A fiber optic inclination measurement device based on dynamic cursor effect

Abstract

The invention discloses a fiber tilt measuring device based on dynamic cursor effect, comprising a fiber tilt meter module, a fiber coupler, a fiber Bragg grating demodulator and a computer; the fiber tilt meter module comprises a top plate and a weight, the weight is suspended on the top plate, a first aluminum foil and a second aluminum foil are respectively pasted on both sides of the weight, the reflection surface of the first aluminum foil is arranged opposite to the first fiber FC jumper head; the reflection surface of the second aluminum foil is arranged opposite to the second fiber FC jumper head; the two fiber FC jumper heads are respectively connected to the input end of the fiber coupler, the output end of the fiber coupler is connected to the input end of the fiber Bragg grating demodulator, and the output end of the fiber Bragg grating demodulator is connected to the computer through an Ethernet cable. The beneficial effects of the invention are: the use of the dynamic cursor effect greatly improves the sensitivity and resolution of the interferometer, especially the high sensitivity when the angle changes slightly.

Description

Technical Field

[0001] The invention relates to the technical field of optical fiber tilt sensors, and in particular to an optical fiber tilt angle measuring device based on a dynamic vernier effect. Background Art

[0002] Inclinometers are widely used to measure the angles and directions of walls, holes, and dams. Among them, fiber optic inclinometers have attracted widespread attention for their excellent characteristics such as corrosion resistance, low cost, strong resistance to electromagnetic interference, and high precision, and have become an important research direction in the field of optical sensing. In recent years, with the emergence of many excellent new fiber optic inclinometers, the resolution and sensitivity of measurements have also been continuously improved. Traditional fiber optic inclinometers use fiber Bragg gratings, which are low in cost and easy to install. However, they have low sensitivity to tilt measurement, especially when the angle changes are very small, they often cannot detect the corresponding changes. Summary of the invention

[0003] The purpose of the present invention is to provide a highly sensitive optical fiber tilt measurement device based on a dynamic vernier effect in view of the deficiencies in the prior art.

[0004] The technical scheme adopted by the present invention is: an optical fiber tilt measurement device based on dynamic cursor effect, comprising an optical fiber tilt meter module, an optical fiber coupler, an optical fiber Bragg grating demodulator and a computer; the optical fiber tilt meter module comprises a top plate and a weight, the weight is suspended on the top plate, a first aluminum foil and a second aluminum foil are respectively pasted on both sides of the weight, the reflection surface of the first aluminum foil is arranged opposite to the first optical fiber FC jumper head; the reflection surface of the second aluminum foil is arranged opposite to the second optical fiber FC jumper head; the two optical fiber FC jumper heads are respectively connected to the input end of the optical fiber coupler, the output end of the optical fiber coupler is connected to the input end of the optical fiber Bragg grating demodulator, and the optical fiber Bragg grating is connected to the input end of the optical fiber coupler. The output end of the demodulator is connected to the computer through an Ethernet cable; the fiber Bragg grating demodulator transmits signal light to two fiber FC jumper heads through a fiber coupler. The signal light is emitted from the inner end face of the fiber FC jumper head to the aluminum foil, and then reflected to the surface of the fiber FC jumper head. Part of the light returns to the fiber Bragg grating demodulator, and the other part of the light is reflected by the fiber FC jumper head, reflected to the corresponding aluminum foil and then reflected again; the light is reflected multiple times between the end faces of the two fiber FC jumper heads and the corresponding aluminum foil, forming two Fabry-Perot interferometer structures respectively, and the interference waves of the two Fabry-Perot interferometer structures meet at the fiber coupler to form a composite vernier spectrum.

[0005] According to the above scheme, the distance between the reflective surface of the first aluminum foil and the inner end surface of the first optical fiber FC jumper head is L1, and the distance between the reflective surface of the second aluminum foil and the inner end surface of the second optical fiber FC jumper head is L2, and L1 and L2 are not equal.

[0006] According to the above solution, the weight is a square structure.

[0007] According to the above scheme, the top of the heavy object is suspended on the top plate by a first suspension rope and a second suspension rope of equal length.

[0008] According to the above scheme, two optical fiber FC jumper heads are respectively installed on two brackets, and the brackets are arranged on the base.

[0009] According to the above solution, the top plate, the bracket and the base are all fixed on the back plate.

[0010] The present invention also provides a method for measuring inclination angle based on the above-mentioned inclination measuring device, characterized in that the method comprises:

[0011] The tilt measurement device is provided, wherein a signal light is input, and the signal light reaches two optical fiber FC jumper heads respectively through an optical fiber coupler, and the light is reflected multiple times between the end faces of the two optical fiber FC jumper heads and the corresponding aluminum foils to form two Fabry-Perot interferometer structures, and the interference waves of the two interferometer structures meet at the optical fiber coupler to form a composite vernier spectrum, and the composite vernier spectrum is coupled in the optical fiber coupler to form an interference superposition spectrum; a fiber grating demodulator monitors the interference superposition spectrum, and the interference superposition spectrum will produce a vernier effect to form an envelope during the tilting process, and the change of the tilt angle causes the cavity length of the Fabry-Perot interferometer structures at both ends to change, thereby causing the free spectral range of the envelope to change, and the wavelength at the envelope trough changes accordingly, and the change of the wavelength at the envelope trough is monitored by a computer and a fiber grating demodulator, and the demodulation tilt angle information is analyzed, and then a relationship curve between the wavelength and the tilt angle is drawn, so as to demodulate the tilt angle change information.

[0012] The beneficial effects of the present invention are as follows: the present invention attaches aluminum foil to both sides of a heavy object, and places optical fiber FC connectors in parallel on the surface side opposite to the reflection surface thereof to form two Fabry-Perot interferometer structures; two interference spectra are superimposed at a coupler to form a large envelope; the movement of the envelope valley of the interference spectrum is demodulated by a fiber grating demodulator and a computer to obtain tilt information; the present invention greatly improves the sensitivity and resolution of the interferometer by utilizing a dynamic cursor effect, and the sensitivity is high especially when the angle changes slightly; a push-pull structure is adopted (when tilting, the cavity length of the Fabry-Perot interferometers at both ends becomes longer and the other becomes shorter), and the two interferometers change simultaneously to perform sensing measurement, thereby reducing the interference of factors such as external temperature fluctuations, and the entire device has high sensitivity, good repeatability and stable structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a schematic diagram of the overall structure of a specific embodiment of the present invention.

[0014] Figure 2 Schematic diagram of the principle structure of the optical fiber inclinometer in this embodiment.

[0015] Wherein: 1. Computer; 2. Fiber Bragg grating demodulator; 3. Fiber coupler; 4. Fiber inclinometer module; 5. Top plate; 6. Base; 7. First suspension rope; 8. Second suspension rope; 9. Weight; 10. First aluminum foil; 11. Second aluminum foil; 12. First fiber FC jumper head; 13. Second fiber FC jumper head; 14. Back plate; 15. First bracket; 16. Second bracket. DETAILED DESCRIPTION

[0016] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0017] like Figure 1 and Figure 2 The optical fiber tilt measuring device based on the dynamic cursor effect shown in the figure comprises an optical fiber tilt meter module 4, an optical fiber coupler 3, an optical fiber Bragg grating demodulator 2 and a computer 1; the optical fiber tilt meter module 4 comprises a top plate 5 and a weight 9; the weight 9 is suspended on the top plate 5, and a first aluminum foil 10 and a second aluminum foil 11 are respectively pasted on both sides of the weight 9, and the reflection surface of the first aluminum foil 10 is arranged opposite to the first optical fiber FC jumper head 12; the reflection surface of the second aluminum foil 11 is arranged opposite to the second optical fiber FC jumper head 13; the two optical fiber FC jumper heads are respectively connected to the input end of the optical fiber coupler 3, the output end of the optical fiber coupler 3 is connected to the input end of the optical fiber Bragg grating demodulator 2, and the output end of the optical fiber Bragg grating demodulator 2 is connected to the computer 1 through an Ethernet cable;

[0018] The fiber Bragg grating demodulator 2 transmits signal light to the two fiber FC jumper heads through the fiber coupler 3 respectively. The signal light is emitted from the inner end face of the fiber FC jumper head to the corresponding aluminum foil, and then reflected to the corresponding surface of the fiber FC jumper head. Part of the light returns to the fiber Bragg grating demodulator 2, and the other part of the light is reflected by the fiber FC jumper head to the corresponding aluminum foil and then reflected again; the light is reflected multiple times between the end faces of the two fiber FC jumper heads and the corresponding aluminum foil, forming two Fabry-Perot interferometer structures respectively, and the interference waves of the two Fabry-Perot interferometer structures meet at the fiber coupler 3 to form a composite vernier spectrum.

[0019] Preferably, the distance between the reflective surface of the first aluminum foil 10 and the inner end surface of the first optical fiber FC jumper head 12 is L1, and the distance between the reflective surface of the second aluminum foil 11 and the inner end surface of the second optical fiber FC jumper head 13 is L2, and L1 and L2 are not equal.

[0020] Preferably, the weight 9 is a square structure, and the top of the weight 9 is suspended on the top plate 5 by a first suspension rope 7 and a second suspension rope 8 of equal length.

[0021] Preferably, the two optical fiber FC jumper heads are respectively installed on two brackets, and the brackets are arranged on the base 6. Specifically, the first optical fiber FC jumper head 12 is installed on the first bracket 15, and the second optical fiber FC jumper head 13 is installed on the second bracket 16.

[0022] Preferably, the top plate 5 , the bracket and the base 6 are all connected and fixed to the back plate 14 .

[0023] In the present invention, the fiber coupler 3 is used to couple the interference waves of the two interferometer structures; the fiber grating demodulator 2 is used to transmit signal light through the fiber coupler 3 and demodulate the returned interference superposition spectrum; and the computer 1 is used to monitor the returned interference superposition spectrum.

[0024] In this embodiment, the fiber Bragg grating demodulator 2 is a Micron Optics Si255 with a resolution of 1pm, and is used to monitor the waveform of the output spectrum together with the computer 1. The fiber coupler 3 uses a 1×2 fiber coupler with a coupling ratio of 50:50. The end face reflectivity of the fiber FC jumper head is about 4%, and the reflectivity of the aluminum foil is about 8%. The initial placement distance of the fiber FC jumper head from the opposite surface side of the aluminum foil is about 1.039mm and 1.155mm. The lengths of the two suspension ropes 7 are both 10mm.

[0025] A method for measuring an inclination angle based on the inclination measuring device as described above, the method comprising:

[0026] Input signal light, the signal light reaches two fiber FC jumper heads respectively through the fiber coupler 3, the light is reflected multiple times between the end faces of the two fiber FC jumper heads and the corresponding aluminum foils, forming two Fabry-Perot interferometer structures, and the interference waves of the two interferometer structures meet at the fiber coupler 3 to form an interference superposition spectrum; the fiber Bragg grating demodulator 2 demodulates the interference superposition spectrum, and the interference superposition spectrum will produce a vernier effect in the tilting process to form an envelope, and the change in the tilt angle causes the cavity length of the Fabry-Perot interferometer structure at both ends to change, thereby causing the free spectral range of the envelope to change, and the wavelength at the envelope trough changes accordingly, and the computer 1 and the fiber Bragg grating demodulator 2 work together to monitor the change of the wavelength at the envelope trough, analyze the demodulation tilt angle information, and then draw the relationship curve between the wavelength and the tilt angle, so as to demodulate and obtain the tilt angle change information.

[0027] The test results show that the inclination angle measurement accuracy of the present invention is 0.1°, and the measurable inclination angle range is 0-2.5°.

[0028] In this embodiment, two Fabry-Perot interferometer structures are formed on both sides of the weight 9, wherein the signal light is reflected multiple times between the end face of the first optical fiber FC jumper head 12 and the corresponding first aluminum foil 10, forming a first Fabry-Perot interferometer structure, and the signal light is reflected multiple times between the end face of the second optical fiber FC jumper head 13 and the corresponding second aluminum foil 11, forming a second Fabry-Perot interferometer structure. When the optical fiber inclinometer module 4 is tilted by an external force, the weight 9 tilts under the action of gravity; since the two suspension ropes for suspending the weight 9 are exactly the same length, the aluminum foils on both sides of the weight 9 continue to be parallel to the end faces of the corresponding optical fiber FC jumper heads, and the distance between one group of aluminum foils and the corresponding optical fiber FC jumper heads increases, while the distance between the other group of aluminum foils and the corresponding optical fiber FC jumper decreases.

[0029] For a single Fabry-Perot cavity interferometer structure, the free spectral range FSR FP for:

[0030]

[0031] In formula (1), λ m is the wavelength of the trough of the resonant wave (in nm); m+1 is m The wavelength of the adjacent resonance wave is (in nm); λ is the optical wavelength (in nm); L is the cavity length (in mm). In this embodiment, L is the distance between the aluminum foil reflective surface and the corresponding optical fiber FC jumper head.

[0032] When the interference waves of the two Fabry-Perot interferometer structures meet in the fiber coupler 3, they will be superimposed to form an envelope, and the free spectral range FSR of the envelope is e for:

[0033]

[0034] In formula (1), FSR1 is the free spectral range of the first Fabry-Perot interferometer structure (in nm); FSR2 is the free spectral range of the second Fabry-Perot interferometer structure (in nm).

[0035] Wavelength at the envelope trough Changes to:

[0036]

[0037] In formula (3), M1 is the amplification factor of the first Fabry-Perot interferometer structure, which means the amplification factor of the sensing sensitivity when only a single Fabry-Perot interferometer participates; is the wavelength change of the interferometer wave of the first Fabry-Perot interferometer structure (in nm); M2 is the amplification factor of the second Fabry-Perot interferometer structure; is the wavelength change of the interferometer wave in the second Fabry-Perot interferometer structure (in nm).

[0038] In the traditional vernier effect, there is a sensing interferometer and a reference interferometer, so M1 and M2 are equal. In the present invention, both interferometers involved in the dynamic vernier effect are sensing interferometers, so the amplification factor is:

[0039]

[0040]

[0041] Therefore, for the dynamic cursor effect, the overall magnification M e for:

[0042]

[0043] In formulas (4) to (6), L1 is the distance between the first aluminum foil 10 and the first optical fiber FC jumper head 12 (in mm); L2 is the distance between the second aluminum foil 11 and the second optical fiber FC jumper head 13 (in mm).

[0044] It can be seen that the free spectral range of the envelope and the magnification of the sensitivity M e It is related to the cavity length of the two Fabry-Perot cavities (i.e., the distance from the aluminum foil reflective surface of the weight 9 to the end face of the corresponding optical fiber FC jumper head). When tilting occurs, under the influence of gravity, the weight 9 will move, and the distance between the aluminum foil reflective surface and the corresponding optical fiber FC jumper head will change. The distance between one set of aluminum foil reflective surfaces and the corresponding optical fiber FC jumper head will become shorter, while the distance between the other set of aluminum foil reflective surfaces and the corresponding optical fiber FC jumper head will become longer accordingly; the closer the cavity lengths of the two interference cavities are, the smaller the tilt angle is, the greater the magnification of the inclinometer is, and the more sensitive it is. The dynamic cursor occurs, and the free spectral range of the envelope changes, so that the wavelength at the envelope trough changes significantly. By monitoring the wavelength change of the envelope, the change information of the tilt angle can be demodulated.

[0045] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

Claims

1. A method for measuring inclination angle based on an inclination measuring device, characterized in that: The method is: Provided is a tilt measuring device, comprising a fiber inclinometer module, a fiber coupler, a fiber Bragg grating demodulator and a computer; the fiber inclinometer module comprises a top plate and a weight, the weight is suspended on the top plate, a first aluminum foil and a second aluminum foil are respectively pasted on both sides of the weight, a reflective surface of the first aluminum foil is arranged opposite to a first fiber FC jumper head; a reflective surface of the second aluminum foil is arranged opposite to a second fiber FC jumper head; Two optical fiber FC jumper heads are respectively connected to the input end of the optical fiber coupler, the output end of the optical fiber coupler is connected to the input end of the optical fiber Bragg grating demodulator, and the output end of the optical fiber Bragg grating demodulator is connected to the computer through an Ethernet cable; the optical fiber Bragg grating demodulator transmits signal light to the two optical fiber FC jumper heads through the optical fiber coupler, and the signal light is emitted to the aluminum foil through the inner end face of the optical fiber FC jumper head, and then reflected to the surface of the optical fiber FC jumper head. Part of the light returns to the optical fiber Bragg grating demodulator, and the other part of the light is reflected by the optical fiber FC jumper head, reflected to the corresponding aluminum foil, and then reflected again; The light is reflected multiple times between the end faces of the two fiber FC jumper heads and the corresponding aluminum foils, forming two Fabry-Perot interferometer structures respectively. The interference waves of the two Fabry-Perot interferometer structures meet at the fiber coupler to form a composite vernier spectrum. Input signal light, the signal light reaches two fiber FC jumper heads respectively through the fiber coupler, the light is reflected multiple times between the end faces of the two fiber FC jumper heads and the corresponding aluminum foils, forming two Fabry-Perot interferometer structures, the interference waves of the two interferometer structures meet at the fiber coupler to form a composite vernier spectrum, and the composite vernier spectrum is coupled in the fiber coupler to form an interference superposition spectrum; the fiber Bragg grating demodulator monitors the interference superposition spectrum, and the interference superposition spectrum will produce a vernier effect to form an envelope during the tilting process. The change in the tilt angle causes the cavity length of the Fabry-Perot interferometer structure at both ends to change, thereby causing the free spectral range of the envelope to change, and the wavelength at the envelope trough changes accordingly. The change in wavelength at the envelope trough is monitored by the computer and the fiber Bragg grating demodulator, the demodulation tilt angle information is analyzed, and then the relationship curve between the wavelength and the tilt angle is drawn, thereby demodulating the tilt angle change information.

2. The inclination angle measuring method according to claim 1, characterized in that: The distance between the reflective surface of the first aluminum foil and the inner end surface of the first optical fiber FC jumper head is L1, and the distance between the reflective surface of the second aluminum foil and the inner end surface of the second optical fiber FC jumper head is L2, and L1 and L2 are not equal.

3. The inclination angle measuring method according to claim 1, characterized in that: The weight is a square structure.

4. The inclination angle measuring method according to claim 1, characterized in that: The top of the heavy object is suspended on the top plate through a first suspension rope and a second suspension rope of equal length.

5. The inclination angle measuring method according to claim 4, characterized in that: Two optical fiber FC jumper heads are respectively installed on two brackets, and the brackets are arranged on the base.

6. The inclination angle measuring method according to claim 5, characterized in that: The top plate, the bracket and the base are all fixed on the back plate.

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