CN113091882B - A dual-chamber device for detecting membrane surface vibration and its demodulation method - Google Patents

Abstract

The invention discloses a dual-cavity device for detecting membrane surface vibration and a demodulation method thereof, and relates to the technical field of optical sensing information demodulation; Photodetector: The laser emitted by the laser is divided into two beams of light through the fiber beam splitter, and the beam is transmitted to the dual-cavity device through the optical circulator. The reflected light interferes, and the interference light is transmitted to the photodetector through the optical circulator and converted into an electrical signal; the structure of the dual-cavity device makes the interference signal output by the dual-cavity in a certain phase difference state, and the dual-cavity device contains a displacement drive It promotes the movement of the fiber end face perpendicular to the membrane surface; by using ellipse fitting algorithm to demodulate the phase of the electrical signal converted by the interference beam, the amplitude change of the membrane vibration is analyzed and calculated; the sensitivity and stability of the sensing system are improved.

Description

A dual-chamber device for detecting membrane surface vibration and its demodulation method

technical field

The invention relates to the technical field of optical sensing information demodulation, in particular to a dual-cavity device for detecting vibration of a membrane surface and a demodulation method thereof.

Background technique

The development of society requires multi-level and high-depth acquisition of external information. Various sensors are the main way for us to acquire external information. Optical sensing, especially interferometric optical sensing, has attracted much attention due to its high sensitivity, anti-electromagnetic interference and wide applicability. In interferometric optical sensing, the difference of the interference arms often brings polarization fading. The FP cavity interferometer has the advantages of anti-path interference and anti-polarization fading due to its co-channel transmission and the existence of isotropic medium in the cavity. For the phase fading problem of interferometers, scholars have developed various phase demodulation techniques, such as phase generation carrier method, heterodyne method, 3*3 coupler demodulation method, etc. In view of the short cavity length of the FP cavity interferometer, two-wavelength and three-wavelength phase demodulation technologies have been successively studied.

The current dual-wavelength and three-wavelength FP cavity interferometer phase demodulation technology requires multiple wavelengths of laser light, the required laser cost is high, and the laser center frequency and power stability requirements are more; due to the cavity length of the FP interferometer If there is a big change under the influence of the environment or the large dynamic detection physical quantity, the phase demodulation effect will be degraded, distorted and other unstable phenomena.

The double-cavity device membrane surface vibration detection method based on the ellipse fitting algorithm uses one wavelength and constructs the signal phase difference through the double-cavity structure, which well satisfies the elimination of the direct current of the signal and the normalization of the alternating current by the related unrelated phase demodulation technology. , and the requirement that the phase difference must be in quadrature, has obvious advantages. However, the ellipse fitting algorithm requires that the measured phase of the two signals must be greater than π, otherwise the fitted data will be inaccurate, which limits the use of this technique for small-phase signal demodulation.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a dual-cavity device for detecting the vibration of the membrane surface and a demodulation method thereof. The invention provides the structure of the dual-chamber device for detecting the vibration of the membrane surface and the use range of the phase difference of the dual-chamber; it can reduce the The realization cost of the sensing device improves the sensitivity and stability of the sensing system; at the same time, the frequency and amplitude range of the modulated signal is given; through the application of the modulated signal, the phase demodulation method based on the ellipse fitting algorithm is expanded range of use, making it possible to demodulate small-phase signals.

The object of the present invention can be realized through the following technical solutions:

A dual-cavity device for detecting membrane surface vibration, characterized in that it includes a laser, an optical fiber beam splitter, an optical circulator, an optical fiber, a dual-cavity device and a photodetector;

The working method of the dual-chamber device is as follows:

The laser emitted by the laser is divided into two beams by the fiber beam splitter, and the beam is transmitted to the dual-cavity device through the optical circulator. interference, the interference light is transmitted to the photodetector through the optical circulator and converted into an electrical signal; the parallel light beam emitted by the fiber end face in the double cavity device structure is irradiated on the same film surface, and the fiber end face is dislocated in the axial direction. The length matches the wavelength of the laser, so that the two interference signals output by the dual-cavity device have a certain phase difference;

The dual-cavity device contains a displacement driver fixed on the base, and the displacement driver causes the fiber end face to move perpendicular to the membrane surface; the phase demodulation algorithm is applied to the electrical signal converted by the interference beam, and the amplitude of the membrane vibration is analyzed and calculated. value.

Further, the laser is a single-wavelength narrow linewidth laser.

Further, the dual-cavity device is composed of a fiber end face and a membrane surface. The double beams emitted by the fiber end face are irradiated on the same membrane surface and reflected back to the fiber end face along the original optical path. There are two FP cavities in the same dual-cavity device.

Further, the axial dislocation length of the fiber end face is matched with a specific wavelength, so that the two channels of interference signals output by the dual-cavity device have a certain phase difference, and the phase difference is not equal to π or its integer multiples.

Further, the displacement driver drives the two optical fibers to vibrate at a certain frequency along the direction perpendicular to the membrane surface, and the phase change of the modulation signal reached by its vibration amplitude is greater than π, and its frequency is outside the vibration frequency band of the detected membrane surface;

The invention provides a dual-chamber device for detecting membrane surface vibration, and provides the structure of the dual-chamber device for detecting membrane surface vibration and the application range of the dual-chamber phase difference; the realization cost of the sensing device can be reduced, and the transmission rate can be improved. The sensitivity and stability of the sensor system;

Further, a method for demodulating a dual-chamber device for detecting vibration of the membrane surface, comprising the steps of:

The output signal of each interferometer is:

是腔长为L1的FP干涉仪的初始相位，β是两个干涉仪的相位差，θ_t为待测相位量；S_t为膜面在FP腔轴向上的位移，M_t为双腔装置中位移驱动器施加的振动调制，n为腔介质光折射率，λ₀为光源的波长；Among them, A ₁ and A ₂ are the DC components of the interference signal, B ₁ and B ₂ are the fringe contrasts of the interference signal,

is the initial phase of the FP interferometer with cavity length L1, β is the phase difference between the two interferometers, θ _t is the phase to be measured; S _t is the displacement of the membrane surface in the axial direction of the FP cavity, and M _t is the double cavity The vibration modulation applied by the displacement driver in the device, n is the refractive index of the cavity medium, and λ ₀ is the wavelength of the light source;

Rewrite equation (1) into the following equation

The ellipse equation can be expressed as

I ₁ ² +CI ₂ I ₁ +DI ₂ ² +EI ₁ +FI ₂ +H=0. (3)

Comparing equations (2) and (3), we can get

The parameters A1, A2, B1, B2 and β in equation (1) can be calculated in combination with equation (4)

A pair of quadrature signals containing the phase information to be measured θ _t can be expressed as

Through the arctangent algorithm, θ _t can be obtained, the frequency signal M _t of the modulation signal is filtered out by a filter, and then the displacement S _t of the membrane surface is calculated by equation (1). The invention provides the range of the frequency and amplitude of the modulated signal; at the same time, the application of the modulated signal expands the use range of the phase demodulation method based on the ellipse fitting algorithm, so that it can work in small-phase signal demodulation.

Beneficial effects of the present invention:

1. In the present invention, the laser emitted by the laser is divided into two beams of light through the fiber beam splitter, and the beam is transmitted to the dual-cavity device through the optical circulator. The reflected light from the end face interferes, and the interference light is transmitted to the photodetector through the optical circulator and converted into an electrical signal; the parallel beam emitted by the end face of the fiber in the dual-cavity device structure is irradiated on the same film surface, and the end face of the fiber is in the axial direction. There is dislocation, and the dislocation length matches the wavelength of the laser, so that the two-way interference signals output by the dual-cavity device have a certain phase difference; the dual-cavity device contains a displacement driver fixed on the base, and the displacement driver promotes the end face of the fiber. It moves perpendicular to the membrane surface; the phase demodulation algorithm is used for the electrical signal converted by the interference beam to analyze and calculate the amplitude of the membrane surface vibration; the invention provides the structure of the double-cavity device for detecting the membrane surface vibration and the phase difference of the double-cavity It can reduce the cost of sensing device implementation and improve the sensitivity and stability of the sensing system;

2. The present invention also provides a demodulation method for a dual-cavity device for detecting the vibration of the membrane surface. By using an ellipse-based fitting algorithm on the electrical signal converted by the interference beam, the change of the vibration amplitude of the membrane surface is analyzed and calculated, The invention provides the frequency and amplitude range of the modulated signal; at the same time, the application of the modulated signal expands the use range of the phase demodulation method based on the ellipse fitting algorithm, so that it can work in small-phase signal demodulation.

Description of drawings

In order to illustrate the embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the accompanying drawings that are used in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only These are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained from these drawings without creative efforts.

FIG. 1 is a composition diagram of a dual-chamber device and a demodulation system for detecting membrane surface vibration according to the present invention.

FIG. 2 is a schematic structural diagram of the dual-chamber device in the present invention.

FIG. 3 is a comparison diagram of the demodulation data of the membrane surface vibration under the present invention with and without modulation.

FIG. 4 is a comparison diagram of the demodulation error of the membrane surface vibration with and without modulation according to the present invention.

Detailed ways

The technical solutions in the embodiments of the present invention will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Referring to FIGS. 1 to 4 , this embodiment discloses a dual-cavity device for detecting membrane surface vibration, including a laser, a fiber beam splitter, an optical circulator, several optical fibers, a dual-cavity device, and a photodetector;

The laser emitted by the laser is divided into two beams by the fiber beam splitter, and the beam is transmitted to the dual-cavity device through the optical circulator. Interference, the interference light is transmitted to the photodetector through the optical circulator and converted into an electrical signal;

The parallel beam emitted by the fiber end face in the dual-cavity device is irradiated on the same film surface, and the fiber end face has a certain length of dislocation in the fiber axis. This dislocation length matches the wavelength of the laser, so that the two interference signals form a certain phase difference;

The dual-cavity device contains a displacement driver fixed on the base, and the displacement driver causes the fiber end face to move perpendicular to the membrane surface; the phase demodulation algorithm is applied to the electrical signal converted by the interference beam, and the amplitude of the membrane vibration is analyzed and calculated. value; two optical fibers are fixed on the displacement driver, and two optical fibers are not fixed with the base;

Use piezoelectric ceramics as the displacement driver to drive the two optical fibers to vibrate at a certain frequency along the direction perpendicular to the membrane surface. The phase change of the modulation signal achieved by the vibration amplitude should be greater than π, and its frequency should be outside the vibration frequency band of the detected membrane surface. The laser is a single-wavelength narrow linewidth laser.

The dual-cavity device is composed of an optical fiber end face and a membrane surface, the double beams emitted by the optical fiber end face are irradiated on the same membrane surface and reflected back to the optical fiber end face along the original optical path, and there are two FP cavities in the same dual-cavity device;

The dislocation length of the fiber end face in the axial direction is matched with a specific wavelength, so that the two-way interference signals output by the dual-cavity device have a certain phase difference, and the phase difference is not equal to π or its integer multiples; the invention provides a detection film. The composition of the double-cavity device with surface vibration and the use range of the double-cavity phase difference can reduce the cost of the sensing device and improve the sensitivity and stability of the sensing system;

This embodiment also discloses a demodulation method for the above-mentioned dual-cavity device for detecting the vibration of the membrane surface. By using an ellipse fitting algorithm based on the electrical signal converted from the interference beam, the change of the vibration amplitude of the membrane surface is analyzed and calculated, including the following: step:

The output signal of each interferometer is:

是腔长为L1的FP干涉仪的初始相位，β是两个干涉仪的相位差，θ_t为待测相位量,S_t为膜面在FP腔轴向上的位移，M_t为双腔装置中施加的振动调制，n为腔介质光折射率，λ₀为光源的波长。Among them, A ₁ and A ₂ are the DC components of the interference signal, B ₁ and B ₂ are the fringe contrasts of the interference signal,

is the initial phase of the FP interferometer with the cavity length L1, β is the phase difference between the two interferometers, θ _t is the phase to be measured, S _t is the displacement of the membrane surface in the axial direction of the FP cavity, and M _t is the double cavity The vibration modulation applied in the device, n is the light refractive index of the cavity medium, and λ ₀ is the wavelength of the light source.

Rewrite equation (1) into the following equation

The general ellipse equation can be expressed as

I ₁ ² +CI ₂ I ₁ +DI ₂ ² +EI ₁ +FI ₂ +H=0. (3)

Comparing equations (2) and (3), we can get

The parameters A1, A2, B1, B2 and β in equation (1) can be obtained from equation (4)

A pair of quadrature signals containing the phase information to be measured θ _t can be expressed

Through the arctangent algorithm, θ _t can be obtained, the frequency signal M _t where the modulation signal is located is filtered out by the filter, and then the displacement S _t of the membrane surface is calculated by equation (1); the present invention provides the frequency and amplitude of the modulation signal. At the same time, the application of the modulation signal expands the use range of the phase demodulation method based on the ellipse fitting algorithm, so that it can work in the demodulation of small phase signals.

For the above device and demodulation algorithm, the feasibility and the effectiveness of the modulation setting are verified by experiments. As shown in Figure 3-4, the above device and demodulation algorithm can be used for the detection of membrane surface vibration, and after adding modulation, the device and demodulation algorithm can significantly optimize the performance and error of membrane surface vibration detection.

The working principle of the present invention is:

A dual-cavity device for detecting membrane surface vibration and a demodulation method thereof. During operation, laser light emitted by a laser is divided into two beams of light through an optical fiber beam splitter, and the beams are transmitted to the dual-cavity device through an optical circulator. The light beam in the device is irradiated on the film surface and reflected back to the end face of the fiber, and interferes with the reflected light from the end face of the fiber. The interference light is transmitted to the photodetector through the optical circulator and converted into an electrical signal; the end face of the fiber in the double-cavity device structure emits The parallel beam of the laser is irradiated on the same film surface, and the fiber end face is dislocated in the axial direction. The dislocation length matches the wavelength of the laser, so that the two-way interference signals output by the dual-cavity device have a certain phase difference; the dual-cavity device contains A displacement driver fixed on the base, the displacement driver causes the fiber end face to move perpendicular to the membrane surface; the phase demodulation algorithm is applied to the electrical signal converted by the interference beam, and the amplitude of the membrane surface vibration is analyzed and calculated; its vibration amplitude The phase change of the modulation signal achieved by the value is greater than π, and its frequency is outside the vibration frequency band of the detected membrane surface; the invention provides the structure of the double-cavity device for detecting the vibration of the membrane surface and the use range of the double-cavity phase difference; it can reduce the transmission frequency. The cost of sensing device implementation is improved, and the sensitivity and stability of the sensing system are improved;

At the same time, by using an ellipse fitting algorithm based on the electrical signal converted by the interference beam, the change of the vibration amplitude of the membrane surface is analyzed and calculated, and the invention provides the frequency and amplitude range of the modulation signal; The application range of the phase demodulation method based on the ellipse fitting algorithm is introduced, so that it can work in the demodulation of small phase signals.

In the description of this specification, description with reference to the terms "one embodiment," "example," "specific example," etc. means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one aspect of the present invention. in one embodiment or example. In this specification, schematic representations of the above terms 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 above content is only an example and description of the structure of the present invention, and those skilled in the art can make various modifications or supplements to the specific embodiments described or replace them in similar ways, as long as they do not deviate from the structure of the invention or Anything beyond the scope defined by the claims shall belong to the protection scope of the present invention.

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:

wherein A is₁And A₂Is a direct current component of an interference signal, B₁And B₂For the purpose of fringe contrast of the interference signal,

is the initial phase of the FP interferometer with a cavity length L1, beta is the phase difference of the two interferometers, theta_tThe phase quantity to be measured; s_tFor axial displacement of the membrane surface in the FP chamber, M_tFor 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

The ellipse equation is expressed as

I₁ ²+CI₂I₁+DI₂ ²+EI₁+FI₂+H＝0. (3)

Comparing equations (2) and (3), we obtain

Wherein the parameters A1, A2, B1, B2 and beta in the equation (1) are calculated from the equation (4)

A pair of phase information theta_tIs expressed as

Obtaining theta through an arc tangent algorithm_tFiltering out the frequency signal M of the modulation signal by a filter_tFurther, 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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