WO2015181155A1 - Optical sensor for measuring humidity, strain and temperature - Google Patents

Optical sensor for measuring humidity, strain and temperature Download PDF

Info

Publication number
WO2015181155A1
WO2015181155A1 PCT/EP2015/061570 EP2015061570W WO2015181155A1 WO 2015181155 A1 WO2015181155 A1 WO 2015181155A1 EP 2015061570 W EP2015061570 W EP 2015061570W WO 2015181155 A1 WO2015181155 A1 WO 2015181155A1
Authority
WO
WIPO (PCT)
Prior art keywords
optical sensor
bragg grating
humidity
information
strain
Prior art date
Application number
PCT/EP2015/061570
Other languages
French (fr)
Inventor
Jesper NØRREGAARD
Kristian Nielsen
Original Assignee
Danmarks Tekniske Universitet
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 Danmarks Tekniske Universitet filed Critical Danmarks Tekniske Universitet
Publication of WO2015181155A1 publication Critical patent/WO2015181155A1/en

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/75—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated
    • G01N21/77—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator
    • G01N21/78—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator producing a change of colour
    • G01N21/81—Indicating humidity
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
    • G01K11/00—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00
    • G01K11/32—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres
    • G01K11/3206—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres at discrete locations in the fibre, e.g. using Bragg scattering
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L1/00—Measuring force or stress, in general
    • G01L1/24—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet
    • G01L1/242—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet the material being an optical fibre
    • G01L1/246—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet the material being an optical fibre using integrated gratings, e.g. Bragg gratings
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/75—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated
    • G01N21/77—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator
    • G01N21/7703—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator using reagent-clad optical fibres or optical waveguides
    • G01N21/774—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator using reagent-clad optical fibres or optical waveguides the reagent being on a grating or periodic structure
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/02033—Core or cladding made from organic material, e.g. polymeric material
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/02057—Optical fibres with cladding with or without a coating comprising gratings
    • G02B6/02076—Refractive index modulation gratings, e.g. Bragg gratings
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/02057—Optical fibres with cladding with or without a coating comprising gratings
    • G02B6/02076—Refractive index modulation gratings, e.g. Bragg gratings
    • G02B6/02195—Refractive index modulation gratings, e.g. Bragg gratings characterised by means for tuning the grating
    • G02B6/022—Refractive index modulation gratings, e.g. Bragg gratings characterised by means for tuning the grating using mechanical stress, e.g. tuning by compression or elongation, special geometrical shapes such as "dog-bone" or taper
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/02295—Microstructured optical fibre
    • G02B6/02314—Plurality of longitudinal structures extending along optical fibre axis, e.g. holes
    • G02B6/02319—Plurality of longitudinal structures extending along optical fibre axis, e.g. holes characterised by core or core-cladding interface features
    • G02B6/02333—Core having higher refractive index than cladding, e.g. solid core, effective index guiding
    • 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
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/75—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated
    • G01N21/77—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator
    • G01N21/7703—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator using reagent-clad optical fibres or optical waveguides
    • G01N2021/7706—Reagent provision
    • G01N2021/7723—Swelling part, also for adsorption sensor, i.e. without chemical reaction

Definitions

  • the present invention relates to an optical sensor and an associated method for measuring humidity, strain and temperature.
  • the optical sensor of the present invention offers an enhanced sensitivity and a larger dynamic range.
  • WO 2007/137429 discloses a Fibre Bragg Grating (FBG) humidity sensor comprising an optical fibre having two Bragg gratings. One of these Bragg gratings is sensitive to humidity whereas the other Bragg grating is sensitive to temperature.
  • the humidity sensitive Bragg grating is coated with a specific polymer which expands when it is exposed to humidity. The expansion of the specific polymer introduces a transverse strain in the grating area of the optical fibre. A direct relation between the amount of strain and humidity percentage can be deduced therefrom. It is a disadvantage of the sensor proposed in WO 2007/137429 that a humidity sensitive polymer coating is required.
  • CN 202 869 694 relates to a FBG temperature and humidity sensor.
  • the sensor comprises a fibre having a temperature sensitive element and a humidity sensitive element. Similar to WO 2007/137429 the surface of the FBG of the humidity sensing part of the sensor element is coated with a polyimide layer having a thickness of 30-50 ⁇ .
  • the humidity sensing element is also sensitive to a change of temperature, whereas the temperature sensing element is only sensitive to a change of environment temperature. Similar to WO
  • US 2007/137429 it is a disadvantage of the sensor proposed in CN 202 869 694 that a humidity sensitive polyimide layer is required.
  • US 2007/0183507 suggests a FBG sensor for measuring stain and temperature using information from two FBGs. It is specifically addressed in US 2007/0183507 that the influence of humidity should be avoided. To comply with this requirement a humidity sealing layer being denoted 30 in Fig. 1 is provided.
  • an optical sensor adapted to measure at least three physical parameters, said optical sensor comprising a polymer-based optical waveguide structure comprising :
  • a first Bragg grating structure being adapted to provide information about a first, a second and a third physical parameter
  • a second Bragg grating structure being adapted to provide information about the second and the third physical parameter only
  • a third Bragg grating structure being adapted to provide information about the third physical parameter only.
  • the present invention relates to an optical sensor for measuring three physical parameters.
  • these three parameters are humidity, strain and temperature.
  • the polymer-based optical waveguide applied in the present invention is more elastic and deformable and thereby also more sensitive to external perturbations. This implies for example, that strain levels up to at least 7% may be measured. In comparison strain levels of only 0.5% may be measured using traditional silica-based waveguides.
  • the polymer-based optical waveguide of the present invention has, compared to silica-based sensors, an integrated or built-in sensitivity for measuring humidity.
  • This integrated or built-in sensitivity is advantageous in that it simplifies the overall design of the sensor.
  • optical sensor according to the present invention finds its use within a variety of applications including measurements in for example concrete and composite materials. Moreover, the optical sensor of the present invention is applicable in relation to geotechnical investigations as well as surveillance of nets within fish farming.
  • the optical waveguide structure may comprise a polymer-based optical fibre, such as a single-mode polymer-based micro-structured optical fibre.
  • a polymer-based optical fibre such as a single-mode polymer-based micro-structured optical fibre.
  • the single-mode property of the polymer-based micro-structured optical fibre contributes to enhancing the sensitivity of the sensor compared to multi-mode based sensor arrangements.
  • Information about humidity, strain and temperature is provided by light reflected from the three Bragg gratings. More particularly, information about these parameters is provided via a wavelength shift of the reflected light. Reflected light from the first Bragg grating structure provides information about all three parameters, namely humidity, strain and temperature, whereas reflected light from the second Bragg grating structure provides information about strain and temperature only. To achieve this, the second Bragg grating structure may be encapsulated in a humidity insensitive arrangement, such as a humidity sealing layer. Light reflected from the third Bragg grating structure provides information about
  • the third Bragg grating structure may be encapsulated in a humidity insensitive arrangement as well as a strain insensitive arrangement.
  • the strain insensitive arrangement may be any kind of rigid structure that prevents that the third Bragg grating is stretched, bended and/or extended.
  • One way of implementing the strain insensitive arrangement may be to arrange a rigid steel tube around the third Bragg grating.
  • the optical sensor may further comprise a light source for injecting light into the polymer- based optical waveguide structure, and detection means for detecting light reflected from the Bragg gratings.
  • the light source may in principle involve any type of broadband light source, for example broadband light sources emitting light in the visible range, i.e. between 400 nm and 70 nm. Suitable light source candidates may involve superluminescent diodes (SLD), semiconductor optical amplifiers (SOA), supercontinuum fibre lasers or white light lasers, such as SuperK light sources.
  • SLD superluminescent diodes
  • SOA semiconductor optical amplifiers
  • supercontinuum fibre lasers or white light lasers, such as SuperK light sources.
  • the emitted light may reach the three Bragg gratings via a 3 dB fibre coupler.
  • the same 3 dB coupler may also ensure that reflected light from the three Bragg gratings is able to leave the waveguide in order to be analysed by a spectrometer, such as a CCD spectrometer.
  • the reflections from the three Bragg gratings may thus be analysed by a line CCD spectrometer.
  • a wavelength shift of 10 nm may be achieved.
  • a wavelength shift of 70-80 pm may be achieved for every percent the relative humidity changes.
  • a wavelength shift of around 1 pm may be achieved for every Kelvin the temperature changes.
  • the optical sensor may further comprise processor means for processing the detected light.
  • the detected light may be processed by subtracting information about strain and temperature (second Bragg grating) from information about humidity, strain and temperatu (first Bragg grating).
  • the detected light may be processed by subtracting information about temperature from information about strain and temperature. In this way information about all three parameters (humidity, strain and temperature) may be obtained
  • the present invention relates to a method for measuring at least three physical parameters using an optical sensor comprising a polymer-based optical waveguide structure comprising a first, a second and a third Bragg grating structure, the method comprising the steps of:
  • the first, second and third parameters relates to humidity, strain and temperature, respectively.
  • the humidity, strain and temperature are deduced from light reflections from the Bragg gratings.
  • the optical sensor may comprise a light source for injecting light into the polymer-based optical waveguide structure, and detection means for detecting light reflected from the Bragg gratings.
  • the light source may involve any type of broadband light source, for example broadband light sources emitting light in the visible range. Suitable light source candidates are superluminescent diodes (SLD), semiconductor optical amplifiers (SOA), supercontinuum fibre lasers or white light lasers, such as SuperK light sources.
  • the emitted light may reach the three Bragg gratings via a 3 dB fibre coupler.
  • the same coupler may also ensure that reflected light from the three Bragg gratings is able to leave the waveguide in order to be analysed by a spectrometer, such as a CCD spectrometer.
  • the reflections from the three Bragg gratings may thus be analysed by a line CCD spectrometer.
  • Fig. 1 shows a sensor according to an embodiment of the present invention
  • Fig. 2 shows an optical fibre for use in the sensor.
  • the present invention relates to an optical sensor for measuring a first, a second and a third physical parameter at essentially the same time. These parameters involve measurements of humidity, strain and temperature.
  • Fig. 1 the essential parts of the optical sensor of the present invention are depicted. Compared to a complete sensor the light source and the optical analysing equipment have been left out.
  • the sensor 100 includes a wave guiding structure having a core region 109 with three Bragg gratings 101, 102, 103 arranged or induced therein.
  • a Bragg grating is a well- known structure where the index of refraction varies in a periodic manner along the length of the grating.
  • the periods of the Bragg gratings are selected in view of the wavelength of the light source injecting light into the sensor 100. Preferably, the periods of the gratings are the same.
  • the Bragg gratings may be induced into the core region 109 by various means, such as by UV writing.
  • the core region 109 of the waveguide must be sensitive of humidity. In this way the sensor has an integrated or built-in sensitivity to humidity. This has been achieved by using a waveguide having a polymer-based core region, such as a Polymethylmethacrylat (PMMA)- based waveguide.
  • PMMA Polymethylmethacrylat
  • Bragg grating 102 is still sensitive to strain and temperature variations.
  • Bragg grating 103 in section 108 is only sensitive to temperature variations due to the coating 104 and the rigid encapsulation box 105, the latter here being implemented as a rigid steel tube.
  • the rigid steel tube 105 is secured to the waveguide in a manner that prevents stretching and bending of Bragg grating 103. It should however be noted that other types of arrangements that also prevent that the Bragg grating 103 is stretched, extended and/or bended may be applicable as well.
  • the output signal from the sensor 100 is provided by a wavelength shift from each of the three Bragg gratings in that the wavelength of the reflected light depends on the humidity, strain and temperature of the gratings.
  • Bragg grating 101 humidity, strain and temperature (signal A)
  • Bragg grating 102 strain and temperature (signal B)
  • Bragg grating 103 temperature (signal C)
  • the waveguide is formed by a single-mode optical fibre where at least the core region is manufactured by a polymer material, such as PMMA. More preferably, a plurality of longitudinally arranged holes are provided around the centre of the core region in order to enhance the single-mode properties of the fibre, cf. Fig. 2.
  • Fig. 2 shows an example of a cross-sectional view of an endlessly single-mode polymer- based optical fibre.
  • endlessly is meant that the single-mode property of the optical fibre is independent of the wavelength of the light propagating within the fibre.
  • the core region is surrounded by a plurality of holes arranged in a periodic pattern. The holes extend in the longitudinal direction of the optical fibre.
  • the solid core region itself has a diameter of around 10 ⁇ .

Landscapes

  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Chemical & Material Sciences (AREA)
  • Biochemistry (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Plasma & Fusion (AREA)
  • General Health & Medical Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Engineering & Computer Science (AREA)
  • Length Measuring Devices By Optical Means (AREA)
  • Optical Transform (AREA)

Abstract

The present invention relates to an optical sensor (100) adapted to measure at least three physical parameters, said optical sensor comprising a polymer-based optical waveguide structure comprising a first Bragg grating structure (101) being adapted to provide information about a first, a second and a third physical parameter, a second Bragg grating structure (102) being adapted to provide information about the second and the third physical parameter only, and a third Bragg grating structure (103) being adapted to provide information about the third physical parameter only. The invention further relates to a method for measuring the first, the second and the third physical parameter. Preferably, the first, the second and the third physical parameter, are humidity, strain and temperature, respectively.

Description

OPTICAL SENSOR FOR MEASURING HUMIDITY, STRAIN AND TEMPERATURE FIELD OF THE INVENTION
The present invention relates to an optical sensor and an associated method for measuring humidity, strain and temperature. The optical sensor of the present invention offers an enhanced sensitivity and a larger dynamic range.
BACKGROUND OF THE INVENTION
Various optical sensor arrangements for measuring different physical parameters have been suggested over the years.
For example WO 2007/137429 discloses a Fibre Bragg Grating (FBG) humidity sensor comprising an optical fibre having two Bragg gratings. One of these Bragg gratings is sensitive to humidity whereas the other Bragg grating is sensitive to temperature. The humidity sensitive Bragg grating is coated with a specific polymer which expands when it is exposed to humidity. The expansion of the specific polymer introduces a transverse strain in the grating area of the optical fibre. A direct relation between the amount of strain and humidity percentage can be deduced therefrom. It is a disadvantage of the sensor proposed in WO 2007/137429 that a humidity sensitive polymer coating is required.
CN 202 869 694 relates to a FBG temperature and humidity sensor. The sensor comprises a fibre having a temperature sensitive element and a humidity sensitive element. Similar to WO 2007/137429 the surface of the FBG of the humidity sensing part of the sensor element is coated with a polyimide layer having a thickness of 30-50 μιη. The humidity sensing element is also sensitive to a change of temperature, whereas the temperature sensing element is only sensitive to a change of environment temperature. Similar to WO
2007/137429 it is a disadvantage of the sensor proposed in CN 202 869 694 that a humidity sensitive polyimide layer is required. US 2007/0183507 suggests a FBG sensor for measuring stain and temperature using information from two FBGs. It is specifically addressed in US 2007/0183507 that the influence of humidity should be avoided. To comply with this requirement a humidity sealing layer being denoted 30 in Fig. 1 is provided.
None of the above-mentioned prior art documents disclose an optical fibre-based sensor being capable of measuring humidity, strain and temperature at the same time. It may be seen as an object of embodiments of the present invention to provide a sensor and an associated method for measuring the three physical parameters humidity, strain and temperature.
It may be seen as a further object of embodiments of the present invention to provide an optical sensor and an associated method with an enhanced sensitivity.
DESCRIPTION OF THE INVENTION
The above-mentioned objects are complied with by providing, in a first aspect, an optical sensor adapted to measure at least three physical parameters, said optical sensor comprising a polymer-based optical waveguide structure comprising :
1) a first Bragg grating structure being adapted to provide information about a first, a second and a third physical parameter,
2) a second Bragg grating structure being adapted to provide information about the second and the third physical parameter only, and
3) a third Bragg grating structure being adapted to provide information about the third physical parameter only.
Thus, the present invention relates to an optical sensor for measuring three physical parameters. Preferably, these three parameters are humidity, strain and temperature.
Compared to traditional silica-based fibre sensors the polymer-based optical waveguide applied in the present invention is more elastic and deformable and thereby also more sensitive to external perturbations. This implies for example, that strain levels up to at least 7% may be measured. In comparison strain levels of only 0.5% may be measured using traditional silica-based waveguides.
Moreover, the polymer-based optical waveguide of the present invention has, compared to silica-based sensors, an integrated or built-in sensitivity for measuring humidity. This integrated or built-in sensitivity is advantageous in that it simplifies the overall design of the sensor.
The optical sensor according to the present invention finds its use within a variety of applications including measurements in for example concrete and composite materials. Moreover, the optical sensor of the present invention is applicable in relation to geotechnical investigations as well as surveillance of nets within fish farming.
The optical waveguide structure may comprise a polymer-based optical fibre, such as a single-mode polymer-based micro-structured optical fibre. The single-mode property of the polymer-based micro-structured optical fibre contributes to enhancing the sensitivity of the sensor compared to multi-mode based sensor arrangements.
Information about humidity, strain and temperature is provided by light reflected from the three Bragg gratings. More particularly, information about these parameters is provided via a wavelength shift of the reflected light. Reflected light from the first Bragg grating structure provides information about all three parameters, namely humidity, strain and temperature, whereas reflected light from the second Bragg grating structure provides information about strain and temperature only. To achieve this, the second Bragg grating structure may be encapsulated in a humidity insensitive arrangement, such as a humidity sealing layer. Light reflected from the third Bragg grating structure provides information about
temperature. To achieve this, the third Bragg grating structure may be encapsulated in a humidity insensitive arrangement as well as a strain insensitive arrangement. The strain insensitive arrangement may be any kind of rigid structure that prevents that the third Bragg grating is stretched, bended and/or extended. One way of implementing the strain insensitive arrangement may be to arrange a rigid steel tube around the third Bragg grating.
The optical sensor may further comprise a light source for injecting light into the polymer- based optical waveguide structure, and detection means for detecting light reflected from the Bragg gratings. The light source may in principle involve any type of broadband light source, for example broadband light sources emitting light in the visible range, i.e. between 400 nm and 70 nm. Suitable light source candidates may involve superluminescent diodes (SLD), semiconductor optical amplifiers (SOA), supercontinuum fibre lasers or white light lasers, such as SuperK light sources. The emitted light may reach the three Bragg gratings via a 3 dB fibre coupler. The same 3 dB coupler may also ensure that reflected light from the three Bragg gratings is able to leave the waveguide in order to be analysed by a spectrometer, such as a CCD spectrometer. The reflections from the three Bragg gratings may thus be analysed by a line CCD spectrometer.
In terms of sensitivity the following values are none limiting examples of achievable sensitivities in relation to strain, relative humidity (RH) and temperature (K), respectively: 1) Strain: 10 nm/%
2) Humidity: 70-80 pm/RH%
3) Temperature: ~ -1 pm/K
Thus, for every percent the grating is stretched a wavelength shift of 10 nm may be achieved. Similarly, a wavelength shift of 70-80 pm may be achieved for every percent the relative humidity changes. Finally, a wavelength shift of around 1 pm may be achieved for every Kelvin the temperature changes.
The optical sensor may further comprise processor means for processing the detected light. The detected light may be processed by subtracting information about strain and temperature (second Bragg grating) from information about humidity, strain and temperatu (first Bragg grating). Moreover, the detected light may be processed by subtracting information about temperature from information about strain and temperature. In this way information about all three parameters (humidity, strain and temperature) may be obtained
In a second aspect the present invention relates to a method for measuring at least three physical parameters using an optical sensor comprising a polymer-based optical waveguide structure comprising a first, a second and a third Bragg grating structure, the method comprising the steps of:
1) coupling broadband light into the polymer-based optical waveguide,
2) deriving information A about a first, a second and a third physical parameter from light reflections from the first Bragg grating structure,
3) deriving information B about the second and the third physical parameter only from light reflections from the second Bragg grating structure,
4) deriving information C about the third physical parameter only from light reflections from the third Bragg grating structure, and
5) subtracting information B from information A to obtain information about the first physical parameter, and subtracting information C from information B to obtain information about the second physical parameter.
Similar to the first aspect the first, second and third parameters relates to humidity, strain and temperature, respectively. As disclosed in connection with the first aspect the humidity, strain and temperature are deduced from light reflections from the Bragg gratings. The optical sensor may comprise a light source for injecting light into the polymer-based optical waveguide structure, and detection means for detecting light reflected from the Bragg gratings. Again, the light source may involve any type of broadband light source, for example broadband light sources emitting light in the visible range. Suitable light source candidates are superluminescent diodes (SLD), semiconductor optical amplifiers (SOA), supercontinuum fibre lasers or white light lasers, such as SuperK light sources. The emitted light may reach the three Bragg gratings via a 3 dB fibre coupler. The same coupler may also ensure that reflected light from the three Bragg gratings is able to leave the waveguide in order to be analysed by a spectrometer, such as a CCD spectrometer. The reflections from the three Bragg gratings may thus be analysed by a line CCD spectrometer.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will now be explained in further details with reference to the accompanying figures, wherein
Fig. 1 shows a sensor according to an embodiment of the present invention, and
Fig. 2 shows an optical fibre for use in the sensor.
While the invention is susceptible to various modifications and alternative forms specific embodiments have been shown by way of examples in the drawings and will be described in detail herein. It should be understood, however, that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
DETAILED DESCRIPTION OF THE INVENTION In its most general aspect the present invention relates to an optical sensor for measuring a first, a second and a third physical parameter at essentially the same time. These parameters involve measurements of humidity, strain and temperature. Referring now to Fig. 1 the essential parts of the optical sensor of the present invention are depicted. Compared to a complete sensor the light source and the optical analysing equipment have been left out.
In Fig. 1 the sensor 100 includes a wave guiding structure having a core region 109 with three Bragg gratings 101, 102, 103 arranged or induced therein. A Bragg grating is a well- known structure where the index of refraction varies in a periodic manner along the length of the grating. The periods of the Bragg gratings are selected in view of the wavelength of the light source injecting light into the sensor 100. Preferably, the periods of the gratings are the same. The Bragg gratings may be induced into the core region 109 by various means, such as by UV writing.
The core region 109 of the waveguide must be sensitive of humidity. In this way the sensor has an integrated or built-in sensitivity to humidity. This has been achieved by using a waveguide having a polymer-based core region, such as a Polymethylmethacrylat (PMMA)- based waveguide. Referring again to Fig. 1 the Bragg grating 101 in section 106 is exposed to variations in humidity, strain and temperature because Bragg grating 101 is completely unprotected. Bragg grating 102 in section 107 is protected against humidity by a sealing coating 104. The sealing coating 104 thus prevents that the Bragg grating 102 is exposed to the
environmental humidity. However, Bragg grating 102 is still sensitive to strain and temperature variations. Bragg grating 103 in section 108 is only sensitive to temperature variations due to the coating 104 and the rigid encapsulation box 105, the latter here being implemented as a rigid steel tube. The rigid steel tube 105 is secured to the waveguide in a manner that prevents stretching and bending of Bragg grating 103. It should however be noted that other types of arrangements that also prevent that the Bragg grating 103 is stretched, extended and/or bended may be applicable as well.
The output signal from the sensor 100 is provided by a wavelength shift from each of the three Bragg gratings in that the wavelength of the reflected light depends on the humidity, strain and temperature of the gratings.
As stated above the three Bragg gratings provide the following information: 1) Bragg grating 101 : humidity, strain and temperature (signal A)
2) Bragg grating 102: strain and temperature (signal B) 3) Bragg grating 103: temperature (signal C)
By subtracting (by signal processing) signal B from signal A information about the humidity is obtained. Moreover, by subtracting the signal C from signal B information about the strain is obtained. Information about the temperature is given by signal C. Preferably the waveguide is formed by a single-mode optical fibre where at least the core region is manufactured by a polymer material, such as PMMA. More preferably, a plurality of longitudinally arranged holes are provided around the centre of the core region in order to enhance the single-mode properties of the fibre, cf. Fig. 2.
Fig. 2 shows an example of a cross-sectional view of an endlessly single-mode polymer- based optical fibre. By endlessly is meant that the single-mode property of the optical fibre is independent of the wavelength of the light propagating within the fibre. As seen, the core region is surrounded by a plurality of holes arranged in a periodic pattern. The holes extend in the longitudinal direction of the optical fibre. The solid core region itself has a diameter of around 10 μιη.

Claims

1. An optical sensor adapted to measure at least three physical parameters, said optical sensor comprising a polymer-based optical waveguide structure comprising :
1) a first Bragg grating structure being adapted to provide information about a first, a second and a third physical parameter,
2) a second Bragg grating structure being adapted to provide information about the second and the third physical parameter only, and
3) a third Bragg grating structure being adapted to provide information about the third physical parameter only.
2. An optical sensor according to claim 1, wherein the first, second and third parameters relates to humidity, strain and temperature, respectively.
3. An optical sensor according to claim 1 or 2, wherein the optical waveguide structure comprises a polymer-based optical fibre.
4. An optical sensor according to claim 3, wherein the polymer-based optical fibre comprises a polymer-based micro-structured optical fibre.
5. An optical sensor according to any of the preceding claims, wherein the second Bragg grating structure is encapsulated in a humidity insensitive arrangement.
6. An optical sensor according to claim 5, wherein the humidity insensitive arrangement comprises a humidity sealing layer.
7. An optical sensor according to any of the preceding claims, wherein the third Bragg grating structure is encapsulated in a humidity insensitive arrangement, and a strain insensitive arrangement.
8. An optical sensor according to claim 7, wherein the strain insensitive arrangement comprises a rigid steel tube.
9. An optical sensor according to any of the preceding claims, further comprising a light source for injecting light into the polymer-based optical waveguide structure.
10. An optical sensor according to any of the preceding claims, further comprising detection means for detecting light reflected from the Bragg gratings.
11. An optical sensor according to any of the preceding claims, further comprising processor means for processing the detected light.
12. A method for measuring at least three physical parameters using an optical sensor comprising a polymer-based optical waveguide structure comprising a first, a second and a third Bragg grating structure, the method comprising the steps of:
1) coupling broadband light into the polymer-based optical waveguide,
2) deriving information A about a first, a second and a third physical parameter from light reflections from the first Bragg grating structure,
3) deriving information B about the second and the third physical parameter only from light reflections from the second Bragg grating structure,
4) deriving information C about the third physical parameter only from light reflections from the third Bragg grating structure, and
5) subtracting information B from information A to obtain information about the first physical parameter, and subtracting information C from information B to obtain information about the second physical parameter.
13. A method according to claim 12, wherein the first, second and third parameters relates to humidity, strain and temperature, respectively.
PCT/EP2015/061570 2014-05-26 2015-05-26 Optical sensor for measuring humidity, strain and temperature WO2015181155A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
EP14169826.6 2014-05-26
EP14169826 2014-05-26

Publications (1)

Publication Number Publication Date
WO2015181155A1 true WO2015181155A1 (en) 2015-12-03

Family

ID=50774722

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/EP2015/061570 WO2015181155A1 (en) 2014-05-26 2015-05-26 Optical sensor for measuring humidity, strain and temperature

Country Status (1)

Country Link
WO (1) WO2015181155A1 (en)

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN105628249A (en) * 2015-12-21 2016-06-01 山东大学 Fiber grating sensor insert for mould pressing product detection and manufacturing method thereof
CN107703100A (en) * 2017-09-18 2018-02-16 重庆万泰电力科技有限公司 Multifunctional, air body sensor based on four-quadrant fibre cladding Bragg gratings
CN108168586A (en) * 2018-02-07 2018-06-15 濮阳光电产业技术研究院 A kind of fiber grating humiture integrative sensor
CN108318062A (en) * 2018-03-08 2018-07-24 云南电网有限责任公司电力科学研究院 A kind of fiber grating Temperature Humidity Sensor and temperature/humidity measuring system
DE102017201524A1 (en) 2017-01-31 2018-08-02 Hochschule für angewandte Wissenschaften München Fiber optic detection device and method for operating such a fiber optic detection device
CN109060041A (en) * 2018-09-10 2018-12-21 曲阜师范大学 Fiber optic temperature humidity sensor
CN109341735A (en) * 2018-12-10 2019-02-15 山东省科学院激光研究所 A kind of monitoring device and method
CN109826372A (en) * 2019-01-31 2019-05-31 泰州市康泰建材科技有限公司 Detectable internal moist foam concrete roofing thermal-insulating board and preparation method thereof
CN109855663A (en) * 2019-02-28 2019-06-07 武汉理工大学 The method and device of the quasi-distributed many reference amounts measurement of Bragg fiber grating array
CN111220208A (en) * 2019-12-06 2020-06-02 山东省科学院激光研究所 Novel optical fiber temperature and humidity sensor
WO2021013987A1 (en) 2019-07-24 2021-01-28 SchäferRolls GmbH & Co. KG Technical roll, in particular for paper manufacturing, method for introducing a polymer fibre into an empty duct of a technical roll, and use of a polymer fibre
CN114755202A (en) * 2022-06-15 2022-07-15 中国空气动力研究与发展中心设备设计与测试技术研究所 Polyimide optical fiber distributed humidity sensor and positioning detection method

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20050183507A1 (en) * 2000-01-31 2005-08-25 Weatherford/Lamb, Inc. Fluid diffusion resistant glass-encased optical sensor
EP1626259A1 (en) * 2004-08-12 2006-02-15 Agilent Technologies, Inc. Optical sensing of a physical parameter
US20070065071A1 (en) * 2005-06-30 2007-03-22 Infoscitex Humidity sensor and method for monitoring moisture in concrete

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20050183507A1 (en) * 2000-01-31 2005-08-25 Weatherford/Lamb, Inc. Fluid diffusion resistant glass-encased optical sensor
EP1626259A1 (en) * 2004-08-12 2006-02-15 Agilent Technologies, Inc. Optical sensing of a physical parameter
US20070065071A1 (en) * 2005-06-30 2007-03-22 Infoscitex Humidity sensor and method for monitoring moisture in concrete

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
W. ZHANG ET AL: "An investigation into the wavelength stability of polymer optical fibre Bragg gratings", PROCEEDINGS OF SPIE, vol. 8426, 25 April 2012 (2012-04-25), pages 842619, XP055139405, ISSN: 0277-786X, DOI: 10.1117/12.922306 *
WU YUAN ET AL: "Tunable Polymer Fiber Bragg Grating (FBG) Inscription: Fabrication of Dual-FBG Temperature Compensated Polymer Optical Fiber Strain Sensors", IEEE PHOTONICS TECHNOLOGY LETTERS, IEEE SERVICE CENTER, PISCATAWAY, NJ, US, vol. 24, no. 5, 1 March 2012 (2012-03-01), pages 401 - 403, XP011414490, ISSN: 1041-1135, DOI: 10.1109/LPT.2011.2179927 *

Cited By (20)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN105628249B (en) * 2015-12-21 2018-06-29 山东大学 For the fiber-optic grating sensor inserts and its manufacturing method of pressing detection
CN105628249A (en) * 2015-12-21 2016-06-01 山东大学 Fiber grating sensor insert for mould pressing product detection and manufacturing method thereof
DE102017201524A1 (en) 2017-01-31 2018-08-02 Hochschule für angewandte Wissenschaften München Fiber optic detection device and method for operating such a fiber optic detection device
CN107703100A (en) * 2017-09-18 2018-02-16 重庆万泰电力科技有限公司 Multifunctional, air body sensor based on four-quadrant fibre cladding Bragg gratings
CN108168586A (en) * 2018-02-07 2018-06-15 濮阳光电产业技术研究院 A kind of fiber grating humiture integrative sensor
CN108318062B (en) * 2018-03-08 2023-10-13 云南电网有限责任公司电力科学研究院 Fiber bragg grating temperature and humidity sensor and temperature and humidity measurement system
CN108318062A (en) * 2018-03-08 2018-07-24 云南电网有限责任公司电力科学研究院 A kind of fiber grating Temperature Humidity Sensor and temperature/humidity measuring system
CN109060041A (en) * 2018-09-10 2018-12-21 曲阜师范大学 Fiber optic temperature humidity sensor
CN109341735A (en) * 2018-12-10 2019-02-15 山东省科学院激光研究所 A kind of monitoring device and method
CN109341735B (en) * 2018-12-10 2021-08-20 山东省科学院激光研究所 Monitoring device and method
CN109826372A (en) * 2019-01-31 2019-05-31 泰州市康泰建材科技有限公司 Detectable internal moist foam concrete roofing thermal-insulating board and preparation method thereof
CN109826372B (en) * 2019-01-31 2020-12-08 泰州市康泰建材科技有限公司 Foam concrete roof insulation board capable of detecting internal humidity and manufacturing method thereof
CN109855663A (en) * 2019-02-28 2019-06-07 武汉理工大学 The method and device of the quasi-distributed many reference amounts measurement of Bragg fiber grating array
CN114207398A (en) * 2019-07-24 2022-03-18 舍弗罗尔斯有限两合公司 Industrial roll, in particular for papermaking, method for introducing polymer fibers into the hollow tubes of an industrial roll and use of polymer fibers
DE102019120052A1 (en) * 2019-07-24 2021-01-28 SchäferRolls GmbH & Co. KG Industrial roll, in particular for paper production, method for introducing a polymer fiber into an empty tube of a technical roll and using a polymer fiber
WO2021013987A1 (en) 2019-07-24 2021-01-28 SchäferRolls GmbH & Co. KG Technical roll, in particular for paper manufacturing, method for introducing a polymer fibre into an empty duct of a technical roll, and use of a polymer fibre
US11913171B2 (en) 2019-07-24 2024-02-27 SchäferRolls GmbH & Co. KG Technical roll, in particular for paper manufacturing, method for introducing a polymer fibre into an empty conduit of a technical roll, and use of a polymer fibre
CN111220208A (en) * 2019-12-06 2020-06-02 山东省科学院激光研究所 Novel optical fiber temperature and humidity sensor
CN114755202A (en) * 2022-06-15 2022-07-15 中国空气动力研究与发展中心设备设计与测试技术研究所 Polyimide optical fiber distributed humidity sensor and positioning detection method
CN114755202B (en) * 2022-06-15 2022-09-02 中国空气动力研究与发展中心设备设计与测试技术研究所 Optical fiber distributed humidity sensor based on polyimide and positioning detection method

Similar Documents

Publication Publication Date Title
WO2015181155A1 (en) Optical sensor for measuring humidity, strain and temperature
WO2016087442A1 (en) Compact optical sensor for measuring physical parameters
Chryssis et al. High sensitivity evanescent field fiber Bragg grating sensor
EP2828622B1 (en) A sensor for combined temperature, pressure, and refractive index detection
WO2008155769A3 (en) System and method based on waveguides for the protection of sites
WO2010030587A4 (en) Compact fiber optic sensors and method of making same
CN106568466A (en) Fine core microstructure optical fiber interferometer sensor and temperature and strain detection method therefor
CN102162753A (en) Sensor structure for simultaneously measuring temperature and strain of long period fiber gratings (LPFGs)
CN101581610A (en) Manufacturing method of optical fiber and optical grating polymer encapsulation temperature sensor used for intelligent garment
EP3384248B1 (en) Optical measuring system with an interrogator and a polymer-based single-mode fibre optic sensor system
KR101529610B1 (en) Apparatus and Sensing System for Fiber Bragg Grating Probes Having Controlled Sensitivity and Method for Sensing and Manufacturing thereof
US10876831B2 (en) Force sensing in a distal region of an instrument including single-core or multi-core optical fiber
Zelený et al. Strain measuring 3D printed structure with embedded fibre Bragg grating
KR101504028B1 (en) Apparatus using fiber bragg grating sensors
ATE472092T1 (en) DEVICE AND METHOD FOR MEASURING THE MECHANICAL DEFORMATIONS OF A SECTION
KR101129261B1 (en) FBGFiber Bragg Gratings Acceleration Sensor for Multi-Point Measuring by Series Connection
KR102036260B1 (en) Submergence detection sensor using optical fiber grating
Wu et al. A study of the effect of the position of an edge filter within a ratiometric wavelength measurement system
GB201117611D0 (en) Optical sensor
Yan et al. Development of flexible pressure sensing polymer foils based on embedded fibre Bragg grating sensors
EP3120125B1 (en) Optical fibre pressure sensor comprising in-core cavity and grating
Murayama Structural health monitoring based on strain distributions measured by fiber-optic distributed sensors
Varyshchuk et al. Using a multimode polymer optical fiber as a high sensitivy strain sensor
KR101030728B1 (en) monitoring system using dual wavelength fiber bragg grating sensor and method thereof
CN205449322U (en) Optical fiber grating sensor

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: 15725595

Country of ref document: EP

Kind code of ref document: A1

DPE1 Request for preliminary examination filed after expiration of 19th month from priority date (pct application filed from 20040101)
NENP Non-entry into the national phase

Ref country code: DE

122 Ep: pct application non-entry in european phase

Ref document number: 15725595

Country of ref document: EP

Kind code of ref document: A1