Patent Application
20170336572
The present invention relates generally to sealed bulkhead feedthrough units or assemblies for feeding optical fibers from underwater cables through a bulkhead into an equipment housing for connection to components in the housing, or for example, through the bulkhead of a subsea device.
In subsea production, electrically operated apparatuses below sea level are typically supplied and controlled/monitored by power and communications/control lines tethered to surface operated host facilities. The power and control feeds are provided from the external sources to the subsea devices via cable conductors to submerged process control equipment, pumps and compressors, transformers, motors, and other electrically operated equipment. As these components are disposed subsea and are typically enclosed and protected by water-proof pressure vessels, power and control signals are provided by means of a cable termination and connector, which may be an optical, electrical or hybrid electric/optical penetrator, designed to penetrate and connect to equipment through a bulkhead.
Such penetrator devices may be used to power and control/monitor subsea devices, e.g., electric submersible pump (ESP) equipment which pump hydrocarbons in oil well installations, and also in other applications such as high pressure downhole electrical penetrations and other penetrations to provide power and control signals to various types of subsea equipment. The penetrator extends through the wall or bulkhead of the vessel in which the equipment is located, and is normally connected to cables at one end for connecting the equipment to an external power source. For example, in an ESP application, the connection or penetrator cannot be isolated from the pumping pressure for practical reasons. This creates an extreme environment for the connector or penetrator in terms of pressure, temperature, and high voltage. The penetrator must provide a secure connection as well as maintaining a pressure barrier for both internal pressure created by subsea equipment and external pressure caused by the depth in seawater. The temperatures are increased due to fluid temperatures as well as resistive heating of the control signal elements. These penetrators must also be able to resist sustained intense heat from a hydrocarbon fire and maintain electrical and or optical connectivity and seal integrity in high temperature and material stress situations.
Typically, a bulkhead feedthrough assembly has a first end for coupling to an underwater cable and a second end for coupling to a port in a bulkhead, and has a through bore for feeding optical fibers and electrical leads through the assembly into the housing. However, the fibers and/or leads must be sealed in the through bore in order to prevent seawater from entering the housing should there be a cable leak or other failure outside the housing. In the past, feedthrough bores have generally been sealed by filling the space around the fibers or leads with epoxy cement, which approach results in several disadvantages and unwanted results. For example, once epoxy-filled bores are filled with epoxy, the connection is permanent and the cable can no longer be disconnected, moved, or adjusted. Secondly, the epoxy can create pressure points on optical fibers, which in turn can distort the fibers and possibly block passage of light signals through the fibers and create destructive stresses.
Existing systems, apparatuses, and methods for penetrator assemblies are known and are described in at least U.S. Pat. No penetrator or bulkhead feedthrough connector, such as the penetrator or feedthrough described in U.S. Pat. No. 6,067,395 of Cairns et al., each of which are incorporated by reference herein in their entirety.
Termination of an optical fiber into a ceramic ferrule is commonplace for optical connector solutions. When considering a HTHP (High Temperature, high pressure) exposure of an epoxied termination, this design leaves much to be desired. In practice, the epoxy bond to the fiber will shear and cause the fiber to move (piston) inside of the ferrule and optical performance of the system will be reduced or create a situation in which there is no longer optical continuity.
What is needed is an improved fiber optic connection arrangement and construction that can provide a hermetic seal under extremely high pressures and high temperatures in a subsea environment while avoiding the disadvantages of the epoxy-filled approach. What is needed is a fiber optic connection assembly that prevents optical fibers from degrading over time thereby greatly increasing the useful life of the equipment and preventing unwanted downtime and part replacement.
In order to address this issue in the development of an Optical Feed through System (“OFS”) for use at high temperature and pressure, a more stable mechanical system is required at the mated interface of the connector. The present invention utilizes a small piece of “cane” optical waveguide that is cut, ground and polished to certain dimensions in order to create the equivalent of an epoxied termination without the use of any epoxy. The cane material can also be considered a “fat optical fiber” having a core with a geometry normally achieved in a single mode optical fiber (9-10 micron) while the cladding is much greater in diameter than a typical optical fiber (1.25 mm or 2.5 mm in this embodiment, but could be larger or smaller as desired). 1.25 mm and 2.5 mm outer diameters are common standard commercial component diameters that can be utilized to couple two of the terminations of the present invention together at a mated interface. A device called an alignment sleeve, which may be a split ceramic sleeve, manufactured out of a ceramic tube with a slit down the side, can be used in this way.
The cane is manufactured in long sections of rod coming off of a draw tower and being cleaved at random lengths suitable for handling purposes. Small pieces of this cane material are then further processed by grinding and polishing features into a waveguide termination blank. These features including a waveguide body and a stub are needed for coupling of two mated parts on the mating ends and for fusing a standard optical fiber onto the back end or stub face of the waveguide termination blank to provide optical continuity to the rest of the system. The present invention also helps maintain factory settings and calibrations of the fiber optic for device consistency and proper system operation.
In one embodiment, a cylindrical waveguide component surrounds a fiber optic conductor disposed in a central bore formed in the waveguide.
In one embodiment, the present invention provides an epoxy-less optical fiber termination comprising: a waveguide termination comprising a waveguide body, the waveguide body comprising a waveguide core with a waveguide cladding disposed about the waveguide core, and the waveguide body having a mating end and a stub end, the stub end having a stub comprising a stub core and a stub face and protruding from the stub end of the waveguide body; an optical fiber for communicating an optical communications signal, the optical fiber terminated at and joined to the stub face; a strain relief partially disposed over the stub and disposed over a portion of the optical fiber; and an epoxy fill disposed within the strain relief and about the optical fiber, the epoxy fill adapted to protect and support the optical fiber and the termination of the optical fiber at the stub face.
The epoxy-less optical fiber termination may further comprise wherein the outer diameter of the cladding may be 1.25 mm. The outer diameter of the cladding may be 2.50 mm. The optical fiber may be terminated within a fiber diameter step, the fiber diameter step disposed on the stub face of the stub at a large diameter splice; and the strain relief may be disposed about the entire fiber diameter step and is partially disposed over the stub. The waveguide core may comprise germanium doped fused silica glass and the waveguide cladding may comprise fused silica glass. The operating wavelength of the waveguide termination may be between 1520 and 1600 μm.
In another embodiment, the present invention provides an optical communications network for communicating optical signals, the network comprising: a first device and a second device, the first device and second device adapted to transmit and receive optical signals over the optical communications network; an optical fiber terminated by first and second epoxy-less optical terminations, each of the first and second epoxy-less optical terminations comprising: a waveguide termination comprising a waveguide body, the waveguide body comprising a waveguide core with a waveguide cladding disposed about the waveguide core, and the waveguide body having a mating end and a stub end, the stub end having a stub comprising a stub core and a stub face and protruding from the stub end of the waveguide body; an optical fiber for communicating an optical communications signal, the optical fiber terminated at and joined to the stub face; a strain relief partially disposed over the stub and disposed over a portion of the optical fiber; and an epoxy fill disposed within the strain relief and about the optical fiber, the epoxy fill adapted to protect and support the optical fiber and the termination of the optical fiber at the stub face; wherein the first termination terminates the optical fiber at the first device and the second termination terminates the optical fiber at the second device and the first and second devices are adapted to communicate over the optical fiber.
In the network the outer diameter of the waveguide cladding may be 1.25 mm. The outer diameter of the waveguide cladding may be 2.50 mm. The network may further comprise wherein the optical fiber is terminated within a fiber diameter step, the fiber diameter step disposed on the stub face of the stub at a large diameter splice; and wherein the strain relief is disposed about the entire fiber diameter step and is partially disposed over the stub. The waveguide core may comprise germanium doped fused silica glass and the waveguide cladding may comprises fused silica glass. The operating wavelength of the waveguide termination may be between 1520 and 1600 μm. The first device may be a surface device and the second device may be a subsea termination. The first device may be a subsea termination and the second device may be a subsea network device. The network may further comprise wherein both first device and second device further comprise: an internal epoxy-less optical fiber termination adapted to mate in optical communication with the respective first and second epoxy-less optical terminations of the optical fiber.
In yet another embodiment, the present invention provides a method for producing an epoxy-less optical termination comprising: drawing a silica glass rod; cleaving a cane from the silica glass rod; grinding and polishing the cane to form a waveguide termination blank comprising a waveguide body, the waveguide body comprising a waveguide core with a waveguide cladding disposed about the waveguide core, and the waveguide body having a mating end and a stub end, the stub end having a stub comprising a stub core and a stub face and protruding from the stub end of the waveguide body; securing a strain relief about a portion of the stub; attaching an optical fiber to the stub face of the stub of the waveguide termination blank, the optical fiber passing through the strain relief; and filing the strain relief with an epoxy fill.
The method may further comprise: forming a fiber diameter step by fusing a capillary tube about the optical fiber; splicing the fiber diameter step to the stub face by a large diameter splice; and securing the strain relief about the entire fiber diameter and a portion of the stub. The outer diameter of the waveguide cladding may be 1.25 mm. The outer diameter of the waveguide cladding may be 2.50 mm. The waveguide core may comprise germanium doped fused silica glass and the waveguide cladding may comprise fused silica glass. The operating wavelength of the waveguide termination may be between 1520 and 1600 μm.
In order to facilitate a full understanding of the present invention, reference is now made to the accompanying drawings, in which like elements are referenced with like numerals. These drawings should not be construed as limiting the present invention, but are intended to be exemplary and for reference.
The present invention will now be described in more detail with reference to exemplary embodiments as shown in the accompanying drawings. While the present invention is described herein with reference to the exemplary embodiments, it should be understood that the present invention is not limited to such exemplary embodiments. Those possessing ordinary skill in the art and having access to the teachings herein will recognize additional implementations, modifications, and embodiments, as well as other applications for use of the invention, which are fully contemplated herein as within the scope of the present invention as disclosed and claimed herein, and with respect to which the present invention could be of significant utility.
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While the invention has been described by reference to certain preferred embodiments, it should be understood that numerous changes could be made within the spirit and scope of the inventive concept described. In implementation, the inventive concepts may be automatically or semi-automatically, i.e., with some degree of human intervention, performed. Also, the present invention is not to be limited in scope by the specific embodiments described herein. It is fully contemplated that other various embodiments of and modifications to the present invention, in addition to those described herein, will become apparent to those of ordinary skill in the art from the foregoing description and accompanying drawings. Thus, such other embodiments and modifications are intended to fall within the scope of the following appended claims. Further, although the present invention has been described herein in the context of particular embodiments and implementations and applications and in particular environments, those of ordinary skill in the art will appreciate that its usefulness is not limited thereto and that the present invention can be beneficially applied in any number of ways and environments for any number of purposes. Accordingly, the claims set forth below should be construed in view of the full breadth and spirit of the present invention as disclosed herein.
