Optical waveguides – Optical transmission cable – With electrical conductor in the same cable
Reexamination Certificate
1999-11-12
2001-06-12
Palmer, Phan T. H. (Department: 2874)
Optical waveguides
Optical transmission cable
With electrical conductor in the same cable
C385S100000, C385S102000
Reexamination Certificate
active
06246821
ABSTRACT:
This application is based on and claims the benefit of German Patent Application No. 19852480.3 filed Nov. 13, 1998, and German Patent Application No. 19901354.3 filed Jan. 15, 1999, which are incorporated by reference herein.
BACKGROUND OF THE INVENTION
The invention concerns an optical waveguide, in particular for a vehicle, with an optical fiber composed of a polymer material and a protective layer which encloses the fiber.
A problem in vehicle construction is that the increasing use of electronic components in vehicles has led to an intensive growth in conductors which must be connected. In order to reduce the length of the conductors and their total weight and to simplify the design and the fabrication of the wiring harness, bus systems have been developed. They make data transmission between several components over a common conductor possible and thus reduce the required number of conductors.
High rates of transmission can be achieved through bus systems in particular with optical waveguides which work together with optical or electro-optical components. The optical fibers of the optical waveguide include a light-conductive core which is enclosed by a jacket for routing the light as well as possibly one or more outer protective layers. In vehicle construction polymer optical waveguides, for example composed of polymethylmethacrylate (PMMA) and/or fluorinated PMMA, have proven advantageous. Gradient index fibers with a diameter of 1 mm are suitable. In comparison with glass fibers, they offer the advantages of mechanical robustness, ease of handling and fabrication as a result of the large diameter, and the possibility of operation using visible light. The higher degree of damping in comparison to glass, on the other hand, is subordinated in importance in the short transmission paths in vehicles.
It has proven to be a drawback, however, that additional electrical conductors are necessary for the supply of electric power for sensors and actuators. In addition, the optical properties of the common polymer fibers are destroyed or significantly impaired through the absorption of and chemical reaction with substances in their environment. In addition to operating fluids such as lubricants or fuels, the large number of plastic materials used in vehicles which continuously give off substances such as degassing educts or fuels after conclusion of the manufacturing process present a problem. In addition, as a rule, good protection from moisture and thermal stress is required for the fibers, particularly in the case of use in the engine compartment or of linking of sensors or actuators outside of the chassis. Arranging the fibers in a protective sheath or in a plastic tube as is conventional in the state of the art is inadequate for this purpose, since polymers as a rule are not sufficiently gas-tight.
It is also known to provide metal pipes with a corrugation to improve their flexibility and transverse pressure stability as components of electrical cables. The corrugation is at an angle to the longitudinal axis of the pipe. Both spiral corrugations with crests oriented at an acute angle to the longitudinal axis of the pipe as well as corrugations of closed rings oriented at right angles to the axis are common. Through variation of the depth of the corrugations and the distance between them, the mechanical properties of the pipe such as flexibility can be set within broad limits.
SUMMARY OF THE INVENTION
Against this background, an object of the invention is to develop an optical waveguide which is reliably protected from environmental influences and which facilitates a simple connection of signal processing components with a minimum number of conductors.
This object is achieved according to the invention by providing a protective layer of a metal pipe which has a corrugation at an angle to its longitudinal axis, the pipe forming an electrical conductor and being provided with exterior insulation.
In the invention, a polymer-optical fiber is used such as a gradient index or incremental index fiber which is composed of PMMA, fluorinated PMMA, or another plastic with suitable optical properties. The exterior diameter of the fiber is preferably around 1 mm, while the core diameter is usually clearly greater than the diameter of the jacket so that the simple optical coupling and connecting of the fibers is ensured. It is conceivable for the fiber to be operated with a single wavelength or for several different wavelengths of light to be transmitted over one fiber.
The fiber is enclosed by a surrounding corrugated metal pipe, the corrugation of which may be configured as closed rings or as a spiral shape. Depths and periods of the corrugation are set such that the elastic properties of the metal ensure reliable protection for the fibers both from radial and from axial stresses. The fiber lies free in the pipe, the interior diameter of which is greater than the diameter of the fiber. Therefore the possibility of transmission of force from a tensile load acting axially on the pipe onto the fiber is excluded. The corrugation makes possible a high degree of flexibility of the pipe with a specified minimum bending radius which excludes the possibility of buckling of the fiber and thus an impairment of its optical properties. The minimum bending radius of the pipe is preferably at least 10 times the diameter of the fiber. In addition, the metal pipe forms a moisture-tight resistive layer around the fiber which prevents damage through solvents or gaseous substances from the environment. It is conceivable for the interior of the pipe to be provided with a gelatinous or fluid fill material with hydrophobic or pollution-absorbing properties in which the fiber is embedded.
On the outside, the metal pipe is provided with electrical insulation, for example a layer of a polymer such as a polyolefin, e.g., polyethylene. In addition to compact polymers, expanded materials are also suitable for insulation, e.g., polyurethane foam. It is advantageous to use halogen-free and/or nonflammable materials for the insulation as well as any exterior jacket to improve safety in the case of fire. With the insulation, an electrical conductor is created which serves in particular for supplying power to the components which are connected to the optical fiber. Thus the optical waveguide with its protective pipe forms a hybrid cable which is simultaneously suited for transmission of energy and data. It is fundamentally also possible to transmit electrical signals through the corrugated pipe. Metals with good conductivity such as copper or aluminum are especially suitable as materials for the pipe or—depending on the desired electrical and mechanical properties—alloys such as brass or bronze. If mechanical strength is of foremost importance, steel is also fundamentally conceivable. The electrical insulation in such case will prevent contact corrosion with the body of the vehicle or with other substrates on which the conductor is laid. The wall thickness of the metal pipe is advantageously 100 &mgr;m to several 100 &mgr;m, whereby a conductive cross section of the wall adequate for the transmission of current is necessary which preferably is in the range of one to several mm
2
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The proposed optical waveguide is distinguished through reliable protection of the optical fiber from environmental influences such as mechanical stresses in transverse and longitudinal direction, high temperatures, chemical substances, and vibrations. In addition, good protection from rodents is provided. Interactions between the signals to be transmitted or exterior electromagnetic fields is prevented. Handling of the optical waveguide is simple, with the metal pipe protecting the polymer fiber from damage during processing and installation.
The optical waveguide is preferred for connecting components which require both a supply of electric energy and optical signal transmission. Its use particularly in modular systems is conceivable whereby multiplex operation of the optical waveguide with several wavelengths is advantageous. Along with use i
Hemken Heinz Jurgen
Scheideler Wolfgang
Steinberg Helmut
Zamzow Peter
Alcatel
Palmer Phan T. H.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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