CN101592757A - Cascaded long-period fiber grating device, its manufacturing method, and humidity-sensitive sensing system - Google Patents
Cascaded long-period fiber grating device, its manufacturing method, and humidity-sensitive sensing system Download PDFInfo
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Abstract
本发明涉及级联长周期光纤光栅装置及其制造方法、湿度传感器及湿敏传感系统。所述湿敏传感系统包括：宽带光源；两个长周期光纤光栅相隔一定距离连接起来构成马赫－泽德干涉仪，其两端与宽带光源和光谱采集单元相连；湿度敏感膜，用于感知环境湿度变化信息；光谱采集单元，用于采集环境湿度变化信息；数据处理单元，用于对所采集的包含环境湿度信息的光干涉信号进行分析和处理，最终获得待测环境湿度。本发明得到的光谱具有更精细的结构及更窄的线宽，克服现有技术中灵敏度和分辨率低的问题，可以远距离实时在线监测，测量准确且成本低廉。
The invention relates to a cascaded long-period optical fiber grating device and a manufacturing method thereof, a humidity sensor and a humidity sensitive sensing system. The humidity-sensitive sensing system includes: a broadband light source; two long-period fiber gratings connected at a certain distance to form a Mach-Zehnder interferometer, whose two ends are connected with a broadband light source and a spectrum acquisition unit; a humidity-sensitive film for sensing The environmental humidity change information; the spectrum acquisition unit is used to collect the environmental humidity change information; the data processing unit is used to analyze and process the collected optical interference signal containing the environmental humidity information, and finally obtain the environmental humidity to be measured. The spectrum obtained by the invention has a finer structure and narrower line width, overcomes the problems of low sensitivity and resolution in the prior art, can be remotely monitored online in real time, and has accurate measurement and low cost.
Description
Technical field
The present invention relates to field of sensor measurement, be specifically related to a kind of cascade long-period fiber grating device and manufacture method thereof, utilize the humidity sensor and the humidity sensing system of cascade long-period fiber grating device.
Background technology
Long period fiber grating is to be the tens class gratings to the hundreds of micron in the cycle, and it is by methods such as ultraviolet irradiation, arc discharge, laser thermal effects, and geometry changes or index modulation to constituting periodically along fiber axis.The characteristics of this fiber grating are the core mode of fl transmission to be coupled to the cladding mode of fl transmission, thereby cause the loss at respective wavelength place, one or more loss peaks can occur in transmission spectrum.Long period fiber grating is a kind of Fibre Optical Sensor of function admirable, with respect to the widespread use of bragg grating in strain and temperature sensing, long period fiber grating since to external world the high susceptibility of environment refractive index be more suitable in biological, environmental monitoring and chemical sensitisation, using, therefore be subjected to domestic and international researcher's extensive concern.
For common long period fiber grating, mainly consider the coupling between v cladding mode of core mode and 1 rank.According to mode coupling theory, the resonance wavelength of long period fiber grating
vDetermine by publicity (1):
λ
v＝(n
co-n
v cl)·Λ (1)
N wherein
Co, n
v ClBe respectively the effective refractive index of v cladding mode of optical fiber basic mode (conduction mode) and 1 rank, Λ is the cycle of long period fiber grating.When the refractive index of external environment changed, the effective refractive index of cladding mode can change, and caused that resonance wavelength and transmission peaks amplitude change.By spectroanalysis instrument or other instruments wave length shift and transmission peaks changes in amplitude amount are detected, can obtain external environment change of refractive information.
But because single LPG transmitted spectrum bandwidth ratio is bigger,, will introduce bigger wavelength readings error, limit the raising of the Measurement Resolution of long period fiber grating if the resolution of spectrometer is lower in the measurement environment.
Summary of the invention
For overcoming single long period fiber grating, the purpose of this invention is to provide a kind of have high-resolution cascade long-period fiber grating device and manufacture method, the moisture sensor that utilizes this cascade-connection long period fiber grating and humidity sensing system because of the grating spectrum width causes the problem that resolution is low.This cascade long-period fiber grating device can be applied to the humidity sensor field, utilize the humidity sensor of this cascade long-period fiber grating device to have high resolving power, because having the bandwidth of meticulousr spectral composition and single transmission peaks, the interference spectum of the Mach-Zehnder interferometer that the cascade-connection long period mounting for grating constitutes narrows down greatly, error be can reduce, and then sensitivity and resolution that humidity sensing system is measured improved by the read untrue introducing.
For achieving the above object, the invention provides a kind of cascade long-period fiber grating device, this device comprises:
First long period fiber grating is used for receiving optical signals and it is divided into two-way, the fiber core of leading up to transmission, and one the tunnel is coupled to fibre cladding transmits;
Second long period fiber grating is used for receiving the two ways of optical signals transmitted by optical fiber, and the light signal that will in fibre cladding, transmit again the coupled back into optical fibers fibre core two ways of optical signals is produced interfere;
Optical fiber is connected between described first long period fiber grating and described second long period fiber grating.
Preferably, the transmissivity of described first long period fiber grating and second long period fiber grating is 3dB.
The present invention also provides a kind of manufacture method of above-mentioned cascade long-period fiber grating device, and this method may further comprise the steps:
S1 places single-mode fiber the focal plane of laser instrument laser facula;
S2 utilizes described laser facula, presses the repeatedly described single-mode fiber of transversal scanning of predetermined set scan mode, finishes the making of first long period fiber grating, and described first long period fiber grating has the structural change of periodic refractive index modulation and asymmetry;
S3, mobile single-mode fiber one segment distance adopts the method identical with making first long period fiber grating to make second long period fiber grating.
Preferably, among the step S1, described laser instrument is CO
2Laser instrument.
Preferably, among the step S2, the predetermined set scan mode is:
At first make laser facula along direction transversal scanning single-mode fiber perpendicular to single-mode fiber, make laser facula along the single-mode fiber axial dipole field distance in a grating cycle then, repeat the above-mentioned scanning of laterally stating at next one point, so repeated several times is finished the single pass process;
The above-mentioned scanning process of repeated several times.
Preferably, among the step S3, utilize micro-displacement platform to move described single-mode fiber.
The present invention also provides a kind of humidity sensor that utilizes above-mentioned cascade long-period fiber grating device, and this humidity sensor comprises:
The cascade long-period fiber grating device of said structure;
Humidity sensing film, the surface that it is coated in cascade long-period fiber grating device is used for the variation of perception external environment humidity.
Preferably, the transmissivity of described first long period fiber grating and second long period fiber grating is 3dB.
Preferably, described humidity sensing film is the hydrogel humidity sensing film.
Preferably, described hydrogel humidity sensing film is coated on the single-mode fiber cladding surface between first long period fiber grating and second long period fiber grating.
Preferably, described hydrogel humidity sensing film is coated on the cladding surface of first long period fiber grating and second long period fiber grating and described single-mode fiber.
Preferably, described hydrogel humidity sensing film adopts infusion method to be made in conjunction with the method for uv light irradiation film forming.
The present invention also provides a kind of humidity sensing system that utilizes above-mentioned humidity sensor, and this system comprises:
Wideband light source is used to provide the wide range light signal;
Above-mentioned humidity sensor places the moisture measurement environment, and its two ends link to each other with the spectra collection unit with described wideband light source respectively, is used to respond to moisture measurement ambient humidity information;
Described spectra collection unit is used for gathering the optical interference signals that comprises moisture measurement ambient humidity information that the humidity sensor second long period fiber grating place produces;
Data processing unit is used for the optical interference signals of being gathered is analyzed and handled, and obtains moisture measurement ambient humidity information.
Cascade long-period fiber grating device provided by the invention and manufacture method thereof, and humidity sensor and humidity sensing system have the following advantages and beneficial effect:
1) because the cascade long-period fiber grating device that is provided constitutes the Mach-Zehnder interferometer structure, measuring-signal has meticulousr spectral composition, this cascade long-period fiber grating device can be applied to the humidity sensor field, and then can improve humidity sensor and humidity sensing system resolution;
2), can realize that real-time online remote monitoring ambient humidity changes because signal adopts Optical Fiber Transmission.
Description of drawings
Fig. 1 utilizes laser instrument to make the synoptic diagram of cascade long-period fiber grating device in general single mode fiber in the embodiment of the invention 1;
Fig. 2 A is the embodiment of the invention 1 a cascade long-period fiber grating device structural representation;
Fig. 2 B is the sectional view of single-mode fiber A-A line among Fig. 2 A;
Fig. 2 C is the sectional view of single-mode fiber B-B line among Fig. 2 A;
Fig. 3 is the structural drawing of a kind of embodiment of humidity sensor in the embodiment of the invention 2;
Fig. 4 is the structural drawing of the another kind of embodiment of humidity sensor in the embodiment of the invention 2;
Fig. 5 is the synoptic diagram of humidity sensor in the embodiment of the invention 3;
Fig. 6 is the synoptic diagram of humidity sensor in the embodiment of the invention 4;
Fig. 7 is the structural drawing of humidity sensing system in the embodiment of the invention 5;
Fig. 8 is a humidity sensing system Experimental equipment in the embodiment of the invention 5;
The curve that Fig. 9 changes with humidity for the actual cascade-connection long period grating interference strip contrast that records;
The linear fit curve that Figure 10 changes with humidity for the actual cascade-connection long period grating interference strip contrast that records.
Embodiment
Cascade long-period fiber grating device that the present invention is proposed and manufacture method thereof, and humidity sensor and humidity sensing system are described as follows in conjunction with the accompanying drawings and embodiments.
Cascade long-period fiber grating device according to present embodiment comprises first long period fiber grating, second long period fiber grating and optical fiber.First long period fiber grating is used for receiving optical signals and it is divided into two-way, the fiber core of leading up to transmission, and one the tunnel is coupled to fibre cladding transmits.The light intensity that first long period fiber grating is told two-way light equates, the two-way light intensity is equated, and is unequal also passable, and meeting is weaker relatively but interfere contrast.Second long period fiber grating is used for receiving the two ways of optical signals of being transmitted by optical fiber, and the light signal that will transmit in fibre cladding is the coupled back into optical fibers fibre core again.Distance between first long period fiber grating and the second long period fiber grating center is L, d is the length of long period fiber grating, because fiber core is different with cladding index, two-way light has produced certain optical path difference after passing through the Distance Transmission that length is L, can see tangible interference fringe on its spectrum.Optical fiber is connected between first long period fiber grating and second long period fiber grating.
The transmissivity of first long period fiber grating and second long period fiber grating preferably adopts and is 3dB, and other value also can produce interference, but interferes contrast less better relatively.
The said structure of cascade long-period fiber grating device makes it constitute M-Z type interferometer (Mach-Zehnder interferometer) structure.The intensity I of the output transmitted spectrum of the M-Z type interferometer that is constituted can be expressed as formula (2):
I wherein
CoAnd I
v ClBe respectively first long period fiber grating and output to the luminous energy of v cladding mode transmission of fibre core and single order, α
vBe the loss factor of v cladding mode of single order,
Phase differential for the two-way light of sandwich layer and covering transmission.
Two long period fiber grating in the cascade long-period fiber grating device adopt high frequency CO
2Laser instrument 101 processes, and the manufacture method that provides present embodiment cascade long-period fiber grating device in conjunction with Fig. 1 may further comprise the steps: S1 places single-mode fiber 102 CO that has focused on
2It is fixing that the focal plane of laser instrument 101 laser faculas, single-mode fiber 102 two ends are had the fiber clamp 103 of micro-displacement platform respectively, CO
22 dimension scanning galvanometers of laser instrument 101 inside are by computer control, and then can control the scanning position of the laser facula of focusing.S2, utilize laser facula by computer control gated sweep galvanometer, press repeatedly transversal scanning single-mode fiber 102 of predetermined set scan mode, finish the making of first long period fiber grating 201, first long period fiber grating 201 has the structural change of periodic refractive index modulation and asymmetry; The transmissivity of first long period fiber grating is 3dB, the predetermined set scan mode is: the sweep trace that at first makes laser facula causes the change of melting deformation and material refractive index along the direction transversal scanning single-mode fiber 102 perpendicular to single-mode fiber 102 at single-mode fiber 102 coverings by thermal effect; Make the distance of laser facula then, repeat such scanning process ... so repeat N time (N is an integer), finish the single pass process at next one point along a grating periods lambda of single-mode fiber 102 axial dipole fields.Usually the index modulation of single pass introducing is lower, therefore generally will just can write a desirable long period fiber grating through scanning several times.So far be Λ with regard to processing first cycle, to comprise the transmissivity in N cycle be the asymmetric long period fiber grating of 3dB.S3, the control micro-displacement platform makes single-mode fiber 102 move axially a segment distance L, on same single-mode fiber 102,, adopt method making second second long period fiber grating 202 that transmissivity be 3dB identical with making first long period fiber grating 201 with the be separated by position at L place of first long period fiber grating 201.Single-mode fiber 102 two ends are connected with spectra collection module 105 with wideband light source 104 respectively, to observe the situation of change of grating transmission spectrum.
Fig. 2 is the structural representation of present embodiment cascade long-period fiber grating device, first long period fiber grating 201 and second long period fiber grating 202 are respectively two long period fiber grating that transmissivity is 3dB, grating distance 203 is two distances between the long period fiber grating, in scanning process, the thermal effect of laser not only causes local refraction index changing, also can cause the change of fibre geometry, go up as fibre cladding 206 surfaces and form tangible groove 204.Optical fiber cross section 207 is cross sections of single-mode fiber A-A line, and optical fiber cross section 208 is the cross sections at B-B line groove place, and the center is a fibre core 205, and on the groove cross section 208 at analyzing spot place, fibre cladding has unsymmetric structure.
Embodiment 2
The hydrogel humidity sensing film is coated on the cascade long-period fiber grating device surface among the embodiment 1 in the present embodiment, form humidity sensor, this humidity sensor comprises two asymmetric long period fiber grating that keep at a certain distance away, and the hydrogel humidity sensing film.
Humidity sensor is wherein preferred embodiment a kind of, as shown in Figure 3, this humidity sensor comprises: two transmissivities are first long period fiber grating 301 and second long period fiber grating 302 of 3dB, two grating spacing distances are L, fibre cladding surface-coated hydrogel humidity sensing film 303 between two gratings is to realize the perception of the variation of ambient humidity to external world.
As Fig. 4 is the structural drawing of another embodiment of cascade-connection long period fiber grating humidity sensor, the structure of its structure and embodiment 1 is basic identical, the hydrogel humidity sensing film is coated on two long period fiber grating that different is and between the optical fiber integrally surface at interval, realize sensitivity to humidity.The processing step of coating hydrogel thin film is identical with the process among the embodiment 1.
The light that transmits in the optical fiber through first long period fiber grating 301 after, the energy being coupled of making an appointment with half is in fibre cladding, fibre core more again is coupled back at second long period fiber grating, 302 places.The light that transmits in fibre core and the covering is because the different paths of experience, and 302 places can produce interference in second long period fiber grating, occur the interference fringe of a series of line width, high-fineness in second LPG transmitted spectrum.When external environment humidity changes, the hydrogel humidity sensing film 303 that is coated on the cascade-connection long period fiber grating body structure surface can absorb moisture or discharge moisture, its characteristic (volume and refractive index) can change, the propagation constant that can cause the light that transmits in the covering changes, and then the visibility V that causes interference fringe change (referring to the formula (3) of formula (2), back).Situation of change by the monitoring interference signal finally obtains the external environment humidity information.
Embodiment 3
As shown in Figure 5, humidity sensor comprises that two transmissivities are the asymmetric long period fiber grating 501 and 502 of the L that keeps at a certain distance away of 3dB, and hydrogel humidity sensing film 503.Hydrogel humidity sensing film 503 adopts infusion method to be made in conjunction with the method for uv light irradiation film forming, at first adopt infusion method at fibre cladding surface-coated one deck hydrogel, then the two ends of the cascade long-period fiber grating device that applies hydrogel are fixed with fiber clamp 504, guarantee that whole optical fiber is in straightened condition, and its integral body is positioned over uviol lamp 505 times, come initiated polymerization by UV-irradiation, obtain hydrogel humidity sensing film 503.
Embodiment 4
As shown in Figure 6; humidity sensor comprises that two transmissivities are the asymmetric long period fiber grating 601 and 602 of the L that keeps at a certain distance away of 3dB; and hydrogel humidity sensing film 603, humidity sensor also comprises the stainless steel protection sleeve pipe 604 that is enclosed within the cascade long-period fiber grating device outside.Place exposed cascade long-period fiber grating device in the stainless steel protection sleeve pipe 604 and make it be in straightened condition, at stainless steel protection sleeve pipe 604 two-port place's point epoxide-resin glues in order to the fixing optical fiber at two ends.And be provided with fluting 605 in the corresponding positions that apply hydrogel thin films 603 of stainless steel protection sleeve pipe 604, so that make humidity sensor can experience ambient humidity.
Embodiment 5
As Fig. 7 is the humidity sensing system that uses humidity sensor in the foregoing description in the present embodiment, and this system comprises: wideband light source 701, be used to provide wide range light, and adopt SLED (super-radiance light emitting diode) as spectroscopic light source in the present embodiment; Humidity sensor 702, its two ends link to each other with spectrometer 703 with wideband light source 701 respectively; When wide range light after input optical fibre is transferred to the long period fiber grating that first transmissivity is 3dB, half the luminous energy of can having an appointment is coupled in the fibre cladding, and the energy in the long period fiber grating place covering that second transmissivity is 3dB is by the fibre core that is coupled back again.The light that transmits in fibre core and the covering be because the different paths of experience can produce interference at second long period fiber grating place, forms that a series of intervals equate, the interference fringe of narrow linewidth, is transferred to spectrometer 703 by output optical fibre; Spectrometer 703 is used to receive the interference fringe that humidity sensor 702 produces, and promptly gathers second optical interference signals that comprises moisture measurement ambient humidity information that the long period fiber grating place produces in the cascade long-period fiber grating device; Data processing unit 704 is used to accept optical interference signals that spectrometer 703 the gathers line data of going forward side by side and handles, and by interference signal is carried out discrete Fourier transform (DFT), obtains the contrast information of interference fringe, and then obtains ambient humidity information.
The principle that provides the measurement environment relative humidity of using the humidity sensing system in the present embodiment below is: when ambient humidity increases or reduces, the hydrogel that is coated on the cascade-connection long period fiber grating surface can absorb or discharge moisture accordingly, the characteristic (volume and refractive index) that causes hydrogel changes, and then causing that the characteristic of transmitting light in the covering changes, the contrast that finally shows as interference fringe changes.Conversely, by the interference spectrum signal that returns being carried out the contrast variation that data processing can obtain interference fringe, just can obtain ambient humidity and change.
Be described below based on mathematical expression, the said structure of cascade long-period fiber grating device makes it constitute M-Z type interferometer (Mach-Zehnder interferometer) structure.The intensity I of the output transmitted spectrum of the M-Z type interferometer that is constituted can be expressed as the formula (2) that provides in the preamble.
Hydrogel humidity sensing film in the foregoing description can be a kind of lightly crosslinked cancellated high molecular polymer, because the group of highly-hydrophilic function is arranged in the molecular structure, can absorb a large amount of moisture.Surface-coated hydrogel humidity sensing film in the cascade-connection long period fiber grating structure, when external environment humidity changes, hydrogel can absorb or discharge moisture, the thickness and the refractive index that cause film itself change, this variation can cause that the transport property of cladding mode changes, and causes that finally the visibility V of interference fringe changes.The expression formula of interference spectum being carried out can obtaining after discrete Fourier changes fringe visibility V is formula (3):
V＝(I
max-I
min)/(I
max+I
min)＝2|F(I){k}|
k＝KL/2πλv/|F(I){k}|
k＝0 (3)
Wherein { k} is the Fourier transform of the intensity I of transmitted spectrum to F (I), and it is the function of spatial frequency k, I
MaxBe the maximum intensity of transmitted spectrum of output, I
MinThe minimum strength of transmitted spectrum for output.The humidity sensitive material that should be appreciated that the cascade-connection long period fiber grating humidity sensor that is applied among the present invention is not limited to hydrogel, and can be any material that is suitable for gathering humidity information.
Fig. 8 is the humidity sensing system synoptic diagram.Accuracy in order to verify that humidity sensing system of the present invention is measured places moisture measurement environment constant temperature humidity chamber 705 with humidity sensor 702, and wherein humidity sensor 702 for example adopts the structure among the embodiment 2.Constant temperature humidity chamber 705 produces different humidity environments, the accurately control simultaneously of temperature and humidity among the embodiment in the used constant temperature humidity chamber, the relative humidity scope of chamber is 25%RH～98%RH (RH is a relative humidity), and resolution is 0.1%RH.Temperature value is set at 25 ℃ in the experiment, changes rh value manually, makes it be increased to 98%RH from 25%RH, and step-length is 5%RH.After each change relative humidity, wait for 30 minutes, spectrometer and data processing module carry out the collection and the processing of interference signal behind the relative humidity value stabilization, obtain the contrast information of interference fringe and then obtain the envionmental humidity value.The curve that the interference fringe contrast of humidity sensor shown in Figure 9 changes with humidity.As can be seen from the figure, when humidity during less than 50%RH, interfering contrast not change substantially, mainly is because the hydrogel water absorbing capacity is almost constant or change very little.When humidity 〉=50%RH, interfere contrast to change linear the change with humidity, through linear fit, obtain interfering pass between contrast and the humidity be V=-0.3439+0.0085 (/ %RH) * RH (%RH) (V is for interfering contrast).In actual measurement, by measuring the interference spectum of cascade-connection long period fiber grating, obtain interfering the information of contrast through data processing, can obtain envionmental humidity RH (%RH)=(V+0.3439)/0.0085 (/ %RH), the relative humidity scope that wherein can detect is RH 〉=50%RH.
The humidity sensor that the present invention proposes is based on the Mach-Zehnder interferometer structure of the asymmetric long period fiber grating formation of cascade, and the interference spectum signal of measurement has meticulousr spectral composition, can improve the sensitivity and the Measurement Resolution of humidity sensor.In addition, because signal adopts Optical Fiber Transmission, can realize that real-time online remote monitoring ambient humidity changes.
Above embodiment only is used to illustrate the present invention; and be not limitation of the present invention; the those of ordinary skill in relevant technologies field; under the situation that does not break away from the spirit and scope of the present invention; can also make various variations and modification; therefore all technical schemes that are equal to also belong to category of the present invention, and scope of patent protection of the present invention should be defined by the claims.
Claims (12)
1, a kind of cascade long-period fiber grating device is characterized in that, this device comprises:
First long period fiber grating is used for receiving optical signals and it is divided into two-way, the fiber core of leading up to transmission, and one the tunnel is coupled to fibre cladding transmits;
Second long period fiber grating is used for receiving the two ways of optical signals transmitted by optical fiber, and the light signal that will in fibre cladding, transmit again the coupled back into optical fibers fibre core two ways of optical signals is produced interfere;
Optical fiber is connected between described first long period fiber grating and described second long period fiber grating.
2, device according to claim 1 is characterized in that, the transmissivity of described first long period fiber grating and second long period fiber grating is 3dB.
3, a kind of manufacture method of cascade long-period fiber grating device is characterized in that, this method may further comprise the steps:
S1 places single-mode fiber the focal plane of laser instrument laser facula;
S2 utilizes described laser facula, presses the repeatedly described single-mode fiber of transversal scanning of predetermined set scan mode, finishes the making of first long period fiber grating, and described first long period fiber grating has the structural change of periodic refractive index modulation and asymmetry;
S3, mobile single-mode fiber one segment distance adopts the method identical with making first long period fiber grating to make second long period fiber grating.
4, method according to claim 3 is characterized in that, among the step S1, described laser instrument is CO
2Laser instrument.
5, method according to claim 3 is characterized in that, among the step S2, the predetermined set scan mode is:
At first make laser facula along direction transversal scanning single-mode fiber perpendicular to single-mode fiber, make laser facula along the single-mode fiber axial dipole field distance in a grating cycle then, repeat the above-mentioned scanning of laterally stating at next one point, so repeated several times is finished the single pass process;
The above-mentioned scanning process of repeated several times.
6, method according to claim 3 is characterized in that, among the step S3, utilizes micro-displacement platform to move described single-mode fiber.
7, a kind of humidity sensor is characterized in that, this humidity sensor comprises:
Cascade long-period fiber grating device as claimed in claim 1 or 2;
Humidity sensing film, the surface that it is coated in cascade long-period fiber grating device is used for the variation of perception external environment humidity.
8, humidity sensor according to claim 7 is characterized in that, described humidity sensing film is the hydrogel humidity sensing film.
9, humidity sensor according to claim 8 is characterized in that, described hydrogel humidity sensing film is coated on the single-mode fiber cladding surface between first long period fiber grating and second long period fiber grating.
10, humidity sensor according to claim 8 is characterized in that, described hydrogel humidity sensing film is coated on the cladding surface of the interval optical fiber between first long period fiber grating and second long period fiber grating and this two gratings.
11, humidity sensor according to claim 8 is characterized in that, described hydrogel humidity sensing film adopts infusion method to be made in conjunction with the method for uv light irradiation film forming.
12, a kind of humidity sensing system is characterized in that, this system comprises:
Wideband light source is used to provide the wide range light signal;
Humidity sensor as claimed in claim 7 places the moisture measurement environment, and its two ends link to each other with the spectra collection unit with described wideband light source respectively, is used to respond to moisture measurement ambient humidity information;
Described spectra collection unit is used for gathering the optical interference signals that comprises moisture measurement ambient humidity information that the humidity sensor second long period fiber grating place produces;
Data processing unit is used for the optical interference signals of being gathered is analyzed and handled, and obtains moisture measurement ambient humidity information.
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