also appreciate that examples of electromechanical systems include but are not limited to a variety of consumer electronics systems, as well as other systems such as motorized transport systems, factory automation systems, security systems, and communication/computing systems. Those skilled in the art will recognize that electromechanical as used herein is not necessarily limited to a system that has both electrical and mechanical actuation except as context may dictate otherwise. 
     In a general sense, those skilled in the art will recognize that the various aspects described herein which can be implemented, individually and/or collectively, by a wide range of hardware, software, firmware, or any combination thereof can be viewed as being composed of various types of “electrical circuitry.” Consequently, as used herein “electrical circuitry” includes, but is not limited to, electrical circuitry having at least one discrete electrical circuit, electrical circuitry having at least one integrated circuit, electrical circuitry having at least one application specific integrated circuit, electrical circuitry forming a general purpose computing device configured by a computer program (e.g., a general purpose computer configured by a computer program which at least partially carries out processes and/or devices described herein, or a microprocessor configured by a computer program which at least partially carries out processes and/or devices described herein), electrical circuitry forming a memory device (e.g., forms of random access memory), and/or electrical circuitry forming a communications device (e.g., a modem, communications switch, or optical-electrical equipment). Those having skill in the art will recognize that the subject matter described herein may be implemented in an analog or digital fashion or some combination thereof. 
     All of the above U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in any Application Data Sheet, are incorporated herein by reference, in their entireties. 
     One skilled in the art will recognize that the herein described components (e.g., steps), devices, and objects and the discussion accompanying them are used as examples for the sake of conceptual clarity and that various configuration modifications are within the skill of those in the art. Consequently, as used herein, the specific exemplars set forth and the accompanying discussion are intended to be representative of their more general classes. In general, use of any specific exemplar herein is also intended to be representative of its class, and the non-inclusion of such specific components (e.g., steps), devices, and objects herein should not be taken as indicating that limitation is desired. 
     With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations are not expressly set forth herein for sake of clarity. 
     The herein described subject matter sometimes illustrates different components contained within, or connected with, different other components. It is to be understood that such depicted architectures are merely exemplary, and that in fact many other architectures can be implemented which achieve the same functionality. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively “associated” such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality can be seen as “associated with” each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated can also be viewed as being “operably connected”, or “operably coupled”, to each other to achieve the desired functionality, and any two components capable of being so associated can also be viewed as being “operably couplable”, to each other to achieve the desired functionality. Specific examples of operably couplable include but are not limited to physically mateable and/or physically interacting components and/or wirelessly interactable and/or wirelessly interacting components and/or logically interacting and/or logically interactable components. 
     While particular aspects of the present subject matter described herein have been shown and described, it will be apparent to those skilled in the art that, based upon the teachings herein, changes and modifications may be made without departing from the subject matter described herein and its broader aspects and, therefore, the appended claims are to encompass within their scope all such changes and modifications as are within the true spirit and scope of the subject matter described herein. Furthermore, it is to be understood that the invention is defined by the appended claims. It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to “at least one of A, B, and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.” 
     While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.