WO1990002322A1 - Parameter measurement using refractive index change - Google Patents

Parameter measurement using refractive index change Download PDF

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Publication number
WO1990002322A1
WO1990002322A1 PCT/GB1989/001012 GB8901012W WO9002322A1 WO 1990002322 A1 WO1990002322 A1 WO 1990002322A1 GB 8901012 W GB8901012 W GB 8901012W WO 9002322 A1 WO9002322 A1 WO 9002322A1
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WO
WIPO (PCT)
Prior art keywords
parameter
waveguide
light
reference material
refractive index
Prior art date
Application number
PCT/GB1989/001012
Other languages
French (fr)
Inventor
Christopher Davies
Robert Marc Clement
Original Assignee
Red Kite Technology Limited
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 Red Kite Technology Limited filed Critical Red Kite Technology Limited
Publication of WO1990002322A1 publication Critical patent/WO1990002322A1/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L11/00—Measuring steady or quasi-steady pressure of a fluid or a fluent solid material by means not provided for in group G01L7/00 or G01L9/00
    • G01L11/02—Measuring steady or quasi-steady pressure of a fluid or a fluent solid material by means not provided for in group G01L7/00 or G01L9/00 by optical means
    • 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
    • G01D5/268—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 using optical fibres
    • 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
    • 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
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/41—Refractivity; Phase-affecting properties, e.g. optical path length
    • G01N21/43—Refractivity; Phase-affecting properties, e.g. optical path length by measuring critical angle
    • G01N21/431—Dip refractometers, e.g. using optical fibres

Definitions

  • the present invention relates to the measuremen of a parameter of a material using refractive index changes induced by changes in the aforementioned parameter.
  • Optical fibres generally have a central core, entirely surrounded by a plastics or glass sheath (the cladding) .
  • the refractive index of the core In order for optical transmission along such a fibre to take place, the refractive index of the core must be greater than that of the cladding. It is well known that the relative refractive index of the core and cladding will determine the transmission characteristics of light along the optical fibre.
  • apparatus for measuring a parameter of a tes material which comprises means for holding a quantity of reference material having known variation of refractive index thereof with changes in the above-mentioned parameter; means for subjecting the reference material to the parameter of the test material; an elongate optical waveguide at least partly immersed in the reference material; and means for measuring th transmission of light passed along the optical waveguide, so a to provide a measurement depending on the value of the paramet of the reference material and thus of the test material.
  • the parameter is temperature
  • the means for holding the reference material (which may, for example, be a substantially closed receptacle, or a conduit through which the reference material is passed in use) is generally thermally conducting and is in thermal contact with the test material (for example, immersed in the test material) in order to ensure that the reference material is at substantially the same temperature as the test material.
  • the means for holding the reference material is preferably a substantially closed receptacle having provision to allow the reference material to be subject to the same pressure as the test material.
  • the apparatus preferably further includes a ligh source (such as a laser) optically coupled to an end of the waveguide, and light detection means arranged to generate a signal representative of the quantity of light transmitted fro the light source via the waveguide.
  • a ligh source such as a laser
  • light detection means arranged to generate a signal representative of the quantity of light transmitted fro the light source via the waveguide.
  • the light detection means may, in one embodiment of the invention, be coupled to an output end of the waveguide remote from the light source end. However, this may necessitate the location of processing electronics at the output end; according to another embodiment of the invention, therefore, the waveguide may be provided with a reflective end remote from the light source. In this case, the light detection means is coupled to an output end of the waveguide remote from the reflective end.
  • the optical waveguide used in the apparatus according to the invention preferably comprises an elongate body with a polygonal (for example, rectangular or square) cross-section, preferably with geometrically parallel flat surfaces along the length of the waveguide (or at least along the portion of waveguide which is in contact with the test material) .
  • a waveguide with such parallel surfac substantially minimises distortion and loss of clarity of the transmitted optical beam.
  • the flat surfaces of the body of polygonal cross-section may advantageously be polished to optical quality.
  • apparatus for measuring a parameter of a test material through changes in the refractiv index thereof produced by or related to changes in the parameter including an elongate optical waveguide along whic light is passed by internal reflection, the waveguide having a least one portion in optical contact with the test material i which the transverse cross-section of the portion which is in contact with the test material has at least one straight side.
  • the present invention further comprise a method of measuring a parameter of a test material through changes In the refractive index thereof produced by or related to changes in the relevant parameter, which comprises transmitting light along the waveguide of apparatus according to the invention » monitoring attenuation of light along the waveguide so as to provide a measurement depending on the value of the parameter of the reference material and thus of the test material.
  • Figure 1 is a section in a vertical central plan of a temperature probe according to the invention.
  • Figure 2 shows part of the probe shown in Figure 1 at enlarged scale
  • FIG. 3 shows part of a pressure probe accordin to the invention which is a modification of the temperature probe shown in Figure 2;
  • Figure 4 is a sectional view of a further embodiment of temperature probe according to the invention.
  • Figure 5 is a block diagram of a system for usin the probes shown in Figures 1 to 4; and Figure 6 is a block diagram of an alternative system for using probes according to the invention.
  • a temperature probe is immersed in a test fluid material 11, of which the temperature is to be measured.
  • Th probe 10 includes a thermally conducting elongate vessel 12 containing a reference fluid 13, and especially a liquid, of which the variation of optical refractive index with changes temperature thereof is known.
  • An elongate optical transducer or optical waveguide 14 is immersed in the fluid 13 and is of a suitable high quality transparent material such as glass.
  • the cross section of the transducer 14 may be circular but is preferabl polygonal, especially of rectangular or square cross-section.
  • the end and side faces of the transducer 14 are preferably polished to optical quality.
  • a photo-detector 15 is positioned against the bottom face of the transducer 14, to receive all the light emitting therefrom and to produce an electrical signal dependent on the intensity of that light.
  • FIG. 2 shows the transducer 14 in more detail
  • the upper and lower lengths 16,17 of all the side faces of th transducer 14 and also the upper end face 18 are all provided with a mirror-like reflective coating, such as deposited silv or aluminium.
  • the faces 1 between the lengths 16,17 are lef clear.
  • An optical prism 19 is optically connected with one side face of the transducer by means of a cement or liquid layer 20 having substantially the same refractive index as th transducer 14 and prism 19. There is no reflective coating the region of the layer 20, so that light 21 entering in the direction shown, will pass through the prism 19, the layer 20 and into the transducer 14, where it is reflected downwardly the reflective coating.
  • the light will be partly reflected within the transducer and partly transmitted into the fluid 13.
  • the ratio of the intensity of the reflected to the transmitted light depends on the refractive indices of the material of the transducer 14 and of the fluid 13.
  • the magnitude of the electrical signal from the photo-detector 15 will also depend on the refractive indices. More importantly variations in the refractive index of the fluid 13 due to variations in a parameter thereof such as temperature or pressure, will produce a corresponding variation in the electrical signal.
  • Figures 1 and 2 show how the probe 10 can be use to measure temperature of the fluid 11 as a consequence of the changes in refractive index of the fluid 13 with temperature.
  • Figure 3 shows a probe used to sense a different parameter of a test fluid, in this case the pressure (it is known that the refractive indices of certain fluids change wit pressure) .
  • a first optical waveguide sensor 2 and a second waveguide 14a thermally bonded along their lengths are inserted in the test liquid; the first waveguide is for temperature compensation and the second waveguide is analogous to waveguide 14 of Figures 1 and 2.
  • Upper and lower lengths 16a, 17a of the waveguide are clad and the central portion la is unclad.
  • waveguide 14 has a reflective coating 30, such that the signal transmitted along the waveguide can be reflected back to a photodetector (not shown) at or near the input end face 18a.
  • the signal from waveguide 14a (carrying an indication of temperature) is sent to the processing hardware to compensate for the effect of temperature changes. If the refractive index of the material is changed by changes of temperature and pressure, one of these parameters can be held constant and the probe 10 used to measure the other parameter. If temperature cannot be held constant, the embodiment of Figure 3 is normally used.
  • FIG. 4 A further embodiment (this time of a temperatur sensor) of a device having a reflective end 30 is shown in Figure 4, in which like parts to those of Figure 1 are denote by like reference numerals.
  • a photodetector (not shown) can be provided at or near the input end face 18a.
  • inventions of Figures 3 and 4 have the advantage that it is not necessary for delicate electronic components (such as photodetectors) to be placed in potential hostile environment.
  • Figure 5 shows how a probe 10 of the type illustrated in Figure 1 can be connected optically and electrically.
  • a light source which is preferably a laser 2 emits light to a beam splitter 23, from which part of the bea is fed back through a loop comprising a photo-detector compensator 24 and a line 25 to the laser 22, to stabilize an regulate the light output thereof.
  • the remaining light from the beam splitter 23 enters the transducer of the probe 10, as described above.
  • the probe 10 emits an electrical signal from the photo-detect 15 along a line 26 to processing hardware 27 and hence to a display 28, which displays the temperature of the fluid 11.
  • Figure 6 illustrates the way in which a sensor probe with a reflective end may be used.
  • a light source 31 (which is preferably a laser) sends part of its output to the sensor 32 and part to a reference photodiode 33.
  • the reflected output f om sensor 3 is detected by signal photodiode 34.
  • the outputs from photodiodes 33 and 34 are processed by signal processor 35, which generates a record or display at 36 of the calculated parameter, depending on the difference between the signal fro photodiode 34 and that from photodiode 33.
  • the invention is applicable to measuring suitable parameters of fluid which could be solid, liquid, vapour or gaseous.
  • a polygonal or flat-sided cross-section for the transducer or optical waveguide described in the embodiments above, it has been foun that a polygonal or flat-sided cross-section is advantageous i transducers or optical waveguides of the optical fibre type. This is especially so where the normal cladding of the optical fibre is removed from the core thereof, for use in measuring the refractive index of material in which the optical fibre is immersed.
  • Parameters other than temperature or pressure ca be measured using apparatus according to the invention, such as, for example, the concentration of a constituent which causes changes in the refractive index of the material.
  • concentration of a constituent which causes changes in the refractive index of the material is the glucose concentration in blood.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Investigating Or Analysing Materials By Optical Means (AREA)
  • Measuring Temperature Or Quantity Of Heat (AREA)

Abstract

The apparatus comprises a receptacle for holding a quantity of reference material having known variation of refractive index with changes in the test parameter (which may be temperature, pressure or the like); an elongate optical waveguide in contact with the reference material which is itself in thermal contact (in the case of temperature measurement) or under the same pressure (in the case of pressure measurement); and means for measuring the transmission of light passed along the optical waveguide, so as to provide a measurement depending on the value of the parameter of the reference material and thus of the test material.

Description

Parameter Measurement using Refractive Index Change
The present invention relates to the measuremen of a parameter of a material using refractive index changes induced by changes in the aforementioned parameter.
It is known to measure and indicate or record t refractive index of various liquids by detecting the attenuation of internally reflected light passing through a transparent optical waveguide, such as a glass rod, an optica fibre or the like.
Optical fibres generally have a central core, entirely surrounded by a plastics or glass sheath (the cladding) . In order for optical transmission along such a fibre to take place, the refractive index of the core must be greater than that of the cladding. It is well known that the relative refractive index of the core and cladding will determine the transmission characteristics of light along the optical fibre.
According to one aspect of the present invention, there is provided apparatus for measuring a parameter of a tes material, which comprises means for holding a quantity of reference material having known variation of refractive index thereof with changes in the above-mentioned parameter; means for subjecting the reference material to the parameter of the test material; an elongate optical waveguide at least partly immersed in the reference material; and means for measuring th transmission of light passed along the optical waveguide, so a to provide a measurement depending on the value of the paramet of the reference material and thus of the test material. here the parameter is temperature, the means for holding the reference material (which may, for example, be a substantially closed receptacle, or a conduit through which the reference material is passed in use) is generally thermally conducting and is in thermal contact with the test material (for example, immersed in the test material) in order to ensure that the reference material is at substantially the same temperature as the test material.
Where the parameter is pressure, the means for holding the reference material is preferably a substantially closed receptacle having provision to allow the reference material to be subject to the same pressure as the test material.
The apparatus preferably further includes a ligh source (such as a laser) optically coupled to an end of the waveguide, and light detection means arranged to generate a signal representative of the quantity of light transmitted fro the light source via the waveguide.
The light detection means may, in one embodiment of the invention, be coupled to an output end of the waveguide remote from the light source end. However, this may necessitate the location of processing electronics at the output end; according to another embodiment of the invention, therefore, the waveguide may be provided with a reflective end remote from the light source. In this case, the light detection means is coupled to an output end of the waveguide remote from the reflective end.
The optical waveguide used in the apparatus according to the invention preferably comprises an elongate body with a polygonal (for example, rectangular or square) cross-section, preferably with geometrically parallel flat surfaces along the length of the waveguide (or at least along the portion of waveguide which is in contact with the test material) . The use of a waveguide with such parallel surfac substantially minimises distortion and loss of clarity of the transmitted optical beam. The flat surfaces of the body of polygonal cross-section may advantageously be polished to optical quality.
According to another aspect of the invention, therefore, there is provided apparatus for measuring a parameter of a test material through changes in the refractiv index thereof produced by or related to changes in the parameter, including an elongate optical waveguide along whic light is passed by internal reflection, the waveguide having a least one portion in optical contact with the test material i which the transverse cross-section of the portion which is in contact with the test material has at least one straight side. The present invention further comprise a method of measuring a parameter of a test material through changes In the refractive index thereof produced by or related to changes in the relevant parameter, which comprises transmitting light along the waveguide of apparatus according to the invention» monitoring attenuation of light along the waveguide so as to provide a measurement depending on the value of the parameter of the reference material and thus of the test material.
Various embodiments of the invention are described, by way of example only, with reference to the accompanying drawings, in which:
Figure 1 is a section in a vertical central plan of a temperature probe according to the invention;
Figure 2 shows part of the probe shown in Figure 1 at enlarged scale;
Figure 3 shows part of a pressure probe accordin to the invention which is a modification of the temperature probe shown in Figure 2;
Figure 4 is a sectional view of a further embodiment of temperature probe according to the invention;
Figure 5 is a block diagram of a system for usin the probes shown in Figures 1 to 4; and Figure 6 is a block diagram of an alternative system for using probes according to the invention.
In the embodiment of Figure 1, a temperature probe, indicated generally at 10, is immersed in a test fluid material 11, of which the temperature is to be measured. Th probe 10 includes a thermally conducting elongate vessel 12 containing a reference fluid 13, and especially a liquid, of which the variation of optical refractive index with changes temperature thereof is known.
An elongate optical transducer or optical waveguide 14 is immersed in the fluid 13 and is of a suitable high quality transparent material such as glass. The cross section of the transducer 14 may be circular but is preferabl polygonal, especially of rectangular or square cross-section. The end and side faces of the transducer 14 are preferably polished to optical quality.
A photo-detector 15 is positioned against the bottom face of the transducer 14, to receive all the light emitting therefrom and to produce an electrical signal dependent on the intensity of that light.
Figure 2 shows the transducer 14 in more detail The upper and lower lengths 16,17 of all the side faces of th transducer 14 and also the upper end face 18 are all provided with a mirror-like reflective coating, such as deposited silv or aluminium. The faces 1 between the lengths 16,17 are lef clear. An optical prism 19 is optically connected with one side face of the transducer by means of a cement or liquid layer 20 having substantially the same refractive index as th transducer 14 and prism 19. There is no reflective coating the region of the layer 20, so that light 21 entering in the direction shown, will pass through the prism 19, the layer 20 and into the transducer 14, where it is reflected downwardly the reflective coating.
On reacnrng cne transducer faces which are devo of reflective coating, the light will be partly reflected within the transducer and partly transmitted into the fluid 13. The ratio of the intensity of the reflected to the transmitted light depends on the refractive indices of the material of the transducer 14 and of the fluid 13. Thus, the magnitude of the electrical signal from the photo-detector 15 will also depend on the refractive indices. More importantly variations in the refractive index of the fluid 13 due to variations in a parameter thereof such as temperature or pressure, will produce a corresponding variation in the electrical signal.
Figures 1 and 2 show how the probe 10 can be use to measure temperature of the fluid 11 as a consequence of the changes in refractive index of the fluid 13 with temperature.
Figure 3 shows a probe used to sense a different parameter of a test fluid, in this case the pressure (it is known that the refractive indices of certain fluids change wit pressure) .
Referring to Figure 3, a first optical waveguide sensor 2 and a second waveguide 14a thermally bonded along their lengths are inserted in the test liquid; the first waveguide is for temperature compensation and the second waveguide is analogous to waveguide 14 of Figures 1 and 2. Upper and lower lengths 16a, 17a of the waveguide are clad and the central portion la is unclad.
Instead of having a photodetector at the end, waveguide 14 has a reflective coating 30, such that the signal transmitted along the waveguide can be reflected back to a photodetector (not shown) at or near the input end face 18a.
The signal from waveguide 14a (carrying an indication of temperature) is sent to the processing hardware to compensate for the effect of temperature changes. If the refractive index of the material is changed by changes of temperature and pressure, one of these parameters can be held constant and the probe 10 used to measure the other parameter. If temperature cannot be held constant, the embodiment of Figure 3 is normally used.
A further embodiment (this time of a temperatur sensor) of a device having a reflective end 30 is shown in Figure 4, in which like parts to those of Figure 1 are denote by like reference numerals. A photodetector (not shown) can be provided at or near the input end face 18a.
The embodiments of Figures 3 and 4 have the advantage that it is not necessary for delicate electronic components (such as photodetectors) to be placed in potential hostile environment.
Figure 5 shows how a probe 10 of the type illustrated in Figure 1 can be connected optically and electrically. A light source, which is preferably a laser 2 emits light to a beam splitter 23, from which part of the bea is fed back through a loop comprising a photo-detector compensator 24 and a line 25 to the laser 22, to stabilize an regulate the light output thereof.
The remaining light from the beam splitter 23 enters the transducer of the probe 10, as described above. The probe 10 emits an electrical signal from the photo-detect 15 along a line 26 to processing hardware 27 and hence to a display 28, which displays the temperature of the fluid 11.
Figure 6 illustrates the way in which a sensor probe with a reflective end may be used.
A light source 31 (which is preferably a laser) sends part of its output to the sensor 32 and part to a reference photodiode 33. The reflected output f om sensor 3 is detected by signal photodiode 34. The outputs from photodiodes 33 and 34 are processed by signal processor 35, which generates a record or display at 36 of the calculated parameter, depending on the difference between the signal fro photodiode 34 and that from photodiode 33. The invention is applicable to measuring suitable parameters of fluid which could be solid, liquid, vapour or gaseous.
In addition to the use of a polygonal or flat-sided cross-section for the transducer or optical waveguide described in the embodiments above, it has been foun that a polygonal or flat-sided cross-section is advantageous i transducers or optical waveguides of the optical fibre type. This is especially so where the normal cladding of the optical fibre is removed from the core thereof, for use in measuring the refractive index of material in which the optical fibre is immersed.
Parameters other than temperature or pressure ca be measured using apparatus according to the invention, such as, for example, the concentration of a constituent which causes changes in the refractive index of the material. One such parameter is the glucose concentration in blood.

Claims

CLAIMS :
1. Apparatus for measuring a parameter of a test material, which comprises means for holding a quantity of reference material having known variation of refractive index thereof with changes in said parameter; means for subjecting the reference material to the parameter of the test material; an elongate optical waveguide in contact with in the reference material; and means for measuring the transmission of light passed along the optical waveguide, so as to provide a measurement depending on the value of the parameter of the reference material and thus of the test material.
2. Apparatus according to claim 1, wherein said means for holding a quantity of reference material comprises a substantially closed receptacle in which said optical waveguide is at least partially immersed.
3. Apparatus according to claim 2, wherein said parameter is temperature and said receptacle is thermally conducting.
4. Apparatus according to claim 2, wherein said parameter is pressure and said receptacle includes means to ensure that said reference material is subject to substantially the same pressure as said test material.
5. Apparatus according to any of claims 1 to 4, wherein said waveguide has at least one portion in optical contact with said reference material of which the transverse cross-section of said portion has a straight side.
6. Apparatus according to claim 5, wherein the cross-section of said portion is polygonal, such as rectangular or square. 7. Apparatus according to any of claims 1 to 6, which further includes a light source optically coupled to an end of the waveguide, and light detection means arranged to generate a signal representative of the quantity of light transmitted from the light source via the waveguide.
7. Apparatus according to claim 7, wherein said waveguide has a reflective end remote from said light source end, said light detection means being coupled to an output end of said waveguide remote from said reflective end.
8. Apparatus for measuring a parameter of a test material through changes in the refractive index thereof produced by or related to changes in said parameter, including an elongate optical waveguide along which light is passed by internal reflection, the waveguide having at least one portion in optical contact with said material and in which the transverse cross-section of the said portion has a straight side.
9. Apparatus according to claim 8, wherein the cross-section of said portion is polygonal, such as rectangular or square.
10. A method of measuring a parameter of a test material through changes in the refractive index thereof produced by or related to changes in said parameter, which comprises transmitting light along the waveguide of apparatus according to any of claims 1 to 9, monitoring attenuation of light along said waveguide so as to provide a measurement depending on the value of the parameter of the reference material and thus of the test material.
PCT/GB1989/001012 1988-08-31 1989-08-31 Parameter measurement using refractive index change WO1990002322A1 (en)

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GB8820537A GB2223841A (en) 1988-08-31 1988-08-31 Parameter measurement using refractive index change
GB8820537.2 1988-08-31

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GB2256270A (en) * 1991-05-31 1992-12-02 De Beers Ind Diamond Determination of the condition of or change in state of an environment
CN107677341A (en) * 2017-10-30 2018-02-09 吉林大学 Fiber optic interferometric level sensing device and method based on air refraction

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GB2256270A (en) * 1991-05-31 1992-12-02 De Beers Ind Diamond Determination of the condition of or change in state of an environment
GB2256270B (en) * 1991-05-31 1995-04-19 De Beers Ind Diamond Determination of the condition of or change in state of an environment
CN107677341A (en) * 2017-10-30 2018-02-09 吉林大学 Fiber optic interferometric level sensing device and method based on air refraction
CN107677341B (en) * 2017-10-30 2023-04-07 吉林大学 Optical fiber interference water level sensing device and method based on air refractive index

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GB2223841A (en) 1990-04-18
GB8820537D0 (en) 1988-09-28
AU4191489A (en) 1990-03-23

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