Underwater Fiber Optic System

Abstract

The optical fiber system includes an optical fiber cable including at least one microstructured optical fiber within a jacket, and a barrier mechanism responsive to a breach in the optical fiber cable through which water from the environment surrounding the optical fiber cable can enter a void in the microstructured optical fiber, the barrier mechanism responsive to the breach by operating to provide a barrier across the void in the microstructured optical fiber, the barrier configured to inhibit movement of water along the void.

Description

[Technical Field]

[0001] The present invention relates to an underwater optical fiber system. [Background technology]

[0002] Optical fibers are widely used to transmit data carried by light signals, using multiple fibers to carry individual data channels in parallel. For convenience and protection, multiple fibers are bundled together within a protective outer jacket to form a fiber optic cable. Cables are installed in a variety of environments to carry data between transmitting and receiving locations over large or small distances. In some situations, cables are deployed underwater to carry data across oceans, seas, rivers, and lakes. Submarine cables are susceptible to damage, including cable severance, from ship anchors, fishing activities, seabed motion, and other physical impacts and disturbances. Similar damage is also incurred by underwater cables in non-marine environments.

[0003] Traditionally, underwater cables contain solid-core optical fibers. In the event of damage, water can penetrate the interior of the cable, entering the spaces between the optical fibers and between the optical fibers and the outer jacket. Protection can be provided by incorporating techniques such as absorbent materials or water-swellable tapes or threads within the cable's structure, which expand upon exposure to water to form a barrier against water ingress into the cable's interior. Another approach is to divide the cable into sections and include stop joints or other physical barriers that prevent water from progressing through them, thereby limiting the length of the cable through which water can penetrate. Examples of such configurations are shown in US 4,834,479, US 4,913,517, and US 5,861,575 [1, 2, 3].

[0004] Recently, optical fibers containing longitudinal voids within the internal structure of individual fibers have been developed. These include, but are not limited to, hollow-core optical fibers and fibers with microstructured cladding formed from a specific arrangement of longitudinal voids. The superior optical propagation characteristics of hollow-core optical fibers compared to solid-core optical fibers, including reduced optical loss and increased propagation velocity and optical bandwidth, make them particularly attractive for use in long-distance communications. However, hollow-core fibers pose a risk when cable damage occurs, especially in underwater environments. Water ingress into the voids in the core and cladding adversely affects propagation performance, which depends on the voids being filled with air or gas. Therefore, the fiber must be replaced when a damaged cable is repaired. In subsea environments, the problem is exacerbated because increased water pressure at depth can further force water into the fiber, necessitating replacement of very long fibers.

[0005] Therefore, there is interest in techniques aimed at inhibiting the ingress of water into hollow-core optical fibers in optical cables. Summary of the Invention

[0006] Features and embodiments are set forth in the accompanying claims.

[0007] According to a first aspect of certain embodiments described herein, an optical fiber system is provided that includes an optical fiber cable including at least one microstructured optical fiber within a jacket; and a barrier mechanism responsive to a breach in the optical fiber cable through which water from an environment surrounding the optical fiber cable can enter a void in the microstructured optical fiber, the barrier mechanism responsive to the breach by operating to provide a barrier across the void in the microstructured optical fiber, the barrier configured to inhibit movement of water along the void.

[0008] These and further features of particular embodiments are set forth in the accompanying independent and dependent claims. It will be understood that features of the dependent claims may be combined with each other and with features of the independent claims in combinations other than those explicitly set forth in the claims. Furthermore, the approaches described herein are not limited to particular embodiments such as those described below, but include and are contemplated as including any suitable combination of features set forth herein. For example, a system may be provided according to the approaches described herein, including any one or more of the various features described below, as appropriate.

[0009] For a better understanding of the invention and to show how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which: [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 shows a simplified schematic representation of a first example of an optical fiber cable system having a barrier mechanism as disclosed herein. [Figure 2] FIG. 2 shows a simplified schematic representation of a second example fiber optic cable system having a barrier mechanism as disclosed herein. [Figure 3] FIG. 3 shows a simplified schematic representation of a third example fiber optic cable system having a barrier mechanism as disclosed herein. [Figure 4A] FIG. 4A shows a simplified schematic representation of a fourth example fiber optic cable system having a barrier mechanism as disclosed herein. [Figure 4B] FIG. 4B shows a simplified schematic representation of the example of FIG. 4A after operation of the barrier mechanism. [Figure 5A] FIG. 5A shows a simplified schematic representation of a fifth example fiber optic cable system having a barrier mechanism as disclosed herein. [Figure 5B] FIG. 5B shows a plan view of the example barrier feature of FIG. 5A. [Figure 6A]FIG. 6A shows a simplified schematic representation of a sixth example fiber optic cable system having a barrier mechanism as disclosed herein. [Figure 6B] FIG. 6B shows a simplified schematic representation of the example of FIG. 6A after operation of the barrier mechanism. [Figure 7A] FIG. 7A shows a simplified schematic representation of a seventh example of an optical fiber cable system having a barrier mechanism as disclosed herein. [Figure 7B] FIG. 7B shows a simplified schematic representation of the example of FIG. 7A after operation of the barrier mechanism. DETAILED DESCRIPTION OF THE INVENTION

[0011] Configurations and features of specific examples and embodiments are disclosed / described herein. Some configurations and features of specific examples and embodiments may be implemented in a conventional manner, and for the sake of brevity, they will not be discussed / described in detail. Therefore, it will be understood that configurations and features not described in detail in the systems described herein may be implemented in accordance with any conventional techniques for implementing such configurations and features.

[0012] The approach described herein relates to microstructured optical fibers, particularly hollow-core optical fibers described in more detail below, and the inclusion of such optical fibers in optical fiber cables intended for underwater deployment. Optical fiber cables include multiple optical fibers arranged in a bundle and substantially parallel orientation surrounded by an outer protective layer, such as a jacket or sheath. The jacket can be formed, for example, from a polymeric material, a low-smoke, zero-halogen material, or stainless steel tubing. The jacket can house only the optical fibers, or in some instances, can include other elements to make the cable more robust and resistant to damage. They can include a central strength member made of a high-tensile material, such as glass-reinforced plastic, fiber-reinforced plastic, stranded steel, nylon, or para-aramid yarn, that runs the length of the cable to resist sharp bends and potential damage to the optical fibers, around which the optical fibers are arranged, bundled, wrapped, or twisted, and one or more buffer layers of polymer material to secure and protect the individual or paired fibers. Strength members that surround the fibers, such as those in the form of a layer between the fiber bundle and the jacket, can also be used. Nevertheless, cables are still susceptible to damage, including total or partial cable severance, especially when exposed to areas with aquatic environments.

[0013] Fiber optic cables can contain optical fibers of any type or design, including two or more types in a single cable. If an underwater cable contains hollow-core or other microstructured fibers with voids within the fiber's internal structure, it is desirable to limit water ingress to individual fibers when the cable is damaged, as the presence of water in the voids degrades optical performance. In marine environments, cables can be deployed at considerable depths. High water pressures at depth can cause greater and more rapid water ingress from damaged sections along individual fibers, distributing damage along the length of the cable that can extend far from the original damaged section. The cable or individual fibers within the cable can be rendered inoperable, requiring extensive and costly repairs or replacements.

[0014] Techniques are proposed herein to prevent or inhibit water ingress or limit the spread of water ingress along the length of cables containing microstructured fibers with internal voids, with the goal of minimizing water damage and allowing more localized repairs instead of replacing significant lengths of cable.

[0015] The term "microstructured fiber" is used herein to refer to any optical fiber having one or more internal longitudinal voids, which may define or form a portion of the fiber core, the fiber cladding, or both. More specifically, a microstructured fiber has an internal structure that includes an array or arrangement of holes, capillaries, or lumens within the fiber material that are parallel to the longitudinal axis and defined within the material, such as glass, and extend along the length of the fiber. The arrangement of holes can be referred to as the microstructure, and typically the microstructure forms at least a portion of the fiber's cladding and may also or alternatively define the core. All such structures are susceptible to damage, for example, when included in a fiber optic cable deployed underwater, due to water ingress when the fiber breaks.

[0016] The microstructured configuration that defines the core can provide a hollow-core optical fiber, in which a cladding, typically but not necessarily microstructured, surrounds a central hollow void or region that provides the light-guiding core. The microstructured capillary is typically supported within a larger outer cladding tube made of glass. Light propagation in air (or other gases, or vacuum), enabled by the absence of a solid glass core, reduces the proportion of guided light waves propagating in the glass compared to solid-core fibers, offering advantages such as increased propagation velocity, reduced losses due to both absorption and scattering, and reduced nonlinear interactions. Hollow-core fibers are therefore highly attractive for long-distance communications applications; they enable data transmission at near the speed of light in a vacuum, at high optical powers, and over wide optical bandwidths, relatively free from problems such as nonlinear and thermo-optical effects that can affect light traveling in solid-core fibers. Hollow-core fibers can be categorized into two main classes or types according to their light-guiding mechanism: hollow-core photonic bandgap fibers (HCPBFs, also known as hollow-core photonic crystal fibers (HCPCFs)) and antiresonant hollow-core fibers (AR-HCFs or ARFs). In HCPBFs, the structured cladding region contains a regular, closely packed array of many small glass capillaries, from which a central group is removed to define a substantially circular hollow core. The periodicity of the cladding structure provides a substantially periodically structured refractive index and, therefore, a photonic bandgap effect that confines propagating light waves toward the core. In ARFs, the structured cladding contains a much smaller number of large glass capillaries or tubes and has a structure that lacks a high degree of periodicity; therefore, the photonic bandgap effect is not significant, but the tubes are evenly spaced, providing some periodicity on larger scales.This structure provides anti-resonance for propagating wavelengths that are not resonant with the wall thickness of the cladding capillary, where the cladding capillary encloses a hollow void or cavity that provides the hollow core of the fiber, and which can support anti-resonantly guided optical modes.

[0017] This disclosure is applicable to all types of microstructured fibers, including those of the two major classes of hollow-core fibers and their associated subtypes, as well as other hollow-core designs. Other examples include microstructured solid-core fibers, in which a void structure is provided only in the cladding region around a core defined in a solid material. The cladding can be an array of many capillaries to provide a photonic effect, or it can be a single ring of large voids separated by glass struts supporting a central solid core (suspended-core fiber). All other designs of optical fiber with one or more internal voids are also relevant. Note that there is some overlapping use of terminology in the art for various classes of microstructured or "holey" fibers. For purposes of this disclosure, the term "microstructured fiber" is intended to include all types having a longitudinal void or voids in the internal structure, and the terms "hollow-core fiber" and "hollow-core microstructured fiber" are intended to include all types of those fibers having the hollow cores described above. Statements made with specific reference to hollow-core fibers will be understood to be applicable to all microstructured fibers unless the content indicates otherwise. However, this disclosure is particularly relevant herein because the particular enhanced optical properties of hollow-core optical fibers outlined above make such fibers highly advantageous for telecommunications applications.

[0018] We propose to address the problem of water ingress into voids in hollow-core and other microstructured fibers contained in optical fiber cables by providing a system including an optical fiber cable and a means, arrangement, device, or mechanism capable of responding in the event of damage affecting the cable by providing or introducing a barrier that traverses and acts to inhibit the movement of water along the voids of a microstructured fiber or fibers, thereby reducing or limiting the physical extent of damage caused by the presence of water. Inhibiting water movement can include preventing water from entering the interior of the fiber, inhibiting water movement along the void beyond the location of the barrier, and slowing the ingress of water into or along the void. Both the physical containment of water that has penetrated the fiber and slowing the spread of water within the fiber reduce the amount of fiber or cable that must be repaired or replaced. In particular, damage to the cable can include a tear in the cable, which can also result in the creation of a tear in one or more microstructured fibers within the cable, thereby allowing water to enter the voids in the fiber. In various examples, the barrier providing mechanism may be operated to install a barrier across a fiber void when a breach in the cable is detected, and in another example, installation of the barrier may be by formation of the barrier in response to the presence of water entering the cable through a breach.

[0019] For simplicity, examples will generally be described in the context of a single optical fiber; however, it should be understood that a particular fiber within a fiber optic cable will typically have one or more additional optical fibers, and more typically, will have multiple additional optical fibers. The various proposed barrier mechanisms can be configured to operate on a single fiber, a group of fibers, or all of the fibers in a cable, and those skilled in the art will recognize where their various alternatives are most appropriate. When an individual barrier mechanism is associated with fewer than all of the microstructured fibers in a cable, an additional barrier mechanism can be provided at the same location to address all of the microstructured fibers. In some arrangements, multiple barrier mechanisms can be provided at intervals along the cable. This allows the cable to be "compartmentalized" into distinct sections so that any water is locally contained rather than entering fiber voids, where the barriers can be thought of as cutoff walls that stop the widespread flow of water along the length of the cable. If this is not otherwise apparent from the appearance of the system of mechanisms attached to the cable, the location(s) where a barrier or barriers can be provided can be identified. For example, visual markers corresponding to the barrier locations can be provided on the outside of the cable jacket. Alternatively, detectable tags can be incorporated into the structure of the cable at relevant locations, such as RFID transponders or similar elements that are detectable using a separate detector device. Detectable tags or other placements that are incorporated into the structure of the cable may be preferred because they are less susceptible to wear and tear on the cable after deployment.

[0020] In a first group of examples, a barrier is introduced into the gap between adjacent sections or portions of optical fiber to provide a barrier or blocking wall between the two portions that inhibits (reduces or prevents) the movement of water from one portion to another. The barrier can be fully waterproof, completely blocking the flow of water, or partially waterproof, slowing or reducing the rate of water movement. For convenience, the examples are presented with adjacent portions of optical fiber that are physically separated from one another, their ends spaced apart to define a gap. The two portions of optical fiber are optically aligned end-to-end so that light transmitted out the end of one fiber portion is coupled to the adjacent end of the second fiber portion, preferably with minimal optical loss. The gap can be a narrow, empty gap for free-space light propagation between the fiber portions, and optical coupling can be facilitated by an optical configuration between the ends of the fiber portions that includes one or more optical elements, including any of lenses, mirrors, Faraday rotator materials, etc. The inclusion or exclusion of such optical features can be selected according to the requirements for accommodating the particular choice of barrier mechanism and / or for achieving efficient coupling between the fiber types of the two fiber sections, which may or may not be the same. Both fiber sections can be microstructured optical fiber of the same or different configuration or design, and one fiber section can be microstructured optical fiber and the other fiber section can be solid-core optical fiber. If one of the fiber sections is a solid-core section, the barrier can be configured to maintain the integrity of the microstructured fiber by extending into the void, inhibiting water flow along the void from the location of the cleft away from the gap, rather than preventing flow between the fiber sections.

[0021] Alternatively, adjacent portions of optical fiber may be contiguous sections of the same optical fiber, in which slots, holes, perforations, apertures, or other openings are formed to provide the gaps. The openings generally extend transversely to the length of the fiber and preferably penetrate all voids in the fiber's microstructure, allowing the barrier to access and block all voids. The sections of fiber remain physically connected to one another by other portions of the fiber structure not penetrated by the openings, such as the outer cladding or outer jacket. This maintains or promotes optical alignment of the adjacent sections and provides a simpler construction than using two separate sections of fiber. As used herein, the term "gap" between two sections or sections is understood to include both the alternatives of a space between adjacent ends of two physically distinct and separate portions of optical fiber, or an opening in the optical fiber's microstructure that divides the optical fiber into two sections that would otherwise be physically continuous.

[0022] FIG. 1 shows a simplified schematic representation of an exemplary system employing a gap between fiber portions, which may be used with two sections of microstructured fiber or one section of microstructured fiber and one section of solid-core fiber. Optical fiber 10 includes a first optical fiber portion 10a, which may be a microstructured optical fiber, such as a hollow-core fiber, and a second optical fiber portion 10b, which may or may not be a microstructured optical fiber. Optical fiber 10 is typically bundled with other optical fibers (not shown) in a fiber optic cable intended for deployment in an underwater environment, such as a subsea location. Optical fiber portions 10a, 10b are arranged end-to-end in sequence for transmission of light between portions 10a, 10b, thereby forming overall optical fiber 10. Other optical fiber portions may be included beyond the first and second portions shown to extend the overall length of optical fiber 10 and / or to accommodate additional barrier mechanisms or other optical elements, such as amplifiers. Optical configuration 12 is disposed between adjacent ends of optical fiber portions 10 a, 10 b, the ends being spaced apart by a gap. Optical configuration 12 may include free space, with the ends of optical fiber portions 10 a, 10 b positioned (possibly treated to reduce reflections via anti-reflective coatings or angled end faces) and aligned so that light propagates across the gap between optical fiber portions 10 a, 10 b. Alternatively, optical elements such as mirrors, lenses, prisms, etc. may be used in the optical configuration to improve optical coupling between optical fiber portions 10 a, 10 b.

[0023] The barrier mechanism 20 includes a pressure housing or pressure cell 22 that surrounds the gap / optical arrangement 12 and expels water from the gap 12 when the cable is submerged in water. The first and second optical fiber portions 10a, 10b (within the cable) pass through the wall of the pressure housing 22. A reservoir 24 for supplying an inert gas, such as argon or other noble gases, nitrogen, or sulfur hexafluoride (but not excluding other inert gases), is also included. In some examples, the reservoir 24 holds an inert gas that is already in a gaseous state. In other examples, the reservoir 24 holds a pressurized, liquefied gas material that expands to a gaseous state when released from the reservoir 24. The reservoir 24 has rigid walls to withstand water pressure at great depths and maintain its shape. The reservoir 24 is in gas communication with the interior of the pressure housing 22 using a valve 26 (gas flow valve) disposed between the reservoir 24 and the pressure housing 22 to control the flow of gas from the reservoir 24 to the pressure housing 22. In this example, the gas flow valve 26 is located in a pipe or similar gas flow conduit 25 connecting the reservoir 24 to the pressure housing 22, although in another example, the reservoir 24 and the pressure housing 22 may share a common wall with an opening through which the valve is disposed. Under normal conditions, with no cable damage, the valve 26 is closed and the reservoir 24 is filled with gas or liquefied gas remaining in the reservoir. The valve 26 is controlled by a breach detection system 28 either via a wired or other physical connection 30, or wirelessly, depending on the implementation. The breach detection system 28 is configured to detect the occurrence of damage to the cable that would cause a breach that would allow water ingress, and can operate, for example, by monitoring the internal pressure of the cable or by monitoring an optical signal via an optical time domain reflectometer. A breach will cause the internal pressure to change, and thus, identifying a pressure change can be attributed to the occurrence of a breach (other configurations for breach detection are possible, and the functionality of the breach detection system 28 is outside the scope of this disclosure).If a breach is detected, the breach detection system 28 communicates this information to the valve 26, which opens, providing a path for gas flow from the reservoir 24 to the pressure housing 22. Thus, in this example, the breach mechanism 20 responds to the occurrence of a breach by allowing gas to flow from the reservoir 24 to the pressure housing 22. The gas can reach the gap between the fiber portions 10a, 10b and enter the voids in the microstructure of one or both of the fiber portions 10a, 10b. If the gas is at or above the water pressure of the surrounding environment, the internal pressure within the fiber equals or exceeds the external pressure, and water cannot flow into the void. The gas's occupation of the void acts as a barrier across the void, inhibiting the movement of any water that enters the void through the breach in the cable. The gas is propelled along the void by its high pressure, thereby protecting a significant length of fiber, if the pressure is sufficient.

[0024] To accomplish this using the barrier system of Figure 1, reservoir 24 should contain pressurized gas. Pressurization can be implemented above water to an appropriate level prior to underwater deployment of the cable to match or exceed the water pressure at the water depth where the cable will be submerged.

[0025] In variations of this example, gas can be delivered to the voids in the microstructured fiber prior to detection of a breach in the cable, and either before, during, or after deployment of the cable. In such an example, the breach detection system 28 is not required for operation of the barrier mechanism 20; rather, the barrier is already present if a breach occurs. This can protect longer lengths of optical fiber because pressurized gas can be pre-existing at or near the breach, thereby limiting or completely eliminating the amount of optical fiber through which water can infiltrate along the optical fiber from the breach. Introduction of gas during or after deployment may require remote control of the valve 26.

[0026] In another variation, the reservoir may not be pre-filled with gas, but may contain a material or materials capable of generating a suitable inert gas through a chemical change or reaction when needed. In some examples, the material may generate gas through decomposition, such as the decomposition of sodium azide, guanidine nitrate, or tetrazole (without excluding other materials). Sufficient material may be included relative to the size of the reservoir to allow the gas pressure to be increased to the required level. The gas may be held in the reservoir for release into the pressure housing via a valve in response to detection of a breach in the cable. Alternatively, the valve may be omitted or set open, allowing the gas to disperse into the pressure housing and through gaps along the voids in the optical fiber(s) as it is generated, thereby pre-forming a barrier within the fiber(s). In the case of a chemical reaction to generate the gas, the barrier mechanism may be configured to trigger the chemical reaction, such as by bringing two or more materials into contact or applying heat, in response to detection of a breach in the cable. As mentioned earlier, the "ingredients" for generating the inert gas can be a liquid form of gas, in which case a valve is required to maintain sufficient pressure within the reservoir.

[0027] FIG. 2 shows a simplified schematic representation of another exemplary system using a gas as a barrier. System 20 includes the same elements as the system of FIG. 1 and further includes a second pressure housing 32 enclosing reservoir 24. Second pressure housing 32 is shown as completely enclosing both reservoir 24 and first pressure housing 22 around gap / optical configuration 12, with the two separated by a barrier wall. Alternatively, second pressure housing 32 could be separate from first pressure housing 22, enclosing only the reservoir. Second pressure housing 32 includes a second valve 36 for water flow (water flow valve) in its wall, which, when opened when the system is submerged in water, allows water to flow through valve 36 and fill the interior of second pressure housing 32. The system is positioned with second valve 36 closed, preventing water from entering the second pressure housing.

[0028] In this example, reservoir 24 is configured to be compressible (e.g., by being formed with walls of a flexible or deformable material, such as a bladder) and filled with an inert gas. If a breach occurs, breach detection system 28 (not shown, see FIG. 1 ) is additionally or alternatively configured to send a signal to operate second valve 36 to open, thereby allowing water to enter second pressure housing 32. The pressure of the received water compresses reservoir 24, forcing gas out of reservoir 24 into pressure housing 22, into gaps, and into voids in one or both portions of optical fiber 10 a. First valve 26 can be opened in conjunction with second valve 36, or can be omitted. Further alternatively, second valve 36 can be omitted, leaving reservoir 24 permanently exposed to the pressure of the surrounding water, such that gas is gradually forced out of the reservoir and into the optical fiber portion(s) as the cable is submerged and pressure increases. This allows the barrier to be in place before a cable tear occurs. Similarly, the second valve can be configured to open under the influence of increased water pressure, so that it opens automatically when the cable is submerged in water.

[0029] A particular feature of this configuration is its simple reversible function: if the water pressure is reduced, especially if the cable is raised to the surface for maintenance, repair or replacement, the reservoir compression is reduced and the gas pressure is regulated so that it is not at a dangerously high level when the cable surfaces.

[0030] Figure 3 shows a simplified schematic representation of a further example of an optical fiber system with a barrier mechanism. As in the previous example, optical fiber 10 again includes first and second portions 10a, 10b, whose ends are optically aligned and separated by a narrow gap 12 (the space between physically separated fiber portions, or an opening in the fiber structure, as described with respect to Figure 1), preferably allowing light transmission between fiber portions 10a, 10b with minimal optical loss. Both first and second optical fiber portions 10a, 10b comprise microstructured optical fibers, such as hollow-core optical fibers, in this example.

[0031] The barrier mechanism 20 includes a solid gate 40 aligned with the gap 12 but disposed laterally from the optical fiber. The gate 40 is formed from a water-impermeable material, such as metal, plastic, or glass. The gate 40 is substantially flat and has a thickness that substantially matches or is thinner than the length of the gap 12 along the length of the optical fiber. The gate 40 moves laterally, thereby allowing it to be inserted into the gap 12 in the form of a gate valve or sluice valve, covering at least one end of the fiber segments 10a and 10b. This provides a barrier across the voids in the fiber segments and inhibits (prevents or limits) the flow of water through the gate. Thus, when the gate 40 is positioned in the gap 12, water cannot move from one fiber segment to the other. If the thickness of the gate 40 is the same as the length of the gap 12, it creates a barrier across the voids in both fiber segments 10a and 10b when positioned in the gap. If the gate 40 is thinner than the length of the gap 12, it can be positioned to slide close to cover only the end of one of the fiber segments 10a, 10b, thereby forming a barrier across only the void of that fiber segment. This still prevents water movement between the fiber segments 10a, 10b, thereby protecting either the fiber segment 10a, 10b on the other side of the gate 40 from water intrusion at the location of the cable breach. A thinner gate 40 may be easier to slide smoothly into the gap 12 than a gate 40 the same size as the gap 12. A pair of thin gates 40, each associated with only the end of one fiber segment, could also be provided. They could be inserted simultaneously into the gap when a cable breach occurs, and only one could be positioned corresponding to the breached fiber segment to contain water within that fiber segment. In any of these configurations, the gate 40 or gates 40 could include a coating, surface layer, or wrapping (not shown) of a water-swellable material that expands when exposed to water.This can enhance the sealing of voids by the gates in place, allowing the movement of water between fiber portions to be more effectively restricted or prevented.

[0032] To deploy the gate 40 when a breach occurs, the breach mechanism also includes an actuator or drive mechanism 42 coupled to the gate 40, which operates to move the gate 40 from its starting position (FIG. 3) to the side of the gap 12 into the gap in response to a breach. Any suitable actuator or drive configured to create mechanical motion can be used, such as a motor with a worm-drive action or an electromagnet to pull or push the gate between two positions. More passive configurations may also be preferred, such as a water-swellable material that expands and pushes the gate 40 when exposed to water, or expanding gas that is released to push the gate 40 by opening a valve that can be actuated by water pressure or remote control. These latter types of actuators may be easier to implement and operate than electrical and electromagnetic options, but they only provide gate deployment and cannot easily be reversed to retract the gate once the cable is repaired. As shown in FIG. 3, the motion can be linear, allowing the gate 40 to be advanced into the gap or rotated to swing the gate 40 into the gap 12. Any or all variations apparent to those skilled in the art are within the scope of this disclosure, and the exact implementation is not critical. The actuator 42 can be controlled by the breach detection system 28 (either wired via control line 30 or remotely via a suitable transceiver (not shown)) so that when a breach in the cable is detected, the barrier mechanism 20 responds by operating the actuator 42 to move the gate 40 into the gap, providing a barrier across the void in at least one portion of the optical fibers 10 a, 10 b. A water-activated option can automatically deploy the gate 40 when water enters the breach detection system.

[0033] An equivalent configuration for actuator 42 is to provide movement of one or more of optical fiber portions 10 a, 10 b to properly position gate 40 to form a barrier across the void, rather than movement of gate 40. Any configuration that provides suitable relative movement between gate 40 and optical fiber portions 10 a, 10 b can be used.

[0034] Barrier systems including gates can be installed at intervals along the optical fiber / fiber optic cable, and two barrier systems, one on each side of the damage location, can be activated simultaneously in response to a breach, thereby sealing off the section of fiber containing the breach.

[0035] The barrier system including the gate can be configured for reversible operation when the actuator is configured to reverse the movement of the gate 40 from a deployed position within the gap 12 back to a resting position aligned with the gap 12. This allows the barrier system to be operated to remove the barrier from the optical fiber after the tear or damage has been repaired, thereby restoring light transmission along the optical fiber.

[0036] To maintain some light transmission along the optical fiber after the barrier is inserted, the gate can be formed from a material that is transparent at the wavelength(s) carried in the optical fiber of the cable, such as a suitable glass. This can allow at least some function of the optical cable to continue after a break while awaiting repair.

[0037] FIG. 4A shows a simplified schematic representation of a further embodiment employing a gap between two portions of optical fiber and the active insertion of a previously external barrier into the gap in response to a breach in the cable. In this example, the barrier comprises a viscous fluid that is injected or pumped into the gap when a breach in the cable is detected. By viscous, we mean that the fluid has a higher viscosity than water, particularly seawater if the cable is deployed in a marine environment, and preferably is significantly more viscous than water. Water that enters the gap and comes into contact with the viscous fluid cannot easily mix with or penetrate the viscous fluid, thereby preventing water movement beyond the barrier and protecting the fiber on the other side of the gap from water ingress. Furthermore, the viscosity does not specifically damage the microstructured fiber because it inhibits the viscous fluid in the gap from easily entering and moving along voids in the fiber portion (the voids have very small widths and the fluid penetration time is increased by viscosity).

[0038] As before, the system includes an optical fiber 10 including a first portion 10a and a second portion 10b positioned on either side of a gap 12. The barrier mechanism 20 includes a reservoir or container 60 holding a quantity of viscous fluid 64. The reservoir 60 has an outlet 62 aligned in fluid communication with the gap 12 so that the viscous fluid can exit the reservoir 60 and flow into the gap 12. The outlet 62 may include a nozzle or drain, or may simply be an opening in the wall of the reservoir. Depending on the configuration, the outlet 62 may be opened or closed by a valve or membrane that opens when fluid transfer is required. In response to detection of a breach by the breach detection system 28, the barrier mechanism is actuated to transfer a portion of the viscous fluid 64 from the reservoir 60 into the gap. Any suitable means for moving the viscous fluid 64 may be used. For example, a plunger arrangement may be provided to push the viscous fluid 64 out of the reservoir 60. The reservoir 60 can be compressible or formed with flexible walls, and a mechanism can crush the reservoir 60 to force the viscous fluid 64 out through the outlet 62. The outlet 62 can be previously closed and then opened (by movement of a valve or rupture of a membrane), allowing the viscous fluid 64 to flow out under gravity or under the force of the pressure of the stored viscous fluid. The reservoir 60 can comprise a simple bag or pouch, for example, of plastic or plasticized foil, and a rupturing element is provided that is moved to pierce the bag and create an outlet in the appropriate position to deliver the viscous fluid 64 into the gap 12. The reservoir can contain a volume of pressurized or liquefied gas that is released to expand within the reservoir and force the viscous fluid 64 out the outlet 62.

[0039] Figure 4B shows the system of Figure 4A after a quantity of viscous fluid 64 has been delivered into gap 12. Viscous fluid 64 is allowed to flow to fill the gap, thereby creating the necessary barrier 66 across the voids in both optical fiber portions 10a, 10b. To better contain and direct the flow of viscous fluid to the desired location, a housing (not shown) can be provided around gap 12 to receive the delivered viscous fluid 64.

[0040] The viscous fluid can be any fluid of appropriate viscosity. Higher viscosity (more viscous) fluids provide a more effective barrier, but cause the viscous fluid to flow more slowly through the gap and around the fiber ends, resulting in slower barrier formation. A balance between these aspects can be achieved when selecting a viscous fluid. For example, the viscous fluid can include oil or grease. Another example is an epoxy resin, which sets after being pumped into the gap and strengthens the barrier over time. Resins can be provided by pumping two or more fluids that react together to form a hardenable material. However, this creates a more permanent barrier, which is more difficult to remove after repairing the cable than a fluid-based barrier. Other suitable viscous fluids include mineral oils blended from alkanes and silicone oils such as hexamethyldisiloxane and polydimethylsiloxane.

[0041] Using a viscous fluid to form the barrier avoids the need for precise alignment of the gate with the gap and fiber end in the gate-barrier example of Figure 3. The viscous fluid simply flows to fill the gap and conforms to the available space, requiring only basic alignment between the gap and the fluid source. Conversely, however, it provides a barrier that cannot be easily reversible or remotely retracted from the gap when it is no longer needed, in the way that a gate can. Thus, the two configurations have opposing advantages and can be chosen accordingly.

[0042] 5A shows a simplified schematic representation of another embodiment using a gap between two portions of optical fiber, which are arranged to propagate light across the gap as previously described. The optical fiber 10 includes two portions 10a, 10b of a microstructured optical fiber, such as a hollow-core optical fiber, with a gap 12 between them. The barrier feature 20 in this example includes a component, such as a plug 50 of material, which may include a planar sheet, that is disposed in the gap. The plug 50 has a central opening 52 that is arranged so that light can be sent through the opening to propagate from one fiber portion 10a, 10b to the other fiber portion 10a, 10b.

[0043] 5B shows a plan view of plug 50 with central opening 52. In this example, plug 50 and opening 52 are circular, so that plug 50 has the appearance of a washer, with the sheet of material forming a ring around central opening 52, although other shapes can be used if desired.

[0044] The material forming the plug is a water-swellable material, which has the property that when the material is exposed to water, it absorbs that water and expands or increases in volume accordingly. Examples of suitable materials include superabsorbent polymers (SAPs), water-swellable rubbers, and water-swellable elastomers. The shape and dimensions of the plug 50 and openings 52 are selected for the strength of this expansion property so that exposure to water causes sufficient swelling to nearly or completely close the openings (reducing or closing the openings), thereby making the plug 50 continuous or nearly continuous across the voids in the fiber portions 10a, 10b. The SAP can be modified with a stiffening agent to create a more robust barrier and / or a foaming agent to generate foam to further impede water movement.

[0045] In this example, the mechanism that operates barrier feature 20 is the expansion properties of the water-swellable material; barrier feature 20 responds to a breach in the cable by expanding plug 50, which expansion provides the necessary barrier across the void. If a breach occurs that allows water to enter a void in the optical fiber, the water can move through the void along one or other of fiber portions 10a, 10b until it reaches gap 12. The water then flows out of the void and into the gap, where it is absorbed by the water-swellable material of plug 50, causing plug 50 to expand and close opening 52. Once the opening is closed, plug 50 forms a barrier across the void between the two fiber portions 10a, 10b, inhibiting further movement of water that could otherwise enter the void in the other fiber portion. Thus, damage to the optical fiber is limited in extent.

[0046] 5A, plug 50 is shown as being limited to one optical fiber 10, but it can be sized to cover several optical fibers, and indeed the entire cable in which the optical fibers are routed. Plug 50 need not be in the form of a planar sheet, and other forms of material can be used appropriately to accommodate the gap.

[0047] This embodiment can be considered passive in that the actual presence of water entering through a breach directly activates the breach mechanism, and does not require explicit detection of a breach and subsequent activation of the breach mechanism in response to that detection. This provides a significant simplification.

[0048] It is also possible to implement a barrier in response to a cleft without including a gap in the optical fiber. Some examples are now described.

[0049] FIG. 6A shows a simplified schematic cross-sectional representation of an example optical fiber cable system with barrier capabilities that does not require any gaps in the optical fiber. The system includes a fiber cable 100 including at least one microstructured optical fiber 10, such as a hollow-core fiber having a hollow core 76 surrounded by a microstructured cladding 78 (only one fiber is shown for simplicity). The cable 100 includes an outer jacket 102 surrounding the optical fiber(s) 10. The cable also includes a barrier-forming material 70, which is added during manufacture of the cable 100 and disposed within the outer jacket 102 around the fiber(s) 10. The barrier-forming material 70 includes a viscosity modifier, which is a material that has properties that increase the viscosity of water when mixed with water, making it more viscous. The ability of water to penetrate exposed voids in the microstructured optical fiber(s) 10 depends on several parameters, including the pressure and viscosity of the water. The penetration time t is calculated as t = ((32ηL 2 ) / (d 2 p0))t h It depends directly on the viscosity η according to (where L is the penetration depth, d is the diameter of the fiber core (or other void), p0 is the water pressure, and t h (where ρ is a dimensionless constant that can be set to 0.1). Therefore, if the viscosity of the water around the breach in the cable 100 can be increased, the penetration of the surrounding water into the void can be slowed, limiting the extent of damage to the fiber(s) 10 and the cable 100.

[0050] FIG. 6B shows the optical fiber cable system of FIG. 6A after being placed in water and a breach occurs. In this case, the breach is in the form of a cut in the cable 10, creating a broken end 104 where the voids in the microstructured optical fiber (10) are exposed to the surrounding water. The breach also exposes the barrier-forming material 70, allowing it to disperse outward and enter the surrounding water. The barrier-forming material 70 acts to substantially increase the viscosity of the water near the broken end 70, creating a localized water mass with a modified viscosity higher than the original water viscosity. The increased viscosity means that any water 74 that might penetrate the voids in the optical fiber(s) does so much more slowly, inhibiting water movement along the fiber and limiting the longitudinal extent of exposure to water. The mass of water 72 with increased viscosity coats the cable 100 and the ends of the fibers 10 therein, thus acting as a barrier and preventing unthickened water beyond the mass of water 72 from entering the void. The viscosity-altering properties of the barrier-forming material 70 can be thought of as a barrier feature in this example of the optical fiber cable system, which responds to a breach in the cable 100 by increasing the viscosity of nearby water, thereby introducing or providing a barrier across the voids in the optical fiber(s) 10. The difference between this example and other examples is that in this example, the barrier is formed at the location of the breach, and therefore acts to inhibit the initial movement of water into the microstructured optical fiber. In other examples, depending on the location of the barrier feature, the barrier is introduced at a location separate from the breach, and therefore acts to inhibit further movement of water that has already penetrated into the voids in the fiber, so that the water cannot move further or easily along the fiber.

[0051] Examples of suitable viscosity modifiers are xanthan gum, methyl cellulose and other cellulose derivatives, which are used in large quantities in the oil industry to thicken muddy waters, and biomimetic compounds based on the mucus produced by hagfish (a fish of the class Hagfish and order Hagfish).Other viscosity modifiers can also be used if suitable, an example being superabsorbent polymers.

[0052] FIG. 7A shows a simplified schematic cross-sectional representation of another example of an optical fiber cable system with barrier capabilities that does not require any gaps in the optical fiber. The system includes a fiber cable (not shown) containing at least one microstructured optical fiber 10, such as a hollow-core fiber having a hollow core 76 surrounded by a microstructured cladding 78 (only one fiber is shown for simplicity). The system also includes a heat source 80 operative to apply heat H (i.e., deliver thermal energy) to the optical fiber 10. The heat source 80 implements the barrier mechanism 20. The heat source 80, as shown in the general depiction of FIG. 7A, can have any suitable design. Examples include an electric heating element in contact or near contact with the outer surface of the optical fiber 10 and having an associated power source. The heating element can be ring-shaped to wrap around the optical fiber 10, rod-shaped to deliver thermal energy to one side of the optical fiber 10, multiple heating elements distributed over a localized area of ​​the optical fiber 10, or some other configuration that would be apparent to one skilled in the art. Other alternatives include a light source, such as a laser diode, configured to apply one or more focused beams of laser light to the optical fiber 10. Other heat sources may also be used if preferred. Heat may be provided by a chemical reaction, such as, for example, an exothermic reduction-oxidation (redox) reaction, such as the thermite or Goldschmidt reaction. If a breach in the cable 100 occurs, the breach detection system 28 detects the breach as described above and sends an activation signal to the heat source 80.

[0053] FIG. 7B shows the optical fiber cable system of FIG. 7A after the barrier system 20 has been activated via the breach detection system to respond to the breach. In response to the breach, the heat source generates and transmits thermal energy to the optical fiber 10. The thermal energy is absorbed by the material (typically glass) of the optical fiber 10, particularly the glass that defines its microstructure (the glass is between the voids), raising the temperature to a level sufficient to soften or melt the glass. This results in the destruction of the optical fiber 10's microstructure and core, forming an amorphous or unstructured solid body of molten glass 82 that closes and blocks the voids in the optical fiber 10, thus creating a barrier to the movement of any water 74 that has entered the voids. Any such water is therefore inhibited (prevented or impeded, depending on the extent of the damage) from moving through the barrier and into the void beyond the barrier. The fiber "downstream" of the barrier is thereby protected from water ingress, as in the various examples described above that introduce barriers into the optical fiber gaps. Multiple heat sources 80 can be provided spaced along the optical fiber so that a pair of heat sources 80 on either side of a cleft can be actuated together to close a section of the optical fiber containing the cleft, protecting a more distal portion of the optical fiber. Individual heat sources can be configured to act on a single fiber, a group of fibers, or all of the fibers in the cable, or on the entire cable if the outer jacket of the cable is easily heated or melts, or has thermal properties that allow rapid transfer of heat energy through the jacket to the optical fiber within.

[0054] Some of the barrier systems described herein can be considered "active" because they actively activate at least one element of the system in response to a detected damage or breach. In such a configuration, direct communication from the breach detection system to the barrier system (e.g., Figures 1 and 3) can be omitted; instead, an operator on the surface receiving a breach detection signal from the breach detection system can manually initiate barrier system operation in response. This requires providing remote control of the barrier system, for example, via the barrier system's radio transceiver or the like, but allows for human assessment of the breach, such as with respect to severity and location, to determine whether or not a barrier needs to be deployed, and thus, whether or not optical communications need to be interrupted. In another alternative, the breach detection system can communicate with an on-water computer system, which evaluates the need to activate a barrier mechanism (e.g., via an algorithm or neural network) and sends an activation signal to one or more barrier mechanisms on the cable as appropriate. Also, communication via a surface computer can be used without any evaluation stage, whereby activation of the breach system is automatic in response to a breach in the cable, which may be more convenient, as it directly implements underwater communication between the breach detection system and the barrier mechanism, especially if multiple barrier mechanisms are provided along the length of the cable.

[0055] The various embodiments described herein are presented solely to aid in the understanding and teaching of the claimed features. These embodiments are provided merely as a representative sample of embodiments and are not intended to be exhaustive and / or exclusive. It is understood that the advantages, embodiments, examples, functions, features, structures, and / or other aspects described herein are not to be construed as limitations on the scope of the invention as defined in the claims or on the equivalents of the claims, and that other embodiments may be used and changes may be made without departing from the scope of the claimed invention. Various embodiments of the invention may suitably comprise, consist of, or consist essentially of any suitable combination of the disclosed elements, components, features, parts, steps, means, etc., other than those specifically described herein. Furthermore, this disclosure may include other inventions not currently claimed but which may be claimed in the future.

[0056] reference [1] US4834479 [2] US4913517 [3] US5861575

Claims

1. A fiber optic system, An optical fiber cable containing at least one microstructured optical fiber within the jacket, A barrier mechanism that responds to a tear in the optical fiber cable, wherein water from the environment surrounding the optical fiber cable can enter the voids of the microstructured optical fiber through the tear. Includes, The barrier mechanism responds to the tear by acting to provide a barrier across the void in the microstructured optical fiber, and the barrier is configured to suppress the movement of water along the void. Fiber optic system.

2. An optical fiber system according to claim 1, wherein the microstructured optical fiber is a hollow core optical fiber.

3. An optical fiber system according to claim 1 or claim 2, The microstructured optical fiber is a first optical fiber portion, and the optical fiber cable includes a second optical fiber portion, the second optical fiber portion crossing the gap and optically aligning with the first optical fiber portion for the propagation of light between the first optical fiber portion and the second optical fiber portion. The barrier mechanism operates to provide the barrier by bringing the barrier into the gap. Fiber optic system.

4. An optical fiber system according to claim 3, wherein the gap includes an opening in the microstructured optical fiber that extends laterally through the void between the first portion of the optical fiber and the second portion of the optical fiber.

5. An optical fiber system according to claim 3, wherein the first portion of the optical fiber and the second portion of the optical fiber are physically separated from each other, and the gap is the space between the end of the first portion of the optical fiber and the end of the second portion of the optical fiber.

6. An optical fiber system according to claim 3, wherein the second optical fiber portion includes a microstructured optical fiber, and the barrier, when provided, suppresses the movement of water between the first optical fiber portion and the second optical fiber portion.

7. The optical fiber system according to claim 4, wherein the barrier includes a gas, and the barrier mechanism is A pressure housing surrounding the aforementioned gap, A reservoir that communicates with the pressure housing for supplying inert gas and gas flow Includes, The barrier mechanism operates to provide the barrier by allowing the inert gas from the reservoir to flow into the pressure housing and subsequently along the void. Fiber optic system.

8. The optical fiber system according to claim 7, further comprising a gas flow valve for controlling the flow of gas from the reservoir to the pressure housing, wherein the barrier mechanism allows an inert gas from the reservoir to flow into the pressure housing by opening the valve.

9. An optical fiber system according to claim 7, wherein the reservoir comprises a pressurized inert gas or one or more materials for generating an inert gas.

10. The optical fiber system according to claim 7, wherein the reservoir is compressible, and the barrier mechanism further includes a second pressure housing surrounding the reservoir and a water flow valve configured to allow water from the surrounding environment to enter the second pressure housing, the barrier mechanism further operates by allowing water from the surrounding environment to enter the second pressure housing, opening the water flow valve to compress the reservoir, thereby forcing an inert gas from the reservoir into the pressure housing and the void.

11. An optical fiber system according to claim 3, wherein the barrier includes a solid gate aligned with the gap, and the barrier mechanism includes an actuator configured to provide relative motion between the gate and the first and second portions of the optical fiber, and operates to bring the barrier across the void, thereby causing the relative motion to occur and positioning the gate in the gap.

12. An optical fiber system according to claim 3, wherein the barrier comprises a viscous fluid having a higher viscosity than the water in the surrounding environment, and the barrier mechanism comprises a reservoir in fluid flow communication with a gap for supplying the viscous fluid, and operates to provide the barrier by delivering the viscous fluid from the reservoir to the gap so as to cross the void.

13. An optical fiber system according to claim 3, wherein the barrier includes a plug of water-swellable material disposed in the gap and having a central opening, through which light can propagate between the first portion of the optical fiber and the second portion of the optical fiber, the barrier mechanism includes an expansion property of the water-swellable material in response to contact with water, and the barrier mechanism operates to provide the barrier by causing expansion of a sheet of water-swellable material when water is present in the gap in order to close or reduce the central opening.

14. An optical fiber system according to claim 13, wherein the water-swellable material comprises a superabsorbent polymer, a superabsorbent polymer with a curing agent, or a superabsorbent polymer with a foaming agent.

15. An optical fiber system according to claim 1 or claim 2, wherein the barrier includes a glass solid, and the barrier mechanism includes a heat source configured to supply thermal energy to the microstructured optical fiber to melt the glass defining the microstructure, and operates to provide the barrier such that the glass melts into a solid that closes the voids in the microstructured optical fiber by melting the glass defining the microstructure.

16. An optical fiber system according to claim 1 or claim 2, wherein the barrier comprises a mass of water with increased viscosity, the barrier mechanism comprises a viscosity modifier contained within the optical fiber cable, the barrier mechanism provides the barrier by releasing the viscosity modifier through a crack in the optical fiber cable into water near the crack, thereby increasing the viscosity of the water, and the barrier mechanism operates to form the barrier across voids of the microstructured optical fiber exposed by the crack.

17. An optical fiber system according to claim 16, wherein the viscosity modifier comprises xanthan gum, methylcellulose or other cellulose derivatives, or a biometric compound based on mucus produced by fish of the order Halibutiformes.

18. An optical fiber system according to claim 7, wherein the barrier mechanism is configured to respond to a tear, by being operated by a tear detection system configured to detect a tear in the optical fiber cable.

19. An optical fiber system according to claim 18, further comprising a tear detection system configured to detect a tear in the optical fiber cable and to send a signal to the barrier mechanism to operate the barrier mechanism to provide the barrier across the void in the microstructure optical fiber.

20. An optical fiber system according to claim 19, wherein the tear detection system is configured to detect a tear in the optical fiber cable by monitoring the internal pressure of the optical fiber cable and identifying a change in the internal pressure as a tear.

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