Graphene coated optic fibers

A graphene coated optic fiber is disclosed. An optic fiber core is encapsulated within a graphene capsule. An optic fiber having cladding layer encapsulated within a graphene capsule is also disclosed. The graphene capsule may comprise a single layer of graphene, bi-layer of graphene, or multiple layers of graphene. An optical circuit is disclosed that transmits ultraviolet light across an optic fiber encapsulated with graphene.

This application claims the benefit of U.S. patent application Ser. No. 14/070,574 filed on Nov. 3, 2013, which is also hereby incorporated by reference.

BACKGROUND

Fiber optic cables are favored for modern data communication. Fiber optic cable offers large bandwidth for high-speed data transmission. Signals can be sent farther than across copper cables without the need to “refresh” or strengthen the signal. Fiber optic cables offer superior resistance to electromagnetic noise, such as from adjoining cables. In addition, fiber optic cables require far less maintenance than metal cables, thereby making fiber optic cables more cost effective.

Optical fiber is made of a core that is surrounded by a cladding layer. The core is the physical medium that transports optical data signals from an attached light source to a receiving device. The core is a single continuous strand of glass or plastic that is measured (in microns) by the size of its outer diameter. The larger the core, the more light the cable can carry. All fiber optic cable is sized according to its core diameter. The three diameters of the most commonly available multimode cores are 50-micron, 62.5-micron, and 100-micron, although single-mode cores may be as small as 8-10 microns in diameter. The cladding is a thin layer that surrounds these micrometer sized fiber cores. It is the core-cladding boundary that contains the light waves within the core by causing the high-angle reflection as measured relative to a line perpendicular to this boundary, such as a core-diametral line, enabling data to travel throughout the length of the fiber segment. Typically, the core and cladding are made of high-purity silica glass. The light signals remain within the optical fiber core due to total or near-total internal reflection within the core, which is caused by the difference in the refractive index between the cladding and the core.

The cladding is typically coated with a layer of acrylate polymer or polymide, thereby forming an insulating jacket. This insulating jacket protects the optic fiber from damage. This coating also reinforces the optic fiber core, absorbs mechanical shocks, and provides extra protection against excessive cable bends. These insulating jacket coatings are measured in microns and typically range from 250 microns to 900 microns.

Strengthening fibers are then commonly wrapped around the insulating jacket. These fibers help protect the core from crushing forces and excessive tension during installation. The strengthening fibers can be made of KEVLAR™ for example. An outer cable jacket is then provided as the outer layer of the cable. The outer cable jacket surrounds the strengthening fibers, the insulating jacket, the cladding and the optic fiber core. Typically, the outer cable jacket is colored orange, black, or yellow.

It is highly desirable to develop advanced optic fibers that can transmit data at higher rates, thereby increasing data bandwidth.

SUMMARY

A graphene coated optic-fiber is disclosed that includes an optic fiber core. The optic-fiber also includes a graphene capsule that encapsulates the optic fiber core. The graphene capsule forms a cladding layer. The graphene capsule may be formed of a monolayer of graphene, a bi-layer graphene, or multilayer graphene. The graphene capsule may be deposited onto the optic fiber core through a Chemical Vapor Deposition (CVD) process. The graphene capsule is formed of a graphene cylinder with two circular graphene end surfaces. The graphene cylinder is formed through a CVD process. The two circular graphene end surfaces are adhered to end surfaces of the optic fiber core. Carbon-carbon bonds may be formed between the two circular graphene end surfaces and the graphene cylinder via exposure to a carbon atmosphere. The optic fiber core may be made of silica, a halide-chalcogenide glass, PbO glass, or Lanthanum dense flint glass.

A graphene coated optic-fiber is disclosed that includes an optic fiber core and a cladding layer surrounding the optic fiber core. A graphene capsule encapsulates the cladding layer, thereby also encapsulating the optic fiber core. The graphene capsule forms an optic-waveguide. The graphene capsule is formed of a monolayer of graphene, a bi-layer graphene, or multilayer graphene. The optic fiber core and cladding layer may be formed of silica. The graphene capsule can be deposited on the silica cladding through a CVD process.

An optical circuit is disclosed that includes an ultraviolet light source and an ultraviolet receiver circuit. An optic fiber optically connects the ultraviolet light source to the ultraviolet receiver circuit. The optic fiber includes an optic fiber core encapsulated with graphene. The optic fiber may further include a cladding layer between the optic fiber core and the graphene.

Further aspects of the invention will become apparent as the following description proceeds and the features of novelty which characterize this invention are pointed out with particularity in the claims annexed to and forming a part of this specification.

DETAILED DESCRIPTION

While the invention has been shown and described with reference to a particular embodiment thereof, it will be understood to those skilled in the art, that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

FIG. 1illustrates a diagram of carbon atoms1002in a diamond lattice forming an atomically contiguous sheet of graphene1000. Graphene sheet1000, also referred to as a graphene lattice1000, is a flat monolayer of carbon atoms1002that are tightly packed into a two-dimensional lattice, thereby forming a sheet of graphene. Graphene lattice1000is 97.7% optically transparent. Thus, light used in combination with fiber optic cables can pass through a graphene layer for purposes of data transmission within a fiber optic communications network. Graphene lattice1000is an extremely strong material due to the covalent carbon-carbon bonds. It is desirable to utilize graphene lattices1000that are defect free as the presence of defects reduces the strength of graphene lattice1000. The intrinsic strength of a defect free sheet of graphene100is 42 Nm−1, making it one of the strongest materials known. The strength of graphene is comparable to the hardness of diamonds. Graphene is also a highly flexible material. Multiple monolayers of graphene sheet1000can be grown on top of each other to create a multi-layer graphene sheet. As discussed inFIG. 11, graphene exhibits a wavelength dependent index of refraction. It is therefore possible for graphene to function as a cladding layer in optic fiber applications when paired with an appropriate fiber optic core that has an index of refraction higher than that of graphene.

FIG. 2illustrates a process schematic of fabricating an optic fiber108having a core100encapsulated by a graphene layer120that forms cladding around the optic fiber core100. Initially, an optic fiber core100was prepared and cleaned with alcohol and acetone. Preferably, optic fiber core100is made of silica. However, other materials for optic fiber core100may be used. The use of silica is exemplary. In process step A, a copper layer102is deposited around the middle of optic fiber core100. Copper layer102may be deposited via a sputtering method. One exemplary thickness for copper layer102is 1.3 μm. An exemplary length for copper layer102is 0.5 cm to 2 cm. However, any length of copper layer102may be created. Copper layer102is a sacrificial layer deposited to support the deposition of graphene layer104on optic fiber core100. Alternatively, sacrificial copper film102may be evaporated onto optic fiber core100through use of an electron-beam evaporation process. Note that optic fiber core regions100A and100B are not covered by copper film102. Next in step B, optic fiber core100with copper layer102is placed within a Chemical Vapor Deposition (CVD) chamber. In one exemplary process, under a controlled temperature and pressure of 900° C. and 1 MPa and catalyzed by copper layer102, a monolayer of graphene104was grown on copper layer102in 2 hours using H2and CH4at 50 sccm. Multilayer graphene can be grown on optic fiber core100through longer growth times. Subsequently, the temperature within the CVD chamber was increased to 1100° C. and the pressure was decreased to 100 kPa and held constant for a period of 10 hours during which the copper atoms evaporated off, thereby leaving a graphene cylinder104surrounding optic fiber core100without any intervening copper layer102. Silica optic fiber core100is resilient to morphological changes at 900-1100° C. required for the CVD growth of high-quality graphene due to the high melting point of silica of 1600° C.

Next, in step C, bare optic fiber core ends100A and100B are cut off and removed from the portion of optic fiber core100covered with graphene cylinder104. In step C, graphene cylinder104covers the length of the remaining portion of optic fiber core100. However, the ends of optic fiber core100remain uncovered with graphene. In this step, optic fiber core100and graphene cylinder104are cleaned with acetone, alcohol and deionized water. In step D, premade circular graphene films106are applied to the ends of optic fiber100, thereby encapsulating optic fiber100within a graphene capsule120formed of graphene cylinder104and graphene ends106. Subsequently in step E, optic fiber core may optionally be exposed to a carbon atmosphere to create carbon-carbon bonds between graphene ends106and graphene cylinder104. Graphene cylinder104functions as a cladding layer around optic fiber100. Cladding104is one or more layers of materials of lower refractive index, in intimate contact with a core material100of higher refractive index. The cladding104causes light to be confined to the core of the fiber100by total internal reflection at the boundary between the two layers. Light propagation in the cladding104is suppressed in typical fiber. Some fibers can support cladding modes in which light propagates in the cladding104as well as the core100. Further, due to its strength and flexibility, graphene cylinder104functions to provide mechanical support to optic fiber core100. Circular graphene sheets106protect the ends of optic fiber core100from mechanical damage.

The above process for forming a graphene capsule120around optic fiber core100is exemplary. Other processes may be used to form an optic fiber formed of a silica optic fiber core100surrounded by a graphene capsule120functioning as a cladding layer. For example, CVD may be used to entirely grow a graphene capsule around silica optic fiber100. CVD of graphene onto a solid circular rod such as a nanowire or a silica optic fiber core100produces a graphene capsule that completely encapsulates silica optic fiber100. This graphene capsule is formed of a cylinder of graphene surrounding optic fiber core100along its length with graphene surfaces covering the two ends of the graphene cylinder. The process begins with evaporating a sacrifical copper film102onto the silica optic fiber core100as shown inFIG. 2. An electron-beam evaporation process is used to deposit the copper film onto the silica optic fiber. Next, silica optic fiber core100having sacrifical copper layer102is inserted into a CVD chamber. Silica optic fiber core100is heated to 1000° C. CVD of graphene is the performed on optic fibers core100with durations varying from 15 min up to 7 h at 1000° C. Given the fact that that the melting temperature of the copper is ˜1084° C., along with the high temperature during the growth of ˜1000° C., and the low pressure in the chamber, 100-500 mTorr, copper film102de-wets and evaporates during the CVD process. Ethylene (C2H4) or CH4is introduced into the CVD chamber as the carbon-containing precursor, in addition to the H2/Ar flow. The precursor feeding time, typically in the order of a few to tens of seconds, determines the number of layers of graphene grown. The sample may then be cooled to room temperature within 5 min in a flow of 133 sccm Ar at 20 Torr chamber pressure. Silica optic fiber core100is resilient to morphological changes at ˜1000° C. required for the CVD growth of high-quality graphene due to the high melting point of silica of 1600° C. During this CVD process, sacrificial copper layer102de-wets and evaporates exposing silica optic fiber core100directly to graphene layer104and106. In this process, graphene ends106are formed on optic fiber core through CVD deposition.

A monolayer of graphene120may be formed on optic fiber core100. Alternatively, multilayer graphene120may be formed on optic fiber core100. The number of graphene sheets is determined by the growth time and is independent of tube diameter and tube length. As a consequence of this process, a silica optic fiber core100is encapsulated within a graphene capsule120. Graphene capsule120provides mechanical strength to optic fiber core100.

Processes for creating tubular graphene structures, also known as carbon nanotubes, have been demonstrated on 70 nm Nickel (Ni) nanowires as described in the following publication, hereby incorporated by reference: Rui Wang, Yufeng Hao, Ziqian Wang, Hao Gong, and John T. L. Thong inLarge-Diameter Graphene Nanotubes Synthesized Using Ni Nanowire Templates, Nano Lett. 2010, 10, 4844-4850, American Chemical Society, Oct. 28, 2010. However, unlike the process disclosed by Wang utilizing a sacrificial Ni nanowire template, the present invention utilizes a silica optic fiber core100that is retained as an essential component of the optic fiber contained within a cylindrical graphene sheet, i.e. a carbon nanotube, capped at both ends to encapsulate optic fiber core100. Processes for direct chemical vapor deposition of graphene on dielectric surfaces such as silica are described in the following publication, hereby incorporated by reference: Ariel Ismach, Clara Druzgalski, Samuel Penwell, Adam Schwartzberg, Maxwell Zheng, Ali Javey, Jeffrey Bokor, and Yuegang Zhang,Direct Chemical Vapor Deposition of Graphene on Dielectric Surfaces, Nano Lett. 2010, 10, 1542-1548, American Chemical Society, Apr. 2, 2010.

In another exemplary process, graphene capsule120may be deposited directly on to optic fiber core100without the use of a metal catalyst, such as sacrificial copper layer102. The CVD is performed in an atmospheric pressure hot-wall quartz tube furnace. CH4is used as a carbon precursor gas, mixed with auxiliary reduction (H2) and carrier (Ar) gases. The optic fiber core100is heated to 1000° C. (at a rate of 30° C./min) under H2(50 sccm) and Ar (1000 sccm) atmosphere and kept at 1000° C. for 3 min. Then, 300 sccm CH4is introduced to initiate the formation of graphene. The typical growth time is 30-60 min. After the deposition, the CH4flow is stopped, leaving other gases to flow for further 3 min to remove residual reaction gases before allowing the chamber to naturally cool to room temperature (20° C./min) in the same H2—Ar atmosphere. The graphene layer104can also be deposited directly on SiO2by using other hydrocarbon precursors, such as C2H2, showing the generality of the process. The growth of graphene directly on a silica substrate is reported in the following publication, hereby incorporated by reference: Jie Sun, Niclas Lindvall, Matthew T. Cole, Teng Wang, Tim J. Booth, Peter Bøggild, Kenneth B. K. Teo, Johan Liu, and August Yurgens.Controllable chemical vapor deposition of large area uniform nanocrystalline graphene directly on silicon dioxide. Journal of Applied Physics 111, 044103 (2012).

While optic fiber core100may be formed of silica, other glasses with higher indicies of refraction may be used for optic fiber core100. For example, it may be desirable to make optic fiber core from halide-chalcogenide glasses. The processes discussed above are not compatible with halide-chalcogenide glasses due to the high temperatures of the CVD process. Halide-chalcogenide glasses have a melting temperature of 378° C. and would not survive a CVD process at 900-1100° C. However, a variety of low-temperature graphene synthesis techniques are known with very low thermal budgets. With these techniques, the halide-chalcogenide glasses are heated to temperatures around 300° C. for graphene growth. For example, a halide-chalcogenide optic fiber core100may be heated in a CVD chamber to 300° C. and exposed to a benzene precursor as the carbon source to create a monolayer of graphene. This process is reported in the following publication, hereby incorporated by reference: Zhancheng Li, Ping Wu, Chenxi Wang, Xiaodong Fan, Wenhua Zhang, Xiaofang Zhai, Changgan Zeng, Zhenyu Li, Jinlong Yang, and Jianguo Hou.Low-Temperature Growth of Graphene by Chemical Vapor Deposition Using Solid and Liquid Carbon Sources. ACSNANO VOL. 5, NO. 4, 3385-3390, 2011. In an alternative low temperature process, graphene film may be synthesized on a halide-chalcogenide optic fiber100at 280° C. utilizing a microwave plasma treatment in combination with PolyMethylMethacrylate (PMMA). With this process, a layer of PMMA is spin-coated onto a halide-chalcogenide optic fiber core100at room temperature. The PMMA coated halide-chalcogenide optic fiber core100is then inserted into a slot antenna-type microwave plasma CVD system for microwave plasma treatment at 280° C. The plasma treatment time is 30 seconds. This plasma treatment process is disclosed in the following publication, hereby incorporated by reference: Takatoshi Yamada, Masatou Ishihara, and Masataka Hasegawa.Low Temperature Graphene Synthesis from Poly(methyl methacrylate)Using Microwave Plasma Treatment. Applied Physics Express 6 (2013) 115102-1.

Silica optic fiber core100may have a various diameters depending upon the wavelength of light it is configured to support. For example, for transmitting UV light with a wavelength of 200-400 nm, silica optic fiber may have a diameter larger than the 200-400 nm wavelength range of the light. For transmitting light having a wavelength in the range of 400-600 nm in the violet-yellow spectrum, silica optic fiber may have a diameter larger than 400-600 nm. For transmitting light having a wavelength in the range of 600-800 nm in the orange to red spectrum, silica optic fiber may have a diameter larger than 600-800 nm. For light having a wavelength in the range of 800-1000 nm in the infrared spectrum, silica optic fiber may have a diameter larger than 800-1000 nm. These diameter ranges are merely exemplary and are non-limiting.

FIG. 3illustrates a flow chart2000depicting an exemplary process of fabricating an optic fiber108having a core100encapsulated by a graphene layer120that forms cladding around the optic fiber core100. The process begins with START2002. An optic fiber core made of silica is prepared and cleaned with acetone and alcohol in step2004. In step2006, a thin sacrificial layer of copper is formed onto the surface of optic fiber core100. Next in step2008, a CVD process is performed depositing graphene layer104onto optic fiber core100during which the sacrificial copper layer102evaporates. Then in step2010, the ends of optic fiber core100not covered by graphene cylinder104are cut for example, by a laser. In this step, optic fiber core100and graphene cylinder104are cleaned. In step2012, circular sheets of graphene106are applied to the ends of optic fiber core100, thereby forming a graphene capsule encapsulating optic fiber core100. In step2014, exposing graphene sheets106and graphene cylinder104to a carbon atmosphere creates carbon-carbon bonds between graphene cylinder and graphene sheets106, thereby further creating a graphene capsule encapsulating optic fiber core100. The process ENDS with step2016.

FIG. 4illustrates a process schematic of fabricating an optic fiber114having a core110and cladding112encapsulated by a graphene layer120. Initially, an optic fiber114was prepared and cleaned with alcohol and acetone. Optic fiber core110may be formed of silica. Optic fiber cladding112may also be formed of silica. In this example, as both core110and cladding112are formed of silica, CVD processes may be used to deposit graphene on fiber114. The use of silica for core110and cladding112is exemplary. Other materials for optic fiber core110and cladding112may be used.

In process step A, a copper layer102is deposited around the middle of optic fiber114. Copper layer102may be deposited via a sputtering method. One exemplary thickness for copper layer102is 1.3 μm. An exemplary length for copper layer102is 0.5 cm to 2 cm. However, any length of copper layer102may be created. Copper layer102is a sacrificial layer deposited to support the deposition of graphene layer104on optic fiber114. Alternatively, sacrificial copper film102may be evaporated onto optic fiber core100through use of an electron-beam evaporation process. Note that optic fiber core regions114A and114B are not covered by copper film102. Next in step B, optic fiber114with copper layer102is placed within a Chemical Vapor Deposition (CVD) chamber. In one exemplary process, under a controlled temperature and pressure of 900° C. and 1 MPa and catalyzed by copper layer102, a monolayer of graphene104was grown on copper layer102in 2 hours using H2and CH4at 50 sccm. Multilayer graphene can be grown on optic fiber core100through longer growth times. Subsequently, the temperature within the CVD chamber was increased to 1100° C. and the pressure was decreased to 100 kPa and held constant for a period of 10 hours during which the copper atoms evaporated off, thereby leaving a graphene cylinder104surrounding optic fiber114without any intervening copper layer102. Silica optic fiber114is resilient to morphological changes at 900-1100° C. required for the CVD growth of high-quality graphene due to the high melting point of silica of 1600° C.

Next, in step C, bare optic fiber ends114A and114B are cut off and removed from the portion of optic fiber114covered with graphene cylinder104. In step C, graphene cylinder104covers the length of optic fiber114. However, the ends of optic fiber114remain uncovered with graphene. In this step, optic fiber114and graphene cylinder104are cleaned with acetone, alcohol and deionized water. In step D, premade circular graphene films106are applied to the ends of optic fiber114, thereby encapsulating optic fiber114within a graphene capsule formed of graphene cylinder104and graphene ends106. Subsequently in step E, optic fiber may optionally be exposed to a carbon atmosphere to create carbon-carbon bonds between graphene ends106and graphene cylinder104. Cladding112is one or more layers of materials of lower refractive index, in intimate contact with a core material110of higher refractive index. The cladding112causes light to be confined to the core of the fiber110by total internal reflection at the boundary between the two layers. Light propagation in the cladding112is suppressed in typical fiber. Some fibers can support cladding modes in which light propagates in the cladding112as well as the core110. Due to its strength and flexibility, graphene cylinder104functions to provide mechanical support to optic fiber114. Circular graphene sheets106protect the ends of optic fiber114from mechanical damage. Graphene cylinder, due to its optic properties, may function as an optic waveguide in combination with cladding112.

The above process for forming a graphene capsule around optic fiber114is exemplary. Other processes may be used to form an optic fiber formed of a silica optic fiber core110and cladding112surrounded by a graphene capsule. For example, CVD may be used to entirely grow a graphene capsule around silica optic fiber114. CVD of graphene onto a solid circular rod such as a nanowire or a silica optic fiber114produces a graphene capsule that completely encapsulates silica optic fiber114. This graphene capsule is formed of a cylinder of graphene surrounding optic fiber114along its lengths with graphene surfaces covering the two ends of the graphene cylinder. The process begins with evaporating a sacrificial copper film102onto the silica optic fiber114as shown inFIG. 4. An electron-beam evaporation process is used to deposit the copper film102onto the silica optic fiber114. Next, silica optic fiber114having sacrificial copper layer102is inserted into a CVD chamber. Silica optic fiber114is heated to 1000° C. CVD of graphene is the performed on optic fibers114with durations varying from 15 min up to 7 h at 1000° C. Given the fact that that the melting temperature of the copper is ˜1084° C., along with the high temperature during the growth of ˜1000° C., and the low pressure in the chamber, 100-500 mTorr, copper film102de-wets and evaporates during the CVD process. Ethylene (C2H4) or CH4is introduced into the CVD chamber as the carbon containing precursor, in addition to the H2/Ar flow. The precursor feeding time, typically in the order of a few to tens of seconds, determines the number of layers of graphene grown. The sample may then be cooled to room temperature within 5 min in a flow of 133 sccm Ar at 20 Torr chamber pressure. Silica optic fiber114is resilient to morphological changes at ˜1000° C. required for the CVD growth of high-quality graphene due to the high melting point of silica of 1600° C. During this CVD process, sacrificial copper layer102de-wets and evaporates exposing silica optic fiber114directly to graphene layer104and106. In this process, graphene ends106are formed on optic fiber114through CVD deposition.

A monolayer of graphene120may be formed on optic fiber114. Alternatively, multilayer graphene120may be formed on optic fiber114. The number of graphene sheets is determined by the growth time and is independent of tube diameter and tube length. As a consequence of this process, a silica optic fiber114is encapsulated within a graphene capsule120. Graphene capsule120provides mechanical strength to optic fiber114. It is contemplated that the above discussed CVD process of graphene deposition may occur on conventional silica optic fibers having dimensions of 8-10-microns, 50-microns, 62.5-microns, and 100-microns. These diameter ranges are merely exemplary and are non-limiting. Another process of forming a graphene capsule120can be performed through wrapping optic fiber core100with a prefabricated sheet of graphene, thereby forming a graphene cylinder104around optic fiber core100. Circular graphene ends106can then be adhered to the ends of optic fiber core, thereby encapsulating optic fiber core. Carbon-carbon bonds can be formed between graphene cylinder104and circular graphene ends106by exposure to a carbon atmosphere.

Processes for creating tubular graphene structures, also known as carbon nanotubes, have been demonstrated on 70 nm Nickel (Ni) nanowires as described in the following publication, hereby incorporated by reference: Rui Wang, Yufeng Hao, Ziqian Wang, Hao Gong, and John T. L. Thong inLarge-Diameter Graphene Nanotubes Synthesized Using Ni Nanowire Templates, Nano Lett. 2010, 10, 4844-4850, American Chemical Society, Oct. 28, 2010. However, unlike the process disclosed by Wang utilizing a sacrificial Ni nanowire template, the present invention utilizes a silica optic fiber114that is retained as an essential component of the optic fiber contained within a cylindrical graphene sheet, i.e. a carbon nanotube, capped at both ends to encapsulate optic fiber114. Processes for direct chemical vapor deposition of graphene on dielectric surfaces such as silica are described in the following publication, hereby incorporated by reference: Ariel Ismach, Clara Druzgalski, Samuel Penwell, Adam Schwartzberg, Maxwell Zheng, Ali Javey, Jeffrey Bokor, and Yuegang Zhang,Direct Chemical Vapor Deposition of Graphene on Dielectric Surfaces, Nano Lett. 2010, 10, 1542-1548, American Chemical Society, Apr. 2, 2010.

In another exemplary process, graphene capsule120may be deposited directly on to optic fiber114without the use of a metal catalyst, such as sacrificial copper layer102. The CVD is performed in an atmospheric pressure hot-wall quartz tube furnace. CH4is used as a carbon precursor gas, mixed with auxiliary reduction (H2) and carrier (Ar) gases. The optic fiber core100is heated to 1000° C. (at a rate of 30° C. /min) under H2(50 sccm) and Ar (1000 sccm) atmosphere and kept at 1000° C. for 3 min. Then, 300 sccm CH4is introduced to initiate the formation of graphene. The typical growth time is 30-60 min. After the deposition, the CH4flow is stopped, leaving other gases to flow for further 3 min to remove residual reaction gases before allowing the chamber to naturally cool to room temperature (20° C./min) in the same H2—Ar atmosphere. The graphene layer104can also be deposited directly on SiO2by using other hydrocarbon precursors, such as C2H2, showing the generality of the process. The growth of graphene directly on a silica substrate is reported in the following publication, hereby incorporated by reference: Jie Sun, Niclas Lindvall, Matthew T. Cole, Teng Wang, Tim J. Booth, Peter Boggild, Kenneth B. K. Teo, Johan Liu, and August Yurgens.Controllable chemical vapor deposition of large area uniform nanocrystalline graphene directly on silicon dioxide. Journal of Applied Physics 111, 044103 (2012).

While optic fiber114may be formed of silica, other glasses with higher indicies of refraction may be used for optic fiber core110and cladding112. For example, it may be desirable to make optic fiber core110and cladding112from halide-chalcogenide glasses. The processes discussed above are not compatible with halide-chalcogenide glasses due to the high temperatures of the CVD process. Halide-chalcogenide glasses have a melting temperature of 378° C. and would not survive a CVD process at 900-1100° C. However, a variety of low-temperature graphene synthesis techniques are known with very low thermal budgets. With these techniques, the halide-chalcogenide glasses are heated to temperatures around 300° C. for graphene growth. For example, a halide-chalcogenide optic fiber core100may be heated in a CVD chamber to 300° C. and exposed to a benzene precursor as the carbon source to create a monolayer of graphene. This process is reported in the following publication, hereby incorporated by reference: Zhancheng Li, Ping Wu, Chenxi Wang, Xiaodong Fan, Wenhua Zhang, Xiaofang Zhai, Changgan Zeng, Zhenyu Li, Jinlong Yang, and Jianguo Hou.Low-Temperature Growth of Graphene by Chemical Vapor Deposition Using Solid and Liquid Carbon Sources. ACSNANO VOL. 5, NO. 4, 3385-3390, 2011. In an alternative low temperature process, graphene film may be synthesized on a halide-chalcogenide optic fiber core100at 280° C. utilizing a microwave plasma treatment in combination with PolyMethylMethacrylate (PMMA). With this process, a layer of PMMA is spin-coated onto a halide-chalcogenide optic fiber core100at room temperature. The PMMA coated halide-chalcogenide optic fiber core100is then inserted into a slot antenna-type microwave plasma CVD system for microwave plasma treatment at 280° C. The plasma treatment time is 30 seconds. This plasma treatment process is disclosed in the following publication, hereby incorporated by reference: Takatoshi Yamada, Masatou Ishihara, and Masataka Hasegawa.Low Temperature Graphene Synthesis from Poly(methyl methacrylate)Using Microwave Plasma Treatment. Applied Physics Express 6 (2013) 115102-1.

FIG. 5illustrates a flow chart3000depicting an exemplary process of fabricating an optic fiber116having a core110and cladding112encapsulated by a graphene layer120that forms mechanical support and an optic wave guide around cladding112. The process begins with START3002. An optic fiber having a core and cladding made of silica is prepared and cleaned with acetone and alcohol in step3004. In step3006, a thin sacrificial layer of copper is formed onto the surface of optic fiber114. Next in step3008, a CVD process is performed depositing graphene layer104onto optic fiber114during which the sacrificial copper layer102evaporates. Then in step3010, the ends of optic fiber core114not covered by graphene cylinder104are cut for example, by a laser. In this step, optic fiber114and graphene cylinder104are cleaned. In step3012, circular sheets of graphene106are applied to the ends of optic fiber114, thereby forming a graphene capsule encapsulating optic fiber114. In step3014, exposing graphene sheets106and graphene cylinder104to a carbon atmosphere creates carbon-carbon bonds between graphene cylinder and graphene sheets106, thereby further creating a graphene capsule encapsulating optic fiber116. The process ENDS with step3016.

FIG. 6illustrates Scanning Electron Microscope (SEM) images of a pure optic fiber that is not coated with graphene adjacent to an optic fiber that is coated with graphene at three different resolutions.FIG. 6(a)illustrates an SEM image of a pure silica optic fiber that is not coated with graphene at a magnification of 150×.FIG. 6(b)illustrates an SEM image of a optic fiber coated with a graphene cylinder at a magnification of 150×. The graphene cylinder is a monolayer of graphene in portions and multilayer graphene in other portions. The graphene coated areas are a bit darker than the pure silica fiber, particularly in the areas where the graphene is multilayer.FIG. 6(c)illustrates an SEM image of a pure silica optic fiber that is not coated with graphene at a magnification of 800×.FIG. 6(d)illustrates an SEM image of a optic fiber coated with a graphene cylinder at a magnification of 800×. InFIG. 6(d), it can been seen that the graphene conforms highly to the contours of the optic fiber. The darker areas of graphene indicate that monolayer graphene may be overlapped to form bi-layer or multilayer graphene.FIG. 6(e)illustrates an SEM zoomed-in image of a pure silica optic fiber that is not coated with graphene at a magnification of 800×.FIG. 6(f)illustrates an SEM image of a optic fiber coated with a graphene cylinder at a magnification of 1200×. At this resolution, it can be seen inFIG. 6(f)that the surface of the silica fiber is very clean and smooth and covered with a highly conforming layer of graphene. InFIG. 6(f), graphene layer is in portions a monolayer and in portions a bi-layer, as evidenced by the darker wrinkled areas of graphene.

FIG. 7illustrates an (a) Optical Microscope (OPM) image of a graphene covered silica fiber114adjacent to a pure silica fiber118not coated with graphene along with a (b) higher resolution OPM image of a graphene coated silica fiber114. InFIG. 7(a), the silica optic fiber114is encapsulated by a graphene capsule120. It is observed the that graphene encapsulated optic fiber is darker in color than the pure silica fiber below it that is not covered with graphene. In addition, the pure silica fiber that is not covered with graphene has a smoother appearing surface than the graphene encapsulated fiber that shows the various layers of the graphene coating. InFIG. 7(b), graphene encapsulated optic fiber104is viewed at a higher optical resolution revealing the graphene capsule120deposited on the fiber. The various shading or coloring differences on the surface of fiber104show the graphene deposition in either a monolayer, bi-layer, or multilayer of graphene.FIG. 7(b)illustrates that the graphene conforms to the contours of optic fiber104and uniformly covers it.

FIG. 8illustrates SEM images of an end of an optic fiber core110and cladding112completely coated with graphene106. Optic fiber core110is visible inFIG. 8(a)andFIG. 8 (b)as a white dot at the center of the image. Surrounding optic fiber core110is silica cladding112. The mottled transparent surface covering the end of optic fiber core110and silica cladding112is graphene coating106. The various differences of color of graphene coating106reveals that portions of graphene coating106are formed of a monolayer of graphene, a bi-layer of graphene, or a multilayer of graphene. The darker portions of graphene layer106, appearing as veins, have the most number of overlapping graphene layers.

FIG. 9illustrates SEM images of an end of an optic fiber core110and cladding112partially coated with graphene1000adjacent to an end of an optic fiber core110and cladding112that is not coated with any graphene.FIG. 9is provided to compare and contrast the end of an optic fiber core110and cladding112that is partially covered with graphene1000inFIG. 9(a)and not covered at all with graphene inFIG. 9(b)to the optic fiber core110and cladding end ofFIG. 8(a) and (b)that is completely covered with graphene sheet106. InFIG. 9(b), the end of optic fiber core110and cladding112is bright and uniform in color and texture. InFIG. 9(b), a portion of the end of cladding112is covered with graphene layer1000that shows variances in color/texture due to the fact that some of layer1000is a monolayer, a bi-layer, or multilayer of graphene. The darker the color of graphene layer1000indicates more layers of graphene compared to lighter areas in color.

FIG. 10illustrates a Raman spectra of a graphene coated optic fiber108or116and an optic fiber not coated with graphene for comparison. The black solid curve presents the Raman spectra of graphene coating120of fiber108or116. The narrow D, G and 2D peaks at 1350 cm−1, 1580 cm−1and 2690 cm−1show the graphene coating120on fiber108or116is of high quality. To compare and contrast, the grey dashed curve presents the Raman spectra of a silica fiber100or114without a graphene coating120. Note that there area no peaks in the window of 1200 cm−1to 3200 cm−1for the fiber not coated with graphene.

FIG. 11illustrates the wavelength dependence of the index of refraction n for graphene. The index of refraction of graphene n is dependent upon the wavelength of light. Light having a wavelength from 200 nm to 400 nm is in the ultraviolet spectrum. Light having a wavelength in the range of 400 nm to 600 nm is in the violet-yellow spectrum. Light having a wavelength in the range of 600 nm to 800 nm is in the orange to red spectrum. Light having a wavelength in the range of 800 nm to 1000 nm is in the infrared spectrum. The wavelength dependence of the index of refraction n for graphene is reported in the following reference hereby incorporated by reference: Alex Gray, Mehdi Balooch, Stephane Allegret, Stefan De Gendt, and Wei-E Wang.Optical detection and characterization of graphene by broadband spectrophotometry. Journal of Applied Physics 104, 053109 (2008). As shown inFIG. 11, graphene has an index of refraction n<1 at 200 nm. Graphene exhibits an index of refraction n<1.5 below a wavelength of 260 nm. Silica is a common material for optic fiber cores100and110. Silica has an index of refraction of n=1.5. Thus, when optic fiber core100is made of silica and propagates light having a wavelength of less than 260 nm, graphene layer120can function as cladding because graphene layer120has a lower index of refraction than that of silica. An exemplary UV optic circuit utilizing a deep UV LED to emit deep UV light having a wavelength of 245 nm through an optic fiber core100encapsulated in a graphene cladding layer120is shown inFIG. 12. At 245 nm, optic fiber core100or110may be made of silica and encapsulated by a graphene layer120for cladding. Deep UV LEDs having a wavelength of 210 nm are also known and may be used in combination with optic fiber core100or110, allowing for smaller diameter sizes for optic fiber core100or110with a silica core and graphene cladding120.

Referring again toFIG. 11, graphene generally exhibits an index of refraction below 3 up to 900 nm. While optic fiber core100/110is generally made of silica (SiO2), other types of glasses may be used for optic fiber core100/110. In particular, a variety of high index of refraction glasses may be used for optic fiber core100/110. Through utilizing a glass with a higher index of refraction, it is possible to utilize a graphene layer120as a cladding layer at higher wavelengths of light. For example, halide-chalcogenide glasses have properties that make them suitable for optical fibers and they are reported to have indices of refraction n ranging from 2.54 to 2.87 as reported in the following reference hereby incorporated by reference: Jan Wasylak, Maria Lacka, Jan Kucharski.Glass of high refractive index for optics and optical fiber. Opt. Eng. 36(6) 1648-1651 (June 1997) Society of Photo-Optical Instrumentation Engineers. As illustrated inFIG. 11, when optic fiber core100/110is made of a Halide-chalcogenide glass with an index of refraction of 2.87, graphene can be used as a cladding layer120for light of wavelengths of less than 910 nm, which is in the infrared portion of the spectrum. Thus, for the deep UV, visible, and a portion of the infrared spectrum Halide-chalcogenide glass may be used for optic fiber core100/110and propagate light from 200 nm to 900 nm with a graphene cladding layer120. The use of silica and halide-chalcogenide glasses are merely exemplary. It is contemplated that any glass may be utilized for optical fiber core100/110in connection with a graphene cladding capsule120with the limitation that the propagation of light wavelengths is limited to the range such that the index of refraction of the graphene is less than the index of refraction of the particular glass used for optic fiber core100/110. Examples of other high index refraction glasses include PbO glass that has an index of refraction of n=2. Lanthanum dense flint glass has a refractive index of n=1.8. Flint glass has a refractive index of 1.62. To utilize graphene as a cladding layer, it may be desirable to utilize a monolayer of graphene. Alternatively, it may be desirable to grow multilayer graphene to form a cladding layer.

FIG. 12illustrates an opto-electronic circuit utilizing a graphene coated optic fiber308. Input data is received by transmitter circuitry300. Transmitter circuitry300controls a light source302, such as a laser, to transmit light signals across optic fiber308. In a preferred embodiment, light source302is a deep ultraviolet laser or LED having a wavelength of 245 nm and power of 30-70 μW having an AlGaN structure. An exemplary optic cable308is of the form shown inFIG. 2 or 5that includes a silica optic fiber core100/110encapsulated by a graphene capsule120. The core100may additionally be surrounding by a cladding112, which is also encapsulated by graphene capsule120. The silica optic fiber core100in this example has a diameter of 250 nm to 405 nm. As the wavelength of the UV light is 245 nm, graphene capsule120functions as a cladding layer due to the fact that at a wavelength of 245 nm, graphene has an index of refraction that is less than silica as shown byFIG. 11. Light source302is turned ON and OFF corresponding to the input data to transmit a signal across optic cable308. A receiver circuit304receives the deep UV signals emitted by deep UV LED302. Receiver circuit304receives the light impulses signifying the input data signal. Detector circuit306converts the received optical signal into output data. Developing circuitry that operates based on light transmitted at higher optical frequencies will allow for faster data transmission and hence, increased bandwidth. The use of UV light will greatly enhance data transmission rates over existing optical wavelengths.FIG. 12shows a unidirectional optical transmission circuit that in that data is transmitted from light source302across fiber308to receiver circuitry304.

FIG. 13illustrates a pair of microchips310and312configured to communicate with each other across a optic fibers318and320. Microchip310includes transmitter circuitry300A and a light source302A, which is typically a laser. Microchip310also includes a controller314A and memory316A. Controller314A controls the operation of chip310A. Memory316A stores data that is to be sent to chip312, or is received from chip312. Microchip312includes transmitter circuitry300B and a light source302B, which is typically a laser. Microchip310also includes a controller314B and memory316B. Controller314B controls the operation of chip310. Memory316B stores data that is to be sent to chip310, or is received from chip310. Transmitter circuitry300A prepares data from memory316A to be sent across dedicated optic fiber transmission line318to receiver circuitry304B, which is an optic detector. Detector circuit306B converts the optic signals received by receiver circuitry304B into data that is stored in memory316B. Transmitter circuitry300B prepares data from memory316B to be sent across dedicated optic fiber transmission line320to receiver circuitry304A, which is an optic detector. Detector circuit306A converts the optic signals received by receiver circuitry304A into data that is stored in memory316A. Typically, optic fibers transmit signals in a single direction. Thus, two optic fiber transmission lines318and320are required for bi-directional communication as shown inFIG. 13. It is contemplated that lasers302A and302B are ultraviolet lasers and optic fibers318and320are formed of optic fiber cores100/110that are encapsulated by graphene capsules120. However, any wavelength of light might be used. The use of ultraviolet light is merely exemplary. The optic circuitry ofFIG. 13can be used in combination with Small Form-factor Pluggable (SFP) transceivers, which are available in a variety of transmitter and receiver types that can function as transmitters300/302and receivers304/306. As each fiber318and320is unidirectional for communication, the combined pair of them is required to form an optical fiber cable.

While the invention has been shown and described with reference to a particular embodiment thereof, it will be understood to those skilled in the art, that various changes in form and details may be made therein without departing from the spirit and scope of the invention.