Patent Description:
Fiber optic (FO) sensors can be used for detecting parameters such as strain, temperature, pressure, current, voltage, chemical composition, and vibration. FO sensors are attractive components because they are thin, lightweight, sensitive, robust to harsh environments, and immune to electromagnetic interference (EMI) and electrostatic discharge. FO sensors can be arranged to simultaneously measure multiple parameters distributed in space with high sensitivity in multiplexed configurations over long optical fiber cables. One example of how this can be achieved is through fiber Bragg grating (FBG) sensors. A FBG sensor is formed by a periodic modulation of the refractive index along a finite length (typically a few mm) of the core of an optical fiber. This pattern reflects a wavelength, called the Bragg wavelength, determined by the periodicity of the refractive index profile. The Bragg wavelength is sensitive to external stimulus (strain and/or temperature, etc.) that changes the periodicity of the grating and/or the index of refraction of the fiber. Thus, FBG sensors rely on the detection of small wavelength changes in response to stimuli of interest. In some implementations, FO sensors can be attached to structures and operated to detect parameters, e.g., strain, temperature, vibration, related to the health of the structures. <CIT> describes systems and methods for automatic handling of optical fibers and transporting the same, as well as automatic assembly of the optical fibers into optical devices and transportation of the same. A spool facilitates handling, storing, and transporting of the optical fiber. A cassette receives an electronic module and the optical fiber, with or without a corresponding spool, and presents the fiber in a manner that facilitates automatic assembly of optical assemblies. The cassette also facilitates handling, storing, and transporting of the optical assemblies.

Embodiments described herein involve an apparatus as defined in claim <NUM>.

Embodiments involve a method of installing optical fiber on a structure as defined in claim <NUM>.

Embodiments involve a system as defined in claim <NUM>.

Throughout the specification reference is made to the appended drawings wherein:.

Fiber optic (FO) sensors have been explored considerably for downhole sensing in oil and gas production and in some academic studies for structural health monitoring. Parameters including strain, temperature, pressure, current, voltage, and/or chemical composition can be sensed by FO sensors. FO sensors offer many advantages over their electrical counterparts. They are thin (<NUM>-<NUM> diameter, for example), lightweight, sensitive, robust to harsh environments, and immune to electromagnetic interference (EMI) and electrostatic discharge.

Some embodiments disclosed herein involve apparatuses for attaching FO sensors to structures. Fiber optic sensors can be deployed on various types of structures, e.g., bridges, roadways, railways, and electrical devices such as transformers, to monitor the structural health of the structures. The disclosed embodiments can facilitate mounting FO sensors to the structures in such a way that strain from the structures is transmitted to the sensors. The approaches discussed herein provide for attachment of FO sensors that is flexible enough to attach the FO sensors to a variety of different substrates, e.g. concrete, metal, and wood. Repeatability of the attachment is desired so that at least some or most of the FO sensors have the same pre-strain once attached. The disclosed attachment approaches can be simple and rapid to perform to facilitate the deployment of multiple FO sensors on a structure. Installing optical fibers on structures involves extensive fiber handling during the install. Optical fibers are fragile, and breaks and/or tangles cost time, which is detrimental e.g. because roads must be shut down to service a structure. According to various configurations, the sensors may be fiber Bragg grating (FBG) strain sensors, Fabry Perot sensors, and/or other interferometric optical sensors. In some cases, the sensors may include one or more of electrical and/or resistive sensors, mechanical sensors, and/or other types of strain gages. In some cases, a combination of different types of sensors may be used.

Uniquely, FO sensors can simultaneously measure multiple parameters distributed in space with high sensitivity in multiplexed configurations over long FO cables. One example of how this can be achieved is through fiber Bragg grating (FBG) sensors. An FBG is formed by a periodic modulation of the refractive index along a finite length (typically a few mm) of the core of an optical fiber. This pattern reflects a wavelength, called the Bragg wavelength, determined by the periodicity of the refractive index profile. The Bragg wavelength is sensitive to external stimulus (strain and temperature, etc.) that change the periodicity of the grating and/or the index of refraction of the fiber. Thus FBG sensors rely on the detection of small wavelength changes in response to stimuli of interest. An example of having multiple FBG sensors along one fiber cable is shown in <FIG>. A broadband light source is used and multiple FBG sensor elements, each tuned to be primarily reflective to a different wavelength are on the same optical fiber bus at different distances. Each FBG is designated to measure a different (combination of) parameter(s). Noticeably, installing such a long fiber cable with multiple sensors in the field is not a trivial task. Fiber sensors are typically very delicate and fragile thus should be handled carefully. Each sensor should be installed reliably, free from manual error. Fiber segment between two sensing points should be properly handled to avoid sag or kink that can introduce optical power loss and/or reduce the robustness of the sensing fiber in the field.

FO sensors can simultaneously measure multiple parameters distributed in space with high sensitivity in multiplexed configurations over long FO cables. One example of how this can be achieved is through fiber Bragg grating (FBG) sensors. <FIG> shows a wavelength multiplexed system <NUM> can use a compensated sensor array comprising multiple FBG sensors <NUM>, <NUM>, <NUM> disposed on a single optical fiber <NUM>. The sensors <NUM> - <NUM> may be arranged to sense parameters including one or more of temperature, strain, and/or vibration, for example. As indicated in <FIG>, input light is provided by the light source <NUM>, which may comprise or be a light emitting diode (LED) or superluminescent laser diode (SLD), for example. The spectral characteristic (intensity vs. wavelength) of broadband light is shown by inset graph <NUM>. The intensity is highest near the middle of the spectrum and falls off at the spectrum edges. The sensors <NUM>, <NUM>, <NUM> include compensation, e.g., one or more of different reflectivities and different attenuations, that decreases the difference in the intensity of the output signal light reflected by the sensors to compensate for the input light that is non-uniform in intensity, e.g., due to spectral non-uniformity of the light source and/or scattering losses in the optical fiber. The input light is transmitted via the optical fiber (FO) cable <NUM> to the first FBG sensor <NUM>. The first FBG sensor <NUM> reflects a portion of the light in a first wavelength band having a central wavelength, λ1. Light having wavelengths other than within the first wavelength band is transmitted through the first FBG sensor <NUM> to the second FBG sensor <NUM>. The spectral characteristic of the light transmitted to the second FBG sensor <NUM> is shown in inset graph <NUM> and exhibits a notch <NUM> at the first wavelength band centered at λ1 indicating that light in this wavelength band is reflected by the first sensor <NUM>.

The second FBG sensor <NUM> reflects a portion of the light in a second wavelength band having a central wavelength, λ2. Light that is not reflected by the second FBG sensor <NUM> is transmitted through the second FBG sensor <NUM> to the third FBG sensor <NUM>. The spectral characteristic of the light transmitted to the third FBG sensor <NUM> is shown in inset graph <NUM> and includes notches <NUM>, <NUM> centered at λ1 and λ2.

The third FBG sensor <NUM> reflects a portion of the light in a third wavelength band having a central or peak wavelength, λ3. Light that is not reflected by the third FBG sensor <NUM> is transmitted through the third FBG sensor <NUM>. The spectral characteristic of the light transmitted through the third FBG sensor <NUM> is shown in inset graph <NUM> and includes notches <NUM>, <NUM>, <NUM> centered at λ1, λ2, and λ3.

Light in wavelength bands <NUM>, <NUM>, <NUM>, having central wavelengths λ1, λ2 and λ3 (illustrated in inset graph <NUM>) is reflected by the first, second, or third FBG sensors <NUM>, <NUM>, <NUM>, respectively, along the FO cables <NUM> and <NUM>' to an the optical wavelength demultiplexer <NUM>. Compensating input characteristics of sensors <NUM>, <NUM>, <NUM> cause the difference in the intensity peaks of the light <NUM>, <NUM>, <NUM> to be reduced when compared to the intensity peaks from an uncompensated sensor array.

From the wavelength demultiplexer <NUM>, the sensor light <NUM>, <NUM>, <NUM> may be routed to a wavelength shift detector <NUM> that generates an electrical signal responsive to shifts in the central wavelengths λ1, λ2 and λ3 and/or wavelength bands of the sensor light. The wavelength shift detector <NUM> receives reflected light from each of the sensors and generates corresponding electrical signals in response to the shifts in the central wavelengths λ1, λ2 and λ3 or wavelength bands of the light reflected by the sensors <NUM> - <NUM>. The analyzer <NUM> may compare the shifts to a characteristic base wavelength (a known wavelength) to determine whether changes in the values of the parameters sensed by the sensors <NUM> - <NUM> have occurred. The analyzer <NUM> may determine that the values of one or more of the sensed parameters have changed based on the wavelength shift analysis and may calculate a relative or absolute measurement of the change.

In some cases, instead of emitting broadband light, the light source may scan through a wavelength range, emitting light in narrow wavelength bands to which the various sensors disposed on the FO cable are sensitive. The reflected light is sensed during a number of sensing periods that are timed relative to the emission of the narrowband light. For example, consider the scenario where sensors <NUM>, <NUM>, and <NUM> are disposed on a FO cable. Sensor <NUM> is sensitive to a wavelength band (WB1), sensor <NUM> is sensitive to wavelength band WB2, and sensor <NUM> is sensitive to WB3. The light source may be controlled to emit light having WB1 during time period <NUM> and sense reflected light during time period 1a that overlaps time period <NUM>. Following time period 1a, the light source may emit light having WB2 during time period <NUM> and sense reflected light during time period 2a that overlaps time period <NUM>. Following time period 2a, the light source may emit light having WB3 during time period <NUM> and sense reflected light during time period 3a that overlaps time period <NUM>. Using this version of time domain multiplexing, each of the sensors may be interrogated during discrete time periods. When the intensity of the narrowband light sources varies, a compensated sensor array as discussed herein may be useful to compensate for the intensity variation of the sources.

The FO cable may comprise a single mode (SM) FO cable or may comprise a multi-mode (MM) FO cable. While single mode fiber optic cables offer signals that are easier to interpret, to achieve broader applicability and lower costs of fabrication, multi-mode fibers may be used. MM fibers may be made of plastic rather than silica, which is typically used for SM fibers. Plastic fibers may have smaller turn radii when compared with the turn radii of silica fibers. This can offer the possibility of curved or flexible configurations, for example. Furthermore, MM fibers can work with less expensive light sources (e.g., LEDs) as opposed to SM fibers that may need more precise alignment with superluminescent diodes (SLDs). Therefore, sensing systems based on optical sensors in MM fibers may yield lower cost systems.

In the last few years the quality and cost of fiber optic sensors and their readout technologies have significantly improved. To realize now further acceptance of FO sensing e.g., for structural health monitoring or industrial process control, improvement regarding handling, installing and bonding fiber sensors are needed to allow for simple, reliable and robust sensor installation in the field.

Embodiments described herein involve techniques for controlled and (semi)automatic installation and bonding procedures that will enable even unskilled labor to safely and reliably install FO sensors onto surfaces in the field. An integrated system is described that installs FO sensors to surface in an automatic or semi-automatic way. Different components for fiber handling and fiber installation synergize to adapt to limited working conditions in the field while maintaining reliable sensing performance and system robustness.

Embodiments described herein describe the field installation difficulties in a systematic way. The system combines functions of fiber spooling and unspooling, sensing point identification, sensing point installation, and non-sensing segment management. The system accommodates to installation of FO sensors in one fiber spool over large space. The system accommodates to installation of FO sensors where working space for operators are limited, such as on a boom lift.

According to various configurations, a cassette may be used for handling optical fiber having a plurality of sensors while it is being installed on a surface. <FIG> illustrates an example cassette <NUM> for handling optical fiber <NUM> in accordance with embodiments described herein. Embodiments described herein involve a cassette <NUM> that houses an optical fiber spool <NUM> inside a cassette body in accordance with embodiments described herein. A cassette in accordance with embodiments described herein is described in further detail in <CIT>. The cassette may have one or more additional mechanisms that may be useful for the installation of optical fiber sensors. For example, the cassette has one or more mounting points <NUM> configured to allow mounting of the cassette during installation of the optical fiber. For example, the mounting points <NUM> may include one or more of a magnet and a carabiner attachment point.

The cassette <NUM> may include an optical fiber monitor <NUM> may be disposed at an optical fiber exit point of the cassette <NUM>. The optical fiber monitor <NUM> may be configured to monitor at least one parameter of the optical fiber <NUM> as the optical fiber is extracted from the cassette. For example, the at least one parameter includes a spooling length, a spooling condition, a total length dispensed, an approximate distance to an optical sensor, a fiber tension, and/or a fiber integrity.

According to various embodiments, as the optical fiber <NUM> is extracted from the cassette <NUM>, the optical fiber monitor <NUM> is configured to detect the presence of markers and thus determine the location of the one or more sensors along the optical fiber <NUM>. In some cases, the optical fiber monitor <NUM> may be able to determine a total length of optical fiber dispensed. A spool monitor <NUM> may be disposed on or near the cassette. The spool monitor <NUM> may be configured to display one or more of the parameters monitored by the optical fiber monitor <NUM>. For example, the spool monitor <NUM> may be configured to display the total amount of optical fiber <NUM> dispensed and/or the distance to the next optical sensor. A fiber monitor is described in further detail in <CIT>.

According to various embodiments, a sub-spooling system <NUM> can be included in the system <NUM> which spools fiber <NUM> released from the original cassette <NUM> into a sub-spool system <NUM> as shown in <FIG>. According to various embodiments, the sub-spool has a defined radius. For example, the sub-spool may have a radius in a range of about <NUM> to about <NUM>. The sub-spool can then be installed onto the surface as an integral that will benefit sag management for fibers between two sensing points. According to various embodiments, a fiber monitor <NUM> may be included in the system <NUM>.

<FIG> is a conceptual diagram that provides a perspective view of an installation tool <NUM> in accordance with some embodiments. The installation tool <NUM> comprises a body <NUM> and one or more contact portions <NUM>, <NUM> supported by the body <NUM> and configured to secure the optical fiber <NUM>. As shown in <FIG>, in some implementations, the optical fiber <NUM> being installed to the structure <NUM> may include an FO sensor <NUM>. During the installation process, the optical fiber <NUM> is secured such that the FO sensor <NUM> is disposed between the contact portions <NUM>, <NUM>. Embodiments described herein may be used in conjunction with an adhesive stamp for installing an optical fiber to a structure. A stamp for installation of optical sensors is described in further detail in <CIT>.

The installation tool <NUM> further includes an adhesive dispenser <NUM> proximate the body <NUM>. The adhesive dispenser <NUM> is capable of dispensing at least one adhesive. The adhesive dispenser <NUM> can be configured to dispense adhesive to one or more locations of the optical fiber <NUM> and/or the structure <NUM>. According to some aspects, the installation tool <NUM> can be configured such that the adhesive dispenser <NUM> dispenses the adhesive to the optical fiber <NUM> and the structure <NUM> after the optical fiber <NUM> is secured by the contact portions <NUM>, <NUM> and is pressed against the structure <NUM>. The adhesive dispenser <NUM> may be configured to dispense adhesive to multiple locations of the optical fiber <NUM> and/or structure <NUM> during the time that the contact portions <NUM>, <NUM> secure the optical fiber <NUM>.

A dispenser controller (not shown) can be included to control the operation of the adhesive dispenser <NUM>. For example, the dispenser controller may control the timing, type, flow rate, and/or amount of adhesive dispensed to one or multiple locations of the optical fiber <NUM>.

Optionally, the installation device <NUM> includes a cure device <NUM> configured to generate a curing energy and to direct the curing energy toward the adhesive dispensed to the optical fiber <NUM> and the structure <NUM>. In some embodiments, the installation device may implement a fully or partially automated process. In one example, after the installation process is initiated, e.g., by pressing a switch <NUM> on the body <NUM>, the installation process proceeds with little or no interaction needed by the operator. In another example, the installation process may rely on the operator to initiate certain aspects of the installation process, e.g., by activating one or more switches <NUM>, <NUM>, <NUM>, <NUM> that trigger one or more installation processes. Optionally, the installation device <NUM> is a hand-held device that includes a handle <NUM> configured to allow an operator to grasp the installation device <NUM>. A stamp tool is described in further detail in <CIT>.

<FIG> shows the fiber installation tool <NUM> that is configured to mount optical fiber <NUM> to a surface of a structure <NUM> to be monitored. The installed fiber segment may contain or not contain a sensing point. In some cases, a fiber sub-spool <NUM> is configured to be installed to the structure <NUM> using the fiber installation tool <NUM>.

In a semi-automatic installation scenario, an operator <NUM> is involved that will operate the system as shown in <FIG>. In some cases a boom lift <NUM> can be used and installation is onto the surface of a bridge, for example. In some cases, the fiber cassette <NUM> can be attached to the boom lift as shown in example <NUM>. The installation tool <NUM> can be hand-held. The fiber cassette <NUM> may be able to spool in coordination with the movement of the boom lift <NUM> to reach an installation point. In some embodiments, the fiber cassette <NUM> will unspool the sensing fiber <NUM> and provide a signal when unspooled to a point that should be fixed to the structure <NUM> surface in order to perform sensing and/or to secure the fiber <NUM> and minimize fiber sag. The installation tool <NUM> can be used to hold a certain segment of the fiber <NUM> and position the fiber segment to the surface to be mounted. The cassette <NUM> may be able to spool/unspool accordingly to guarantee a certain fiber length between the fiber spool and the segment held by the installation tool <NUM> in order to position the segment onto the surface. Then the installation tool <NUM> may apply a mounting mechanism, which may fix the fiber segment to the surface. The mounting mechanism can be adhesive glues dispensed from and cured by the tool <NUM>. The mounting mechanism can be fiber-mounting tapes dispensed from the tool <NUM>, for example. Once a segment of the fiber is fixed to the surface, the segment can be released from the tool <NUM>. The operator <NUM> can move on to the next installation point.

In some cases, the fiber cassette <NUM> can be carried by the operator <NUM> as the operator <NUM> moves from one installation point to another as shown in example <NUM>. The fiber cassette <NUM> may be able to spool in coordination with the movement of the operator <NUM>. Once an installation site is reached, the operator <NUM> can use the installation tool <NUM> to hold a certain segment of the fiber and position the fiber segment to the surface to be mounted. The cassette <NUM> may be able to spool/unspool accordingly to guarantee a certain fiber length between the cassette <NUM> and the segment held by the installation tool <NUM> in order to position the segment onto the surface. Then the installation tool <NUM> applies certain mounting mechanisms which fixes the fiber segment to the surface.

In some embodiments, the fiber cassette <NUM> can be temporarily attached to the structure <NUM> as shown in example <NUM>. The cassette <NUM> may be monitored via its mounting points, while the operator <NUM> is adjusting the position of the boom lift <NUM> or preparing the next installation point.

<FIG> shows a process for installing optical fiber to a structure in accordance with embodiments described herein. The smart fiber cassette is configured <NUM> according to the distribution of FO sensors on a fiber cable and the desired installation points on the structure. The fiber is loaded <NUM> onto the smart cassette. The installation starts and the smart cassette is attached <NUM> to an operator, structure, and/or a translation stage (e.g., boom lift). The cassette unspools <NUM> and the operator and/or the translation stage moves to reach the installation point. The fiber monitor on the cassette may show a condition of the spool and whether a sensor and/or installation point is approaching.

Optionally, if a sub-spool is desired to manage extra fiber length between two sensing points, the smart cassette may be loaded <NUM> into a sub-spool system to create a sub-spool. The sub-spool may be transferred and mounted to the structure. The smart cassette may be released from the sub-spool system and reattached to the operator and/or translation stage.

Once an installation point is reached, the integrated installation tool may be used <NUM> to install at least a segment of the optical fiber to the structure. The smart cassette may be configured to spool and/or unspool to facilitate the installation. In the event that the operator and/or translation stage needs to move without the fiber cassette, optionally, the fiber cassette can be temporarily attached <NUM> to an adjacent point of the last installation point on the structure. In some cases, the optical fiber may be pre-strained prior to installation. A tool that can be used to pre-strain the optical fiber is described in further detail in <CIT>. The installation may be finished <NUM> once all of the desired optical fiber is installed onto the structure.

In some cases, the installation of the optical fiber may be automatically installed using an installation robot as shown in <FIG>. In an automatic installation case, all the aforementioned components can be integrated into a fiber installation robot <NUM>. The robot <NUM> can travel along a defined path <NUM> on the surface of the structure <NUM>, e.g., a preinstalled rail. The smart fiber cassette <NUM> having an integrated fiber monitor <NUM> dispenses the fiber as the robot <NUM> moves and the fiber mounting module <NUM> fixes the fiber <NUM> to the surface at specific points. In some cases, the robot <NUM> can create sub-spools whenever needed and transfer the sub-spool to the surface and fix it in place.

<FIG> shows another example of a fiber installation robot that shows climbing arms in accordance with embodiments described herein. The robot <NUM> can climb on the structure <NUM> and move along a programed path using climbing arms <NUM>, <NUM>. The smart fiber cassette <NUM> may have an integrated fiber monitor <NUM> dispenses the fiber as the robot <NUM> moves and the fiber mounting module <NUM> fixes the fiber <NUM> to the surface at specific points.

<FIG> illustrates an example of a system <NUM> incorporating the fiber cassette <NUM> in and the sub-spooling system <NUM> in accordance with embodiments described herein. A sub spool can be fixed by UV glue/spiral coil at several points to maintain its shape after being released from the sub-spooling system with the installation tool <NUM>. The sub spool can then be transferred and mounted to the structure surface. The fiber cassette can be detached from the sub-spooling system once a sub spool is created and transferred.

The systems described herein can be implemented by a computer using well-known computer processors, memory units, storage devices, computer software, and other components. A high-level block diagram of such a computer is illustrated in <FIG>. Computer <NUM> contains a processor <NUM>, which controls the overall operation of the computer <NUM> by executing computer program instructions which define such operation. It is to be understood that the processor <NUM> can include any type of device capable of executing instructions. For example, the processor <NUM> may include one or more of a central processing unit (CPU), a graphical processing unit (GPU), a field-programmable gate array (FPGA), and an application-specific integrated circuit (ASIC). The computer program instructions may be stored in a storage device <NUM> and loaded into memory <NUM> when execution of the computer program instructions is desired. Thus, the steps of the methods described herein may be defined by the computer program instructions stored in the memory <NUM> and controlled by the processor <NUM> executing the computer program instructions. The computer <NUM> may include one or more network interfaces <NUM> for communicating with other devices via a network. The computer <NUM> also includes a user interface <NUM> that enable user interaction with the computer <NUM>. The user interface <NUM> may include I/O devices <NUM> (e.g., keyboard, mouse, speakers, buttons, etc.) to allow the user to interact with the computer. Such input/output devices <NUM> may be used in conjunction with a set of computer programs in accordance with embodiments described herein. The user interface may include a display <NUM>. The computer may also include a receiver <NUM> configured to receive data from the user interface <NUM> and/or from the storage device <NUM>. According to various embodiments, <FIG> is a high-level representation of possible components of a computer for illustrative purposes and the computer may contain other components.

Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties used in the specification and claims are to be understood as being modified in all instances by the term "about. " Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein. The use of numerical ranges by endpoints includes all numbers within that range (e.g. <NUM> to <NUM> includes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>) and any range within that range.

The various embodiments described above may be implemented using circuitry and/or software modules that interact to provide particular results. One of skill in the computing arts can readily implement such described functionality, either at a modular level or as a whole, using knowledge generally known in the art. For example, the flowcharts illustrated herein may be used to create computer-readable instructions/code for execution by a processor. Such instructions may be stored on a computer-readable medium and transferred to the processor for execution as is known in the art.

Claim 1:
An apparatus, comprising:
a cassette (<NUM>) configured to hold optical fiber (<NUM>) comprising one or more optical sensors, the cassette comprising a spool (<NUM>) configured to one or more of extract and retract the optical fiber from the cassette; characterized by:
a pre-strain mechanism configured to apply a predetermined pre-strain to the one or more optical sensors;
an optical fiber installation tool configured to mount the optical fiber comprising the one or more pre-strained optical sensors to a surface.