Patent Publication Number: US-2005135759-A1

Title: Optical fiber assembly

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT  
      One of the coinventors of this patent application, Samuel DiVita, has worked for the United States Government in various capacities since 1942. Thus, the United States Government will have rights in this patent application. 
    
    
     FIELD OF THE INVENTION  
      An optical fiber assembly comprised of nanoparticles.  
     BACKGROUND OF THE INVENTION  
      Optical fibers are amorphous glass assemblies that typically contain one functional material adapted to transmit light. It is an object of this invention to provide an optical fiber assembly that has several functionalites in addition to the transmission of light.  
     SUMMARY OF THE INVENTION  
      In accordance with this invention, there is provided a fiber assembly comprised of nanoparticles, wherein said nanoparticles are a mixture of nanomagnetic particles and nanooptical particles. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The invention will be described by reference to the following Figures, in which like numerals refer to like elements, and in which:  
       FIG. 1  is  
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      FIGS.,  1 ,  2 ,  3 , and  4  are each a sectional view of one preferred fiber assembly of the invention;  
       FIGS. 5 and 6  illustrate applications of one preferred fiber assembly of the Invention;  
       FIG. 7  is a schematic of an optical isolator using Faraday rotation;  
       FIGS. 8A, 8B , and  8 C illustrate the use spintronics with one preferred fiber assembly of the invention;  
       FIG. 9  is a schematic of a fiber optical device comprised of nanoparticles;  
       FIG. 10  is a schematic of a surface accoustic wave (SAW) device;  
       FIG. 11  is a schematic of an optical device with two parallel assemblies; and  
       FIG. 12  is a flow diagram illustrating one preferred process of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBOIDMENTS  
      A Nanosized Cluster  
       FIG. 1  is a top view of a nanosized cluster  10  that is comprised of nanoparticles with different functionalities. The nanoparticles  12  have optical properties. The nanoparticles  14  have electro-optical properties. The nanoparticles  16  have magnetic properties. The nanoparticles  17  have acoustic properties.  
      In the preferred embodiment depicted in  FIG. 1 , the nanosized cluster  10  has a substantially circular-cross sectional shape  18 . In one aspect of this embodiment, the nanosized cluster  10  is a fiber  10 . In this aspect, for the purposes of simplicity of representation, only the unshaded portion of the fiber  10  is shown as having the nanoparticles  12 / 14 / 16 / 17 , it will be apparent that, in this aspect, the entire fiber  10  is preferably comprised of said nanoparticles.  
      In the preferred nanosized cluster  20  depicted in  FIG. 2 , the nanoparticles  12 / 14 / 16 / 17  are disposed on the outside surface  22  of the optical fiber  20 . In this embodiment, the optical fiber  20  is made from glass (such as, e.g., fused silica), and the nanoparticles  12 / 14 / 16  are coated on the exterior surface(s) of such glass fiber.  
      In the preferred nanosized cluster  30  depicted in  FIG. 3 , the nanoparticles  12 / 14 / 16 / 17  comprise the core  36  of fiber  30 , which is also comprised of sheath  38 .  
      In the preferred nanosized cluster  40  depicted in  FIG. 4 , a hollow fiber  40  is depicted with a sheath  42  and a hollow center  44 . In this embodiment, the nanosized particles  12 / 14 / 16 / 17  are disposed on both the inner and outer surfaces,  46  and  48  respectively, of the fiber  40 . In another embodiment, not shown, the nanosized particles  12 / 14 / 16 / 17  are disposed only on the inner surface  46 . In yet another embodiment, not shown, such nanosized particles  12 / 14 / 16 / 17  are disposed only on the outer surface  48 .  
      The nanosized clusters depicted in  FIGS. 1, 2 , and  3  generally have a maximum dimension (such as, e.g., their diameters) of from about 2 to about 200 micrometers, nanometers. In one embodiment, the maximum dimension of the nanosized clusters is from about 10 to about 100 micrometers.  
      The naanoparticles  12 / 14 / 16 / 17  generally have a maximum dimension of from about 1 to about 500 nanometers. In one embodiment, such nanoparticles have a maximum dimension of from about 10 to about 100 nanometers.  
      One may utilize any of the optical nanoparticles disclosed in the art. Reference may be had, e.g., to U.S. Pat. No. 6,329,058 (nanosized transparent metal oxide particles, such as titanium oxide), U.S. Pat. No. 5,777,776 (nanosized pigment particles), U.S. Pat. No. 6,190,731 (nanosized metallic ink particles), U.S. Pat. No. 5,434,878 (nanosized optical scattering particles, such as titania and alumina), U.S. Pat. No. 5,023,139 (nanosized sheath/core optical particles), and the like. The entire disclosure of each of these United States patents is hereby incorporated by reference into this specification.  
      In one embodiment, the optical nanoparticles  12  comprise or consist essentially of titanium oxide. In another embodiment, the optical nanoparticles  12  comprise or consist essentially of one or more of the oxides of tantalum. In another embodiment, the optical nanoparticles  12  comprise or consist essentially of silica.  
      The optical nanoparticle(s)  12  can function to transmit light, disperse light, diffract light, and/or reflect light. In one embodiment, the optical nanoparticles will have an index of refraction of from about 1.2 to about 10, and preferably from about 2 to about 3.  
      The optical nanoparticles, unlike the other nanoparticles, require no energy besides light to perform their function(s).  
      Referring again to  FIG. 1 , one may use any of the electro-optical nanoparticles known to those skilled in the art. Reference may be had, e.g., to a text by B. E. A. Saleh et al. entitled “Fundamentals of Photonics (John Wiley &amp; Sons, Inc., New York, N.Y., 1991). Referring to Chapter 15 of such book, the electro-optical nanoparticles may be used as semiconducting materials. Referring to Chapter 16 of such book, the electro-optical nanoparticles may be used as light-emitting devices. Referring to Chapter 17 of such book, the electroptical nanoparticles may be used as photon detectors. Referring to Chapter 18 of such book the electrooptical nanoparticles may be used as electrooptical materials such as, e.g., photorefractive materials.  
      Similarly, one may use any of the nanoparticles known to those skilled in the art that have acoustic properties. Thus, e.g., referring to Chapter 20 of such Saleh et al. text, the nanoparticles may have acousto-otpical properties wherein the particles are used to change the interaction between sound and light.  
      In another embodiment, one may use nanoparticles that exhibit the surface acoustic wave (SAW) phenomenon. As is known to those skilled in the art, particles possessing this property, when subjected to electrical energy, generate a surface wave of sound energy. Reference may be had, e.g., to U.S. Pat. Nos. 6,323,577, 6,310,425, 6,310,424, 6,310423, 6,291,924, 6,275,123, and the like. The entire disclosure of each of these United States patents is hereby incorporated by reference into this specification.  
      One may use any of the magnetic nanoparticles known to those skilled in the art. Thus, e.g., reference may be had to U.S. Pat. Nos. 5,741,435, 6,262,949 (magneto-optical nanosized particles), U.S. Pat. No. 6,251,474 (nanosized ferrite particles), and the like. In one aspect of this emobidment, the nanosized particles exhibit the magentooptical effect.  
      The magnetooptical effect is well known to those skilled in the art and is described, e.g., in the aforementioned Saleh text; see, e.g., pages 225 through 227 of such text. This effect, which is also often referred to as the Faraday effect, involves the fact that certain materials act as polarization rotators when placed in a static magnetic field. The angle of rotation is proportional to various factors, such as the magnetic flux density. Yttrium-iron-garnet particles (YIG), terbium-gallium-garnet particles (TGG), terbium, aluminum-garnet particles (TbAIG), and other material exhibit this effect.  
      Applicants have described nanoparticles with optical, mangetic, electrooptical, and acoustic properties in conjunction with this invention. This has been done merely for the sake of illustration; it will be appreciated that nanoparticles with other properties also may be used in conjunction with his invention. Thus, e.g., nanopartices with piezoelectric, electrostrictive, thermoelectric, giant-magneto, electromagneto, and other effects also may be used.  
      One may custom design the property or properties desired in the nanoparticle or nanoparticles to be used in the optical fiber. Thus, via the process of this invention, one may deposit specified amounts of specified nanoparticles with specified properties to achieve any function or combination of functions desired.  
      Preparation of the Preferred Coated Optical Fiber  
      In one preferred embodiment, illustrated in  FIGS. 1, 2 ,  3 , and  4 , the preferred nanoparticle cluster assembly is an coated optical fiber comprised of two or more of the nanoparticles  12 ,  14 ,  16 , and  17 . These coated optical fibers can be prepared by means well known to those skilled in the art.  
      In one embodiment, an optical fiber is used as a substrate, the substrate is coated with one or more-coating materials comprising the desired nanoparticle(s). In this embodiment, it is preferred that the optical fiber to be coated have certain specified properties.  
      The optical fiber substrate preferably has a low loss. As is known to those skilled in the art, fiber loss is energy loss per unit length. Thus, e.g., silica fibers have a fiber loss of 0.5 decibels per kilometer of length. Reference may be had, e.g., to U.S. Pat. No. 6,219,176, the entire disclosure of which is hereby incorporated by reference into this specification. This patent discloses, e.g., that “ . . . in recent years, a manufacturing technique and using technique for a low-loss (e.g., 0.2 dB/km) optical fiber have been established, and an optical communication system using the optical fiber as a transmission line has been put to practical use. Further, to compensate for losses in the optical fiber and thereby allow long-haul transmission, the use of an optical amplifier for amplifying signal light has been proposed or put to practical use.” The use of an optical fiber substrate with a fiber loss of less than about 0.2 decibels per kilometer is preferred in the process of this invention.  
      The optical fiber substrate used in the process of this invention has a preferably low dispersion property. In general, the dispersion of the fiber is such that its bit rate x its length exceeds 100 (gigabits/second)-kilometer. Reference may be had, e.g., to U.S. Pat. Nos. 6,292,601, 6,061,483, and the like. The entire disclosure of each of these United States patents is hereby incorporated by reference into this specification.  
      The optical fiber substrate used in the process of this invention can either be a single-mode fiber, or a multi-mode fiber. For implantable device applications, where light is used to transfer energy, multi-mode fibers are preferred. For communication applications, a single mode optical fiber is preferred.  
      In single mode fiber applications, a polarized light source is preferred. One such device is illustrated in  FIG. 5 .  
      Referring to  FIG. 5 , a light source  50  generates a light beam  52  which, as is well known to those skilled in the art, has a propration direction in the direction of arrow  54 , an electrical field in the direction of arrow  56 , and a magnetic field in the direction of arrow  58 . This light beam  52  passes through the center of single mode optical fiber  60 .  
      If single mode optical fiber  60  is homogeneous, without any dielectrical or magnetic properties with the exception of light bending, then light beam  52  exits the distal end  62  of optical fiber  60  substantially unchanged. However, if single mode optical fiber  60  is not homogeneous, and contains nanoparticles  12 ,  14 ,  16 , and/or  17 , then the light beam  52  will be substantially changed.  
       FIG. 6  illustrates what happens to the light beam  52  when it passes through a single mode optical fiber  70  comprised of nanomagnetic particles  16 . In the embodiment depicted in  FIG. 6 , for the sake of simplicity of representation, such nanomagnetic particles  16  have been shown disposed on only a portion of the inside surface of the optical fiber  70 .  
      As will be apparent, the light beam  52  will be affected by the nanomagnetic particles  16  in fiber  70 , so that it becomes transformed to light beam  53 . The direction of light beam  53  is the same as the direction of light beam  52 , but its electrical and magnetic fields have been rotated. Thus, as will be shown more clearly by reference to  FIG. 7 , the optical fiber  70  acts as an optical isolator.  
       FIG. 7  is a copy of diagram 6.6-5 from page 234 of the Saleh, in which device  70  (see  FIG. 6 ) has been identified as the preferred Faraday rotator. Referring to such Saleh text, the optical isolator device in question transmits light in only one direction, thus acting as a one-way valve. These optical isolators are useful in preventing reflected light from returning back to the source. Because of the small size of the optical fiber used, optical isolators such as optical isolator  70  may be implanted within a living organism.  
       FIG. 8  is a schematic of controlled spintronic device. As is disclosed in U.S. Pat. No. 6,249,453, “spintronic devices make use of the electron spin as well as its charge. It is anticipated that spintronics devices will have superior properties compared to their semiconductor counterparts based on reduced power consumption due their inherent nonvolatility, elimination of the initial booting-up of random access memory, rapid switching speed, ease of fabrication, and large number of carriers and good thermal conductivity of metals. Such devices include giant magnetoresistance (GMR) and tunneling magnetoresistance (TMR) structures that consist of ferromagnetic films separated by metallic or insulating layers, respectively. Switching of the magnetization direction of such elementary units is by means of an external magnetic field that is generated by current pulses in electrical leads that are in proximity. A system whereby the magnetization direction is controlled by an applied voltage is discussed at length in U.S. Ser. No. 09/467,808, incorporated herein by reference. Such as system comprises a ferromagnetic device with first and second ferromagnetic layers. The ferromagnetic layers are disposed such that they combine to form an interlayer with exchange coupling. An insulating layer and a spacer layer are located between the ferromagnetic layers. When a direct bias voltage is applied to the interlayer with exchange coupling, the direction of magnetization of the second ferromagnetic layer.” The entire disclosure of this United States patent is hereby incorporated by reference into this specification.  
      One of the most fundamental spintronic devices is the magnetic tunnel junction; reference may be had, e.g., to U.S. Pat. Nos. 6,269,018, 6,097,625, 6,023,395, 6,226,160, 6,114,719, and the like. The entire disclosure of each of these United States patents is hereby incorporated by reference into this specification.  
      As is known to those skilled in the art, the magnetic tunnel junction is just two layers of ferromagnetic material separated by a magnetic barrier. When the spin orientation of the electrons in the two ferromagnetic layers are the same, a voltage is quite likely the pressure the electrons to tunnel through the barrier, resulting in high current flow. But flipping the spins in one of the two layers, so that the two layers have oppositely aligned spins, restricts the flow of current. See, e.g., page 33 of the December, 2001 issue of I.E.E.E. Spectrum (published by the Institute of Electrical and Electronics Engineers, New York, N.Y.).  
       FIG. 8  illustrates a device  90  for flipping the spin of the material within device  90 , thereby affecting its current flow properties. Referring to  FIG. 8 , and in the preferred embodiment depicted therein, light beam  52  from light source  50  enters the proximal end  100  of optical fiber  102 . As it travels the light delivery region  104  of fiber  102 , its magnetic polarization properties are unaffected. However, when it travels through spintronic region  106 , it flips the spin of the nanomagnetic particles  16  disposed within such region; and it simultaneously aligns the spin of the electrons flowing through spintronic section  106  (see  FIGS. 8   b  and  8   c , from said IEEE Spectrum article).  
      Referring again to  FIG. 8 , optical fiber  102 , in addition to containing magnetic nanoparticles  16 , also contains a coating of semiconductive material. In the top half  108  of the optical fiber, gallium arsenide semiconductive material (not shown) is coated on the inside surface of the optical fiber  102 . In the bottom half  110  of the optical fiber  102 , zinc selenide is coated on the inside surface of the optical fiber  102 . The travel of the light beam  52  through the fiber  102  affects the spins of both of electrons in each of these semiconductive materials.  
      If the spins of the electrons within the gallium arsenide material and the spins of the electrons within the zinc selenide material are aligned, current flow through the fiber device  102  will be large. If, however, the spins of the electrons within the two materials are not aligned, current flow will be restricted. Thus, by choosing the type of semiconductive materials, and the type of magnetic nanoparticles  16 , one can either reduce or increase current flow through the device, in addition to the transmission of the light  52 .  
      In another embodiment, not shown, one may apply an external magnetic field in addition to the magnetic nanoparticles  16 .  
       FIG. 9  is a schematic of a device  10  that is comprised of a core of nanoparticles that may, e.g., be electrical nanoparticles  122 . The electrical nanoparticles  122  are chosen to have a high electrical conductivity.  
      Disposed around core  121  is a first sheath  124  of material that conducts heat but not electricity. Such first sheath  124  may comprise or consist essentially of, e.g., aluminum nitride.  
      Disposed about first sheath  124  is a second sheath  126 , which may be made of glass fiber.  
      As will be apparent to those skilled in the art, when device  120  is implanted in a living organism, it will transmit electricity internally but not pass any such electricity or heat to its external surroundings within the organism. The aluminum nitride prevents the transmission of electricity from core  121  to such surroundings. The heat transmitted from such core  121  to the aluminum nitride first sheath may be dissipated in heat sink  128 , to which the aluminum nitride is operatively connected. In one embodiment, heat sink  128  is a battery, which forms a circuit with core  121  and load  123 . The heat is conducted via line  140 , along the direction  142 . The current flows in the direction of arrow  130 .  
      Referring again to  FIG. 9 , and in one preferred embodiment, in addition to electricity being transmitted through the device in the direction of arrow, light from light beam  52  may simultaneously be transmitted through the glass portion of the assembly.  
       FIG. 10  is a schematic view of a SAW (surface acoustic wave) device  160 . Device  160  is comprised of core  162  of glass which is covered by sheath  164 . In the embodiment depicted, for the purposes of simplicity of representation, sheath  164  is shown only partially enclosing core  162 . In most embodiments, it is preferred that the sheath  164  entirely enclose core  162 .  
      The sheath  164  is preferably of a material selected from the group consisting of piezoelectric material, electrostrictive material, and mixtures thereof. When voltage is supplied from power supply  166  to sheath  164 , the material in sheath  164  mechanically deforms, causing a change in the configuration of its surface. The change in configuration will preferably travel down the length of the sheath  164  in the form of a wave  1168 .  
      As will be apparent to those skilled in the art, because of the small size of the optical fibers used, the assembly  160  may be disposed within a living organism and be used to stimulate such organism.  
      In one embodiment, in addition to providing such mechanical stimulation, the device  160  may also provide light (from light beam  52 ) via light port  170 . In addition, the device also may provide electrical stimulation through conductor  172 .  
      In the embodiment depicted in  FIG. 10 , conductor  172  is connected to transducer  174  via line  176 , which may convert some or all of the electrical current into sound, light, magnetic energy, and the like. In addition, transducer  174  may act as a power supply to convert the electrical energy into electrical pulses, which may be used to stimulate a heart.  
      In the embodiment depicted, the device  160  is connected to a controller  180 , via line  182 . The controller  180  is preferably connected to one or more of the organs of the living organism; and, thus, it can modify the output of device  160  depending upon the need of such organ(s), to deliver one or more of mechanical stimulation, light energy, electrical energy, acoustic energy, and the like.  
       FIG. 11  depicts a device  200  which is similar to the device  160  but contains two substantially parallel assemblies  202  and  204 . Each of devices  202  and  204  is similar to the device  160 , with the exception that device  202  is adapted to transmit light to target  206 , via line  208 ; and device  204  is adapted to transmit either electrical energy and/or transduced electrical energy to target  210  via line  212 . As will be apparent, the separation of the conductor  172  from chamber  202  facilitates the transmission of light.  
      A Preferred Process for Making the Devices of This Invention  
       FIG. 12  is a flow diagram illustrating one preferred process of the invention. Referring to  FIG. 12 , and in the preferred embodiment depicted therein, in step  220  raw materials are charged to a mixer via line  222 . The raw materials will be mixed in a stoichiometry so that the desired end product(s) will be produced.  
      In one embodiment, in addition to the desired raw material(s), one also charges liquid to mixer  220  via line  224 . It is preferred to charge sufficient liquid so that one produces a solution and/or a slurry with a solids content of from about 5 to about 60 weight percent.  
      In step  226 , the slurry from step  220  is transferred via line  228  to a furnace, in which a rod is formed from the slurry. This rod, which is often referred to as a “cylindrical preform,” may be formed by conventional means. Reference may be had, e.g., to U.S. Pat. Nos. 4,199,337, 4,224,046 (optical fiber preform), U.S. Pat. No. 4,682,294 (optical fiber preform), and the like. The entire disclosure of each of these United States patents is hereby incorporated by reference into this specification. One may also refer to pages 65-67 of G. P. Agrawal&#39;s “Fiber-Optic Communication Systems” (John Wiley and Sons, Inc., New York, N.Y., 1997) for the process for preparing such a fiber preform.  
      Once the preform has been produced, in step  230  the preform is clad with a coating of nanoparticles. One may clad such preform by conventional coating means. Thus, by way of illustration and not limitation, one may use the MCVD (modified chemical vapor deposition), OVD (outside vapor deposition), and/or vapor-axial deposition (VAD). Reference may be had, e.g., to page 66 of such Agrawal text. Reference may also be had to United States patents discussing such MCVD technique (see U.S. Pat. Nos. 6,015,396, 6,122,935, 5,397,372, 4,389,230, 6,131,413), such OVD technique (see U.S. Pat. No. 6,295,843), and/or said VAD technique (see U.S. Pat. Nos. 6,131,415, 4,801,322, 5,281,248, and the like). The entire disclosure of each of these United States patents is hereby incorporated by reference into this specification.  
      In such step  232  of the process, one may etch the clad fiber. As is known to those skilled in the art, one may conduct such etching by chemical, mechanical, or lithographic means. See, e.g., U.S. Pat. No. 6,285,127 (etched glass spacer), U.S. Pat. No. 6,281,136 (etched glass), U.S. Pat. Nos. 6,105,852, 6,071,374, and the like. The entire disclosure of each of these United States patents is hereby incorporated by reference into this specification.  
      As will be apparent, the function of the etching step  232  is to form a one or more specified grooves or indentations in the optical fiber and/or the cladding. As will be apparent, by the judicious use of masking, one may etch only selected portions of the substrate.  
      In step  234 , the etched substrate is optionally coated with one or more additional coating materials. Such additional coatings may be applied by conventional means such as, e.g., chemical vapor deposition, plasma activated chemical vapor deposition, physical vapor deposition, ion implantation, sputtering, ion plating, plasma polymerization, laser deposition, electron beam deposition, molecular beam chemical vapor deposition, plasma deposition, and the like. Reference may be had to H. K. Pulker&#39;s “Coating on Glass” (Elsevier, Amsterdam, The Netherlands, 1999).  
      In one embodiment, chemical vapor deposition is used in step  234 . This technique is very well known. Reference may be had, e.g. to U.S. Pat. Nos. 4,561,871, 5,338,328, 5,296,011, 4,528,009, 4,206,968, and the like. The entire disclosure of each of these United States patents is hereby incorporated by reference into this specification.  
      In another embodiment, plasma coating is used. Reference may be had to U.S. Pat. No. 5,540,959, the entire disclosure of which is hereby incorporated by reference into this specification. This patent claims a process for preparing a coated substrate in which mist particles are created from a dilute liquid, the mist particles are contacted with a pressurized carrier gas and contacted with radio frequency energy while being heated to form a vapor, and the vapor is then deposited onto a substrate. The coated substrate is then preferably heated.  
      It is to be understood that the aforementioned description is illustrative only and that changes can be made in the apparatus, in the ingredients and their proportions, and in the sequence of combinations and process steps, as well as in other aspects of the invention discussed herein, without departing from the scope of the invention as defined in the following claims.