Fiber optic sensor cavity length demodulation system and fiber optic sensor cavity length demodulation method

Abstract

A Fabry-Perot sensor cavity length demodulation system and a Fabry-Perot sensor cavity length demodulation method. The demodulation system comprises: a first light source (1) emitting light of a first wavelength; a second light source (2) emitting light of a second wavelength; a wavelength division multiplexer (3) receiving light from the first light source (1) and light from the second light source (2); a fiber coupler (4) receiving and coupling light of the first light source (1) and light of the second light source (2); a Fabry-Perot sensor (5) receiving coupled light from the fiber coupler (4) such that the coupled light is reflected at a first plane and a second plane of the Fabry-Perot sensor (5) to interfere and return the interference light to the fiber coupler (4); a demultiplexer (6) receiving the interference light and separating the interference light into a first light beam (L1) and a second light beam (L2); a first detector (7) and a second detector (8) respectively receiving the first light beam (L1) and the second light beam (L2) and transmitting a first interference signal of the first light beam (L1) and a second interference signal of the second light beam (L2) to a processor (9), the processor (9) being configured to obtain and analyze a first curve (S1) of the first interference signal and a second curve (S2) of the second interference signal to determine an inflection point of a physical quantity to be measured causing a cavity length change in the first curve (S1) and / or the second curve (S2), the first curve (S1) being a curve of light intensity of the first interference signal with respect to the cavity length, and the second curve (S2) being a curve of light intensity of the second interference signal with respect to the cavity length.

Description

TECHNICAL FIELD

[0001] The present application relates to a Fabry-Perot sensor cavity length demodulation system and a Fabry-Perot sensor cavity length demodulation method. BACKGROUND

[0002] Optical fiber Fabry-Perot (F-P) sensor has the advantages of small volume, high sensitivity, good stability, and immunity to electromagnetic interference, and is widely used in strain, temperature, pressure and other measurement fields. The optical fiber Fabry-Perot sensor senses the measured quantity by measuring the change of the cavity length, and the accuracy of the cavity length demodulation directly affects the accuracy of the measurement. Therefore, the fast and accurate demodulation of the cavity length of the optical fiber Fabry-Perot sensor is of great significance.

[0003] 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 measured information. After photoelectric conversion, signal acquisition and signal demodulation, the required information is extracted. At present, the representative research on Fabry-Perot cavity sensor demodulation system is FISO company in Canada, Davidson company in the United States and Opsens company in Canada. The first two companies use non-scanning correlation scanning technology, and the Opsens company uses white light polarization interference technology. Both technologies require high-quality optical wedge and linear array CCD, which is costly, and because the spectral image needs to be collected, the demodulation rate cannot be improved, so it is not suitable for measuring rapidly changing signals, such as explosion pressure measurement. The intensity demodulation method demodulates the cavity length by detecting the reflected light intensity of the sensor, which has high sensitivity and fast demodulation rate. In the intensity demodulation method, the sensor output light intensity and the Fabry-Perot sensor cavity length form a sinusoidal relationship. When the measured physical quantity dynamically and reciprocally changes, the interference light intensity curve will have obvious inflection points. However, when the inflection point is exactly the highest point or the lowest point of the sinusoidal curve, the inflection point cannot be accurately determined. Therefore, it is easy to make mistakes when measuring the changing physical quantity by using a single wavelength. SUMMARY

[0004] The present application relates to a Fabry-Perot sensor cavity length demodulation system, comprising: a first light source emitting light of a first wavelength; a second light source emitting light of a second wavelength; a wavelength division multiplexer receiving light from the first light source and light from the second light source; a fiber coupler receiving and coupling light from the wavelength division multiplexer; a Fabry-Perot sensor receiving the coupled light from the fiber coupler such that the coupled light is reflected at a first plane and a second plane of the Fabry-Perot sensor to interfere, and returning the interfered light to the fiber coupler; a demultiplexer receiving the interfered light and separating the interfered light into a first light beam and a second light beam; a first detector and a second detector respectively receiving the first light beam and the second light beam and transmitting a first interference signal of the first light beam and a second interference signal of the second light beam to a processor, the processor being configured to acquire and analyze a first curve of the first interference signal and a second curve of the second interference signal to determine an inflection point of a to-be-measured physical quantity causing a cavity length change of the Fabry-Perot sensor in the first curve and / or the second curve, wherein the first curve is a curve of light intensity of the first interference signal versus the cavity length, and the second curve is a curve of light intensity of the second interference signal versus the cavity length.

[0005] Advantageously, based on the analysis result of the processor, when both the first curve and the second curve show an inflection point not located at a wave crest or a wave trough, the processor determines the inflection point of the to-be-measured physical quantity based on either one of the first curve and the second curve.

[0006] Advantageously, based on the analysis result of the processor, when only one of the first curve and the second curve shows an inflection point not located at a wave crest or a wave trough, the processor determines the inflection point of the to-be-measured physical quantity based on the one curve.

[0007] Advantageously, the first light source and the second light source are semiconductor lasers.

[0008] Advantageously, the first wavelength is in a range of 1300 nm to 1320 nm, and the second wavelength is in a range of 1540 nm to 1560 nm.

[0009] Advantageously, the first wavelength is 1310 nm, and the second wavelength is 1550 nm.

[0010] The present application also relates to a fiber-optic Fabry-Perot sensor cavity length demodulation method, comprising the following steps: guiding light of a first wavelength emitted by a first light source and light of a second wavelength emitted by a second light source to a wavelength division multiplexer; the wavelength division multiplexer receives the light from the first light source and the light from the second light source and transmits to a fiber coupler; the fiber coupler couples the light of the first light source and the light of the second light source and transmits the coupled light to a Fabry-Perot sensor; the coupled light is reflected at a first plane and a second plane of the Fabry-Perot sensor, so that interference occurs; the interference light is guided back to the fiber coupler and guided to a demultiplexer by the fiber coupler; the interference light is divided into a first light beam and a second light beam by the demultiplexer; the first light beam and the second light beam are received by a first detector and a second detector respectively, and a first interference signal of the first light beam and a second interference signal of the second light beam are transmitted to a processor, the processor analyzes a first curve of the first interference signal and a second curve of the second interference signal to determine an inflection point of a to-be-measured physical quantity causing a change in the cavity length of the Fabry-Perot sensor in the first curve and / or the second curve, the first curve being a curve of the light intensity of the first interference signal with respect to the cavity length, and the second curve being a curve of the light intensity of the second interference signal with respect to the cavity length.

[0011] Advantageously, based on the analysis result of the processor, when both the first curve and the second curve show an inflection point not located at a wave crest or a wave trough, the processor determines the inflection point of the to-be-measured physical quantity based on either one of the first curve and the second curve.

[0012] Advantageously, based on the analysis result of the processor, when only one of the first curve and the second curve shows an inflection point not located at a wave crest or a wave trough, the processor determines the inflection point of the to-be-measured physical quantity based on the one curve.

[0013] Advantageously, the first light source and the second light source are semiconductor lasers.

[0014] Advantageously, the first wavelength is in a range of 1300 nm to 1320 nm, and the second wavelength is in a range of 1540 nm to 1560 nm.

[0015] Advantageously, the first wavelength is 1310 nm, and the second wavelength is 1550 nm.

[0016] The above features and advantages of the present application, as well as other features and advantages thereof, are readily apparent from the following detailed description of the best modes for carrying out the present teachings when taken in connection with the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is a schematic diagram showing a Fabry-Perot sensor cavity length demodulation system according to the present application.

[0018] Figure 2The diagram shows a first curve of the first interference signal and a second curve of the second interference signal obtained by the Fabry-Perot sensor cavity length demodulation system according to the present invention, showing that only the second curve has an inflection point that is not located at a peak or a trough.

[0019] In different figures, the same elements are represented by the same reference numerals. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. The same reference numerals in the drawings represent the same components. It should be noted that the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0021] Unless otherwise defined, the technical or scientific terms used herein shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms “first,” “second,” and similar terms used in this patent application specification and claims do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, “an” or “a” and similar terms do not necessarily indicate a quantity limitation. Terms such as “comprising” or “including” mean that the element or object preceding the word encompasses the element or object listed following the word and its equivalents, without excluding other elements or objects. Terms such as “connected” or “linked” are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as “upper,” “lower,” “left,” and “right” are used only to indicate relative positional relationships; these relative positional relationships may change accordingly when the absolute position of the described object changes.

[0022] In the following, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0023] Figure 1 This is a schematic diagram illustrating the Fabry-Perot sensor cavity length demodulation system according to the present invention. Figure 1As shown, the Fabry-Perot sensor cavity length demodulation system includes a first light source 1 and a second light source 2. The first light source 1 emits light of a first wavelength, and the second light source 2 emits light of a second wavelength. Preferably, the first wavelength is in the range of 1300nm to 1320nm, more preferably, the first wavelength is 1310nm. Preferably, the second wavelength is in the range of 1540nm to 1560nm, more preferably, the second wavelength is 1550nm. Using the first and second wavelengths of light as described above can reduce fiber optic loss and is beneficial for long-distance transmission. Those skilled in the art will understand that any two wavelengths of light can be used. The first and second light sources are preferably semiconductor lasers.

[0024] The Fabry-Perot sensor cavity length demodulation system also includes a wavelength division multiplexer 3, which receives light of a first wavelength and a second wavelength; an optical fiber coupler 4, such as a 1*2 coupler, which receives and couples the first and second wavelength light from the wavelength division multiplexer 3; and a Fabry-Perot sensor 5, which has a cavity and a diaphragm. The light received by the Fabry-Perot sensor is reflected at the bottom of the cavity and the diaphragm, respectively, hence the bottom of the cavity and the diaphragm are referred to as the first plane and the second plane, respectively. The Fabry-Perot sensor receives the coupled light from the optical fiber coupler 4, which is reflected at the first and second planes of the Fabry-Perot sensor, resulting in multi-beam interference. The interfering light then returns to the optical fiber coupler. The principle of interference light generated by light reflected from two reflecting planes a certain distance apart is well known to those skilled in the art and will not be elaborated further.

[0025] After the interfering light returns to the fiber coupler, it is further transmitted to the demultiplexer 6, which splits the interfering light into a first beam L1 and a second beam L2. The first beam and the second beam are transmitted to the first detector 7 and the second detector 8 (e.g., photodetectors), respectively, and the first detector 7 and the second detector 8 obtain the first interference signal of the first beam and the second interference signal of the second beam.

[0026] As the measured physical quantity (pressure, temperature, stress, etc.) changes repeatedly, the cavity length of the Fabry-Perot sensor changes, and the output light intensity of the sensor also changes accordingly. The relationship between the output light intensity and the cavity length is as follows:

[0027]

[0028] Where I R Let L be the reflected light intensity and L be the cavity length. Therefore, for the first and second interference signals, a curve of light intensity versus cavity length can be formed, such as a sine curve, as described below.

[0029] The Fabry-Perot sensor cavity length demodulation system also includes a processor 9 (e.g., a high-speed acquisition card), which receives a first interference signal and a second interference signal, obtaining a first curve S1 of the first interference signal and a second curve S2 of the second interference signal. The first curve is a curve of the light intensity of the first interference signal relative to the cavity length (the horizontal axis is the cavity length, and the vertical axis is the light intensity), and the second curve is a curve of the light intensity of the second interference signal relative to the cavity length (the horizontal axis is the cavity length, and the vertical axis is the light intensity). By analyzing the first and second curves, the inflection point of the measured physical quantity causing the cavity length change can be determined based on the following methods: 1. If both curves in the first and second curves show inflection points that are not located at peaks or troughs, then the inflection point of the measured physical quantity can be determined based on either the first or second curve. 2. If only one of the first and second curves shows an inflection point that is not located at a peak or trough, such as... Figure 2 As shown, the inflection point P of the measured physical quantity is determined based on this curve. Since the wavelengths of the first and second beams are different, the first curve formed by the first beam and the second curve formed by the second beam will be offset from each other and will not coincide. Therefore, for example, when the inflection point of the first curve occurs at a peak or trough, the inflection point in the second curve will not be located at a peak or trough. Thus, the cavity length can be determined based on the inflection point of the second curve. After determining the inflection point, the cavity length value on the horizontal axis can be obtained using calibration methods known to those skilled in the art, thereby obtaining the change in cavity length, which can further determine the measured physical quantity.

[0030] Furthermore, when the change in cavity length of the Fabry-Perot sensor is exactly the least common multiple of the first and second wavelengths, the inflection points on both the first and second curves will appear at either a peak or a trough. However, generally speaking, the least common multiple of the first and second wavelengths is much larger than the change in cavity length of the Fabry-Perot sensor, so there will not be a situation where the inflection points on both curves appear at the same peak or trough.

[0031] The operation steps of the Fabry-Perot sensor cavity length demodulation method according to the present invention are as follows: Light of a first wavelength emitted from a first light source and light of a second wavelength emitted from a second light source are guided to a wavelength division multiplexer; the wavelength division multiplexer receives light from the first light source and light from the second light source and transmits it to an optical fiber coupler; the optical fiber coupler couples the light from the first light source and the light from the second light source and transmits the coupled light to the Fabry-Perot sensor; the coupled light is reflected at a first plane and a second plane of the Fabry-Perot sensor, thereby causing interference; the interference light is guided back to the optical fiber coupler and guided to a demultiplexer through the optical fiber coupler; the interference light is split into a first beam and a second beam by the demultiplexer; the first beam and the second beam are received by a first detector and a second detector respectively, and the first interference signal of the first beam and the second interference signal of the second beam are transmitted to a processor, which analyzes the first curve of the first interference signal and the second curve of the second interference signal to determine the inflection point of the measured physical quantity that causes the cavity length change in the first curve and / or the second curve.

[0032] This application uses two light sources with different wavelengths. Within the range of changes in the length of the Fabry-Perot cavity, the inflection point can be accurately determined, thereby identifying the inflection point of the reciprocating physical quantity to be measured.

[0033] While the best mode for carrying out many aspects of this teaching has been described in detail, it will be understood by those skilled in the art that various modifications and alterations can be made to the specific embodiments described above without departing from the spirit of the invention, and various combinations can be made to the various technical features and structures proposed in this invention without exceeding the protection scope of this invention.

Claims

1. A Fabry-Perot sensor cavity length demodulation system, characterized in that, The demodulation system includes: The first light source (1) emits light of the first wavelength; The second light source (2) emits light of the second wavelength; Wavelength division multiplexer (3) receives light from the first light source (1) and light from the second light source (2); Fiber optic coupler (4) receives and couples light from wavelength division multiplexer (3); The Fabry sensor (5) receives coupled light from the fiber coupler (4), causing the coupled light to be reflected at the first and second planes of the Fabry sensor to interfere, and causing the interference light to return to the fiber coupler; The demultiplexer (6) receives the interference light and splits it into a first beam (L1) and a second beam (L2). The first detector (7) and the second detector (8) receive the first beam and the second beam respectively, and transmit the first interference signal of the first beam and the second interference signal of the second beam to the processor (9). The processor is configured to analyze a first curve (S1) of the first interference signal and a second curve (S2) of the second interference signal to determine the inflection point of the measured physical quantity that causes the change in the cavity length of the Fabry sensor in the first curve and / or the second curve, wherein the first curve is the curve of the light intensity of the first interference signal relative to the cavity length, and the second curve is the curve of the light intensity of the second interference signal relative to the cavity length.

2. The demodulation system as described in claim 1, characterized in that, Based on the analysis results of the processor (9), when both the first curve and the second curve show inflection points that are not located at peaks and troughs, the processor determines the inflection point of the physical quantity to be measured based on either the first curve or the second curve.

3. The demodulation system as described in claim 1, characterized in that, Based on the analysis results of the processor (9), when only one of the first curve and the second curve shows an inflection point that is not located at a peak or trough, the processor determines the inflection point of the physical quantity to be measured based on that one curve.

4. The demodulation system as described in claim 1, characterized in that, The first light source and the second light source are semiconductor lasers.

5. The demodulation system as described in claim 1, characterized in that, The first wavelength is in the range of 1300nm to 1320nm, and the second wavelength is in the range of 1540nm to 1560nm.

6. The demodulation system as described in claim 5, characterized in that, The first wavelength is 1310nm, and the second wavelength is 1550nm.

7. A method for demodulating the cavity length of an optical fiber Fabry-Perot sensor, characterized in that, The demodulation method includes the following steps: The light of the first wavelength emitted by the first light source (1) and the light of the second wavelength emitted by the second light source (2) are guided to the wavelength division multiplexer (3); The wavelength division multiplexer (3) receives light from the first light source and light from the second light source and transmits it to the fiber optic coupler (4); The light from the wavelength division multiplexer is coupled through the fiber optic coupler (4) and the coupled light is transmitted to the Fabry sensor (5); The coupled light is reflected at the first and second planes of the Fabry-Perot sensor, thus causing interference; The interference light is guided back to the fiber coupler (4), and then guided to the demultiplexer (6) through the fiber coupler; The interference light is split into a first beam (L1) and a second beam (L2) by a demultiplexer (6); The first beam and the second beam are received by the first detector (7) and the second detector (8) respectively, and the first interference signal of the first beam and the second interference signal of the second beam are transmitted to the processor (9). The processor compares the first curve (S1) of the first interference signal and the second curve (S2) of the second interference signal to determine the inflection point of the physical quantity to be measured that causes the change of the cavity length of the Fabry sensor in the first curve and / or the second curve, wherein the first curve is the curve of the light intensity of the first interference signal relative to the cavity length, and the second curve is the curve of the light intensity of the second interference signal relative to the cavity length.

8. The demodulation method as described in claim 7, characterized in that, Based on the processor's comparison results, when both the first curve and the second curve show inflection points that are not located at peaks and troughs, the processor determines the inflection point of the physical quantity to be measured based on either the first curve or the second curve.

9. The demodulation method as described in claim 7, characterized in that, Based on the comparison results of the processor, when only one of the first and second curves shows an inflection point that is not located at a peak or trough, the processor determines the inflection point of the physical quantity to be measured based on that one curve.

10. The demodulation method as described in claim 7, characterized in that, The first light source and the second light source are semiconductor lasers.

11. The demodulation method as described in claim 7, characterized in that, The first wavelength is in the range of 1300nm to 1320nm, and the second wavelength is in the range of 1540nm to 1560nm.

12. The demodulation method as described in claim 11, characterized in that, The first wavelength is 1310nm, and the second wavelength is 1550nm.

Images