Underwater optical fiber system

Abstract

A fiber optic system includes a fiber optic cable including at least one microstructure fiber within a sheath; and a barrier mechanism responsive to a notch of the fiber optic cable through which water from an environment surrounding the fiber optic cable may enter the void of the microstructure fiber; wherein the barrier mechanism is responsive to the gap by a barrier that operates to introduce the void across the microstructure optical fiber, the barrier configured to inhibit movement of water along the void.

Description

Technical Field

[0001] The present invention relates to underwater optical fiber systems. Background Art

[0002] Optical fiber is widely used to transmit data carried by light signals, with multiple fibers used to carry separate data channels in parallel. For convenience and protection, multiple fibers are often bundled together and placed in a protective outer sheath to form a fiber optic cable. Cables are installed in a variety of environments and are used to transmit data over long and short distances between sending and receiving locations. In some cases, cables are deployed underwater to transmit data across oceans, seas, rivers, and lakes. Undersea cables are susceptible to damage, including cable breaks caused by ship anchors, fishing activities, seabed movement, and other physical shocks and disturbances. Underwater cables in non-marine environments can also be subject to damage.

[0003] Conventionally, underwater cables contain solid optical fibers. If damage occurs, water may penetrate into the interior of the cable, entering the spaces between the fibers and between the fibers and the outer sheath. Protection can be provided by established techniques, such as incorporating water-absorbing materials or water-swellable tapes or yarns into the cable structure; these materials swell in the presence of water, forming a barrier that prevents water from invading the interior of the cable. Another approach is to incorporate stop joints or other physical barriers that divide the cable into sections through which water cannot pass; thereby limiting the length of the cable that water can penetrate. Examples of such arrangements are given in US 4,834,479, US 4,913,517 and US 5,861,575 [1, 2, 3].

[0004] Recently, optical fibers have been developed that include longitudinal voids in the internal structure of a single fiber. These include, but are not limited to, hollow core fibers and microstructured cladding fibers formed by a specific arrangement of longitudinal voids. Compared to solid core fibers, hollow core fibers have superior light propagation properties, including reduced optical losses, increased propagation speed, and optical bandwidth, which make them particularly attractive in the telecommunications field. However, hollow core fibers are particularly vulnerable to damage to the cables in underwater environments. Water ingress into the voids in the core and cladding will have a negative impact on the propagation capabilities, as these depend on whether the voids are filled with air or gas. Therefore, the optical fiber needs to be replaced when repairing damaged cables. In an undersea environment, the increased water pressure at depth forces water further into the interior of the fiber, which exacerbates the problem because longer fibers need to be replaced.

[0005] Therefore, technologies aimed at suppressing water intrusion into hollow-core optical fibers in optical cables have attracted much attention. Summary of the invention

[0006] Various aspects and embodiments are set out in the accompanying claims.

[0007] According to a first aspect of certain embodiments described herein, there is provided an optical fiber system comprising: an optical fiber cable including at least one microstructured optical fiber within a sheath; and a barrier mechanism responsive to a breach in the optical fiber cable, through which water from the surrounding environment of the optical fiber cable may enter the voids of the microstructured optical fiber; wherein the barrier mechanism responds to the breach by operating to introduce a barrier across the voids of the microstructured optical fiber, the barrier being configured to inhibit the movement of water along the voids.

[0008] These and other aspects of certain embodiments are set forth in the accompanying independent and dependent claims. It should be understood that the features of the dependent claims may be combined with each other and with the features of the independent claims in ways other than the combinations explicitly set forth in the claims. Furthermore, the methods described herein are not limited to the specific embodiments described below, but include and contemplate any suitable combination of the features presented herein. For example, a system may be provided according to the methods described herein that includes any one or more of the various features described below. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0010] Figure 1 A simplified schematic diagram of a first example of a fiber optic cable system having a barrier mechanism disclosed herein is shown;

[0011] Figure 2 A simplified schematic diagram of a second example of a fiber optic cable system having a barrier mechanism disclosed herein is shown;

[0012] Figure 3 A simplified schematic diagram showing a third example of a fiber optic cable system having a barrier mechanism disclosed herein;

[0013] Figure 4A A simplified schematic diagram showing a fourth example of a fiber optic cable system having a barrier mechanism disclosed herein;

[0014] Figure 4B Shows Figure 4A A simplified schematic diagram of an example after the barrier mechanism operates;

[0015] Figure 5A A simplified schematic diagram showing a fifth example of a fiber optic cable system having a barrier mechanism disclosed herein;

[0016] Figure 5B Shows Figure 5A A plan view of an example barrier mechanism;

[0017] Fig. 6AA simplified schematic diagram showing a sixth example of a fiber optic cable system having a barrier mechanism disclosed herein;

[0018] Figure 6B shows the barrier mechanism after operation Fig. 6A A simplified schematic diagram of an example of;

[0019] Fig. 7A a simplified schematic diagram showing a seventh example of a fiber optic cable system having a barrier mechanism disclosed herein; and

[0020] Figure 7B shows the barrier mechanism after operation Fig. 7A A simplified schematic diagram of an example of . DETAILED DESCRIPTION

[0021] Aspects and features of certain examples and embodiments are discussed / described herein. Some aspects and features of certain examples and embodiments may be implemented in a conventional manner, and for the sake of brevity, these aspects and features are not discussed / described in detail. Therefore, it should be understood that aspects and features of the systems discussed herein (not described in detail) may be implemented according to any conventional techniques for implementing these aspects and features.

[0022] Methods described herein are related to microstructured optical fibers, particularly hollow core optical fibers discussed in more detail below, and such optical fibers are incorporated into optical fiber cables for underwater deployment. Optical fiber cables include multiple optical fibers, which are substantially arranged in parallel into bundles and surrounded by an outer protective layer (e.g., a sheath or protective sleeve). The sheath can be made of, for example, a polymer material, a low smoke halogen-free material, or a stainless steel tube. The sheath can only accommodate the optical fiber, or other elements can be included in some examples to make the cable stronger and more resistant to damage. These 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, which extends along the cable length to resist tight bending and potential damage to the optical fiber, and the optical fiber is arranged, bundled, wrapped, wound, or twisted around the member, and one or more polymer material buffer layers to fix and protect individual or grouped optical fibers. Strength members around the optical fiber can also be used, such as in the form of a layer between an optical fiber bundle and the sheath. Nevertheless, the cable is still susceptible to damage, including all or part of the cable breaking, particularly under severe conditions exposed to an underwater environment.

[0023] Fiber optic cables may contain optical fibers of any type or design, including two or more types in one cable. When underwater cables include hollow or other microstructured optical fibers with voids in the internal structure of the fibers, it is desirable to limit the intrusion of water into the individual fibers in the event of cable damage, as water in the voids can degrade optical performance. In marine environments, cables may be located at considerable depths. The higher water pressure at depth can cause water to penetrate further and faster along the individual fibers from the point of damage, resulting in distributed damage over the length of the cable, which may be remote from the original damage location. The cable or individual fibers within the cable may become unusable, requiring extensive and expensive repair or replacement.

[0024] Technology to prevent or inhibit water intrusion or limit the extent of water penetration along the length of a cable containing microstructured optical fibers with internal voids is intended to minimize damage caused by water and enable more localized repairs rather than replacing large amounts of cable.

[0025] As used herein, the term "microstructured optical fiber" refers to any optical fiber having one or more internal longitudinal voids, wherein the voids may define or form a portion of the optical fiber core, the optical fiber cladding, or both. In more detail, a microstructured optical fiber has an internal structure comprising an array or arrangement of holes, capillaries, or cavities within the optical fiber material, which extend along the length of the optical fiber parallel to the longitudinal axis and are confined within a material such as glass. The arrangement of holes may be referred to as a microstructure, and typically the microstructure forms at least a portion of the optical fiber cladding and may additionally or alternatively define the core. All such structures are susceptible to the intrusion of water if the optical fiber breaks, for example if included in an optical fiber cable deployed underwater and becomes damaged.

[0026] The microstructured configuration defining the core can provide a hollow core fiber, in which a cladding that is usually, but not necessarily, also microstructured surrounds a central void or region that provides the light-conducting core. The microstructured capillaries are usually supported by a larger outer cladding tube made of glass. Since there is no solid glass core, light can propagate in air (or other gas or vacuum), reducing the proportion of guided light waves propagating in glass compared to solid core fibers, thereby providing benefits such as increased propagation speed, reduced losses from both absorption and scattering, and reduced nonlinear interactions. As a result, hollow core fibers are very attractive for telecommunication applications; they are able to transmit data at speeds close to the speed of light in a vacuum, with higher optical powers and wider optical bandwidths, and are relatively immune to problems such as nonlinearities and thermo-optical effects that can affect light propagating in solid core fibers. Hollow core fibers can be divided into two main categories or types based on their optical guiding mechanism: hollow core photonic bandgap fibers (HCPBF, also called hollow core photonic crystal fibers, HCPCF) and antiresonant hollow core fibers (AR-HCF or ARF). In an HCPBF, the structured cladding region comprises a regular close-packed array of many small glass capillaries from which a central group is excluded to define a substantially circular hollow core. The periodicity of the cladding structure provides a substantially periodic structure of the refractive index, so that the photonic bandgap effect confines the propagating light waves to the core. In an ARF, the structured cladding comprises a much smaller number of larger glass capillaries or tubes whose structure lacks a high degree of periodicity, so that the photonic bandgap effect is not significant, but which has some periodicity over a larger area due to the uniform spacing of the tubes. The structure provides anti-resonance for propagating wavelengths that are not resonant with the wall thickness of the cladding capillaries, wherein the cladding capillaries surround a central void or cavity that provides the hollow core of the fiber and is capable of supporting anti-resonantly guided optical modes.

[0027] The present disclosure applies to all types of microstructured optical fibers, including the two main types of hollow core optical fibers and subtypes associated therewith, as well as other hollow core designs. Other examples include microstructured solid core optical fibers, in which the void structure is only provided in the cladding region, surrounding a core defined in a solid material. The cladding may be an array of many capillaries to provide photonic effects, or a single larger void ring separated by glass pillars supporting a central solid core (suspended core optical fiber). All other optical fiber designs with one or more internal voids are also relevant. Please note that in the art, the terminology of various types of microstructured or "holey" optical fibers is somewhat overlapping. For the purposes of the present disclosure, the term "microstructured optical fiber" is intended to cover all types having one or more longitudinal voids in the internal structure, and the terms "hollow core optical fiber" and "hollow core microstructured optical fiber" are intended to cover all types of these optical fibers having a hollow core as described above. Unless the context indicates otherwise, the description specifically referring to the hollow core optical fiber should be understood to apply to all microstructured optical fibers. However, since the hollow core optical fibers outlined above have particularly enhanced optical properties, such optical fibers have significant benefits for telecommunication applications, so the present disclosure is particularly relevant here.

[0028] To solve the problem of water intrusion into the voids of hollow fibers and other microstructured fibers in optical fiber cables, a system is proposed, which includes an optical fiber cable and components, arrangements, devices or mechanisms that can respond to cable damage by setting or introducing a barrier across the voids of the microstructured optical fiber to prevent water from moving along the voids, thereby reducing or limiting the extent of physical damage caused by the presence of water. Inhibiting the movement of water can include preventing water from invading the interior of the optical fiber, preventing water from moving along the voids outside the barrier position, and slowing the flow of water invading the voids or along the voids. Physically limiting water that penetrates into the optical fiber and slowing the diffusion of water within the optical fiber can reduce the number of optical fibers or cables that need to be repaired or replaced. Specifically, cable damage includes a breach in the cable, and may also cause breaches in one or more microstructured optical fibers inside the cable, thereby allowing water to penetrate into the voids in the optical fiber. In various examples, when a breach in the cable is detected, the mechanism that provides the barrier can be operated so that the barrier is set across the voids of the optical fiber, while in other examples, the barrier can be set in a manner that forms a barrier by responding to water entering the cable through the breach.

[0029] For simplicity, examples are generally described in the context of a single optical fiber, but it should be understood that a particular optical fiber is contained within a fiber optic cable, typically with one or more additional optical fibers, and more typically with a large number of additional optical fibers. The various proposed barrier mechanisms can be configured to operate on a single optical fiber, a group of optical fibers, or all optical fibers in the cable; it will be clear to those skilled in the art where these various alternatives are best suited. If an individual barrier mechanism is associated with less than all microstructured optical fibers in the cable, an additional barrier mechanism can be provided at the same location to handle all microstructured optical fibers. In some arrangements, multiple barrier mechanisms can be provided at intervals along the cable. This allows the cable to be "segmented" into separate sections to locally contain any water that enters the optical fiber voids, where the barrier can be considered as a partition that prevents water from flowing extensively along the length of the cable. If this is not apparent from the appearance of the cable plus barrier mechanism system, the location where the barrier can be set can be made identifiable. For example, a visual mark corresponding to the barrier location can be set on the outside of the cable jacket. In an alternative, a detectable tag, such as an RFID transponder or a similar element that can be detected by using a separate detector device, can be incorporated at a relevant location of the cable structure. Detectable tags or other arrangements incorporated into the cable structure may be preferred because they are less susceptible to wear and tear on the cable after deployment.

[0030] In a first set of examples, a barrier is introduced into the gap between adjacent segments or portions of an optical fiber so as to provide a barrier or partition between the two portions, thereby inhibiting (reducing or preventing) water from moving from one portion to another. The barrier may be completely waterproof, thereby completely blocking the flow of water, or partially waterproof, thereby slowing down or reducing the speed at which water moves. For convenience, the examples are presented in the form of adjacent portions of optical fiber physically separated from each other, with their ends spaced apart to define a gap. The two portions of the optical fiber are optically aligned end to end so that light transmitted from the end of one of the optical fiber portions is coupled to the adjacent end of the second optical fiber portion, preferably with minimal light loss. The gap may be an empty narrow gap for free space light propagation between the optical fiber portions, or optical coupling may be facilitated by an optical arrangement between the ends of the optical fiber portions, the optical arrangement including one or more optical elements, including lenses, mirrors, Faraday rotator materials, etc. Whether to include such an optical arrangement may be selected based on the requirements of accommodating the selection of a particular barrier mechanism and / or the requirements of achieving effective coupling between the optical fiber types of the two portions of optical fiber, which may be the same or different. The two fiber portions can be microstructured fibers, having the same or different configurations or designs, or one fiber portion can be a microstructured fiber and the other fiber portion can be a solid fiber. In the case where one of the fiber portions is a solid portion, the barrier can be configured to maintain the integrity of the microstructured fiber by extending into the void to inhibit water from flowing along the void from a breach location away from the gap rather than blocking flow between the fiber portions.

[0031] Alternatively, adjacent portions of the optical fiber may be continuous segments of the same optical fiber in which grooves, holes, perforations, apertures or other openings are formed to provide gaps. The openings typically extend transversely to the length of the optical fiber and preferably pass through all voids in the optical fiber microstructure so that the barrier can enter and block all voids. The portions of the optical fiber are physically connected to each other by other portions of the optical fiber structure that the openings do not pass through (e.g., an outer cladding or outer jacket). Optical alignment of adjacent portions is thereby maintained or facilitated, thereby providing a simpler arrangement than using two separate optical fiber portions. Herein, the term "gap" between two segments or portions of an optical fiber should be understood to cover two alternatives: the space between adjacent ends of two physically distinct and separate optical fiber portions, or an opening in an optical fiber microstructure that divides the optical fiber into two segments that are otherwise physically continuous.

[0032] Figure 1 A simplified schematic diagram of an example system utilizing a gap between fiber sections is shown, which can be used with two portions of microstructured optical fiber or a portion of microstructured optical fiber and a portion of solid optical fiber. The optical fiber 10 includes a first portion 10a of the optical fiber, which is a microstructured optical fiber, such as a hollow core optical fiber, and a second portion 10b of the optical fiber, which may or may not be a microstructured optical fiber. The optical fiber 10 is typically bundled with other optical fibers within a fiber optic cable (not shown) that is intended to be deployed in an underwater environment, such as a seafloor location. The fiber sections 10a, 10b are arranged end-to-end in sequence to transmit light between the sections 10a, 10b to form the overall optical fiber 10. In addition to the first and second sections shown, other fiber sections may also be included to extend the overall length of the optical fiber 10 and / or accommodate additional barrier mechanisms or other optical components, such as amplifiers. The optical arrangement 12 is positioned between adjacent ends of the fiber sections 10a, 10b, the ends being spaced apart via a gap. The optical arrangement 12 may comprise free space, with the ends of the fiber portions 10a, 10b positioned (and possibly treated to reduce reflections by anti-reflection coatings or beveled end faces) and aligned so that light propagates across the gap between the fiber portions 10a, 10b. Alternatively, optical elements may be used in the optical arrangement to improve the optical coupling between the fiber portions 10a, 10b, such as mirrors, lenses, prisms, etc.

[0033] The barrier mechanism 20 includes a pressure housing or pressure cell 22 surrounding the gap / optical arrangement 12 to exclude water from the gap 12 when the cable is submerged. The first and second optical fiber parts 10a, 10b (inside the cable) pass through the wall of the pressure housing 22. A reservoir 24 for supplying an inert gas (e.g., argon or other rare gases, nitrogen, or sulfur hexafluoride (other inert gases are not excluded)) 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 state of a gas material that expands into a gaseous state when released from the reservoir 24. The reservoir 24 has a rigid wall so as to withstand the water pressure at depth and maintain its shape. The reservoir 24 is connected to the internal gas flow of the pressure housing 22, and a valve 26 (gas flow valve) is arranged 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, a valve 26 for gas flow is located on a pipe or similar gas flow conduit 25 connecting the reservoir 24 to the pressure shell 22, but in other examples, the reservoir 24 and the pressure shell 22 may share a common wall with an aperture in which the valve 26 is located. Under normal circumstances, when the cable is not damaged, the valve 26 is closed and the reservoir 24 is filled with gas or liquefied gas, which is retained in the reservoir. The valve 26 is controlled by a breach detection system 28, which may be controlled by a wired or other physical connection 30 or wirelessly, depending on the specific embodiment. The breach detection system 28 is configured to detect whether damage has occurred to the cable, which damage may cause a breach and cause water intrusion, and may operate by monitoring the internal pressure in the cable or monitoring an optical signal via optical time domain reflectometry. A breach causes a change in the internal pressure, so the identification of the pressure change can be attributed to the occurrence of the breach (other breach detection arrangements are also possible; the functionality of the breach detection system 28 is beyond the scope of this disclosure). When a breach is detected, the breach detection system 28 transmits this information to the valve 26, which opens to provide a gas flow path from the reservoir 24 to the pressure housing 22. Thus, the breach mechanism 20 in this example responds to the presence of a breach by allowing gas to flow from the reservoir 24 into the pressure housing 22. The gas reaches the gap between the optical fiber portions 10a, 10b and is able to enter the voids in the microstructure of one or both of the optical fiber portions 10a, 10b. If the gas is equal to or higher than the water pressure of the surrounding environment, the internal pressure within the optical fiber is equal to or exceeds the external pressure, and water cannot flow into the void. The occupation of the void by the gas acts as a barrier across the void, which inhibits the movement of any water that enters the void through the breach in the cable along the void. Under the impetus of higher pressure, the gas can penetrate along the void, thereby protecting a considerable length of optical fiber when the pressure is sufficient.

[0034] To utilize Figure 1To achieve this with the barrier system in the embodiment of the invention, the reservoir 24 should contain pressurized gas. Before deploying the cable underwater, it can be pressurized on the surface to an appropriate level to match or exceed the water pressure at the depth where the cable will be submerged.

[0035] In a variation of this example, gas may be delivered to the microstructured optical fiber interstices before a cable breach is detected (before, during, or after cable deployment). In such an example, breach detection system 28 is not required for operation of barrier mechanism 20; rather, if a breach occurs, the barrier is already present. This may protect longer optical fibers because pressurized gas may already be present at or near the breach location, so the amount of optical fiber through which water may infiltrate the breach is limited or eliminated entirely. Introducing gas during or after deployment may require remote control of valve 26.

[0036] In another variation, the reservoir may not be pre-filled with gas, but may contain one or more materials from which suitable inert gases can be produced by chemical changes or reactions when needed. In some examples, the material can produce gas by decomposition, such as the decomposition of sodium azide, guanidine nitrate or tetrazole (other materials are not excluded). Sufficient material can be contained relative to the size of the reservoir to achieve the desired level of gas pressure. The gas can be retained in the reservoir for release into the pressure housing via a valve in response to a detected cable breach. Alternatively, the valve can be omitted or set to open so that the gas can be dispersed into the pressure housing through the gap when it is produced and along the gap in the optical fiber, thereby forming a barrier in advance in (multiple) optical fibers. In the case of a chemical reaction for producing gas, the barrier mechanism can be configured to trigger a chemical reaction in response to a detected cable breach, such as by contacting two or more materials or applying heat. As described above, the "material" that produces the inert gas may be a liquefied form of the gas, in which case a valve is required to maintain sufficient pressure in the reservoir.

[0037] Figure 2 A simplified schematic diagram of another example system utilizing gas as a barrier is shown. System 20 includes Figure 1 The system of FIG. 1 is similar to the system of FIG. 2 , but further includes a second pressure housing 32 surrounding the reservoir 24. The second pressure housing 32 is depicted as completely surrounding the reservoir 24 and the first pressure housing 22 is depicted as surrounding the gap / optical arrangement, the two separated by a partition 34. Alternatively, the second pressure housing 32 can be separate from the first pressure housing 22 and only surround the reservoir. A second valve 36 (water flow valve) is provided on the wall of the second pressure housing 32 for the flow of water, so if the valve 36 is opened when the system is submerged, water will flow through the valve 36 to fill the interior of the second pressure housing 32. When the system is deployed, the second valve 36 is closed to prevent water from entering the second pressure housing.

[0038] In this example, the reservoir 24 is configured to be compressible (e.g., by forming the walls with a flexible or deformable material, such as a bladder), and is filled with an inert gas. In the event of a breach, a breach detection system (not shown, see Figure 1 ) is additionally or alternatively configured to send a signal to operate the second valve 36 to open, allowing water to enter the second pressure housing 32. The pressure of the incoming water compresses the reservoir 24 and forces the gas to flow out of the reservoir 24 and into the first pressure housing 22, into the gap and into the void in one or both parts of the optical fiber 10a, 10b. The first valve 26 can be opened together with the second valve 36, or it can be omitted. As another option, the second valve can be omitted so that the reservoir 24 is permanently exposed to the pressure of the surrounding water, and as the cable is placed in the water and the pressure increases, the gas will gradually be forced to flow out of the reservoir and into the optical fiber section. This allows the barrier to be put in place before the cable breach. Similarly, the second valve can be configured to open under the influence of the increase in water pressure, so that it will automatically open when the cable is submerged.

[0039] A special feature of this configuration is its simple reversible function. If the water pressure decreases, especially if the cable is being raised to the surface for maintenance, repair or replacement, the compression of the water reservoir is reduced and the air pressure is adjusted so that when the cable comes to the surface it is not at a dangerously high level.

[0040] Figure 3 A simplified schematic diagram of another example of an optical fiber system having a barrier mechanism is shown. As in the previous example, an optical fiber 10 again includes a first portion 10a and a second portion 10b, which are optically aligned and whose ends are separated by a narrow gap 12 (a space between physically separated optical fiber portions, or an opening in an optical fiber structure, as described with respect to FIG. Figure 1 The first fiber section 10a and the second fiber section 10b are spaced apart to allow light transmission between the fiber sections 10a and 10b with minimal light loss. In this example, the first fiber section 10a and the second fiber section 10b both comprise microstructured optical fibers, such as hollow core optical fibers.

[0041] The barrier mechanism 20 includes a solid gate 40, which is aligned with the gap 12 but laterally offset from the optical fiber 10. The gate 40 is made of a water-impermeable material (e.g., metal, plastic, or glass). The gate has a substantially planar shape, and its thickness substantially matches the length of the gap 12 in the direction of the optical fiber length, or is thinner than the gap 12. The gate 40 is movable in the lateral direction so that it can be introduced into the gap 12 in the manner of a gate valve or a sluice valve, and covers the end of at least one of the optical fiber parts 10a, 10b, where it provides a barrier across the gap in the optical fiber part to block (prevent or limit) water from flowing through the gate. Therefore, when the gate 40 is located in the gap 12, water cannot move from one optical fiber part to another optical fiber part. If the thickness of the gate 40 is the same as the gap length 12, when the gate 40 is located in the gap, it will form a barrier across the gap in the two optical fiber parts 10a, 10b. If the gate 40 is thinner than the gap length 12, it can be arranged to slide tightly only on the end of one fiber section 10a, 10b, so as to form a barrier across the gap in the fiber section only. This will still prevent water from moving between the fiber sections 10a, 10b, thereby protecting the fiber sections 10a, 10b located on the other side of the gate 40 from water entering the cable gap position. A thinner gate 40 may be easier to move smoothly into the gap 12 than a gate 40 of the same size as the gap 12. A pair of thinner gates 40 can be provided, each gate associated with only the end of one fiber section. In the event of a cable gap, these gates can be introduced into the gap at the same time, or only one gate can be deployed, corresponding to the fiber section where the gap has occurred, so as to contain water in the fiber section. In any of these arrangements, the gate 40 can be provided with a coating or surface layer or wrap of a water-swellable material (not shown), which will swell when exposed to water. This can enhance the seal of the gap by the deployed gate, thereby more effectively limiting or preventing the movement of water between the fiber sections.

[0042] To position 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 ( Figure 3 ) into the gap on one side of gap 12. Any suitable actuator or drive configured to produce mechanical movement may be used, such as a motor operating a worm gear, or an electromagnet for pulling or pushing the gate between two positions. A more passive arrangement may be preferred, such as a water-swellable material that expands when exposed to water and pushes the gate 40, or an expanding gas that is released by opening a valve that can be activated by water contact or remotely controlled to push the gate 40. These latter types of actuators may be easier to implement and operate than electric and electromagnetic options, but only provide deployment of the gate and cannot be easily reversed to retract the gate once the cable is repaired. The motion may be linear, such as Figure 3 As shown, the gate 40 is advanced into the gap, or may be rotatable to swing the gate 40 into the gap. Any and all variations apparent to those skilled in the art are within the scope of the present disclosure; the exact implementation is not important. The actuator 42 may be controlled by the breach detection system 28 (wired via the 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, i.e., operates the actuator 42 to move the gate 40 to introduce it into the gap, thereby providing a barrier across the gap in at least a portion of the optical fibers 10a, 10b. A water-activated option may automatically deploy the gate 40 when water enters the vicinity of the breach mechanism.

[0043] An equivalent arrangement is that the actuator 42 moves one or more of the fiber sections 10a, 10b, rather than moving the gate 40, to properly position the gate 40 to form a barrier across the gap. Any arrangement that provides appropriate relative movement between the gate 40 and the fiber sections 10a, 10b may be used.

[0044] Barrier systems including gates may be installed at intervals along the optical fiber / fiber optic cable, and when a breach occurs, two barrier systems may be activated simultaneously, one barrier system on either side of the damaged location, thereby sealing off a section of optical fiber containing the breach.

[0045] The barrier system including the gate can be configured for reversible operation if the actuator is configured to provide reverse movement of the gate 40 to return it from a deployed position in the gap 12 to a rest position aligned with the gap 12. This allows the barrier system to be operated to remove the barrier from the optical fiber after repairing the breach or damage, thereby restoring light transmission along the optical fiber.

[0046] To maintain some light transmission in the fiber after the barrier is set up, the gate can be made of a material, such as a suitable glass, that is transparent to the wavelengths carried by the fiber in the cable. This allows at least some continued functionality of the cable after the breach while it awaits repair.

[0047] Figure 4AA simplified schematic diagram of another embodiment is shown that utilizes a gap between two portions of an optical fiber and actively introduces a previously external barrier into the gap in response to a cable breach. In this example, the barrier comprises a viscous fluid that is injected or otherwise directed into the gap when a cable breach is detected. Viscosity refers to the viscosity of the fluid being higher than water, particularly higher than seawater if the cable is deployed in a marine environment, and preferably significantly higher than the viscosity of water. Water that enters the gap and encounters the viscous fluid does not readily mix or penetrate it, thereby hindering the movement of water across the barrier and protecting the optical fiber on the other side of the gap from water intrusion. Additionally, the viscosity inhibits the viscous fluid in the gap from easily entering and moving along the void in the optical fiber portion (the void has a very small width, and the penetration time of the fluid increases with increasing viscosity), so as not to cause any particular damage to the microstructured optical fiber.

[0048] As previously described, the system includes an optical fiber 10, which includes a first portion 10a and a second portion 10b, which are arranged on both sides of the gap 12. The barrier mechanism 20 includes a reservoir or container 60 for containing a certain amount of viscous fluid 64. The reservoir 60 has an outlet 62, which is aligned with the gap 12 to achieve fluid flow communication so that the viscous fluid can leave the reservoir 60 and flow into the gap 12. The outlet 62 may include a nozzle or an outlet tube, or may be simply an opening in the reservoir wall. Depending on the configuration, the outlet 62 may be open, or may be closed by a valve or membrane that is opened when fluid delivery is required. In response to the gap detection system 28 detecting the gap, the barrier mechanism is activated to transport a portion of the viscous fluid 64 from the reservoir 60 to the gap. Any suitable component for moving the viscous fluid 64 can be used. For example, a piston device can be provided to push the viscous fluid 64 out of the reservoir 60. The reservoir 60 may be compressible or formed with flexible walls, and a mechanism may squeeze the reservoir 60 to force the viscous fluid 64 to flow out through the outlet 62. The outlet 62 may be closed in advance and then opened (moving a valve or breaking a membrane), and the viscous fluid 64 can flow out under gravity or the pressure of the stored viscous fluid. The reservoir 60 may include a simple bag or pouch, such as plastic or plasticized foil, and be provided with a breaking element that moves to pierce the bag, thereby forming an outlet at a suitable location to deliver the viscous fluid 64 into the gap 12. The reservoir may include a certain amount of pressurized or liquefied gas that is released so as to be able to expand within the reservoir and force the viscous fluid 64 to flow out of the outlet 62.

[0049] Figure 4B shows the flow of a certain amount of viscous fluid 64 into the gap 12. Figure 4AThe viscous fluid 64 is able to flow to fill the gap, thereby creating the desired barrier 66 across the space between the two optical fiber portions 10a, 10b. In order to better control the viscous fluid and direct it to the desired location, a housing (not shown) can be provided around the gap 12 to receive the delivered viscous fluid 64.

[0050] The viscous fluid can be any fluid with appropriate viscosity. A fluid with a higher viscosity (greater stickiness) will provide a more effective barrier, but will also result in a slower flow of the viscous fluid into the gap and the ends of the optical fibers, resulting in a slower barrier formation. A balance can be struck between these aspects when selecting a viscous fluid. For example, a viscous fluid can include an oil or grease. Another example is an epoxy resin, which will solidify after being delivered to the gap, strengthening the barrier over time. The resin can be provided by delivering two or more fluids that react together to form a hardenable material. However, this will produce a more permanent barrier that is more difficult to remove after the cable is repaired than a barrier that remains in a fluid state. Other suitable viscous fluids include mineral oils (e.g., blends of alkanes) and silicone oils (e.g., hexamethyldisiloxane or polydimethylsiloxane).

[0051] Using a viscous fluid to form a barrier avoids Figure 3 The mid-gate barrier example eliminates the need for precise alignment of the gate with the gap and the fiber end. The viscous fluid simply flows in to fill the gap, conforming to the available space, requiring only basic alignment between the gap and the fluid source. However, in contrast, it provides a barrier that is not easily reversible and cannot be remotely retracted into the gap like a gate when no longer required. Therefore, the two arrangements have opposing benefits and can be selected accordingly.

[0052] Figure 5A A simplified schematic diagram of another embodiment is shown which utilizes a gap between two portions of an optical fiber, which gap is used for light propagation as previously described. The optical fiber 10 comprises two portions 10a, 10b of a microstructured optical fiber (e.g., a hollow core optical fiber) with a gap 12 therebetween. The barrier mechanism 20 in this example comprises a block of material, such as a plug 50 of material, which may comprise a planar sheet, and is positioned in the gap. The plug 50 has a central aperture 52, which is positioned so that light can be transmitted through the aperture, thereby propagating from one optical fiber portion 10a, 10b to the other optical fiber portion 10a, 10b.

[0053] Figure 5B There is shown a plan view of a plug 50 and its central aperture 52. In this example, the plug 50 and aperture 52 are circular, giving the plug 50 the appearance of a gasket, with the sheet of material forming an annulus around the central aperture 52, although other shapes may be used if preferred.

[0054] The material forming the plug is a water-swellable material, which has the property of absorbing the water it contacts and expanding or swelling to increase its volume. Examples of suitable materials include super absorbent polymers (SAP), water-swellable rubbers, and water-swellable elastomers. The shape and size of the plug 50 and the aperture 52 are selected based on the strength of this swelling property, so that contact with water causes sufficient swelling to almost or completely close the aperture (aperture reduction or closure), so that the gap in the plug 50 across the optical fiber portion 10a, 10b becomes continuous or nearly continuous. The SAP can be modified with a hardener to create a more solid barrier, and / or modified with a foaming agent to produce foam, thereby additionally hindering the movement of water.

[0055] In this example, the operating mechanism of the barrier mechanism 20 is the swelling property of the water-swellable material, so that the barrier mechanism 20 responds to the breach of the cable by causing the expansion of the plug 50; this expansion provides the desired barrier across the void. If a breach occurs that allows water to enter the void in the optical fiber, the water can move along one or the other of the optical fiber portions 10a, 10b, through the void, until it reaches the gap 12. The water can then flow out of the void and into the gap, where it is absorbed by the water-swellable material of the plug 50, causing the plug 50 to expand and close the aperture 52. Once the aperture is closed, the plug 50 forms a barrier across the void and between the two portions of the optical fiber 10a, 10b, thereby preventing further movement of water that may have entered the void in the other optical fiber portion, thereby limiting the extent of damage to the optical fiber.

[0056] Figure 5A The plug 50 shown in FIG. 1 is located within a single optical fiber 10, but it can be sized to accommodate multiple optical fibers, or even an entire cable in which the optical fibers are located. The plug 50 need not be a planar sheet; other shapes of material can be used as needed to accommodate the gap.

[0057] This embodiment may be considered passive, as the notch mechanism is activated directly by the actual presence of water in the notch, and there is no need to actively detect the notch and then activate the notch mechanism in response to the detection. This provides considerable simplification.

[0058] The barrier can also be implemented in response to a breach without involving gaps in the optical fiber. Some examples are discussed below.

[0059] Fig. 6AA simplified schematic cross-sectional view of an example of an optical fiber cable system having barrier capabilities is shown that does not require any gaps in the optical fiber. The system includes an optical fiber cable 100 that includes at least one microstructured optical fiber 10, such as a hollow core optical fiber having a hollow core 76 surrounded by a microstructured cladding 78 (only one optical fiber is shown for simplicity). The cable 100 includes an outer jacket 102 surrounding the optical fiber 10. The cable also includes a barrier-forming material 70 that is disposed within the outer jacket 102 surrounding the optical fiber(s) 10 and is added during the manufacturing process of the cable 100. The barrier-forming material 70 includes a viscosity modifier, which is a material having the property that, when mixed with water, it increases the viscosity of the water, thereby thickening the water. The ability of water to penetrate into the exposed gaps of the microstructured optical fiber 10 depends on several parameters, including the pressure and viscosity of the water. The penetration time t is directly dependent on the viscosity η, according to t=((32ηL 2 ) / (d 2 p0))t h (where L is the penetration depth, d is the diameter of the core (or other void) in the fiber, p0 is the pressure of the water, and t h is a dimensionless constant and can be set to 0.1). Therefore, if the viscosity of the surrounding water at the gap of the cable 100 can be increased, the speed at which the surrounding water penetrates into the gap can be slowed down, and the degree of damage to the (multiple) optical fibers 10 and the cable 100 can be limited.

[0060] Figure 6B Shows the underwater deployment after the breach Fig. 6A1. The fiber optic cable system in FIG. 1. In this case, the breach manifests itself as a break in the cable 10, forming a break end 104, where the voids of the microstructured optical fiber (10) are exposed to the surrounding water. The breach also exposes the barrier-forming material 70, causing it to disperse outward into the surrounding water. The barrier-forming material 70 acts to significantly increase the viscosity of the water near the break end 70, forming a local body of water 72, whose viscosity is higher than that of the original water. The increase in viscosity means that water 74 that may penetrate into the voids of the optical fiber (s) penetrates much more slowly; its movement along the optical fiber is inhibited, and the longitudinal extent of water exposure is limited. The body of water 72 with increased viscosity covers the end of the cable 100 and the optical fiber (s) 10 therein, thereby acting as a barrier to prevent unthickened water outside the body of water 72 from entering the voids. The viscosity-changing property of the barrier-forming material 70 can be considered as a barrier mechanism of the fiber optic cable system in this example, which responds to the breach in the cable 100 to introduce or provide a barrier across the voids in the optical fiber 10 by causing an increase in the viscosity of the nearby water. The difference between this example and other examples is that in this example, the barrier is formed at the notch, thus playing a role in inhibiting the initial movement of water into the microstructured optical fiber. In other examples, depending on the position of the barrier mechanism, the barrier is introduced at a position separated from the notch, so that the barrier plays a role in inhibiting the further movement of water that has penetrated the void of the optical fiber, so that the water cannot move or easily move further along the optical fiber.

[0061] Examples of suitable viscosity modifiers are xanthan gum, which is used extensively in the oil industry to thicken drilling muds, methylcellulose and other cellulose derivatives, and biomimetic compounds based on the mucus produced by hagfish (class Hagfish and order Hagfishes). Other viscosity modifiers may also be used as desired; one example is a superabsorbent polymer.

[0062] Fig. 7A A simplified schematic cross-sectional view of another example of an optical fiber cable system having barrier capabilities that does not require any gaps in the optical fiber is shown. The system includes an optical fiber cable (not shown) that includes at least one microstructured optical fiber 10, such as a hollow core optical fiber having a hollow core 76 surrounded by a microstructured cladding 78 (for simplicity, only one optical fiber is shown). The system also includes a heat source 80 that is operable to apply heat H (deliver thermal energy) to the optical fiber 10. The heat source 80 implements the barrier mechanism 20. The heat source 80 can have any convenient design, such as Fig. 7A. Examples include an electric heating element in contact or near contact with the outer surface of the optical fiber 10, having an associated power source. The heating element can be annular so as to be wrapped around the optical fiber 10, or can be a strip to deliver thermal energy to one side of the optical fiber 10, or can be a plurality of heating elements dispersed over a localized area of ​​the optical fiber 10, or some other configuration apparent to those skilled in the art. Other alternatives include a light source, such as a laser diode, configured to apply one or more focused laser beams to the optical fiber 10. Other heat sources may also be used as desired. Heat may be provided by a chemical reaction, such as an exothermic reduction-oxidation (redox) reaction, such as an aluminothermic reaction or a Goldschmidt reaction. In the event of a breach in the cable, the breach detection system 28 detects the breach as described above and sends a start signal to the heat source 80.

[0063] Figure 7B Shows Fig. 7A A fiber optic cable system in which the barrier system 20 is activated by a breach detection system in response to the breach. In response to the breach, a heat source generates thermal energy and delivers it to the optical fiber 10. The thermal energy is absorbed by the material of the optical fiber 10 (typically glass), particularly the glass defining the microstructure (the glass is located between the voids), and the temperature is raised to a level sufficient to soften or melt the glass. This causes the microstructure and core of the optical fiber 10 to collapse, forming an amorphous or unstructured molten glass solid 82, which closes and blocks the voids in the optical fiber 10, thereby forming a barrier to the movement of any water 74 that has entered the voids. Thus, any such water is inhibited (prevented or hindered, depending on the degree of collapse) from moving beyond the position of the barrier and into the voids on the far end of the barrier. Thus, the optical fiber on the "downstream" side of the barrier is protected from water intrusion in the same manner as the various examples of introducing barriers into the gaps between optical fibers described above. Multiple heat sources 80 can be arranged at intervals along the optical fiber, so that a pair of heat sources 80 located on both sides of the breach can be activated simultaneously to close the optical fiber segment containing the breach and protect the further portion of the optical fiber. A single heat source may be arranged to act on a single fiber, a group of fibers, or all of the fibers in a cable, or the entire cable if the outer jacket of the cable is susceptible to heating and melting, or has thermal properties that quickly transfer thermal energy through the jacket to the fibers inside.

[0064] Some of the barrier systems described herein may be considered "active" in that at least one element of the system actively operates upon detection of damage or a breach. In such an arrangement, direct communication from the breach detection system to the barrier system (e.g., Figure 1 and Figure 3Alternatively, a surface operator receiving a gap detection signal from the gap detection system may manually activate the barrier system in response. This requires providing remote control of the barrier system, for example by means of a radio transceiver or similar device in the barrier system, but allows a human assessment of the gap, for example as to severity or location, so that a determination can be made as to whether it is necessary to introduce a barrier and thereby interrupt optical communications. In other alternatives, the gap detection system may communicate with a computer system on the surface which assesses (for example by means of an algorithm or neural network) whether operation of a barrier mechanism is required and sends an operating signal to one or more barrier mechanisms of the cable as required. It is also possible to use communication via a surface computer without any assessment stage in order to automatically activate a gap mechanism in response to a gap in the cable; this may be more convenient than achieving underwater communication directly between the gap detection system and the barrier mechanism, particularly if multiple barrier mechanisms are provided along the length of the cable.

[0065] Various embodiments are intended only to aid understanding and teach the claimed features. These embodiments are provided only as representative samples of embodiments and are not exhaustive and / or exclusive. It should be understood that the advantages, embodiments, examples, functions, features, structures, and / or other aspects described herein should not be considered as limitations on the scope of the invention defined by the claims or limitations on the equivalents of the claims, and other embodiments may be used and modifications may be made without departing from the scope of the claimed invention. Various embodiments of the present invention may appropriately include, consist of, or consist essentially of appropriate combinations of disclosed elements, components, features, parts, steps, devices, etc., rather than those specifically described herein. In addition, the present disclosure may include other inventions that are not currently claimed but may be claimed in the future.

[0066] refer to

[0067] [1] US 4,834,479

[0068] [2] US 4,913,517

[0069] [3] US 5,861,575

Claims

1. An optical fiber system, comprising: An optical fiber cable comprising at least one microstructured optical fiber within a sheath; as well as a barrier mechanism, responsive to a breach in the optical fiber cable, through which water from the surrounding environment of the optical fiber cable can enter the interstices of the microstructured optical fiber; Wherein the barrier mechanism responds to the breach by operating to introduce a barrier across the interstices of the microstructured optical fiber, the barrier being configured to inhibit movement of water along the interstices.

2. The optical fiber system of claim 1, wherein the microstructured optical fiber is a hollow core optical fiber.

3. The optical fiber system of claim 1 or 2, wherein the microstructured optical fiber is a first portion of an optical fiber, and the optical fiber cable includes a second portion of an optical fiber, the second portion of the optical fiber being optically aligned with the first portion of the optical fiber across a gap for propagating light between the first portion of the optical fiber and the second portion of the optical fiber; And wherein the barrier mechanism operates to introduce the barrier by introducing the barrier into the gap.

4. The optical fiber system of claim 3, wherein the gap comprises an opening in the microstructured optical fiber, the opening extending laterally through the void between the first portion of the optical fiber and the second portion of the optical fiber.

5. The 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 a space between an end of the first portion of the optical fiber and an end of the second portion of the optical fiber.

6. The optical fiber system of any one of claims 3 to 5, wherein the second portion of the optical fiber comprises a microstructured optical fiber, and when the barrier is provided, the barrier inhibits the movement of water between the first portion of the optical fiber and the second portion of the optical fiber.

7. The optical fiber system according to any one of claims 4 to 6, wherein the barrier comprises a gas and the barrier mechanism comprises: a pressure housing surrounding the gap; as well as a reservoir for conveying an inert gas and in gas flow communication with the pressure housing; Wherein the barrier mechanism operates by allowing inert gas from the reservoir to flow into the pressure housing and then along the gap to introduce the barrier.

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

9. The optical fiber system of claim 7 or 8, wherein the reservoir contains a pressurized inert gas or one or more materials for generating the inert gas.

10. An optical fiber system according to any one of claims 7 to 9, wherein the reservoir is compressible, and the barrier mechanism further includes a second pressure shell surrounding the reservoir, and a water flow valve configured to allow water from the surrounding environment to enter the second pressure shell, the barrier mechanism also operating by opening the water flow valve to allow water from the surrounding environment to enter the second pressure shell and compress the reservoir, thereby forcing the inert gas from the reservoir into the pressure shell and into the gap.

11. An optical fiber system according to any one of claims 3 to 6, wherein the barrier comprises a solid gate aligned with the gap, and the barrier mechanism comprises an actuator configured to provide relative movement between the gate and the first portion of the optical fiber and the second portion of the optical fiber, and the barrier mechanism operates to introduce the barrier across the gap by activating the actuator to cause the relative movement and position the gate in the gap.

12. An optical fiber system according to any one of claims 3 to 5, wherein the barrier comprises a viscous fluid having a viscosity greater than that of water in the surrounding environment, and the barrier mechanism comprises a reservoir for supplying the viscous fluid and communicating with the gap fluid flow, and operates by delivering the viscous fluid from the reservoir into the gap to introduce the barrier across the gap.

13. An optical fiber system according to any one of claims 3 to 5, wherein the barrier comprises a plug of water-swellable material positioned in the gap and having a central aperture through which light can propagate between the first portion of the optical fiber and the second portion of the optical fiber, and the barrier mechanism comprises swelling properties of the water-swellable material in response to contact with water, and when water is present in the gap, the barrier mechanism operates by causing expansion of a sheet of water-swellable material to introduce the barrier so as to close or reduce the central aperture.

14. The optical fiber system of claim 13, wherein the water-swellable material comprises a superabsorbent polymer, a superabsorbent polymer with a hardening agent, or a superabsorbent polymer with a blowing agent.

15. The optical fiber system of claim 1 or 2, wherein the barrier comprises a solid of glass, and the barrier mechanism comprises a heat source configured to deliver thermal energy to the microstructure optical fiber to melt the glass defining the microstructure, and the barrier mechanism operates to introduce the barrier by melting the glass defining the microstructure, thereby melting the glass into a solid that closes the voids of the microstructure optical fiber.

16. The optical fiber system of claim 1 or 2, wherein the barrier comprises a body of water having increased viscosity, and the barrier mechanism comprises a viscosity modifier included within the optical fiber cable, the barrier mechanism operating to introduce the barrier by releasing the viscosity modifier through a breach in the optical fiber cable into surrounding water near the breach to increase the viscosity of the water and form the barrier across interstices of the microstructured optical fiber exposed by the breach.

17. The fiber optic system of claim 16, wherein the viscosity modifier comprises xanthan gum, methylcellulose or other cellulose derivatives, or a biomimetic compound based on mucus produced by fish of the order Hagfish.

18. The fiber optic system of any one of claims 7 to 15, wherein the barrier mechanism responds to the breach by being configured to be operable by a breach detection system configured to detect a breach in the fiber optic cable.

19. The fiber optic system of claim 18, further comprising a notch detection system configured to detect a notch in the fiber optic cable and send a signal to the barrier mechanism to cause the barrier mechanism to operate to introduce the barrier across the interstices of the microstructured optical fiber.

20. The fiber optic system of claim 19, wherein the breach detection system is configured to detect a breach in the fiber optic cable by monitoring an internal pressure of the fiber optic cable and identifying a change in the internal pressure as a breach.

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