WO2014072845A1 - Système de réflectométrie en domaine de fréquences optiques (ofdr) ayant de multiples fibres par chaîne de détection - Google Patents

Système de réflectométrie en domaine de fréquences optiques (ofdr) ayant de multiples fibres par chaîne de détection Download PDF

Info

Publication number
WO2014072845A1
WO2014072845A1 PCT/IB2013/058445 IB2013058445W WO2014072845A1 WO 2014072845 A1 WO2014072845 A1 WO 2014072845A1 IB 2013058445 W IB2013058445 W IB 2013058445W WO 2014072845 A1 WO2014072845 A1 WO 2014072845A1
Authority
WO
WIPO (PCT)
Prior art keywords
optical
measurement paths
sensing
frequency domain
fiber
Prior art date
Application number
PCT/IB2013/058445
Other languages
English (en)
Inventor
Jeroen Jan Lambertus Horikx
Gert Wim 't Hooft
Milan Jan Henri MARELL
Merel Danielle Leistikow
Jinfeng Huang
Eibert Gerjan VAN PUTTEN
Original Assignee
Koninklijke Philips N.V.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Koninklijke Philips N.V. filed Critical Koninklijke Philips N.V.
Publication of WO2014072845A1 publication Critical patent/WO2014072845A1/fr

Links

Classifications

    • 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
    • G01M11/30—Testing of optical devices, constituted by fibre optics or optical waveguides
    • G01M11/31—Testing of optical devices, constituted by fibre optics or optical waveguides with a light emitter and a light receiver being disposed at the same side of a fibre or waveguide end-face, e.g. reflectometers
    • G01M11/3172—Reflectometers detecting the back-scattered light in the frequency-domain, e.g. OFDR, FMCW, heterodyne detection
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
    • G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
    • G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
    • G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
    • G01D5/35338—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using other arrangements than interferometer arrangements
    • G01D5/35354—Sensor working in reflection
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
    • G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
    • G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
    • G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
    • G01D5/35383—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using multiple sensor devices using multiplexing techniques

Definitions

  • the present invention relates to systems for optical analysis, more particularly the present invention relates to an optical frequency domain reflectometry (OFDR) system and a method for obtaining optical frequency domain reflectometry data.
  • OFDR optical frequency domain reflectometry
  • Optical Frequency Domain Reflectometry In Optical Frequency Domain Reflectometry (OFDR), light from a tunable laser source is coupled into a measurement fiber, or more generally, a device under testing (DUT), and the reflected or backscattered light is made to interfere with light from the same source that has travelled along a reference path yielding information about the fiber, or the DUT.
  • OFDR Optical Frequency Domain Reflectometry
  • the interference between the light that is coming from a single fixed scattering point on the measurement fiber and the reference light creates a detector signal that has a constant frequency, this frequency being proportional to the difference of the travel time of the light along the measurement path and the reference path.
  • the position of the scattering point can be computed from the observed frequency.
  • the detector signal When multiple scatterers are present in the measurement fiber, the detector signal will be a superposition of different frequencies, each frequency indicative of the position of the respective scatterer.
  • a Fourier transform of the detector signal (a 'scattering profile') can be computed; in graphs of the amplitude and phase of the transformed signal, the amplitude and phase of the different frequencies that are present in the detector signal (which correspond to different scatterer positions) will be shown at their respective positions along the horizontal axis of the graph.
  • the amplitude and phase of the scattered light can be affected by external influences acting on the fiber.
  • external influences acting on the fiber E.g., when the fiber is deformed by external stresses, or when the temperature of the fiber is modified, effects will be seen on the phase and/or amplitude of the scattering profile.
  • a separate interferometer is created for every sensing fiber.
  • Each sensing fiber has its own measurement path (or arm), its own reference (or arm), its own beam combiner and its own detection chain, detector electronics, and one digital acquisition channel per detector.
  • OFDR systems capable of using polarization diversity are normal.
  • a detection chain comprises two detectors attached to a polarizing beam splitter, and a polarization controller for balancing the light from the reference arm on the two detectors.
  • OFDR Optical Frequency Domain Reflectometry
  • the invention provides an OFDR system comprising:
  • an optical radiation source capable of emitting optical radiation within a certain wavelength band
  • CP1 a first coupling point arranged for splitting the radiation from the optical radiation source (LS),
  • CP2 a second coupling point
  • ODU optical detection unit
  • the plurality of measurement paths have different optical path lengths, so as to allow the optical detection unit (ODU) to essentially uncorruptedly detect optical radiation from parts of the respective optical sensing fibers that are intended to have a sensory function.
  • ODU optical detection unit
  • multiple optical sensing fibers share a reference path (or reference arm), and in some embodiments, it is possibly also to share one beam combiner. Consequently, one single optical detection unit can serve more than one sensing fiber. This is obtained by different optical path length for the measurement paths (or measurement arms) to which sensing fibers are connected, and in such a manner that data corruption by overlap in the scattering profile can be prevented or at least reduced to an acceptable degree. This can be done by selection of optical properties of the respective measurement paths so as to ensure that they exhibit optical path lengths which are different to allow the optical detection unit to discriminate the respective reflected radiation parts from the sensing fibers, and/or by proper signal processing on the data provided by the optical detection unit. In some cases a partial overlap can be acceptable, while in other cases the optical lengths of the measurement paths are selected to differ so as to allow non-overlapping optical radiation parts from the relevant parts of radiation from all the connected sensing fibers.
  • the different optical path lengths result in a relative offset of the frequencies of the detector signal components that result from the respective reflected radiation parts from the sensing fibers.
  • the discrimination occurs because they end up at different positions in the Fourier transform, which separates different frequencies.
  • the underlying reason that a scatterer causes a signal component with a certain frequency is that the travel time of the light that reaches the detector via the scatterer and the travel time of the light that reaches the detector via the reference path are different, so that they correspond to different laser frequencies, as the laser is scanning.
  • the difference in laser frequency which is the frequency of the detector signal, is proportional to this travel time difference, and can thus be manipulated by changing the optical path lengths of the measurement paths.
  • a typical scan duration is of the order of tens of milliseconds, while preferred changes of the travel time differences or delays of the measurement path lengths are of the order of tens of nanoseconds, for example a difference of travel time difference within 5-100 ns, or within 10-80 ns, or within 20-60 ns.
  • Embodiments of the invention for demanding applications of distributed optical sensing using OFDR typically use polarization diversity as this provides the highest precision.
  • polarization diversity is not essential to the invention, since the invention also works in embodiments without polarization-diverse measurements.
  • the plurality of measurement paths have different optical properties selected so as to provide optical path lengths which differ so as to allow the optical detection unit (ODU) to detect non-overlapping optical radiation from said parts of the respective optical sensing fibers that are intended to have a sensory function.
  • ODU optical detection unit
  • an overlap may be acceptable, which will be explained in the following.
  • a separate optical circulator is connected in each of at least two of the plurality of measurement paths between the first coupling point (CP1) and sensing fibers connected to the respective measurement paths.
  • each of the plurality of sensing fibers is connected to the second coupling point (CP2) via respective separate optical circulators.
  • each of the plurality of measurement paths is connected to the first coupling point (CP1) via respective separate optical circulators.
  • At least two sensing fibers are connected to the first coupling point (CP1) via one common optical circulator.
  • at least two sensing fibers may be connected to the common optical circulator via an optical splitter.
  • At least one of the plurality of measurement paths has a delay fiber inserted, so as to influence its optical path length.
  • a plurality of measurement paths have different delay fibers with providing different delays.
  • At least two of the plurality of measurement paths have different physical path lengths serving to provide different optical path lengths.
  • three or more measurement paths have different physical path lengths serving to provide different optical path lengths.
  • At least two of the plurality of measurement paths have different optical properties serving to provide different optical path lengths, e.g. different refraction index values.
  • three or more measurement paths have different optical properties, e.g. refraction index values, serving to provide different optical path lengths.
  • at least two of the plurality of measurement paths have different optical path lengths by means of a combination of different physical path lengths and different optical properties.
  • the OFDR system may comprise a plurality of sensing fibers connected to respective ones of the plurality of measurement paths.
  • the plurality of sensing fibers are arranged within a sensing probe or catheter, so as to allow sensing of a shape of the sensing probe.
  • the optical radiation source may comprise a laser source arranged for scanning over a wavelength range, e.g. scanning over a small wavelength range within the range 320-2200 nm which is the range over which quartz-based optical fibers could transmit, as a specific example of a scanning wavelength range is 1530-1550 nm.
  • a laser source arranged for scanning over a wavelength range, e.g. scanning over a small wavelength range within the range 320-2200 nm which is the range over which quartz-based optical fibers could transmit, as a specific example of a scanning wavelength range is 1530-1550 nm.
  • the OFDR system comprises a control system arranged to control the scanning wavelength of the laser source.
  • the detection unit is arranged for polarization-diverse detection of the combined optical radiation from the reference path and the plurality of measurement paths.
  • the optical detection unit may comprise a polarizing beam splitter (PBS) connected to two detectors (Dl, D2) serving to detect radiation of respective different polarization.
  • PBS polarizing beam splitter
  • a polarization controller is arranged between the optical radiation source and the first coupling point.
  • the OFDR system is based on a transmissive interferometer (a Mach-Zender interferometer).
  • a scan of the said wavelength band of the radiation source may be considered to include, but not limited to, a substantially continuous variation of the wavelength in an appropriate interval, e.g. within a wavelength of 1530-1550 nm.
  • a scan may also be considered as a relatively large number of wavelengths, preferably homogeneously distributed, measured in a fixed order, typically from one end to the other of the interval.
  • an optical circulator is a non-reversible optical component, where radiation, or light, entering from a first port, exits from a second port and then, upon reentering the optical circulator via the second port, the radiation exits the optical circulator from a third port thereby causing separation between radiation entering the first port and exiting the third port. It would be appreciated by the skilled person in optics that various suitable optical circulators may be applied in the context of the present invention.
  • optical path length may be considered to be the product of the geometric length and the index of refraction of the medium through which the radiation, or light, is propagating.
  • Optical path length is important because it determines the phase of the light and governs interference and diffraction of light as it propagates.
  • the polarization e.g. the first and second polarization
  • the polarization may be linearly, circularly or elliptically polarized depending on the circumstances and the application of the invention.
  • the 'coupling point' is understood an optical coupling point of two or more optical paths, e.g. in the form of an optical combiner or optical splitter.
  • the coupling point serves to combine or split incoming optical radiation from one or more incoming optical paths into one or more outgoing optical paths.
  • the present invention may facilitate a broad spectrum of use.
  • the invention is applicable in all fields where distributed sensing using the method of OFDR can be used. Properties that can be measured with this technique are, e.g., strain and temperature.
  • a field of particular interest might be the simultaneous measurement of strain in cores of a helical multi-core fiber, for the purpose of shape-sensing, in particular for medical applications.
  • the measurement branch of the OFDR system may also find application in other areas of optics, e.g. telecommunication, where such detection and analysis is required.
  • the OFDR system comprises optical sensing fibers connected to respective plurality of measurement paths, the optical sensing fibers being arranged for providing reflections for OFDR along a sensing length (l s ) of the optical sensing fiber.
  • the optical sensing fibers are arranged within a probe or catheter.
  • one or more optical sensing fibers may be placed centrally.
  • one or more optical sensing fibers may be placed peripherally, such as being helically arranged.
  • the optical sensing fibers preferably include spatially distributed optical elements, such as Fiber Bragg Gratings or other types of optical elements such as known to the skilled person.
  • one central optical sensing fiber and one or more, such as three, peripheral optical sensing fibers, such as the one or more peripheral optical sensing fibers being helically arranged.
  • one optical sensing fiber may have a plurality of optical cores being arranged for e.g. shape-sensing.
  • the OFDR system may comprise a catheter or probe with the plurality of optical sensing fibers arranged therein and connected to respective measurement paths, and a signal processing system connected to receive the electrical signal generated by the optical detection unit.
  • the OFDR system may be or may form part of a medical device or system.
  • the OFDR system comprises a plurality of sub systems according to the first aspect, wherein each sub system comprises a plurality of measurement paths connected to a common reference path and an optical detector unit. It is to be understood, that one or more OFDR systems according to the first aspect of the invention, serving to operate a plurality of optical sensing fibers, may be used also together with prior art OFDR systems that serve to operate other optical sensing fiber(s).
  • the invention provides a method for obtaining optical frequency domain reflectometry (OFDR) data, the method comprising:
  • the OFDR system and method of the first and second aspects may be used in a medical application, such as used for medical scanning or medical diagnosis purposes.
  • FIG. 1 shows a schematic embodiment of a prior art OFDR system with separate measurement paths and reference paths and detection units for each sensing fiber
  • FIG. 2 shows a schematic embodiment of an OFDR system suitable for multiple sensing fibers according to the present invention
  • FIG. 3 shows a prior art single sensing fiber polarization diverse OFDR system to explain the principle of polarization diversity
  • FIG. 4 shows a schematic embodiment with two sensing fibers connected via separate optical circulators
  • FIG. 5 shows a diagram of the scattering profile of a sensing fiber with length l s , connected to an optical circulator via a connecting fiber with length l c ,
  • FIG. 6 shows a diagram of the scattering profile for the embodiment of FIG. 4
  • FIG. 7 shows a schematic embodiment where two sensing fibers are connected via one single optical circulator and an optical splitter
  • FIG. 8 shows a diagram of the scattering profile for the embodiment of FIG. 7,
  • FIG. 9a and 9b show examples of amplitude versus fiber index spectra based on Fourier transforms of detector signals obtained from the embodiment of FIG. 7,
  • FIG. 10 shows a generalization to N sensing fibers of the embodiment of FIG.
  • FIG. 11 shows a variant of the embodiment of FIG. 10 for connecting N sensing fibers
  • FIG. 12 shows a generalization to N sensing fibers of the embodiment of FIG.
  • FIG. 13 shows a flow chart of a method according to the present invention.
  • FIG. 1 shows an example of a prior art OFDR system, where two optical sensing fibers SF1, SF2 are connected to a laser source LS via respective measurement paths MP1, MP2 and connected to respective reference paths RFP1, RFP2.
  • two detection system with respective detectors Dl, D2 and polarization beam splitters PBS are required, thereby also requiring an analyzing or processing system equipped to analyze the outputs from the total of four detectors Dl, D2.
  • all elements within the dashed boxes need to be copied, thus resulting in two detector signals for each sensing fiber which needs to be analyzed.
  • FIG. 2 shows a schematic embodiment of the invention, serving to illustrate the principle of the invention.
  • An optical radiation source in the form of a scanning laser LS, e.g. capable of being scanned over the wavelength range 1530-1550 nm.
  • the laser LS is connected to a first coupling point CPl, e.g. an optical splitter, where the optical radiation is split to a plurality of measurement paths, here three measurement paths MP1, MP2, MP3 are illustrated and connected to respective optical sensing fibers SF1, SF2, SF3.
  • a reference path RFP is connected to receive optical radiation from the first coupling point CPl .
  • the sensing fibers SF1, SF2, SF3 are illustrated here as arranged within a probe or catheter PR, such as an optical shape sensing probe or catheter.
  • Optical radiation reflected parts from the sensing fibers SF1, SF2, SF3 and measurement paths MP1, MP2, MP3 as well as from reference path RFP are received at a second coupling point CP2, and an optical detection unit ODU is connected to this second coupling point CP2 to receive the combined optical radiation from all measurement paths MP1, MP2, MP3 and the reference path RFP, and to convert them to one or more electrical signals E, e.g. digital electrical signals representing the detected combined optical radiation.
  • the further signal processing equipment required to process the output E from the optical detection unit ODU is not shown, but it is outside the focus of the present invention.
  • Each measurement path MP1, MP2, MP3 has an optical path length LI, L2, L3 associated thereto, and according to the invention these optical path lengths LI, L2, L3 are selected to be different, so as to allow the optical detection unit ODU to discriminate.
  • the goal of providing different optical path lengths LI, L2, L3 can be achieved in different ways, e.g. introducing optical delays, different physical path lengths, or introducing in general an optical element which serves the to introduce an optical path length difference in one or more of the measurement paths MP1, MP2, MP3.
  • the principle behind polarization diverse measurement using an OFDR system will be explained in spite of the fact that this is not essential to the invention, however the specific embodiments of the invention described later use this principle.
  • the detector signal When multiple scatterers are present in the measurement fiber, the detector signal will be a superposition of different frequencies, each frequency indicative of the position of the respective scatterer.
  • a Fourier transform of the detector signal (a 'scattering profile') can be computed; in graphs of the amplitude and phase of the transformed signal, the amplitude and phase of the different frequencies that are present in the detector signal (which correspond to different scatterer positions) will be shown at their respective positions along the horizontal axis of the graph.
  • the amplitude and phase of the scattered light can be affected by external influences acting on the fiber.
  • external influences acting on the fiber E.g., when the fiber is deformed by external stresses, or when the temperature of the fiber is modified, effects will be seen on the phase and/or amplitude of the scattering profile.
  • a known solution to this problem of 'polarization fading' is polarization-diverse detection, usually in the embodiment of a polarizing beam splitter (PBS) with separate detectors for the two polarization states transmitted by the PBS.
  • PBS polarizing beam splitter
  • the refractive index depends on the state of polarization of the light. Consequently, the phases of the Fourier transforms of the detector signals in a polarization-diverse measurement will vary upon modification of the input polarization state of the light that is sent into the measurement fiber.
  • two measurements need to be performed; for the second measurement the input polarization state of the light sent to the fiber is made orthogonal to the polarization state used in the first measurement. In this manner, four detector signals are obtained (two detector signals for each of two input polarization states).
  • a single effective scattering profile may be computed that, when compared to the effective scattering profile of the reference state, provides the desired information about the external influences on the fiber as a function of position. See, e.g., patent application US2011/0109898 Al .
  • Fig. 3 illustrates a prior art OFDR system with one single sensing fiber SF for distributed sensing, and capable of performing the measurements described in the above sections.
  • a tunable laser is connected to an interferometer via a polarization controller pc thus introducing two polarizations PLl, PL2.
  • a splitter distributes the light over the reference path RFP and the measurement path MP of the interferometer.
  • An optical circulator C is used to attach the sensing fiber to the measurement arm.
  • the light from the reference path RFP and the measurement path MP is combined and sent to a polarization-diverse detection system consisting of a polarizing beam splitter PBS and two detectors Dl, D2.
  • a fraction of the laser light is sent to a wavelength reference cell HCN, filled with a gas, e.g. HCN gas, that contains absorption lines with very well-known wavelengths in the range over which the laser LS is scanned.
  • a gas e.g. HCN gas
  • Part of the laser light is also sent to an auxiliary interferometer AUX, which generates a signal that is used to linearize the scan. All detector signals are digitized by a signal acquisition system; the digitized signals are sent to a computer for further processing.
  • Scan linearization is required to ensure a one-to-one correspondence between scatterer position on the fiber and frequency of the detector signal.
  • Linearization can be done in one of several ways.
  • the signal from the auxiliary interferometer AUX can be used to make the laser frequency depend linearly on time, by means of a feedback loop.
  • Another possibility is to use the signal from the auxiliary interferometer AUX to define the sampling moments of the signal acquisition system.
  • all detector signals can be sampled at a constant rate, but the digitized signal from the auxiliary interferometer AUX is used as input to a resampling algorithm that computes interpolated signals corresponding to a precisely linear scan.
  • the polarization controller pc is used to create a first polarization state PL1 that balances the amount of light from the reference path on the two detectors Dl and D2.
  • the laser LS is then scanned over a wavelength range that is slightly larger than the desired range, and all detector signals are digitized and stored. Then, the polarization is changed to a second state PL2 that is orthogonal to the first state PL1. Again, the laser LS is scanned and the detector signals are digitized and stored. For each scan separately, all data are linearized; the co-linearized wavelength calibration signal is then used to select the sub-ranges of sampled signals that correspond to the desired wavelength interval.
  • the selected signal sub-ranges of Dl and D2 for the first and second polarization state are then Fourier transformed using an implementation of the Discrete Fourier Transform (e.g. a Fast Fourier Transform, FFT), and from these four scattering profiles a single effective scattering profile is computed.
  • FFT Fast Fourier Transform
  • the output of the Discrete Fourier Transform is in the form of discrete bins, which can be referred to by their index number.
  • DFT Discrete Fourier Transform
  • n is the group index in the interferometer
  • c is the center of the desired wavelength range of the laser scan and ⁇ the desired range.
  • the optical path length difference equals n-Al.
  • a section of fiber containing Fiber Bragg Gratings that is 2 to 4 meters distant from the point on the sensing fiber for which the length of the measurement arm is equal to the length of the reference arm will then correspond to a fiber index range of approximately 50000-100000.
  • the time-sampled data used to compute the scattering spectrum may be linearized using a relatively simple, but therefore fast, interpolation algorithm. To keep the interpolation error small the samples need to be close together, resulting in a relatively large number of sampling points. In an example: one million points may be present in the desired wavelength range, and thus in the result of the Discrete Fourier Transform.
  • Discrete Fourier Transforms of the measured detector signals are used to arrive at the scattering profile of the sensing fiber. Neighboring points of a Fourier transform correspond to points on the sensing fiber that are a distance Az apart, with Az given by Eq.(2).
  • the zero-frequency point of the computed Fourier transform (fiber- index equal to 0) corresponds to the (possibly virtual) point on the sensing fiber for which the lengths of the reference arm and the measurement arm of the interferometer are equal.
  • the maximum frequency corresponds to a (possibly virtual) point on the sensing fiber that is at a distance L from the zero-frequency point, with L given by
  • N/2+1 ... N-l The points with fiber indices in the range N/2+1 ... N-l correspond to negative frequencies.
  • FIG. 4 shows an OFDR system embodiment according to the invention that is capable of measuring two sensing fibers SF1, SF2 using a single reference path, a single polarization beam splitter PBS and detectors Dl, D2.
  • a separate optical circulator CI, C2 is used for each sensing fiber SF1, SF2.
  • the optical path length of the measurement path to which sensing fiber SF1 is attached is made to be different from the length of the measurement path to which sensing fiber SF2 is attached.
  • a delay dl is introduced in the measurement path for sensing fiber SF2 to provide this measurement path difference.
  • the reference path is common to both fibers SF1 , SF2.
  • the settings of the polarization controller pc required for balancing the amount of light from the reference path on the two detectors Dl and D2 need to be determined only once for the plurality of sensing fibers, limiting the complexity of the alignment procedure compared to prior art systems.
  • FIG. 5 illustrates backscattered light, amplitude 'a' and position 'p', from a sensing fiber SF of length l s which is attached to an optical circulator C of a measurement system via a connecting fiber CF of length l c .
  • Backscattered light from both the sensing fiber SF and the connecting fiber CF will reach the detectors, and will end up in the computed scattering profile.
  • No backscattered light will reach the detectors from (virtual) positions that lie before the circulator C or after the physical end of the sensing fiber SF.
  • the use of a circulator C to connect the sensing fiber SF to the measurement system ensures that the backscattered light from the connecting fiber CF and the sensing fiber SF occupies a space of limited extent in the scattering profile.
  • the zero-frequency point of the scattering profile corresponds to the (possibly virtual) point on the sensing fiber SF for which the optical lengths of the reference path and the measurement path of the interferometer are equal.
  • FIG. 5 schematically shows the contributions of the connecting fiber CF and the sensing fiber SF to the computed scattering profile for the case that the equal-length point lies at a distance lo to the left of the start of the connecting fiber CF.
  • the embodiment of FIG. 4 has measurement paths with different optical path lengths for the two sensing fibers SF1 , SF2. Consequently, the distance lo for sensing fiber SF1 is different from the distance lo for sensing fiber SF2.
  • the difference between these distances expressed in meters (i.e. physical length), is denoted ⁇ 12 in the following.
  • the optical path length difference equals « ⁇ 12 , where n is the refractive index of the fibers.
  • the difference in optical length between the two measurement paths (length of measurement path 2 minus length of measurement path 1) that is required to create this difference is equal to 2 « ⁇ 12 . If the refractive indices of the measurement paths and the fibers are all equal, the required difference between the physical lengths of the two measurement paths is equal to 2 ⁇ 12 . See Eq.(2) for the conversion factor between fiber index and position.
  • FIG. 6 including schematics (a), (b), and (c) will be described in the following.
  • the location of the start of the connecting fiber for sensing fiber 1 relative to the zero- frequency point for interferometer 1 will be denoted IQ.
  • the location of the start of the connecting fiber for sensing fiber 2 relative to the zero-frequency point for interferometer 2 will be equal to lo + ⁇ 12 .
  • interferometer 1 is the interferometer that consists of the combination of the measurement path to which sensing fiber 1 is attached and the common reference path
  • interferometer 2 is the combination of the measurement path to which sensing fiber 2 is attached and the same common reference path.
  • the magnitude of the shift ⁇ 12 should be chosen in such a manner that the data coming from neither sensing fiber is contaminated. At the very least, this implies that the sensing fiber data do not overlap in the scattering profile, giving rise to the condition
  • the data of sensing fiber 1 will have an overlap with the data of connecting fiber 2 in the scattering profile.
  • the scattered signal of a sensing fiber is much stronger than the Rayleigh scattering of a connecting fiber (e.g. when the sensing fiber contains FBGs) this overlap may be acceptable.
  • the connecting fiber data also contains spurious reflections from connectors, fiber splices etc. that are strong enough to contaminate overlapping sensing fiber data. In this case, or in the case that the signal of the sensing fiber and the connecting fiber are of comparable strength, it would be wise to increase the magnitude of the shift ⁇ 12 ⁇ a larger value, to prevent any overlap:
  • L is related to the number of points N in the Discrete
  • Eq.(5b) may also be viewed as a lower limit on the number of sampling points in the wavelength scan in order for the invention to work at all. In practice, a larger number of points will likely be used, e.g. in order to be able to apply a simple but fast algorithm for interpolatory
  • Equations 5(a) and 5(b) can be combined into a single equation: hl + hl ⁇ ll ⁇ L - (h +hl + hl) (5C)
  • the invention can also be made to work for the case that the reference path is longer than each of the measurement paths, in such a manner that the zero-frequency point lies beyond the end point of both sensing fibers. This case would amount to making l 0 sufficiently negative; the positive and negative frequency parts of the sensing fiber data would then trade places and would appear reversed in position.
  • the shift ⁇ 12 can be made negative in such a manner that for all points on sensing fiber 1 the measurement path is longer than the reference path, while for all points on sensing fiber 2 the measurement path is shorter than the reference path. Only the data for sensing fiber 2 will then appear reversed in position. Depending on the magnitude of ⁇ 12 two situations can be distinguished.
  • FIG. 7 shows another embodiment in which two sensing fibers SFl , SF2 share an optical circulator C.
  • an optical splitter '50/50' is used to connect the two sensing fibers SFl , SF2 to a single optical circulator C.
  • the reference path and optical detection unit ODU is still common to both sensing fibers SFl , SF2.
  • a delay dl is introduced in the measurement path of one sensing fiber SF2, while the measurement path of the other sensing fiber SFl does not have such delay.
  • this embodiment can only be used if the strength of the signal of at least one of the sensing fibers is strong enough to not be corrupted by overlapping Rayleigh scattering data of a connecting fiber. Additionally, the lengths of the connecting fibers between the splitter and the sensing fibers SFl , SF2 must differ by an amount that is sufficient to ensure that the data of the two sensing fibers SFl , SF2 do not overlap in the single scattering profile computed from the detector signals.
  • FIG. 8 schematically shows the relation between fiber lengths and scattering profile for the case that two sensing fibers SFl , SF2 share an optical circulator C.
  • the case is shown when the equal-length point lies at a distance lo to the left of the start of the fiber with length l c that connects the splitter '50/50' to the circulator C.
  • the fiber labels have been chosen such that connection fiber 2 is longer than connection fiber 1.
  • the signal of sensing fiber SFl needs to be sufficiently strong compared to the (Rayleigh scattering) signal fr m connecting fiber SF2 to not become corrupted by it.
  • connection fiber 2 should be free from splices and connectors in that region. In the setup shown in FIGS. 7 and 8, it is possible to place the zero-frequency point somewhere in the range between the circulator and the start of sensing fiber SF1 , in which case lo becomes negative.
  • FIGS. 9a and 9b show examples of amplitude (logarithmic scale) of the Fourier transforms of the detector signals D l and D2 for a single polarization state for an embodiment of the invention according to FIG. 7.
  • the horizontal axis indicates fiber index.
  • FIG. 9a shows only sensing fiber SF1 attached, while FIG 9b shows sensing fiber SF2 also attached, using 5 m of additional delay fiber.
  • the example measurements are performed on a multi-core sensing fiber containing Fiber Bragg Gratings (FBG), using a setup of FIG. 7.
  • the part of the sensing fiber containing the FBGs corresponds to the region of increased amplitude in the fiber index range of approximately 104000-155000.
  • the FBGs of core 2 of the sensing fiber show up in the fiber index range of 230000-281000, due to the inserted delay fiber.
  • the example embodiments are shown with only two sensing fibers connected to respective two measurement paths, but in general the invention can be used for more than two sensing fibers.
  • FIG. 10 shows a generalized version for measuring N sensing fibers simultaneously, SF1 .. . SFN, and this embodiment is a generalization of the embodiment of FIG. 4. Only the components of the first and last sensing fiber are shown.
  • a power splitting ratio of the first coupling point CP1 i.e. the first splitter, is more general than the nominal 50/50 splitting ratio, and has thus been indicated by the parameter a.
  • FIG. 1 1 shows an embodiment of the invention for measuring N sensing fibers SF1 , SFN simultaneously which is a variation on the embodiment of FIG. 10. It differs from the embodiment of FIG. 10 in the configuration of the splitters and combiners.
  • the first splitter CP1 distinguishes between the single reference path and the common part of all measurement paths, and the separate measurement paths are combined into a common path that is then combined with the single reference path, while in FIG. 11, a single first splitter CP1 distributes the incoming light equally over N measurement paths and the reference path, and the measurement paths and the reference path are combined in a single combining element CP2.
  • FIG. 12 shows an embodiment of the invention for measuring N sensing fibers SF1, SFN simultaneously which is a variation on the embodiment of FIG. 7.
  • a single optical circulator C is shared by all sensing fibers SF1, SFN.
  • this embodiment can only be used if the strength of the signal of the sensing fibers SF1, SF2 is strong enough to not be corrupted by
  • the relevant signal is created by the interference between light from the reference path and light backscattered by a sensing fiber.
  • the strength of this signal is proportional to the product of the amplitude at the PBS of the light that has travelled along the reference path and the amplitude of the light that comes from the measurement path. Note that the amplitude of the light is proportional to the square root of the power level of the light.
  • the strength of the backscattered power per unit length of the sensing fiber for unit input power is denoted by ⁇ ).
  • This invention according to the embodiment of FIG. 12:
  • FIGS. 10, and 12 show the same strength of the interference signal as the embodiment of the state of the art, when the first splitter is chosen to be a standard 50/50 splitter.
  • /9, while for the state of the art, for FIGS. 10 and 12: S Vr
  • the relative performance of the embodiment of FIG. 1 1 becomes worse for N>2.
  • FIG. 13 illustrates steps S1-S7 of a method according to the invention for obtaining optical frequency domain reflectometry (OFDR) data.
  • the steps are: - providing (SI) an optical radiation source (LS) and emitting (S2) optical radiation within a certain wavelength band, the radiation source being optically connected to a first coupling point (CP1) arranged for splitting the optical radiation from the optical radiation source (LS),
  • the plurality of measurement paths have different optical path lengths, so as to allow the detection of essentially uncorrupted optical radiation from parts of the respective optical sensing fibers that are intended to have a sensory function.
  • the invention is applicable in all fields where distributed sensing using the method of Optical Frequency Domain Reflectometry can be used. Properties that can be measured with this technique are, e.g., strain and temperature. A field of particular interest might be the simultaneous measurement of strain in cores of a helical multi-core fiber, for the purpose of shape-sensing.
  • the invention can be used to lower the price of a measurement system or to simultaneously measure more than one shape sensing fiber using only a single measurement system.
  • the invention may be applied in shape sensing for medical applications, where the shape sensing function is used in a medical probe or catheter for spatial location of medical scanning or medical treatment purposes.
  • the invention provides an optical frequency domain reflectometry (OFDR) system with an optical radiation source (LS) connected to a plurality of OFDAR systems
  • OFDR optical frequency domain reflectometry
  • LS optical radiation source
  • the measurement paths (MPl, MP2, MP3) are arranged for optical connection to respective optical sensing fibers (SFl, SF2, SF3).
  • the measurement paths (MPl, MP2, MP3) have different optical path lengths (LI, L2, L3), so as to allow an optical detection unit (ODU) to essentially uncorruptedly detect optical radiation from parts of the respective optical sensing fibers (SFl, SF2, SF3) that are intended to have a sensory function.
  • the optical detection unit (ODU) is connected to the reference path (RFP) and the measurement paths (MPl, MP2, MP3) via a second coupling point (CP2).
  • the common reference path (RFP) for several measurement paths (MP1, MP2, MP3), only one detection chain is required to serve several sensing fibers (SF1, SF2, SF3).
  • a computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems. Any reference signs in the claims should not be construed as limiting the scope.

Abstract

La présente invention porte sur un système de réflectométrie en domaine de fréquences optiques (OFDR) qui comporte une source de rayonnement optique (LS) connectée à une pluralité de trajets de mesure (MP1, MP2, MP3) et un trajet de référence (RFP) par l'intermédiaire d'un premier point de couplage (CP1). Les trajets de mesure (MP1, MP2, MP3) sont agencés pour connexion optique à des fibres de détection optique respectives (SF1, SF2, SF3). Les trajets de mesure (MP1, MP2, MP3) ont différentes longueurs de trajet optique (L1, L2, L3), de manière à autoriser une unité de détection optique (ODU) à détecter essentiellement de manière non corrompue un rayonnement optique provenant de parties des fibres de détection optique respectives (SF1, SF2, SF3) qui sont destinées à avoir une fonction sensorielle. L'unité de détection optique (ODU) est connectée au trajet de référence (RFP) et au trajet de mesure (MP1, MP2, MP3) par l'intermédiaire d'un second point de couplage (CP2). Ainsi, par l'intermédiaire du trajet de référence commun (RFP) pour plusieurs trajets de mesure (MP1, MP2, MP3), uniquement une chaîne de détection est nécessaire pour desservir plusieurs fibres de détection (SF1, SF2, SF3).
PCT/IB2013/058445 2012-11-09 2013-09-11 Système de réflectométrie en domaine de fréquences optiques (ofdr) ayant de multiples fibres par chaîne de détection WO2014072845A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US201261724324P 2012-11-09 2012-11-09
US61/724,324 2012-11-09

Publications (1)

Publication Number Publication Date
WO2014072845A1 true WO2014072845A1 (fr) 2014-05-15

Family

ID=49261580

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/IB2013/058445 WO2014072845A1 (fr) 2012-11-09 2013-09-11 Système de réflectométrie en domaine de fréquences optiques (ofdr) ayant de multiples fibres par chaîne de détection

Country Status (1)

Country Link
WO (1) WO2014072845A1 (fr)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2014136020A3 (fr) * 2013-03-07 2014-12-11 Koninklijke Philips N.V. Suréchantillonage adaptatif pour interpolations en temps réel précises
WO2015193191A1 (fr) * 2014-06-18 2015-12-23 Koninklijke Philips N.V. Alignement multicœur dans une détection de forme optique
CN107014325A (zh) * 2017-05-11 2017-08-04 中国科学院声学研究所 一种无线无源声表面波应变传感器
WO2019029163A1 (fr) * 2017-08-09 2019-02-14 武汉隽龙科技股份有限公司 Appareil et procédé d'élimination d'un évanouissement de polarisation dans une ofdr

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2192984A (en) * 1986-07-25 1988-01-27 Plessey Co Plc Optical sensing arrangement
WO2006068875A2 (fr) * 2004-12-14 2006-06-29 Luna Innovations Inc. Compensation de changements de phase variant dans le temps dans les mesures interferometriques
WO2007149230A2 (fr) * 2006-06-16 2007-12-27 Luna Innovations Incorporated Discrimination de l'effort et de la tempÉrature distribuÉs dans une fibre À maintien de la polarisation
WO2009054193A1 (fr) * 2007-10-26 2009-04-30 Murata Manufacturing Co., Ltd. Analyseur de spectre optique
US20110109898A1 (en) 2009-09-18 2011-05-12 Luna Innovations Incorporated Optical position and/or shape sensing
US20120069347A1 (en) * 2010-09-17 2012-03-22 Luna Innovations Incorporated Compensating for non-ideal multi-core optical fiber structure
US20120194823A1 (en) * 2011-01-28 2012-08-02 The Regents Of The University Of Colorado, A Body Corporate Spectral Phase Analysis For Precision Ranging

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2192984A (en) * 1986-07-25 1988-01-27 Plessey Co Plc Optical sensing arrangement
WO2006068875A2 (fr) * 2004-12-14 2006-06-29 Luna Innovations Inc. Compensation de changements de phase variant dans le temps dans les mesures interferometriques
WO2007149230A2 (fr) * 2006-06-16 2007-12-27 Luna Innovations Incorporated Discrimination de l'effort et de la tempÉrature distribuÉs dans une fibre À maintien de la polarisation
WO2009054193A1 (fr) * 2007-10-26 2009-04-30 Murata Manufacturing Co., Ltd. Analyseur de spectre optique
US20110109898A1 (en) 2009-09-18 2011-05-12 Luna Innovations Incorporated Optical position and/or shape sensing
US20120069347A1 (en) * 2010-09-17 2012-03-22 Luna Innovations Incorporated Compensating for non-ideal multi-core optical fiber structure
US20120194823A1 (en) * 2011-01-28 2012-08-02 The Regents Of The University Of Colorado, A Body Corporate Spectral Phase Analysis For Precision Ranging

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
B. J. SOLLER; M. WOLFE; M. E. FROGGATT: "Polarization resolved measurement of Rayleigh backscatter in fiber-optic components", OFC TECHNICAL DIGEST, 2005

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2014136020A3 (fr) * 2013-03-07 2014-12-11 Koninklijke Philips N.V. Suréchantillonage adaptatif pour interpolations en temps réel précises
WO2015193191A1 (fr) * 2014-06-18 2015-12-23 Koninklijke Philips N.V. Alignement multicœur dans une détection de forme optique
CN107014325A (zh) * 2017-05-11 2017-08-04 中国科学院声学研究所 一种无线无源声表面波应变传感器
CN107014325B (zh) * 2017-05-11 2019-04-26 中国科学院声学研究所 一种无线无源声表面波应变传感器
WO2019029163A1 (fr) * 2017-08-09 2019-02-14 武汉隽龙科技股份有限公司 Appareil et procédé d'élimination d'un évanouissement de polarisation dans une ofdr

Similar Documents

Publication Publication Date Title
EP2907249B1 (fr) Système de réflectométrie de domaine de fréquence optique (ofdr)
US10545070B2 (en) Dispersion correction in optical frequency-domain reflectometry
US10697824B2 (en) Dynamic sensitivity distributed acoustic sensing
CN107430013B (zh) 使用参考光纤干涉数据配准测量的光纤干涉数据
JP6291313B2 (ja) 光周波数領域反射測定方法、光周波数領域反射測定装置およびそれを用いた位置または形状を測定する装置
EP3207340B1 (fr) Détection brillouin distribuée utilisant une corrélation
WO2006099056A2 (fr) Calcul de la birefringence dans un guide d'onde en fonction de la diffusion de rayleigh
US20160266005A1 (en) Methods and apparatus for simultaneous optical parameter measurements
CN113465528B (zh) 基于光频域反射高速分布式应变测量系统和方法
WO2014072845A1 (fr) Système de réflectométrie en domaine de fréquences optiques (ofdr) ayant de multiples fibres par chaîne de détection
JP6306922B2 (ja) 光周波数領域反射測定方法、光周波数領域反射測定装置およびそれを用いた位置または形状を測定する装置
Wada et al. Analytical investigation of response of birefringent fiber Bragg grating sensors in distributed monitoring system based on optical frequency domain reflectometry
CN114577244A (zh) 用于储能系统电池阵列监测的多参量分布式光纤传感系统及方法
WO2004005973A2 (fr) Detection de la diversite de polarisation sans separateur de faisceau polarisant
EP3242621B1 (fr) Système optique de détection de forme, appareil médical et procédé de détection optique de forme
JP6274555B2 (ja) 群遅延演算を用いたｏｆｄｒ方式光ファイバ計測方法及びそれを実施する装置
JP2011158330A (ja) 光線路測定装置及び光線路測定方法
WO2022259436A1 (fr) Dispositif de traitement de signal, système de détection de vibration et procédé de traitement de signal
Liehr et al. A novel fiber optic technique for quasi-distributed and dynamic measurement of length change and refractive index
CN117917026A (zh) 光脉冲试验方法以及光脉冲试验装置
Morozov et al. Two-frequency detector of Brillouin and Raman scattering

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 13770512

Country of ref document: EP

Kind code of ref document: A1

NENP Non-entry into the national phase

Ref country code: DE

122 Ep: pct application non-entry in european phase

Ref document number: 13770512

Country of ref document: EP

Kind code of ref document: A1