CN115615957A - Phase shift Bragg grating, hydrogen sensor and hydrogen concentration sensing method - Google Patents
Phase shift Bragg grating, hydrogen sensor and hydrogen concentration sensing method Download PDFInfo
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- CN115615957A CN115615957A CN202211265087.6A CN202211265087A CN115615957A CN 115615957 A CN115615957 A CN 115615957A CN 202211265087 A CN202211265087 A CN 202211265087A CN 115615957 A CN115615957 A CN 115615957A
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- 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
- G01N21/45—Refractivity; Phase-affecting properties, e.g. optical path length using interferometric methods; using Schlieren methods
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- 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
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- 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
- G01N21/45—Refractivity; Phase-affecting properties, e.g. optical path length using interferometric methods; using Schlieren methods
- G01N2021/458—Refractivity; Phase-affecting properties, e.g. optical path length using interferometric methods; using Schlieren methods using interferential sensor, e.g. sensor fibre, possibly on optical waveguide
Abstract
The invention discloses a phase shift Bragg grating, which comprises a single-mode fiber, a Bragg grating, an optical microcavity and a resonant film, wherein the Bragg grating is formed in the single-mode fiber, one end face of the single-mode fiber is connected to one end of the optical microcavity, and the resonant film is formed at the other end of the optical microcavity; the distance between the Bragg grating and the optical microcavity is smaller than the grating period of the Bragg grating, and the reflected light intensity formed by the Bragg grating is the same as the reflected light intensity formed by the resonant film. The phase-shift Bragg grating has the advantages of small grating preparation amount, high measurement precision and simplicity in manufacturing. The invention also provides a hydrogen sensor and a hydrogen concentration sensing method based on the phase-shift Bragg grating.
Description
Technical Field
The invention relates to the field of optical fiber sensing, in particular to a phase shift Bragg grating, a hydrogen sensor and a hydrogen concentration sensing method.
Background
Hydrogen plays an important role in basic raw materials and reserve power energy in the fields of petrochemical industry, automobiles and the like, and is receiving more and more attention. However, since hydrogen has small molecules and is colorless and odorless, it is very easy to leak and explode during production, storage and transportation, and thus is hardly noticed. The explosion limit of hydrogen in air is 4.1% -74.2% (volume concentration), and explosion happens when exposed fire occurs, thus posing great threat to the safety of people's lives and properties. Therefore, it is important to monitor the content of hydrogen in the production, storage or transportation environment by using a hydrogen sensor.
At present, hydrogen sensors already available on the market are mainly classified into semiconductor type, electrochemical type, thermoelectric type, optical type, and the like according to different working principles. Although semiconductor type, electrochemical type and thermoelectric type sensors have the advantages of good detection sensitivity, high reaction speed and the like, the semiconductor type, electrochemical type and thermoelectric type sensors cannot be separated from electricity and heat, and the danger of potential introduction of electric sparks to cause explosion exists. The sensor working based on the optical principle has the advantages of good electromagnetic interference resistance, high safety and sensitivity, small volume, light weight, stable performance, explosion resistance and easiness in forming a space multipoint monitoring system. The fiber hydrogen sensor is mainly combined with Pd or alloy thereof to realize hydrogen sensing according to the principles of a microcavity, an evanescent field, a fiber grating, an interferometer and the like. In 1984, butler and Ginley manufactured the first hydrogen sensor; in 1999, sutapun et al first reported FBG-type hydrogen sensors; in 2013, li tao et al proposed a patent of a miniature optical fiber hydrogen sensor based on FP interference type, which indicated that at the other end of the hollow optical fiber, a palladium film was coated by evaporation, and that it was not possible to form a palladium film by evaporation directly on the end face because the end face was not provided with a substrate. Poplar vibration and the like coats a palladium membrane on the outer wall of an FP cavity formed by a capillary tube and a single-mode multimode fiber, and the size of the FP cavity is changed after the palladium membrane absorbs hydrogen, so that the length of the FP cavity is changed to form the hydrogen sensor. However, the hydrogen sensor has the disadvantages of difficulty in coating the end face, insufficient sensitivity, long response time, short service life of the sensor, and poor repeatability.
Chinese patent No. CN201510362721.1 discloses a phase-shift fiber grating hydrogen sensor based on a fiber grating microcavity, which comprises a broadband light source, a single-mode transmission fiber and a Pt/WO (platinum/tungsten) coated layer 3 The fiber grating microcavity phase shift fiber grating sensing head, the air chamber and the spectrometer of the film form a sensing measurement system; the output end of the broadband light source is connected with a single-mode transmission optical fiber, and the single-mode transmission optical fiber is connected with the Pt/WO plated layer in the air chamber 3 The input end of the fiber grating microcavity phase shift fiber grating sensing head of the film is connected and plated with Pt/WO 3 The output end of the fiber grating microcavity phase shift fiber grating sensing head of the film is connected with a single-mode transmission fiber, and the single-mode transmission fiber is connected with a spectrometer; the fiber grating microcavity phase-shifting fiber grating sensor head consists of a fiber grating microcavity and a Pt/WO 3 The microcavity is processed in the middle of the grating region of the fiber grating, the fiber grating uses a Bragg fiber grating, the width of the microcavity is between 3 and 5 mu m, and Pt/WO 3 The film fills up the micro-cavity, the depth is between 66.6 μm and 76 μm, and a phase shift fiber grating is formed; with the change of the hydrogen concentration, pt/WO 3 The film reacts with hydrogen gas to change the refractive index of the film, and in this structure, light of a specific wavelength is reflected and the remaining transmitted light is transmitted through Pt/WO 3 The position of a peak in a transmission window caused by phase shift can be changed, and the concentration of the hydrogen can be obtained by measuring the change of the peak; the spectrometer serves as a signal demodulation part.
The hydrogen sensor is characterized in that a micro-cavity is formed in the middle of the grid region of the Bragg fiber grating by processing, and then Pt/WO sensitive to hydrogen is filled in the micro-cavity 3 The phase shift fiber grating sensing head is formed by the film, the grating preparation amount of the Bragg fiber grating is large, the difficulty of manufacturing the micro-cavity in the middle of the grating area of the Bragg fiber grating is large, and the Bragg fiber grating is easy to be sensedThe grating is damaged.
Disclosure of Invention
In order to solve the defects of the prior art, the invention provides the phase shift Bragg grating which has the advantages of small grating preparation amount, high measurement precision and simplicity in manufacturing.
The invention also provides a hydrogen sensor and a hydrogen concentration sensing method based on the phase-shift Bragg grating.
The technical problem to be solved by the invention is realized by the following technical scheme:
a phase shift Bragg grating comprises a single-mode fiber, a Bragg grating, an optical microcavity and a resonant film, wherein the Bragg grating is formed in the single-mode fiber, one end face of the single-mode fiber is connected to one end of the optical microcavity, and the resonant film is formed at the other end of the optical microcavity; the distance between the Bragg grating and the optical microcavity is smaller than the grating period of the Bragg grating, and the intensity of the reflected light formed by the Bragg grating is the same as that of the reflected light formed by the resonant film.
A hydrogen sensor comprises the phase-shift Bragg grating and a hydrogen sensitive film, wherein the hydrogen sensitive film is formed on the resonant thin film.
A hydrogen concentration sensing method comprising the steps of:
step 100: coupling an excitation light signal with a first wavelength and a detection light signal with a second wavelength into the hydrogen sensor together, so that the excitation light signal drives the resonant film to generate resonance;
step 200: acquiring a detection optical signal reflected by the hydrogen sensor to obtain a frequency spectrum of the hydrogen sensor;
step 300: and calculating the hydrogen concentration according to the resonance peak of the frequency spectrum.
The invention has the following beneficial effects: the phase-shift Bragg grating utilizes the resonance film to reflect detection optical signals, so that the Bragg grating forms phase shift, only half of the grating needs to be prepared, the preparation amount of the grating is small, and meanwhile, the phase-shift Bragg grating is matched with an FP interferometer formed among the end face of the single-mode optical fiber, the optical microcavity and the resonance film, and senses the external environment in an optical excitation light detection mode, so that more precise and weaker signal measurement can be realized, meanwhile, the Bragg grating improves the end face reflectivity of the single-mode optical fiber, the cavity light coupling efficiency of the FP interferometer is also enhanced, and the sharpness of a reflection spectrum is improved.
Drawings
FIG. 1 is a schematic diagram of a phase-shifted Bragg grating according to the present invention;
FIG. 2 is an equivalent diagram of a phase-shifted Bragg grating according to the present invention;
FIG. 3 is a schematic plan view of a resonant film in a phase-shifted Bragg grating according to the present invention;
FIG. 4 is a schematic structural diagram of a phase-shifted Bragg grating according to the present invention;
FIG. 5 is a schematic diagram of another phase-shifted Bragg grating according to the present invention;
FIG. 6 is a schematic diagram of another phase-shifted Bragg grating according to the present invention;
FIG. 7 is a schematic structural diagram of a hydrogen sensor according to the present invention;
FIG. 8 is a block diagram illustrating the steps of a hydrogen concentration sensing method according to the present invention;
fig. 9 is a schematic view of the principle of the photo-excitation light detection means employed in the hydrogen concentration sensing method shown in fig. 8.
Detailed Description
The invention is described in detail below with reference to the drawings, wherein examples of the embodiments are shown in the drawings, wherein like or similar reference numerals refer to like or similar elements or elements having like or similar functions throughout. The embodiments described below with reference to the accompanying drawings are illustrative and intended to explain the present invention and should not be construed as limiting the present invention.
In the description of the present invention, it is to be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like, indicate orientations or positional relationships based on those shown in the drawings, and are used only for convenience in describing the present invention and for simplicity in description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed in a particular orientation, and be operated, and thus, are not to be construed as limiting the present invention.
Furthermore, the terms "first", "second", "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first," "second," or "third" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless specifically defined otherwise.
In the present invention, unless otherwise expressly stated or limited, the terms "mounted," "connected," "secured," "disposed," and the like are to be construed broadly and can, for example, be fixedly connected, detachably connected, or integrally formed; can be mechanically or electrically connected; they may be directly connected or indirectly connected through intervening media, or may be connected through the interconnection of two elements or through the interaction of two elements. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.
Example one
As shown in fig. 1, a phase-shift bragg grating includes a single-mode fiber 101, a bragg grating 102, an optical microcavity 103, and a resonant film 104, where the bragg grating 102 is formed in the single-mode fiber 101, one end surface of the single-mode fiber 101 is connected to one end of the optical microcavity 103, and the resonant film 104 is formed on the other end of the optical microcavity 103; the distance between the bragg grating 102 and the optical microcavity 103 is smaller than the grating period of the bragg grating 102, and the intensity of the reflected light formed by the bragg grating 102 is the same as the intensity of the reflected light formed by the resonant thin film 104.
When an optical detection signal is coupled into the phase-shifted bragg grating from the other end surface of the single-mode fiber 101, the optical detection signal firstly passes through the bragg grating 102, then enters the optical microcavity 103, is reflected by the resonant thin film 104, then passes through the bragg grating 102 again, and finally leaves the phase-shifted bragg grating. In the phase-shift bragg grating, the end surface of the single-mode fiber 101, the optical microcavity 103 and the resonant film 104 form an FP interferometer, and the end surface of the single-mode fiber 101 and the resonant film 104 serve as two reflecting surfaces of the FP interferometer to respectively reflect the detection optical signals, and the two reflected detection optical signals interfere to form a resonant signal; meanwhile, the detection optical signal passes through the bragg grating 102 twice through reflection of the resonant thin film 104, as shown in fig. 2, it is equivalent to forming a virtual bragg 102' identical to the bragg grating 102 on the other end of the optical microcavity 103, when the distance between the bragg grating 102 (facing one end of the optical microcavity 103) and the optical microcavity 103 (facing one end of the bragg grating 102) is less than the grating period of the bragg grating 102, and the intensity of the reflected light formed by the bragg grating 102 is the same as the intensity of the reflected light formed by the resonant thin film 104, the optical microcavity 103 forms a phase shift point inserted between the bragg grating 102 and the virtual bragg 102', so that a phase jump twice as long as the optical microcavity 103 is generated between the originally uniform bragg grating 102 and the virtual bragg 102', and the detection optical signal forms a phase shift signal; the reflected signal of the phase-shifted Bragg grating is formed by the superposition of the resonance signal and the phase-shifted signal.
When the stress in the resonant film 104 changes, the resonant frequency of the resonant film changes, which causes the peak of the resonant signal to shift; when the wavelength of the detection optical signal is equal to the wavelength of the phase-shift signal, the peak shift of the resonance signal is maximum, and more precise and weaker signal measurement can be realized.
The phase-shift Bragg grating utilizes the reflection of the resonant film 104 on a detection optical signal to enable the Bragg grating 102 to form phase shift, and simultaneously cooperates with an FP interferometer formed among the end face of the single-mode fiber 101, the optical microcavity 103 and the resonant film 104 to sense the external environment in a light-excited light detection mode, so that more precise and weaker signal measurement can be realized, meanwhile, the Bragg grating 102 improves the end face reflectivity of the single-mode fiber 101, also enhances the cavity light coupling efficiency of the FP interferometer, and improves the sharpness of a reflection spectrum.
Generally, the distance between the bragg grating 102 and the resonant film 104 satisfies pi phase change to form a pi phase shift fiber grating, so as to better improve the cavity light coupling efficiency of the FP interferometer.
In this embodiment, the optical microcavity 103 has a cavity length of 10-200 μm
The single-mode optical fiber 101 comprises a fiber core 105 and a cladding 106, wherein the cladding 106 is wrapped around the outer periphery of the fiber core 105, and the refractive indexes of the fiber core 105 and the cladding 106 are different, so that an optical signal can be totally reflected at the interface of the fiber core 105 and the cladding 106 and further transmitted forwards in the fiber core 105.
The cladding 106 of the single-mode fiber 101 is connected with the cavity wall 107 of the optical microcavity 103, and the core 105 of the single-mode fiber 101 is connected with the optical microcavity 103, but the radial direction of the optical microcavity 103 should be larger than the diameter of the core 105; the bragg grating 102 is formed in a core 105 of the single-mode optical fiber 101, and the bragg grating 102 may also extend to a cladding 106 of the single-mode optical fiber 101 according to specific requirements.
In a specific implementation manner, as shown in fig. 4, the optical microcavity 103 is formed by a hollow tube 113 (a quartz tube or a hollow fiber) connected to an end face of the single-mode fiber 101, for example, the end face of the single-mode fiber 101 is welded to the end face of the hollow tube 113 by a welding method, a lumen of the hollow tube 113 is used as the optical microcavity 103, and a wall of the hollow tube 113 is used as a cavity wall 107 of the optical microcavity 103; the resonance film 104 is formed on the other end surface of the hollow tube 113.
In another specific implementation manner, as shown in fig. 5, the optical microcavity 103 is formed by a polymer microstructure 114 formed on an end face of the single-mode optical fiber 101, for example, a two-photon polymerization method is used to fabricate the polymer microstructure 114 with the optical microcavity 103 on the end face of the single-mode optical fiber 101, and the polymer microstructure 114 is used as a cavity wall 107 of the optical microcavity 103; the resonant film 104 is formed on the polymer microstructure 114.
In yet another specific implementation manner, as shown in fig. 6, the optical microcavity 103 is formed by recessing an end face of the single-mode fiber 101, for example, the end face of the single-mode fiber 101 is directly etched by using a laser ablation wet etching method, so as to form an inwardly recessed optical microcavity 103 at a fiber core 105 of the end face, and a cladding 106 of the single-mode fiber 101 on the end face thereof serves as a cavity wall 107 of the optical microcavity 103; the resonance thin film 104 is formed on an end face of the single mode optical fiber 101.
As shown in fig. 3, the resonant thin film 104 includes a fixing region 108, a resonant region 109, and a plurality of suspension regions 110, where the fixing region 108 is attached to and fixed on a cavity wall 107 of the optical microcavity 103, and the resonant region 109 is suspended above the optical microcavity 103 and corresponds to the fiber core 105 of the single-mode optical fiber 101; each suspension region 110 is connected between the resonance region 109 and the fixed region 108, a hollow-out region 111 is formed between adjacent suspension regions 110, and the optical microcavity 103 is exposed from the hollow-out region 111.
In this embodiment, the resonant thin film 104 is a graphene film with a single-layer structure or a multi-layer structure, and has a thickness of 0.3-5.0 nm.
The resonant film 104 exposes the optical microcavity 103 through the hollow-out region 111, so that the optical microcavity 103 and the external environment are at the same air pressure value, the influence of the air pressure difference between the optical microcavity 103 and the external environment on the resonant motion of the resonant film 104 is avoided, and the sensing precision can be improved; meanwhile, the connection stress between the fixed region 108 and the resonance region 109 is reduced, and the sensitivity rate and sensitivity of the resonance region 109 are improved.
In this embodiment, the hollow areas 111 are circular, four in number, and are uniformly distributed on the peripheral circumference of the resonance area 109, and the sensitivity rate and sensitivity of the resonance film 104 can be changed by changing the shape and size of the resonance film 104.
Example two
As shown in fig. 7, a hydrogen sensor 10 includes a phase-shifted bragg grating according to the first embodiment and a hydrogen sensitive film 112, wherein the hydrogen sensitive film 112 is formed on the resonant thin film 104.
The hydrogen sensitive film 112 can be combined with hydrogen, and after being combined with hydrogen, the hydrogen sensitive film drives the resonant film 104 to deform together, so as to change the film internal stress of the resonant film 104, and cause the peak shift of the resonant signal. When the hydrogen concentration in the external environment is different, the position and the drift amount of the resonance peak on the frequency spectrum are also different, so that the size and the change of the hydrogen concentration in the external environment can be calculated through the position and the drift amount of the resonance peak on the frequency spectrum.
In this embodiment, the hydrogen sensitive film 112 includes a chromium alloy film and a palladium alloy film, the thickness of the chromium alloy film is 5-20nm, and the thickness of the palladium alloy film is 20-200nm.
The palladium alloy film is used to combine with hydrogen to cause deformation of the resonant thin film 104, and the chromium alloy film is used to improve the binding force between the palladium alloy film and the resonant thin film 104 and prevent the palladium alloy film from being separated from the resonant thin film 104.
The hydrogen sensitive film 112 formed on the resonant thin film 104, the resonant thin film 104 is used as a substrate, and the chromium alloy and the palladium alloy are sequentially formed on the resonant thin film 104 by magnetron sputtering or vacuum evaporation, etc. to form the hydrogen sensitive film 112, and the hydrogen sensitive film 112 has the same shape as the resonant thin film 104, the resonant thin film 104 may be etched first to form a desired shape, and then the chromium alloy and the palladium alloy are sequentially formed on the resonant thin film 104 to form the hydrogen sensitive film 112, or the chromium alloy and the palladium alloy may be sequentially formed on the resonant thin film 104 to form the hydrogen sensitive film 112, and then the resonant thin film 104 and the hydrogen sensitive film 112 are simultaneously etched to form the desired shape after the hydrogen sensitive film 112 is formed.
EXAMPLE III
As shown in fig. 8, a hydrogen concentration sensing method includes the steps of:
step 100: an excitation optical signal having a first wavelength and a detection optical signal having a second wavelength, which is equal to the phase-shifted wavelength of the hydrogen sensor 10, are coupled into the hydrogen sensor 10 according to the second embodiment, so that the excitation optical signal drives the resonant film 104 to generate resonance.
In this step 100, preferably, the second wavelength of the detection optical signal is equal to the phase-shifted signal wavelength of the phase-shifted bragg grating, so as to maximize the peak shift of the resonance signal.
Specifically, a light-excited light detection device is used to measure the frequency spectrum of the hydrogen sensor 10, as shown in fig. 9, the light-excited light detection device includes an excitation laser 1, a signal generator 3, an electro-optic modulator 2, a detection laser 4, an optical fiber coupler 5, an optical fiber circulator 6, a band-pass filter 7, a photodetector 8 and a spectrometer 9, the optical fiber coupler 5 has a first incident end, a second incident end and an exit end, the optical fiber circulator 6 has an incident end, a reflecting end and a transmitting end, the excitation laser 1 is connected to the first incident end of the optical fiber coupler 5 through the electro-optic modulator 2, the detection laser 4 is connected to the second incident end of the optical fiber coupler 5, the exit end of the optical fiber coupler 5 is connected to the incident end of the optical fiber circulator 6, the photodetector 8 is connected to the reflecting end of the optical fiber circulator 6 through the band-pass filter 7, and the other end face of the single-mode fiber 101 of the hydrogen sensor 10 is connected to the transmitting end of the optical fiber circulator 6; the signal generator 3 is connected with and controls the electro-optical modulator 2, and the frequency spectrograph 9 is connected with and controls the photoelectric detector 8.
The excitation laser 1 emits an excitation light signal with a first wavelength to the electro-optical modulator 2, the detection laser 4 emits an excitation light signal with a second wavelength to the optical fiber coupler 5, and then the electro-optical modulator 2 modulates the light intensity of the excitation light signal under the periodic signal of the signal generator 3, so that the light intensity of the excitation light signal changes periodically and enters the optical fiber coupler 5, and enters the hydrogen sensor 10 after being coupled with the detection light signal.
In this embodiment, the optical fiber coupler 5 is a 90% to 10 optical fiber coupler 5, that is, when coupling is performed, the excitation optical signal accounts for 90% of the total optical signal, and the detection optical signal accounts for 10% of the total optical signal.
Preferably, an optical isolator 11 is further connected between the detection laser 4 and the second incident end of the optical fiber coupler 5, and the optical isolator 11 only allows the detection optical signal to be transmitted from the detection laser 4 to the optical fiber coupler 5, but does not allow the detection optical signal to be transmitted from the optical fiber coupler 5 to the detection laser 4, so as to avoid the detection optical signal from being reflected back to the detection laser 4 during transmission to cause damage to the detection laser 4.
When the excitation light signal coupled into the hydrogen sensor 10 acts on the resonant film 104, the resonant film 104 is irradiated by the excitation light signal with periodically changing light intensity, so that the periodically changing thermal expansion or contraction is generated, and the resonant motion is forced to be formed.
The detection optical signal coupled into the hydrogen sensor 10 is modulated and reflected by the resonant thin film 104, and then carries the resonance information of the resonant thin film 104.
Step 200: the detection optical signal reflected by the hydrogen sensor 10 is acquired, and the frequency spectrum of the hydrogen sensor 10 is obtained.
In this step S200, the detection optical signal reflected by the hydrogen sensor 10 reenters the optical fiber circulator 6, and is captured by the photodetector 8 through the band-pass filter 7 from the reflection end of the optical fiber circulator 6. The photodetector 8 converts the reflected detection optical signal into a corresponding electrical signal and provides the electrical signal to the spectrum analyzer 9, and the spectrum analyzer 9 outputs a corresponding spectrum.
The band-pass filter 7 is used for filtering the excitation optical signal doped in the detection optical signal.
Step 300: and calculating the hydrogen concentration according to the resonance peak of the frequency spectrum.
In this step 300, the shift amount of the resonance peak, which is correlated with the hydrogen concentration, can be obtained by comparing the frequency spectrum with the initial frequency spectrum of the hydrogen sensor 10, and the hydrogen concentration can be calculated.
The initial spectrum of the hydrogen sensor 10 refers to the spectrum of the hydrogen sensor 10 in a hydrogen-free environment obtained through the above-described steps 100 to 300.
Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the embodiments of the present invention and not for limiting the same, and although the embodiments of the present invention are described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions can be made on the technical solutions of the embodiments of the present invention, and these modifications or equivalent substitutions cannot make the modified technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.
Claims (10)
1. A phase shift Bragg grating is characterized by comprising a single-mode fiber, a Bragg grating, an optical microcavity and a resonant thin film, wherein the Bragg grating is formed in the single-mode fiber, one end face of the single-mode fiber is connected to one end of the optical microcavity, and the resonant thin film is formed at the other end of the optical microcavity; the distance between the Bragg grating and the optical microcavity is smaller than the grating period of the Bragg grating, and the reflected light intensity formed by the Bragg grating is the same as the reflected light intensity formed by the resonant film.
2. A phase shifted bragg grating according to claim 1, wherein a distance between the bragg grating and the resonant film satisfies a pi phase change.
3. A phase-shifted bragg grating according to claim 1, wherein the optical microcavity has a cavity length of between 10-200 μm.
4. The phase-shifted bragg grating according to claim 1, wherein the resonant thin film is a graphene film of a single-layer structure or a multi-layer structure.
5. The phase-shifted bragg grating as claimed in claim 1, wherein the resonant film comprises a fixed region, a resonant region and a plurality of suspension regions, the fixed region is attached to a cavity wall of the optical microcavity, and the resonant region is suspended from the optical microcavity and corresponds to a core of the single-mode optical fiber; each suspension area is connected between the resonance area and the fixed area, a hollow area is arranged between the adjacent suspension areas, and the optical microcavity is exposed from the hollow area.
6. A hydrogen sensor comprising the phase-shifted Bragg grating as claimed in any one of claims 1 to 5 and a hydrogen sensitive film formed on the resonant thin film.
7. A hydrogen sensor according to claim 6, characterized in that the hydrogen-sensitive membrane comprises a chromium alloy membrane and a palladium alloy membrane.
8. The hydrogen sensor according to claim 7, wherein the chromium alloy film has a thickness of 5 to 20nm, and the palladium alloy film has a thickness of 20 to 200nm.
9. A hydrogen concentration sensing method, characterized by comprising the steps of:
step 100: coupling an excitation light signal having a first wavelength and a detection light signal having a second wavelength together into the hydrogen sensor of any one of claims 6-8 such that the excitation light signal drives the resonant film into resonance;
step 200: acquiring a detection optical signal reflected by the hydrogen sensor to obtain a frequency spectrum of the hydrogen sensor;
step 300: and calculating the hydrogen concentration according to the resonance peak of the frequency spectrum.
10. The hydrogen concentration sensing method according to claim 9, wherein the second wavelength of the detection optical signal is equal to a phase shift wavelength of the hydrogen gas sensor.
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