Advanced fiber optic sensor integration with marine platforms for undersea monitoring and climate applications

Abstract

An apparatus for underwater fiber optic sensing includes an optical fiber-based sensing element, and a waterproof housing including an electronic component and an optical interrogation system for enabling quasi-distributed or distributed sensing of a parameter. The electronic component provides first power to the optical interrogation system and enables data communication between the electronic component and the optical interrogation system. The electronic component derives the first power from second power received from an external device and enables data communication between the electronic component and the external device. Also, a system for quasi-distributed or distributed underwater fiber optic sensing includes the optical fiber-based sensing apparatus and a buoy, wherein the buoy is the external device and is structured and configured to provide the second power to the electronic component. Further, a fiber optic-based sensing elements includes a plurality of protective layers surrounding a sensing layer for protecting against harsh marine conditions.

Description

CLIENT / MATTERNO. 214001-02161 PCTADVANCED FIBER OPTIC SENSOR INTEGRATION WITH MARINE PLATFORMS FOR UNDERSEA MONITORING AND CLIMATE APPLICATIONSCROSS REFERENCE TO RELATED APPLICATIONS:[0001J This application claims priority to U.S. Provisional Patent Application Serial No.63 / 748,135, filed on January 22, 2025 and titled “Advanced Fiber Optic Sensor Integration with Marine Platforms for Undersea Monitoring and Climate Applications,” the disclosure of which is incorporated herein by reference.STATEMENT OF GOVERNMENT INTEREST:

[0002] This invention was made with government support under grant DE-AR0001839 awarded by the Department of Energy (DOE). The government has certain rights in the invention.FIELD OF THE INVENTION:

[0003] The disclosed concept relates generally to optical fiber sensor technology for marine sensing applications, and, in particular, to distributed optical fiber sensing combined with mobile marine sensing platforms for enabling ubiquitous monitoring of physical and chemical sensing parameters, amongst others, with distributed interrogation capability.BACKGROUND OF THE INVENTION:

[0004] Monitoring of marine environments is essential for applications such as subsea infrastructure integrity assessment, environmental compliance, offshore energy production, maritime security, and climate-related observation. Conventional marine sensing approaches typically rely on fixed sensor nodes, autonomous underwater vehicles (AUVs), or ship-based surveys. While these systems can provide high-quality data, they are often limited in spatial coverage, temporal resolution, deployment duration, or cost-effectiveness.

[0005] Distributed optical fiber sensing (DOFS) technologies, such as distributed acoustic sensing (DAS), distributed temperature sensing (DTS), and distributed strain sensing (DSS), have emerged as powerful tools for continuous, high-resolutionCLIENT / MATTERNO. 214001-02161 PCTmonitoring along the length of an optical fiber. These systems can detect a wide range of physical phenomena, including acoustic fields, temperature gradients, strain events, and vibration signatures. However, traditional DOFS deployments are typically static, relying on permanently installed fiber-optic cables, such as along pipelines or integrated into fixed infrastructure. As a result, sensing coverage is constrained to the physical footprint of the installed fiber, limiting adaptability and responsiveness to dynamic marine environments.SUMMARY OF THE INVENTION:

[0006] In one embodiment, an optical fiber-based sensing apparatus for quasi-distributed or distributed underwater fiber optic sensing in marine applications is provided. The apparatus includes an optical fiber-based sensing element, and a submersible waterproof housing including therein an electronic component and an optical interrogation system, wherein the optical interrogation system is structured and configured for interrogating the optical fiber-based sensing element and enabling quasi-distributed or distributed sensing of a parameter along the optical fiber-based sensing element. The electronic component is structured and configured for providing first power to the optical interrogation system and for enabling data communication between the electronic component and the optical interrogation system, and wherein the electronic component is structured and configured to derive the first power from second power received from an external device and enable data communication between the electronic component and the external device.

[0007] In another embodiment, a system for quasi-distributed or distributed underwater fiber optic sensing in marine applications is provided that includes an optical fiber-based sensing apparatus as just described and a buoy. In this embodiment, the buoy is the external device and is structured and configured to provide the second power to the electronic component.

[0008] In still another embodiment, an optical fiber-based sensing element for quasidistributed or distributed underwater fiber optic sensing in marine applications is provided that includes an optical fiber core, a sensing layer coating the core, and a plurality of protective layers comprising (i) a gas permeable secondary polymer cladding layer surrounding sensing layer, a gas permeable strength layer surrounding the gasCLIENT / MATTERNO. 214001-02161 PCTpermeable secondary polymer cladding layer, and a liquid impermeable and gas permeable outer tube surrounding gas permeable strength layer, or (ii) a liquid permeable secondary polymer cladding layer surrounding the sensing layer, a liquid permeable strength layer surrounding the liquid permeable secondary polymer cladding layer, and a liquid permeable outer tube surrounding the liquid permeable strength layer.BRIEF DESCRIPTION OF THE DRAWINGS:

[0009] A full understanding of the invention can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which:

[0010] FIG. 1 is a schematic diagram of a system for distributed underwater fiber optic sensing according to an exemplary embodiment of the disclosed concept;

[0011] FIG. 2 is a block diagram of a BristlemouthS-enabled buoy forming a part of the system of FIG. 1 according to an exemplary embodiment of the disclosed concept;

[0012] FIG. 3 is a schematic diagram of a BristlemouthO-enabled optical fiber-based sensing apparatus forming a part of the system of FIG. 1 according to one particular exemplary embodiment for performing quasi-distributed temperature sensing;

[0013] FIG. 4 is a schematic diagram of a Bristlemouth®-enabled optical fiber-based sensing apparatus forming a part of the system of FIG. 1 according to another particular exemplary embodiment for performing distributed temperature sensing;

[0014] FIG. 5 is a schematic diagram of a Bristlemouth®-enabled optical fiber-based sensing apparatus forming a part of the system of FIG. 1 according to another particular exemplary embodiment for performing distributed dissolved CO2 and / or pH sensing;FIG. 6 is a schematic diagram of a Bristlemouth®-enabled optical fiber-based sensing apparatus forming a part of the system of FIG. 1 according to yet another particular exemplary embodiment for performing combined distributed temperature sensing and dissolved CO2 and / or pH sensing;

[0015] FIG. 7 is a schematic diagram of a Bristlemouth®-enabled optical fiber-based sensing apparatus forming a part of the system of FIG. 1 according to another particular exemplary embodiment for performing according to still another particular exemplary embodiment for performing combined distributed sensing of temperature, dissolved CO2CLIENT / MATTERNO. 214001-02161 PCTand pH level with optical fibers using optical time domain reflectometry (OTDR) using multiple different (selectable) wavelengths;[00161 FIG. 8 is a cross-sectional diagram of an optical fiber-based sensing element according to one particular exemplary embodiment of the disclosed concept for gas sensing;

[0017] FIG. 9 is a cross-sectional diagram of an optical fiber-based sensing element according to another particular exemplary embodiment of the disclosed concept for liquid sensing;

[0018] FIG. 10 is a schematic diagram of a Bristlemouth®-enabled optical fiber-based sensing apparatus forming a part of the system of FIG. 1 according to another particular exemplary embodiment for performing quasi-distributed acoustic sensing; and

[0019] FIG. 11 is a schematic diagram of a Bristlemouth®-enabled optical fiber-based sensing apparatus forming a part of the system of FIG. 1 according to another particular exemplary embodiment for performing distributed temperature sensing.DETAILED DESCRIPTION OF THE INVENTION:

[0020] As used herein, the singular form of “a”, “an”, and “the” include plural references unless the context clearly dictates otherwise.

[0021] As used herein, the statement that two or more parts or components are “coupled” shall mean that the parts are joined or operate together either directly or indirectly, i.e., through one or more intermediate parts or components, so long as a link occurs.

[0022] As used herein, “directly coupled” means that two elements are directly in contact with each other.

[0023] As used herein, the term “number” shall mean one or an integer greater than one (i.e., a plurality).

[0024] As used herein, the term “quasi -distributed sensing” shall mean parameter sensing at a plurality of discrete points along an optical fiber using a plurality of structures provided in the optical fiber (such as FBGs) and using an interrogation method (such as an FBG interrogator method).CLIENT / MATTERNO. 214001-02161 PCT

[0025] As used herein, the term “distributed sensing” shall mean continuous parameter sensing along an optical fiber using an interrogation method (such as an OTDR interrogator method).

[0026] Directional phrases used herein, such as, for example and without limitation, top, bottom, left, right, upper, lower, front, back, and derivatives thereof, relate to the orientation of the elements shown in the drawings and are not limiting upon the claims unless expressly recited therein.

[0027] The disclosed concept will now be described, for purposes of explanation, in connection with numerous specific details in order to provide a thorough understanding of the disclosed concept. It will be evident, however, that the disclosed concept can be practiced without these specific details without departing from the spirit and scope of this innovation.

[0028] As described herein, the disclosed concept provides optical fiber sensing technology that has been conceived and developed for marine sensing applications, such as, without limitation, undersea and climate applications and marine aquaculture. More specifically, in the disclosed concept, distributed optical fiber sensing is combined with mobile marine sensing platforms for enabling ubiquitous monitoring of physical and chemical sensing parameters, amongst others, with distributed interrogation capability. For example, and without limitations, those parameters may include temperature, vibration, strain, CO2, pH, oxygen, nitrates / nitrites, and / or heavy metal pollutants. The non-limiting exemplary embodiments described herein relate to CO2, pH, temperature and acoustics, but it will be understood that the structures and systems described herein may also be used to sense strain, oxygen, nitrates / nitrites, and / or heavy metal pollutants. A unique set of requirements for marine sensing applications includes an interrogation system that has a size, weight, and power (SW&P) that is aligned with the requirements of long-term deployable marine sensing platforms and appropriate interfaces. In addition, as described herein, the disclosed concept provides a number of variations of suitable optical fiber sensor interrogators for use in the sensing system of the disclosed concept in order to uniquely align with the requirements for marine sensing applications while also satisfying the stringent constraints of deployment.CLIENT / MATTERNO. 214001-02161 PCT

[0029] FIG. 1 is a schematic diagram of a system 5 for distributed underwater fiber optic sensing according to an exemplary embodiment of the disclosed concept. As described herein, system 5 provides for distributed optical fiber-based sensing of a number of parameters, such as, without limitation, physical parameters like temperature or vibrations, or chemical parameters such as dissolved CO2 or pH level. In the exemplary embodiment, power and data for system 5 is provided using the Bristlemouth® open connectivity standard. In the Bristlemouth® open connectivity standard, power and data are provided over a simple two-wire bus capable of efficient power delivery and networking underwater, including automatic device discovery, networking, and communication between modules. The Bristlemouth® open connectivity standard enables plug-and-play integration of underwater devices, such as sensors, instruments, and payloads, on platforms such as buoys and moorings.

[0030] Referring to FIG. 1, system 5 includes a Bristlemouth®-enabled buoy 10 that is coupled to a Bristlemouth®-enabled optical fiber-based sensing apparatus 15. Bristlemouth®-enabled buoy 10 is structured and configured to provide power to Bristlemouth®-enabled optical fiber-based sensing apparatus 15, and to provide data to and receive data from Bristlemouth®-enabled optical fiber-based sensing apparatus 15 according to the Bristlemouth® open connectivity standard. Bristlemouth®-enabled buoy 10 is also structured and configured to provide remote telemetry (e.g., satellite or cellular data backhaul via supported platforms) for system 5 so that the data collected by Bristlemouth®-enabled optical fiber-based sensing apparatus 15 can be communicated to a remote location. In addition, as described in more detail herein, Bristlemouth®-enabled optical fiber-based sensing apparatus 15 is structured and configured to perform the distributed optical fiber-based parameter sensing (physical and / or chemical parameters) as described above using a number of optical fiber-based sensing elements 20. Also, in the exemplary embodiment, as seen in FIG. 1, Bristlemouth®-enabled optical fiber-based sensing apparatus 15 is coupled to a buoy 12 to support Bristlemouth®-enabled optical fiber-based sensing apparatus 15 while it is deployed and submerged. Furthermore, in one non-limiting aspect of the disclosed concept, in order to satisfy (SW&P) requirements, Bristlemouth®-enabled optical fiber-based sensing apparatus 15 (i) consumes no more than 40 W at no more than 30 VDC, (ii) has dimensions (L x H x D) of no more than 420CLIENT / MATTERNO. 214001-02161 PCTmm x 420 mm x 88 mm; and (iii) has a weight of no more than 7 kg (i) consumes no more than 40 W at no more than 30 VDC, (ii) has dimensions (L x H x D) of no more than 420 mm x 420 mm x 88 mm; and (iii) has a weight of no more than 7 kg.

[0031] FIG. 2 is a block diagram of BristlemouthO-enabled buoy 10 according to an exemplary embodiment of the disclosed concept. As seen in FIG. 2, Bristlemouth®- enabled buoy 10 includes a number of solar panels 25 for solar energy collection. Solar panels 25 are coupled to power regulation and control system 30, which in turn is coupled to an energy storage system 35, such as a sealed, marine-rated battery system. Power regulation and control system 30 includes a charge controller (e.g., a Maximum Power Point Tracking (MPPT) charge controller or a Pulse Width Modulation (PWM) charge controller) structured and configured for regulating the power from solar panels 25 and preventing over-charging and deep discharging of energy storage system 35. Power regulation and control system 30 also includes a voltage regulator / DC-DC converter structured and configured for stepping the voltage up or down to match the other electronics Bristlemouth®-enabled buoy 10.

[0032] Bristlemouth®-enabled buoy 10 further includes a Bristlemouth® hub printed circuit board assembly (PCBA) 40. Bristlemouth® hub PCBA 40 functions as the central connection point (hub) within the Bristlemouth® network that is implemented in system 5. Bristlemouth® hub PCBA 40 manages the distribution of both power and data over a single two- wire bus to all connected modules, including Bristlemouth®-enabled optical fiber-based sensing apparatus 15, and includes a microcontroller, a power management circuit, and Bristlemouth® connection ports, among other components. Bristlemouth®- enabled buoy 10 also includes satellite and cellular telemetry modules 45 for enabling remote communication of data to and from Bristlemouth®-enabled buoy 10 (the backhaul functionality described above) . Finally, Bristlemouth®-enabled buoy 10 also includes control electronics 50 for controlling the operation of Bristlemouth®-enabled buoy 10.

[0033] Referring again to FIG. 1, Bristlemouth®-enabled optical fiber-based sensing apparatus 15 includes a watertight, submersible housing 55 (rated for significant depth (e.g., -100 m)) having dual Bristlemouth® ports 60 for enabling connection to the two- wire Bristlemouth® bus of Bristlemouth®-enabled buoy 10. A Bristlemouth® node PCBA 65 and an optical interrogation system 70 (described herein in variousCLIENT / MATTERNO. 214001-02161 PCTembodiments) are provided inside housing 55, and optical sensing element(s) 20 are coupled to optical interrogation system 70 through housing 55. Bristlemouth® node PCBA 65 includes a microcontroller (typically STM32-class), Bristlemouth® interface circuitry (e.g., power conditioning, signaling), and connectors (e.g., UART / RS-232 / RS-485) for making power and data connections to optical interrogation system 70.

[0034] FIG. 3 is a schematic diagram of Bristlemouth®-enabled optical fiber-based sensing apparatus 15 according to one particular exemplary embodiment. This exemplary embodiment provides for quasi-distributed temperature sensing with optical fibers using fiber Bragg gratings (FBGs). In particular, and as seen in FIG. 3, in this embodiment, optical interrogation system 70 includes an FBG interrogator 85 (including a broadband light source) and an optical circulator 80. In addition, in this embodiment, optical fiberbased sensing element 20 includes an optical fiber 90 (typically a single mode fiber) having a plurality of FBGs 95 provided in the core of optical fiber 90. The broadband light output of FBG interrogator 85 is provided to the first port of optical circulator 80. The second port of optical circulator 80 is coupled to the end of optical fiber-based sensing element 20, and the third port of optical circulator 80 is coupled to the input of FBG interrogator 85. In the exemplary embodiment, optical fiber-based sensing element 20 includes one or more outer protective layers as described elsewhere herein to protect optical fiber-based sensing element 20 from the often harsh conditions of the sea while deployed.

[0035] In operation, the light generated by FBG interrogator 85 enters optical fiber-based sensing element 20 and a specific wavelength of light (called the nominal Bragg wavelength) is reflected by each FBG 95 depending on the characteristics of the FBG 95 (i.e., the grating period / spacing of the FBG 95). FBG interrogator 85 is structured and configured to measure the reflected wavelength of each FBG 95 at any particular time. Since temperature affects both the effective refractive index of optical fiber 90 and the grating period / spacing of each FBG 95, temperature changes will cause shifts in the Bragg wavelength (i.e., shifts from the nominal Bragg wavelength) of each FBG 95. Such wavelengths shifts, once detected in FBG interrogator 85), can be converted to a temperature reading via calibration. In the exemplary embodiment, each FBG 95 has a different nominal Bragg wavelength, and wavelength division multiplexing may be usedCLIENT / MATTERNO. 214001-02161 PCTto read a plurality (e.g., dozens to hundreds) of temperature points along optical fiberbased sensing element 20.[00361 FIG. 4 is a schematic diagram of BristlemouthO-enabled optical fiber-based sensing apparatus 15 according to another particular exemplary embodiment. This exemplary embodiment provides for distributed temperature sensing with optical fibers using Raman scattering and optical time domain reflectometry (OTDR), which enables optical fiber-based sensing element 20 to act as a continuous distributed temperature sensor along its entire length. In particular, and as seen in FIG. 4, in this embodiment, optical interrogation system 70 includes a Rayleigh OTDR system 100 (commercially available or custom built), a first optical circulator 105, an Erbium-doped fiber amplifier (EDFA) 135, a second optical circulator 110, and a Raman wave division multiplexing (WDM) filter 115. As is known, a Rayleigh OTDR system, such as Rayleigh OTDR system 100, is structured and configured to launch short laser pulses into an optical fiber, measure the light that is scattered or reflected back, and use time-of-flight to map events vs. distance along the fiber. In this embodiment, optical fiber-based sensing element 20 includes a single mode optical fiber.

[0037] In addition, as seen in FIG. 4, the output of Rayleigh OTDR system 100 is coupled to the first port of optical circulator 105. The second port of optical circulator 105 is coupled to the first port of optical circulator 110 through EDFA 135. The second port of optical circulator 110 is coupled to the end of optical fiber-based sensing element 20, and the third port of optical circulator 110 is coupled to third port of optical circulator 105 through Raman WDM filter 115. The fourth port of optical circulator 105 is coupled to the input of Rayleigh OTDR system 100.

[0038] In operation, a short laser pulse is launched into optical fiber-based sensing element 20 by Rayleigh OTDR system 100 through optical circulators 105 and 110 and EDFA 135. At every point along optical fiber-based sensing element 20, a tiny fraction of light is scattered and is passed to Rayleigh OTDR system 100 through Raman WDM filter 115. The scattered light includes a Stokes component (weakly temperature dependent) and an Anti-Stokes component (strongly temperature dependent). The ratio of anti-Stokes intensity to Stokes intensity is used to calculate temperature in Rayleigh OTDR system 100 at various positions along optical fiber-based sensing element 20. InCLIENT / MATTERNO. 214001-02161 PCTaddition, Raman WDM fdter 115 isolates the Stokes and Anti-Stokes components from the powerful pump light, allowing Rayleigh OTDR system 100 to accurately measure temperature changes along optical fiber-based sensing element 20.

[0039] FIG. 5 is a schematic diagram of BristlemouthO-enabled optical fiber-based sensing apparatus 15 according to another particular exemplary embodiment. This exemplary embodiment provides for sensing of dissolved CO2 and / or pH with optical fibers using optical time domain reflectometry (OTDR), which enables optical fiberbased sensing element 20 to act as a continuous distributed CO2 and / or pH sensor along its entire length. In particular, and as seen in FIG. 5, in this embodiment, optical interrogation system 70 includes a Rayleigh OTDR system 100 (e.g., as described above), and an optical circulator 120. As seen in FIG. 5, the output of Rayleigh OTDR system 100 is coupled to the first port of optical circulator 120. The second port of optical circulator 120 is coupled to the end of optical fiber-based sensing element 20, and the third port of optical circulator 120 is coupled to the input of Rayleigh OTDR system 100.

[0040] In addition, in this embodiment, optical fiber-based sensing element 20 is a functionalized optical fiber that includes a multi-mode optical fiber 125 and a sensing layer 130 that is provided around (i.e. coats as a coating layer) multi-mode optical fiber 125 in an area where the cladding has been removed or thinned. Sensing layer 130 is a chemically sensitive coating that enables optical fiber-based sensing element 20 to measure CO2 and / or pH by interacting with CO2 or H+ions, thereby changing the optical properties of sensing layer 130 and / or multi-mode optical fiber 125 and modulating the reflected light. As a result, OTDR techniques may be used to measure the CO2 concentration or pH at various locations along optical fiber-based sensing element 20. In one exemplary embodiment, coating layer 130 comprises a pH-sensitive dye (such as HPTS, Phenol red, or Bromothymol blue) that is provided in a polymer coating (created, for example, using a sol-gel or hydrogel process). \

[0041] In operation, a light pulse is launched into optical fiber-based sensing element 20 by Rayleigh OTDR system 100. At the location of coating layer 130, the local environment affects one or more optical properties of sensing layer 130 and / or multimode optical fiber 125, such as light absorption, refractive index, fluorescence or loss. Rayleigh OTDR system 100 detects changes in backscattered or reflected light vs.CLIENT / MATTERNO. 214001-02161 PCTdistance, where the magnitude of the change provides CO2 concentration or pH level and the time delay provides the location of where the change occurred.[00421 FIG. 6 is a schematic diagram of BristlemouthO-enabled optical fiber-based sensing apparatus 15 according to yet another particular exemplary embodiment. This exemplary embodiment provides for combined distributed sensing of temperature and dissolved CO2 and / or pH with optical fibers using optical time domain reflectometry (OTDR). As such, this embodiment is in essence a combination of the systems of FIGS.4 and 5 described above that uses two channels of Rayleigh OTDR system 100.

[0043] FIG. 7 is a schematic diagram of BristlemouthO-enabled optical fiber-based sensing apparatus 15 according to still another particular exemplary embodiment. This exemplary embodiment provides for combined distributed sensing of temperature, dissolved CO2 and pH level with optical fibers using optical time domain reflectometry (OTDR) using multiple different (selectable) wavelengths. As seen in FIG. 7, Bristlemouth®-enabled optical fiber-based sensing apparatus 15 of this embodiment includes a first laser source 175 at a first wavelength, a second laser source 189 at a second wavelength, a third laser source 185 at 115 nm. First, second, and third laser sources 175, 180, 185 are provided to a coupler 190, which in turn is coupled to a three to one optical switch 195. Optical switch 195 allows for selection of one of first, second, and third laser sources 175, 180, 185 for use in Bristlemouth®-enabled optical fiberbased sensing apparatus 15 at any particular time. The first output of optical switch 195 is provided to the first port of an optical circulator 200. The second port of optical circulator 200 is provided to the end of a first optical fiber-based sensing element 20 that is structured and configured for distributed CO2 sensing as described herein. The third port of optical circulator 200 is coupled to a first photodetector 215. The second output of optical switch 195 is provided to the first port of an optical circulator 205. The second port of optical circulator 205 is provided to the end of a second optical fiber-based sensing element 20 that is structured and configured for distributed pH sensing as described herein. The third port of optical circulator 205 is coupled to a second photodetector 220. The third output of optical switch 195 is provided to the first port of an optical circulator 210. The second port of optical circulator 210 is provided to the end of a third optical fiber-based sensing element 20 that is structured and configured forCLIENT / MATTERNO. 214001-02161 PCTdistributed temperature sensing as described herein. The third port of optical circulator 210 is coupled to third photodetectors 225 through a Raman WDM filter 240. The outputs of first, second, and third photodetectors 215, 220, 225 are provided to a data acquisition (DAQ) system 230, which in turn is coupled to a field programmable gate array (FPGA) 235. DAQ system 230 and FBGA 235 together function to provide OTDR functional for measuring dissolved CO2, pH levels and temperature along each of the optical fiber-based sensing elements 20 as described herein.

[0044] FIG. 8 is a cross-sectional diagram of an optical fiber-based sensing element 20 according to one particular exemplary embodiment for gas sensing that may be used in BristlemouthO-enabled optical fiber-based sensing apparatus 15 as shown in FIGS. 1, 5, 6, 7, 10 or 11. Optical fiber-based sensing element 20 of this particular exemplary embodiment includes an optical core 140, a sensing layer 130 as described herein in any of a number of various embodiments surrounding optical core 140, a gas permeable secondary polymer cladding layer 145 surrounding sensing layer 130, a gas permeable strength layer 150 surrounding gas permeable secondary polymer cladding layer 145, and a liquid (.e.g., water) impermeable and gas permeable outer tube 155 surrounding gas permeable strength layer 150. Core 140 is the central glass core of optical fiber-based sensing element 20 and may be a non-core fiber (NCF). Sensing layer 130 acts as the primary cladding and has a refractive index that is lower than the refractive index of optical core 140. Gas permeable secondary polymer cladding layer 145 provides additional optical cladding and mechanical protection for the inner layers and may be a PDMS polymer. Liquid (.e.g., water) impermeable and gas permeable strength layer 150 may be made of a standard aramid yam material. Liquid (.e.g., water) impermeable and gas permeable outer tube 155 allows for the ingress of gas but blocks water and may be an expanded Polytetrafluoroethylene tube. The embodiment of FIG. 8 may be particularly useful for CO2 sensing as described herein.

[0045] FIG. 9 is a cross-sectional diagram of an optical fiber-based sensing element 20 according to another particular exemplary embodiment for liquid sensing that may be used in Bristlemouth®-enabled optical fiber-based sensing apparatus 15 as shown in FIGS. 1, 5, 6 , 7, 10 or 11. Optical fiber-based sensing element 20 of this particular exemplary embodiment includes an optical core 140 as described above, a sensing layerCLIENT / MATTERNO. 214001-02161 PCT130 as described herein in any of a number of various embodiments surrounding optical core 140, a liquid permeable secondary polymer cladding layer 160 surrounding sensing layer 130, a liquid permeable strength layer 165 surrounding liquid permeable secondary polymer cladding layer 160, and a liquid permeable outer tube 170 surrounding liquid permeable strength layer 165. Liquid permeable secondary polymer cladding layer 160 provides additional optical cladding and mechanical protection for the inner layers and may be a water (ion) permeable polymer, such as a pH insensitive hydrogel like poly(2- hydroxyethyl methacrylate) (pHEMA), which will have lower refractive index than optical core 140 when in a swollen state. Since liquid permeable secondary polymer cladding layer 160 will be soft in this embodiment, liquid permeable strength layer 165 should be designed in a way that it does not damage liquid permeable secondary polymer cladding layer 160. Liquid permeable outer tube 170 allows for the ingress of liquid (water) and may be a perforated or slotted (e.g., with micron or mm sized perorations or slots) Polyvinyl Chloride (PVC), Thermoplastic Polyurethane (TPE) or Thermoplastic Elastomer (TPU) tube. The embodiment of FIG. 9 may be particularly useful for pH sensing as described herein.

[0046] Moreover, according to further aspect of the disclosed concept, Bristlemouth®- enabled optical fiber-based sensing apparatus 15 may also provide for distributed acoustic sensing using OTDR. In particularizing. 10 is a schematic diagram of a Bristlemouth®-enabled optical fiber-based sensing apparatus 15 according to another particular exemplary embodiment for performing quasi-distributed acoustic sensing. As seen in FIG. 10, this embodiment includes an optical fiber-based sensing element 20 for quasi -distributed acoustic sensing that includes an optical fiber 90 (typically a single mode fiber) having a plurality of FBGs 95 provided in the core of optical fiber 90. The broadband light output of FBG interrogator 85 is provided to the first port of optical circulator 80. The second port of optical circulator 80 is coupled to the end of optical fiber-based sensing element 20, and the third port of optical circulator 80 is coupled to the input of FBG interrogator 85. In the exemplary embodiment, optical fiber-based sensing element 20 includes one or more outer protective layers as described elsewhere herein to protect optical fiber-based sensing element 20 from the often-harsh conditions of the sea while deployed. In addition, FIG. 11 is a schematic diagram of aCLIENT / MATTERNO. 214001-02161 PCTBristlemouth®-enabled optical fiber-based sensing apparatus 15 according to yet another particular exemplary embodiment for performing distributed acoustic sensing. As seen in FIG. 11, optical interrogation system 70 in this embodiment includes a phase OTDR system 240 (commercially available or custom built), and an optical circulator 245. As is known, a phase OTDR system, such as phase OTDR system 240, is structured and configured to launch short laser pulses into an optical fiber, measure the light that is scattered or reflected back, and use phase comparisons are used to determine local phases changes, which are indicative of local strain changes resulting from vibrations (acoustic events). Time delay is used to determine the position of such local strain changes. In this embodiment, optical fiber-based sensing element 20 includes a single mode optical fiber. Moreover, in the embodiments of FIGS. 4, 6, and 7 as described herein, an optical fiberbased sensing element 20 for acoustic sensing as shown in FIG. 10 or FIG. 11 may be provided in place or in addition to the optical fiber-based sensing element 20 used for or distributed temperature sensing. In such embodiments, as noted above, acoustic or vibrational energy is inferred from how it dynamically strains the fiber of optical fiberbased sensing element 20.

[0047] While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure.Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of disclosed concept which is to be given the full breadth of the claims appended and any and all equivalents thereof.

Claims

CLIENT / MATTERNO. 214001-02161 PCTWhat is claimed is:

1. An optical fiber-based sensing apparatus for quasi -distributed or distributed underwater fiber optic sensing in marine applications, comprising:an optical fiber-based sensing element; anda submersible waterproof housing including therein an electronic component and an optical interrogation system, wherein the optical interrogation system is structured and configured for interrogating the optical fiber-based sensing element and enabling quasi-distributed or distributed sensing of a parameter along the optical fiber-based sensing element, wherein the electronic component is structured and configured for providing first power to the optical interrogation system and for enabling data communication between the electronic component and the optical interrogation system, and wherein the electronic component is structured and configured to derive the first power from second power received from an external device and enable data communication between the electronic component and the external device.

2. The optical fiber-based sensing apparatus according to claim 1, wherein the waterproof submersible housing including the electronic component and the optical interrogation system: (i) consumes no more than 40 W at no more than 30 VDC, (ii) has dimensions (L x H x D) of no more than 420 mm x 420 mm x 88 mm; and (iii) has a weight of no more than 7 kg.

3. The optical fiber-based sensing apparatus according to claim 1, wherein the electronic component is structured and configured to provide the first power to the optical interrogation system and to enable data communication between the electronic component and the optical interrogation system according to the Bristlemouth protocol.

4. The optical fiber-based sensing apparatus according to claim 1, wherein the parameter is temperature, wherein optical fiber-based sensing element comprises a fiber having a plurality of fiber Bragg gratings therein, and wherein the optical interrogation system comprises a broadband light source and a fiber Bragg grating interrogator.CLIENT / MATTERNO. 214001-02161 PCT5. The optical fiber-based sensing apparatus according to claim 1, wherein the parameter is temperature, wherein optical fiber-based sensing element comprises a single mode fiber, and wherein the optical interrogation system comprises a Rayleigh optical time domain reflectometry system.

6. The optical fiber-based sensing apparatus according to claim 5, wherein optical interrogation system comprises a fiber amplifier for amplifying light received from the Rayleigh optical time domain reflectometry system to enable amplified light to be provided to the single mode fiber, and a Raman wavelength division multiplexing (WDM) filter to enable filtering of backscattered and / or reflected light received from the single mode fiber and to enable filtered backscattered and / or reflected light to be provided to the Rayleigh optical time domain reflectometry system.

7. The optical fiber-based sensing apparatus according to claim 6, wherein the parameter is a chemical parameter, wherein the optical fiber-based sensing element comprises an optical fiber core coated with a sensing layer, and wherein the optical interrogation system comprises a Rayleigh optical time domain reflectometry system.

8. The system according to claim 7, wherein the chemical parameter is CO2 or pH level.

9. The optical fiber-based sensing apparatus according to claim 7, wherein the sensing layer comprises a polymer.

10. The optical fiber-based sensing apparatus according to claim 8, wherein sensing layer comprises a base sensing layer matrix and a pH-sensitive dye.

11. The optical fiber-based sensing apparatus according to claim 1, wherein the optical fiber-based sensing element comprises an optical fiber core coated with a sensingCLIENT / MATTERNO. 214001-02161 PCTlayer, wherein the optical fiber-based sensing element further comprises a gas permeable secondary polymer cladding layer surrounding the sensing layer, a gas permeable strength layer surrounding the gas permeable secondary polymer cladding layer, and a liquid impermeable and gas permeable outer tube surrounding gas permeable strength layer.

12. The optical fiber-based sensing apparatus according to claim 11, wherein the gas permeable secondary polymer cladding layer comprises PDMS.

13. The optical fiber-based sensing apparatus according to claim 11, wherein the gas permeable strength layer comprises aramid yarn material.

14. The optical fiber-based sensing apparatus according to claim 11, wherein the liquid impermeable and gas permeable outer tube allows for the ingress of gas but blocks water.

15. The optical fiber-based sensing apparatus according to claim 14, wherein the liquid impermeable and gas permeable outer tube is an expanded Polytetrafluoroethylene tube.

16. The optical fiber-based sensing apparatus according to claim 1, wherein optical fiber-based sensing element comprises an optical fiber core coated with a sensing layer, wherein the optical fiber-based sensing element further comprises a liquid permeable secondary polymer cladding layer surrounding the sensing layer, a liquid permeable strength layer surrounding the liquid permeable secondary polymer cladding layer, and a liquid permeable outer tube surrounding the liquid permeable strength layer.

17. The optical fiber-based sensing apparatus according to claim 16, wherein the liquid permeable secondary polymer cladding layer comprises a water (ion) permeable polymer.CLIENT / MATTERNO. 214001-02161 PCT18. The optical fiber-based sensing apparatus according to claim 17, wherein the water (ion) permeable polymer comprises a pH insensitive hydrogel.

19. The optical fiber-based sensing apparatus according to claim 18, wherein the pH insensitive hydrogel is poly(2-hydroxyethyl methacrylate) (pHEMA).

20. The optical fiber-based sensing apparatus according to claim 15, wherein the gas permeable outer tube allows for the ingress of water and comprises a perforated or slotted Polyvinyl Chloride (PVC), Thermoplastic Polyurethane (TPE) or Thermoplastic Elastomer (TPU) tube.

21. The optical fiber-based sensing apparatus according to claim 1, wherein the parameter is temperature, wherein the optical interrogation system comprises an optical time domain reflectometry system, and wherein the system further comprises a second optical fiberbased sensing element coupled to the optical interrogation system, wherein the optical interrogation system is also structured for interrogating the second optical fiber-based sensing element and enabling distributed sensing of a chemical parameter along the second optical fiberbased sensing element.

22. The optical fiber-based sensing apparatus according to claim 21, wherein the chemical parameter is CO2 or pH level.

23. The optical fiber-based sensing apparatus according to claim 1, wherein the parameter is temperature, wherein the optical interrogation system comprises an optical time domain reflectometry system, wherein the system further comprises a second optical fiber-based sensing element coupled to the optical interrogation system, wherein the optical interrogation system is also structured for interrogating the second optical fiber-based sensing element and enabling distributed sensing of a CO2 along the second optical fiber-based sensing element, and wherein the system further comprises a third optical fiber-based sensing element coupled to the optical interrogation system, wherein the optical interrogation system is also structured forCLIENT / MATTERNO. 214001-02161 PCTinterrogating the third optical fiber-based sensing element and enabling distributed sensing of a pH level along the third optical fiber-based sensing element.

24. The optical fiber-based sensing apparatus according to claim 23, further comprising a plurality of light sources each structured for providing a different wavelength of light, and a switch for selecting among the plurality of light sources for providing light of a selected wavelength to the first, second and third optical fiber-based sensing elements.

25. A system for quasi-distributed or distributed underwater fiber optic sensing in marine applications, comprising:optical fiber-based sensing apparatus according to claim 1; and a buoy, wherein the buoy is the external device and is structured and configured to provide the second power to the electronic component.

26. The system according to claim 25, wherein the buoy is solar powered and is structured and configured for satellite and / or cellular wireless communication.

27. The system according to claim 25, wherein the electronic component is structured and configured to provide the first power to the optical interrogation system and to enable data communication between the electronic component and the optical interrogation system according to the Bristlemouth protocol, and wherein the buoy is structured and configured to provide the second power to the electronic component and enable data communication between the buoy and the electronic component according to the Bristlemouth protocol.

28. An optical fiber-based sensing element for quasi-distributed or distributed underwater fiber optic sensing in marine applications, comprising:an optical fiber core;a sensing layer coating the core; anda plurality of protective layers comprising (i) a gas permeable secondary polymer cladding layer surrounding sensing layer, a gas permeable strength layer surroundingCLIENT / MATTERNO. 214001-02161 PCTthe gas permeable secondary polymer cladding layer, and a liquid impermeable and gas permeable outer tube surrounding gas permeable strength layer, or (ii) a liquid permeable secondary polymer cladding layer surrounding the sensing layer, a liquid permeable strength layer surrounding the liquid permeable secondary polymer cladding layer, and a liquid permeable outer tube surrounding the liquid permeable strength layer.

29. The optical fiber-based sensing element according to claim 28, wherein the plurality of protective layers comprise the gas permeable secondary polymer cladding layer surrounding sensing layer, the gas permeable strength layer surrounding the gas permeable secondary polymer cladding layer, and the liquid impermeable and gas permeable outer tube surrounding gas permeable strength layer.

30. The optical fiber-based sensing element according to claim 29, wherein the gas permeable secondary polymer cladding layer comprises PDMS.

31. The optical fiber-based sensing element according to claim 30, wherein the gas permeable strength layer comprises aramid yarn material.

32. The optical fiber-based sensing element according to claim 30, wherein the liquid impermeable and gas permeable outer tube allows for the ingress of gas but blocks water.

33. The optical fiber-based sensing element according to claim 32, wherein the liquid impermeable and gas permeable outer tube is an expanded Polytetrafluoroethylene tube.

34. The optical fiber-based sensing element according to claim 28, wherein the plurality of protective layers comprises the liquid permeable secondary polymer cladding layer surrounding the sensing layer, the liquid permeable strength layer surrounding the liquid permeable secondary polymer cladding layer, and the liquid permeable outer tube surrounding the liquid permeable strength layer.CLIENT / MATTERNO. 214001-02161 PCT35. The optical fiber-based sensing element according to claim 34, wherein the liquid permeable secondary polymer cladding layer comprises a water (ion) permeable polymer.

36. The optical fiber-based sensing element according to claim 35, wherein the water (ion) permeable polymer comprises a pH insensitive hydrogel.

37. The optical fiber-based sensing element according to claim 36, wherein the pH insensitive hydrogel is poly(2-hydroxyethyl methacrylate) (pHEMA).

38. The optical fiber-based sensing apparatus according to claim 34, wherein the gas permeable outer tube allows for the ingress of water and comprises a perforated or slotted Polyvinyl Chloride (PVC), Thermoplastic Polyurethane (TPE) or Thermoplastic Elastomer (TPU) tube.

39. The system according to claim 7, wherein the parameter is vibrations, strain, CO2 level, pH, oxygen level, nitrates / nitrites levels, and / or heavy metal pollutant levels.

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