WO2021212271A1 - Fabry-perot sensor cavity length demodulation system and fabry-perot sensor cavity length demodulation method - Google Patents

Abstract

Disclosed are a Fabry-Perot sensor cavity length demodulation system and a Fabry-Perot sensor cavity length demodulation method. The demodulation system comprises: a light source (1); a circulator (2) having a first port (21), a second port (22) and a third port (23), the circulator (2) being configured to receive light emitted from the light source (1) through the first port (21) and to transmit the light to a Fabry-Perot sensor (3) through the second port (22); the Fabry-Perot sensor (3), which is configured to receive the light from the second port (22) such that the light is respectively reflected at a first plane and a second plane of the Fabry-Perot sensor (3) so as to produce multi-beam interference, and to make interference light return to the second port (22) of the circulator (2) and transmit same from the second port (22) to the third port (23); a detector (4), which is configured to receive the interference light from the third port (23) to create a curve of the light intensity of the interference light versus the cavity length of the Fabry-Perot sensor (3); and a processor (5), which is configured to receive the curve and divide the curve into an integer wavelength portion and a non-integer wavelength portion, wherein for the integer wavelength portion, the processor (5) calculates the number of integer wavelengths contained in the integer wavelength portion and thus calculates a first cavity length variation; and for the non-integer wavelength portion, the processor (5) calculates, on the basis of a function of the light intensity and the cavity length, a second cavity length variation, and calculates the total cavity length variation by adding the first cavity length variation and the second cavity length variation together.

Description

Fabryper sensor cavity length demodulation system and Fabryper sensor cavity length demodulation method Technical field

The invention relates to a Fabry Perot sensor cavity length demodulation system and a Fabry Perot sensor cavity length demodulation method.

Background technique

Fiber-optic Fabry-Perot (F-P) sensors have the advantages of small size, high sensitivity, good stability, immunity from electromagnetic interference, etc., and are widely used in measurement fields such as strain, temperature, and pressure. The optical fiber Fabry Perot sensor senses the measurement by measuring the change of cavity length, and the rate and accuracy of cavity length demodulation directly affect the rate and accuracy of measurement. Therefore, the rapid and accurate demodulation of the cavity length of the fiber Fabry-Perot sensor is of great significance.

In optical fiber sensing applications, the demodulation system is responsible for continuously sending optical signals to the optical fiber sensor and receiving the returned optical signals carrying the information to be measured. After photoelectric conversion, signal acquisition, and signal conditioning, the information we need is extracted come out. For the current research on the demodulation system of the Fabry cavity sensor, the representative ones are FISO in Canada, Davidson in the United States, and Opsens in Canada. The first two companies use non-scanning correlation scanning technology, and Opsens uses white light polarization interference technology. Both of these technologies require well-made wedge and linear CCD, which are expensive, and because of the need to collect spectral images, the solution The rate of modulation cannot be increased, so it is not suitable for measuring rapidly changing signals, such as the measurement of explosion pressure. The intensity demodulation method is the oldest and simplest method used by the fiber Fabry Perot sensor. It obtains the cavity length information of the fiber Fabry Perot sensor by measuring the change of the output light intensity. It has the characteristics of low cost and fast demodulation rate. In the experiment, a monochromatic light source is used, and a photodetector is directly used to receive the reflected light. As the cavity length changes, the sensor output light intensity changes accordingly. The relationship between reflected light intensity and cavity length is as follows:

Where I _R is the intensity of reflected light, and L is the cavity length.

Taking the cavity length as the abscissa and the reflected light intensity as the ordinate, the reflected light intensity has a sinusoidal relationship with the cavity length. Obviously, an output light intensity corresponds to multiple cavity lengths, that is, the output light intensity is a multi-valued function of the cavity length, so The cavity length cannot be calculated directly from the output light intensity.

Summary of the invention

From the following detailed description of the best mode for implementing the present teaching in conjunction with the accompanying drawings, the above-mentioned features and advantages and other features and advantages of the present teaching will be apparent.

Description of the drawings

Fig. 1 is a schematic diagram showing a cavity length demodulation system of a Fabry Perot sensor according to a first embodiment of the present invention.

FIG. 2 shows a curve obtained by the cavity length demodulation system of the Fabry Perot sensor according to the first embodiment of the present invention.

FIG. 3 is a schematic diagram showing a cavity length demodulation system of a Fabry Perot sensor according to a second embodiment of the present invention.

4a and 4b respectively show the first curve and the second curve obtained by the cavity length demodulation system of the Fabryper sensor according to the second embodiment of the present invention.

FIG. 5 shows a third curve obtained by the cavity length demodulation system of the Fabry Perot sensor according to the second embodiment of the present invention.

In different drawings, the same elements are denoted by the same reference numerals.

Detailed ways

In order to make the objectives, technical solutions, and advantages of the technical solutions of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of specific embodiments of the present invention. The same reference numerals in the drawings represent the same components. It should be noted that the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by a person of ordinary skill in the art without creative work shall fall within the protection scope of the present invention.

Unless otherwise defined, the technical or scientific terms used herein shall have the usual meanings understood by those with ordinary skills in the field to which the present invention belongs. The "first", "second" and similar words used in the specification and claims of the patent application of the present invention do not denote any order, quantity or importance, but are only used to distinguish different components. Similarly, similar words such as "one" or "one" do not necessarily indicate quantitative restrictions. "Include" or "include" and other similar words mean that the element or item appearing before the word encompasses the element or item listed after the word and its equivalents, but does not exclude other elements or items. Similar words such as "connected" or "connected" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "Down", "Left", "Right", etc. are only used to indicate the relative position relationship. When the absolute position of the described object changes, the relative position relationship may also change accordingly.

Hereinafter, the cavity length demodulation system of the Fabry-Perot sensor of the present invention will be described in detail with reference to the accompanying drawings.

<First embodiment>

Fig. 1 is a schematic diagram showing a cavity length demodulation system of a Fabry Perot sensor according to a first embodiment of the present invention. FIG. 2 shows a curve obtained by the cavity length demodulation system of the Fabry Perot sensor according to the first embodiment of the present invention.

As shown in FIG. 1, the Fabry-Perot sensor cavity length demodulation system includes a light source 1 (for example, a semiconductor laser), and the wavelength of the light emitted by it is preferably in the range of 640 nm to 660 nm, more preferably 650 nm. The light emitted by the light source 1 is transmitted to the first port 21 of the circulator 2. The circulator also has a second port 22 and a third port 23. The light is transmitted from the first port 21 to the second port 22 and then to the Fabry sensor 3 . The Fabryper sensor has a cavity and a diaphragm. The light received by the Fabryper sensor is reflected at the bottom of the cavity and the diaphragm respectively. Therefore, the bottom of the cavity and the diaphragm are called the first plane and the second plane, respectively. At the Fabry Perot sensor, light is reflected at the first plane and the second plane of the Fabry Perot sensor to cause multi-beam interference, and the interference light returns to the second port of the circulator, and then is transmitted to the third port. The interference light emitted from the third port is transmitted to the detector 4 (for example, a photodetector), and the detector receives the interference light and forms a curve of the light intensity of the interference light with respect to the cavity length of the Fabryper sensor, as shown in FIG. 2. The processor 5 receives the curve and divides the curve into an integral wavelength part and a non-integral wavelength part. For the integral wavelength part, the processor calculates the number of integral wavelengths contained in the integral wavelength part, and then calculates the first cavity length For the non-integral wavelength part, the processor calculates the second cavity length change based on the function of the light intensity and the cavity length, and calculates it by adding the first cavity length change and the second cavity length change The amount of total cavity length change. For example, in Figure 2, from point A to point B is the whole wavelength part, denoted as n, then the first cavity length change is nλ/2, from point B to point C is the non-integer wavelength part, based on the light intensity and The function of the cavity length is used to calculate the second cavity length change, and finally the first cavity length change and the second cavity length change are added to obtain the total cavity length change. The method of calculating the change of the second cavity length based on the function of light intensity and cavity length is well known to those skilled in the art. For example, the cavity length is the abscissa, the reflected light intensity is the ordinate, and the reflected light intensity and the cavity length are sinusoidal. From the sine relationship, the cavity length change can be obtained from the light intensity. At this time, one light intensity corresponds to one cavity length.

A polarizer 6 can also be arranged between the light source and the circulator, so that the light from the light source forms linearly polarized light, and the linearly polarized light is transmitted to the circulator. In this case, the circulator is a polarization-maintaining circulator.

The light source in this application emits light with a wavelength of 650 nm. Under the condition of the same cavity length change, the number of interference fringes formed by the short-wavelength light source is larger, so that the demodulation is more accurate. In addition, the present application adopts the principle of interference and superposition of linearly polarized light, which avoids incoherent superposition between non-polarized light, which is beneficial to improve the contrast of interference fringes, thereby improving the sensitivity of the optical fiber F-P demodulation system. The Fabry Perot sensor used in this application preferably has a large cavity diameter and a thin diaphragm. Thus, according to the Fabry Perot cavity sensitivity calculation formula (1), it can be known that the Fabry Perot cavity has higher sensitivity.

Where S is the sensitivity, a is the diameter of the diaphragm, μ is the Poisson's ratio, E is the Young's modulus, and h is the diaphragm.

<Second Embodiment>

FIG. 3 is a schematic diagram showing a cavity length demodulation system of a Fabry Perot sensor according to a second embodiment of the present invention. 4a and 4b respectively show the first curve S1 and the second curve S2 obtained by the cavity length demodulation system of the Fabry Perot sensor according to the second embodiment of the present invention. FIG. 5 shows a third curve S3 obtained by the cavity length demodulation system of the Fabry Perot sensor according to the second embodiment of the present invention.

The difference between the second embodiment and the first embodiment is that a quarter wave plate 7 is provided between the polarizer 6 and the polarization-maintaining circulator 2, and a quarter-wave plate 7 is provided downstream of the third port 23 of the polarization-maintaining circulator. The polarization beam splitting prism 8 and the detector include a first detector 41 and a second detector 42. After the light emitted by the light source 1 passes through the polarizer, it forms linearly polarized light. The direction of the polarizer and the fast and slow axis of the quarter wave plate are at an angle of 45 degrees, so that linearly polarized light will become circularly polarized light after passing through the quarter wave plate. The circularly polarized light enters the Fabry Perot sensor through the polarization maintaining circulator, and multi-beam interference occurs between the two parallel surfaces of the Fabry Perot sensor. The interference light is transmitted to the polarization beam splitting prism 8 through the third port of the polarization maintaining circulator, and after passing through the polarization beam splitting prism, the circularly polarized light is divided into two linearly polarized lights, namely the first light beam L1 and the second light beam L2. The phase difference between the first beam and the second beam is π/2. The first beam and the second beam are received by the first detector and the second detector respectively, forming a first curve and a second curve of light intensity versus cavity length And the first curve of the light intensity formed by the first beam relative to the cavity length is proportional to sin(wt+φ1), as shown in Figure 4a, the second curve of the light intensity formed by the second beam relative to the cavity length is proportional to cos (wt+φ1), as shown in Figure 4b. The first curve and the second curve are input to the processor 5, and the processor performs a division operation to obtain a third curve proportional to tan (wt+φ1), as shown in FIG. 5. The third curve is steeper than the first curve and the second curve, which helps to improve the accuracy of demodulation.

Next, the processor divides the third curve into an entire wavelength part and a non-integer wavelength part. For the entire wavelength part, the processor calculates the number of integer wavelengths contained in the entire wavelength part (for example, 19 in FIG. 5), and Then the first cavity length change is calculated. For the non-integer wavelength part (point A to B and C to D), the processor calculates the second cavity length change based on the function of the light intensity and the cavity length , The total cavity length change is calculated by adding the first cavity length change and the second cavity length change.

The operation steps of the method for demodulating the cavity length of a Fabry-Perot sensor according to the present invention are as follows: the light emitted by the light source is guided to a circulator, the circulator has a first port, a second port, and a third port. The port enters the circulator and is transmitted to the Fabry Perot sensor via the second port; the light is reflected at the first plane and the second plane of the Fabry Perot sensor to cause multi-beam interference to form interference light, and the interference light returns to the circulator The second port is transmitted from the second port to the third port; the detector receives the interference light from the third port of the circulator to form a curve of the intensity of the interference light relative to the cavity length of the Fabry Perot sensor; using the processor Receive the curve and divide the curve into an integral wavelength part and a non-integral wavelength part. For the integral wavelength part, the processor calculates the number of integral wavelengths contained in the integral wavelength part, and then calculates the first cavity length change amount For the non-integral wavelength part, the processor calculates the second cavity length change based on the function of the light intensity and the cavity length, and calculates the total cavity by adding the first cavity length change and the second cavity length change Long change amount.

Additionally, the demodulation method further includes disposing a polarizer between the light source and the circulator, disposing a quarter wave plate between the polarizer and the polarization-maintaining circulator, and setting the third port 23 of the polarization-maintaining circulator. The step of setting a polarization beam splitter prism downstream. When the polarizer is provided, the circulator is a polarization maintaining circulator. In addition, the detectors are arranged as a first detector and a second detector to respectively receive the first light beam and the second light beam split by the polarization beam splitting prism.

This application divides the curve of light intensity versus cavity length into an integer wave part and a non-integer wave part, calculates the number of integer wavelengths in the integer wave part, obtains the first cavity length change, and calculates the second cavity length in the non-integer wave part The amount of change. In this way, the demodulation speed is guaranteed and the demodulation accuracy is improved, and the high-speed and accurate demodulation of the Fabry Perot sensor is realized.

Although the best mode for implementing many aspects of this teaching has been described in detail, those skilled in the art will understand that various modifications and variations can be made to the above specific embodiments without departing from the concept of the present invention. Modifications, and various combinations of various technical features and structures proposed by the present invention can be made without exceeding the protection scope of the present invention.

Claims (14)

1. A Fabry-Perot sensor cavity length demodulation system, characterized in that, the demodulation system includes:

   light source;

   A circulator having a first port, a second port and a third port, the circulator being arranged to receive the light emitted from the light source via the first port, and to transmit the light to the Fabry sensor via the second port;

   The Fabryper sensor is arranged to receive the light from the second port so that the light is reflected at the first plane and the second plane of the Fabryper sensor to cause multi-beam interference, and the interference light is returned to the circulator The second port, and transmit from the second port to the third port;

   The detector is arranged to receive the interference light from the third port and form a curve of the light intensity of the interference light with respect to the cavity length of the Fabryper sensor;

   A processor, which is arranged to receive the curve and divide the curve into a whole wavelength part and a non-integer wavelength part. For the whole wavelength part, the processor calculates the number of whole wavelengths contained in the whole wavelength part, and then calculates The first cavity length change amount. For the non-integer wavelength part, the processor calculates the second cavity length change amount based on the function of the light intensity and the cavity length. Add and calculate the total cavity length change.
2. The demodulation system according to claim 1, wherein the demodulation system further comprises:

   The polarizer is arranged to receive the light from the light source, form linearly polarized light, and transmit the linearly polarized light to the circulator, the circulator being a polarization-maintaining circulator.
3. The demodulation system according to claim 2, wherein the demodulation system further comprises:

   The quarter wave plate is arranged to receive linearly polarized light from the polarizer, convert the linearly polarized light into circularly polarized light, and transmit the circularly polarized light to the polarization maintaining circulator.
4. The demodulation system according to claim 3, wherein the demodulation system further comprises:

   A polarization beam splitting prism, which is arranged to receive the interference light from the third port and divide the interference light into a first beam and a second beam,

   Wherein, the detector includes a first detector and a second detector, respectively arranged to receive the first light beam and the second light beam, and form a first curve of the first light beam and a second curve of the second light beam,

   Wherein, the processor receives the first curve and the second curve, and divides the first curve and the second curve to obtain a third curve,

   Wherein, the processor divides the third curve into an integral wavelength part and a non-integral wavelength part. For the integral wavelength part, the processor calculates the number of integral wavelengths contained in the integral wavelength part, and then calculates the first cavity Length variation. For the non-integer wavelength part, the processor calculates the second cavity length variation based on the function of the light intensity and the cavity length, which is calculated by adding the first cavity length variation and the second cavity length variation The total cavity length change amount.
5. The demodulation system according to claim 4, wherein the first curve is a sine curve, the second curve is a cosine curve, and the third curve is a tangent curve.
6. The demodulation system according to claim 1, wherein the wavelength of the light emitted by the light source is in the range of 640 nm to 660 nm.
7. The demodulation system according to claim 6, wherein the wavelength of the light emitted by the light source is 650 nm.
8. A method for demodulating the cavity length of a Fabry Perot sensor, characterized in that the demodulating method includes the following steps:

   Guiding the light emitted by the light source to the circulator, the circulator having a first port, a second port, and a third port, the light enters the circulator from the first port, and is transmitted to the Fabry sensor via the second port;

   The light is reflected at the first plane and the second plane of the Fabry-Perot sensor to cause multi-beam interference to form interference light. The interference light returns to the second port of the circulator and is transmitted from the second port to the third port;

   Use the detector to receive the interference light from the third port of the circulator to form a curve of the intensity of the interference light with respect to the cavity length of the Fabry Perot sensor;

   The processor receives the curve and divides the curve into an integral wavelength part and a non-integral wavelength part. For the integral wavelength part, the processor calculates the number of integral wavelengths contained in the integral wavelength part, and then calculates the first cavity Length variation. For the non-integer wavelength part, the processor calculates the second cavity length variation based on the function of the light intensity and the cavity length, which is calculated by adding the first cavity length variation and the second cavity length variation The total cavity length change amount.
9. The demodulation method according to claim 8, wherein the demodulation method further comprises: disposing a polarizer between the light source and the circulator, the polarizer receiving light from the light source to form linearly polarized light , And transmit the linearly polarized light to the circulator, which is a polarization-maintaining circulator.
10. The demodulation method according to claim 9, wherein the demodulation method further comprises providing a quarter wave plate between the polarizer and the polarization maintaining circulator, which receives linearly polarized light from the polarizer , Designed to convert linearly polarized light into circularly polarized light and transmit the circularly polarized light to the polarization maintaining circulator.
11. The demodulation method according to claim 10, wherein the demodulation method further comprises disposing a polarization beam splitting prism downstream of the third port of the polarization-maintaining circulator, which receives the signal from the third port of the polarization-maintaining circulator. Interference light, which divides the interference light into a first beam and a second beam;

    Wherein, the detector includes a first detector and a second detector, respectively receiving the first light beam and the second light beam, and forming a first curve of the first light beam and a second curve of the second light beam,

    Wherein, the processor is used to receive the first curve and the second curve, and divide the first curve and the second curve to obtain a third curve,

    Wherein, the processor is used to divide the third curve into an integral wavelength part and a non-integral wavelength part. For the integral wavelength part, the processor calculates the number of integral wavelengths contained in the integral wavelength part, and then calculates the first The cavity length change amount. For the non-integer wavelength part, the processor calculates the second cavity length change amount based on the function of the light intensity and the cavity length, which is obtained by adding the first cavity length change amount and the second cavity length change amount Calculate the total cavity length change.
12. The demodulation method according to claim 11, wherein the first curve is a sine curve, the second curve is a cosine curve, and the third curve is a tangent curve.
13. The demodulation method according to claim 8, wherein the wavelength of the light emitted by the light source is in the range of 640 nm to 660 nm.
14. The demodulation method according to claim 13, wherein the wavelength of the light emitted by the light source is 650 nm.

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