WO2003056381A1

WO2003056381A1 - Superconductor optical switch

Info

Publication number: WO2003056381A1
Application number: PCT/US2002/023791
Authority: WO
Inventors: Erzhen Gao; Qiyuan Ma
Original assignee: Supertron Technologies, Inc.
Priority date: 2001-07-26
Filing date: 2002-07-24
Publication date: 2003-07-10
Also published as: WO2003056381A8; AU2002365067A1

Abstract

A superconductor optical switch (100) comprising a superconductor microbridge (110), a bias current source, and a pulse current source. The superconductor microbridge is formed from a superconducting material wherein the superconducting material can transition at a critical level between a superconducting optically reflective state and a non- superconducting optically transparent state. When the bias current source is actuated and the pulse current source is not actuated, the superconductor microbridge is maintained in its superconducting optically reflective state. When the pulse current source is actuated concurrently with the bias current source being actuated, the superconductor microbridge is maintained in its non-superconducting optically transparent state. In different aspects, an optical system including the superconductor optical switch (100) can alternatively accept light that is either reflected from, or transmitted through, the superconductor optical switch as a switch signal. In different aspects, the critical level can be a critical electric current level, a critical magnetic flux level, or a critical superconductor temperature level.

Description

SUPERCONDUCTOR OPTICAL SWITCH

Field of the Invention

This disclosure relates to optical switches, and more particularly to superconductor optical switches having components formed at least partially from a superconducting material.

Background of the Invention

Superconductor optical switches include components formed from superconducting materials. The properties of superconducting materials make superconductor optical switches suitable for a very high rate of optical switching by utilizing rapid transition characteristics between a superconducting state and a normal (i.e., non-superconducting) state. There has been difficulty in providing effective implementation of superconductor optical switches. A superconducting material is in its superconducting state only if each one of the electric current flowing through the superconducting material, the temperature of the superconducting material, and the magnetic field applied to the superconducting material are below their respective critical values. The critical electric current (I ), the critical temperature (Tc), and the critical magnetic field (He) of a superconducting material are each dependent on the chemical composition of the material and on the presence or absence of defects in the superconducting material.

Certain prior art superconductor optical switches use superconductor microbridges that transition the superconductor optical switches between their normal and their superconducting states. Pulse current signals are applied across the superconductor microbridge. The pulse current signals are configured so that the value of the electric current flowing through the superconductor microbridge transitions between a prescribed full value and a null value. At the prescribed full value, there is sufficient electric current being applied to the superconductor microbridge to position the superconductor microbridge in its normal state. At the null value, there is virtually no electric current flowing across the superconductor microbridge, and therefore the superconducting material of the superconductor microbridge remains in its superconducting state. Since the prescribed full value for electric current requires a much greater current in the superconductor microbridge than the null value, time is required for the current to transition between the prescribed full value and the null value. This relatively large transition time is reflected by a decreased potential switching rate of the superconductor optical switch. Since minimizing the switching rate of superconductor optical switches is desired, as with any switch, a decreased switching rate diminishes the effective utilization of the superconductor optical switch.

Electric contacts are applied to the input and output of superconductor optical switches. Fabricating electric contacts in superconductor switching devices involves the application of a metal that is electrically isolated from the superconductor. To limit the flow of electric current through the superconductor, there is an electric insulator layer formed between each electric contact and the superconducting material. This addition of the electric insulator layer requires an additional layering fabrication step.

It would therefore be desired to provide a superconductor optical switch that would provide an increased switching rate. In another aspect, it would also be desired to provide an optical device using a plurality of superconductor microbridges wherein each superconductor microbridge exhibits different superconductor transition characteristics. In yet another embodiment, it is desired to provide a bias circuit that would bias the superconductor microbridge of the superconductor optical switch to near the transition level of the switch. A small pulse current is thereupon applied to transition the superconductor optical switch between its normal and superconductor states. It would also be desired to limit the number of steps necessary to fabricate superconductor optical switches.

Summary of the Invention

It is therefore desired to provide a superconductor optical switch comprising a superconductor microbridge, a bias current source, and a pulse current source. The superconductor microbridge is formed from a superconducting material wherein the superconducting material can transition at a critical level between a superconducting optically reflective state and a non-superconducting optically transparent state. When the bias current source is actuated and the pulse current source is not actuated, the superconductor microbridge is maintained in its superconducting optically reflective state. When the pulse current source is actuated concurrently with the bias current source being actuated, the superconductor microbridge is maintained in its non-superconducting optically transparent state. In different aspects, an optical system including the superconductor optical switch can alternatively accept light that is either reflected from, or transmitted through, the superconductor optical switch as a switch signal. In different aspects, the critical level can be a critical electric current level, a critical magnetic flux level, or a critical superconductor temperature level. Brief Description Of The Drawings

FIG. 1 shows a schematic diagram of one embodiment of an optical system including a superconductor optical switch;

FIG. 2 shows a schematic diagram of another embodiment of the optical system including a superconductor optical switch;

FIG. 3 shows a top view of an embodiment of the superconductor optical switch as shown in FIGs. 1 and 2;

FIG. 4 shows a side cross-sectional view of one embodiment of the superconductor optical switch of FIG. 1; FIG. 5 shows a top view of another embodiment of the superconductor optical switch as shown in FIGs. 1 and 2;

FIG. 6 shows a side cross-sectional view of the superconductor optical switch of FIG. 5;

FIG. 7 shows a graph plotting an electric pulse current superimposed on an electric bias current of a superconductor optical switch;

FIG. 8 shows a top view of another embodiment of the superconductor optical switch in which the temperature of the superconductor microbridge is varied to transition the superconducting material of the superconductor microbridge between its superconducting and its normal states; FIG. 9 shows another embodiment of the superconductor optical switch in which the temperature of the superconductor microbridge is varied to transition the superconducting material of the superconductor microbridge between its superconducting and its normal states;

FIG. 10 shows one embodiment of a temperature control device of the embodiment of the superconductor optical switch shown in FIG. 9; FIG. 11 shows another embodiment of a superconductor optical switch in which the magnetic field applied to the superconductor microbridge is varied to transition the superconducting material of the superconductor microbridge between its superconducting and its normal states; FIG. 12 shows one embodiment of a magnetic field control device of the superconductor optical switch shown in FIG. 11;

FIG. 13 shows a cross-sectional view of one embodiment of an array of superconductor optical switches; and

FIG. 14 shows a side cross-sectional view of one embodiment of the superconductor optical switch of FIG. 2.

Throughout the figures, the same reference numerals and characters, unless otherwise stated, are used to denote like features, elements, components or portions of the illustrated embodiments.

Detailed Description of the Embodiments In this disclosure, the term "superconducting" describes a material whose electric resistance decreases to effectively zero when any one of the following occurs: the temperature of the superconducting material is reduced below a critical temperature (Tc) value; the electric current of the superconducting material is reduced below a critical electric current (Ic) value; or the magnetic field applied to the material is reduced below a critical magnetic field (He) value. The values of the critical electric current (Ic), critical temperature (Tc), and the critical magnetic field (He) of superconducting material are each dependant on the chemical composition of the superconducting material and on the presence or absence of defects in the superconducting material. The term "superconductor" describes a device, object, or other apparatus that includes a component that is formed at least partially

from superconducting material.

If the temperature, the electric current, or the magnetic field applied to the superconducting material rises above the respective critical values of the superconducting material, then the superconducting material leaves its superconducting state and enters its normal state. As the superconducting material enters its normal state, the properties of the superconducting material approach that of a typical superconducting material. In its normal state, the superconducting material is characterized by normal state resistivity and relatively low optical reflectivity. When the superconducting material is in its superconducting state, the superconducting material exhibits many of the properties of a theoretically perfect electric conductor and exhibits high optical reflectivity.

The term "superconducting material" comprises the metallic superconducting materials, the compound superconducting materials, and the oxide superconducting materials. Metallic superconducting materials are those superconducting materials that are formed from a single metal, such as Nb. Compound superconducting materials are those superconducting materials that are formed from a compound of materials such as MgB₂, NbSe, and NbTi. Oxide superconducting materials are those superconducting materials that are formed from oxides of compound or metallic superconducting materials. Oxide superconducting materials include superconducting oxides of metallic or compound materials such as YBaCuO and BiBaCaCuO. These examples of superconducting materials are intended to be exemplary in nature and not limited in scope since a wide variety of superconducting materials are presently known, and new superconducting materials are often being discovered.

FIG. 1 shows a view of one embodiment of the optical assembly 90 including a superconductor optical switch 100, an optical source 102, a plurality of channels 118, and an optical converter 119. The superconductor optical switch 100 receives light from an optical source 102. The optical source 102 generates a plurality of substantially parallel incident light beams 111. The incident light beams 111 are applied to an incident face 107 of the superconductor optical switch 100. The superconductor optical switch 100 includes certain components that are formed from, or coated with, a superconducting material. The superconductor optical switch 100 further comprises one or more superconductor microbridges 110. Each superconductor microbridge 110 is deposited on the incident face 107 and may be considered as an optical shutter that is used to control the transmission of optical signals into a respective one of the plurality of channels indicated as channel A 118 and channel B 118.

Each superconductor microbridge 110 may be opened by becoming optically reflective to allow light to pass across the superconductor optical switch 100 from the incident face 107 through the respective superconductor microbridge 110 into the respective channel A 118 or channel B 118 as shown in FIG. 1. Alternatively, each superconductor microbridge 110 may be switched to a closed position by becoming optically reflective as indicated by one of the superconductor microbridges 110 in FIG. 1. When a superconductor microbridge 110 is in its closed position, light directed from the optical source 102 to that superconductor microbridge 110 is limited from passing through the superconductor microbridge 110 to the respective channel 118. Those superconductor microbridges 110 that are in their respective open positions pass light from the optical source 102 to the optical converter 119. Those superconductor microbridges 110 that are in their respective closed positions limit light from passing from the optical source 102 to the optical converter 119. While there are two superconductor microbridges 110 shown associated with their respective channel A 118 and channel B 118, it is envisioned that a larger number of corresponding superconductor microbridges and channels may be provided as desired. Each superconductor microbridge 110, as described relative to the embodiment of superconductor optical switch 100 of FIG. 1 is configured to act as an optical switch when it switches between its open and closed states. The structure and operation of the superconductor microbridges 110 provide for the operation of the superconductor optical switch 100.

FIG. 2 shows another embodiment of optical assembly 90 that includes the superconductor optical switch 100. In this embodiment, the superconductor optical switch

100 is angled at an angle θ from the incident light beams 111 supplied by the optical source

102. In the FIG. 2 embodiment, the channels 118 of the superconductor optical switch 100 reflect certain regions of light to the optical converter 119 that it is desired to indicate as a "high" state. This indication of a "high" state compares with those regions of the superconductor optical switch 100 where the light is pennitted to be transmitted through the superconductor microbridges 110 and the channels 118 as is the case in the embodiment of superconductor optical switch 100 shown in FIG. 1. Additionally, the superconductor optical switch 100 transmits those regions of the optical light that it is desired to indicate as a "low" state (where the light is effectively discarded) instead of considering as a "low" state those regions of the superconductor optical switch where the light is reflected (as in the embodiment shown in FIG. 1). Controlling the regions of the superconductor optical switch 100 that transmit light compared to those regions in the embodiments of superconductor optical switch 100 shown in FIGs. 1 and 2 depends on transitioning the respective regions between their superconducting state and their non-superconducting (or normal) state as described below. Therefore, any embodiment of superconductor optical switch 100 as described below could be positioned in either the configuration of optical assembly 90 shown in FIG. 1 (where the high values are transmitted) or in the configuration of optical assembly 90 shown in FIG. 2 (where the high values are reflected). Each superconductor microbridge 110 can be biased with a bias current source and a pulse current source. The superconductor microbridge is formed from a superconducting material such that the superconducting material transitions at a critical electric current, temperature, or magnetic field level between a superconducting optically reflective state and a non-superconducting optically transparent state. When the bias current source is actuated and the pulse current source is not actuated, the superconductor microbridge is maintained in its superconducting optically reflective state. When the pulse current source is actuated concurrently with the bias current source being actuated, the superconductor microbridge is maintained in its non-superconducting optically transparent state. In different aspects, an optical system including the superconductor optical switch 100 can alternatively accept light that is either reflected from, or transmitted through, the superconductor optical switch 100 as a switch signal. In different aspects, the critical level can be a critical electric current density level, a critical magnetic flux level, or a critical superconductor temperature level. It is envisioned that the superconductor optical switch 100 may be configured as a discrete element or one of a plurality of superconductor optical switches arranged in an array of superconductor optical switches.

In one embodiment of the superconductor optical switch 100 shown in FIG. 2, it is preferred to angle an incident face 140 so that the incident angle 142 at which the incident light beams 111 from the optical source 102 strike the incident face 140 of the superconductor optical switch 100 equals the reflection angle 144 at which light is reflected from the incident face 140 of the superconductor optical switch 100 through the optical converter 119. This making the incident angle 142 equal to the reflection angle 144 ensures that the optical dimensions, phase, and characteristics of the incident light beams 111 applied from the optical source 102 are maintained in the light beams 118 that contact the optical converter 119. One benefit of the embodiment of superconductor optical switch 100 shown in FIG. 2 is that an entire refrigeration unit 148 can be applied at the backside of the superconductor optical switch 100. Light travelling through the superconductor optical switch 100 in the embodiment shown in FIG. 2 is not being used, so the refrigeration unit 148 does not affect light to be used as a signal. The refrigeration unit 148 is known in the industry as a "cold head." Another advantage of the embodiment of superconductor optical switch 100 shown in FIG. 2 is that light being transmitted from the optical source 102 that is applied to the incident face 140 of the superconductor optical switch 100 is being reflected to follow channels 118 and does not have to pass through the thickness of a substrate 115 (such as shown in FIG. 3) of the superconductor optical switch 100. Although the substrate 115 is relatively thin in many embodiments of the superconductor optical switch 100, a certain amount of the light will be diffracted, absorbed, or otherwise lost as it passes through the substrate 115 of the superconductor optical switch 100. As such, since the light that is utilized by the optical converter 119 in the embodiment shown in FIG. 2 is reflected on the incident face 140 of the superconductor optical switch 100, relatively little attenuation occurs of the original signal applied from the optical source 102.

FIGs. 3 and 4 show one embodiment of superconductor optical switch 100 in which the superconductor optical switch 100 operates by changing the electric current through the superconductor microbridge 110 above or below the critical electric current (Ic). The superconductor optical switch 100 comprises the plurality of superconductor regions 132, 134, electric contacts 106 (attached to each of the respective superconductor regions 132, 134), a superconductor microbridge 110 that extends between the superconductor regions 132, 134, a pulse current source 220 that provides a controllable electric current flow from the electric contact 106 connected to superconductor region 132 to the electric contact 106 connected to superconductor region 134, an electrical insulator 122 that generally surrounds - li the superconductor regions 132, 134, superconductor microbridges 110, a substrate 115 on which the electrical insulator 122 and the remainder are mounted, and an optical converter 119. In the embodiment of superconductor optical switch 100 shown in FIGs. 3 and 4, the temperature of the superconductor optical switch 100 is maintained at a level below the critical temperature Tc so that the superconductor regions of the superconductor optical switch 100 (e.g., the superconductor regions 132, 134 and the superconductor microbridge 110) can transition between their superconducting states and their normal states by altering the electric current applied to the superconductor microbridge 110.

Superconductor regions 132 and 134 are each of a sufficient cross-sectional area so that the application of an electric current flowing from the electric contact 106 connected to superconductor region 132 to the electric contact 106 connected to superconductor region 134 will not result in the electric current in the superconductor regions 132, 134 rising to the level of the critical electric current Ic during typical operation. As such, the superconductor regions 132, 134 will remain in their superconducting states throughout operation. By comparison, the area of the superconductor microbridge 110, taken in cross-section to the axial direction of the superconductor microbridge 110 is limited to an area such as 20 m x 200 m. Therefore, depending upon the electric current applied by the pulse current source 220, the electric current necessary to be flowing through the superconductor microbridge 110 can be raised to a level sufficient so that the electric current is raised above its critical value to transition the superconducting material from its superconducting state to its normal, non-superconducting state. In this manner, an electronic controller can regulate the current applied by the pulse current source 220 to control whether the electric current flowing through the superconductor microbridge is above or below the electric current needed to transition the superconductor microbridge between its superconducting and normal states. In its "on" state (when the superconductor microbridge 110 is in its normal or non- superconducting state), light that is applied to the superconductor microbridge 110 passes through the superconductor microbridge 110 and continues to, and through, the substrate

115. By comparison, when the pulse current source 220 is below a level where the electric current of the superconductor microbridge 110 is below its critical level (also assuming the temperature and the magnetic flux also are below their respective critical values), then the superconducting material in the superconductor microbridge 110 will transition to its off or superconducting, state. If the superconducting material of the superconductor microbridge

110 is in its superconducting state, the light applied to the superconducting material will be reflected since most optical or other electromagnetic waves cannot penetrate into a superconducting material that is in its superconductor state. Therefore, the superconductor microbridge 110 transitioning to its superconducting state results in the respective superconductor microbridge as shown in FIGs. 1 and 2 of the superconductor optical switch 100 being in its off or closed state.

A side cross-sectional view of the superconductor optical switch 100 shown in FIGs. 1 and 3 is illustrated in FIG. 4. In the superconductor optical switch 100, metal is used in combination with the superconducting materials in switching applications at distinct locations to provide distinct purposes: electric conductivity and optical reflectivity. The metal layer 121 is separated from the superconducting material forming the superconductor microbridge 110 and/or the superconductor regions 132, 134 (see FIG. 3) by an electrical insulator 122. Metal is selected, based on the optical reflectivity characteristics of metal, to reflect light that would otherwise come in contact with the superconducting material. The metal layer 121 that is optically reflective acts to reflect almost all of the incident light beams 111. The metal layer 120 may be, e.g., a layer of gold that can be quite thin. Other optically reflective metals may also be used inside one embodiment of superconductor optical switch 100. An electric insulator layer may be placed between the metal layer 121 and the superconductor microbridge 110.

A side cross-sectional view of the superconductor optical switch 100 shown in FIGs. 2 and 3 is illustrated in FIG. 14. The difference in use between the superconductor optical switch 100 shown in FIGs. 1 and 4 and the superconductor optical switch 100 shown in FIGs. 2 and 14 is that the FIG. 1 embodiment transmits the light that is being used while the FIG. 2 embodiment reflects the light that is being used. As such, the embodiment of superconductor optical switch 100 shown in FIG. 4 reflects light that is not being used. Since the metal layer 121 shown in the FIG. 4 embodiment is a reflective layer, the metal coating reflects any light that is applied to the upper portion of the superconductor optical switch 100 that is not applied to the optical window 124.

The FIG. 14 embodiment, that is intended to be used as illustrated in the FIG. 2 embodiment, must absorb or transmit (not reflect) light that it is not desired to use. As such, the metal layer 121 is coated with an insulator layer 1402 that absorbs the light that impinges on the portions of the upper surface of the superconductor optical switch 100 that do not coincide with the optical window 124, the microbridge 100, and/or the superconductor regions 132, 134. The light that is applied to the optical window 124, and is used at a signal, in the embodiment of superconductor optical switch 100 shown in FIG. 14 will be selectively reflected by the optical window 124. The outlines of elements 106 and 120 are illustrated in FIG. 3. Those locations above the superconductor regions 132, 134, and 110, that are not coated by any reflective metal layer 120, are considered to define the optical window 124 since light can confroUably pass through the optical window 124. Therefore, the superconductor microbridge 110 can be considered to operate the optical window 124. Considering the superconductor microbridge 110 that forms the optical window 124, when the superconductor microbridge 110 is in its normal or non-superconducting state, light applied from above the superconductor microbridge 110 will pass through the superconductor microbridge 110 and will continue to pass through the substrate 115 when the superconductor microbridge 110 is in its normal state. By comparison, when the superconducting material of the superconductor microbridge 110 is in its superconducting state, the superconductor microbridge 110 will reflect light that is applied from above to the superconductor microbridge 110. In this manner, the superconductor microbridge 110 forming the superconductor optical switch transitions between its "on" and "off states. Bias current sources 222 and pulse current sources 220 are applied between the electric contacts 106 electrically connected between the superconductor regions 132, 134. As such, current that flows between the electric contacts 106 of the superconductor regions 132 and 134 flows across the superconductor microbridge 110.

The top and front views of one embodiment of superconductor optical switch 100 of the present invention are shown respectively in FIGs. 5 and 6, and as such these two figures should be considered together. The superconductor optical switch 100 comprises a substrate 115, an electrical insulator 406 (that is typically coated with a metal layer as shown as 121 in FIG. 3), a first superconductor region 408, a second superconductor region 410, a bias electric contact 412 located proximate to the first superconductor region 408, a pulse electric contact 414 located proximate to the first superconductor region 408, a bias electric contact 416 located proximate to the second superconductor region 410, a pulse electric contact 418 located proximate to the second superconductor region 410, a bias current source 220 that extends between the bias electric contact 412 and the bias electric contact 416, a pulse current source 222 that extends between the pulse electric contact 414 and the pulse electric contact 418, and a plurality of superconductor microbridges 430a, 430b, 430c and 430d. Each one of the superconductor microbridges 430a through 43 Od extends from the first sμperconductor region 408 to the second superconductor region 410 and is laterally defined by the electric insulator 406. In one embodiment, both the first superconductor region 408 and the second superconductor region 410 are in electric contact with the respective contact superconductor region 450, 452 that allows electric contact from the respective bias electric contacts 412, 416 and the respective pulse electric contact 414, 418 to be in electric communication with the respective superconductor region 408, 410. In another embodiment, the respective bias electric contacts 412, 416 and/or the respective pulse electric contacts 414, 418 may be located within the respective superconductor regions 408 and 410. In other words, each respective bias electric contact 412, 416 and each respective pulse electric contact 414, 418 is in communication with its respective superconductor region 408, 410.

The superconductor region 408 and the superconductor region 410 are both configured, as illustrated in the embodiment in FIG. 5, so that the height of each superconductor region 408, 410 is relatively high as indicated by respective dimensions dl and d2. The dimensions dl and d2 are especially large in comparison to the relative widths of each respective superconductor microbridge 430a to 430d, shown as d3 to d6. Each superconductor microbridge 430a to 430d is configured with a different width, namely d3 to d6. For example, the superconductor microbridge 430a with a width d3 is the thinnest superconductor microbridge. The next superconductor microbridge 430b having width d4 is thicker than superconductor microbridge 430a having width d3. Superconductor microbridge 430c has width d5 which is greater than the width of either of the superconductor microbridges 430a and 430b. Finally, the width of superconductor microbridge 430d indicated by d6 is thicker than that of superconductor microbridges 430a, 430b, and 430c, as indicated by the respective widths d3, d4, and d5. This increase in the cross-sectional areas of the superconductor microbridges 430a to 430d resulting from their respective increasing widths d3 to d6, may alternatively be provided by, e.g., increasing the thickness of the respective superconductor microbridges in a direction indicated as in and out of the paper as shown in the embodiment in FIG. 5. Even though one of the dimensions is shown as being altered across the superconductor microbridges 430a to 430d, it is envisioned that altering other cross-sectional thicknesses as well as the cross-sectional dimension of the respective superconductor microbridges 430a to 430d will provide similar results since the current that goes through the superconductor microbridge is proportional to the cross-sectional area of the superconductor microbridge. A side view of another embodiment of the superconductor optical switch 100 shown in FIG. 5 is shown in FIG. 6. Considering FIG. 6, the relative positioning of the components of one embodiment of the superconductor optical switch 100 upon the substrate 115 becomes evident. In the first superconductor region 408, each superconductor microbridge 430a through 430d, and the second superconductor region 410 actually form a continuous superconductor region extending between the superconductor regions 408 and 410 from the substrate 115 to the incident face 107 (excluding a deposited metal) of the superconductor optical switch 100. Each one of the metal layers 121 is mounted to, and in electric contact with, its respective insulator region 406. The insulator region 406 is formed prior to the deposition of, and underneath a general outline of, each one of the pulse electric contacts 414, 418 and the bias electric contacts 412 and 416. In one embodiment, the insulator regions 406 are formed by ion implantation of an electrically insulative material. The insulator region 406 therefore generally forms an electric insulator when deposited within the superconducting material. To fabricate the superconductor microbridges, it may be desired to leave spaces adjacent to^' the side of the superconductor microbridges with the optically reflective metal, so that the portion adjacent to the side of the optical window is already insulated. There is no need to deposit the electric insulator as an additional layering step as with prior art systems, and therefore the processing time and costs can be reduced. In one embodiment, the insulator region 406 extends all the way vertically through the superconductor regions 408, 410. Alternatively, the insulator region 406 can extend for only a relatively brief vertical distance from the upper surface. The ion-implantation process can be precisely controlled so that the depth of the insulator region 406 can be accurately controlled. Whatever the distance is that the insulator region 406 extends below the metal layer 121, 414, 416, 418, the insulator region 406 acts to limit the flow of electricity from the metal layer 121 into the superconductor regions 408, 410. A reflective metal layer 120 extends on the incident face 107 of the superconductor optical switch 100 between the regions delineated for the superconductor microbridges 403a through 430d to reflect light impinging from the optical source 102 shown in FIGs. 1 and 2 at the regions covered by the metal layers 120, 121.

As mentioned above, if any one of the temperature, the electric current, or the magnetic field of the superconducting material rises above its respective critical value, then the superconducting material leaves its superconducting state and enters its normal state. As the superconducting material enters its normal state, the properties of the superconducting material leave those of a superconductor and approach those of a typical semiconducting material. In its normal state, the superconductor is characterized by normal state resistivity and relatively low reflectivity. As the superconducting material approaches or is in its superconducting state, the superconducting material exhibits many of the properties of a theoretically perfect conductor.

The embodiment of superconductor optical switch 100 described relative to FIGs. 3 and 5 performs its switching functions by varying the electric current (I) flowing across the superconductor microbridge to transition the superconducting material between its superconductor and its normal states. In the embodiments of superconductor optical switch 100 shown in FIGs. 3 and 5 where the superconducting materials is in its superconducting states, the electric resistance of the superconducting material approaches zero, and the superconducting material reflects light, and other electromagnetic radiation, applied to the surface of the superconducting material. The electric current applied from the bias electric contact 412 to the bias electric contact 416 is maintained at a level so that when no electric current flows across the pulse electric contacts 414, 418, the electric current across each of superconductor microbridges 430a, 430b, 430c and 430d is below the level necessary to raise the electric current in any of the superconductor microbridges 430a to 430d above its

critical electric current value Ic.

Transition in the superconductor optical switch 100 from its optically opaque, superconducting state to their optically transparent, non-superconducting state can also be made by varying the temperature and the magnetic field that is applied to the superconducting material forming the superconductor microbridges to transition the superconductor microbridges between their superconducting and their normal states.

Since the electric current is below the critical electric current level Ic (assuming that the temperature and the magnetic field are also below their respective critical values Tc and He), the superconducting (reflective) material of the superconductor microbridges remains in its superconducting state, but is approaching its normal or non-superconducting state (assuming that the electric bias applied between the pulse electric contacts 414 and 418 is negligible). The electric current applied to the bias current source 220 is maintained at this level during the operation of the pulse current source 222. The pulse current source 222 acts in addition to the bias current applied by the bias current source 220. The cross-sectional areas, and the widths of each of the superconductor microbridges increase from superconductor microbridge 430a to superconductor microbridge 430d. Therefore, as the current applied to the pulse current source 222 is increased, as mentioned above, the electric current varies between the different superconductor microbridges as a function of the cross- sectional area of each superconductor microbridge.

Due to the different widths and cross-sectional areas of the superconductor microbridges 430a through 430d, those superconductor microbridges with a smaller cross- sectional area will reach a higher electric current I then those superconductor microbridges having a larger cross-sectional area, provided that the current applied across each superconductor microbridge is identical. The superconductor microbridge 430a will be the first superconductor microbridge to have its electric current reach its critical electric current value Ic and thus to transition from its superconducting state to its normal state. As the pulse current source 222 further increases, the next superconductor microbridge to reach its critical electric current value Ic to transition from its superconducting state and thus to its normal state will be superconductor microbridge 430b. Similarly, an increase in the pulse current source 222 will be reflected by the transitioning the superconductor microbridge 430c and then the superconductor microbridge 43 Od from their superconducting states to their normal states.

As each superconductor microbridge 430a to 430d is transitioned from its superconducting state to its normal state (to turn the superconductor optical switch 100 associated with that superconductor microbridge on), the resistivity of the high temperature superconducting material within that respective superconductor microbridge 430a to 430d also transitions from allowing light to pass through the superconductor microbridge to being fully reflective of light that is impinging on that superconductor microbridge. Therefore, as the pulse current source 222 increases its electric current, initially all of the superconductor microbridges 430a through 43 Od are in their transparent state and allow light to pass there through. As each superconductor microbridge transitions into its normal non- superconducting state, and therefore becomes transparent, light is allowed to pass through that respective superconductor microbridge through the substrate 115 behind the superconductor microbridge, and continues through the superconductor optical switch 100.

FIG. 7 illustrates one embodiment of biased pulse waveforms that may be applied to the superconductor optical switch 100 to transition the superconductor microbridge between its normal and its superconducting states. The superconductor optical switch 100 of the present invention does not require a large pulse current, as required by the prior-art optical switches (where the pulse current waveform is either fully on or fully off). The amount of time needed to turn on the large pulse current to a value sufficient to transition the superconducting material in the superconductor microbridges to their superconducting state and thus to turn the superconductor optical switch "off in the superconductor optical switch 100 is reduced considerably. Such a large pulse, (which is not required by the distinct bias and pulse electric current sources in the present invention) requires a powerful laser, the switching rate 13 limited (since such a powerful laser requires some duration to be turned completely on or off) .

In the embodiment of the superconductor optical switch 100 shown in FIGs. 3 and 5, a distinct bias current source is applied in addition to a constant bias current source that is applied to the superconductor optical switch. The bias value of the superconductor optical switch brings the superconductor optical switch to a value near its superconducting/normal state transition, and thus a relatively small pulse is necessary to transition the superconductor optical switch. The superconductor microbridges 430a to 430d are configured to transition at different total currents since they have different cross-sectional areas (e.g. widths). Each superconductor microbridge in the chain of superconductor microbridges transitions at a different current density so that the superconductor microbridge 430a transitions at the lowest electric current density; superconductor microbridge 430b transitions at the next lowest current density; and then superconductor microbridge 430c and 43 Od respectively transition at respectively higher current densities.

The embodiment of superconductor optical switch 100 shown in FIG. 5 may be considered as an analog to digital converter, and can be used to provide optical data communications. This configuration of superconductor microbridges 430a to 430d allows for the generation of what can be considered as a digital signal. For example, when the superconductor microbridge 430a transitions from its superconducting state to its normal state, while the remaining superconductor microbridges 430b - 43 Od remain in their superconducting states, the light passing through only superconductor microbridge 430a indicates, e.g., a digital 00 value. When superconductor microbridge 430b transitions from its superconducting state to its normal state, while the superconductor microbridges 430c and 43 Od remain in their superconducting states, the superconductor optical switch 100 may be considered to be producing a digital 01 value. When superconductor microbridge 430c then goes to its normal state, while superconductor microbridge 430d remains in its superconducting state, the superconductor optical switch 100 may be considered as producing a digital 10 value. Finally, when superconductor microbridge 430d is transitioned so that all of the superconductor microbridges are in their normal states, this represents digital 11 value for the superconductor optical switch 100. A typical microprocessor can be connected to an optical detector to indicate which of the superconductor microbridges 430a to 430d are transmitting light.

Additionally, providing the distinct pulse/bias cuπent sources as shown in the embodiments of the present invention allows for the superconductor optical switch to be quickly turned off by deactuating only the pulse cuπent source while the bias cuπent source remains active. Providing a pulse current source that can be actuated on top of a bias cuπent source is very important. If the cuπent source applying cuπent to the superconductor optical switch 100 does not include biasing, it is difficult and expensive to make the superconductor optical switch operate because the power that must be applied to increase the electric cuπent is too large to allow for quick optical switching operations. The advantage of having the bias cuπent source 220 and the pulse current source 222 act in concert is illustrated relative to the embodiment of superconductor optical switch shown in FIG. 6. The application of the bias cuπent source 220 brings the cuπent applied across each of the superconductor microbridges 430a - 430d to a bias level 710. The pulse cuπent level applied by the pulse cuπent source 222 is superimposed on the bias cuπent level applied by the bias cuπent source, thereby raising the total cuπent level to the sum of the bias cuπent level and the pulse cuπent level. The cuπent level that is necessarily applied by a cuπent source to transition the superconductor optical switch 100 between the bias cuπent level and the total cuπent level in the embodiment as shown in FIG. 7 is considerably less than the level of cuπent of the pulse cuπent level. Thus, the switching rate of the embodiments of superconductor optical switch 100 shown in FIGs. 1 through 6 is considerably faster than prior art switches, and may operate in the picosecond range.

Cuπents applied across each of the superconductor microbridges do not have to be turned entirely on or off, but instead, only the pulse cuπent source 222 has to be actuated. This actuation of the pulse cuπent source 222 above the level of the bias cuπent source 222 enables quicker switching of the superconductor optical switch 100. These concepts can be applied to a multi level systems wherein a plurality of layers including superconductor optical switches (and/or other elements) are vertically layered in a similar manner to standard integrated circuits using silicon technology. While the embodiment of superconductor optical switch 100 shown in FIG. 5 includes a pulse cuπent source 222 and a separate bias cuπent source 220, it is possible to combine these separate cuπent sources into one pulse/bias cuπent source. These embodiments of superconductor optical switch 100 has the potential to operate extremely quickly, e.g., the speed of transition could be as fast as 1 picosecond in certain embodiments.

FIGs. 8 and 9 shows two other embodiments of the superconductor optical switch 100. In these embodiments of the superconductor optical switch 100, instead of the electric cuπent (I) being varied across the superconductor microbridge 110 to a level above or below the critical electric cuπent (Ic), the temperature of the superconductor microbridge 110 is instead varied to a temperature above or below the critical temperature (Tc) to transition the superconducting material of the superconductor microbridge 110 between its superconducting and normal states. The FIG. 8 embodiment of superconductor optical switch includes applying a highly focused optical source, such as a laser, to a portion of the superconductor microbridge to alter the temperature of the superconducting material. The application of light from the optical source to the superconductor microbridge raises the temperature of a portion of the superconductor microbridge to a temperature that is sufficient to transition the superconductor optical switch 100 between its superconducting and normal states. The pulse cuπent source 222 and the bias cuπent source 220 may be applied to the optical element 802, as described above

The FIG. 9 embodiment of superconductor optical switch 100 includes an optical heater element 902 that can generate heat that can be directed at a small target, such as a superconductor microbridge. An electric cuπent applied to the optical heater element 902 actuates the optical heater element. The optical heater element 902, however, is directed along a path that is not coincident with the light that is either passed through the superconductor microbridge, or be reflected by the superconductor microbridge, to effect operation of the superconductor optical switch 100. The embodiment of superconductor optical switch 100 shown in FIG. 9 is configured with a single optical heater element 902. It is envisioned that multiple optical heater elements 902 could be applied. For example, FIG. 10 shows one embodiment of optical heater element 902 that may be utilized in place of the optical heater element 902 shown in FIG. 9. The embodiment of optical heater element 902 shown in FIG. 10 includes distinct optical heater elements 1002, 1004 are each actuated by applying distinct bias and pulse electric currents. The optical heater element 902 in FIG. 10 includes a bias optical heater portion 1002 and a pulse optical heater portion 1004. The pulse cuπent source 222 and the bias cuπent source 220 may be applied to the heater element 902, as described herein. The bias optical heater portion 1002, which is continuously applied to the superconductor microbridge, maintains the temperature of the superconducting material of the superconductor microbridge at a temperature just below the critical temperature (Tc). The pulse optical heater portion 1004, by comparison, is actuated when it is desired to transition the superconductor microbridge from its superconducting to its normal state. Therefore, if it is desired to deactuate the superconductor microbridge, the pulse optical heater portion 1004 is similarly deactuated. In this manner, the amount of heat applied to the superconductor microbridge from the pulse optical heater portion 1004 to cause the transition is limited. Similarly, the time necessary to heat the superconductor microbridge to a temperature sufficient to transition the superconductor microbridge from its superconducting to its normal state is limited. The pulse cuπent source 222 and the bias cuπent source 220 may be applied to the respective heater elements 1004, 1002 as described above.

Another embodiment of superconductor optical switch 100 is shown in FIG. 11. In the FIG. 11 embodiment of superconductor optical switch 100, each superconductor microbridge 110 is transitioned between its normal and its superconducting states by the application of a magnetic field applied to the superconductor microbridge. The embodiment of superconductor optical switch 100 shown in FIG. 11 further includes a magnetic field generator 1110. An electric cuπent is applied to the magnetic field generator 1110 to generate a magnetic field. One embodiment of magnetic field generator 1110 includes a coil 1112 that generates a magnetic field by electric cuπent flowing therethrough. The bias cuπent source 220 and the pulse cuπent source 222 are applied to the coil 1112 as described above. The quantity of magnetic field generated by such coils is known using Maxwell's equations. Application of electric cuπent to the magnetic field generator 1110 results in a magnetic field being generated across the superconductor microbridge. When a sufficient magnetic field is applied to the superconductor microbridge from the magnetic field generator, the superconducting material of the superconductor microbridge transitions from its superconducting state to its normal state. When the magnetic field level in the superconductor microbridge 110 is reduced below its critical magnetic field (He) level, the superconducting material of the superconductor microbridge transitions back to its superconducting state.

The embodiment of the superconductor optical switch 100 shown in FIG. 11 is configured with a single magnetic field generator 1110. It is envisioned that multiple magnetic field generators 1110 could be applied. For example, FIG. 12 shows one embodiment of magnetic field generator 1110 that may be utilized in place of the magnetic field generator 1110 shown in FIG. 11. The embodiment of magnetic field generator 1110 shown in FIG. 12 includes a bias magnetic field generator 1210 and a pulse magnetic field generator 1212. A distinct electric cuπent is applied to actuate each magnetic field generator 1210, 1212. The bias magnetic field generator 1210, during normal operation, is continuously applied to the superconductor microbridge 110 to maintain the magnetic field of the superconductor microbridge 110 at a magnetic field level just below that of the critical magnetic field (He). The pulse magnetic field generator 1212, by contrast, is actuated when it is desired to transition the superconductor microbridge from it's superconducting to its normal state. Therefore, if it is desired to deactuate the superconductor microbridge, the pulse magnetic field generator 1212 is deactuated. In this manner, the amount of variation of the magnetic field that must be optically applied to the superconductor microbridge from the pulse magnetic field generator 1212 can be limited. Similarly, the time necessary to apply the magnetic field to the superconductor microbridge 110 to transition the superconductor microbridge 110 between its superconducting and its normal states is limited.

As such, it can be understood that the concepts described here relating to electric cuπent applied to the superconductor microbridges can similarly be applied to temperature, optical level, and/or magnetic cuπent density of the superconductor microbridges. All of the embodiments of superconductor optical switch 100 can utilize bias cuπent to actuate the respective device to provide rapid switching of the superconductor microbridge between its superconducting and its normal states.

Fig. 13 shows one embodiment of an integrated circuit aπay of superconductor optical switches 1300. The integrated circuit aπay of superconductor optical switches 1300 is configured with the plurality of superconductor optical switches 100. Each one of the superconductor optical switches 100 included in the integrated circuit aπay of superconductor optical switches 1300 may be configured as any embodiment of superconductor optical switch shown in, e.g., FIGs. 1 to 6 and 8 to 12. Each superconductor optical switch 100 in the integrated circuit aπay of superconductor optical switches 1300 includes one or more superconductor microbridges 110, and a plurality of superconductor regions 132, 134. Also shown in the embodiment of integrated circuit aπay of superconductor optical switches 1300 of FIG. 13 are a plurality of pulse cuπent sources II to 19, in addition to bias cuπent source IA. The bias cuπent source IA is concuπently connected to each one of the superconductor optical switches 100. As such, the bias cuπent source IA applies a cuπent level between the superconductor regions 132, 134 in each superconductor optical switch 100 in the integrated circuit aπay of superconductor optical switches 1300. Alternatively, individual bias cuπent sources can be applied to each one of the superconductor optical switches 100. Using the common bias cuπent source IA is most desirable in those instances where the configuration, dimensions, etc., of each superconductor optical switch 100 in the integrated circuit aπay of superconductor optical switches 1300 are similar. It is therefore desirable that the bias cuπent source I_B, similar in operation to the bias cuπent source I_B as shown in the above embodiments of superconductor optical switches, maintain the cuπent level for flowing through the superconductor microbridge 110 of each superconductor optical switch 100 that is at a level slightly below the critical cuπent level Ic (when the respective pulse cuπent source is deactuated).

Individual pulse cuπent sources II to 19, similar in operation to the pulse cuπent source Ip 222 described above, are applied as pulse cuπent to each respective superconductor optical switch 100 in the integrated circuit aπay of superconductor optical switches 1300. As described above, each pulse cuπent source II to 19, when combined with the biased cuπent source for that particular superconductor optical switch 100, is sufficient to transition the superconducting material in each superconductor microbridge 110 of the respective superconductor optical switch 100 between its normally operating superconducting state and its deactuated, non-superconducting state. Though the embodiment of integrated circuit aπay of superconductor optical switches 1300 shown in FIG. 13 is configured in a 3 x 3 aπay, it is envisioned that the concept of providing an aπay can be aπanged in a 2 x 2, 4 x 4, 2 x 4 or any other desired symmetrical or asymmetrical aπay. In addition, the integrated circuit aπay of superconductor optical switches does not actually have to be in an aπay as such; it can be provided in whatever configuration or orientation of superconductor optical switches is desired.

While the principles of the invention have been described above in connection with the specific apparatus and associated method, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of the invention.

Claims

hat Is Claimed Is:

1. A superconductor optical switch comprising: a superconductor microbridge formed from superconducting material, wherein the superconducting material can transition at a critical level between a superconducting optically reflective state and a non-superconducting optically transparent state; a bias- cuπent source; a pulse cuπent source, wherein when the bias cuπent source is actuated and the pulse cuπent source is not actuated, the superconductor microbridge is maintained in its superconducting optically reflective state; and wherein when the pulse cuπent source is actuated concurrently with the bias cuπent source being actuated, the superconductor microbridge is maintained in its non- superconducting optically transparent state.

2. The superconductor optical switch of claim 1, further comprising an optical heater element that varies the temperature of the superconducting material of the superconductor microbridge to transition the superconductor microbridge between its superconducting optically reflective state and its non-superconducting optically transparent state, wherein the critical value is a critical temperature value.

3. The superconductor optical switch of claim 1, further comprising an magnetic flux element that varies the magnetic flux of the superconducting material of the superconductor microbridge to transition the microbridge between its superconducting optically reflective state and its non-superconducting optically transparent state, wherein the critical value is a critical magnetic flux value.

4. The superconductor optical switch of claim 1, further comprising an electric cuπent element that varies the electric cuπent of the superconducting material of the superconductor microbridge to transition the superconductor microbridge between its superconducting optically reflective state and its non-superconducting optically transparent state, wherein the critical value is a critical electric cuπent value.

5. The superconductor optical switch of claim 1, further comprising: a first superconductor region; and a second superconductor region, wherein the superconductor microbridge extends between the first superconductor region and the second superconductor region.

6. The superconductor optical switch of claim 6, wherein both a pulse cuπent source and a bias cuπent source is applied from across the first superconductor region to the second superconductor region.

7. The superconductor optical switch of claim 6, wherein a pulse cuπent source is applied from across the first superconductor region to the second superconductor region.

8. The superconductor optical switch of claim 6, wherein a bias cuπent source is applied across the first superconductor region to the second superconductor region.

9. The superconductor optical switch of claim 6, wherein said superconductor microbridge includes a plurality of superconductor microbridges extending between the first superconductor region and the second superconductor region.

10. The superconductor optical switch of claim 9, wherein each one of the plurality of superconductor microbridges has a different cross-sectional area.

11. The superconductor optical switch of claim 1 , wherein the superconductor optical switch is aπanged as one of a plurality of superconductor optical switches aπanged in an integrated circuit aπay of superconductor optical switches.

12. A method of operating a superconductor optical switch comprising: providing a superconductor microbridge formed from superconducting material, wherein the superconducting material can transition at a critical value between a superconducting optically reflective state and a non-superconducting optically transparent state; providing a bias cuπent source; providing a pulse cuπent source; constantly applying the bias cuπent source; and controllably applying the pulse cuπent source, wherein when the bias cuπent source is actuated and the pulse cuπent source is not actuated, the superconductor microbridge is maintained in its superconducting optically reflective state, and wherein when the pulse cuπent source is actuated concuπently with the bias cuπent source being actuated, the superconductor microbridge is maintained in its non-superconducting optically transparent state.

13. The method of operating the superconductor optical switch of claim 12, wherein the critical value is a critical temperature value, and further comprising varying the temperature of the superconducting material of the superconductor microbridge to transition the microbridge between its superconducting optically reflective state and its non- superconducting optically transparent state.

14. The method of operating the superconductor optical switch of claim 12, wherein the critical value is a critical magnetic flux value, and further comprising varying the magnetic flux applied to the superconducting material of the superconductor microbridge to transition the superconductor microbridge between its superconducting optically reflective state and its non-superconducting optically transparent state.

15. The method of operating the superconductor optical switch of claim 12, wherein the critical value is an electric cuπent value, and further comprising varying the electric cuπent of the superconducting material of the superconductor microbridge to transition the superconductor microbridge between its superconducting optically reflective state and its non-superconducting optically transparent state.

16. The method of operating the superconductor optical switch of claim 12, wherein the superconductor microbridge includes a plurality of superconductor microbridges extending between the first superconductor region and the second superconductor region, and wherein each one of the plurality of superconductor microbridges has a different cross-sectional area.

17. The method of operating the superconductor optical switch of claim 16, wherein the confroUably applying of the pulse cuπent source is applied to transition the superconducting material in only certain ones of the plurality of superconductor microbridges between a superconducting optically reflective state and a non-superconducting optically transparent state.

18. A superconductor optical switch comprising: a first superconductor region; a second superconductor region; a confroUably superconductive portion confroUably electrically connecting the first superconductor region and the second superconductor region; an electric insulator portion that suπounds the first superconductor region, the second superconductor region, and the confroUably superconductive superconductor region; a fabricated chemical etching, ion-implanted insulator region formed by ion implantation of an electrically insulative material within said first superconductor region; and a metal layer physically contacting at least a portion of said ion-implanted insulator region, wherein the metal layer contacts only the ion-implanted insulator region of the first superconductor region.

19. A superconductor region to be connected to one or more other superconductor regions by a confroUably superconductive portion to form a superconductor optical switch, the superconductor region comprising: a superconductor region laterally surrounded, except for said confroUably superconductor portion, by an insulator; an insulator region formed by ion implantation of an electrically insulative material within said superconductor region; and a metal layer physically contacting at least a portion of said ion-implanted insulator region, wherein the metal layer contacts only the ion-implanted insulator region of the superconductor region.

20. The superconductor region of claim 19, wherein the superconductor includes a metal superconductor.

22. The superconductor region of claim 19, wherein the superconductor includes an oxide superconductor.

23. The superconductor region of claim 19, wherein the superconductor region is substantially planar.

24. The superconductor region of claim 19, wherein the superconductor microbridge includes a plurality of superconductor microbridges, each one of the plurality of superconductor microbridges having a different cross-sectional area.

25. A superconductor optical switch comprising: a first superconductor region; a second superconductor region; a superconductor microbridge connecting the first superconductor region and the second superconductor region; an insulator that surrounds the first superconductor region, the second superconductor region, and the superconductor microbridge; an insulator region formed by ion implantation of an electrically insulative material within said first superconductor region; and a metal layer physically contacting at least a portion of said ion-implanted insulator region, wherein the metal layer contacts only the ion-implanted insulator region of the first superconductor region.

26. The superconductor optical switch of claim 25, wherein the superconductor includes a metal superconductor.

27. The superconductor optical switch of claim 25, wherein the superconductor includes an oxide superconductor.

28. The superconductor optical switch of claim 25, wherein the superconductor microbridge includes a plurality of superconductor microbridges, each one of the plurality of superconductor microbridges having a different cross-sectional area.

29. A confroUably superconductive portion that connects a first high temperature superconductor region to a second superconductor region, the confroUably superconductive portion comprising a plurality of superconductor microbridges connecting the first superconductor region to the second superconductor region, each one of the plurality of superconductor microbridges having a different cross-sectional area.