CN111220187A - Cascade long period fiber grating multiplexing demodulation device based on low coherent interference principle - Google Patents
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- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
- G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
- G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
- G01D5/35383—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using multiple sensor devices using multiplexing techniques
- G01D5/35396—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using multiple sensor devices using multiplexing techniques using other forms of multiplexing
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- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
- G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
- G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
- G01D5/35306—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using an interferometer arrangement
- G01D5/35332—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using an interferometer arrangement using other interferometers
Abstract
The invention provides a cascade long-period fiber grating multiplexing demodulation device based on a low-coherence interference principle, which comprises a broadband light source, a first coupler, a cascade long-period fiber grating, a second coupler, a Fizeau interferometer, a linear array InGaAs and data storage and processing equipment, wherein the broadband light source is connected with a port optical signal of the first fiber coupler, the first fiber coupler is connected with at least 2 cascade long-period fiber grating sensors, the cascade long-period fiber grating sensors are connected with the second fiber coupler through optical signals, the input end of the Fizeau interferometer at the other interface of the second fiber coupler is optically connected, an output optical signal of the Fizeau interferometer reaches the linear array InGaAs, and the linear array InGaAs and the data storage and processing equipment are connected. The invention provides a low-coherence interference principle-based cascade long-period fiber grating multiplexing and demodulating device which has the advantages of stability, high spatial resolution, large multiplexing number and low cost.
Description
Technical Field
The invention relates to the technical field of optical fiber sensing, in particular to a cascade long-period optical fiber grating multiplexing demodulation device based on a low-coherence interference principle.
Background
Cascade long period optical fiber grating and sensing principle thereof
The cascade long-period fiber grating is formed by engraving 2 long-period fiber gratings with the same parameters on the same optical fiber, is used as a special structure of the long-period fiber grating and is also a long-period fiber grating in essence, and sensing information is obtained based on the fact that the sensing and the measurement of the cascade long-period fiber grating are the change of the grating wavelength or the transmission depth at the position of the resonance wavelength caused by the external environment. The mechanism of the cascade long-period fiber grating for sensing comprises temperature-induced deformation and thermo-optic effect, strain-induced deformation and elasto-optic effect, refractive index-induced effective refractive index change and the like. Based on the basic sensing mechanisms, parameters such as temperature, strain, bending and refractive index of the structure can be monitored.
The cascade long-period fiber grating is the homodromous coupling between a core layer basic mode and a plurality of cladding modes of the fiber, works in a transmission mode, and has larger loss peak bandwidth. Because of no reflection characteristic, the time division multiplexing scheme for measuring the reflection delay of the pulsed light is not suitable for a long-period fiber grating array; the loss band characteristics of multiple wide spectrums of the transmission spectrum of the long-period fiber grating cause that the wavelength division multiplexing scheme cannot be realized. These factors create difficulties for multiplexing and modulating the cascaded long-period fiber grating sensing signals.
Low coherence interference technique
The low coherence interference technology is an interference system which uses broad spectrum light as a light source and utilizes zero-order interference fringes as a reference position according to a white light coherence principle so as to obtain accurate measurement absolute position information in a large range. The low coherence interference system is used for obtaining a detection signal, the sensor structure is an interferometer, the demodulation part is a scanning type interferometer, different sensors are designed by adopting different optical path differences, and multiplexing of multiple sensing can be realized. Because the information content of each sensor is demodulated in a low-coherence system in an interferometer mode, environmental noise caused by factors such as unstable light sources and the like can be avoided, and the low-coherence system has high anti-interference performance; all data of the interferogram are fully utilized to evaluate the measured signal, so that the method has the effect of average effect favored by a precision measurement theory and obtains higher measurement precision; the optical fiber low-coherence interference system is constructed, a tunable laser light source used by the high-coherence interference system is not needed, precious and precise equipment such as a spectrometer, a network analyzer and a vector analyzer are not needed for signal analysis and processing, and the system cost is far lower than that of the wavelength division multiplexing, time division multiplexing and other systems widely used at present.
Disclosure of Invention
In order to solve the existing problems, the invention provides a cascade long-period fiber grating multiplexing and demodulating device based on the low coherent interference principle, which has the advantages of stability, high spatial resolution, large multiplexing number and low cost, and for the purpose, the invention provides the cascade long-period fiber grating multiplexing and demodulating device based on the low coherent interference principle, the device comprises a broadband light source, a first coupler, a cascade long-period fiber grating, a second coupler, a Fizeau interferometer, a linear array InGaAs and data storage and processing equipment, the broadband light source is connected with a port optical signal of the first fiber coupler, the first fiber coupler is connected with at least 2 cascade long-period fiber grating sensors, the cascade long-period fiber grating sensors are connected with the second fiber coupler through optical signals, and the other interface of the second fiber coupler is connected with an input end of the Fizeau interferometer, and the output optical signals of the Fizeau interferometer reach the linear array InGaAs, and the linear array InGaAs and the data storage are connected with a processing device.
The invention further improves that the number of the cascade long-period fiber bragg gratings is N, N is a positive integer and is more than or equal to 2, and the first fiber coupler is connected with at least 2 cascade long-period fiber bragg grating sensors.
According to the further improvement of the invention, the center wavelength position of the broadband light source is 1565nm, the spectral range is 60nm, and the bandwidth of the resonance loss peak of the long-period fiber grating sensor is covered.
In a further improvement of the invention, the grating of the cascaded long-period fiber grating sensor consists of two identical long-period fiber gratings with coupling strength of 3dB, and the grating is designed to meet the requirement of high visibility of interference fringes.
In a further improvement of the invention, the optical path difference introduced by the cascade long-period fiber grating and the Fizeau interferometer is smaller than the coherence length of the broadband light source, so that the design is to meet the condition of low coherence interference.
The invention is further improved by presetting the distance l between the long-period fiber gratings of each cascaded long-period fiber gratingiInstead, this is designed to prevent the interference fringes of different sensors from overlapping.
The invention provides a cascade long-period fiber grating multiplexing and demodulating device based on a low-coherence interference principle, which can calculate the position of the resonance loss peak wavelength of a sensor through measurement and further demodulate the information to be measured, and can realize multiplexing of a plurality of sensors by arranging a series of sensors with different optical path differences in parallel.
Drawings
FIG. 1 is a schematic of the present invention;
illustration of the drawings:
1. a broadband light source; 2. a first coupler; 3. cascading long-period fiber gratings; 4. a second coupler; 5. a Fizeau interferometer;
6. linear array InGaAs; 7. a data storage and processing device.
Detailed Description
The invention is described in further detail below with reference to the following detailed description and accompanying drawings:
the invention provides a low-coherence interference principle-based cascade long-period fiber grating multiplexing and demodulating device which has the advantages of stability, high spatial resolution, large multiplexing number and low cost.
As an embodiment of the present invention, the present invention provides a cascade long period fiber grating multiplexing and demodulating apparatus based on the low coherence interference principle as shown in fig. 1, the apparatus comprises a broadband light source 1, a first coupler 2, a cascade long period fiber grating 3, a second coupler 4, a fizeau interferometer 5, a linear array InGaAs6 and a data storage and processing device 7, and is characterized in that: the broadband light source 1 is connected with port optical signals of a first optical fiber coupler 2, the first optical fiber coupler 2 is connected with at least 2 cascaded long-period optical fiber grating sensors 3, the cascaded long-period optical fiber grating sensors 3 are connected with a second optical fiber coupler 4 through optical signals, the other interface of the second optical fiber coupler 4 is optically connected with the input end of a Fizeau interferometer 5, output optical signals of the Fizeau interferometer 5 reach a linear array InGaAs6, and the linear array InGaAs6 and a data storage and processing device 7 are connected.
The number of the cascade long-period fiber bragg gratings is N, N is a positive integer and is not less than 2, the first fiber coupler is connected with at least 2 cascade long-period fiber bragg grating sensors, the central wavelength position of the broadband light source 1 is 1565nm, the spectral range is 60nm, and the bandwidth of a resonance loss peak of the long-period fiber bragg grating sensors is covered.
In order to meet the requirement that the interference fringes have higher visibility, the grating of the cascade long-period fiber grating sensor 3 consists of two long-period fiber gratings with the same coupling strength of 3 dB.
In order to satisfy the condition of low coherence interference, the optical path difference introduced by the cascade long-period fiber grating 3 and the Fizeau interferometer 5 should be smaller than the coherence length of the broadband light source 1.
To prevent the interference fringes of different sensors from overlapping, the distance l between the long-period fiber gratings of each cascade long-period fiber grating 3 should be presetiDifferent.
The working principle of the application is as follows:
monochromatic light with certain wavelength lambda emitted from a broadband light source is divided into N beams of light with equal amplitude through the beam splitting of the coupler 1 and then is respectively incident and emitted into LPGP-1, LPGP-2, … … and LPGP-N.
The optical path difference introduced by the optical signal in each sensor is different by presetting the optical path difference in each cascaded long-period fiber grating sensor. Multiple paths of light are transmitted in the sensor, wherein the light path of one cascaded long-period fiber grating sensor is a reference arm, and the rest of the sensor comprises the distance l between the cascaded long-period light long-period fiber gratingsiIn contrast, the optical paths of the FBG sensor are all used as sensing arms forAnd (4) measuring parameters. Each sensing arm and the reference arm have different optical path differences and are larger than the coherence length of the light source, so that the light paths do not interfere when being converged by the optical fiber coupler.
The light field radiated by the broadband light source enters the electric vector of a certain cascade long period fiber grating sensor after being split by the beam splitter
And (4) showing. The electric vector expression obtained by a coupling mode theory and a transmission matrix after the cascade long-period fiber grating sensor is as follows:
wherein, T0Representing the transmission coefficient, T, of the core layer of a long-period fiber gratingjThe transmission coefficient of the LP0j th order cladding mode of the long-period fiber grating is shown, and the delta phi represents the phase difference introduced by two arms of the cascade long-period fiber grating sensor:
When light beams enter the Fizeau interferometer, the optical path difference caused by the Fizeau interferometer is matched with the optical path difference caused by the cascade long-period fiber grating sensor, and obvious low-coherence interference fringes can be generated in a corresponding local area of the linear array InGaAs. The electric vector of the optical field obtained on the linear array InGaAs can be expressed as:
wherein: r represents the reflectivity of the beamsplitter in the fizeau interferometer,
representing the phase difference introduced by the fizeau interferometer:
wherein: n is the refractive index of the fizeau interferometer and h is the thickness of the fizeau interferometer.
The expression of the interference light intensity detected by a certain wavelength lambda on the linear array InGaAs is as follows:
the interference signals finally acquired by the linear array InGaAs are all wavelengths (lambda) of the broadband light source1～λ2) Superposition of monochromatic wavelength interference signals:
the linear array InGaAs outputs the received signal to a signal processing device, and the signal processing device demodulates the interference fringe signal. The information of the interference fringes is related to the transmission spectrum information of the cascade long-period fiber grating, and a computer can be used for carrying out fast Fourier transform on the interference signals, reducing the transmission spectrum of the cascade long-period fiber grating and obtaining the shift of the resonance wavelength caused by the external parameter (temperature, stress, refractive index and the like) transformation.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention in any way, but any modifications or equivalent variations made according to the technical spirit of the present invention are within the scope of the present invention as claimed.
Claims (6)
1. Cascade long period fiber grating multiplexing demodulation device based on low coherent interference principle, the device is by broadband light source (1), first coupler (2), cascade long period fiber grating (3), second coupler (4), Fizeau interferometer (5), linear array InGaAs (6) and data storage and processing equipment (7), its characterized in that: the broadband light source (1) is connected with port optical signals of a first optical fiber coupler (2), the first optical fiber coupler (2) is connected with at least 2 cascaded long-period optical fiber grating sensors (3), the cascaded long-period optical fiber grating sensors (3) are connected with a second optical fiber coupler (4) through optical signals, the other interface of the second optical fiber coupler (4) is connected with the input end of a Fizeau interferometer (5) in an optical mode, output optical signals of the Fizeau interferometer (5) reach linear array InGaAs (6), and the linear array InGaAs (6) and data storage are connected with processing equipment (7).
2. The device according to claim 1, wherein the device comprises: the number of the cascade long-period fiber gratings (3) is N, N is a positive integer and is more than or equal to 2.
3. The device according to claim 1, wherein the device comprises: the center wavelength position of the broadband light source (1) is 1565nm, the spectral range is 60nm, and the bandwidth of the resonance loss peak of the long-period fiber grating sensor is covered.
4. The device according to claim 1, wherein the device comprises: the grating of the cascade long-period fiber grating sensor (3) consists of two long-period fiber gratings with the same coupling strength of 3 dB.
5. The device according to claim 1, wherein the device comprises: the optical path difference introduced by the cascade long-period fiber grating (3) and the Fizeau interferometer (5) is smaller than the coherence length of the broadband light source (1).
6. The device according to claim 1, wherein the device comprises: the distance l between the long-period fiber gratings of each cascade long-period fiber grating (3) should be presetiDifferent.
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Inventor after: Hu Xingliu Inventor after: Shen Hao Inventor after: Fang Ting Inventor after: Si Haifei Inventor after: Miao Songcen Inventor before: Hu Xingliu Inventor before: Miao Songcen Inventor before: Si Haifei Inventor before: Fang Ting Inventor before: Shen Hao |