CN113091882B - Double-cavity device for detecting membrane surface vibration and demodulation method thereof - Google Patents

Double-cavity device for detecting membrane surface vibration and demodulation method thereof Download PDF

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CN113091882B
CN113091882B CN202110424821.8A CN202110424821A CN113091882B CN 113091882 B CN113091882 B CN 113091882B CN 202110424821 A CN202110424821 A CN 202110424821A CN 113091882 B CN113091882 B CN 113091882B
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俞本立
时金辉
光东
吴许强
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Anhui University
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Abstract

The invention discloses a double-cavity device for detecting membrane surface vibration and a demodulation method thereof, relating to the technical field of optical sensing information demodulation; comprises a laser, an optical fiber beam splitter, an optical circulator, an optical fiber, a double-cavity device and a photoelectric detector; laser emitted by the laser is divided into two beams of light by the optical fiber beam splitter, the light beams are transmitted to the double-cavity device by the optical circulator, the light beams in the double-cavity device irradiate on the film surface and are reflected back to the optical fiber, the light beams interfere with the reflected light on the end surface of the optical fiber, and the interfered light is transmitted to the photoelectric detector by the optical circulator and is converted into an electric signal; the double-cavity device structure makes the interference signal output by the double cavity present a certain phase difference state, and the double-cavity device contains a displacement driving structure which promotes the end face of the optical fiber to move vertical to the film surface; performing phase demodulation on the electric signal converted from the interference light beam by adopting an ellipse fitting algorithm, and analyzing and calculating the amplitude change of the membrane surface vibration; the sensitivity and the stability of the sensing system are improved.

Description

Double-cavity device for detecting membrane surface vibration and demodulation method thereof
Technical Field
The invention relates to the technical field of optical sensing information demodulation, in particular to a double-cavity device for detecting membrane surface vibration and a demodulation method thereof.
Background
The development of the society needs to acquire external information in a multi-level and high-depth manner, and various sensors are the main modes for acquiring the external information. Optical sensing, particularly interferometric optical sensing, is gaining attention for its high sensitivity, electromagnetic interference resistance, and broad applicability. The difference of interference arms in interference type optical sensing often brings polarization fading, and the FP cavity interferometer has the advantages of path interference resistance and polarization fading resistance due to the existence of the same-path transmission and the isotropic medium in the cavity; in response to the phase fading problem of interferometers, researchers have developed various phase demodulation techniques, such as phase-generated carrier, heterodyne, 3 x 3 coupler demodulation, and the like. Aiming at the characteristic that the FP cavity interferometer is short in cavity length, the dual-wavelength and three-wavelength phase demodulation technology is successively researched.
The conventional phase demodulation technology of the dual-wavelength and three-wavelength FP cavity interferometer needs lasers with multiple wavelengths, the cost of the needed lasers is high, and the requirements on the stability of the center frequency and the power of the lasers are high; since the cavity length of the FP interferometer is greatly changed by the influence of the environment or the large dynamic detection physical quantity, the phase demodulation effect may be unstable, such as deterioration and distortion.
The double-cavity device membrane surface vibration detection method based on the ellipse fitting algorithm uses one wavelength, and the signal phase difference is constructed through the double-cavity structure, so that the requirements of a related passive phase demodulation technology on signal direct current quantity elimination, alternating current quantity normalization and phase difference needing to be orthogonal are well met, and the method has obvious advantages. However, the ellipse fitting algorithm requires that the phase quantity to be measured of two signals must be greater than pi, otherwise the fitting data will be inaccurate, which limits the use of this technique for small-phase signal demodulation.
Disclosure of Invention
The invention aims to provide a double-cavity device for detecting membrane surface vibration and a demodulation method thereof, and provides the structure of the double-cavity device for detecting membrane surface vibration and the application range of double-cavity phase difference; the cost of realizing the sensing device can be reduced, and the sensitivity and the stability of the sensing system are improved; simultaneously, the range of the frequency and the amplitude of the modulation signal is given; by applying the modulation signal, the application range of the phase demodulation method based on the ellipse fitting algorithm is expanded, so that the phase demodulation method can work in small-phase signal demodulation.
The purpose of the invention can be realized by the following technical scheme:
a double-cavity device for detecting membrane surface vibration is characterized by comprising a laser, an optical fiber beam splitter, an optical circulator, an optical fiber, a double-cavity device and a photoelectric detector;
the working method of the double-cavity device comprises the following steps:
laser emitted by the laser is divided into two beams of light by the optical fiber beam splitter, the light beams are transmitted to the double-cavity device by the optical circulator, the light beams in the double-cavity device irradiate on the film surface and are reflected to the end surface of the optical fiber, the light beams interfere with the reflected light of the end surface of the optical fiber, and the interference light is transmitted to the photoelectric detector by the optical circulator and is converted into an electric signal; parallel light beams emitted by the end faces of the optical fibers in the double-cavity device structure irradiate on the same film surface, the end faces of the optical fibers are staggered in the axial direction, and the length of the dislocation is matched with the wavelength of a laser, so that two paths of interference signals output by the double-cavity device form a certain phase difference;
the double-cavity device comprises a displacement driver fixed on the base station, wherein the displacement driver drives the end face of the optical fiber to move vertical to the film surface; and analyzing and calculating the amplitude of the vibration of the membrane surface by adopting a phase demodulation algorithm on the electric signal converted by the interference light beam.
Further, the laser is a single wavelength narrow linewidth laser.
Furthermore, the double-cavity device is composed of an optical fiber end face and a film face, double light beams emitted by the optical fiber end face irradiate on the same film face and are reflected back to the optical fiber end face along an original light path, and two FP cavities exist in the same double-cavity device.
Furthermore, the dislocation length of the end face of the optical fiber in the axial direction is matched with a specific wavelength, so that two paths of interference signals output by the double-cavity device have a certain phase difference, and the phase difference is not equal to pi or integral multiple thereof.
Furthermore, the displacement driver drives the two optical fibers to vibrate at a certain frequency along the direction vertical to the membrane surface, the phase change of a modulation signal reached by the vibration amplitude of the two optical fibers is greater than pi, and the frequency of the two optical fibers is out of the vibration frequency band of the detected membrane surface;
the invention provides a double-cavity device for detecting membrane surface vibration, which gives the structure of the double-cavity device for detecting membrane surface vibration and the application range of double-cavity phase difference; the cost for realizing the sensing device can be reduced, and the sensitivity and the stability of the sensing system are improved;
further, a demodulation method of the double-cavity device for detecting membrane surface vibration comprises the following steps:
the output signals of the interferometers are as follows:
Figure BDA0003028925880000031
wherein A is1And A2Is a direct current component of an interference signal, B1And B2For the purpose of fringe contrast of the interference signal,
Figure BDA0003028925880000032
is the initial phase of the FP interferometer with a cavity length L1, beta is the phase difference of the two interferometers, thetatThe phase quantity to be measured; stFor the axial displacement of the membrane surface in the FP chamber, MtFor vibration modulation applied by displacement driver in dual-cavity device, n is optical refractive index of cavity medium, lambda0Is the wavelength of the light source;
rewriting equation (1) to the following equation
Figure BDA0003028925880000041
The ellipse equation can be expressed as
I1 2+CI2I1+DI2 2+EI1+FI2+H＝0. (3)
Comparing equations (2) and (3), it is possible to obtain
Figure BDA0003028925880000042
The parameters A1, A2, B1, B2 and beta in equation (1) can be calculated by combining equation (4)
Figure BDA0003028925880000043
A pair of phase information thetatCan be expressed as
Figure BDA0003028925880000044
By means of an arctan algorithm, θ can be obtainedtFiltering out the frequency signal M of the modulation signal by a filtertFurther, the displacement S of the film surface is calculated from equation (1)t. The invention provides the range of the frequency and the amplitude of the modulation signal; application of simultaneous modulation signals, extended based on ellipsesThe phase demodulation method of the fitting algorithm is used in a range that the phase demodulation method can work in small-phase signal demodulation.
The invention has the beneficial effects that:
1. laser emitted by a laser is divided into two beams of light by an optical fiber beam splitter, the light beams are transmitted to a double-cavity device through an optical circulator, the light beams in the double-cavity device irradiate on a film surface and are reflected to an optical fiber end face, interference is generated between the light beams and reflected light of the optical fiber end face, and the interference light is transmitted to a photoelectric detector through the optical circulator and is converted into an electric signal; parallel light beams emitted by the end faces of the optical fibers in the double-cavity device structure irradiate on the same film surface, the end faces of the optical fibers are staggered in the axial direction, and the length of the dislocation is matched with the wavelength of a laser, so that two paths of interference signals output by the double-cavity device form a certain phase difference; the double-cavity device comprises a displacement driver fixed on the base station, wherein the displacement driver drives the end face of the optical fiber to move vertical to the film surface; analyzing and calculating the amplitude of the vibration of the membrane surface by adopting a phase demodulation algorithm on an electric signal converted from the interference light beam; the invention provides the structure of a double-cavity device for detecting membrane surface vibration and the application range of double-cavity phase difference; the cost of realizing the sensing device can be reduced, and the sensitivity and the stability of the sensing system are improved;
2. the invention also provides a demodulation method of the double-cavity device for detecting the membrane surface vibration, which analyzes and calculates the change of the membrane surface vibration amplitude value by adopting an ellipse fitting algorithm based on the electric signal converted by the interference light beam, and provides the ranges of the frequency and the amplitude value of the modulation signal; meanwhile, due to the application of the modulation signals, the application range of the phase demodulation method based on the ellipse fitting algorithm is expanded, so that the phase demodulation method can work in small-phase signal demodulation.
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In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a block diagram of a dual chamber device and demodulation system for detecting membrane surface vibration according to the present invention.
FIG. 2 is a schematic diagram of the construction of a dual chamber device of the present invention.
FIG. 3 is a graph showing the comparison of the vibration demodulation data of the film surface with and without modulation according to the present invention.
FIG. 4 is a graph showing the comparison of demodulation errors of the membrane surface vibration with and without modulation according to the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be described clearly and completely below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Referring to fig. 1 to 4, the present embodiment discloses a dual-cavity apparatus for detecting membrane surface vibration, which includes a laser, an optical fiber beam splitter, an optical circulator, a plurality of optical fibers, a dual-cavity apparatus, and a photodetector;
laser emitted by the laser is divided into two beams of light by the optical fiber beam splitter, the light beams are transmitted to the double-cavity device through the optical circulator, the light beams in the double-cavity device irradiate on the film surface and are reflected to the end surface of the optical fiber, then the light beams are interfered with reflected light of the end surface of the optical fiber, and the interfered light is transmitted to the photoelectric detector through the optical circulator and is converted into an electric signal;
parallel light beams emitted by the end face of the optical fiber in the double-cavity device irradiate on the same film surface, the end face of the optical fiber has dislocation with a certain length in the axial direction of the optical fiber, and the dislocation length is matched with the wavelength of the laser, so that two paths of interference signals form a certain phase difference;
the double-cavity device comprises a displacement driver fixed on the base station, wherein the displacement driver drives the end face of the optical fiber to move vertical to the film surface; analyzing and calculating the amplitude of the vibration of the membrane surface by adopting a phase demodulation algorithm on an electric signal converted from the interference light beam; the two optical fibers are fixed on the displacement driver and are not fixed with the base station;
the piezoelectric ceramic is used as a displacement driver to drive the two optical fibers to vibrate at a certain frequency along the direction vertical to the membrane surface, the phase change of a modulation signal reached by the vibration amplitude of the two optical fibers is greater than pi, and the frequency of the two optical fibers is outside the vibration frequency band of the membrane surface to be detected; the laser is a narrow linewidth laser with single wavelength.
The double-cavity device consists of an optical fiber end face and a film face, double light beams emitted by the optical fiber end face irradiate on the same film face and are reflected back to the optical fiber end face along an original light path, and two FP cavities are arranged in the same double-cavity device;
the dislocation length of the end face of the optical fiber in the axial direction is matched with a specific wavelength, so that two paths of interference signals output by the double-cavity device have a certain phase difference, and the phase difference is not equal to pi or integral multiple thereof; the invention provides the structure of a double-cavity device for detecting membrane surface vibration and the application range of double-cavity phase difference; the cost of realizing the sensing device can be reduced, and the sensitivity and the stability of the sensing system are improved;
the embodiment also discloses a demodulation method of the double-cavity device for detecting the membrane surface vibration, wherein the change of the membrane surface vibration amplitude is analyzed and calculated by adopting an ellipse fitting algorithm based on an electric signal converted by the interference light beam, and the method comprises the following steps:
the output signals of the interferometers are as follows:
Figure BDA0003028925880000071
wherein A is1And A2Is a direct current component of an interference signal, B1And B2For the purpose of fringe contrast of the interference signal,
Figure BDA0003028925880000081
is the initial phase of the FP interferometer with a cavity length L1, beta is the phase difference of the two interferometers, thetatFor the phase quantity to be measured, StFor the axial displacement of the membrane surface in the FP chamber, MtFor vibration modulation applied in dual-cavity devices, n being the cavity medium light refractionRate, λ0Is the wavelength of the light source.
Rewriting equation (1) to the following equation
Figure BDA0003028925880000082
A general ellipse equation can be expressed as
I1 2+CI2I1+DI2 2+EI1+FI2+H＝0. (3)
Comparing equations (2) and (3), it is possible to obtain
Figure BDA0003028925880000083
The parameters A1, A2, B1, B2 and β in equation (1) can be obtained from equation (4)
Figure BDA0003028925880000084
A pair of phase information thetatCan express the orthogonal signal
Figure BDA0003028925880000091
By means of an arctan algorithm, θ can be obtainedtFiltering out the frequency signal M of the modulation signal by a filtertFurther, the displacement S of the film surface is calculated from equation (1)t(ii) a The invention provides the range of the frequency and the amplitude of the modulation signal; meanwhile, due to the application of the modulation signals, the application range of the phase demodulation method based on the ellipse fitting algorithm is expanded, so that the phase demodulation method can work in small-phase signal demodulation.
For the device and the demodulation algorithm, feasibility and effectiveness of modulation setting are verified through experiments. As shown in fig. 3-4, the device and the demodulation algorithm can be used for detecting the membrane surface vibration, and after modulation is added, the device and the demodulation algorithm obviously optimize the performance and the error of the membrane surface vibration detection.
The working principle of the invention is as follows:
a double-cavity apparatus and its demodulation method used for detecting the membrane face vibration, while working, the laser that the laser sends out is divided into two bunches of light through the fiber beam splitter, the light beam transmits to the double-cavity apparatus through the optical circulator, the light beam irradiates on membrane face and reflects back to the fiber end in the double-cavity apparatus, and interfere with reflecting light of the fiber end, the interference light transmits to the photodetector and turns into the electrical signal through the optical circulator; parallel light beams emitted by the end faces of the optical fibers in the double-cavity device structure irradiate on the same film surface, the end faces of the optical fibers are staggered in the axial direction, and the length of the dislocation is matched with the wavelength of a laser, so that two paths of interference signals output by the double-cavity device form a certain phase difference; the double-cavity device comprises a displacement driver fixed on the base station, wherein the displacement driver drives the end face of the optical fiber to move vertical to the film surface; analyzing and calculating the amplitude of the vibration of the membrane surface by adopting a phase demodulation algorithm on the electric signal converted by the interference light beam; the phase change of the modulation signal reached by the vibration amplitude is larger than pi, and the frequency of the modulation signal is out of the vibration frequency band of the detected membrane surface; the invention provides the structure of a double-cavity device for detecting membrane surface vibration and the application range of double-cavity phase difference; the cost for realizing the sensing device can be reduced, and the sensitivity and the stability of the sensing system are improved;
meanwhile, the change of the vibration amplitude of the membrane surface is analyzed and calculated by adopting an ellipse fitting algorithm based on an electric signal converted from the interference light beam, and the range of the frequency and the amplitude of a modulation signal is given; meanwhile, due to the application of the modulation signal, the application range of the phase demodulation method based on the ellipse fitting algorithm is expanded, so that the phase demodulation method can work in small-phase signal demodulation.
In the description herein, references to the description of "one embodiment," "an example," "a specific example" or the like are intended to mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
The foregoing is merely illustrative and explanatory of the present invention and various modifications, additions or substitutions may be made to the specific embodiments described by those skilled in the art without departing from the scope of the invention as defined in the accompanying claims.

Claims (1)

1. A double-cavity device for detecting membrane surface vibration is characterized by comprising a laser, an optical fiber beam splitter, an optical circulator, an optical fiber, a double-cavity device and a photoelectric detector; the laser is a narrow linewidth laser with single wavelength;
the double-cavity device consists of an optical fiber end face and a film face, double light beams emitted by the optical fiber end face irradiate on the same film face and are reflected back to the optical fiber end face along an original light path, and two FP cavities are arranged in the same double-cavity device;
the dislocation length of the end face of the optical fiber in the axial direction is matched with a specific wavelength, so that two paths of interference signals output by the double-cavity device have a certain phase difference, and the phase difference is not equal to pi or integral multiple thereof;
the working method of the double-cavity device comprises the following steps:
laser emitted by the laser is divided into two beams of light by the optical fiber beam splitter, the light beams are transmitted to the double-cavity device by the optical circulator, the light beams in the double-cavity device irradiate on the film surface and are reflected to the end surface of the optical fiber, the light beams interfere with the reflected light of the end surface of the optical fiber, and the interference light is transmitted to the photoelectric detector by the optical circulator and is converted into an electric signal; parallel light beams emitted by the end faces of the optical fibers in the double-cavity device structure irradiate on the same film surface, the end faces of the optical fibers are staggered in the axial direction, and the length of the dislocation is matched with the wavelength of a laser, so that two paths of interference signals output by the double-cavity device form a certain phase difference;
the double-cavity device is internally provided with a displacement driver fixed on the base station, and the displacement driver drives the end face of the optical fiber to move vertical to the film surface; the displacement driver drives the two optical fibers to vibrate at a certain frequency along the direction vertical to the film surface, the phase change of a modulation signal reached by the vibration amplitude of the two optical fibers is larger than pi, and the frequency of the two optical fibers is out of the vibration frequency band of the detected film surface; the two optical fibers are fixed on the displacement driver and are not fixed with the base station;
analyzing and calculating the amplitude of the vibration of the membrane surface by adopting a phase demodulation algorithm on an electric signal converted from the interference light beam; the phase demodulation algorithm specifically comprises the following steps:
the output signals of the interferometers are as follows:
Figure FDA0003682888740000021
wherein A is1And A2Is a direct current component of an interference signal, B1And B2For the purpose of fringe contrast of the interference signal,
Figure FDA0003682888740000022
is the initial phase of the FP interferometer with a cavity length L1, beta is the phase difference of the two interferometers, thetatThe phase quantity to be measured; stFor axial displacement of the membrane surface in the FP chamber, MtFor vibration modulation applied by displacement driver in dual-cavity device, n is optical refractive index of cavity medium, lambda0Is the wavelength of the light source;
rewriting equation (1) to the following equation
Figure FDA0003682888740000023
The ellipse equation is expressed as
I1 2+CI2I1+DI2 2+EI1+FI2+H＝0. (3)
Comparing equations (2) and (3), we obtain
Figure FDA0003682888740000024
Wherein the parameters A1, A2, B1, B2 and beta in the equation (1) are calculated from the equation (4)
Figure FDA0003682888740000031
A pair of phase information thetatIs expressed as
Figure FDA0003682888740000032
Obtaining theta through an arc tangent algorithmtFiltering out the frequency signal M of the modulation signal by a filtertFurther, the displacement S of the film surface is calculated from equation (1)t(ii) a I.e. the amplitude of the membrane surface vibration.
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