Patent Document

CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a national stage application under 35 U.S.C. §371 of International Application No. PCT/IL2008/000494 filed Apr. 10, 2008, which is incorporated by reference herein in its entirety, and which claims benefit of priority to each of the following applications, the disclosures of which are hereby incorporated by reference in their entireties. 
     U.S. patent application Ser. No. 11/734,747, filed Apr. 12, 2007 and entitled LIGHT ACTIVATED OPTICAL SWITCH THAT INCLUDES A PIEZOELECTRIC ELEMENT WITH LAYERS OF PIEZOELECTRIC MATERIAL HAVING DIFFERENT PIEZOELECTRIC CHARACTERISTICS; 
     U.S. patent application Ser. No. 11/734,750, filed Apr. 12, 2007 and entitled LIGHT ACTIVATED OPTICAL SWITCH THAT INCLUDES A PIEZOELECTRIC ELEMENT AND A CONDUCTIVE LAYER; and 
     U.S. Provisional Patent Application Ser. No. 60/911,469, filed Apr. 12, 2007 and entitled LOGIC GATES FOR OPTICAL SIGNALS. 
     U.S. patent application Ser. No. 11/974,483, filed Oct. 15, 2007, which is a continuation of U.S. Pat. No. 7,283,698 is also incorporated by reference herein in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to light activated switches and logic gates generally. 
     BACKGROUND OF THE INVENTION 
     The U.S. Patents of the present inventor, Dr. Gary Neal Poovey, U.S. Pat. Nos. 7,072,536 and 7,283,698, the disclosures of which are hereby incorporated by reference, together with the publications listed hereinbelow, the disclosures of which are hereby incorporated by reference, are believed to represent the current state of the art: 
     U.S. Pat. Nos. 6,594,411; 4,961,618; 5,414,789; 2,936,380; 3,680,080; 3,965,388; 3,995,311; 4,023,887; 4,128,300; 4,262,992; 4,689,793; 4,764,889; 4,978,842; 5,078,464; 5,109,156; 5,146,078; 5,168,382; 6,005,791; 6,609,840; 7,263,262; 3,987,310; 4,053,794; 6,757,459; 6,804,427; 6,320,994; 6,487,333; 6,178,033; 5,425,115; 6,075,512; 6,697,548; 6,594,411; 5,703,975; 6,320,994; 5,134,946; 7,283,695; 5,414,789; 4,961,618; 2,936,380; 3,680,080; 3,965,388; 3,995,311; 4,023,887; 4,128,300; 3,995,311; 4,023,887; 4,128,300; 4,262,992; 4,689,793; 4,764,889; 4,961,618; 4,978,842; 5,078,464; 5,109,156; 5,146,078; 5,168,382; 6,005,791; 6,609,840; 7,263,262; 6,151,428; 5,999,284; 5,315,422; 5,144,375; 5,101,456; 4,932,739; 4,701,030; 4,630,898; 3,987,310 and 4,053,794; and 
     U.S. Published Patent Application Nos.: 2005/0129351; 2006/0045407; 2004/0091201 and 2004/0037708. 
     Alexei Grigoriev, et al., “Subnanosecond piezoelectric x-ray switch”, Applied Physics Letters 89, 021109, 2006. 
     SUMMARY OF THE INVENTION 
     The present invention seeks to provide improved optical switches, logic gates and logic functionality. 
     There is thus provided in accordance with a preferred embodiment of the present invention an optical switch including: 
     a light passageway having a changeable cross-sectional area; 
     an activation light responsive piezoelectric element associated with the light passageway, the activation light responsive piezoelectric element being operative to change its shape in response to activation light impinging thereon; and 
     a conductive element operatively associated with the piezoelectric element for enhancing activation light responsiveness thereof, 
     the activation light responsive piezoelectric element being associated with the light passageway and being operative such that changes in the shape of the piezoelectric element cause changes in the changeable cross-sectional area of the light passageway sufficient to govern the passage of light along the light passageway. 
     Preferably, the light passageway, the piezoelectric element and the conductive element are configured and operative such that impingement of activation light within a first range of threshold levels on the piezoelectric element causes the light passageway to prevent passage of light of a first range of wavelengths therethrough and impingement of activation light within a second range of threshold levels, lying outside of the first range of threshold levels, on the piezoelectric element causes the light passageway to allow passage of light of a first range of wavelengths therethrough. 
     In accordance with a preferred embodiment of the present invention, the conductive element comprises a layer of a conductive material extending along a surface of the piezoelectric element. 
     Preferably, the piezoelectric element comprises at least two layers of piezoelectric material having different piezoelectric characteristics. 
     In accordance with a preferred embodiment of the present invention, the at least two layers of piezoelectric material have different crystal orientations. 
     Preferably, the conductive element is disposed between two layers of the piezoelectric element. 
     In accordance with a preferred embodiment of the present invention, there is also provided a light coupler operative to direct the activation light and signal light into the light pathway, at least one characteristic of the activation light governing whether the signal light passes through the passageway. 
     Additionally in accordance with a preferred embodiment of the present invention there is provided an optical switch including: 
     a light passageway having a changeable cross-sectional area; and 
     an activation light responsive piezoelectric element associated with the light passageway, the activation light responsive piezoelectric element being operative to change its shape in response to activation light impinging thereon, 
     the activation light responsive piezoelectric element including at least two layers of piezoelectric material having different piezoelectric characteristics, the piezoelectric element being associated with the light passageway and being operative such that changes in the shape of the piezoelectric element cause changes in the changeable cross-sectional area of the light passageway sufficient to govern the passage of light along the light passageway. 
     Preferably, the light passageway and the piezoelectric element are configured and operative such that impingement of activation light within a first range of threshold levels on the piezoelectric element causes the light passageway to prevent passage of light of a first range of wavelengths therethrough and impingement of activation light within a second range of threshold levels, lying outside of the first range of threshold levels, on the piezoelectric element causes the light passageway to allow passage of light of a first range of wavelengths therethrough. 
     Additionally in accordance with a preferred embodiment of the present invention there is provided a logic gate including at least one gate having at least one of NOT, AND, OR, NAND and NOR functionality including at least one optical switch actuated by light, the at least one optical switch including: 
     a signal light passageway having a changeable cross-sectional area; and 
     an activation light responsive piezoelectric element associated with the light passageway, the activation light responsive piezoelectric element being operative to change its shape in response to activation light impinging thereon; 
     the activation light responsive piezoelectric element being associated with the light passageway and being operative such that changes in the shape of the piezoelectric element cause changes in the changeable cross-sectional area of the light sufficient to govern the passage of signal light along the light passageway. 
     Preferably the logic gate also includes light conduits supplying the activation light to the at least one optical switch and which carry signal light which carries digital information to and from the at least one light switch. 
     In accordance with a preferred embodiment of the present invention, the signal light has a wavelength which is greater than that of the activation light. 
     Preferably, the signal light has a wavelength which is approximately twice that of the activation light. 
     In accordance with a preferred embodiment of the present invention, the signal light has a wavelength of 1500 nm. and the activation light has a wavelength of approximately 750 nm. 
     There is additionally provided in accordance with a preferred embodiment of the present invention a logic gate providing NOT functionality and wherein the at least one optical switch comprises a single optical switch and wherein the signal light has a wavelength of approximately twice that of the activation light. 
     There is additionally provided in accordance with a preferred embodiment of the present invention a logic gate providing AND functionality and wherein the at least one optical switch comprises a single optical switch and wherein the signal light has a wavelength greater than that of the activation light, the logic gate also including: 
     first and second logic inputs receiving signal light; 
     a first light conduit receiving a first portion of the signal light received at the first logic input; 
     a second light conduit receiving a second portion of the signal light received at the first logic input; 
     a third light conduit receiving a first portion of the signal light received at the second logic input; 
     a fourth light conduit receiving a second portion of the signal light received at the second logic input; 
     a first wavelength modifier operative to decrease the wavelength of the light along the second light conduit to the wavelength of the activation light; 
     a second wavelength modifier operative to decrease the wavelength of the light along the fourth light conduit to the wavelength of the activation light; 
     a first phase matcher operative to match the phase of the light along the second light conduit to that the activation light; 
     a second phase matcher which matches the phase of the light along the fourth light conduit to the activation light; and 
     a phase shifter operative to cause wavelength reduced and phase matched light along the second and fourth light conduits to be mutually out of phase by 180 degrees, 
     light along the first and third light conduits being supplied as a signal light input to the optical switch; and 
     wavelength reduced and phase matched light along the second and fourth light conduits being supplied together with additional activation light as activation light to the optical switch. 
     There is additionally provided in accordance with a preferred embodiment of the present invention a logic gate providing NAND functionality and wherein the first optical switch comprises a first optical switch and a second optical switch and wherein the signal light has a wavelength greater than that of the activation light, the logic gate also including: 
     first and second logic inputs receiving signal light inputs; 
     a first wavelength modifier operative to decrease the wavelength of signal light at the first input to the wavelength of the activation light; 
     a second wavelength modifier operative to decrease the wavelength of signal light at the second input to the wavelength of the activation light; 
     a third wavelength modifier operative to decrease the wavelength of signal light from the first optical switch; 
     a first light conduit supplying part of the light from the first wavelength modifier to a first light absorber; 
     a second light conduit supplying part of the light from the first wavelength modifier to the first optical switch; 
     a third light conduit supplying part of the light from the second wavelength modifier to a second light absorber; 
     a fourth light conduit supplying part of the light from the second wavelength modifier to the first optical switch; 
     a fifth light conduit supplying signal light from the first optical switch to the third wavelength modifier; and 
     a sixth light conduit supplying light wavelength modified light from the third wavelength modifier to the second optical switch as activation light. 
     There is additionally provided in accordance with a preferred embodiment of the present invention a logic gate providing OR functionality and wherein the at least one optical switch comprises a single optical switch and wherein the signal light has a wavelength greater than that of the activation light, the logic gate also including: 
     first and second logic inputs receiving signal light inputs; 
     a first wavelength modifier operative to decrease the wavelength of the light along the first light input to the wavelength of the activation light; 
     a second wavelength modifier operative to decrease the wavelength of the light along the second light input to the wavelength of the activation light; 
     a first phase matcher operative to match the phase of wavelength modified light from the first wavelength modifier to match the phase of actuation light; 
     a second phase matcher operative to match the phase of the light from the second wavelength modifier to match the phase of the actuation light; 
     a first light conduit supplying part of the light from the first phase matcher to a first light absorber; 
     a second light conduit supplying part of the light from the second phase matcher to a second light absorber; 
     a first phase shifter; 
     a second phase shifter; 
     a third light conduit supplying part of the light from the first phase matcher to the first phase shifter, thereby to cause light from the first phase matcher to be out of phase with the activation light; and 
     a fourth light conduit supplying part of the light from the second phase matcher to a second phase shifter, thereby to cause light from the first phase matcher to be out of phase with the supplied activation light, 
     a fifth light conduit supplying light from the first phase shifter to the optical switch; and 
     a sixth light conduit supplying light from the second phase shifter to the optical switch, 
     the optical switch receiving the activation light and signal light from the fifth and sixth light conduits. 
     There is additionally provided in accordance with a preferred embodiment of the present invention a logic gate providing OR functionality and wherein the at least one optical switch comprises first and second optical switches and wherein the signal light has a wavelength greater than that of the activation light, the logic gate also including: 
     first and second logic inputs receiving signal light inputs; 
     a first wavelength modifier operative to decrease the wavelength of the light along the first light input to the wavelength of the activation light; 
     a second wavelength modifier operative to decrease the wavelength of the light along the second light input to the wavelength of the activation light; 
     first and second light conduits supplying wavelength modified light from the first and second wavelength modifiers; 
     a power limiter receiving light from the first wavelength modifier and second wavelength modifier via the respective first and second light conduits and being operative to maintain light output therefrom at a predetermined power level; 
     a third light conduit supplying power limited light from the power limiter to the first optical switch; 
     a third wavelength modifier receiving signal light from the first optical switch and being operative to decrease the wavelength of the light to the wavelength of the activation light; and 
     a fourth light conduit supplying light from the third wavelength modifier to the second optical switch. 
     There is still further provided in accordance with a preferred embodiment of the present invention a logic gate providing OR functionality and wherein the at least one optical switch comprises a single optical switch and wherein the signal light has a wavelength greater than that of the activation light, the logic gate also including: 
     first and second logic inputs receiving signal light; 
     a first light conduit receiving a first portion of the signal light received at the first logic input; 
     a second light conduit receiving a second portion of the signal light received at the first logic input; 
     a third light conduit receiving a first portion of the signal light received at the second logic input; 
     a fourth light conduit receiving a second portion of the signal light received at the second logic input; 
     a first wavelength modifier operative to decrease the wavelength of the light along the second light conduit to the wavelength of the activation light; 
     a second wavelength modifier operative to decrease the wavelength of the light along the fourth light conduit to the wavelength of the activation light; and 
     a phase shifter operative to cause wavelength modified light from the first wavelength modifier to be out of phase by 180 degrees with respect to the light from the second wavelength modifier, 
     the optical switch receiving light from the first and third light conduits, the second wavelength modifier and the phase shifter. 
     Additionally there is provided a logic gate wherein the at least one optical switch is constructed as described hereinabove and logic functionality employing or more logic gates as described hereinabove. 
     Further in accordance with a preferred embodiment of the present invention there is provided an optical switch including: 
     a signal channel configured to guide a signal light; 
     a piezoelectric element adjacent to the signal channel; and 
     a conductive layer adjacent to the piezoelectric element; 
     wherein passage of the signal light through the signal channel is controlled by the application of an activation light to the piezoelectric element and wherein the conductive layer enhances an electrical field applied to the piezoelectric element in response to the activation light. 
     Preferably, the conductive layer is adhered to a surface of the piezoelectric element. 
     In accordance with a preferred embodiment of the present invention, application of the activation light to the piezoelectric element causes the shape of the piezoelectric element to change such that the signal light is not able to pass through the signal channel. 
     Preferably, the signal channel comprises a chamber that is filled with a compressible material. 
     Preferably, the piezoelectric element forms a portion of the chamber. 
     In accordance with a preferred embodiment of the present invention, the piezoelectric element comprises at least two layers that have different piezoelectric characteristics. 
     Preferably, the conductive layer is adhered between two layers of the piezoelectric element. 
     There is additionally provided in accordance with a preferred embodiment of the present invention a method for operating an optical switch, the method including: 
     applying a signal light to an optical switch that comprises a piezoelectric element and at least one conductive layer adjacent to the piezoelectric element; and 
     applying an activation light to the piezoelectric element to change the state of the optical switch; 
     wherein the conductive layer enhances an electrical field applied to the piezoelectric element in response to the applied activation light. 
     Preferably, applying the activation light to the piezoelectric element causes the shape of the piezoelectric element to change such that the signal light is not able to pass through the optical switch. 
     Preferably, applying the activation light comprises applying two light signals, which are out of phase with each other, to the piezoelectric element and then removing one of the light signals, leaving the remaining light signal as the activation light. 
     There is additionally provided a method for operating an optical switch, the method including: 
     applying a signal light to a signal channel, the signal channel being adjacent to a piezoelectric element that is adjacent to at least one conductive layer; and 
     applying an activation light to the piezoelectric element to change the shape of the piezoelectric element such that the signal light is prevented from passing through the signal channel, 
     wherein the conductive layer enhances an electrical field applied to the piezoelectric element in response to the applied activation light. 
     Additionally there is provided an optical switch including: 
     a signal channel configured to guide a signal light; 
     a piezoelectric element adjacent to the signal channel; 
     a conductive layer adjacent to the piezoelectric element; and 
     means for applying an activation light to the piezoelectric element to change the shape of the piezoelectric element such that the signal light is prevented from passing through the signal channel; 
     wherein the conductive layer enhances an electrical field applied to the piezoelectric element in response to the applied activation light. 
     There is additionally provided a method for operating an optical switch, the method including: 
     applying a signal light to an optical switch that comprises a piezoelectric element, the piezoelectric element including at least two layers of piezoelectric material that have different piezoelectric characteristics; and 
     applying an activation light to the piezoelectric element to change the state of the optical switch. 
     Preferably, applying the activation light to the piezoelectric element causes the shape of the piezoelectric element to change such that the signal light is not able to pass through the optical switch. 
     Preferably, the change in the shape of the piezoelectric element causes a change in a dimension of a signal channel of the optical switch. 
     In accordance with a preferred embodiment of the present invention, applying the activation light comprises applying two light signals, which are out of phase with each other, to the piezoelectric element and then removing one of the light signals, leaving the remaining light signal as the activation light. 
     In accordance with a preferred embodiment of the present invention, the conductive layer adjacent to the piezoelectric element enhances an electrical field applied to the piezoelectric element in response to the applied activation light. 
     There is also provided an optical switch including: 
     a signal channel configured to guide a signal light; and 
     a piezoelectric element adjacent to the signal channel, the piezoelectric element including at least two layers of piezoelectric material that have different piezoelectric characteristics; 
     wherein passage of the signal light through the signal channel is controlled by the application of an activation light to the piezoelectric element. 
     Preferably, application of the activation light to the piezoelectric element causes the shape of the piezoelectric element to change such that the signal light is not able to pass through the signal channel. 
     There is also provided a method for operating an optical switch, the method including: 
     applying a signal light to a signal channel, the signal channel being adjacent to a piezoelectric element that has at least two layers of piezoelectric material that have different piezoelectric characteristics; and 
     applying in activation light to the piezoelectric element to change the shape of the piezoelectric element such that the signal light is prevented from passing through the signal channel. 
     Additionally there is provided an optical switch including: 
     a signal channel configured to guide a signal light; 
     a piezoelectric element adjacent to the signal channel, the piezoelectric element including at least two different layers that have different piezoelectric characteristics; and 
     means for applying an activation light to the piezoelectric element to change the shape of the piezoelectric element such that the signal light is prevented from passing through the signal channel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be understood and appreciated more fully from the following detailed description, taken in conjunction with the drawings in which: 
         FIG. 1A  depicts an optical switch that includes a signal channel and a piezoelectric element and that is controlled by an activation light; 
         FIG. 1B  illustrates the piezoelectric element from  FIG. 1A  in an activated state that results from the application of an activation light to the piezoelectric element; 
         FIG. 2A  is a cross-sectional view of the signal channel and the piezoelectric element of  FIG. 1A  when the piezoelectric element is in a non-activated state, taken along the lines IIA-IIA in  FIG. 1A ; 
         FIG. 2B  is a cross-sectional view of the signal channel and the piezoelectric element from  FIG. 1B  when the piezoelectric element is in an activated state, taken along the lines IIB-IIB in  FIG. 1B ; 
         FIG. 3  depicts a graph of optical signal attenuation vs. a dimension of a signal channel; 
         FIGS. 4A and 4B  illustrate a technique for changing the state of an optical switch that involves applying an activation light having a shorter wavelength than the signal light; 
         FIGS. 5A and 5B  illustrate a technique for changing the state of an optical switch in which applying the activation light involves providing two light signals, which are out of phase with each other, to the piezoelectric element and then removing one of the light signals, leaving the remaining light signal as the activation light; 
         FIG. 6A  depicts an embodiment of a light activated optical switch that includes a signal channel, a piezoelectric element, and a conductive layer adjacent to the piezoelectric element; 
         FIG. 6B  illustrates the piezoelectric element of  FIG. 6A  in an activated state that results from the application of an activation light to the piezoelectric element; 
         FIG. 7  illustrates the action of an electrical field of the light on the electrons of a conductive layer; 
         FIG. 8  depicts an optical switch system that includes a light activated optical switch as described above with reference to  FIGS. 1A-7 ; 
         FIG. 9  depicts an embodiment of an optical switch and an optical coupler that is used to couple the signal light and the activation light into the same signal channel; 
         FIG. 10A  depicts an embodiment of a piezoelectric element that has more than two layers of piezoelectric material with different piezoelectric characteristics; 
         FIG. 10B  depicts an embodiment of a light activated optical switch that includes a conductive layer sandwiched between two layers of a piezoelectric element; 
         FIG. 10C  depicts an embodiment of a light activated optical switch that includes multiple conductive layers sandwiched between a multilayer piezoelectric element; 
         FIG. 10D  depicts an embodiment of a light activated optical switch that includes a multilayer piezoelectric element and a conductive layer on two different sides of the signal channel; 
         FIG. 10E  depicts an embodiment of a light activated optical switch that includes a multilayer piezoelectric element and a conductive layer on each of two sides of the signal channel; 
         FIG. 11A  depicts an embodiment of a light activated optical switch that includes a signal channel and a piezoelectric element, where a portion of the signal channel includes a chamber that is filled with a compressible material; 
         FIG. 11B  illustrates the piezoelectric element from  FIG. 11A  in an activated state that results from the application of an activation light to the piezoelectric element; 
         FIG. 12A  depicts an embodiment of a light activated optical switch that includes a signal channel, a piezoelectric element, and a conductive layer adjacent to the piezoelectric element in which the signal channel is an optical fiber and the piezoelectric element and conductive layer are formed in a band entirely around the circumference of the optical fiber; 
         FIG. 12B  illustrates the piezoelectric element from  FIG. 12A  in an activated state that results from the application of an activation light to the piezoelectric element; 
         FIG. 13A  depicts an embodiment of a light activated optical switch that includes a signal channel, a transparent piezoelectric element, and a conductive layer adjacent to the piezoelectric element in which the signal channel includes the transparent piezoelectric element; 
         FIG. 13B  illustrates the piezoelectric element from  FIG. 13A  in an activated state that results from the application of an activation light to the piezoelectric element; 
         FIGS. 14A and 14B  are simplified illustrations of an optical switch, in accordance with another preferred embodiment of the present invention; 
         FIGS. 15A and 15B  are cross-sectional views of the signal channel and the piezoelectric element of  FIGS. 14A and 14B , taken along the lines XVA-XVA in  FIG. 14A  and XVB-XVB in  FIG. 14B ; 
         FIGS. 16A and 16B  are simplified illustrations of an optical switch, in accordance with yet another preferred embodiment of the present invention; 
         FIGS. 17A and 17B  are cross-sectional views of the signal channel and the piezoelectric element of  FIGS. 16A and 16B , taken along the lines XVIIA-XVIIA in  FIG. 16A  and XVIIB-XVIIB in  FIG. 16B ; 
         FIGS. 18A and 18B  are simplified illustrations of an optical switch, in accordance with still another preferred embodiment of the present invention; 
         FIGS. 19A and 19B  are cross-sectional views of the signal channel and the piezoelectric element of  FIGS. 18A and 18B , taken along the lines XIXA-XIXA in  FIG. 18A  and XIXB-XIXB in  FIG. 18B ; 
         FIG. 20  is a schematic drawing of a logical NOT gate; 
         FIG. 21  is a schematic drawing of a logical AND gate that uses an optical switch; 
         FIG. 22  is a second schematic drawing of a logical AND gate that uses optical switches; 
         FIG. 23  is a schematic drawing of a logical OR gate that uses optical switches and phase matching devices; 
         FIG. 24  is a schematic drawing of a logical OR gate that uses optical switches and a power limiter; and 
         FIG. 25  is a schematic drawing of a logical OR gate that uses an optical switch. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Light actuated optical switches are used to construct AND, OR, and NOR logic gates. Light signals coming into the logic gates are processed so that the output of the logic gates conforms to the needed specification for each kind of gate. The light signals are all that are used to operate the logic gates, and no external battery is required using light actuated optical switches, the logic gates will have dimensions that will fit within semiconductor logic design dimensions. 
     Computers will be able to be made that function on light signals instead of electrical signals. Transistors of transistor based logic gates switch in 10E−9 seconds, and this limits the speed of transistor based logic gates. Light can travel three microns in 10E−14 seconds. Logic gates based on light actuated switches can be much faster than transistor based logic gates. 
     An optical switch includes a signal channel and a piezoelectric element that is adjacent to the signal channel. The piezoelectric element changes shape in response to an activation light and the piezoelectric element is configured relative to the signal channel such that the change in shape of the piezoelectric element causes a change in a dimension of the signal channel. For example, the change in shape of the piezoelectric element causes a dimension of the signal channel to be reduced far enough that a signal light is no longer able to pass through the signal channel. Using this phenomenon, the state of the optical switch is controlled by controlling the application of the activation light to the piezoelectric element. In an embodiment, the optical switch allows a signal light to pass through the signal channel when the activation light is not applied to the piezoelectric element and blocks the signal light from passing through the signal channel when the activation light is applied to the piezoelectric element. Because the shape of the piezoelectric element determines whether or not light passes through the signal channel, the function of the optical switch depends on the ability of the piezoelectric element to change shape. 
     In accordance with an embodiment of the invention, the piezoelectric element has at least two layers of piezoelectric material with each layer having different piezoelectric characteristics. The piezoelectric characteristics of the layers are selected to enhance the performance of the piezoelectric element and ultimately to enhance the performance of the optical switch. In an embodiment, the piezoelectric characteristics of the layers are selected to produce a piezoelectric element that exhibits sufficient shape change in response to an activation light to block a signal light from passing through a signal channel. 
       FIG. 1A  depicts an optical switch  100  that includes a signal channel  102  and a piezoelectric element  104  and that is controlled by an activation light. The signal channel guides the transmission of light within a confined area along a defined path. The signal channel is formed by a light guiding structure, or combination of structures, which can guide light within a confined area along a defined path. Structures that can form the signal channel include, for example, an optical fiber, substrates such as lithium niobate or other transparent piezoelectric materials that include a signal channel, an optical waveguide, and a chamber for holding a compressible material. In the embodiment of  FIG. 1A , the signal channel is formed by a monolithic light guiding element. 
     The piezoelectric element  104  is formed of piezoelectric material. Examples of piezoelectric material that can be used to form the piezoelectric element include crystalline piezoelectric material such as quartz (SiO 2 ), lithium niobate (LiNbO 3 ), lead zirconate (PbZrO 3 ), lead titanate (PbTiO 3 ), and lead zirconate titanate. Examples of piezoelectric materials that can be oriented in a magnetic field are lead zirconate and lead titanate or lead zicronate titanate. Quartz and lithium niobate are examples of transparent piezoelectric materials. 
     The piezoelectric element  104  has at least two layers  106  and  108  of piezoelectric material having different piezoelectric characteristics. The different piezoelectric characteristics of the different layers may include, for example: 1) different degrees of expansion and/or shrinkage in response to the same electrical field; 2) different responses to the same electrical field, for example, one of the layers expands in response to an electrical field having a first orientation and the other layer expands in response to an electrical field having a second orientation that is perpendicular to the first orientation; 3) different polarities; 4) different strains; 5) different hysteresis; 6) different capacitances; 7) different impedances; 8) different resistivities; 9) different thermal histories; and 10) different electromagnetic histories. 
     The piezoelectric characteristics of a piezoelectric material are a function of, for example: 1) the type of piezoelectric material; 2) the crystal orientation of the piezoelectric material; 3) doping levels within the piezoelectric material; 4) the density of the piezoelectric material; 5) the void density of the piezoelectric material; 6) the chemical constituency of the piezoelectric material; 7) the thermal history of the piezoelectric material; 8) the electromagnetic history of the piezoelectric material. The desired piezoelectric characteristic of each layer of piezoelectric material can be achieved by, for example, manipulating one or more of the above-identified parameters. 
     In an embodiment, layers of piezoelectric material that exhibit different degrees of expansion and/or shrinkage in response to the same electrical field are integrated into a piezoelectric element to cause the piezoelectric element to change shape or bend in response to the activation light. For example, if two adjacent layers of a piezoelectric element, which are adhered to each other into a monolithic element, expand different amounts in response to the same activation light, the piezoelectric element will bend. In an embodiment, the piezoelectric element includes at least two layers of piezoelectric material, having different piezoelectric characteristics, which are formed as a monolithic element. For example, the piezoelectric element is formed by building layers of piezoelectric material on top of each other using semiconductor processing techniques, e.g., crystal growth, deposition, sputtering, ion implantation, etc. In an embodiment, the layers of the piezoelectric element have different crystal orientations so that the two layers respond differently to the same electrical field. For example, the two layers have crystal orientations that are perpendicular to each other. In another embodiment, at least one of the layers of the piezoelectric element is made of an organic material. 
     Using a piezoelectric element with layers of piezoelectric material having different piezoelectric characteristics, the response of the piezoelectric element can be selected to optimize on/off switching. For example, the piezoelectric characteristics of the layers can be selected to: 1) maximize the shape change of the piezoelectric element in response to the activation light; 2) minimize hysteresis; 3) reduce the amount of power required to change the shape of the piezoelectric element; and 4) reduce the amount of heat generated by the switching technique. 
     Operation of the optical switch  100  depicted in  FIG. 1A  is now described with reference to  FIGS. 1A and 1B .  FIG. 1A  illustrates the piezoelectric element  104  in a non-activated state. In the non-activated state, the shape of the piezoelectric element is unchanged from its normal state, where the normal state of the piezoelectric element is the state of the element in the absence of an activation light. In the embodiment of  FIG. 1A , the piezoelectric element is basically flat in the non-activated state. The flat shape of the piezoelectric element allows a signal light  110  to pass through the signal channel  104  as indicated by the signal light entering and exiting the signal channel. 
       FIG. 1B  illustrates the piezoelectric element  104  in an activated state that results from the application of an activation light  112  to the piezoelectric element. In the embodiment of  FIG. 1B , the activation light is applied to the piezoelectric element by directing the activation light into the signal channel  102  in parallel with the signal light  110 . The activation light supplies an electrical field that effects the piezoelectric material. In the activated state, the shape of the piezoelectric element changes shape enough that the signal light is blocked from passing through the signal channel. The blocking of the signal light is indicated by the lack of the signal light exiting the signal channel. Once the activation light is removed from the signal channel, the piezoelectric element returns to its normal shape and the signal light is able once again to pass through the signal channel. 
     As described above, activation of the piezoelectric element  104  in response to the activation light  112  causes the shape of the piezoelectric element to change, thereby causing at least one dimension of the signal channel  102  to change.  FIG. 2A  is a cross-sectional view of the signal channel and the piezoelectric element of  FIG. 1A  when the piezoelectric element is in a non-activated state.  FIG. 2B  is a cross-sectional view of the signal channel and the piezoelectric element of  FIG. 1B  when the piezoelectric element is in an activated state. In the activated state, the piezoelectric element extends into the signal channel and reduces at least one dimension of the signal channel. As illustrated in  FIGS. 2A and 2B , the cross-sectional area of the signal channel is smaller in the activated state ( FIG. 2B ) than it is in the non-activated state ( FIG. 2A ). 
     As seen in the embodiment of  FIGS. 1A-2B , there is still an opening in the signal channel  102  even when the piezoelectric element  104  is in the activated state. Although there is still an opening in the signal channel even when the piezoelectric element is in the activated state, the opening in the signal channel is small enough that the signal light  110  is blocked from passing through the signal channel. The ability of a signal light to pass through the signal channel is a function of the dimensions of the signal channel and of the wavelength of the signal light. In general, light having a shorter wavelength is able to pass through a signal channel with a smaller dimension than light having a longer wavelength. 
       FIG. 3  depicts a graph of optical signal attenuation vs. a dimension of a signal channel. As illustrated in  FIG. 3 , the optical signal attenuation changes rapidly once the signal channel dimension reaches a certain dimension, referred to herein as the cutoff dimension. For example, at a dimension smaller than the cutoff dimension (e.g., about 5 angstroms), the attenuation rapidly rises and at a dimension larger than the cutoff dimension, the attenuation rapidly falls. The sharp response to a change in the signal channel dimension around the cutoff dimension, as indicated in  FIG. 3 , enables fast on/off switching by toggling the activation light such that a dimension of the signal channel switches between being larger or smaller than the cutoff dimension. 
     As described above, the state of the optical switch  100  is activated by applying an activation light  112  to the piezoelectric element  104 . Activation light can be applied to the piezoelectric element using different techniques. Some exemplary techniques for applying activation light to the piezoelectric element are described with reference to  FIGS. 4A-5B . 
       FIGS. 4A and 4B  illustrate a technique for changing the state of optical switch  100  that involves applying an activation light  112  having a shorter wavelength than the signal light  110 . Referring to  FIG. 4A , the optical switch  100  is in an on state when no activation light is applied to the piezoelectric element  104  and the signal light  110  passes through the signal channel  102 . As illustrated in  FIG. 4B , activation light  112  is applied to the piezoelectric element  104  to change the state of the optical switch  100  from on to off. In the off state, the activation light  112  causes the piezoelectric element  104  to change shape and block the passage of the signal light  110  through the signal channel  102 . In this example, the activation light  112  has a shorter wavelength than the signal light  110 . In particular, the wavelength of the activation light  112  is short enough that the activation light  112  is still able to pass through the signal channel even when the optical switch  100  is in an off state.  FIG. 4B  illustrates the case in which the activation light  112 , which has a shorter wavelength than the signal light  110 , is able to pass through the signal channel  102  even when the optical switch  100  is in the off state. 
       FIGS. 5A and 5B  illustrate a technique for changing the state of an optical switch  100  in which applying the activation light involves providing two light signals  112 A and  112 B, which are out of phase with each other, to the piezoelectric element  104  and then removing one of the light signals, light signal  112 A in the illustrated embodiment, leaving the remaining light signal, light signal  112 B in the illustrated embodiment, as the activation light. In this embodiment, the two signals  112 A and  112 B are out of phase with each other such that their electrical fields effectively cancel each other out (e.g., 180 degrees out of phase). Because the two out of phase signals cancel each other out, while the two out of phase signals are simultaneously applied to the piezoelectric element  104 , the piezoelectric element  104  is not activated. Once one of the light signals is removed, the electrical field of the remaining light signal is no longer canceled out and the remaining light signal activates the piezoelectric element.  FIG. 5A  illustrates the signal light  110  and both components of the out of phase light signals  112 A and  112 B passing through the signal channel  102 . As described above, the piezoelectric element  104  is not activated in this case because the two out of phase light signals cancel each other out. In  FIG. 5B , one of the out of phase light signals  112 A is removed, leaving the remaining light signal  112 B as the activation light. The activation light activates the piezoelectric element  104  and blocks the passage of the signal light  110  (and the activation light in this case) through the signal channel. In another embodiment, the power of one of the two light signals can be increased above the other light signal to overcome the canceling effect thereby providing the activation light. 
     Another technique for optimizing the performance of a light activated optical switch is to enhance the electrical field that is applied to the piezoelectric element in response to the activation light. In accordance with an embodiment of the invention, at least one conductive layer is located adjacent to the piezoelectric element of a light activated optical switch to enhance the electrical field that is applied to the piezoelectric element in response to the activation light. The conductive layer has free electrons or electron holes that are drawn to and collect at a surface adjacent to the piezoelectric element when the activation light is applied to the piezoelectric element. The collection of free electrons near the piezoelectric element enhances the electrical field that is applied to the piezoelectric element in response to the activation light. The enhanced electrical field can be used to enhance the performance of the piezoelectric element and ultimately to enhance the performance of the optical switch. For example, the enhanced electrical field contributed from the adjacent conductive layer enables the piezoelectric element to be activated with lower power and/or quicker than is possible when there is not a conductive layer adjacent to the piezoelectric element. 
     Without the conductive layer the electric field of the activation light alone activates the piezoelectric element. When a conductive layer is used, the conductive layer supplies charges that are gathered or dispersed by the electric field of the activation light. The electric field of the gathered charges adds to the electric field of the activation light. In this case, the piezoelectric element is acted upon by the electric field of the activation light and the electric field of the gathered charges. In the case of dispersed charges, matter is composed of positive and negative charges so when one is dispersed the other is expressed. In this case the electric field of the expressed charges adds to the electric field of the activation light and the effect on the piezoelectric element is enhanced. Electrons move in metal conductors, but positive holes can move in a semiconductor. 
       FIG. 6A  depicts an embodiment of a light activated optical switch  120  that includes a signal channel  122 , a piezoelectric element  124 , and a conductive layer  126  adjacent to the piezoelectric element  124 . The signal channel  122  and piezoelectric element  124  are similar to those described above, although the piezoelectric element  124  does not necessarily include different layers of piezoelectric material having different piezoelectric characteristics. The conductive layer  126  is a highly conductive material such as lead, tungsten, other metals, silicon doped with boron, silicon doped with arsenic, doped gallium arsenide, and/or other semiconductor materials. In an embodiment, the conductive layer  126  is adhered to a surface of the piezoelectric element  124 . For example, the conductive layer  126  may be deposited on a major surface of the piezoelectric element  124  using a metal deposition technique. In an alternative embodiment, the conductive layer  126  is formed of a semiconductor material with positive or negative charges that move instead of only negative charges. 
     Operation of the optical switch  120  depicted in  FIG. 6A  is now described with reference to  FIGS. 6A and 6B .  FIG. 6A  illustrates the piezoelectric element  124  in a non-activated state. In the non-activated state, the shape of the piezoelectric element  124  is unchanged from its normal state, where the normal state of the piezoelectric element  124  is the state of the element in the absence of an activation light. In the embodiment of  FIG. 6A , the piezoelectric element  124  is basically flat in the non-activated state. The flat shape of the piezoelectric element allows a signal light  128  to pass through the signal channel  122  as indicated by the signal light  128  entering and exiting the signal channel  122 . 
       FIG. 6B  illustrates the piezoelectric element  124  in an activated state that results from the application of an activation light  129  to the piezoelectric element  124 . In the embodiment of  FIG. 6B , the activation light  129  is applied to the piezoelectric element  124  by directing the activation light  129  into the signal channel  122  in parallel with the signal light  128 . When the activation light  129  is applied to the piezoelectric element, free electrons are drawn to the surface of the conductive layer  126  that is nearest the piezoelectric element  124 . In the activated state, the shape of the piezoelectric element  124  changes shape enough that the signal light  128  is blocked from passing through the signal channel  122 . The blocking of the signal light  128  is indicated by the lack of the signal light  128  exiting the signal channel  122 . The additional electrons near the piezoelectric material, which are associated with the conductive layer  126 , cause an increase in the electric field that is applied to the piezoelectric material of piezoelectric element  124 . The increase in the electrical field that is associated with the conductive layer  126  provides benefits that include, for example, increasing the magnitude of the change in shape of the piezoelectric element  124 , increasing the speed at which the piezoelectric element  124  changes shape, and/or reducing the amount of activation light required to achieve the desired shape change. 
       FIG. 7  illustrates the action of an electrical field  130  of the activation light  129  on the electrons of the conductive layer  126  of  FIGS. 6A and 6B . In  FIG. 7 , surface  132  is the surface of the conductive layer  126  nearest the activation light  129  and the surface  134  is the surface of the conductive layer  126  farthest from the activation light  129 . The comb-like structure in  FIG. 7  represents the electrical field under the influence of the conductive layer  126 . Each tooth  136  of the comb-like structure represents a portion of the electrical field and some of the teeth have wide extensions  138  at their ends. These wide extensions  138  represent the larger field that is contributed by the charges that move in the conductive layer  126  that is adjacent to the piezoelectric element  124 . The charges that move in response to the electric field of the activation light  129  are represented by dashed lines  140 . When the electric field is negative the charges in the conductive layer  126  are driven away from the near surface  132  of the conductive layer and enhance the negative field. When the electric field is positive the charges in the conductive layer come to the near surface  132  of the conductive layer and enhance the electric field. If the conductive layer  126  is not present, no charges would move because piezoelectric materials are not conductors but dielectric materials. Referring to  FIG. 7 , if the conductive layer  126  was removed leaving only a piezoelectric element (not shown), the teeth  136  on the comb like structure would have no extensions  138  on them. 
       FIG. 8  depicts an optical switch system  150  that includes a light activated optical switch  152  as described above with reference to  FIGS. 1A-7 . The optical switch system  150  of  FIG. 8  also includes an activation light system  154 , which includes an activation light source  156  and an activation light controller  158 . The optical switch system  150  is optically connected to a signal light source  160  to receive a signal light  161 . In the embodiment of  FIG. 8 , the signal light  161  is provided to the optical switch  152  via a signal light path  162  and an activation light  163  is provided to the optical switch  152  via an activation light path  164  and the signal light path  162 . The signal light  161  and activation light  163  are combined at a coupler  166 . The output of the optical switch  152  goes through an output path  168 . 
     The activation light system  154  controls the application of activation light  163  to the piezoelectric element (not shown) of the optical switch  152 . In the embodiment of  FIG. 8 , the activation light source  156  is a light source such as a light emitting diode (LED) or a laser that generates an activation light with the desired characteristics, e.g., the desired wavelength, intensity, phase of the activation light in relation to the other light in the signal channel, and polarization, and the activation light controller  158  controls the transmission of the activation light  163  from the activation light system. In an embodiment, the intensity of the activation light  163  must be great enough to sufficiently change the shape of the piezoelectric element of the optical switch  152  and in an embodiment, the intensity of the activation light  163  is greater than the intensity of the signal light  161 . The wavelength of the activation light  163  can be shorter or longer than the wavelength of the signal light  161 . As described above, if the wavelength of the activation light  163  is short enough, the activation light  163  may pass through the signal channel even when the piezoelectric element is activated and the signal light  163  is blocked. 
     The activation light system  154  can be configured to provide the activation light  163  to the optical switch  152  in many different ways. For example, in one embodiment, the activation light  163  is switched on and off by a second light activated optical switch, in another embodiment the angle of a mirror is changed to provide the activation light  163 , in another embodiment, an LED or laser is turned on/off, and in other embodiments, other switches may be employed to control the activation light  163 . The signal light source  160  generates the signal light  161  that is switched on and off by the optical switch  152  (i.e., allowed to pass through the optical switch  152  and blocked from passing through the optical switch  152 ). In an embodiment, the signal light source  160  is an optical transmitter that transmits digital data by modulating an optical signal (e.g., frequency or amplitude modulation). In an embodiment, the signal light  161  that is output by the signal light source  160  is an optical signal that communicates digital data in some way (e.g., amplitude or frequency modulation, logic, etc.) while the activation light  163  that is output by the activation light source  156  does not communicate digital data. For example, the signal light  161  may carry digital data in a modulated light format while the activation light  163  is not modulated to carry digital data. 
     In operation, the signal light  161  is provided to the optical switch  152  via the signal light source  160  and the application of the activation light  163  to the piezoelectric element of the optical switch  152  is controlled by the activation light system  154 . In one embodiment, the signal light  161  passes through the optical switch  152  when the activation light system  154  does not provide an activation light  163  to the optical switch  152  and is blocked from passing through the optical switch  152  when the activation light system  154  does provide an activation light  163  to the optical switch  152 . 
     In the optical switches described with reference to  FIGS. 1A-6B , the signal light and activation light are transmitted in the same signal channel. Various techniques can be used to combine the signal light and the activation light into the same signal channel.  FIG. 9  depicts an embodiment of an optical switch  152  and an optical coupler  166  that is used to couple the signal light  161  and the activation light  163  into the same signal channel  122 . In the embodiment of  FIG. 9 , the signal light  161  travels in signal light path  162 , such as a signal fiber, and the activation light  163  travels in activation light path  164 , such as an activation fiber. The signal light  161  and activation light  163  are coupled into the signal channel  122  by the optical coupler  166 . It is appreciated that, although in the illustrated embodiment of  FIG. 9  an optical coupler is shown, other suitable techniques for coupling the signal light  161  and the activation light  163  into the same signal channel  122  can be used. 
       FIGS. 10A-10E  depict different embodiments of the light activated optical switches described above with reference to  FIGS. 1A-9 .  FIG. 10A  depicts an embodiment of a light activated optical switch  170  in which the piezoelectric element  172  has more than two layers  174  of piezoelectric material with different piezoelectric characteristics. In the illustrated embodiment of  FIG. 10 , the piezoelectric element  172  has four layers  174  of piezoelectric material. In one embodiment, the different layers  174  of piezoelectric material each have a different piezoelectric characteristic and in another embodiment, the different layers of piezoelectric material have alternating piezoelectric characteristics. It should be understood that the number and arrangement of piezoelectric layers  174  can include many different variations. 
       FIG. 10B  depicts an embodiment of a light activated optical switch  176  in which a conductive layer  178  is sandwiched between two layers  180  of a piezoelectric element  182 . This embodiment allows the piezoelectric element  182  to be oriented by placing charges on the conductive layer  178  and causes the change in shape of each layer  180  of the piezoelectric element  182  to be enhanced because of the proximity of the piezoelectric layers  180  to the conductive layer  178 . 
       FIG. 10C  depicts an embodiment of a light activated optical switch  184  in which multiple conductive layers  185  are sandwiched between multiple different layers  186  of the piezoelectric element  187 . In this example, the conductive layers  185  are alternately adhered between different layers  186  of the piezoelectric element  187 . The multiple layers  185  of conductive material between the piezoelectric layers  186  allow each layer  186  of piezoelectric material to be polarized individually to different orientations by applying a charge to the conductive layers  185 . This enables the action of the piezoelectric layers  186  working against each other to accentuate the change in shape of the piezoelectric element  187 . 
     In general, the multiple conductive layers allow the hysteresis of the piezoelectric element to be managed. The multiple conductive layers allow a reduction in the temperature that the piezoelectric element must be raised to in order to change the orientation of the piezoelectric material. The multiple conductive layers allow the change in shape of the piezoelectric element to be enhanced. The multiple conductive layers allow the management of many mechanical, electrical, thermal, and other physical characteristics of the optical switch to be managed to make the optical switch easier to be constructed, maintained, and used. In an embodiment, the different layers of piezoelectric material and the conductive layers are formed in a monolithic stack structure. The monolithic stack structure can be formed, for example, using known semiconductor processing techniques, e.g., crystal growth, metal deposition, sputtering, ion implantation, etc. 
     In some cases, the hysteresis of a piezoelectric element can limit how quickly a light activated optical switch, which is made with a piezoelectric element, can be changed from one state to another. In an embodiment, a 3000 angstroms thick layer of lead zirconate titonate (PZT) is deposited on a substrate. The layer of PZT has a given percentage of lead and a given percentage of zirconium and titanium. Next, a 3000 angstrom layer of PZT is deposited on the first layer, with this layer having more lead and zirconium while reducing the percentage of titanium on top of that. Using these layers, the hysteresis that the resulting piezoelectric element displays is reduced in comparison to a piezoelectric element that does not include similar layers. If more alternating layers are deposited to build up a piezoelectric element, a quickly responding piezoelectric element can be fabricated. If all of this is deposited upon a conductive layer, the electric field of the activation light is enhanced to make a light activated optical switch that responds even faster. 
       FIG. 10D  depicts an embodiment of a light activated optical switch  188  that includes a multilayer piezoelectric element  189  on one side of the signal channel  190  and conductive layers  191  on two sides of signal channel  190 . The response of the switch is enhanced by a multiplicity of conductive layers  191 . 
       FIG. 10E  depicts an embodiment of a light activated optical switch  192  that includes a multilayer piezoelectric element  194  and a conductive layer  196  on two sides of a signal channel  198 . In an embodiment,  FIG. 10E  represents a cross-sectional view of an optical fiber that includes a piezoelectric element and a conductive layer formed in a band entirely around the circumference of the optical fiber. In this embodiment, the fiber is a compressible material. 
       FIG. 11A  depicts an embodiment of a light activated optical switch  200  that includes a signal channel  202 , a piezoelectric element  204 , and a conductive layer  206 , where a portion of the signal channel includes a chamber  208  that is filled with a compressible material. The compressible material may be, for example, a gas such as argon or nitrogen or a material such as a petroleum distillate or a silicon rubber. The chamber  208  filled with the compressible material is adjacent to the piezoelectric element  204  such that the piezoelectric element  204  can expand into the chamber  208  when activated by an activation light. In an embodiment, the piezoelectric element  204  forms a portion of the chamber  208 . In an embodiment, at least a portion of the chamber  204  is formed by a transparent material. 
     Operation of the optical switch  200  depicted in  FIG. 11A  is now described with reference to  FIGS. 11A and 11B .  FIG. 11A  illustrates the piezoelectric element  204  in a non-activated state. In the non-activated state, the shape of the piezoelectric element  204  is unchanged from its normal state, where the normal state of the piezoelectric element  204  is the state of the element in the absence of an activation light. In the embodiment of  FIG. 11A , the piezoelectric element  204  is basically flat in the non-activated state and does not protrude into the chamber  208 . The flat shape of the piezoelectric element  204  allows a signal light  210  to pass through the signal channel  202  (including the chamber  208 ) as indicated by the signal light  210  entering and exiting the signal channel  202 . 
       FIG. 11B  illustrates the piezoelectric element  204  in an activated state that results from the application of an activation light  212  to the piezoelectric element  204 . In the embodiment of  FIG. 11B , the activation light  212  is applied to the piezoelectric element  204  by directing the activation light  212  into the signal channel  202  in parallel with the signal light  210 . When the activation light  212  is applied to the piezoelectric element  204 , the piezoelectric element  204  protrudes into the chamber  208 , thereby compressing the compressible material within the chamber. In the activated state, the shape of the piezoelectric element  204  changes enough that the signal light  210  is blocked from passing through the signal channel  202 . The blocking of the signal light  210  is indicated by the lack of the signal light  210  exiting the signal channel  202 . When the activation light  212  is removed from the signal channel  202 , the piezoelectric element  204  returns to its normal state allowing the signal light  210  to pass. In the absence of the activation light  212 , the pressure of the compressed material within the chamber  208  helps to return the piezoelectric element  204  to its normal state. 
       FIG. 12A  depicts an embodiment of a light activated optical switch  220  that includes a signal channel  222 , a piezoelectric element  224 , and a conductive layer  226  adjacent to the piezoelectric element in which the signal channel  222  is an optical fiber and the piezoelectric element  224  and conductive layer  226  are formed in a band entirely around the circumference of the optical fiber.  FIG. 12A  illustrates the piezoelectric element  224  in a non-activated state. In the non-activated state, the shape of the piezoelectric element  224  is unchanged from its normal state, where the normal state of the piezoelectric element  224  is the state of the element in the absence of an activation light. In the embodiment of  FIG. 12A , the piezoelectric element  224  is basically flat in the non-activated state. The flat shape of the piezoelectric element  224  allows a signal light  230  to pass through the signal channel  222  as indicated by the signal light  230  entering and exiting the signal channel  222 .  FIG. 12B  illustrates the piezoelectric element  224  in an activated state that results from the application of an activation light  232  to the piezoelectric element  224 . In the embodiment of  FIG. 12B , the activation light  232  is applied to the piezoelectric element  224  by directing the activation light  232  into the signal channel  222  in parallel with the signal light  230 . In the activated state, the shape of the piezoelectric element  224  changes enough that the signal light  230  is blocked from passing through the signal channel  222 . For example, the change in shape of the piezoelectric element  224  has the effect of squeezing the optical fiber like a belt to choke the passage of the signal light  230 . The blocking of the signal light  230  is indicated by the lack of the signal light  230  exiting the signal channel  222 . Once the activation light  232  is removed from the signal channel  222 , the piezoelectric element  224  returns to its normal shape and the signal light  230  is able once again to pass through the signal channel  222 . 
       FIG. 13A  depicts an embodiment of a light activated optical switch  240  that includes a signal channel  242 , a piezoelectric element  244 , and a conductive layer  246  adjacent to the piezoelectric element  244  in which the piezoelectric element  244  is made of a transparent material and forms at least a portion of the signal channel  242 .  FIG. 13A  illustrates the piezoelectric element  244  in a non-activated state. In the non-activated state, the shape of the piezoelectric element  244  is unchanged from its normal state, where the normal state of the piezoelectric element  244  is the state of the element in the absence of an activation light. In the embodiment of  FIG. 13A , the piezoelectric element  244  is basically flat in the non-activated state. The flat shape of the piezoelectric element  244  allows a signal light  250  to pass through the signal channel  242  as indicated by the signal light  250  entering and exiting the signal channel  242 .  FIG. 13B  illustrates the piezoelectric element  244  in an activated state that results from the application of an activation light  252  to the piezoelectric element. In the embodiment of  FIG. 13B , the activation light  252  is applied to the piezoelectric element  244  by directing the activation light  252  into the signal channel  242  in parallel with the signal light  250 . In the activated state, the shape of the piezoelectric element  244  changes enough that the signal light  250  is blocked from passing through the signal channel  242 . For example, the change in shape of the piezoelectric element  244  has the effect of squeezing the signal channel  242  like a belt to choke the passage of the signal light  250 . The blocking of the signal light  250  is indicated by the lack of the signal light  250  exiting the signal channel  242 . Once the activation light  252  is removed from the signal channel  242 , the piezoelectric element  244  returns to its normal shape and the signal light  250  is able once again to pass through the signal channel  242 . 
     In an embodiment, the piezoelectric element and the signal channel are configured relative to each other such that application of the activation light changes the state of the optical switch from off (light is blocked) to on (light passes through the signal channel) instead of from on to off. 
     Some piezoelectric materials have a crystal orientation that must be aligned with the electric field that will cause it to change shape. Other piezoelectric materials can be heated up in a magnetic field and oriented to respond in the desired direction to the electric field that will be applied. In constructing a light activated optical switch, the orientation of the crystal or the magnetic orientation of the piezoelectric material should be directed to have the maximum shape change at right angles (that is perpendicular) to the direction of the signal light in the signal channel. In an embodiment, the electric field that triggers the switching is at right angles (that is perpendicular) to the path of the light in the light channel. 
     A description of a desired interaction follows. The electric field in volts needed to activate a light activated optical switch is calculated using the power in watts of the light in the channel. The Poynting vector equation which is written E=(2μ o  c P) 1/2  is used to make this calculation. Where μ o  is 4 pi×10E−7 Weber/amp-meter, c is 3×10E+8 meters/second, E is the electric field in volts, and P is power in watts. Using this relation, it is found that the voltage developed by a 150-milliwatt signal in a fourth of a micron channel is 10 volts. In an embodiment, this voltage is employed to activate a light triggered optical switch to turn on or off the switch (e.g., allow the signal light to pass through the signal channel or to block the signal light from passing through the signal channel). An example of the size change that 10 volts could cause is as follows: In a channel that is 2065 angstroms in height, 10 volts will change that size by 40 angstroms when lead zicronate titonate is used. Lead zicronate titonate has a piezoelectric strain coefficient of 3.90 times 10E−10 meters/volt. 818 nm light (8180 angstroms), commonly used for fiber optics, will be able to travel in a channel just bigger than 2045 angstroms and will not travel down a channel smaller. When the 2065 angstroms channel changes to 2014 angstroms, the signal light will be blocked. Light of 8056 angstroms wavelength or shorter could still pass through the signal channel. The light activated optical switch can be turned on or off at a rate in 10E−11 seconds or faster. It makes use of effects that the electric and magnet fields of the light have on the medium through which the light travels. The equation for the attenuation (A) of the signal inside a wave-guide, which will give the decibels of attenuation per mile of travel for the signal is as follows:
 
 A =( K/a   3/2 )((1/2)( f/f   o ) 3/2 +( f/f   o ) −1/2 )/(( f/f   o ) 2 −1) −1/2   eq. (1)
 
     The K is a constant for the material that the walls of the channel are made of; the value of K is 821.3 for lead. Since in an embodiment, only one wall of the optical switch is mostly lead, the optical switch may not follow exactly the graph of  FIG. 3 , but the graph is given for illustrative purposes. The lower case “a” in the equation is the length of a side of the wave-guide. The frequency (f) of the signal being considered is in ratio against the cutoff frequency (f o ) in the channel. This equation is for the TE 0,1  mode of wave propagation. In an embodiment, the sizes of the waveguides are chosen so that this is the only mode possible. As this relation is studied for shrinking waveguide dimensions for a given signal, the attenuation increases as the size of the signal channel shrinks and proceeds to infinity as the cutoff frequency is reached. This equation is on page 263 of Radio Engineers&#39; Handbook written by Frederick Terman, and published by McGraw-Hill Book Company, Inc, 1943. 
     Reference is now made to  FIG. 14A , which illustrates an optical switch  300  that includes a signal channel  302  and a plurality of piezoelectric elements which are preferably unevenly spaced along the length of the signal channel  302 . In the illustrated embodiment three generally rectangular piezoelectric elements  304 ,  305  and  306  are distributed along the length of the signal channel  302  with non-uniform spacing therebetween. The shape of the piezoelectric elements  304 ,  305  and  306  is controlled by an activation light. The signal channel  302  guides the transmission of light within a confined area along a defined path. The signal channel  302  is formed by a light guiding structure, or combination of structures, which can guide light within a confined area along a defined path. Structures that can form the signal channel include, for example, an optical fiber, substrates such as lithium niobate or other transparent piezoelectric materials that include a signal channel, an optical waveguide, and a chamber for holding a compressible material. In the embodiment of  FIG. 14A , the signal channel  302  is preferably formed by a monolithic light guiding element. 
     The piezoelectric elements  304 ,  305  and  306  are preferably formed of piezoelectric material. Examples of piezoelectric material that can be used to form the piezoelectric elements include crystalline piezoelectric material such as quartz (SiO 2 ), lithium niobate (LiNbO 3 ), lead zirconate (PbZrO 3 ), lead titanate (PbTiO 3 ), and lead zirconate titanate. Examples of piezoelectric materials that can be oriented in a magnetic field are lead zirconate and lead titanate or lead zicronate titantae. Quartz and lithium niobate are examples of transparent piezoelectric materials. 
     The piezoelectric elements  304 ,  305  and  306  preferably each include at least two layers  307  and  308  of piezoelectric material having different piezoelectric characteristics. The different piezoelectric characteristics of the different layers  307  and  308  may include, for example: 1) different degrees of expansion and/or shrinkage in response to the same electrical field; 2) different responses to the same electrical field, for example, one of the layers expands in response to an electrical field having a first orientation and the other layer expands in response to an electrical field having a second orientation that is perpendicular to the first orientation; 3) different polarities; 4) different strains; 5) different hysteresis; 6) different capacitances; 7) different impedances; 8) different resistivities; 9) different thermal histories; and 10) different electromagnetic histories. 
     Operation of the optical switch  300  depicted in  FIG. 14A  is now described with additional reference to  FIG. 14B .  FIG. 14A  illustrates the piezoelectric elements  304 ,  305  and  306  in a non-activated state. In the non-activated state, the shape of the piezoelectric elements  304 ,  305  and  306  is unchanged from its normal state, where the normal state of the piezoelectric elements  304 ,  305  and  306  is the state of the element in the absence of an activation light. In the embodiment of  FIG. 14A , the piezoelectric elements  304 ,  305  and  306  are basically flat in the non-activated state. The flat shape of the piezoelectric elements  304 ,  305  and  306  allows a signal light  310  to pass through the signal channel  302  as indicated by the signal light  310  entering and exiting the signal channel  302 . 
       FIG. 14B  illustrates the piezoelectric elements  304 ,  305  and  306  in an activated state that results from the application of an activation light  312  to the piezoelectric elements  304 ,  305  and  306 . In the embodiment of  FIG. 14B , the activation light  312  is applied to the piezoelectric elements  304 ,  305  and  306  by directing the activation light  312  into the signal channel  302  in parallel with the signal light  310 . The activation light  312  supplies an electrical field that effects the piezoelectric material. In the activated state, the shape of the piezoelectric elements  304 ,  305  and  306  changes enough so that the signal light  310  is blocked from passing through the signal channel  302 . The blocking of the signal light  310  is indicated by the lack of the signal light  310  exiting the signal channel  302 . Once the activation light  312  is removed from the signal channel  302 , the piezoelectric elements  304 ,  305  and  306  return to normal shape and the signal light  310  is able once again to pass through the signal channel  302 . 
     As described above, activation of the piezoelectric elements  304 ,  305  and  306  in response to the activation light  312  causes the shape of the piezoelectric elements  304 ,  305  and  306  to change, thereby causing at least one dimension of the signal channel  302  to change.  FIG. 15A  is a cross-sectional view of the signal channel  302  and the piezoelectric element  305  of  FIG. 14A  when the piezoelectric element  305  is in a non-activated state.  FIG. 15B  is a cross-sectional view of the signal channel  302  and the piezoelectric element  305  of  FIG. 14B  when the piezoelectric element  305  is in an activated state. In the activated state, the piezoelectric element  305  extends into the signal channel  302  and reduces at least one dimension of the signal channel  302 . As illustrated in  FIGS. 15A and 15B , the cross-sectional area of the signal channel  302  is smaller in the activated state ( FIG. 15B ) than it is in the non-activated state ( FIG. 15A ). 
     As seen in the embodiment of  FIGS. 14A-15B , there is still an opening in the signal channel  302  even when the piezoelectric elements  304 ,  305  and  306  are in the activated state. Although there is still an opening in the signal channel  302  even when the piezoelectric elements  304 ,  305  and  306  are in the activated state, the opening in the signal channel  302  is small enough that the signal light  310  is blocked from passing through the signal channel  302 . The ability of a signal light  310  to pass through the signal channel  302  is a function of the dimensions of the signal channel  302  and of the wavelength of the signal light  310 . In general, light having a shorter wavelength is able to pass through a signal channel  302  having a smaller dimension than light having a longer wavelength. 
     Reference is now made to  FIG. 16A  which illustrates an optical switch  400  that includes a signal channel  402  and a plurality of piezoelectric elements which are preferably unevenly spaced along the length of the signal channel  402 . In the illustrated embodiment, four generally circular cylindrical piezoelectric elements  404 ,  405 ,  406  and  407  are distributed along the length of the signal channel  402  with non-uniform spacing therebetween. The shape of the piezoelectric elements  404 ,  405 ,  406  and  407  is controlled by an activation light. The signal channel  402  guides the transmission of light within a confined area along a defined path. The signal channel is formed by a light guiding structure, or combination of structures, which can guide light within a confined area along a defined path. Structures that can form the signal channel include, for example, an optical fiber, substrates such as lithium niobate or other transparent piezoelectric materials that include a signal channel, an optical waveguide, and a chamber for holding a compressible material. In the embodiment of  FIG. 16A , the signal channel  402  is preferably formed by a monolithic light guiding element. 
     The piezoelectric elements  404 ,  405 ,  406  and  407  are preferably formed of piezoelectric material. Examples of piezoelectric material that can be used to form the piezoelectric element include crystalline piezoelectric material such as quartz (SiO 2 ), lithium niobate (LiNbO 3 ), lead zirconate (PbZrO 3 ), lead titanate (PbTiO 3 ), and lead zirconate titanate. Examples of piezoelectric materials that can be oriented in a magnetic field are lead zirconate and lead titanate or lead zicronate titantae. Quartz and lithium niobate are examples of transparent piezoelectric materials. 
     The piezoelectric elements  404 ,  405 ,  406  and  407  preferably each include at least two layers  408  and  409  of piezoelectric material having different piezoelectric characteristics. The different piezoelectric characteristics of the different layers may include, for example: 1) different degrees of expansion and/or shrinkage in response to the same electrical field; 2) different responses to the same electrical field, for example, one of the layers expands in response to an electrical field having a first orientation and the other layer expands in response to an electrical field having a second orientation that is perpendicular to the first orientation; 3) different polarities; 4) different strains; 5) different hysteresis; 6) different capacitances; 7) different impedances; 8) different resistivities; 9) different thermal histories; and 10) different electromagnetic histories. 
     Operation of the optical switch  400  depicted in  FIG. 16A  is now described with additional reference to  FIG. 16B .  FIG. 16A  illustrates the piezoelectric elements  404 ,  405 ,  406  and  407  in a non-activated state. In the non-activated state, the shape of the piezoelectric elements  404 ,  405 ,  406  and  407  is unchanged from its normal state, where the normal state of the piezoelectric elements  404 ,  405 ,  406  and  407  is the state of the element in the absence of an activation light. In the embodiment of  FIG. 16A , the piezoelectric elements  404 ,  405 ,  406  and  407  are basically flat in the non-activated state. The flat shape of the piezoelectric elements  404 ,  405 ,  406  and  407  allows a signal light  410  to pass through the signal channel  402  as indicated by the signal light  410  entering and exiting the signal channel  402 . 
       FIG. 16B  illustrates the piezoelectric elements  404 ,  405 ,  406  and  407  in an activated state that results from the application of an activation light  412  to the piezoelectric elements  404 ,  405 ,  406  and  407 . In the embodiment of  FIG. 16B , the activation light  412  is applied to the piezoelectric elements  404 ,  405 ,  406  and  407  by directing the activation light  412  into the signal channel  402  in parallel with the signal light  410 . The activation light  412  supplies an electrical field that effects the piezoelectric material. In the activated state, the shape of the piezoelectric elements  404 ,  405 ,  406  and  407  changes enough so that the signal light  410  is blocked from passing through the signal channel  402 . The blocking of the signal light  410  is indicated by the lack of the signal light  410  exiting the signal channel  402 . Once the activation light  412  is removed from the signal channel  402 , the piezoelectric elements  404 ,  405 ,  406  and  407  return to normal shape and the signal light  410  is able once again to pass through the signal channel  402 . 
     As described above, activation of the piezoelectric elements  404 ,  405 ,  406  and  407  in response to the activation light  412  causes the shape of the piezoelectric elements  404 ,  405 ,  406  and  407  to change, thereby causing at least one dimension of the signal channel  402  to change.  FIG. 17A  is a cross-sectional view of the signal channel  402  and the piezoelectric element  406  of  FIG. 16A  when the piezoelectric element  406  is in a non-activated state.  FIG. 11B  is a cross-sectional view of the signal channel  402  and the piezoelectric element  406  of  FIG. 16B  when the piezoelectric element  406  is in an activated state. In the activated state, the piezoelectric element  406  extends into the signal channel  402  and reduces at least one dimension of the signal channel  402 . As illustrated in  FIGS. 17A and 17B , the cross-sectional area of the signal channel  402  is smaller in the activated state ( FIG. 17B ) than it is in the non-activated state ( FIG. 17A ). 
     As seen in the embodiment of  FIGS. 16A-17B , there is still an opening in the signal channel  402  even when the piezoelectric elements  404 ,  405 ,  406  and  407  are in the activated state. Although there is still an opening in the signal channel  402  even when the piezoelectric elements  404 ,  405 ,  406  and  407  are in the activated state, the opening in the signal channel  402  is small enough that the signal light  410  is blocked from passing through the signal channel  402 . The ability of a signal light  410  to pass through the signal channel  402  is a function of the dimensions of the signal channel  402  and of the wavelength of the signal light  410 . In general, light having a shorter wavelength is able to pass through a signal channel having a smaller dimension than light having a longer wavelength. 
     Reference is now made to  FIG. 18A , which illustrates an optical switch  500  that includes a signal channel  502  and a plurality of piezoelectric element which are preferably unevenly spaced along the length of the signal channel  502 . In the illustrated embodiment three generally oval cylindrical piezoelectric elements  504 ,  505  and  506  are distributed along the length of the signal channel  502  with non-uniform spacing therebetween. The shape of the piezoelectric elements  504 ,  505  and  506  is controlled by an activation light. The signal channel  502  guides the transmission of light within a confined area along a defined path. The signal channel  502  is formed by a light guiding structure, or combination of structures, which can guide light within a confined area along a defined path. Structures that can form the signal channel include, for example, an optical fiber, substrates such as lithium niobate or other transparent piezoelectric materials that include a signal channel, an optical waveguide, and a chamber for holding a compressible material. In the embodiment of  FIG. 18A , the signal channel  502  is preferably formed by a monolithic light guiding element. 
     The piezoelectric elements  504 ,  505  and  506  are preferably formed of piezoelectric material. Examples of piezoelectric material that can be used to form the piezoelectric element include crystalline piezoelectric material such as quartz (SiO 2 ), lithium niobate (LiNbO 3 ), lead zirconate (PbZrO 3 ), lead titanate (PbTiO 3 ), and lead zirconate titanate. Examples of piezoelectric materials that can be oriented in a magnetic field are lead zirconate and lead titanate or lead zicronate titantae. Quartz and lithium niobate are examples of transparent piezoelectric materials. 
     The piezoelectric element  504 ,  505  and  506  preferably each include at least two layers  507  and  508  of piezoelectric material having different piezoelectric characteristics. The different piezoelectric characteristics of the different layers  507  and  508  may include, for example: 1) different degrees of expansion and/or shrinkage in response to the same electrical field; 2) different responses to the same electrical field, for example, one of the layers expands in response to an electrical field having a first orientation and the other layer expands in response to an electrical field having a second orientation that is perpendicular to the first orientation; 3) different polarities; 4) different strains; 5) different hysteresis; 6) different capacitances; 7) different impedances; 8) different resistivities; 9) different thermal histories; and 10) different electromagnetic histories. 
     The piezoelectric characteristics of a piezoelectric material are a function of, for example: 1) the type of piezoelectric material; 2) the crystal orientation of the piezoelectric material; 3) doping levels within the piezoelectric material; 4) the density of the piezoelectric material; 5) the void density of the piezoelectric material; 6) the chemical constituency of the piezoelectric material; 7) the thermal history of the piezoelectric material; 8) the electromagnetic history of the piezoelectric material. The desired piezoelectric characteristic of each layer of piezoelectric material can be achieved by, for example, manipulating one or more of the above-identified parameters. 
     Preferably, layers of piezoelectric material that exhibit different degrees of expansion and/or shrinkage in response to the same electrical field are integrated into a piezoelectric element to cause the piezoelectric element to change shape or bend in response to the activation light. For example, if two adjacent layers of a piezoelectric element, which are adhered to each other into a monolithic element, expand different amounts in response to the same activation light, the piezoelectric element will bend. In an embodiment, the piezoelectric element includes at least two layers of piezoelectric material, having different piezoelectric characteristics, which are formed as a monolithic element. For example, the piezoelectric element is formed by building layers of piezoelectric material on top of each other using semiconductor processing techniques, e.g., crystal growth, deposition, sputtering, ion implantation, etc. In an embodiment, the layers of the piezoelectric element have different crystal orientations so that the two layers respond differently to the same electrical field. For example, the two layers have crystal orientations that are perpendicular to each other. In another embodiment, at least one of the layers of the piezoelectric element is made of an organic material. 
     By using a piezoelectric element with layers of piezoelectric material having different piezoelectric characteristics, the response of the piezoelectric element can be selected to optimize on/off switching. For example, the piezoelectric characteristics of the layers can be selected to: 1) maximize the shape change of the piezoelectric element in response to the activation light; 2) minimize hysteresis; 3) reduce the amount of power required to change the shape of the piezoelectric element; and 4) reduce the amount of heat generated by the switching technique. 
     Operation of the optical switch  500  depicted in  FIG. 18A  is now described with additional reference to  FIG. 18B .  FIG. 18A  illustrates the piezoelectric elements  504 ,  505  and  506  in a non-activated state. In the non-activated state, the shape of the piezoelectric elements  504 ,  505  and  506  is unchanged from its normal state, where the normal state of the piezoelectric elements  504 ,  505  and  506  is the state of the element in the absence of an activation light. In the embodiment of  FIG. 18A , the piezoelectric elements  504 ,  505  and  506  are basically flat in the non-activated state. The flat shape of the piezoelectric elements  504 ,  505  and  506  allows a signal light  510  to pass through the signal channel  502  as indicated by the signal light  510  entering and exiting the signal channel  502 . 
       FIG. 18B  illustrates the piezoelectric elements  504 ,  505  and  506  in an activated state that results from the application of an activation light  512  to the piezoelectric elements  504 ,  505  and  506 . In the embodiment of  FIG. 18B , the activation light  512  is applied to the piezoelectric elements  504 ,  505  and  506  by directing the activation light  512  into the signal channel  502  in parallel with the signal light  510 . The activation light  512  supplies an electrical field that effects the piezoelectric material. In the activated state, the shape of the piezoelectric elements  504 ,  505  and  506  change enough so that the signal light  510  is blocked from passing through the signal channel  502 . The blocking of the signal light  510  is indicated by the lack of the signal light  510  exiting the signal channel  502 . Once the activation light  512  is removed from the signal channel  502 , the piezoelectric elements  504 ,  505  and  506  return to normal shape and the signal light  510  is able once again to pass through the signal channel  502 . 
     As described above, activation of the piezoelectric elements  504 ,  505  and  506  in response to the activation light  512  causes the shape of the piezoelectric elements  504 ,  505  and  506  to change, thereby causing at least one dimension of the signal channel  502  to change.  FIG. 19A  is a cross-sectional view of the signal channel  502  and the piezoelectric element  505  of  FIG. 18A  when the piezoelectric element  505  is in a non-activated state.  FIG. 19B  is a cross-sectional view of the signal channel  502  and the piezoelectric element  505  of  FIG. 18B  when the piezoelectric element  505  is in an activated state. In the activated state, the piezoelectric element  505  extends into the signal channel  502  and reduces at least one dimension of the signal channel  502 . As illustrated in  FIGS. 19A and 19B , the cross-sectional area of the signal channel  502  is smaller in the activated state ( FIG. 19B ) than it is in the non-activated state ( FIG. 19A ). 
     As seen in the embodiment of  FIGS. 18A-19B , there is still an opening in the signal channel  502  even when the piezoelectric elements  504 ,  505  and  506  are in the activated state. Although there is still an opening in the signal channel  502  even when the piezoelectric elements  504 ,  505  and  506  are in the activated state, the opening in the signal channel  502  is small enough that the signal light  510  is blocked from passing through the signal channel  502 . The ability of a signal light  510  to pass through the signal channel  502  is a function of the dimensions of the signal channel  502  and of the wavelength of the signal light  510 . In general, light having a shorter wavelength is able to pass through a signal channel having a smaller dimension than light having a longer wavelength. 
     It is appreciated that all computer logic can be done with three logic gates. These are the AND, OR, and NOR logic gates. These handle digital signals in specific ways that are described using a truth table. The truth table gives the signal that will be output from the gate when specified signals are input into the gate. 
     
       
         
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 INPUT A 
                 INPUT B 
                 AND OUTPUT 
               
               
                   
               
             
             
               
                 0 
                 0 
                 0 
               
               
                 0 
                 1 
                 0 
               
               
                 1 
                 0 
                 0 
               
               
                 1 
                 1 
                 1 
               
               
                   
               
             
          
         
       
     
     Table 1 is a truth table for the logical AND gate. The ones in the A and B input columns indicate that a digital signal pulse is entering the gate. The inputs can come in on the A input or the B input. Only when an input signal is found on both the A input and B input does an output pulse result from the AND gate. 
     
       
         
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 INPUT A 
                 INPUT B 
                 OR OUTPUT 
               
               
                   
               
             
             
               
                 0 
                 0 
                 0 
               
               
                 0 
                 1 
                 1 
               
               
                 1 
                 0 
                 1 
               
               
                 1 
                 1 
                 1 
               
               
                   
               
             
          
         
       
     
     Table 2 is a truth table for the logical OR gate. When an input signal is found on either the A input and B input or both an output pulse results from the OR gate. 
     
       
         
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                 INPUT A 
                 INPUT B 
                 NOR OUTPUT 
               
               
                   
               
             
             
               
                 0 
                 0 
                 1 
               
               
                 0 
                 1 
                 0 
               
               
                 1 
                 0 
                 0 
               
               
                 1 
                 1 
                 0 
               
               
                   
               
             
          
         
       
     
     Table 3 is a truth table for the logical NOR gate. Only when an input signal is not found on both the A input and B input does an output pulse result from the NOR gate. A NOR gate is often explained as an OR gate with a NOT gate on its output. 
     The logical NOT gate takes a signal and transforms it into its opposite. When there is a signal coming in, no signal is sent out, and when no signal is coming in, then a signal is sent out. 
     In present computer circuits, three transistors may be used to make a logical AND or A logical OR gate for electrical digital signals. In present computer circuits, four transistors may be used to make a logical NOR gate. Transistors switch in 10E−9 seconds. This determines how fast a computer can be made to function. Present computers function on the flow of electronic digital signals not light signals. Light signals are also called optical or photonic signals. 
     The present invention includes AND, OR and NOR logic gates based upon fiber optical switches that are actuated by light and not actuated by an electrical signal or transistor circuit. They require no battery, and if the correct switch is chosen, the gates can be made small enough for semiconductor size constraints. One example of a light activated optical switch is disclosed in U.S. Pat. No. 7,072,536, which incorporated by reference herein. Although one example of a light activated optical switch is identified, the logic gates can be formed using other type of light actuated optical switches. 
     In an embodiment of the present invention, the light that carries the digital information for the logic is a 1500 nm wavelength signal as in commonly used in present fiber optic channels. This signal can be changed into a 750 nm signal by using a Periodically Poled Lithium Niobate (PPLN) crystal that will double the frequency of the input signal. This frequency doubling makes the wavelength of the signal half of the original wavelength. The change to half of the wavelength is merely an example, as is PPLN. Other wave lengths and means could be used. 
     With a different configuration PPLN crystals can also produce 1500 nm wavelength light out of 750 nm light. Generally a PPLN element functions only for specific wavelengths and not for others at the same time. During these conversions, power is lost, but optical amplifiers can be used to boost the signal back up to necessary levels. For the present disclosure, the power boosting that is needed, will be included in the frequency doubling function. 
     Light can be in a fiber optic channel with light that is 180 degrees out of phase, and the electric field of the light will not be expressed. The light that is 180 degrees out of phase with it cancels the power of the light. 
     Reference is now made to  FIG. 20 , which is a schematic of a logical NOT gate  600  for fiber optic systems. In  FIG. 20 , an optical channel  601 , such as an optical fiber, brings in a 1500 nm signal that is needed by the logic gate  600 . An optical channel  603 , such as an optical fiber, that brings in the 1500 nm signal that will be changed by the logical NOT gate  600 . A wavelength reducer  605  doubles the frequency of the incoming signal so that it will be converted to a 750 nm signal, and it has incorporated in it any optical amplification function needed to prepare the signal to be useful after the frequency conversion is accomplished. Optical channel  601  joins with the output of wavelength reducer  605  and enters optical switch  607 . Optical switch  607  is a light activated optical switch as described above. Optical switch  607  will allow the 1500 nm signal to be output until a 750 nm signal comes from the wavelength reducer  605 . When a 750 nm signal comes from wavelength reducer  605 , no signal is output from optical switch  607 . Optical channel  609  provides the output signal from the logical NOT gate  600 . An output signal is only provided when no signal is input on optical channel  603 , thus providing a logical NOT gate. 
     Reference is now made to  FIG. 21 , which is a schematic of a logical AND gate  610 . An optical channel  611 , such as an optical fiber, supplies a higher frequency wave length signal to an optical switch  612  to actuate switch  612 . Optical channel  611  joins with the other fiber optic channels to enter optical switch  612  after the phase of the light in optical channel  611  is matched to the light entering a first logical input provided to the logical AND gate  610  along an optical channel  614 , by phase matcher  616 . Optical channel  614  divides, with half of the light going into a wavelength reducer  618 , then to phase matcher  616  and then joins with other optical channels to provide inputs to the optical switch  612 . The other half of the light in optical channel  614  is input directly into optical switch  612 . 
     A second logical input is provided to the logical AND gate  610  along an optical channel  620 . Optical channel  620  divides, with half of the light going into a wavelength reducer  622 , then to phase matcher  624  and then joins with other optical channels to provide inputs to the optical switch  612 . The other half of the light in optical channel  614  is input directly into optical switch  612 . 
     An optical channel  626  joins with the other fiber optic channels to provide inputs to optical switch  612  after the phase of the light in optical channel  626  is matched to the light of second logical input on optical channel  620  by phase matcher  624 . The output of the logical AND gate  610  is provided along optical channel  628 , and provides AND functionality as shown in Table 1. 
     A phase shifter  629  is provided so that inputs from optical channels  614  and  620  will be mutually out of phase by 180 degrees. Thus, optical switch  612  will open and provide an output signal when light is input along both optical channels  614  and  620  and will be closed and no output signal will be provided when light is only input on one of channels  614  and  620 . It is appreciated that no output signal will be provided when there is no light input on either of channels  614  and  620 . 
     Thus, the present invention provides a logical AND gate wherein digital signal lights coming into the first and second data inputs are divided into two channels one of which the wavelength is shortened and the phase is matched to switch activation signals. Additionally, a logical AND gate is provided where in the activation light that is phase matched to the shortened wavelength signal that goes into the optical switch and only opens to let a data signal out of the gate when a data signal is received into both inputs thereby satisfying the requirements of a logical AND gate. 
     Reference is now made to  FIG. 22 , which is a schematic illustration of a logical AND gate  630  that uses two light activated optical switches  632  and  634  to handle the digital light signal data. A first logical input signal of 1500 nm light is provided to the logical AND gate  630  along an optical channel  636  and a second logical input signal of 1500 nm light is provided to the logical AND gate  630  along an optical channel  638 . A first optical channel  640 , such as an optical fiber, supplies an actuation signal of 1500 nm light to optical switch  632  and a second optical channel  642  supplies an actuation signal of 1500 nm light to optical switch  634 . 
     A first and second wavelength reducer  642  and  646  double the frequency of the 1500 nm light so that it becomes 750 nm light. The power is also boosted up to the level needed to activate a light activated optical switch after the frequency is doubled. Optical switches have been designed to activate with an activation light power of 150 milliwatts. One half of the digital light signal output by wavelength reducers  642  and  646  along an optical channel  647  is provided to a light absorber  648  The other half of the light signal output from wavelength reducers  642  and  646  joins with the optical signal input on optical channel  640 , which is needed to make the logical AND gate  630  work. Optical switch  632  will allow the 1500 nm signal on optical channel  640  to pass through it until a 750 nm signal strong enough to close it is input to an optical channel  650 . This will occur when a 1500 nm signal comes in to the gate on optical channels  636  and  638 . An optical channel  652  provides the output signal from switch  632  to a wavelength reducer  654 . Wavelength reducer  654  doubles the frequency of the 1500 min signal output by optical switch  632  along optical channel  652 . 
     Optical channel  642  provides a 1500 nm signal into the logical AND gate  630  and joins it with the output of wavelength reducer  654 . Optical switch  634  will allow the 1500 nm signal from optical channel  642  to exit the switch as long as no signal is output from optical switch  632  via wavelength reducer  654 . 
     When there is only a signal entering on one of optical channels  636  and  638 , the 750 nm signal input into optical switch  632  is not sufficient to make switch  632  close and stop the flow of 1500 nm light from optical channel  640 . When a signal is provided on both optical channels  636  and  638 , the signal is sufficient to turn off the 1500 nm signal from optical channel  640 . 
     As long as the signal from optical channel  640  is output from switch  632  there will be no signal provided from optical switch  634 . 
     Only when a 1500 nm signal is provided on both optical channels  636  and  638  does the source light from optical channel  640  get turned off by optical switch  632  and only then is the input provided by optical channel  642  output from switch  634 , thus providing a logical AND gate, with an output of 1500 nm light only when a 1500 nm signal is provided on both optical channels  636  and  638 . This logical AND gate operates as in Table 1. 
     It is appreciated that the change to half of the wavelength is provided merely as an example. Other wave lengths and means could be used. 
     Thus, the present invention provides a logical AND gate wherein the wavelength of the two input signals are immediately shortened and divided to provide light for the activation of optical switches. Also provided is a logical AND gate wherein light with the wavelength shortened actuates a switch once a data signal enter both inputs of the gate that sends a data wavelength signal that is supplied to a second optical switch. The wavelength of the output signal is increased to be an actuating signal for second optical switch assuring that a data signal only leaves the logical AND gate when two inputs come into the two data ports of the gate there by satisfying the requirements of an logical AND gate. 
     Reference is now made to  FIG. 23 , which is a schematic illustration of a logical OR gate  700 . A first logical input signal of 1500 nm light is provided to the logical OR gate  700  along an optical channel  702  and a second logical input signal of 1500 nm light is provided to the logical AND gate  700  along an optical channel  704 . An optical channel  706  provides a source of 750 nm light that feeds an optical switch  708 . Optical switch  708  will remain closed and no output 1500 nm signal will be provided unless the 750 nm signal from optical channel  706  is canceled. 
     A first and second wavelength reducer  710  and  712  double the frequency of the 1500 mm signals provided along optical channels  702  and  704  so they become 750 nm signals. An optical amplifier integrated into the device boosts the power lost in the change of the frequency up again to a useful level. 
     Optical channel  714  carries the 750 nm signal output from wavelength reducer  710  to a phase matcher  716 . The phase matcher  716  makes the phase of the 750 nm signal from along optical channel  714  to be in phase with the source signal of 750 nm light along optical channel  706 . 
     An optical channel  718  provides the output from wavelength reducer  712  to a phase matcher  720 . The phase matcher  720  makes the phase of the signal along optical channel  718  to be in phase with the source signal of 750 nm light along optical channel  706 . 
     Optical channels  722  and  724  provide half of the light from the phase matchers  716  and  720 , respectively, to light absorbers  726  and  728 . Phase shifters  730  are half wave length paths that put the signals from optical channels  702  and  704  180 degrees out of phase with the light along optical channel;  706  that they have been specifically phase matched with. When they mix with the light along optical channel  706  they will cancel half of it out. 
     An optical channel  732  carries the 750 nm source light from phase matcher  720 , and joins it with the signals from phase shifters  730  and an optical channel  740 , which is a source of 1500 nm light that will flow out of switch  708  until a signal of sufficient power comes from optical channel  706  to shut it off. The signal is output from switch  708  along an optical channel  742 , thus providing a logical OR gate. 
     As long as the source of 750 nm light from optical channel  706  is fed into switch  708  no signal from source of 1500 nm light from optical channel  740  will be allowed to come out of the logical OR gate, but if a signal comes into either optical channel  702  or  704  then the light from optical channel  706  will be canceled to half power and a 1500 nm signal will be allowed to come out of the logical OR gate. 
     In addition, if a signal is provided on both optical channels  702  and  704  they will be of sufficient power together to totally cancel the source of 750 nm light from optical channel  706 , resulting in an output signal being provided by the logical OR gate  700 . 
     The last paragraph explained how the logical OR gate disclosed herein fulfills the requirements of the logical OR gate truth table seen in Table 2. When a signal is provided along optical channel  702  or  704  or both then a 1500 nm signal comes out of the logical OR gate  700 . 
     By providing a Logical NOT gate, as described in  FIG. 20 , on the output of a logical OR gate, described in  FIG. 23 , a logical NOR gate is made, which will function as the truth table shone in Table 3. 
     Reference is now made to  FIG. 24 , which is an alternative logical OR gate  800 . Lines  802  and  804  are optical channels or fibers that provide the optical digital signals A and B coming into the gate. These are 1500 nm light signals. Lines  806  and  807  are sources of 1500 nm light for the function of the logical OR gate. 
     Wavelength reducers  808  and  810  are frequency doublers that also boost the power of the light to levels that can activate a light activated optical switch after the frequency is doubled. Line  812  is a network of optical channels or fibers that carry the signals A and B from wavelength reducers  808  and  810  and combine with the signal from line  806  and carry all this into power limiter  814 . 
     Power limiter  814  allows power levels to pass on that are below a certain maximum. Lines numbered  818  are optical channels or fibers that carry signals from power limiter  814  to switch  816  to wavelength reducer  820 . Switch  816  is a light activated optical switch. Wavelength reducer  820  doubles the frequency of the signal coming out of switch  816 . 
     Switch  830  is a light activated optical switch. Line  807  is an optical channel or fiber that brings a 1500 nm signal to combine with the output of wavelength reducer  820  and carry it on to switch  830 . As long as there is a signal from wavelength reducer  820  no signal will come out of Switch  830 . 
     When a 1500 nm signal enters from Line  802  (the A signal) it is converted to 750 nm light in reducer  808  and passes through power limiter  814  unchanged and turns off the 1500 nm signal from Line  806  in switch  816 . So, no signal goes on to turn off the signal from Line  807  and the OR gate sends out a signal. When a signal comes from Line  804  (the B signal) passing through reducer  810  (doubling the frequency), power limiter  814  to switch  816 , and no signal from  806  goes on to turn off switch  830 . This allows a signal to go from Line  807  out of the gate through switch  830 . 
     If signals come from both Lines  802  and  804 , then the double output of the reducers  808  and  810  is limited by limiter  814  to be appropriate for shutting off the signal from line  806  in switch  816 . This will allow the signal from Line  807  to exit the logical OR gate. When a signal comes in to A or B or both then a 1500 nm signal comes out of the logical OR gate. This then functions as truth table in Table 2 proscribes, which describes the function of a logical, OR gate. 
     A logic gate providing OR functionality and wherein the at least one optical switch includes first and second optical switches and wherein the signal light has a wavelength greater than that of the activation light, the logic gate also including first and second logic inputs receiving signal light inputs, a first wavelength modifier operative to decrease the wavelength of the light along the first light input to the wavelength of the activation light; a second wavelength modifier operative to decrease the wavelength of the light along the second light input to the wavelength of the activation light; first and second light conduits supplying wavelength modified light from the first and second wavelength modifiers; a power limiter receiving light from the first wavelength modifier and second wavelength modifier via the respective first and second light conduits and being operative to maintain light output therefrom at a predetermined power level; a third light conduit supplying power limited light from the power limiter to the first optical switch; a third wavelength modifier receiving signal light from the first optical switch and being operative to decrease the wavelength of the light to the wavelength of the activation light; and a fourth light conduit supplying light from the third wavelength modifier to the second optical switch. 
     Reference is now made to  FIG. 25 , which is a schematic of a logical OR gate  900 . Optical channel  902  provides a first input to the logical gate  900 . Optical channel is a fiber optic channel that carries the light signal into the logic gate where it is divided in half. Half of the light is taken to a frequency increasing device numbered  905 . From frequency increasing device  905  the light proceeds through a half wave path numbered  906  that makes the light from  905  out of phase with the light it will meet from frequency increasing device  908 . The light from the half wave path  906  then combines with the light of the logic gate to inter optical switch  910 . The other half of the light from line  902 , which is logical input A joins with the other light of the logic gate to enter optical switch  910 . Line  904  is input B to the logic gate. Line  904  is a fiber optic channel that carries the light signal into the logic gate where it is divided in half. Half of the light is taken into a frequency increasing device numbered  908 . The light from frequency increasing device numbered  908  then combines with the other light in the logic gate to inter the optical switch numbered  910 . The other half of the light from line  904  joins with the other light of the logic device to inter optical switch  910 . Line  912  is the output of the logical OR device. 
     A logic gate providing OR functionality and wherein the at least one optical switch includes a single optical switch and wherein the signal light has a wavelength greater than that of the activation light, the logic gate also including first and second logic inputs receiving signal light, a first light conduit receiving a first portion of the signal light received at the first logic input, a second light conduit receiving a second portion of the signal light received at the first logic input, a third light conduit receiving a first portion of the signal light received at the second logic input, a fourth light conduit receiving a second portion of the signal light received at the second logic input, a first wavelength modifier operative to decrease the wavelength of the light along the second light conduit to the wavelength of the activation light, a second wavelength modifier operative to decrease the wavelength of the light along the fourth light conduit to the wavelength of the activation light and a phase shifter operative to cause wavelength modified light from the first wavelength modifier to be out of phase by 180 degrees with respect to the light from the second wavelength modifier, the optical switch receiving light from the first and third light conduits, the second wavelength modifier and the phase shifter. 
     A logical NOR gate that functions as the truth table in Table 3 shows is made by putting the logical NOT gate of  FIG. 20  on the output of the logical OR gate of  FIG. 24  or  25 . Although some examples of logic gates, which utilize light activated optical switches, are described, other embodiments of AND, OR, NOR and NOT logic gates can be produced using light activated optical switches. 
     It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove. Rather the invention includes both combinations and subcombinations of various features described hereinabove as well as modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not in the prior art.

Technology Category: g