CN112050976A - Frequency modulation continuous wave laser interference pressure sensor and detection method thereof - Google Patents

Abstract

The invention relates to a frequency-modulated continuous wave laser interference pressure sensor and a detection method thereof, which overcomes the problem that high-precision pressure measurement cannot be performed in the prior art. The invention includes a semiconductor laser, the semiconductor laser is connected with the first port of the fiber circulator through the single-mode fiber, the second port of the fiber circulator is connected with the fiber collimator through the single-mode fiber, and the third port of the fiber circulator is connected with the photodetector. A diaphragm-type faeber cavity mechanism is arranged behind the optical fiber collimator. The diaphragm-type faeber cavity mechanism includes a partial reflection mirror and an elastic diaphragm, and the partial reflection mirror is pasted on the rear side of the optical fiber collimator. The elastic diaphragm is arranged on the rear side of the partial reflector, and the elastic diaphragm is pasted on the end face of the air-filled cavity mechanism. The inflatable cavity mechanism includes a stainless steel tube, and the hollow part of the stainless steel tube is an inflatable cavity. The fiber collimator is fixed to the left port of the stainless steel tube. The elastic diaphragm is fixed to the right port of the stainless steel tube.

Description

Frequency-modulated continuous wave laser interferometric pressure sensor and detection method thereof

Technical field:

The invention belongs to the technical field of pressure sensing, and relates to a frequency-modulated continuous wave laser interference high-precision pressure measuring instrument, in particular to a frequency-modulated continuous wave laser interference pressure sensor and a detection method thereof.

Background technique:

Pressure sensing has a very important measurement and testing technology in scientific research, military, medicine and other fields. Optical fiber pressure sensors have many advantages such as high precision, fast response speed, high temperature resistance, flameproof, explosion-proof, and electromagnetic interference resistance, so they have received extensive attention in various fields. At present, the more common fiber optic pressure sensors mainly include wavelength-modulated fiber Bragg grating pressure sensors and phase-modulated fiber optic Fibre Cavity pressure sensors. The fiber Bragg grating pressure sensor has a simple structure and can be flexibly multiplexed, but it is easily disturbed by the ambient temperature, resulting in inaccurate measurement results. The signal arm and the reference arm of the fiber optic cavity pressure sensor have the same optical path, so it has strong anti-electromagnetic interference ability, simple structure, small sensor probe, and unparalleled advantages in transmission distance. In terms of detection technology, the current fiber optic Fibre cavity pressure sensor mainly adopts white light interferometry technology, that is, the pressure measurement is realized according to the spectral information obtained by reflection or transmission. This interferometric pressure measurement technology is difficult and has low resolution. Spectral analyzers with a high degree of precision have greatly increased the cost of measurement.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a frequency modulated continuous wave laser interference pressure sensor and a detection method thereof, which overcome the problem of inability to perform high-precision pressure measurement in the prior art, have a simple structure, and greatly improve the sensitivity of pressure measurement , accuracy and stability, reducing measurement costs.

To achieve the above object, the technical scheme adopted in the present invention is:

A frequency-modulated continuous wave laser interference pressure sensor, which is characterized in that it includes a semiconductor laser, the semiconductor laser is connected to a first port of a fiber circulator, the second port of the fiber circulator is connected to a fiber collimator through a single-mode fiber, and the third port of the fiber circulator is connected to a fiber collimator. It is connected with the photodetector, and a diaphragm-type Fibonacci cavity mechanism is arranged behind the optical fiber collimator. The optical fiber circulator, the optical fiber collimator, the photodetector and the diaphragm-type Fibonacci cavity mechanism constitute an optical fiber pressure sensing system.

The diaphragm-type faber cavity mechanism includes a partial reflecting mirror and an elastic membrane, the elastic membrane is arranged on the rear side of the partial reflecting mirror, and the elastic membrane is pasted on the end face of the air-filled cavity mechanism.

The inflatable cavity mechanism includes a stainless steel tube, and the hollow part of the stainless steel tube is an inflatable cavity.

Part of the mirror is attached to the back of the fiber collimator.

The fiber collimator is fixed to the left port of the stainless steel tube.

The elastic diaphragm is fixed to the right port of the stainless steel tube.

The elastic diaphragm is made of SUS631 stainless steel with high elastic properties.

The semiconductor lasers are respectively connected to two or multiple optical fiber pressure sensing systems through optical fiber couplers.

A detection method using the frequency-modulated continuous wave laser interference pressure sensor of claim 1, wherein the linear frequency-modulated laser emitted by the semiconductor laser enters the fiber circulator and the fiber collimator sequentially through the single-mode fiber, and is then collimated by the fiber. The collimation of the collimator is that the space beam is coupled into the diaphragm-type Fibonacci cavity. The space beam is reflected on the surface of the partial mirror and the surface of the elastic diaphragm and superimposed to generate a dynamic beat frequency signal, which is collimated by the optical fiber. The optical fiber circulator is coupled back to the single-mode fiber again and enters the fiber circulator, and it is converted into an electrical signal from the port 3 of the fiber circulator and reaches the photodetector. By detecting the initial phase change of the beat frequency signal, the change amount of the optical path difference of the two reflected beams can be obtained, that is, It can detect the change of the cavity length of the Fibonacci cavity, and then realize the high-precision pressure measurement according to the pressure deformation principle of the diaphragm;

Among them, the relationship between the variation δφ _b0 of the initial phase of the beat signal and the pressure variation ΔP is:

In the formula, h represents the thickness of the diaphragm, γ is the radius of the Faber cavity, that is, the effective pressure-sensitive radius of the diaphragm, μ is the Poisson’s ratio of the diaphragm material, E is the elastic modulus of the diaphragm material, and n is the air refraction rate (n=1), λ ₀ is the wavelength of the light wave in vacuum.

Compared with the prior art, the present invention has the following advantages and effects:

1. The present invention is a new type of pressure measuring instrument and method based on frequency modulation continuous wave interference technology, which greatly improves the sensitivity, precision and stability of pressure measurement, and currently belongs to high-precision measurement technology in the field of pressure detection.

2. The frequency modulation continuous wave interference pressure measurement system of the present invention has a simple structure, is easy to manufacture, and has a compact structure and good performance.

3. The sensitivity and linearity of the frequency-modulated continuous wave interference pressure measurement system of the present invention will not change with the pressure range.

Description of drawings

Fig. 1 is the structural representation of the present invention;

Fig. 2 is the structural schematic diagram of the pressure measurement sensing part in the present invention;

Figure 3 is a graph showing the relationship between the initial phase offset of the beat signal (also the cavity length variation) and the pressure to be measured during the pressure measurement process;

FIG. 4 is a schematic diagram of the dual multiplex pressure measurement system of the present invention.

In the figure, 1-semiconductor laser, 2-fiber circulator, 3-fiber collimator, 4-partial mirror, 5-elastic diaphragm, 6-photodetector, 7-stainless steel tube, 8-gas-filled cavity, 9- - Fiber coupler.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

1 and 2, the present invention is a frequency-modulated continuous wave laser interferometric pressure sensor, comprising a semiconductor laser 1, the semiconductor laser 1 is connected to an optical fiber pressure sensing system through a single-mode optical fiber, and the optical fiber pressure sensing system includes an optical fiber loop 2, fiber collimator 3 and photodetector 6. The semiconductor laser 1 is connected to the first port of the fiber circulator 2, the second port of the fiber circulator 2 is connected to the fiber collimator 3 through a single-mode fiber, and the third port of the fiber circulator 2 is connected to the photodetector 6. The optical fiber collimator 3 is provided with a diaphragm-type Faber cavity mechanism. The diaphragm-type Faber chamber mechanism includes a partial mirror 4 and an elastic diaphragm 5 (such as a high-elastic diaphragm made of SUS631 stainless steel), and the partial mirror 4 is pasted on the On the rear side of the optical fiber collimator 3, an elastic diaphragm 5 is arranged on the rear side of the partial reflecting mirror 4, and the elastic diaphragm 5 is pasted on the end face of the air-filled cavity mechanism. The inflatable cavity mechanism includes a 316 stainless steel tube 7 , and the hollow part of the 316 stainless steel tube 7 is an inflatable cavity 8 . The elastic diaphragm 5 is fixed to the right port of the 316 stainless steel tube 7 , and the optical fiber collimator 3 is fixed to the left port of the stainless steel tube 7 .

The detection method of the frequency-modulated continuous wave laser interference pressure sensor of the present invention includes the following steps: the linear frequency-modulated laser emitted by the semiconductor laser enters the fiber circulator and the fiber collimator in turn through the single-mode fiber, and then is collimated by the fiber collimator into a space beam coupling Entering the diaphragm-type faeber cavity mechanism, the space beam is reflected on the surface of the partial mirror and the elastic diaphragm and superimposed to generate a dynamic beat frequency signal. The beat frequency signal is coupled back to the single-mode fiber by the fiber collimator again. The optical fiber circulator emits from the third port of the optical fiber circulator and reaches the photodetector and converts it into an electrical signal. By detecting the change in the initial phase of the beat frequency signal, the change in the optical path difference between the two reflected beams can be obtained, and the cavity length of the Fibonacci cavity can be detected. The amount of change, and then according to the principle of diaphragm pressure deformation, to achieve high-precision pressure measurement;

Among them, the relationship between the variation δφ _b0 of the initial phase of the beat signal and the pressure variation ΔP is:

In the formula, h represents the thickness of the diaphragm, γ is the radius of the Faber cavity, that is, the effective pressure-sensitive radius of the diaphragm, μ is the Poisson’s ratio of the diaphragm material, E is the elastic modulus of the diaphragm material, and n is the air refraction rate (n=1), λ ₀ is the wavelength of the light wave in vacuum.

Example 1:

As shown in Figures 1 and 2, the first embodiment is a frequency-modulated continuous wave laser interference optical fiber pressure sensor, and the elastic diaphragm 5 of the diaphragm-type faeper cavity structure is made of SUS631 stainless steel material with high elastic properties. The optical fiber collimator 3 is fixed to the left port of the 316 stainless steel tube 7 by AB glue, and the elastic diaphragm 5 (such as a high elastic diaphragm made of SUS631 stainless steel) is pasted on the right end face of the air-filled cavity structure, and then fixed to the 316 stainless steel tube 7 right port. The single-mode semiconductor laser 1 is connected to one port of the optical fiber circulator 2 through a single-mode optical fiber, which is connected by welding or flange connection. The adjacent outgoing ports of the fiber circulator 2 are connected to the pigtail of the fiber collimator 3 through a single-mode fiber, and the third port of the fiber circulator 2 is connected to the pigtail of the photodetector 6 through a single-mode fiber. The partial reflection mirror 4 is arranged at the rear end of the optical fiber collimator 3, and the partial reflection mirror 4 is placed behind the optical fiber collimator 3 as an independent device. The partial reflection mirror 4 can also be attached to the optical fiber collimator 3 by gluing or mechanical fixing. The function of the partial reflection mirror 4 is realized by plating a partially reflecting and partially transmitting optical film material on the exiting end face of the optical fiber collimator 3 .

The detection method of the frequency modulated continuous wave laser interferometric pressure sensor includes the following steps: using a semiconductor laser 1 to transmit a frequency linearly modulated frequency modulated continuous wave laser by means of current modulation, the laser is coupled to an input port of a fiber circulator 2 through an optical fiber, from The adjacent output ports of the fiber circulator 2 are output, and the output light is incident to the fiber collimator 3 through the single-mode fiber, and the fiber collimator 3 passes through the partial reflector 4, and part of the light is reflected as reference light, and part of the light is reflected. After projection, it is irradiated to an elastic diaphragm (such as a high-elasticity diaphragm made of SUS631 stainless steel) 5 and reflected as signal light. An interference beat frequency signal is formed. The beat frequency signal is coupled back to the optical fiber optical path by the fiber collimator 3, and is incident from the original exit port of the fiber circulator 2, exits from the third port of the fiber circulator 2, and is received and converted by the photodetector 6. for electrical signals.

Assuming that the average light intensity of the light reflected by the partial mirror is I ₁ , and the average light intensity of the light reflected by the elastic diaphragm (such as a high-elastic film made of SUS631 stainless steel) is I ₂ , then the light intensity of the beat frequency signal

Δν为光学频率调制宽度，ν_m为调制信号的频率，c为光速，t为时间，l₀为光波在真空中的波长，ν_b为拍频信号频率，φ_b0为拍频信号初相位，OPD为两反射光之间的光程差。显然where I ₀ =I ₁ +I ₂ , V is the contrast of the beat signal, and

Δν is the optical frequency modulation width, ν _m is the frequency of the modulating signal, c is the speed of light, t is the time, l ₀ is the wavelength of the light wave in vacuum, ν _b is the frequency of the beat signal, φ _b0 is the initial phase of the beat signal, OPD is the optical path difference between the two reflected lights. obviously

For this frequency-modulated continuous wave laser interference pressure sensor, since there is air between the two mirrors, and the refractive index of air is approximately 1, then the optical path difference OPD=2d, where d is the distance between the partial mirror and the SUS631 stainless steel diaphragm. The initial phase of the beat signal can be written as

n is the refractive index of air (n=1), and d is the distance between the reflecting surface of the partial mirror 4 and the surface of the SUS631 stainless steel diaphragm. When the center position of the SUS631 stainless steel diaphragm is deformed to δd, the offset corresponding to the initial phase of the beat signal φ _b0 is

The FM continuous wave beat frequency signal is converted _into an electrical signal by the photodetector, and processed by the signal processing circuit for phase discrimination. The relative change δd of the distance between the two mirrors, according to the diaphragm pressure principle, the corresponding relationship between the change ΔP of the pressure F (it may also be the pressure P) uniformly acting on the diaphragm and the change Δl of the cavity length of the FP cavity is:

In the formula, h represents the thickness of the diaphragm, γ is the radius of the Faber cavity, that is, the effective pressure-sensitive radius of the diaphragm, μ is the Poisson’s ratio of the diaphragm material, and E is the elastic modulus of the diaphragm material. The relationship between the variation δφ _b0 of the initial phase of the available beat signal and the pressure variation ΔP can be written as:

即可计算出珐珀腔腔长随压力的变化量，也就可以进一步计算出压强的变化量(压力变化量)，如图3所示。The beat frequency signal is incident from port 2 of the optical fiber circulator, and exits from port 3 of the optical fiber circulator, reaches the photodetector 6, and is converted into an electrical signal. By measuring the change of the initial phase

The variation of the cavity length of the Fibonacci cavity with the pressure can be calculated, and the variation of the pressure (pressure variation) can be further calculated, as shown in Figure 3.

In this embodiment, the elastic film 5 for providing signal light can be a partial reflection film or a total reflection film, a metal elastic film, or a silicon material or other elastic film. The center of the elastic diaphragm deforms with the external pressure. Both the partial reflector 4 and the metal reflector must be strictly perpendicular to the direction of the laser beam emitted by the fiber collimator 3 to ensure that the reflected reference light and signal light can pass through the fiber with maximum power. The collimator 3 is coupled back to the original optical fiber path.

Example 2:

This embodiment is a two-channel frequency-modulated continuous wave laser interference fiber pressure sensor. Referring to Figure 4, the single-mode frequency-modulated continuous-wave laser 1 is connected to a two-channel fiber pressure sensing system. Specifically, the single-mode frequency-modulated continuous-wave laser passes through The 1x2 fiber optic couplers 9 are respectively connected to two fiber optic pressure sensing systems. The laser power output by the single-mode frequency-modulated continuous wave laser 1 is evenly distributed by the 1x 2 fiber coupler 9 to the two channels of frequency-modulated continuous wave laser interference fiber pressure sensors. The two channels of fiber pressure sensing systems measure the target pressure independently, and can At the same time, the pressure measurement of two independent targets can be realized, and the pressure measurement of the same target at different positions can also be realized.

Those in the art can further expand the number of optical fiber pressure sensing systems on the basis of the above two forms, such as setting up three-way and multi-way pressure sensing systems, and the expansion methods of three-way and multi-way pressure sensing systems are related to The expansion method of the two-channel fiber optic pressure sensing system is similar, except that the 1x 2 fiber optic coupler 2 is replaced with a 1x 3 or 1x N fiber optic coupler, and each channel is the same as the single-channel FM continuous wave laser fiber optic pressure sensor.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Any equivalent structural changes made by using the contents of the description and drawings of the present invention shall be included in the patent protection of the invention. within the range.

Claims (9)

1. A frequency-modulated continuous wave laser interference pressure sensor, characterized in that: comprising a semiconductor laser (1), the semiconductor laser (1) is connected with an optical fiber circulator (2) port one, and the optical fiber circulator (2) port two passes through a single mode The optical fiber is connected to the optical fiber collimator (3), and the third port of the optical fiber circulator (2) is connected to the photodetector (6). 2), an optical fiber collimator (3), a photodetector (6) and a diaphragm-type Fibonacci cavity mechanism constitute an optical fiber pressure sensing system. 2. The frequency-modulated continuous wave laser interference pressure sensor according to claim 1, characterized in that: the diaphragm-type Faber cavity mechanism comprises a partial reflection mirror (4) and an elastic diaphragm (5), and the elastic diaphragm (5) is provided with On the rear side of the partial reflecting mirror (4), an elastic diaphragm (5) is pasted on the end face of the air-filled cavity mechanism. 3 . The frequency modulated continuous wave laser interference pressure sensor according to claim 2 , wherein the inflatable cavity mechanism comprises a stainless steel tube ( 7 ), and the hollow part of the stainless steel tube ( 7 ) is an inflatable cavity ( 8 ). 4 . 4. The frequency modulated continuous wave laser interference pressure sensor according to claim 3, characterized in that: the partial reflection mirror (4) is pasted on the rear side of the optical fiber collimator (3). 5 . The frequency modulated continuous wave laser interference pressure sensor according to claim 4 , wherein the optical fiber collimator ( 3 ) is fixed to the left port of the stainless steel tube ( 7 ). 6 . 6 . The frequency modulated continuous wave laser interference pressure sensor according to claim 5 , wherein the elastic diaphragm ( 5 ) is fixed to the right port of the stainless steel tube ( 7 ). 7 . 7 . The frequency modulated continuous wave laser interference pressure sensor according to claim 6 , wherein the elastic diaphragm ( 5 ) is made of SUS631 stainless steel material with high elastic properties. 8 . 8 . The frequency modulated continuous wave laser interference pressure sensor according to claim 7 , wherein the semiconductor laser ( 1 ) is respectively connected to two or multiple optical fiber pressure sensing systems through an optical fiber coupler ( 9 ). 9 . 9. A detection method using the frequency-modulated continuous wave laser interference pressure sensor according to claim 1 is characterized in that: the linear frequency-modulated laser emitted by the semiconductor laser enters the fiber circulator and the fiber collimator successively through the single-mode fiber, and is then The optical fiber collimator is collimated by coupling the space beam into the diaphragm-type Fibonacci cavity mechanism. The space beam is reflected on the surface of the partial mirror and the surface of the elastic diaphragm and superimposed to generate a dynamic beat frequency signal. The beat frequency signal is generated by the optical fiber. The collimator is coupled back to the single-mode fiber again and enters the fiber circulator. It exits from port 3 of the fiber circulator and reaches the photodetector and is converted into an electrical signal. The change in the optical path difference between the two reflected beams can be obtained by detecting the change in the initial phase of the beat signal. , you can detect the change of the cavity length of the Fibonacci cavity, and then realize the high-precision pressure measurement according to the pressure deformation principle of the diaphragm; Among them, the relationship between the variation δφ _b0 of the initial phase of the beat signal and the pressure variation ΔP is:

In the formula, h represents the thickness of the diaphragm, γ is the radius of the Faber cavity, that is, the effective pressure-sensitive radius of the diaphragm, μ is the Poisson’s ratio of the diaphragm material, E is the elastic modulus of the diaphragm material, and n is the air refraction rate (n=1), λ ₀ is the wavelength of the light wave in vacuum.

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