WO2006024043A2

WO2006024043A2 - Undersea optical amplifier module having coupled outboard splice enclosures

Info

Publication number: WO2006024043A2
Application number: PCT/US2005/031967
Authority: WO
Inventors: Savino S. Camporeale; John Bradley Hunter; Robert G. Deluca; David S. Devincentis; Mark K. Young
Original assignee: Red Sky Systems, Inc.
Priority date: 2004-08-18
Filing date: 2005-08-18
Publication date: 2006-03-02
Also published as: WO2006024043A3

Abstract

An optical amplifier module is coupled to a proximal end of an optical fiber splice enclosure that is located outboard of the amplifier module. At a distal end of the optical splice enclosure, a cable terminating body receiving portion is provided for interfacing with a came terminating body. The cable terminating body receiving portion includes a radial aperture that is arranged to align with a radial cavity in the cable terminating body so that a shear pin may be extended through the radial aperture and into the radial cavity to thereby couple the cable terminating body to the optical fiber splice enclosure.

Description

Undersea Optical Amplifier Module having Coupled Outboard Splice Enclosures

Field of the Invention

The invention relates to telecommunications and more particularly to an undersea optical amplifier module having a splice enclosure that is coupled to an outboard end.

Background of the Invention

In undersea optical transmission systems optical signals that are transmitted through an optical fiber cable become attenuated over the length of the cable, which may span thousands of miles. To compensate for this signal attenuation, optical repeaters are strategically positioned along the length of the cable.

In a typical optical repeater, the optical fiber cable carrying the optical signal enters the repeater and is coupled through at least one amplifier and various components, such as optical couplers and decouplers, before exiting the repeater. These optical components are coupled to one another via optical fibers. Repeaters are housed in a sealed structure that protects the repeaters from environmental damage. Conventional repeaters are quite large and typically include complex mechanical gimbals (which provides free angular movement in two directions). Gimbals are often used in combination with other bend limiting arrangements, to reduce local bending that is imposed on the coupled undersea optical fiber cable.

Summary of the Invention

An optical amplifier module is coupled to a proximal end of an optical fiber splice enclosure that is located outboard of the amplifier module. At a distal end of the optical splice enclosure, a cable terminating body receiving portion is provided for interfacing with a cable terminating body. The cable terminating body receiving portion includes a radial aperture that is arranged to align with a radial cavity in the cable terminating body so that a shear pin may be extended through the radial aperture and into the radial cavity to thereby couple the cable terminating body to the optical fiber splice enclosure. In a first embodiment of the invention, the optical fiber splice enclosure is coupled to a bulkhead that forms an end of the amplifier module using a threaded fastener such as a bolt.

In a second embodiment of the invention, the proximal end of the optical fiber splice enclosure is coupled to a bulkhead that forms an end of the amplifier module using a shear pin that extends through a radial aperture in the optical splice enclosure and into a radial cavity within the bulkhead.

In a third embodiment of the invention, the optical splice enclosure includes a female threaded portion (i.e., a portion having radially inward projecting threads) that is arranged in an annular manner around the interior perimeter of the proximal end. The optical splice enclosure is threadedly engagable with a corresponding male threaded portion (i.e., a portion having radially outward projecting threads) of a bulkhead that forms an end of the amplifier module and where the male threaded portion is arranged in an annular manner around a perimeter of a coupling portion of the bulkhead.

Advantageously, the optical amplifier module with coupled outboard splice enclosures facilitates the direct termination of an undersea optical fiber cable to a rigid body without the need for complex mechanical bend limiters. Substantial size and weight decreases are realized as a result and repeaters using from the inventive optical amplifier module are both less expensive to produce and more easily deployed in the field.

Brief Description of the Drawings

FIG 1 is a pictorial representation of a first embodiment of an undersea amplifier module having coupled outboard splice enclosures in accordance with the invention;

FIG 2 is an exploded view of the arrangement shown in FIG 1;

FIG 3 is a cross sectional view of the first embodiment of an undersea amplifier module, outboard splice enclosure and cable terminating body arranged in accordance with the invention where the splice enclosure is coupled to a bulkhead of the module using a threaded fastener such as a bolt;

FIG 4 is a cross sectional view of a second embodiment of an undersea amplifier module, outboard splice enclosure and cable terminating body arranged in accordance with the invention where the splice enclosure is coupled to a bulkhead using a shear pin; and

FIG 5 is a cross sectional view of a third embodiment of an undersea amplifier module, outboard splice enclosure and cable terminating body arranged in accordance with the invention where the splice enclosure includes a female threaded portion that is threadedly engagable with a corresponding male portion of a bulkhead of the amplifier module.

Detailed Description

FIG 1 shows an optical amplifier module 10 that is coupled to a proximal end of each of a pair of optical fiber splice enclosures 12 and 14 at each of the outboard ends of the optical amplifier module 10. Cable segment 15 and 16, for example cable segments enclosing optical fibers (not shown), are coupled, respectively to each of a pair of cable terminating bodies 17 and 19. The cable terminating bodies 17 and 19 are, in turn coupled to a distal end of each optical fiber splice enclosure 12 and 14, respectively, as shown.

Cable terminating bodies 17 and 19 include semi-conical shaped interior volumes to facilitate the termination of undersea cable using conventional cable terminating techniques. Typically, cable segments 15 and 16 are configured to carry electric power in addition to information signals in the contained optical fibers. Thus, the arrangement shown in FIG 1 couples two cable segments together physically, optically and electrically as described below in detail.

The physical connection allows mechanical forces (e.g., tensile and torsional forces) to be transmitted between cable segments. For example, a tensile force applied to cable segment 15 is transmitted through cable terminating body 17 to the optical fiber splice enclosures 12. The tensile force is then coupled to the optical amplifier module 10 (and more particularly through the tension sleeve 11) to optical splice enclosure 14 and cable terminating body 19 through to cable segment 16. As described in text accompanying FIGs 2 - 6, the optical amplifier module 10, splice enclosures 12 and 14 and cable terminating bodies 17 and 19 are fixedly coupled in an intimate mechanical configuration to form a rigid stress-bearing body. The optical amplifier module 10 shown in FIG 1 includes a cylindrical tension sleeve 11 and bulkheads 35 that cap each end of the cylindrical tension sleeve 10 to create an enclosed volume that is utilized to house one or more optical amplifiers (not shown in FIG I)- By selecting suitably robust materials such as steel alloys for the tension sleeve 10 and bulkheads 35 and 36, the optical amplifier module forms a pressure vessel to provide protection to optical amplifiers against external sources of pressure and tension. The optical amplifier module 10, in most applications of the invention, is hermetically sealed using seals between the bulkheads 35 and 36 and tension sleeve 11 and may be further pressurized with an inert gas such as nitrogen to provide a controlled environment for the various optical amplifier components that are contained inside the enclosed volume formed by the tension sleeve 11 and the bulkheads 35 and 36.

Turning briefly to FIG 2, bulkheads 35 and 36 generally are provided with one or more ports 38 to facilitate the interconnection of various optical (e.g., optical fiber) connections from the exterior of the optical amplifier module 10 to the one or more optical amplifiers contained in the interior (not shown in FIG 1). Such ports may be configured using sealing and feed-through techniques to ensure the maintenance of hermeticity of the optical amplifier module 10 which may be desirable in most applications of the invention.

The optical amplifier contained in the optical amplifier module 10 may be chosen from a variety of optical amplifier designs. For example, the exemplary embodiment of the optical amplifier module 10 depicted in the figures can support four erbium-doped fiber amplifiers ("EDFAs"), physically grouped as a dual amplifier unit for each of two fiber pairs. Each optical amplifier includes an erbium doped fiber, an optical pump source, an isolator and a gain flattening filter. The amplifiers are single-stage, forward pumped with cross-coupled pump lasers. A 3 dB coupler (i.e., a 4 port device or "2 x 2" coupler) allows both coils of erbium doped fiber in the dual amplifier to be pumped if one of the two pump lasers fails. Alternatively, in some applications of the invention a "4 x 4" coupler may be used so that all four pump lasers simultaneously pump all four fibers. At the output, an isolator protects against backward-scattered light entering the amplifier. The gain flattening filter is designed to flatten the amplifier gain at the designed input power. An additional optical path may be provided to allow a filtered portion of the W

backscattered light in either fiber to be coupled back into the opposite direction, allowing for COTDR-type (coherent optical time domain reflectometry) line-monitoring. Of course, optical amplifier module 10 may support EDFAs having different configurations such as multistage amplifiers, forward and counter-pumped amplifiers, as well as fiber amplifiers that employ rare-earth elements other than erbium.

The optical fiber splice enclosures 12 and 14 both contain and protect spliced optical fibers. One or more optical fibers housed in cable segments 15 and 16 are terminated in the optical fiber splice enclosures 12 and 14 and spliced to fibers extending into the optical amplifier module 10 through bulkheads 35 and 36. Optical fibers from cable segments 15 and 16 are thereby coupled to optical amplifiers contained in the optical amplifier module 10 to create a continuous optical path between cable segments 15 and 16 so that the cable segments are optically coupled.

Typically, splices are contained in fixtures or other holders (not shown in FIG 1) that are located within the interior volume of the optical splice enclosures 12 and 14. Optical fiber splice enclosures 12 and 14 are preferably fabricated from high strength metal materials and may be of a similar alloy as the tension sleeve 11 and bulkheads 35 and 36.

Optical amplifier module 10, optical fiber splice enclosures 12 and 14 and cable terminating bodies 17 and 19 when assembled as shown in FIG 1 - and in combination with an optical amplifier contained within the optical amplifier module 10 - form optical repeater 100. Electrical conductors within cable segments 15 and 16 are coupled to cable terminating bodies 17 and 19 (often through the steel strength members in the cable segments or via the termination of electrical conducting elements such as copper wires, sheathing or tapes) so that the cable terminating bodies are electrically "live." Electrical power is supplied to the optical amplifiers via a current path from the cable terminating body or cable conducting elements. Current is then passed from the optical amplifiers to the opposite cable segment or cable terminating body as discussed below in more detail.

For example, assuming that cable segment 16 has positive polarity (and current flows from positive to negative) then current is passed to cable terminating body 19, optical fiber splice enclosure 14 and bulkhead 36 - which are all energized elements in intimate electrical contact - at some reference voltage V_ref. A drive circuit, used to provide regulated electrical power to drive the optical amplifier, can be coupled (directly or indirectly through other conductive elements in optical amplifier module 10) to any of the electrically energized elements. Typically, however, the drive circuit is electrically coupled to bulkheads 36 and 35 so that current flows from bulkhead 36 (which forms the positive terminal for the circuit in this example) through the drive circuit and then to bulkhead 35 (which forms the negative terminal for the drive circuit in this example). Voltage is dropped across the drive circuit, ΔV.

Dielectric ring 56, which is disposed between bulkhead 36 and tension sleeve 11, as shown in FIG 1, breaks a conducting path from bulkhead 36 and tension sleeve 11 so that bulkhead 36 and tension sleeve 11 may be maintained at different potential levels V_ref and V_re_f - ΔV, respectively, to allow voltage to be dropped across the drive circuitry.

As shown in FIG 1, bulkhead 35 is in intimate electrical contact with tension sleeve 11 and the proximal end of optical splice enclosure 12. As optical splice enclosure 12 is coupled to cable terminating body 17 at its distal end, current from the drive circuit contained in optical amplifier module 10 and terminating at the bulkhead 35 (as described above) is passed to conductive elements contained in cable segment 15 such that the entire optical repeater 100 functions to electrically couple the cable segments 15 and 16.

Prior to deployment underwater, optical repeater 100 is encased in a dielectric material such as polyethylene to prevent electrical current from passing from the energized metallic components (i.e., cable terminating bodies 17 and 19, bulkheads 35 and 36, tension sleeve 11 and optical splice enclosures 12 and 14) to sea ground.

Referring again to FIG 2, there is shown an exploded view of the repeater 100 described above in the text accompanying FIG 1. The exploded view shows the cylindrical configuration of optical splice enclosures 12 and 14 that creates the interior volume to store optical splices. As shown, the cable terminating bodies 17 and 19 fit into corresponding receiving portions within the optical splice enclosures. In the embodiment of the invention shown in FIG 2, the cable terminating bodies 17 and 19 are secured to the optical splice enclosures 12 and 14, respectively, using pins 32. The pins 32 extend through radial apertures 70 located at the distal ends of the optical splice enclosures 12 and 14 and into radial cavities 85 within the cable terminating bodies 17 and 19. Three pins 32 are shown as being equally spaced around the circumference of each optical splice enclosure 12 and 14, however other numbers and spacings may be advantageously utilized depending on the requirements of a particular application of the invention.

FIG 3 is a cross sectional view of the embodiment of the invention shown in FIGs 1 and 2 and described in the accompanying text. As noted previously, cable terminating body 17 includes a conically shaped interior volume (denoted by reference numeral 18) that facilitates the termination of a cable using conventional terminating techniques. In this embodiment, the proximal end of optical splice enclosure 12 is removably fixedly mounted to bulkhead 35 using threaded fasteners such as "alien-type" bolts 33 that are aligned longitudinally. The heads of bolts 33 bear against flange portion 91 of the optical splice enclosures as shown in FIGs 2 and 3 and fit into corresponding threaded openings in bulkhead 35 (shown by reference numeral 34 in FIG 2).

O-ring or other types of gaskets such as copper gaskets 66 and 68 may be disposed between the optical splice enclosure 12 and bulkhead 35 and between bulkhead 35 and tension sleeve 11 to facilitate a hermetic seal which may be desirable in some applications of the invention.

FIG 4 is a cross sectional view of a second embodiment of the invention. Here, the bulkhead 435 differs from the bulkhead shown in the previous figures by the addition of flange portions 413 that are approximately normal to the end face of the bulkhead 435 and extends longitudinally outward from the distal to the proximal end of the optical splice enclosure 412. Flange portions 413 are arranged with female threaded radial cavities to facilitate the insertion of male threaded pins 432 to extend through female threaded radial apertures in optical splice enclosure 412 to thereby couple the optical splice enclosure 412 to bulkhead 435. Gaskets 466 and 468 are respectively disposed between the optical splice enclosure 412 and bulkhead 435, and bulkhead 435 and tension sleeve 11. Note that in FIGs 3 and 4, the male and female threaded portions are not shown in detail in order to facilitate exposition of the invention in the figures with greatest clarity.

FIG 5 is a cross sectional view of a third embodiment of the invention. In this embodiment, the optical splice enclosure 512 includes a female threaded portion 515 around the inside periphery of the proximal end. The optical splice enclosure 512 is threadedly engagable with a corresponding male threaded coupling portion 537 of bulkhead 535. The optical splice enclosure 512 is removably fixedly screwed onto the bulkhead 535 to thereby couple the optical splice enclosure 512 to bulkhead 535. Gaskets 566 and 568 are respectively disposed between the optical splice enclosure 412 and bulkhead 535, and bulkhead 535 and tension sleeve 11 as required to facilitate hermetic sealing.

Claims

CLAIMS:

1. An optical amplifier module containing at least one optical amplifier, the module comprising: a tension sleeve having an amplifier receiving volume in which the optical amplifier is disposed; a pair of opposing bulkheads that are disposed at opposite ends of the tension sleeve to enclose the optical amplifier within the receiving volume, where at least one of the opposing bulkheads includes a port for coupling the optical amplifier to an element that is outside the receiving volume; and at least one optical splice enclosure that is removably fixedly coupled at a proximal end to one of the bulkheads and having an opening at a distal end for receiving a cable terminating body, the cable terminating body being arranged to electrically and mechanically terminate an undersea cable.

2. The optical amplifier module of claim 1 where the optical splice enclosure is removably fixedly coupled to the bulkhead using a threaded connector.

3. The optical amplifier module of claim 1 where optical splice enclosure is removably fixedly coupled to the bulkhead with a shear pin that extends through a radial aperture in the optical splice enclosure and into a radial cavity within the bulkhead.

4. The optical amplifier module of claim 3 where the shear pin includes a portion having male threads.

5. The optical amplifier module of claim 1 where the optical splice enclosure is cylindrical and includes a female threaded portion located on the interior periphery of the proximal end and is removably fixedly connectable to the bulkhead and where the bulkhead is arranged with a male threaded portion that is threadedly engagable to the female threaded portion.