An EFPI strain sensor based on a collimated optical path

Abstract

The present invention provides an EFPI strain sensor based on a collimated optical path, which includes an EFPI structure disposed on the surface of a structure to be measured, an optical fiber collimator disposed on one side of the EFPI structure, an angle adjuster disposed on the input and output optical paths of the optical fiber collimator, and a demodulation terminal electrically connected to the optical fiber collimator. The optical fiber collimator is disposed on the input and output optical paths of the angle adjuster, and there is an optical path turning between the input and output optical paths of the optical fiber collimator and the input and output optical paths of the EFPI structure. By introducing a spatial collimated optical path, the present invention separates the sensitive structure and the transmission optical fiber of the traditional integrated-connected optical fiber EFPI strain sensor in space; by introducing an angle adjuster, the spatial collimated optical path has the ability of angle deflection, and further enables the sensitive structure and the transmission optical fiber to have the possibility of two-dimensional and three-dimensional layouts in space. The present invention can design and adjust the optical path according to specific installation conditions, meet the angle matching of the sensor and the optical fiber in space, and reduce the installation and wiring limitations of the sensor in a narrow space.

Description

Technical Field

[0001] The present invention relates to the technical field of measurement and testing, and particularly to an EFPI strain sensor based on a collimated optical path. Background Art

[0002] Strain measurement is an important part of structural state perception and evaluation, and is widely used in the state evaluation of many devices such as vehicles, aircraft, pipelines, etc., which is of great significance for device design and operation monitoring.

[0003] At present, commonly used strain sensors include resistance strain gauges, fiber Bragg grating strain sensors, fiber optic EFPI strain sensors, etc. Among them, the resistance strain gauge monitors strain according to the change in resistance value when the resistance wire deforms, and two electrical wires are required for signal measurement at a single measurement point. The fiber Bragg grating strain sensor uses the wavelength drift of the grating reflection for measurement, and multiple measurement points can be multiplexed on a single optical fiber. The fiber optic EFPI strain sensor adopts an interference measurement mechanism, and an EFPI cavity is formed by the fiber end face and the matching reflecting surface. The strain information is obtained by measuring the change in the EFPI cavity length through the fiber reflected optical signal. In the above sensors, signal transmission needs to rely on wires such as electrical wires or optical fibers, and the sensor and the wire are integrally connected.

[0004] In special application conditions, such as in the monitoring of engine rotors, blades or pipelines, the space is often very narrow and does not support wiring with a large radius of curvature, which poses a severe test for the routing of the sensor wires.

[0005] Therefore, a sensor that can be applied in a narrow space is needed. Summary of the Invention

[0006] The present invention is to solve the problem of the use of sensors in narrow spaces, and provides an EFPI strain sensor based on a collimated optical path. By introducing a spatial optical path and an angle adjuster, and adopting spatial optical path adjustment, the sensor and the optical fiber are separated in space, and the optical path can be designed and adjusted according to specific installation conditions to meet the angle matching between the sensor and the optical fiber in space, effectively reducing the installation wiring limitation of sensors in narrow spaces.

[0007] The present invention provides an EFPI strain sensor based on a collimated optical path. The EFPI strain sensor separates the sensor sensitive structure and the transmission optical fiber in space to form a spatial collimated optical path, and an angle adjuster is arranged in the spatial collimated optical path to enable the spatial collimated optical path to have the ability of angle deflection.

[0008] An EFPI strain sensor based on a collimated optical path according to the present invention, as a preferred embodiment, includes an EFPI structure disposed on the surface of a structure to be measured, an optical fiber collimator disposed on one side of the EFPI structure, an angle adjuster disposed on the input and output optical paths of the optical fiber collimator, and a demodulation terminal electrically connected to the optical fiber collimator. The optical fiber collimator is disposed on the input and output optical paths of the angle adjuster, and there is an optical path turn between the input and output optical paths of the optical fiber collimator and the input and output optical paths of the EFPI structure;

[0009] The EFPI structure is used to sense the strain change of the structure to be measured, the optical fiber collimator is used to collimate the optical signal or receive the optical signal, the angle adjuster is used to match the spatial position between the optical fiber collimator and the EFPI structure, and the demodulation terminal is used to emit the optical signal and perform signal processing according to the returned optical signal;

[0010] The optical signal output by the demodulation terminal is collimated by the optical fiber collimator and then output to the angle adjuster in the form of a parallel light beam. The angle adjuster deflects the optical signal and injects it into the EFPI structure; the EFPI structure outputs the optical signal to the angle adjuster, the angle adjuster deflects the optical signal and injects it into the optical fiber collimator, and the optical fiber collimator collects the optical signal and outputs it to the demodulation terminal, and the demodulation terminal performs analysis to obtain the surface strain of the structure to be measured.

[0011] An EFPI strain sensor based on a collimated optical path according to the present invention, as a preferred embodiment, one side of the EFPI structure adjacent to the optical fiber collimator is made of an optically transparent material;

[0012] The EFPI structure includes an EFPI cavity, the EFPI cavity includes at least two interference interfaces and the interference interfaces have optical cleanliness, and the EFPI cavity is perpendicular to the surface of the structure to be measured;

[0013] The EFPI structure is fixed on the surface of the structure to be measured, and the distance between the interference interfaces changes with the strain of the structure to be measured;

[0014] The optical fiber collimator is connected to the demodulation terminal through a pigtail or a fiber optic patch cord;

[0015] The angle adjuster can change the angle of the incident collimated light beam and then emit it. The included angle between the incident light and the emitted light of the angle adjuster is greater than 0° and less than 180°; the included angle between the angle adjuster and the surface of the structure to be measured is greater than 0° and less than 180°.

[0016] The demodulation terminal identifies the EFPI cavity length according to the characteristic parameters of the optical signal reflected and returned by the EFPI structure, and then combines the installation parameters of the EFPI structure to obtain the surface strain of the structure to be measured.

[0017] An EFPI strain sensor based on a collimated optical path according to the present invention, as a preferred embodiment, the fixing method of the EFPI structure on the surface of the structure to be measured is any one of the following: bonding or welding or screwing;

[0018] The EFPI structure is any one of the following: quartz, sapphire, and SiC;

[0019] The angle adjuster can change the vertically incident light beam into a parallel outgoing light beam through a 45-degree metal reflecting surface;

[0020] The method for identifying the EFPI cavity length is to use a broadband light source to perform Fourier transform on the reflected light signal spectrum to obtain the interference spectrum period information, and then obtain the EFPI cavity length.

[0021] In a preferred embodiment, the EFPI strain sensor based on a collimated optical path according to the present invention includes a first rectangular parallelepiped block and a second rectangular parallelepiped block arranged adjacent to each other in the same direction. The first rectangular parallelepiped block includes a left surface and a right surface of the first rectangular parallelepiped block, and the second rectangular parallelepiped block includes a left surface and a right surface of the second rectangular parallelepiped block. The left surface of the first rectangular parallelepiped block, the right surface of the first rectangular parallelepiped block, the left surface of the second rectangular parallelepiped block, and the right surface of the second rectangular parallelepiped block are all perpendicular to the lower surfaces of the first rectangular parallelepiped block and the second rectangular parallelepiped block. The left surface of the first rectangular parallelepiped block and the right surface of the second rectangular parallelepiped block are both roughened, and the right surface of the first rectangular parallelepiped block and the left surface of the second rectangular parallelepiped block are both polished smoothly to form a set of interference interfaces and form an EFPI cavity.

[0022] In a preferred embodiment, the left surface of the first rectangular parallelepiped block, the right surface of the first rectangular parallelepiped block, the left surface of the second rectangular parallelepiped block, and the right surface of the second rectangular parallelepiped block all receive the light signal output after the angle turning by the angle adjuster to generate a reflected light signal, and then enter the demodulation terminal after being deflected by the angle adjuster and collected by the fiber collimator.

[0023] In a preferred embodiment, the reflection spectrum of the EFPI strain sensor based on a collimated optical path according to the present invention is:

[0024] I(v) = C0 + C1cos(4πdv);

[0025] Wherein, C0 and C1 are both constant terms, υ is the wave number, the relationship between υ and the wavelength λ is υ = 1 / λ, and d is the EFPI cavity length.

[0026] In a preferred embodiment, the reflection spectrum after filtering the DC component of the EFPI strain sensor based on a collimated optical path according to the present invention is:

[0027] I(v) = ∫P(f)exp(i2πfv)df;

[0028] Wherein, P is the frequency spectrum distribution corresponding to the interference spectrum, and f is the frequency.

[0029] In a preferred embodiment of the EFPI strain sensor based on a collimated optical path according to the present invention, f = 2d.

[0030] In a preferred embodiment of the EFPI strain sensor based on a collimated optical path according to the present invention, a Fourier transform is performed on the reflected spectrum after filtering out the DC component to obtain the distribution of spectral energy with respect to the EFPI cavity length.

[0031] In a preferred embodiment of the EFPI strain sensor based on a collimated optical path according to the present invention, the strain ε is:

[0032]

[0033] where Δd is the change in the EFPI cavity length, L in is the inner boundary distance after the EFPI structure is installed, and L out is the outer boundary distance after the EFPI structure is installed.

[0034] An EFPI strain sensor based on a collimated optical path includes: an optical fiber collimator for realizing a collimated optical path; an EFPI structure for sensing the strain change of a structure to be measured; an angle adjuster for matching the spatial positions between the optical fiber collimator and the EFPI structure; and a demodulation terminal for emitting an optical signal and performing signal processing based on the returned optical signal.

[0035] One side of the EFPI structure adjacent to the optical fiber collimator should be made of an optically transparent material, which can be but is not limited to quartz, sapphire, or SiC.

[0036] The EFPI structure has a set of interference interfaces forming an EFPI cavity. This interface has good optical cleanliness and is perpendicular to the surface of the structure to be measured at its installation position.

[0037] The EFPI structure is installed on the surface of the structure to be measured by means of bonding, welding, screwing, etc. The interference interface distance (i.e., the EFPI cavity length) changes with the change of the structure strain. The optical fiber collimator is connected to the demodulation terminal through a pigtail or a fiber optic patch cord. It can convert the optical signal output by the demodulation terminal through the optical fiber into a collimated parallel beam, or collect the optical signal and transmit it to the demodulation terminal through a pigtail or a fiber optic patch cord.

[0038] The angle adjuster can change the angle of the incident collimated light beam, including but not limited to changing the vertically incident light beam to a parallel incident light beam through a 45-degree metal reflection surface.

[0039] The demodulation terminal can identify the EFPI cavity length according to the characteristic parameters of the optical signal reflected by the EFPI structure, including but not limited to using a broadband light source, performing a Fourier transform on the reflected optical signal spectrum to obtain the interference spectrum period information, and then obtaining the EFPI cavity length.

[0040] The demodulation terminal can obtain the surface strain of the structure to be measured by measuring the cavity length of the EFPI and matching with the installation parameters of the EFPI structure.

[0041] The present invention discloses a non-intrinsic Fabry-Perot interferometer (EFPI) strain sensor based on a collimated optical path. By introducing a spatial collimated optical path, the sensitive structure and the transmission optical fiber of the traditional integrated fiber EFPI strain sensor are separated in space. At the same time, by introducing an angle regulator, the spatial collimated optical path has the ability of angular deflection, and thus the sensitive structure and the transmission optical fiber have the possibility of two-dimensional and three-dimensional layout in space. The sensor can design and adjust the optical path according to the specific installation conditions to meet the angular matching between the sensor and the optical fiber in space, and effectively reduce the installation and wiring limitations of the sensor in narrow spaces.

[0042] By introducing a spatial optical path and an angle regulator, the present invention separates the sensitive structure of the sensor from the transmission optical fiber in space and supports different angle combinations, effectively expanding the installation and application range of the sensor.

[0043] The present invention has the following advantages:

[0044] By introducing a spatial optical path design, the present invention separates the sensitive structure of the sensor from the transmission optical fiber in space, and thus can effectively expand the installation and use conditions of the sensor, supporting the strain measurement requirements in narrow spaces and special working conditions. Description of the Drawings

[0045] Figure 1 Schematic structural diagrams of Embodiments 1-2 of an EFPI strain sensor based on a collimated optical path;

[0046] Figure 2 Typical interference spectrogram output by an EFPI strain sensor based on a collimated optical path;

[0047] Figure 3 For an EFPI strain sensor based on a collimated optical path Figure 2 Spectral frequency distribution obtained by Fourier transform of the shown interference spectrum;

[0048] Figure 4 Rectangular block paste-type installation strain transfer model diagram of an EFPI strain sensor based on a collimated optical path;

[0049] Figure 5 Schematic structural diagram of Embodiment 3 of an EFPI strain sensor based on a collimated optical path.

[0050] Reference Signs:

[0051] 1. EFPI structure; 11. First rectangular parallelepiped block; 111. Left surface of the first rectangular parallelepiped block; 112. Right surface of the first rectangular parallelepiped block; 12. Second rectangular parallelepiped block; 121. Left surface of the second rectangular parallelepiped block; 122. Right surface of the second rectangular parallelepiped block; 2. Fiber optic collimator; 3. Angle adjuster; 4. Demodulation terminal. Detailed implementation mode

[0052] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments.

[0053] Embodiment 1

[0054] As Figure 1 shown, an EFPI strain sensor based on a collimated optical path separates the sensor sensitive structure and the transmission optical fiber spatially to form a spatial collimated optical path, and an angle adjuster is arranged in the spatial collimated optical path to enable the spatial collimated optical path to have an angle deflection ability;

[0055] The EFPI strain sensor includes an EFPI structure 1 arranged on the surface of the structure to be measured, a fiber optic collimator 2 arranged on one side of the EFPI structure 1, an angle adjuster 3 arranged on the input and output optical paths of the fiber optic collimator 1, and a demodulation terminal 4 electrically connected to the fiber optic collimator 2. The fiber optic collimator 2 is arranged on the input and output optical paths of the angle adjuster 3, and there is an optical path turn between the input and output optical paths of the fiber optic collimator 2 and the input and output optical paths of the EFPI structure 1;

[0056] The EFPI structure 1 is used to sense the strain change of the structure to be measured, the fiber optic collimator is used to collimate the optical signal or receive the optical signal, the angle adjuster 3 is used to match the spatial position between the fiber optic collimator 2 and the EFPI structure 1, and the demodulation terminal 4 is used to emit the optical signal and perform signal processing according to the returned optical signal;

[0057] The optical signal output by the demodulation terminal 4 is collimated by the fiber optic collimator 2 and then output to the angle adjuster 3 in the form of a parallel light beam. The angle adjuster 3 deflects the optical signal and then injects it into the EFPI structure 1; the EFPI structure 1 outputs the optical signal to the angle adjuster 3, the angle adjuster 3 deflects the optical signal and then injects it into the fiber optic collimator 2, the fiber optic collimator 2 collects the optical signal and then outputs it to the demodulation terminal 4, and the demodulation terminal 4 performs analysis to obtain the surface strain of the structure to be measured;

[0058] One side of the EFPI structure 1 adjacent to the fiber optic collimator 2 is composed of an optically transparent material;

[0059] The EFPI structure 1 includes an EFPI cavity. The EFPI cavity includes at least two interference interfaces and the interference interfaces have optical cleanliness. The EFPI cavity is perpendicular to the surface of the structure to be measured;

[0060] The EFPI structure 1 is fixed on the surface of the structure to be measured, and the distance between the interference interfaces changes with the strain of the structure to be measured;

[0061] The fiber optic collimator 2 is connected to the demodulation terminal 4 through a pigtail or a fiber optic patch cord;

[0062] The angle adjuster 3 can change the angle of the incident collimated light beam and then emit it. The included angle between the incident light and the emitted light of the angle adjuster 3 is greater than 0° and less than 180°;

[0063] The demodulation terminal 4 identifies the EFPI cavity length according to the characteristic parameters of the optical signal reflected back by the EFPI structure 1, and then obtains the surface strain of the structure to be measured by combining the installation parameters of the EFPI structure 1;

[0064] The fixing method of the EFPI structure 1 to the surface of the structure to be measured is any one of the following: bonding, welding or screwing;

[0065] The EFPI structure 1 is any one of the following: quartz, sapphire and SiC;

[0066] The angle adjuster 3 can change the vertically incident light beam into a parallel emitted light beam through a 45-degree metal reflecting surface;

[0067] The method for identifying the EFPI cavity length is to use a broadband light source to perform Fourier transform on the reflected optical signal spectrum to obtain the interference spectrum period information, and then obtain the EFPI cavity length;

[0068] The EFPI structure 1 includes a first rectangular parallelepiped block 11 and a second rectangular parallelepiped block 12 arranged adjacent to each other in the same direction. The first rectangular parallelepiped block 11 includes a left surface 111 of the first rectangular parallelepiped block and a right surface 112 of the first rectangular parallelepiped block. The second rectangular parallelepiped block 12 includes a left surface 121 of the second rectangular parallelepiped block and a right surface 122 of the second rectangular parallelepiped block. The left surface 111 of the first rectangular parallelepiped block, the right surface 112 of the first rectangular parallelepiped block, the left surface 121 of the second rectangular parallelepiped block, and the right surface 122 of the second rectangular parallelepiped block are all perpendicular to the lower surfaces of the first rectangular parallelepiped block 11 and the second rectangular parallelepiped block 12. The left surface 111 of the first rectangular parallelepiped block and the right surface 122 of the second rectangular parallelepiped block are both roughened. The right surface 112 of the first rectangular parallelepiped block and the left surface 121 of the second rectangular parallelepiped block are both polished smoothly to form a set of interference interfaces and form an EFPI cavity;

[0069] The left surface 111 of the first cuboid block, the right surface 112 of the first cuboid block, the left surface 121 of the second cuboid block, and the right surface 122 of the second cuboid block all receive the optical signals output after being angularly turned by the angle adjuster 3 to generate reflected optical signals, and then enter the demodulation terminal 4 after being deflected by the angle adjuster 3 and collected by the fiber collimator 2;

[0070] The reflection spectrum is:

[0071] I(v) = C0 + C1cos(4πdv);

[0072] Among them, C0 and C1 are both constant terms, υ is the wave number, the relationship between υ and the wavelength λ is υ = 1 / λ, and d is the cavity length of the EFPI cavity;

[0073] The reflection spectrum after filtering the DC component is:

[0074] I(v) = ∫P(f)exp(i2πfv)df;

[0075] Among them, P is the frequency spectrum distribution corresponding to the interference spectrum, and f is the frequency;

[0076] f = 2d;

[0077] Perform Fourier transform on the reflection spectrum after filtering the DC component to obtain the distribution of the spectral energy with respect to the EFPI cavity length;

[0078] The strain ε is:

[0079]

[0080] Among them, Δd is the change in the EFPI cavity length, and L in is the inner boundary distance after the EFPI structure 1 is installed, that is, L in is the distance between the right surface 112 of the first cuboid block and the left surface 121 of the second cuboid block, and L out is the outer boundary distance after the EFPI structure 1 is installed, that is, L out is the distance between the left surface 111 of the first cuboid block and the right surface 122 of the second cuboid block.

[0081] Embodiment 2

[0082] An EFPI strain sensor based on a collimated optical path. In this embodiment, the EFPI strain sensor is as Figure 1As shown in the figure, it includes an EFPI structure 1, an optical fiber collimator 2, an angle adjuster 3, and a demodulation terminal 4. Among them, the EFPI structure 1 is composed of a cuboid quartz block 11 and a cuboid quartz block 12. The left surface A, the right surface B, the left surface C, and the right surface D of the quartz block 11 are all perpendicular to the lower surface. Among them, the surfaces A and D have been roughened, and the surfaces B and C are polished smoothly to form a set of interference interfaces to form an EFPI cavity. The angle adjuster 3 is a 45-degree isosceles triangle block, and the long side plane is silver-plated to form a reflection interface.

[0083] The EFPI structure 1 and the angle adjuster 3 are installed on the surface of the metal plate 5 to be measured by gluing. The optical fiber collimator 2 is fixed directly above the angle adjuster 3 through a bracket, and its pigtail is connected to the demodulation terminal 4. The demodulation terminal 4 outputs a broadband optical signal of 1530 - 1580 nm. After passing through the optical fiber collimator 2, it is emitted in the form of a parallel light beam to the reflection surface of the angle adjuster 3, and after being deflected by 90 degrees, it is incident on the EFPI structure 1. The four reflection surfaces A, B, C, and D of the EFPI structure 1 will all generate reflected optical signals. After being deflected by the angle adjuster 3 and collected by the optical fiber collimator, they enter the demodulation terminal 4.

[0084] Since the surfaces A and D have been roughened, only the reflected optical signals from the surfaces B and C can form interference. For a low-reflectivity surface, its interference can be treated as two-beam interference. The typical reflection spectrum of the EFPI strain sensor obtained by the demodulation terminal 4 is expressed by formula (1), as Figure 2 shown.

[0085] I(v) = C0 + C1cos(4πdv) (1)

[0086] Where C0 and C1 are both constant terms, υ is the wave number, and its relationship with the wavelength λ is υ = 1 / λ, and d is the cavity length of the EFPI cavity. After filtering out the DC component, the above formula can be written as:

[0087] I(v) = ∫P(f)exp(i2πfv)df (2)

[0088] Where P is the frequency spectrum distribution corresponding to the interference spectrum, f is the frequency, and from formula (3), it can be known that f = 2d. After filtering out the DC component, by performing a Fourier transform on the above spectrum, the distribution of the spectral energy with respect to the EFPI cavity length can be obtained, as Figure 3 shown. According to the abscissa where the peak is located in the figure, the corresponding EFPI cavity length can be obtained.

[0089] On the other hand, since both the cuboid quartz blocks 11 and 12 in the EFPI structure 1 are adhesively connected to the metal plate 5 to be measured through glue, its strain transfer model is as Figure 4 shown and can be given by formula (3).

[0090]

[0091] where Δd is the change in the EFPI cavity length, and L in and L out are respectively the inner boundary distance and the outer boundary distance after the installation of the EFPI structure 1. Substituting the change in the EFPI cavity length into formula (3), the corresponding strain information can be obtained to achieve strain measurement.

[0092] Embodiment 3:

[0093] An EFPI strain sensor based on a collimated optical path, as Figure 5 shown, includes an EFPI structure 1, an optical fiber collimator 2, an angle adjuster 3, and a demodulation terminal 4. The EFPI structure 1, the optical fiber collimator 2, and the demodulation terminal 4 are all the same as those in Embodiment 1, except that the angle adjuster 3 is an equilateral triangle quartz block, and the interface adjacent to the EFPI structure 1 is formed into a reflecting surface through gold plating treatment. The EFPI structure 1 and the angle adjuster 3 are adhesively installed on the surface of the metal plate 5 to be measured. The optical fiber collimator 2 is located above the EFPI structure 1, and its optical axis forms a 60-degree angle with the upper surface of the EFPI structure 1. After the optical signal emitted by the demodulation terminal 4 passes through the optical fiber collimator 2 for the metal to be measured, it is incident on the reflecting interface of the angle adjuster 3 and is converted into a collimated light beam perpendicular to the reflecting surface of the EFPI structure 1 and then incident on the EFPI structure 1. According to the principle of reversibility of the optical path, the reflected optical signal of the EFPI structure 1 is converted by the angle adjuster 3 and then incident on the optical fiber collimator 2 and then enters the demodulation terminal 4. The signal processing process of the demodulation terminal 4 is the same as that in Embodiment 1 and will not be elaborated here.

[0094] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and should be covered within the protection scope of the present invention.

Claims

1. An EFPI strain sensor based on a collimated optical path, characterized in that: The sensor sensitive structure and the transmission optical fiber are spatially separated to form a spatial collimated optical path, and an angle adjuster is arranged in the spatial collimated optical path to enable the spatial collimated optical path to have the ability of angle deflection; It includes an EFPI structure (1) arranged on the surface of the structure to be measured, an optical fiber collimator (2) arranged on one side of the EFPI structure (1), an angle adjuster (3) arranged on the input and output optical paths of the optical fiber collimator (1), and a demodulation terminal (4) electrically connected to the optical fiber collimator (2). The optical fiber collimator (2) is arranged on the input and output optical paths of the angle adjuster (3), and there is an optical path turning between the input and output optical paths of the optical fiber collimator (2) and the input and output optical paths of the EFPI structure (1); The EFPI structure (1) is used to sense the strain change of the structure to be measured, the optical fiber collimator is used to collimate optical signals or receive optical signals, the angle adjuster (3) is used to match the spatial positions between the optical fiber collimator (2) and the EFPI structure (1), and the demodulation terminal (4) is used to emit optical signals and perform signal processing according to the returned optical signals; The optical signal output by the demodulation terminal (4) is collimated by the optical fiber collimator (2) and then output to the angle adjuster (3) in the form of a parallel light beam. The angle adjuster (3) deflects the optical signal and injects it into the EFPI structure (1); the EFPI structure (1) outputs an optical signal to the angle adjuster (3), the angle adjuster (3) deflects the optical signal and injects it into the optical fiber collimator (2), the optical fiber collimator (2) collects the optical signal and then outputs it to the demodulation terminal (4), and the demodulation terminal (4) performs analysis to obtain the surface strain of the structure to be measured; Strain is as follows: ； Among them, Δ d is the change in the EFPI cavity length, L in is the inner boundary distance after the installation of the EFPI structure (1), L out is the outer boundary distance after the installation of the EFPI structure (1).

2. The EFPI strain sensor based on a collimated optical path according to claim 1, characterized in that: One side of the EFPI structure (1) adjacent to the optical fiber collimator (2) is made of an optically transparent material; The EFPI structure (1) includes an EFPI cavity. The EFPI cavity includes at least two interference interfaces and the interference interfaces have optical cleanliness. The EFPI cavity is perpendicular to the surface of the structure to be measured; The EFPI structure (1) is fixed on the surface of the structure to be measured, and the distance between the interference interfaces changes with the strain of the structure to be measured; The optical fiber collimator (2) is connected to the demodulation terminal (4) through a pigtail or a fiber optic patch cord; The angle adjuster (3) can change the angle of the incident collimated light beam and then emit it. The included angle between the incident light and the emitted light of the angle adjuster (3) is greater than 0° and less than 180°; The demodulation terminal (4) performs EFPI cavity length identification according to the characteristic parameters of the optical signal reflected and returned by the EFPI structure (1), and then combines the installation parameters of the EFPI structure (1) to obtain the surface strain of the structure to be measured.

3. The EFPI strain sensor based on a collimated optical path according to claim 2, characterized in that: The fixing method of the EFPI structure (1) on the surface of the structure to be measured is any one of the following: bonding, welding or screwing; The EFPI structure (1) is any one of the following: quartz, sapphire and SiC; The angle adjuster (3) can change the vertically incident light beam to a parallel emitted light beam through a 45-degree metal reflecting surface; The method for identifying the EFPI cavity length is to use a broadband light source to perform Fourier transform on the reflection light signal spectrum to obtain the interference spectrum period information, and then obtain the EFPI cavity length.

4. The EFPI strain sensor based on a collimated optical path according to claim 2, characterized in that: The EFPI structure (1) includes a first cuboid block (11) and a second cuboid block (12) adjacent to each other in the same direction. The first cuboid block (11) includes a left surface (111) of the first cuboid block and a right surface (112) of the first cuboid block. The second cuboid block (12) includes a left surface (121) of the second cuboid block and a right surface (122) of the second cuboid block. The left surface (111) of the first cuboid block, the right surface (112) of the first cuboid block, the left surface (121) of the second cuboid block, and the right surface (122) of the second cuboid block are all perpendicular to the lower surfaces of the first cuboid block (11) and the second cuboid block (12). The left surface (111) of the first cuboid block and the right surface (122) of the second cuboid block are both roughened. The right surface (112) of the first cuboid block and the left surface (121) of the second cuboid block are both polished smoothly to form a set of interference interfaces and form an EFPI cavity.

5. The EFPI strain sensor based on a collimated optical path according to claim 4, characterized in that: The left surface (111) of the first cuboid block, the right surface (112) of the first cuboid block, the left surface (121) of the second cuboid block, and the right surface (122) of the second cuboid block all generate reflection light signals after receiving the light signals output after being turned by the angle of the angle adjuster (3), and then enter the demodulation terminal (4) after being deflected by the angle adjuster (3) and collected by the fiber collimator (2).

6. The EFPI strain sensor based on a collimated optical path according to claim 3, characterized in that: The reflection spectrum is: ； wherein, both C0 and C1 are constant terms, υ is the wave number, and the relationship between υ and the wavelength λ is υ = 1 / λ, d is the cavity length of the EFPI cavity; The reflection spectrum after filtering out the DC component is: ； Among them, P is the frequency spectrum distribution corresponding to the interference spectrum, f is the frequency.

7. An EFPI strain sensor based on a collimated optical path according to claim 6, characterized in that: f =2 d。 8. The EFPI strain sensor based on a collimated optical path according to claim 2, characterized in that: Perform Fourier transform on the reflection spectrum after filtering out the DC component to obtain the distribution of spectral energy with respect to the EFPI cavity length.

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