WO2008115375A1 - Détection de la position et/ou de la forme d'une fibre optique à partir d'une diffusion de rayleigh - Google Patents

Détection de la position et/ou de la forme d'une fibre optique à partir d'une diffusion de rayleigh Download PDF

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Publication number
WO2008115375A1
WO2008115375A1 PCT/US2008/003236 US2008003236W WO2008115375A1 WO 2008115375 A1 WO2008115375 A1 WO 2008115375A1 US 2008003236 W US2008003236 W US 2008003236W WO 2008115375 A1 WO2008115375 A1 WO 2008115375A1
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WIPO (PCT)
Prior art keywords
fiber
core
shape
fiber optic
rayleigh scatter
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PCT/US2008/003236
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English (en)
Inventor
Mark E. Froggatt
Roger C. Duncan
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Luna Innovations Incorporated
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Publication of WO2008115375A1 publication Critical patent/WO2008115375A1/fr

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
    • G01M11/08—Testing mechanical properties
    • G01M11/088—Testing mechanical properties of optical fibres; Mechanical features associated with the optical testing of optical fibres
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/06—Devices, other than using radiation, for detecting or locating foreign bodies ; determining position of probes within or on the body of the patient
    • A61B5/065—Determining position of the probe employing exclusively positioning means located on or in the probe, e.g. using position sensors arranged on the probe
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B34/00—Computer-aided surgery; Manipulators or robots specially adapted for use in surgery
    • A61B34/30—Surgical robots
    • A61B2034/301—Surgical robots for introducing or steering flexible instruments inserted into the body, e.g. catheters or endoscopes

Definitions

  • Fiber optic strain sensors are used in applications such as smart structures and health monitoring.
  • the advantages of these sensors include their small size, low cost, multiplexing capabilities, immunity to electromagnetic interference, intrinsic safety and their capability to be embedded into structures.
  • Many structural devices and objects undergo various shape changes when exposed to certain environments. In some instances, it is necessary to know the degree of change and to compensate for these changes.
  • By embedding or attaching a sensor to the structure one can monitor the dynamic shape or relative position of the structure independently from temperature or load effects. Further by measuring the dynamic shape of a structure, the state of flexible structures can be established. When a degradation of the measured signal occurs, it can be corrected using signal processing.
  • Measurements of the local curvature and torsion along the cable allow reconstruction of the entire cable shape, including the relative position and orientation of the end points.
  • the smart cable for making these measurements comprises a multicore optical fiber, with individual fiber cores constructed to operate in the single mode regime, but positioned close enough to cause cross-talk (mode coupling) between cores over the length of the fiber.
  • This cross-talk is very sensitive to the distribution of strain (curvature and torsion) along the cable.
  • Clements describes the errors in measured curvature as being divided into three classes: those due to instrument noise, systematic errors due to fabrication defects (core geometry, index of refraction variations, etc.), and sensitivity to extrinsic variables such as temperature. Of the three, instrument noise is probably the worst threat to successful shape inversion.
  • a plurality of single mode cores may also be provided in an optical medium comprising a flexible sheet of material.
  • Greenaway et al. U.S. Patent No. 6,301,420 Bl
  • the optical fiber comprises two or more core regions, each core region comprising a substantially transparent core material and having a core refractive index, a core length, and a core diameter.
  • the core regions are arranged within a cladding region.
  • the cladding region comprises a length of first substantially transparent cladding material having a first refractive index.
  • the first substantially transparent cladding material has an array of lengths of a second cladding material embedded along its length.
  • the second cladding material has a second refractive index which is less than the first refractive index, such that radiation input to the fiber propagates along at least one of the core regions.
  • the cladding region and the core regions may be arranged such that radiation input to the optical fiber propagates along one or more of the lengths of the core regions in a single mode of propagation.
  • the optical fiber may be used as a bend sensor, a spectral filter or a directional coupler.
  • a bend sensor comprises a multicore photonic crystal fiber. The measurement of the relative shift in the fringe pattern provides an indication of the extent by which the fiber is bent.
  • the fiber is embedded in a structure, an indication of the extent to which the structure is bent is provided.
  • This type of system is an intensity based system, in contrast to an internal reflection system, therefore not all light is guided by an internal reflection mode and, hence, the system is not as accurate as an internal reflection system.
  • Greenway et al. (U.S. Patent No. 6,389,187 Bl) describe an optical fiber bend sensor that measures the degree and orientation of bending present in a sensor length portion of a fiber assembly.
  • cores are grouped in non-coplanar pairs.
  • An arrangement of optical elements define within each core pair two optical paths which differ along the sensor length.
  • One core of a pair is included in the first path and the other core in the second path.
  • a general bending of the sensor region will lengthen one core with respect to the other. Interrogation of this length differential by means of interferometry generates interferograms from which the degree of bending in the plane of the core pair is extracted. Bend orientation can be deduced from data extracted from multiple core pairs.
  • the apparatus is capable of determining bending of the sensor length, perhaps as a consequence of strain within an embedding structure, by monitoring that component of the bend in the plane of two fiber cores within the sensor length.
  • Interferograms are formed between radiation propagating along two different optical paths, the optical paths differing within a specific region of the fiber. This region, the sensor length, may be only a fraction of the total fiber length. Generally, bending this sensing region will inevitably lengthen one core with respect to the other. Interrogation of this length differential by means of interferometry provides an accurate tool with which to measure bending.
  • defining a sensor length down a potentially long fiber downlead enables strains to be detected at a localized region remote from the radiation input end of the fiber.
  • the fiber assembly can be incorporated in, for example, a building wall, and strains developing in the deep interior of the wall measured.
  • the first and second cores constitute a core pair and component cores of the multicore fiber preferably comprise an arrangement of such core pairs.
  • the coupling means may accordingly be arranged to couple and reflect a portion of radiation propagating in the first core into the second core of the respective pair. This provides the advantage of flexibility.
  • the optical path difference arising between any core pair can be interrogated, enabling the selection of planes any of which may be the plane in which components of a general bend curvature may be measured.
  • Schiffner U.S. Patent No. 4,443,698 describes a sensing device having a multicore optical fiber as a sensing element.
  • the sensing device includes a sensing element in the form of an optical fiber, a device for coupling light into the fiber and a device for measuring changes in the specific physical parameters of the light passing through the fiber to determine special physical influences applied to the fiber.
  • the fiber is a multicore fiber having at least two adjacently extending cores surrounded by a common cladding and a means for measuring the alterations in the light passing through each of the cores. To make the device sensitive to bending and deformation in all directions, the fiber may have two cores and be twisted through 90 degrees or the fiber may have three or more cores which are not disposed in the same plane.
  • the measuring of the amount of change may be by measuring the interference pattern from the superimposed beams of the output from the two cores or by measuring the intensity of each of the output beams separately.
  • an interferometric means for measurement will include a light receiving surface which is arranged in the path of light which passes through the two cores and has been brought into interference by means of superimposition.
  • the sensing means may use a light receiving surface which is a collecting screen in which the interference pattern can be directly observed or the light receiving surface may be the light sensitive surface of a light sensitive detector which will monitor the light intensity of the interference pattern.
  • a beam divider device or devices may be utilized.
  • Haake (U.S. Patent No 5,563,967) describes a fiber optic sensor and associated sensing method including a multicore optical fiber having first and second optical cores adapted to transmit optical signals having first and second predetermined wavelengths, respectively, in a single spatial mode.
  • the first and second optical cores each include respective Bragg gratings adapted to reflect optical signals having first and second predetermined wavelengths, respectively. Based upon the differences between the respective wavelengths of the optical signals reflected by the respective Bragg gratings and the first and second predetermined wavelengths, a predetermined physical phenomena to which the workpiece is subjected can be determined, independent of perturbations caused by other physical phenomena.
  • Optical fiber with Multiple Bragg Gratings at Nominally Equal Wavelengths Applied Optics, Vol. 27, No. 10, April 1, 1998 describe a demodulation system to measure static strain in an optical fiber using multiple, weak, fiber Bragg gratings (FBGs) in a single fiber.
  • FBGs fiber Bragg gratings
  • Kersey et al. in “Fiber Grating Sensors,” Journal of Lightwave Technology, Vol. 15, No. 8, August 1997 describe that a primary advantage of using FBGs for distributed sensing is that large numbers of sensors may be interrogated along a single fiber.
  • mixed WDM wavelength division multiplexing
  • TDM time division multiplexing
  • Froggatt U.S. Patent No. 5,798,521 describes an apparatus and method for measuring strain in Bragg gratings.
  • Optical radiation is transmitted over a plurality of contiguous predetermined wavelength ranges into a reference optical fiber network and an optical fiber network under test to produce a plurality of reference interference fringes and measurement interference fringes, respectively.
  • the reference and measurement fringes are detected and sampled such that each sampled value of the reference and measurement fringes is associated with a corresponding sample number.
  • the wavelength change of the reference optical fiber, for each sample number, due to the wavelength of the optical radiation is determined.
  • Each determined wavelength change is matched with a corresponding sampled value of each measurement fringe.
  • Each sampled measurement fringe of each wavelength sweep is transformed into a spatial domain waveform.
  • the spatial domain waveforms are summed to form a summation spatial domain waveform that is used to determine location of each grating with respect to a reference reflector.
  • a portion of each spatial domain waveform that corresponds to a particular grating is determined and transformed into a corresponding frequency spectrum representation.
  • the strain on the grating at each wavelength of optical radiation is determined by determining the difference between the current wavelength and an earlier, zero-strain wavelength measurement.
  • Chen et al. (U.S. 6,256,090 Bl) describe a method and apparatus for determining the shape of a flexible body.
  • the device uses Bragg grating sensor technology and time, spatial, and wavelength division multiplexing, to produce a plurality of strain measurements along one fiber path.
  • shape determination of the body and the tow cable can be made with minimal ambiguity.
  • the use of wavelength division multiplexing has its limitations in that the ability to have precision with respect to determining the shape and/or position of an object is limited. Wavelength division multiplexing can only be used with sensor arrays that have less than one hundred sensors and, therefore, is insufficient for the application of determining shape and or position of an object with any precision.
  • An object of the present invention is to provide a fiber optic position and/or shape sensing device that employs an optical fiber comprising at least two fiber cores disposed therein coupled with a frequency domain reflectomer.
  • Another object of the present invention is to provide a method for determining position and/or shape of an object using the fiber optic position and shape sensing device.
  • a fiber optic sensing device includes an optical fiber including at least two fiber cores spaced apart so that mode coupling between the fiber cores is reduced, and preferably minimized.
  • Each fiber core has an associated Rayleigh scatter signature and different segments of each fiber core correspond to a portion of the associated Rayleigh scatter signature.
  • a frequency domain refiectometer is coupled to the optical fiber for obtaining a Rayleigh scatter pattern associated with each of multiple fiber segments from each core.
  • the Rayleigh scatter patterns are used to determine a strain parameter for each of the multiple fiber segments from each core. Based on the determined strain parameters, a position and/or shape of a portion of the fiber is(are) determined.
  • the strain parameters are converted into local bend measurements defining a bend in the fiber at a particular location along the fiber which are integrated into a position or a shape.
  • the frequency domain reflectometer may detect a distributed strain field along a portion of each core including multiple segments based on the obtained Rayleigh scatter pattern associated with each of those fiber segments.
  • the optical fiber includes at least two single core optical fibers, and the frequency domain reflectometer detects a distributed one-dimensional strain field along a portion of each of the two single core optical fibers including multiple segments based on the obtained Rayleigh scatter pattern associated with each of those fiber segments.
  • the optical fiber includes three single core optical fibers that are non-coplanar and form a triangular shape.
  • the frequency domain reflectometer detects a distributed strain field along a portion of each of the three single core optical fibers including multiple segments based on the obtained Rayleigh scatter pattern associated with each of those fiber segments.
  • the three fiber cores each have a center, and in one non-limiting example implementation, each center is 120° with respect to each of the other two core centers.
  • a benefit of this technology is the ability to readily obtain many independent strain measurements along the length of the core.
  • at least one hundred Rayleigh scatter patterns along the length of each core are obtained.
  • the frequency domain reflectometer includes a broadband reference reflector. Rayleigh scatter patterns are obtained to establish an optical path length between the broadband reference reflector and the segments corresponding to the obtained Rayleigh scatter patterns.
  • the optical frequency domain reflectometer may also be constructed with an internal optical reference path, and, therefore, not include a broadband reference reflector.
  • the optical fiber may be disposed in, affixed to, coupled with, or conforming to at least a portion of an elongated body whose position and/or shape is to be determined.
  • the elongate body could be a catheter, tube, pipe, sleeve, instrument, tool, wire, line, cavity, vessel, lumen, or conduit.
  • the elongate body can be flexible.
  • a fiber optic method is also provided.
  • a frequency domain reflectometer is coupled to an optical fiber having at least two fiber cores spaced apart so that mode coupling between the fiber cores is reduced.
  • Each fiber core has an associated Rayleigh scatter signature and different segments of each fiber core correspond to a portion of the associated Rayleigh scatter signature.
  • the optical fiber is physically associated with a position and/or shape of an object.
  • the frequency domain reflectometer obtains a Rayleigh scatter pattern associated with each of multiple fiber segments from each core and uses the obtained Rayleigh scatter patterns to determine a strain parameter for each of the multiple fiber segments from each core.
  • the position and/or shape of the object is(are) determined based on the determined strain parameters.
  • a medical instrument system in another aspect, includes a medical instrument and an optical fiber conforming to at least a portion of a shape the medical instrument and including at least two fiber cores spaced apart so that mode coupling between the fiber cores is reduced.
  • Each fiber core has an associated Rayleigh scatter signature, and different segments of each fiber core correspond to a portion of the associated Rayleigh scatter signature.
  • a frequency domain reflectometer coupled to the optical fiber obtains a Rayleigh scatter pattern associated with each of multiple fiber segments from each core and uses the obtained Rayleigh scatter patterns to determine a strain parameter of each of the multiple fiber segments from each core.
  • a computing device determines a position and/or a shape of the portion of the medical instrument based on the determined strain parameters.
  • FIG. 1 is a schematic representation of a fiber optic position and/or shape sensing device having two fiber cores with Bragg gratings.
  • FIG. 2 is a schematic representation of a fiber optic position and/or shape sensing device having two fiber cores where the sensing mechanism is
  • FIG. 3 is a schematic representation of a fiber optic position and/or shape sensing device having three fiber cores with Bragg gratings.
  • FIG. 4 is a schematic representation of a fiber optic position and/or shape sensing device having three fiber cores where the sensing mechanism is
  • FIG. 5 depicts an example embodiment where the optical fiber includes three single core optical fibers with Bragg gratings.
  • FIG. 6 depicts a preferred example embodiment where the optical fiber includes three single core optical fibers and the sensing mechanism is
  • FIG. 7 is a schematic representation of an optical arrangement for the fiber optic position and/or shape sensing device with Bragg gratings.
  • FIG. 8 is a schematic representation of an optical arrangement for the fiber optic position and/or shape sensing device where the sensing mechanism is Rayleigh scatter.
  • FIG. 9 depicts a sensor frame.
  • FIG. 10 is a bend parameter schematic.
  • FIG. 11 depicts the bend geometry
  • FIG. 12 shows the fiber cross-section geometry
  • FIG. 13 is a graphical representation of the percent error between the laser displacement sensors and the fiber optic shape sensors.
  • FIG. 14 is a schematic representation of various example medical applications for the optical technology described in this application.
  • the fiber optic position and/or shape sensing device generally comprises an optical fiber for determining position and shape of an object.
  • the optical fiber comprises at least two fiber cores spaced apart from each other so that mode coupling between the fiber cores is reduced and preferably minimized.
  • the device further comprises a frequency domain reflectometer that transmits light to and receives reflected light from the optical fiber.
  • the optical fiber includes either at least two single core optical fibers positioned in a relative relationship to one another or a multicore optical fiber having at least two fiber cores.
  • the optical fiber may be a multicore optical fiber 20 having at least two fiber cores 30, 40 spaced apart so that mode coupling between the fiber cores is reduced and preferably minimized or completely eliminated. Applicants have found that mode coupling causes distortions.
  • a multicore optical fiber having two fiber cores (as depicted in FIG. 1 and 2) is suitable for use as a positioning device or for determining the two dimensional shape of an object. When determining three dimensional shapes, the multicore optical fiber preferably includes three fiber cores 30, 35, 40 (as shown in FIG. 3 and 4).
  • Multicore optical fiber is fabricated in much the same way as a standard telecommunications optical fiber.
  • the first step in the fabrication process is to design and model the optical parameters for the preform (i.e., refractive index profile, core/cladding diameters, etc.) to obtain the desired waveguide performance.
  • the fabrication of multi-core optical fiber requires the modification of standard over-cladding and fiberization processes. Though numerous methods can be employed to achieve the desired geometry, the preferred methods are the multi-chuck over-cladding procedure and the stack-and-draw process. In both techniques, the original preforms with the desired dopants and numerical aperture are fabricated via the Chemical Vapor Deposition (CVD) process. The preforms are then stretched to the appropriate diameters.
  • CVD Chemical Vapor Deposition
  • the preforms are sectioned to the appropriate lengths and inserted into a silica tube with the other glass rods to fill the voids in the tube.
  • the variation in the two procedures arises in the method in which the preform rods are inserted into the tube.
  • the bait rods and preforms are positioned in the tube on a glass working lathe.
  • a double chuck is used to align the preforms in the tube.
  • the tube is collapsed on the glass rods to form the preform.
  • the preform is then fiberized in the draw tower by a standard procedure known to those of ordinary skill in the art.
  • fiber Bragg gratings 50 may be disposed within and along each fiber core. In one preferred example, at least one hundred (100) fiber Bragg gratings. Each fiber Bragg grating is used to measure strain on the multi-core optical fiber. Fiber Bragg gratings are fabricated by exposing photosensitive fiber to a pattern of pulsed ultraviolet light from an excimer laser, that produces a periodic change in the refractive index of the core.
  • This pattern reflects a very narrow frequency band of light that is dependent upon the modulation period formed in the core.
  • a Bragg grating is either stretched or compressed by an external stimulus. This results in a change in the modulation period of the grating which, in turn, causes a shift in the frequency reflected by the grating. By measuring the shift in frequency, one can determine the magnitude of the external stimulus applied.
  • Bragg gratings are not necessary.
  • An alternative and preferred way (other ways may be used) of measuring strain within an optical fiber uses the intrinsic Rayleigh scatter signature of the fiber. Rayleigh scatter in optical fiber is caused by random fluctuations in the index profile along the fiber length that are the result of minor imperfections in the fiber manufacturing process.
  • the scatter amplitude as a function of distance is a random but static property of that fiber and can be modeled as a long, weak fiber Bragg grating with a random period. Changes in the local period of the Rayleigh scatter caused by an external stimulus (like strain) in turn cause changes in the locally reflected spectrum. This spectral shift can then be calibrated to form a distributed strain sensor.
  • the Rayleigh scatter is interrogated similarly to Bragg gratings in that the complex reflection coefficient of a fiber as a function of wavelength is first obtained.
  • the Rayleigh scatter as a function of length is obtained via the Fourier transform.
  • a sensor is formed by first measuring and storing the Rayleigh scatter signature or profile of the fiber at a baseline state.
  • the scatter profile is then measured when the fiber is in a perturbed state.
  • the scatter profiles from the two data sets are then compared along the entire fiber length in increments of Ax .
  • Each incremental fiber core segment represents a discrete sensing element, and can be considered a strain sensor.
  • the reflected spectrum from that segment shifts proportionally.
  • a complex cross-correlation is performed between reference data and measurement data for each fiber segment. Any change in strain manifests as a shift in the correlation peak. Therefore, to make a distributed strain measurement one simply measures the shift in the cross- correlation peak for each segment along the fiber.
  • Using Rayleigh scatter as a sensing mechanism has advantages. For example, not requiring Bragg gratings greatly reduces cost and increases availability of fiber. Also, the continuous nature of the Rayleigh scatter can improve spatial resolution in some cases by providing strain information at every location in the core. A further advantage with using Rayleigh scatter is that the fiber can be interrogated by a laser at any wavelength, and not necessarily one centered on the wavelength that a Bragg grating happens to be written at. Rayleigh scatter also provides an unambiguous identification of each segment of fiber. In cases where long lengths (e.g., long is only a few meters) of fiber must be measured, multipath reflections in even very weak Bragg gratings can corrupt the strain measurements at distant locations in the fiber.
  • the multi-core optical fiber 20 is coupled to single core optical fibers 55, 57 through a coupling device 25.
  • FIG. 3 and 4 shows an embodiment of the invention where three single core optical fibers 55, 57, 59 are coupled to the multi-core optical fiber 20 through a coupling device 25.
  • the broadband reference reflector 60 has a broadband reference reflector 60 positioned in relation to each strain sensor (again the scatter pattern of a segment of a fiber core corresponds to a strain sensor) to establish an optical path length for each reflector/strain sensor relationship. Nevertheless, the broadband reference reflector is optional and may be replaced with an internal reference path length.
  • An optical frequency domain reflectometer establishes a reference path.
  • the optical frequency domain reflectometer 70 is coupled to the multi-core optical fiber 20 through the single core optical fibers 55, 57, 59 so that the frequency domain reflectometer 70 can receive signals from the fiber strain sensors.
  • One example frequency domain reflectometer is the Luna Distributed Sensing System and is commercially available from Luna Innovations Incorporated.
  • Another example of a commercially available OFDR system is the Optical Backscatter Reflectometer, also available from Luna Innovations.
  • FIGS. 5 and 6 depict an alternative non-limiting example embodiment where the optical fiber includes is at least two single core optical fibers and, preferably, three single core optical fibers 100, 110, 115.
  • the fiber cores are non-coplanar and preferably form a triangular shape.
  • the triangular shape can be such that each fiber core has a center, and each center is 120° with respect to each of the other two core centers. The 120° relationship helps to reduce distortions.
  • the fiber cores are spaced apart such that mode coupling between the fiber cores is reduced and preferably minimized.
  • multiple of Bragg gratings 50 are disposed within each fiber core.
  • the intrinsic Rayleigh scatter of the fiber core is the sensing mechanism.
  • an optional broadband reference reflector 60 is used to establish an optical path length for each reflector/strain sensor relationship.
  • a frequency domain reflectometer 70 is coupled to transmit light to and receive reflected light from the single core optical fibers.
  • the fiber optic position and shape sensing device 10 has a computer 90 coupled to the frequency domain reflectometer 70. It is understood that the optical arrangement shown in FIGS. 7 and 8 is not limited to those devices employing multi-core optical fibers but that it may be used in combination with those devices employing single core optical fibers as well.
  • the computer 90 correlates the signals received from the frequency domain reflectometer 70 to strain measurements. These strain measurements are correlated into local bend measurements. A local bend measurement is defined as the bend between a reference strain sensor and the next set of strain sensors along the fiber. The local bend measurements are integrated into a position or shape. If the optical fiber has only two cores, then shape determination is limited to two dimensions, if there are three or more cores, three dimensional shape is determined, and in both instances, position is determined.
  • the technology effectively determines the shape of an object by measuring the shape of the optical fiber.
  • objects include but are not limited to: a position tracking device, such as a robot, and flexible objects such as medical instruments or flexible structures. Based on these measurements, relative position of a portion of the object is also ascertainable.
  • shape sensing is accomplished using multiple Rayleigh scatter patterns associated with fiber core segments located near the shape of to be sensed. Assuming each sensor segment is sufficiently small to achieve the desired spatial resolution, by detecting a curvature of the object at each individual sensor segment, the overall shape is reconstructed through an integration process.
  • a measure of a 3-dimensional "vector" strain is required.
  • Three or more cores are used, with each core containing multiple strain sensors (preferably one hundred (100) or more).
  • each sensor is collocated in the axial dimension.
  • Three optical fiber cores are fixed together such that their centers are non-coplanar.
  • the core centers are each 120° with respect to each of the other two core centers and form a triangular shape. Any number of optical fiber cores greater than three can also be used for three dimensional bend sensing.
  • the separate cores of the optical fiber are embedded into a monolithic structure.
  • the differential strain between the cores is used to calculate curvature along the length of the fiber. Based on the curvature of the fiber at individual sensing points, the overall shape of the fiber or at least a portion of the fiber may be reconstructed, presuming that each individual strain sensing point is sufficiently small.
  • the fiber may be physically associated with an object, e.g., it can be inserted into, affixed to, aligned with, conformed to or otherwise follow the object. Strain values for each segment of a fiber physically associated with an object whose shape and/or position is(are) to be determined are used to compute a bend angle and bend radius for multiple fiber segments associated with at least a portion of the object shape and/or position is(are) to be determined. Starting from the beginning of the object (although not necessary), this data is used to compute the location of the next sensing triplet along the object and to define a new local coordinate system. An algorithm implemented on a computer interpolates circular arcs between each sensing triplet along the fiber in the region of interest.
  • the geometry of the entire object may be determined by repeating the process for each sensing triplet along the length of the object. Since the fiber Bragg gratings or Rayleigh scatter pattern segments in each sensing fiber are collocated, a triplet of strain values at evenly-spaced segments along the object exists.
  • a local coordinate system (x', y', z') is defined called the sensor frame. This coordinate system has its origin at the center of the object's perimeter for any given sensing triplet.
  • the z' axis points in the direction of the object, and the y' axis intersects with fiber 1. See FIG. 9 (the right part of the figure is an illustration of the fiber in a coordinate system).
  • each core is generally a different distance ⁇ r h r 2 , r 3 ) from the center of curvature, as shown in FIG. 11. Because all of the core segments subtend the same curvature angle, ⁇ , each segment must have a different length.
  • the change in length due to bending the fiber is denoted as ds ⁇ , ds 2 and ds 3 as shown in FIG. 11.
  • Equation 3 In order to solve Equation 3 for r and a, r u r 2 , and r 3 need to be written in terms of r and a. This can be done by analyzing the geometry of the fiber cross-section (FIG. 12) and results in the following expressions for the radii of curvature for each of the fiber cores:
  • Equation 4 Using Equations 4 to make substitutions in Equation 3 the following three equations are derived for r and a. These equations are:
  • Equation 7 It is clear from Equation 7 that the bend angle, a, is dependent only on the differential strains, not the absolute strain values.
  • the bend radius r can be computed in three different ways. Each of these formulae give the same solution for r, but it is useful during implementation to have at least two handy in case one of the differential strains (defined in Equation 6) turns out to be zero.
  • Equation 7 shows that - ⁇ /2 ⁇ a ⁇ /2.
  • the extra ⁇ radians appear in the r calculation. That is, if r is negative, simply negate r and add ⁇ to a. After this operation, r > 0 and o ⁇ a ⁇ 2 ⁇ .
  • the optical fiber includes three single core optical fibers. Shape sensors were surface attached to the outside of an inflatable isogrid boom that was approximately 1.2 m in length.
  • the fiber optic sensor arrays each containing approximately 120 sensors with a 0.5 cm gauge length spaced at 1 cm intervals, center-to-center, ran along the entire axial length of the boom oriented 120° with respect to each other.
  • the boom was fixed at one end while the other end was unattached in a classic cantilever beam set-up.
  • Various weights were then placed on the free-floating end while strain measurements were taken to monitor the dynamic shape of the structure.
  • a standard height gauge was used to directly measure the deflection of the end of the boom for the purposes of data correlation.
  • the height gauge indicated a deflection of 1.7 mm while the fiber optic shape sensors indicated a deflection of 1.76 mm; with a mass of 4 kg suspended from the end, the height gauge indicated a deflection of 2.7 mm while the fiber optic shape sensors indicated a deflection of 2.76 mm.
  • An isogrid boom was fixed at one end while the other end was unattached in a classic cantilever beam set-up.
  • Various weights were then placed on the free-floating end while measurements were taken to monitor the shape/relative position of the structure using the fiber optic position and shape sensing device of the present invention.
  • Laser displacement sensors at four locations were suspended above the boom to directly measure the deflection of the boom for the purposes of data correlation.
  • Table 1 shows the percent error between the laser displacement sensors and fiber optic shape sensors. This data is depicted graphically in FIG. 13.
  • An oscillator (LDS v-203 electrodynamic shaker) driven by a function generator and amplified by a power amplifier was attached to the free end of an isogrid boom which was attached in a classic cantilever beam configuration.
  • a sinusoidal signal was used to drive the shaker with a displacement amplitude of roughly 1.6 mm, peak-to-peak (0.566 RMS) and frequencies of 0.5 and 1.0 Hz.
  • the fiber optic position and shape sensing device of the present invention was attached to the isogrid boom and was used to capture dynamic shape data at roughly 2.189 Hz. Using the dynamic shape data captured by the sensing device while the beam was oscillating, modal analysis was performed. Approximately 2853 samples were taken at the 0.5 Hz oscillation mode.
  • the frequency of oscillation was pinpointed to within roughly ⁇ 0.0004 Hz.
  • the 1.0 Hz oscillation mode was sampled 240 times, yielding an accuracy of approximately ⁇ 0.0046 Hz.
  • the results of this test show that the fiber optic position and shape sensing device is useful to characterize the dynamic performance of a mechanical structure.
  • a series of shape measurements of a 3 m long vertically suspended isogrid boom were performed.
  • the fiber optic position and shape sensing device containing approximately 300 fiber Bragg grating sensors in each of 3 cores with a 0.5 cm gauge length spaced at 1 cm intervals, center-to-center, were positioned along the outside surface of the boom along the entire axial length oriented 120° with respect to each other.
  • the measurements included cantilever bending, axial loading, and dynamic bending (approximately 5 Hz). Comparisons were made with a deflection gauge and were found to correlate to within ⁇ 0.5 mm over the full length of the isogrid boom.
  • the fiber optic position and/or shape sensing device is useful for providing practical shape and/or relative position sensing over extended lengths.
  • the combination of high spatial resolution achieved through multiple strain measurements of the fiber obtained from corresponding Rayleigh backscatter measurements coupled with non-rigid attachment to the object enables higher accuracy than systems described in the background.
  • systems using wave division multiplexing coupled with fiber Bragg gratings are limited in range or have the inability to achieve high spatial resolution.
  • Systems where cross-talk or mode coupling occurs between the fiber cores are difficult to implement because such arrangements are subject to measurement distortions.
  • models required of the mechanical behavior of the object in order to determine the position or shape of the object are required to determine the position or shape of the object.
  • Rayleigh-based sensing adds significant advantage in terms of the availability and cost of multi-core fiber. It also dispenses with the necessity to match the laser scanning wavelength range with the gratings that are written into the fiber. Moreover, with Rayleigh scatter-based sensing, every location along the fiber is a sensing region.
  • the fiber optic position and/or shape sensing device has many applications, a few example of which are identified below. It may be used to monitor true deflection of critical structures as well as the shape of structures.
  • the sensing device serves as a feedback mechanism in a control system.
  • the device is suitable for use as a monitor for the relative position of an object attached to it.
  • Another application is to attach the device to a search and rescue robot in places where global positioning system (GPS) either possesses insufficient resolution or is unavailable.
  • GPS global positioning system
  • the device may be attached to a floating buoy deployed by a ship to make differential GPS measurements.
  • the device may be used for performing modal analysis of mechanical structures.
  • the device is also suitable for medical applications such as minimally invasive surgical techniques as well as biometric monitoring. For example, the shape or position of medical devices or instruments such as catheters and colonoscopes could be determined with sufficient precision as to yield useful information to an end-user or to a control system.
  • FIG. 14 is a schematic representation of non-limiting example medical applications for the optical technology described in this application.
  • An OFDR 70 is coupled to a computer 90 to display various information related to strain, position, and/or shape of a desired portion of one or more optical fibers associated with one or more medical instruments.
  • Example medical instruments illustrated include a precision, robotically-driven manipulator tool 200, a flexible catheter 202, a segmented, robotically-driven scope or probe 204, and a manually-driven scope 206 such as a colonoscope.
  • Each medical instrument 200, 202, 204, and 206 is physically associated in some fashion with an optical fiber that is coupled to the OFDR 70.
  • each optical fiber may be disposed in, affixed to, coupled with, or conforming to at least a portion of the elongate body of its medical instrument.
  • Other physical associations are possible to permit the optical fiber to determine a position and/or shape of a portion of the instrument. Knowing the position and/or shape of a portion of the medical instrument can be very valuable in medical procedures.
  • the OFDR 70 obtains a Rayleigh scatter pattern associated with each of multiple fiber segments (from each core if the fiber includes multiple cores) and using the Rayleigh scatter patterns to determine a strain parameter of each of the multiple fiber segments.
  • a position and/or shape of the object is determined by the computer 90 based on the determined strain parameters.
  • the computer 90 in one example implementation, translates the strain parameters to local bend measurements corresponding to a bend in the object and integrates the local bend measurements to determine the position or shape of the object at the bend.

Abstract

L'invention concerne un dispositif de détection de position et/ou de forme de fibre optique comprenant une fibre optique formée d'au moins deux fibres optiques à cœur unique ou d'une fibre optique à cœurs multiples munie d'au moins deux cœurs de fibre. Dans l'un ou l'autre cas, les cœurs de fibre sont espacés de façon à réduire ou rendre minime le couplage de mode entre les cœurs de fibre. La fibre optique est physiquement associée à un objet. Une contrainte exercée sur au moins une partie de la fibre optique à l'endroit où elle est associée à l'objet est déterminée par une OFDR en exécutant un ou plusieurs motifs de diffusion de Rayleigh pour cette partie de la fibre optique. La contrainte déterminée est utilisée pour déterminer la position et/ou la forme de l'objet.
PCT/US2008/003236 2007-03-16 2008-03-12 Détection de la position et/ou de la forme d'une fibre optique à partir d'une diffusion de rayleigh WO2008115375A1 (fr)

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US8760639B2 (en) 2009-07-23 2014-06-24 Fotech Solutions Limited Distributed optical fibre sensing
US8520197B2 (en) 2009-07-23 2013-08-27 Fotech Solutions Limited Distributed optical fibre sensing
CN102883655A (zh) * 2010-05-07 2013-01-16 皇家飞利浦电子股份有限公司 医学成像系统中的运动补偿和患者反馈
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ITRM20100333A1 (it) * 2010-06-18 2011-12-19 Del Marmo Paolo Persi Sistema per misurare e monitorare la deformazione di oggetti sollecitati da forze esterne .
JP2013542768A (ja) * 2010-10-08 2013-11-28 コーニンクレッカ フィリップス エヌ ヴェ 動的な器具追跡のための一体化されたセンサを持つ柔軟な綱
WO2012101555A1 (fr) * 2011-01-27 2012-08-02 Koninklijke Philips Electronics N.V. Stockage et récupération d'informations spécifiques à un dispositif de détection de forme
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WO2012131550A1 (fr) * 2011-03-31 2012-10-04 Koninklijke Philips Electronics N.V. Procédure médicale assistée par détection de forme
US11064955B2 (en) 2011-03-31 2021-07-20 Koninklijke Philips N.V. Shape sensing assisted medical procedure
US11395702B2 (en) 2013-09-06 2022-07-26 Koninklijke Philips N.V. Navigation system
CN106535809A (zh) * 2014-05-30 2017-03-22 约翰霍普金斯大学 多力感测仪器和机器人外科手术系统的使用方法
CN106535809B (zh) * 2014-05-30 2020-03-03 约翰霍普金斯大学 多力感测仪器和机器人外科手术系统的使用方法
CN108700435A (zh) * 2016-03-11 2018-10-23 光纳株式会社 瑞利测定系统及瑞利测定方法
US11125648B2 (en) 2019-06-07 2021-09-21 Exfo Inc. Duplicate OTDR measurement detection
US11650128B2 (en) 2020-06-30 2023-05-16 Exfo Inc. Optical fiber recognition using backscattering pattern
US11879802B2 (en) 2020-10-22 2024-01-23 Exfo Inc. Testing optical fiber link continuity using OTDR backscattering patterns

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