CN106442364B - Concentration sensor based on F-P cavity formed by coating film on end face of optical fiber - Google Patents
Concentration sensor based on F-P cavity formed by coating film on end face of optical fiber Download PDFInfo
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- CN106442364B CN106442364B CN201611092815.2A CN201611092815A CN106442364B CN 106442364 B CN106442364 B CN 106442364B CN 201611092815 A CN201611092815 A CN 201611092815A CN 106442364 B CN106442364 B CN 106442364B
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- 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
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
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- 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
- G01N21/45—Refractivity; Phase-affecting properties, e.g. optical path length using interferometric methods; using Schlieren methods
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- G—PHYSICS
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- 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
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Abstract
The invention discloses a concentration sensor based on an F-P cavity formed by coating films on the end faces of optical fibers. The first optical fiber and the second optical fiber are respectively located on the left side face and the right side face of the detection cavity, the objective table is located at the bottom of the detection cavity, the glass slide is placed on the objective table, the detachable dropper is located at the top of the detection cavity and is right opposite to the glass slide, liquid to be detected is sucked in by the dropper and is dripped on the glass slide, light emitted by the wide-spectrum light source passes through an F-P cavity formed by the first optical fiber coating end face and the second optical fiber coating end face and becomes a specific wavelength interference peak, a spectrum is displayed on the spectrum analyzer, and due to the fact that the center wavelength of the transmission spectrum and the refractive index of the liquid have a linear relation, the concentration of the liquid is obtained through the refractive index of the liquid. The invention has the advantages of electromagnetic interference resistance, corrosion resistance and repeated use.
Description
Technical Field
The invention provides a concentration sensor for forming an F-P cavity based on a film coating on an optical fiber end face, and belongs to the technical field of liquid concentration detection.
Background
Fiber optic F-P sensors are widely used because of a number of advantages. According to the demodulation principle of the F-P sensor, the quality of the interference signal output by the sensor directly influences the precision and the measurement distance of the demodulation system, and has great influence on the performance requirements of a light source and a light detector which form the demodulation system. However, in practice, the loss of light in the F-P cavity inevitably causes the signal intensity of the sensor to be reduced, the contrast ratio is poor, and the measurement accuracy of the system is reduced.
The improvement of the end face reflectivity of the optical fiber reflected by the sensor can improve the signal quality, the end face reflectivity of the F-P sensor is optimized, the output signal quality is improved, and the continuous high-precision detection of the material refractive index can be realized due to the linear relation between the central wavelength of the transmission spectrum of the optical fiber Fabry-Perot interferometer and the refractive index of the medium in the interference cavity, and the method has the advantages of electromagnetic interference resistance, corrosion resistance and the like, and has good practical value.
The spectrum analyzer is an instrument for detecting spectrum signals and has the advantages of fast dynamic response, wide dynamic range, high sensitivity, small equivalent noise bandwidth, high precision and the like.
Disclosure of Invention
Aiming at the defects of the prior art, the invention designs a sensor with an F-P cavity structure formed by coating a film on the end face of an optical fiber, and accurately measures the concentration of liquid on the basis of the functional relationship between the central wavelength and the refractive index of a transmission spectrum, the reflection wavelength and the cavity length and the functional relationship between the refractive index of the liquid and the concentration; the optical fiber end face is scrubbed through the alcohol cotton ball, so that the cleanness of the optical fiber end face is guaranteed, and the measurement precision is improved for the measurement of the next experiment.
The invention is realized by the following technical scheme: a concentration sensor based on an F-P cavity formed by coating films on the end faces of optical fibers comprises a wide-spectrum light source (1), a first optical fiber (2), a second optical fiber (3), a detection cavity (4), an adjustable object stage (5), a glass slide (6), a detachable dropper (7) and a spectrum analyzer (8); the detection device comprises a first optical fiber (2) and a second optical fiber (3), an object stage (5) is positioned at the bottom of the detection cavity (4), a glass slide (6) is placed on the object stage (5), a detachable dropper (7) is positioned at the top of the detection cavity (4) and is opposite to the glass slide (6), the front cover of the detection cavity (4) can be opened for removing the glass slide (6) and cleaning the end faces of the first optical fiber (2) and the second optical fiber (3), liquid to be detected is sucked in by the dropper (7) and is dripped on the glass slide (6), light emitted by a wide-spectrum light source (1) passes through an F-P cavity formed by the coated end face of the first optical fiber (2) and the coated end face of the second optical fiber (3) to become a specific wavelength interference peak, a spectrum is displayed on a spectrum analyzer (8), and the central wavelength of a transmission spectrum has a linear relation with the refractive index of the liquid, so that the concentration of the liquid is obtained through the refractive index of the liquid; after the detection is finished, the front cover of the detection cavity (4) can be opened, the glass slide (6) is removed by adjusting the height of the objective table (5), and the end faces of the first optical fiber (2) and the second optical fiber (3) are cleaned by cotton balls stained with alcohol.
The working wavelength of the wide-spectrum light source (1) is 1530nm-1580nm.
The end faces of the first optical fiber (2) and the second optical fiber (3) are plated with silver films.
The central wavelength of the first optical fiber (2) and the central wavelength of the second optical fiber (3) are both 1550nm.
The working principle of the invention is as follows: based on the interference characteristic of F-P structure interference, when non-monochromatic parallel light is incident at an incident angle i, only certain specific wavelengths lambda exist in a certain spectral range due to the effect of multi-beam interference k A maximum occurs nearby, and when i =0, the following formula is satisfied:
2nH＝kλ k (1)
wherein n is the refractive index of the liquid in the F-P cavity, H is the length of the F-P cavity, k is the interference order, and lambda k Is the central wavelength of the interference peak.
A standard medium (known as refractive index n) is placed in the detection chamber 0 Corresponding to the k-th order interference peak center wavelength of λ k0 ) The refractive index n and the central wavelength λ of the interference peak are obtained from the formula (1) k The relationship of (c) is:
n＝(n 0 /λ k0 )λ k (2)
as can be seen from the formula (2), for a certain interference order under a specific wavelength, the change of the F-P structure interference transmission peak wavelength is in linear relation with the change of the refractive index of the medium in the cavity.
When the cavity length of the optical fiber F-P cavity meets the condition:
H＝(2m-1)λ b /4n eff (3)
in the formula n eff Is the effective refractive index of the optical fiber, m is the interference order, and the F-P cavity is at lambda b The transmission peak is very large. The length of the substance to be measured can be determined by determining the cavity length H by the equation (3).
The refractive index n of the liquid is related to the liquid concentration level C and the temperature T, i.e.:
n＝n(C，T) (4)
by differentiating the equation (4), the change amount of the liquid refractive index can be obtained as:
in the formula
The sensitivity of the refractive index of a liquid to changes in liquid concentration and temperature, respectively, differs by a factor of 1000 for most liquids. Therefore, if the temperature change during the measurement is not large (Δ T is less than 1 to 2 ℃), the influence of the temperature on the refractive index is negligible, and thus the change in the refractive index is mainly determined by the liquid concentration. The relationship between the change of the liquid concentration and the change of the refractive index is as follows:
for liquids with a linear relationship of refractive index to concentration over a range,
is constant, the concentration of the liquid to be measured can thus be obtained as:
therefore, when different liquids are dropped into the detection chamber (4), the spectrum analyzer (8) outputs a waveform, the refractive index and length of the liquid can be obtained by simple calculation, and the concentration of the liquid can be obtained from the relationship between the refractive index and the concentration of the liquid.
The beneficial effects of the invention are: the invention designs the sensor which forms an F-P cavity structure by coating a film on the end face of the optical fiber, accurately measures the concentration of liquid on the basis of the functional relation of the central wavelength and the refractive index of a transmission spectrum, the reflection wavelength and the cavity length and the functional relation of the refractive index and the concentration of the liquid, and has strong innovation and practical value and good application prospect.
Drawings
FIG. 1 is a schematic structural diagram of a concentration sensor based on an F-P cavity formed by a coating film on an end face of an optical fiber.
Detailed Description
As shown in figure 1, the concentration sensor based on the F-P cavity formed by the coating on the end face of the optical fiber consists of a wide-spectrum light source (1), a first optical fiber (2), a second optical fiber (3), a detection cavity (4), an adjustable object stage (5), a glass slide (6), a detachable dropper (7) and a spectrum analyzer (8); the first optical fiber (2) and the second optical fiber (3) are respectively positioned on the left side surface and the right side surface of the detection cavity (4), the objective table (5) is positioned at the bottom of the detection cavity (4), the glass slide (6) is placed on the objective table (5), the detachable dropper (7) is positioned at the top of the detection cavity (4) and is opposite to the glass slide (6), the front cover of the detection cavity (4) can be opened for removing the glass slide (6) and cleaning the end surfaces of the first optical fiber (2) and the second optical fiber (3); the working principle of the invention is as follows: a liquid to be measured is sucked by a dropper (7) and is dripped on a glass slide (6), light emitted by a wide-spectrum light source (1) passes through an F-P cavity formed by a coated end face of a first optical fiber (2) and a coated end face of a second optical fiber (3) to become a specific wavelength interference peak, a spectrum is displayed on a spectrum analyzer (8), and the concentration of the liquid is obtained through the refractive index of the liquid due to the linear relation between the central wavelength of a transmission spectrum and the refractive index of the liquid; after the detection is finished, the front cover of the detection cavity (4) can be opened, the glass slide (6) is removed by adjusting the height of the objective table (5), and the end faces of the first optical fiber (2) and the second optical fiber (3) are cleaned by cotton balls stained with alcohol.
Claims (4)
1. A concentration sensor based on an F-P cavity formed by coating films on the end faces of optical fibers comprises a wide-spectrum light source (1), a first optical fiber (2), a second optical fiber (3), a detection cavity (4), an adjustable object stage (5), a glass slide (6), a detachable dropper (7) and a spectrum analyzer (8); the first optical fiber (2) and the second optical fiber (3) are respectively positioned on the left side surface and the right side surface of the detection cavity (4), the objective table (5) is positioned at the bottom of the detection cavity (4), the glass slide (6) is placed on the objective table (5), the detachable dropper (7) is positioned at the top of the detection cavity (4) and is opposite to the glass slide (6), the front cover of the detection cavity (4) can be opened for removing the glass slide (6) and cleaning the end surfaces of the first optical fiber (2) and the second optical fiber (3); a liquid to be measured is sucked by a dropper (7) and is dripped on a glass slide (6), light emitted by a wide-spectrum light source (1) passes through an F-P cavity formed by a coated end face of a first optical fiber (2) and a coated end face of a second optical fiber (3) to become a specific wavelength interference peak, a spectrum is displayed on a spectrum analyzer (8), and the concentration of the liquid is obtained through the refractive index of the liquid due to the linear relation between the central wavelength of a transmission spectrum and the refractive index of the liquid; after the detection is finished, the front cover of the detection cavity (4) can be opened, the glass slide (6) is removed by adjusting the height of the objective table (5), and the end faces of the first optical fiber (2) and the second optical fiber (3) are cleaned by cotton balls stained with alcohol.
2. The concentration sensor based on the F-P cavity formed by the optical fiber end face coating film according to claim 1, characterized in that: the end faces of the first optical fiber (2) and the second optical fiber (3) are plated with silver films.
3. The concentration sensor based on the F-P cavity formed by the optical fiber end face coating film according to claim 1, characterized in that: the central wavelength of the first optical fiber (2) and the central wavelength of the second optical fiber (3) are both 1550nm.
4. The concentration sensor based on the F-P cavity formed by the coating on the end face of the optical fiber as claimed in claim 1, wherein: the working wavelength of the broad spectrum light source (1) is 1530nm-1580nm.
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| US6687011B1 (en) * | 1999-04-23 | 2004-02-03 | Korea Advanced Institute Science And Technology | Transmission-type extrinsic fabry-perot interferometric optical fiber sensor |
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| CN102495023A (en) * | 2011-11-22 | 2012-06-13 | 电子科技大学 | Method for determining liquid medium refractive index by using optical fiber sensing technology |
| CN102944328A (en) * | 2012-12-17 | 2013-02-27 | 南京大学 | Preparation method and measurement device for temperature sensor insensitive to refractive index |
| CN204613104U (en) * | 2015-05-12 | 2015-09-02 | 中国计量学院 | A kind of light fibre humidity transducer based on dislocation welding |
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| CN206208747U (en) * | 2016-11-29 | 2017-05-31 | 中国计量大学 | A kind of concentration sensor that F P chambers are constituted based on fiber end face plated film |
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- 2016-11-29 CN CN201611092815.2A patent/CN106442364B/en active Active
Patent Citations (7)
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| US6687011B1 (en) * | 1999-04-23 | 2004-02-03 | Korea Advanced Institute Science And Technology | Transmission-type extrinsic fabry-perot interferometric optical fiber sensor |
| CN101451959A (en) * | 2008-12-30 | 2009-06-10 | 清华大学 | Hydrogen sensor and pd film hydrogen sensing system |
| CN102495023A (en) * | 2011-11-22 | 2012-06-13 | 电子科技大学 | Method for determining liquid medium refractive index by using optical fiber sensing technology |
| CN102944328A (en) * | 2012-12-17 | 2013-02-27 | 南京大学 | Preparation method and measurement device for temperature sensor insensitive to refractive index |
| CN204613104U (en) * | 2015-05-12 | 2015-09-02 | 中国计量学院 | A kind of light fibre humidity transducer based on dislocation welding |
| CN106124414A (en) * | 2016-08-24 | 2016-11-16 | 马鞍山市安工大工业技术研究院有限公司 | A kind of highly sensitive optical fiber EFPI sensor and preparation method thereof |
| CN206208747U (en) * | 2016-11-29 | 2017-05-31 | 中国计量大学 | A kind of concentration sensor that F P chambers are constituted based on fiber end face plated film |
Non-Patent Citations (1)
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