CN115372269B - Method for measuring gas refractive index and concentration based on circular polarization laser - Google Patents
Method for measuring gas refractive index and concentration based on circular polarization laser Download PDFInfo
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- CN115372269B CN115372269B CN202211303620.3A CN202211303620A CN115372269B CN 115372269 B CN115372269 B CN 115372269B CN 202211303620 A CN202211303620 A CN 202211303620A CN 115372269 B CN115372269 B CN 115372269B
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- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
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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
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- G01N21/41—Refractivity; Phase-affecting properties, e.g. optical path length
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- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
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- G01N2021/216—Polarisation-affecting properties using circular polarised light
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Abstract
The invention relates to a method for measuring gas refractive index and concentration based on circular polarization laser, which comprises the following steps: the laser light source emits circular polarized laser, the circular polarized laser is divided into horizontal polarized laser and vertical polarized laser through the polarization beam splitter, the horizontal polarized laser is transmitted into the optical fiber coupler through the first optical fiber, the hollow optical fiber air chamber and the second optical fiber, the vertical polarized laser through the third optical fiber is transmitted into the optical fiber coupler, the two polarized lasers form elliptical polarized laser in the optical fiber coupler, the elliptical polarized laser is transmitted to the polarization measuring instrument through a third connector of the optical fiber coupler, and the refractive index and the concentration of the gas to be measured are calculated according to the polarization parameters in the polarization measuring instrument.
Description
Technical Field
The invention relates to the technical field of laser measurement, in particular to a method for measuring gas refractive index and concentration based on circular polarization laser.
Background
Because some important devices and equipment are easy to generate some toxic, flammable and explosive gases in the process of leakage in the operation process, the existence of the gases directly harms the safety of people and equipment and pollutes the surrounding environment. In order to minimize the existing risks, a low-cost on-line testing method for long-distance trace gases is particularly important and urgent.
Wavelength modulation spectroscopy is a way to enhance the sensitivity of gas measurements, and is especially important when measuring smaller concentrations. The concentration of the gas to be measured is usually calculated by measuring the spectral intensity of the incident light and the emitted light. However, the existing measurement method is not high in precision and is acceptable in some situations with low requirements, but in some environments with high requirements for precision, the existing measurement method cannot accurately measure the concentration of harmful gas in the space, and therefore, it is necessary to develop a system method for accurate measurement.
Disclosure of Invention
The invention aims to solve the technical problem that the existing laser gas measurement method is low in precision, and provides a method for measuring the refractive index and the concentration of gas based on circular polarization laser.
Some embodiments of the invention provide a method for measuring gas refractive index and concentration based on circular polarized laser, comprising the following steps:
the laser source emits circular polarization laser which is divided into horizontal polarization laser and vertical polarization laser through a polarization beam splitter, the horizontal polarization laser is coupled into a first optical fiber through a first coupling lens, the first optical fiber is fused with the left end of a hollow optical fiber air chamber, the right end of the hollow optical fiber air chamber is fused with the left end face of a second optical fiber, the right end face of the second optical fiber is connected with a first connector of an optical fiber coupler, the horizontal polarization laser is transmitted into the hollow optical fiber air chamber containing gas to be measured through the optical fiber, the horizontal polarization laser passing through the hollow optical fiber air chamber is transmitted into the second optical fiber, the horizontal polarization laser passing through the second optical fiber is transmitted into the optical fiber coupler through the first connector of the optical fiber coupler, the vertical polarization laser is coupled into one end face of a third optical fiber through the second coupling lens, the other end face of the third optical fiber is connected with a second connector of the optical fiber coupler, the vertical polarization laser passing through the third optical fiber is transmitted into the optical fiber coupler through the second connector of the optical fiber coupler, the vertical polarization laser is transmitted into the optical fiber coupler and the horizontal polarization laser in the optical fiber coupler, the vertical polarization laser is transmitted into an elliptical polarization laser concentration measurement instrument through the optical fiber coupler, and the elliptical polarization laser, and the concentration measurement instrument is calculated according to be measured.
In some embodiments, calculating the refractive index and the concentration of the gas to be measured according to the polarization parameter in the polarization measuring instrument includes:
determining the phase difference between the horizontally polarized laser and the vertically polarized laser according to the polarization measuring instrument
；
According to the formula of phase difference
To calculate the refractive index n of the gas to be measured 2 Wherein n is 1 Is the refractive index of the optical fiber,
the wavelength of the laser, L is the length of the hollow optical fiber air chamber;
determining the concentration C of the gas to be measured according to the following formula:
wherein n is 0 Is the refractive index of air, k is the proportionality coefficient, P 0 The atmospheric pressure, R is the gas constant of the gas to be measured, and T is the gas temperature of the gas to be measured.
In some embodiments, a sum of a physical length of the first optical fiber, a physical length of the hollow-core fiber gas cell, and a physical length of the second optical fiber is equal to a physical length of the third optical fiber.
In some embodiments, the laser light source has a central output wavelength line width of less than 1nm.
In some embodiments, the polarizing beam splitter comprises a glan prism.
In some embodiments, at least one of the first and second coupling lenses comprises a plano-convex lens made of a calcium fluoride material.
In some embodiments, the first connector and the second connector of the fiber coupler are equal in length.
Compared with the related art, the invention at least has the following technical effects:
the circular polarization laser is divided into two bunches of polarization lasers, one bunch of polarization lasers passes through the gas to be measured, the other bunch of linear polarization lasers does not pass through the gas to be measured, the refractive index and the concentration value of the gas to be measured are determined according to the phase difference of the two bunches of linear polarization lasers, and the measurement accuracy is improved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and those skilled in the art can also obtain other drawings according to the drawings without creative efforts.
Fig. 1 is a schematic structural diagram of a device for measuring refractive index and concentration of a gas according to some embodiments of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention clearer, the present invention will be described in further detail with reference to the accompanying drawings, and it is apparent that the described embodiments are only a part of the embodiments of the present invention, not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The terminology used in the embodiments of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in the examples of the present invention and the appended claims, the singular forms "a", "an", and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise, and "a plurality" typically includes at least two.
It should be understood that the term "and/or" as used herein is merely one type of association that describes an associated object, meaning that three relationships may exist, e.g., a and/or B may mean: a exists alone, A and B exist simultaneously, and B exists alone. In addition, the character "/" herein generally indicates that the former and latter related objects are in an "or" relationship.
It is also noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that an article or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such article or apparatus. Without further limitation, an element defined by the phrase "comprising a" does not exclude the presence of another, identical element in a commodity or a device comprising the element.
The invention provides a method for measuring gas refractive index and concentration based on circular polarization laser, which comprises the following steps:
a method for measuring the refractive index and the concentration of gas based on circular polarized laser comprises the following steps: the laser light source emits circular polarization laser, the circular polarization laser is divided into horizontal polarization laser and vertical polarization laser through a polarization beam splitter, the horizontal polarization laser is coupled into a first optical fiber through a first coupling lens, the first optical fiber is fused with the left end of a hollow optical fiber air chamber, the right end of the hollow optical fiber air chamber is fused with the left end face of a second optical fiber, the right end face of the second optical fiber is connected with a first connector of an optical fiber coupler, the horizontal polarization laser is transmitted into the hollow optical fiber air chamber containing gas to be measured through the optical fiber, the horizontal polarization laser transmitted into the second optical fiber through the hollow optical fiber air chamber is transmitted into the optical fiber coupler through the first connector of the optical fiber coupler, the vertical polarization laser is coupled into one end face of a third optical fiber through a second coupling lens, the other end face of the third optical fiber is connected with a second connector of the optical fiber coupler, the vertical polarization laser is transmitted into the optical fiber coupler through the second connector of the optical fiber coupler, the vertical polarization laser is transmitted into the optical fiber coupler, the horizontal polarization laser and the elliptical polarization laser concentration measuring instrument is calculated according to the optical fiber polarization signal.
The invention divides the circular polarized laser into two bunches of polarized laser, wherein one bunch of polarized laser passes through the gas to be measured, the other bunch of linearly polarized laser does not pass through the gas to be measured, and the refractive index and concentration value of the gas to be measured are determined according to the phase difference of the two bunches of linearly polarized laser.
Alternative embodiments of the present invention are described in detail below with reference to the accompanying drawings.
Fig. 1 is a schematic structural diagram of a device for measuring refractive index and concentration of a gas according to some embodiments of the present invention, and as shown in fig. 1, some embodiments of the present invention provide a method for measuring refractive index and concentration of a gas based on circularly polarized laser, which specifically includes the following steps:
the laser light source 1 emits circularly polarized laser, the circularly polarized laser is divided into horizontally polarized laser and vertically polarized laser through a polarization beam splitter 2, the horizontally polarized laser is coupled into a first optical fiber 4 through a first coupling lens 3, the first optical fiber 4 is fused with the left end of a hollow optical fiber air chamber 5, the right end of the hollow optical fiber air chamber 5 is fused with the left end face of a second optical fiber 6, the right end face of the second optical fiber 6 is connected with a first connector 10-1 of an optical fiber coupler 10, the horizontally polarized laser is transmitted into the hollow optical fiber air chamber 5 containing gas to be measured through the first optical fiber 4, the horizontally polarized laser passing through the hollow optical fiber air chamber 5 is transmitted into the second optical fiber 6, the horizontally polarized laser passing through the second optical fiber 6 is transmitted into the optical fiber coupler 10 through the first connector 10-1 of the optical fiber coupler, the vertically polarized laser is coupled into one end face of a third optical fiber 9 through a second coupling lens 8, for example, the left end face shown in fig. 1, the other end face of the third optical fiber 9, for example, the light is transmitted into an elliptical polarized laser measuring instrument through the second optical fiber coupler 10-10, the elliptical polarized laser, the concentration measuring instrument is calculated according to the third polarized laser, the concentration of the laser, the laser is calculated by the optical fiber coupler 10, and the optical fiber coupler 10, the elliptical polarization measuring instrument, the elliptical polarization laser is connected into the elliptical polarization measuring instrument, and the elliptical polarization optical fiber coupler 10.
In some embodiments, the first, second and third optical fibers 4, 6, 9 are single mode optical fibers.
In some embodiments, calculating the refractive index and the concentration of the gas to be measured according to the polarization parameter in the polarization measuring apparatus 11 specifically includes the following steps:
determining the phase difference between the horizontally polarized laser and the vertically polarized laser according to the polarization measuring instrument 11
；
According to the formula of phase difference
To calculate the refractive index n of the gas to be measured 2 Wherein n is 1 Which is the refractive index of the optical fiber,
the wavelength of the laser, L is the length of the hollow optical fiber air chamber;
determining the concentration C of the gas to be measured according to the following formula:
\8230A, a structure of 82308230a structure of 823030in formula (1) wherein n 0 Is the refractive index of air, k is the proportionality coefficient, P 0 And R is the atmospheric pressure, R is the gas constant of the gas to be measured, and T is the gas temperature of the gas to be measured.
Specifically, the formula (1) is determined in such a manner that, for the gas to be measured, the refractive index thereof satisfies the following formula:
\8230; \ 8230; (2) where n is 0 Is the refractive index of air, k proportionality coefficient is constant, P 0 Is atmospheric pressure, P 2 For gas to be measuredAnd (4) the pressure.
The concentration of the gas to be measured satisfies the following formula:
\8230; ' 8230 '; ' 3),
wherein the content of the first and second substances,
for the mass density of the gas to be measured (unit kg/m) 3 ) M is the molar mass of the gas to be measured,
the gas state equation for the gas to be measured is as follows:
Formula (1) can be obtained by combining formulae (2) to (4).
In some embodiments, as shown in FIG. 1, the sum of the physical length of the first optical fiber 4, the physical length of the hollow-core fiber gas cell 5, and the physical length of the second optical fiber 6 is substantially equal to the physical length of the third optical fiber 9. The optical path difference is conveniently generated in the transmission process of the horizontally polarized laser and the vertically polarized laser, so that the optical path difference between the horizontally polarized laser passing through the gas to be detected and the vertically polarized laser not passing through the gas to be detected, which is caused by the gas to be detected, can be determined, and the phase difference between the horizontally polarized laser and the vertically polarized laser can be further determined.
In some embodiments, the laser light source 1 may be a circularly polarized laser with an arbitrary center output wavelength. The central output wavelength corresponds to the gas characteristic absorption peak of the gas to be measured. For example, the gas to be measured is SO 2 The characteristic absorption peak of the gas is 3980nm, and the laser light source 1 can output circularly polarized laser with the central output wavelength of 3980 nm. The laser light source 1 is, for example, a narrow linewidth laser light source, and the central output wavelength linewidth is less than 1nm.
In some embodiments, the polarization beam splitter 2 includes a glan prism, and can split the circularly polarized laser light into horizontally polarized laser light and vertically polarized laser light having the same energy.
In some embodiments, at least one of the first coupling lens 3 and the second coupling lens 8 comprises a plano-convex lens made of calcium fluoride material. The first coupling lens 3 can focus the horizontally polarized laser light into the first optical fiber 4 for transmission, and the second coupling lens 8 focuses the vertically polarized laser light into the third optical fiber 9 for transmission.
In some embodiments, the hollow-core fiber gas chamber 5 is a gas pool required by any gas, and two ends of the hollow-core fiber gas chamber 5 are respectively welded to the first optical fiber 4 and the second optical fiber 6, so that the horizontally polarized laser can be conveniently transmitted in the hollow-core fiber gas chamber 5.
In some embodiments, the optical fiber coupler 10 is a device combining a horizontally polarized laser and a vertically polarized laser, the horizontally polarized laser and the vertically polarized laser are coupled in the optical fiber coupler 10, and the first connector 10-1 and the second connector 10-2 of the optical fiber coupler 10 have the same length. The first connector 10-1 of the optical fiber coupler 10 is connected with the second optical fiber 6, the second connector 10-2 of the optical fiber coupler 10 is connected with the third optical fiber 9, and the third connector 10-3 of the optical fiber coupler 10 is an output end and is connected with the polarization measuring instrument 11. The refractive index and concentration of the gas to be measured can be calculated according to the polarization parameters of the polarization measuring instrument 11.
Finally, it should be noted that: the embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. The system or the device disclosed by the embodiment corresponds to the method disclosed by the embodiment, so that the description is simple, and the relevant points can be referred to the method part for description.
The above examples are only intended to illustrate the technical solution of the present invention, and not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (6)
1. A method for measuring the refractive index and concentration of gas based on circular polarized laser is characterized in that,
the method comprises the following steps:
the laser source (1) emits circularly polarized laser which is divided into horizontally polarized laser and vertically polarized laser by a polarization beam splitter (2), the horizontally polarized laser is coupled into a first optical fiber (4) by a first coupling lens (3), the first optical fiber (4) is fused with the left end of a hollow optical fiber air chamber (5), the right end of the hollow optical fiber air chamber (5) is fused with the left end of a second optical fiber (6), the right end of the second optical fiber (6) is connected with a first connector (10-1) of an optical fiber coupler (10), the horizontally polarized laser is transmitted into the hollow optical fiber air chamber (5) containing gas to be tested by the first optical fiber (4), the horizontally polarized laser passing through the air chamber (5) is transmitted into the second optical fiber (6), the horizontally polarized laser passing through the second optical fiber (6) is transmitted into the optical fiber coupler (10) by the first connector (10-1) of the optical fiber coupler, the vertically polarized laser passing through the second optical fiber lens (8) is coupled into the third optical fiber coupler (10), the vertically polarized laser is transmitted into the optical fiber coupler (10) by the second optical fiber coupler (9), the third optical fiber coupler (9), the horizontal direction polarization laser and the vertical direction polarization laser transmitted to the optical fiber coupler (10) form elliptical polarization laser in the optical fiber coupler (10), the elliptical polarization laser is transmitted to the polarization measuring instrument (11) through a third connector (10-3) of the optical fiber coupler (10), the refractive index and the concentration of the gas to be measured are calculated according to the polarization parameter in the polarization measuring instrument (11), and the refractive index and the concentration of the gas to be measured are calculated according to the polarization parameter in the polarization measuring instrument (11) comprise:
determining the phase difference between the horizontally polarized laser and the vertically polarized laser according to the polarization measuring instrument (11)
；
According to the formula of phase difference
To calculate the refractive index n of the gas to be measured 2 Wherein n is 1 Which is the refractive index of the optical fiber,
the wavelength of the laser, L is the length of the hollow optical fiber air chamber;
determining the concentration C of the gas to be measured according to the following formula:
wherein n is 0 Is the refractive index of air, k is the proportionality coefficient, P 0 The atmospheric pressure, R is the gas constant of the gas to be measured, and T is the gas temperature of the gas to be measured.
2. The method according to claim 1, characterized in that the sum of the physical length of the first optical fiber (4), the physical length of the hollow-core fiber gas cell (5) and the physical length of the second optical fiber (6) is equal to the physical length of the third optical fiber (9).
3. The method according to claim 1, characterized in that the central output wavelength line width of the laser light source (1) is less than 1nm.
4. Method according to claim 1, characterized in that the polarizing beam splitter (2) comprises a glan prism.
5. The method according to claim 1, characterized in that at least one of the first coupling lens (3) and the second coupling lens (8) comprises a plano-convex lens made of calcium fluoride material.
6. The method according to claim 1, wherein the first connector (10-1) and the second connector (10-2) of the fiber coupler (10) are equal in length.
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| CN100371745C (en) * | 2006-04-24 | 2008-02-27 | 天津大学 | Method of generating hollow hight beam and tuning by utilizing optical fiber intermodal interference |
| US8755649B2 (en) * | 2009-10-19 | 2014-06-17 | Lockheed Martin Corporation | In-line forward/backward fiber-optic signal analyzer |
| US20110261454A1 (en) * | 2009-12-01 | 2011-10-27 | Advalue Photonics, Inc. | All-Fiber Optical Isolator |
| CN102914509B (en) * | 2012-11-08 | 2014-12-31 | 西南石油大学 | Measurement device and testing method of hydrogen sulfide gas concentration of irregular-pore optical fiber |
| CN104458212B (en) * | 2014-12-02 | 2017-05-17 | 中国电子科技集团公司第四十一研究所 | Device and method for measuring integrated optical waveguide polarization extinction ratio |
| CN105388128A (en) * | 2015-11-07 | 2016-03-09 | 包立峰 | Michelson interferometric optical-fiber hydrogen sensor based on PM-PCF |
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| CN106950194B (en) * | 2017-03-17 | 2018-06-12 | 哈尔滨翰奥科技有限公司 | Gas sensor and the method for detecting concentration of SO 2 gas variation |
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| US5671301A (en) * | 1992-12-10 | 1997-09-23 | Sunshine Medical Instruments, Inc. | Optical phase modulator for high resolution phase measurements |
| JP2001293589A (en) * | 2000-04-11 | 2001-10-23 | Fanuc Ltd | Laser beam machining device |
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