CN111649771A - Non-scanning type demodulation system based on optical fiber Fabry-Perot sensor - Google Patents
Non-scanning type demodulation system based on optical fiber Fabry-Perot sensor Download PDFInfo
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- CN111649771A CN111649771A CN202010536834.XA CN202010536834A CN111649771A CN 111649771 A CN111649771 A CN 111649771A CN 202010536834 A CN202010536834 A CN 202010536834A CN 111649771 A CN111649771 A CN 111649771A
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- G—PHYSICS
- G01—MEASURING; TESTING
- 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
- G01D5/35306—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
- G01D5/35309—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 multiple waves interferometer
- G01D5/35312—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 multiple waves interferometer using a Fabry Perot
Abstract
The invention relates to a non-scanning type demodulation system based on an optical fiber Fabry-Perot sensor, and belongs to the technical field of optical fiber sensing. The system comprises: the device comprises a positive lens, a first free-form surface reflector, a second free-form surface reflector, an optical wedge, a plano-convex cylindrical lens, a linear array CCD and a data processor; the positive lens is used for receiving light with cavity length information acquired from the optical fiber Fabry-Perot sensor, the light is emitted to the positive lens through the optical fiber, and the light is dispersed into parallel light; the first free-form surface reflector is used for receiving the parallel light diffused by the positive lens and converting the parallel light into flat top light; the second free-form surface reflector is used for collimating the emergent direction of the flat-top light and ensuring that the signal light incident to the optical wedge is perpendicular to the surface of the optical wedge; the plano-convex column lens is used for converting the rectangular light spot transmitted by the optical wedge into one-dimensional linear light; the linear array CCD is used for detecting one-dimensional linear light transmitted by the plano-convex cylindrical lens and outputting a voltage signal. The invention can effectively demodulate the signal contrast and improve the demodulation precision of the demodulation system.
Description
Technical Field
The invention belongs to the technical field of optical fiber sensing, and relates to a non-scanning type demodulation system based on an optical fiber Fabry-Perot sensor.
Background
An Optical Fiber Fabry-Perot Sensor (Optical Fiber Fabry-Perot Sensor for short) is an interference Optical Fiber Sensor with mature technology and common application. The device has the advantages of simple structure, good stability, small volume, light weight, high sensitivity, strong anti-electromagnetic interference capability and the like, and is widely applied to the fields of bridge structure health monitoring, civil engineering, large civil building safety monitoring and the like.
The core of the fiber Fabry-Perot sensor is a fiber Fabry-Perot cavity, two sections of fibers are fixed in a capillary tube, and two end faces are ensured to be flat and parallel to each other, so that a microcavity with the cavity length L is formed, and the structural schematic diagram of the fiber Fabry-Perot sensor is shown in figure 1. The expressions of the reflected light signals of the Fabry-Perot cavity are respectively as follows:
wherein λ is the wavelength of incident light, I0(lambda) is the incident spectrum, R is the reflectivity of the end face of the Fabry-Perot cavity, and L is the cavity length of the Fabry-Perot cavity. When the measured structure changes, the cavity length L of the sensor also changes. The change of the measured structure can be obtained by demodulating the cavity length L.
The non-scanning type correlation demodulation method utilizes an optical wedge to realize hardware correlation demodulation of a cavity length L, has no movable part and good stability, is a demodulation method which is widely applied to the conventional optical fiber Fabry-Perot sensor, and is characterized in that a demodulation system developed by Fizeau company is shown in figure 2. The optical signal is shaped into one-dimensional linear light by the concave cylindrical reflector, secondary interference is carried out by the optical wedge, and finally the demodulated optical signal is detected and received by the linear array CCD. The linear array CCD received signal can appear a light intensity maximum value in the position that the light wedge thickness equals with the sensor cavity length, through the light wedge thickness that analysis linear array photoelectric detector looks like the maximum light intensity department of sensitive element and corresponds, can demodulate out the cavity length of optic fibre method-amber sensor, by the strain of the long representation measured base member of cavity.
The demodulation system developed by Tianjin university is shown in FIG. 3, and differs from Fizeau in that a polarizer and a crystal wedge are used. The reflected light carrying cavity length information is focused into linear light through the cylindrical lens, the linear light is changed into linear light after passing through the polaroid 1, the linear light is decomposed into e light and o light through the optical wedge, the e light and the o light pass through the polaroid 2, the vibration direction is projected to the same direction, and finally the linear array CCD detects the position of the maximum value of the interference light intensity, so that the cavity length of the measured optical fiber Fabry-Perot sensor can be obtained.
The two systems realize hardware-related demodulation by using the optical wedge, have no movable part and have good stability; however, only a concave cylindrical reflector or a cylindrical lens in the demodulation module shapes the emergent light of the sensor, the signal light energy incident to the surface of the optical wedge is not uniformly distributed and the angle is not vertical, so that the contrast of the demodulation signal is influenced to a certain extent, and the problems specifically existing are as follows:
(1) emergent light of the optical fiber in the demodulation module is in spatial Gaussian distribution, and due to energy concentration, pixels at two ends of the linear array photoelectric detector cannot detect optical signals, so that the measurement range of the system is reduced.
(2) The emergent light angle of the optical fiber of the demodulation module is divergent, and the incident light which is not vertical to the surface of the optical wedge does not contribute to the contrast ratio of the demodulation signal, so that only the background noise is increased.
In summary, for the demodulation system, the incident light with an angle perpendicular to the optical wedge surface can generate interference fringes on the optical wedge surface, i.e. increase the effective demodulation signal contrast, while the light with an incident angle not perpendicular to the optical wedge is received by the CCD, which only increases the dc component in the demodulation signal, i.e. the noise floor, and does not help in cavity length demodulation.
In view of the above problems of the demodulation system, the present invention provides a new non-scanning demodulation system for improving the demodulation accuracy of the demodulation system.
Disclosure of Invention
In view of the above, the present invention provides a non-scanning demodulation system based on an optical fiber fabry-perot sensor, which is used for effectively demodulating signal contrast and improving demodulation accuracy of the demodulation system.
In order to achieve the purpose, the invention provides the following technical scheme:
a non-scanning type demodulation system based on a fiber Fabry-Perot sensor comprises: the device comprises a positive lens, a first free-form surface reflector, a second free-form surface reflector, an optical wedge, a plano-convex cylindrical lens, a linear array CCD and a data processor;
the positive lens is used for receiving light with cavity length information acquired from the optical fiber Fabry-Perot sensor, the light is emitted to the positive lens through the optical fiber, and the light is dispersed into parallel light;
the first free-form surface reflector is used for receiving the parallel light diffused by the positive lens and converting the parallel light into flat top light;
the second free-form surface reflector is used for collimating the emergent direction of the flat-top light and ensuring that the signal light incident to the optical wedge is perpendicular to the surface of the optical wedge;
the plano-convex column lens is used for converting the rectangular light spot transmitted by the optical wedge into one-dimensional linear light;
the linear array CCD is used for detecting one-dimensional linear light transmitted by the plano-convex cylindrical lens and outputting a voltage signal.
Further, the parallel light after being diverged by the positive lens is in Gaussian distribution, and the light intensity expression is as follows:
wherein, ω is0Is the beam waist of a gaussian beam and (x, y) is the spatial coordinate.
Further, the flat-topped beam converted by the first free-form surface reflector is a circular flat-topped beam with uniformly distributed energy, and the homogenized Lorentz function is adopted to express that the flat-topped light intensity distribution is as follows:
wherein the content of the first and second substances,
polar coordinates of a circular flat-topped beam, RFLQ determines the shape of the homogenizing lorentz function for the full width at half maximum of the flat-topped intensity distribution.
Further, the data processor is used for analyzing and processing the output voltage signal by the aid of the convex wave crest, and finding out the thickness of the optical wedge corresponding to the position of the voltage maximum value, namely the cavity length of the Fabry-Perot sensor to be measured.
Further, the demodulation system further includes: the system comprises a broadband light source, an optical fiber Fabry-Perot sensor and a coupler; the coupler is used for connecting the broadband light source, the Fabry-Perot sensor and the optical fiber; the optical fiber Fabry-Perot sensor is used for converting a broadband light source emitted by a signal source into a reflected light signal with cavity length information.
The invention has the beneficial effects that:
(1) the system of the invention utilizes the positive lens, the free-form surface reflector, the planoconvex cylindrical lens and the optical wedge to form a demodulation optical path, wherein the free-form surface reflector shapes signal light, and the influence of chromatic aberration can be avoided;
(2) the system is shaped by the free-form surface reflector, and converted into flat-topped beams with uniform energy distribution in Gaussian distribution, so that the waste of CCD pixels is avoided;
(3) the system is shaped by the free-form surface reflector, and incident light in the demodulation module is vertical to the surface of the optical wedge, so that the effective demodulation signal contrast can be improved, and the demodulation precision of the system is further improved;
(4) the plano-convex cylindrical mirror of the system of the invention shapes the rectangular light spot which penetrates through the optical wedge, and the light intensity utilization rate can be increased.
Drawings
In order to make the object, technical scheme and beneficial effect of the invention more clear, the invention provides the following drawings for explanation:
FIG. 1 is a diagram of a non-fiber Fabry-Perot sensor configuration;
FIG. 2 is a non-scanning coherent demodulation system of Fizeau;
FIG. 3 is a non-scanning type correlation demodulation system of Tianjin university;
FIG. 4 illustrates a non-scanning demodulation system according to the present invention;
FIG. 5 is a graph showing simulation of energy distribution of parallel light and flat-top light;
FIG. 6 is a schematic view of a plano-convex cylindrical lens converging signal light;
fig. 7 is a schematic diagram of the demodulation principle of the data processor.
Detailed Description
Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.
As shown in fig. 4, the non-scanning demodulation system based on the fiber fabry-perot sensor according to the present invention includes: the optical fiber Fabry-Perot sensor comprises a positive lens, a first free-form surface reflector, a second free-form surface reflector, an optical wedge, a plano-convex cylindrical lens, a linear array CCD, a data processor, an optical fiber Fabry-Perot sensor and a coupler;
the positive lens is used for receiving light with cavity length information acquired from the optical fiber Fabry-Perot sensor, the light is emitted to the positive lens through the optical fiber, and the light is dispersed into parallel light; the first free-form surface reflector is used for receiving the parallel light diffused by the positive lens and converting the parallel light into flat top light; the second free-form surface reflector is used for collimating the emergent direction of the flat-top light and ensuring that the signal light incident to the optical wedge is perpendicular to the surface of the optical wedge; the plano-convex column lens is used for converting the rectangular light spot transmitted by the optical wedge into one-dimensional linear light; the linear array CCD is used for detecting one-dimensional linear light transmitted by the plano-convex cylindrical lens and outputting a voltage signal. The coupler is used for connecting the light source, the Fabry-Perot sensor and the optical fiber; the optical fiber Fabry-Perot sensor is used for converting a broadband light source emitted by a signal source into a reflected light signal with cavity length information.
In the demodulation system, light carrying cavity length information is emitted through an optical fiber, and firstly passes through a positive lens, and divergent light is collimated into parallel light; then the first free-form surface reflector converts incident light with Gaussian energy distribution into flat top light with uniform energy distribution. The incident light is in Gaussian distribution, and the expression of the light intensity is as follows:
wherein, ω is0Is the beam waist of a gaussian beam and (x, y) is the spatial coordinate.
Emergent light is a round flat-top light beam with uniformly distributed energy, and the emergent light intensity distribution of the shaping system can be represented by a homogenized Lorentz function:
wherein the content of the first and second substances,
polar coordinates of a circular flat-topped beam, RFLQ determines the shape of the homogenizing lorentz function for the full width at half maximum of the flat-topped intensity distribution.
The simulation of the energy distribution of the incident light and the emergent light is shown in fig. 5, wherein fig. 5(a) is a simulation graph of the incident gaussian beam, and fig. 5(b) is a simulation graph of the emergent flat-top beam.
The second free-form surface reflector collimates the emergent direction of the flat-top light beam. The shaping of the free-form surface mirror ensures that the signal light entering the wedge is perpendicular to its upper surface. Because the linear array CCD pixel has a narrow width (about 100 μm), a plano-convex cylindrical lens as shown in FIG. 6 is also needed to convert the rectangular light spot transmitted by the optical wedge into one-dimensional linear light, which is finally detected by the linear array CCD to output a voltage signal.
As shown in fig. 7, the data processor analyzes and processes the signal with the upward convex peak to find the optical wedge thickness corresponding to the maximum voltage position, that is, the cavity length of the optical fiber fabry-perot sensor to be measured.
Finally, it is noted that the above-mentioned preferred embodiments illustrate rather than limit the invention, and that, although the invention has been described in detail with reference to the above-mentioned preferred embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the scope of the invention as defined by the appended claims.
Claims (5)
1. A non-scanning type demodulation system based on a fiber Fabry-Perot sensor is characterized by comprising: the device comprises a positive lens, a first free-form surface reflector, a second free-form surface reflector, an optical wedge, a plano-convex cylindrical lens, a linear array CCD and a data processor;
the positive lens is used for receiving light with cavity length information acquired from the optical fiber Fabry-Perot sensor, the light is emitted to the positive lens through the optical fiber, and the light is dispersed into parallel light;
the first free-form surface reflector is used for receiving the parallel light diffused by the positive lens and converting the parallel light into flat top light;
the second free-form surface reflector is used for collimating the emergent direction of the flat-top light and ensuring that the signal light incident to the optical wedge is perpendicular to the surface of the optical wedge;
the plano-convex column lens is used for converting the rectangular light spot transmitted by the optical wedge into one-dimensional linear light;
the linear array CCD is used for detecting one-dimensional linear light transmitted by the plano-convex cylindrical lens and outputting a voltage signal.
2. The non-scanning demodulation system based on fiber Fabry-Perot sensor of claim 1, wherein the parallel light after being diverged by the positive lens is Gaussian distributed.
3. The non-scanning demodulation system based on the fiber Fabry-Perot sensor according to claim 1, wherein the flat-topped light converted by the first free-form surface reflector is a circular flat-topped light beam with uniformly distributed energy, and the flat-topped light intensity distribution is represented by a homogenized Lorentz function.
4. The non-scanning demodulation system based on the fiber-optic Fabry-Perot sensor according to claim 1, wherein the data processor is configured to perform analysis processing on the output voltage signal by using an upward convex peak, and find out the thickness of the optical wedge corresponding to the position of the voltage maximum, that is, the cavity length of the Fabry-Perot sensor to be measured.
5. The fiber optic Fabry-Perot sensor based non-scanning demodulation system of claim 1, further comprising: the system comprises a broadband light source, an optical fiber Fabry-Perot sensor and a coupler;
the coupler is used for connecting the broadband light source, the Fabry-Perot sensor and the optical fiber;
the optical fiber Fabry-Perot sensor is used for converting a broadband light source emitted by a signal source into a reflected light signal with cavity length information.
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112804828A (en) * | 2020-12-30 | 2021-05-14 | 武汉先河激光技术有限公司 | System for processing multichannel FPC flexible circuit board |
| CN112945370A (en) * | 2021-02-09 | 2021-06-11 | 中北大学 | All-solid-state Fabry-Perot cavity embedded thin film type vibration sensor and system |
| CN115931022A (en) * | 2023-01-04 | 2023-04-07 | 北京佰为深科技发展有限公司 | Optical fiber Fabry-Perot sensor demodulation system |
| CN116256861A (en) * | 2023-05-09 | 2023-06-13 | 山东省科学院激光研究所 | Optical fiber F-P cavity temperature sensor and packaging protection structure |
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| CN106017519A (en) * | 2016-05-05 | 2016-10-12 | 重庆大学 | Optical fiber Fabry-Perot sensor demodulation system and method |
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Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112804828A (en) * | 2020-12-30 | 2021-05-14 | 武汉先河激光技术有限公司 | System for processing multichannel FPC flexible circuit board |
| CN112804828B (en) * | 2020-12-30 | 2022-08-19 | 武汉先河激光技术有限公司 | System for processing multichannel FPC flexible circuit board |
| CN112945370A (en) * | 2021-02-09 | 2021-06-11 | 中北大学 | All-solid-state Fabry-Perot cavity embedded thin film type vibration sensor and system |
| CN112945370B (en) * | 2021-02-09 | 2022-09-13 | 中北大学 | All-solid-state Fabry-Perot cavity embedded thin film type vibration sensor and system |
| CN115931022A (en) * | 2023-01-04 | 2023-04-07 | 北京佰为深科技发展有限公司 | Optical fiber Fabry-Perot sensor demodulation system |
| CN116256861A (en) * | 2023-05-09 | 2023-06-13 | 山东省科学院激光研究所 | Optical fiber F-P cavity temperature sensor and packaging protection structure |
| CN116256861B (en) * | 2023-05-09 | 2023-07-18 | 山东省科学院激光研究所 | Optical fiber F-P cavity temperature sensor and packaging protection structure |
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Application publication date: 20200911 |