Optical fiber displacement sensing probe of Michelson interferometer based on C-lens

Abstract

The invention discloses an optical fiber displacement sensing probe of a Michelson interferometer based on C-lens, which adopts fiber core offset welding and contrast to generate a measuring arm and a reference arm, so that the optical fiber displacement sensing probe has the advantages that the structure is more compact and simpler, the cost is lower, the interference influence of an external environment is smaller, and the like. Measurement of tiny slits, inner walls and cracks can be realized, and related changes such as the distance, the shape and the displacement of a related object to be measured can be obtained.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber measurement technology, and more specifically to an optical fiber displacement sensing probe of a Michelson interferometer based on a C-lens. Background Art

[0002] Displacement measurement plays a very important role in the fields of medical treatment, ultra-precision manufacturing, aerospace, etc. Compared with inductive displacement sensors, photoelectric displacement sensors and capacitive displacement sensors, optical fiber displacement sensors have high precision, small size, strong anti-electromagnetic interference ability and large measurement range.

[0003] Fiber optic sensor probes are widely used in the measurement field. They use the high sensitivity of fiber optic technology and its superior anti-electromagnetic interference ability to accurately measure the displacement, distance, etc. of the object to be measured. For example, in the aerospace field, fiber optic displacement probes can monitor the slight deformation of certain important parts and are used to monitor the structural changes of aircraft during flight. In structural health monitoring, they are used to monitor the displacement and deformation of bridges, tunnels, and buildings to help evaluate the safety of structures and ensure the stability of buildings and infrastructure. In the manufacturing industry, in robots and automated production lines, they are used to accurately measure the position and movement of workpieces, measure the displacement of products during the production process, and ensure that products meet design standards. Fiber optic displacement sensor probes have become an indispensable tool in modern measurement technology due to their high sensitivity, anti-electromagnetic interference, small size, and easy distribution.

[0004] Fiber optic displacement sensor probes have been widely used in various industries, but in some specific scenarios, the probes need to have specific structures and measurement ranges to measure in some tiny slits, inner walls and cracks, so as to obtain the distance, shape and other properties of the object to be measured. This paper innovatively proposes a fiber optic displacement sensor probe based on a C-lens Michelson interferometer. This probe uses a special optical path to achieve measurement in some narrow environments. It has the advantages of high sensitivity, simple and compact structure, less affected by external interference, and can measure in some narrow occasions. Summary of the invention

[0005] The purpose of the present invention is to overcome the deficiencies of the prior art and to provide an optical fiber displacement sensing probe which has high sensitivity, simple and compact structure, is less affected by external interference, and can perform measurements on specific occasions.

[0006] To solve the above problems, the technical solution of the present invention is as follows:

[0007] A fiber optic displacement sensing probe of a Michelson interferometer based on a C-lens, characterized in that it consists of a light source (1), a single-mode optical fiber (2), a high-reflection film (3), a matte paint (4), a single-mode optical fiber (5), an anti-reflection film (6), an anti-reflection film (7), a C-lens (8) and an air gap (9). The cores of the single-mode optical fiber (2) and the single-mode optical fiber (5) are offset and then fused; the end faces of the single-mode optical fiber (2) and the single-mode optical fiber (5) that are not in contact are coated with a high-reflection film (3); the end faces of the single-mode optical fiber (5) and the single-mode optical fiber (2) that are not in contact are coated with a matte paint (4); the output end face of the single-mode optical fiber (5) has an inclination angle of 8°; the output end face of the single-mode optical fiber (5) has an anti-reflection film (6); the incident end face of the C-lens (8) has an anti-reflection film (7); there is an air gap (9) between the single-mode optical fiber (5) and the C-lens (8); the incident end face of the C-lens (8) has an inclination angle of 8°.

[0008] The working principle of a fiber optic displacement sensing probe of a Michelson interferometer based on a C-lens is as follows: a light source (1) is incident from a single-mode optical fiber (2), and there is a core offset between the single-mode optical fiber (2) and the single-mode optical fiber (5), generating a measuring arm and a reference arm. Part of the light is incident into the single-mode optical fiber (5) in proportion to the offset area to generate measuring light, and the other part is reflected by a high-reflection film (3) to generate reference light. The light beam transmitted to the single-mode optical fiber (5) passes through an anti-reflection film (6), an air gap (9) and an anti-reflection film (7), and is then transmitted to a C-lens (8). The measuring light is collimated by changing the parameters of the C-lens (8) to obtain a required working distance, and is then transmitted to a surface to be measured through the C-lens (8) for reflection. The measuring light reflected from the surface to be measured to the single-mode optical fiber (2) interferes with the other part of the reference light that passes through the high-reflection film (3) in the single-mode optical fiber (2).

[0009] The measurement principle of this optical fiber displacement sensor probe is:

[0010] The light intensity output by the light source is I, and the light intensity of the reference light reflected by the high-reflection film (3) and the light intensity of the measurement light transmitted to the single-mode optical fiber (5) can be expressed as follows:

[0011] I 1 =S 1 I

[0012] I 2 =S 2 I

[0013] In the above formula, S 1 is the ratio of the core fusion area of ​​the single-mode optical fiber (2) and the core area of ​​the single-mode optical fiber (5), S 2 The area of ​​the single-mode optical fiber (2) coated with a high-reflection film (3).

[0014] The optical power coupling efficiency of the measurement light transmitted into the single-mode optical fiber (5) and reflected back to the single-mode optical fiber (5) by the surface to be measured is η. At this time, η can be expressed as follows:

[0015]

[0016] In the above formula, E 0 is the amplitude of the measurement light emitted from the single-mode optical fiber (5), k is the wave number, and w 0 is the spot radius of the measurement light emitted from the single-mode optical fiber (5), E s (x, y, z) is the light field distribution of the light emitted from the output end face of the single-mode optical fiber (5); E r * (x', y', z') is the conjugate light field distribution of the measurement light reflected from the surface to be measured to the output end face of the single-mode optical fiber (5), which can be expressed as follows:

[0017]

[0018]

[0019] In the above formula, L is the optical path of the measuring light emitted from the output end face of the single-mode optical fiber (5) and reflected back to the output end face of the single-mode optical fiber (5) through the end face to be measured, f is the confocal distance, and the relationship between the established coordinate systems is as follows, θ is the inclination angle of the surface to be measured, y=y′, w(L) is the spot radius of the measurement light reflected back to the exit end face of the single-mode optical fiber (5), and R(L) is the curvature radius of the reflected light reflected back to the exit end face of the single-mode optical fiber (5), which can be expressed as follows:

[0020] L=2L f +2n c L c +2d

[0021]

[0022]

[0023] In the above formula, L f is the length of the air gap (9), n c is the refractive index of C-lens (8), L c is the length of C-lens (8), d is the distance from C-lens (8) to the surface to be measured, i.e., the working distance, λ is the wavelength of the light output by the light source (1), ABCD are the elements of the ray matrix M of the measurement light after it is emitted from the output end face, reflected by the surface to be measured, and returned to the output end face, which are respectively expressed as follows:

[0024]

[0025] In the above formula, n air is the refractive index of air, n c is the refractive index of C-lens (8). When the distance between the single-mode optical fiber (5) and C-lens (8) is very small, the ray matrix of C-lens (8) can be written as the ray matrix without tilt angle.

[0026] The light intensity of the measurement light in the single-mode optical fiber (5) reflected by the surface to be measured and transmitted to the single-mode optical fiber (2) can be expressed as follows:

[0027] I 2r =S 2 2 Iη

[0028] I 1 and I 2r Interference occurs in the single-mode optical fiber (2), forming an interference light intensity I int， It can be expressed as follows:

[0029]

[0030] In the above formula, is the phase difference between the measurement light and the reference light reflected back to the single-mode optical fiber (2) by the surface to be measured, which can be expressed as follows:

[0031]

[0032] In the above formula, l smf is the length of the single-mode optical fiber (5).

[0033] This solution uses a core offset method to generate reference light and measurement light. Different from the traditional Michelson interferometer, the optical fiber displacement sensing probe has a compact and simple design structure, low cost, high sensitivity, and is less affected by external environmental interference. It can measure tiny slits, inner walls, and cracks to obtain relevant changes in the distance, shape, displacement, etc. of the object to be measured. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of the structure of a fiber optic displacement sensing probe based on a C-lens Michelson interferometer.

[0035] Figure 2 This is a schematic diagram of the structure of an optical fiber displacement sensor probe.

[0036] Among them: 1. light source; 2. single-mode optical fiber; 3. high-reflection film; 4. matte paint; 5. single-mode optical fiber; 6. anti-reflection film; 7. anti-reflection film; 8. C-lens; 9. air gap; 10. 45° reflector; 11. matte paint. DETAILED DESCRIPTION

[0037] The drawings are merely illustrative and should not be construed as limiting the present patent;

[0038] In order to illustrate the implementation cases, some components in the drawings are partially enlarged or reduced, and do not represent the actual sizes of actual products.

[0039] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments:

[0040] Example 1

[0041] Combined with Figure 1 The optical fiber displacement sensor probe includes a light source 1, a single-mode optical fiber 2, a high-reflection film 3, a matte paint 4, a single-mode optical fiber 5, an anti-reflection film 6, an anti-reflection film 7, a C-lens 8 and an air gap 9;

[0042] The specific working principle in this embodiment is as follows:

[0043] Light source 1 enters single-mode optical fiber 2. Since the cores of single-mode optical fiber 2 and single-mode optical fiber 5 are offset and then fused, a measuring arm and a reference arm are formed. Part of the light is reflected by the high-reflection film 3 to generate reference light, and the other part of the light is incident on the single-mode optical fiber 5 in proportion to the offset area to generate measuring light. The light beam transmitted to the single-mode optical fiber 5 passes through the anti-reflection film 6, the air gap 9 and the anti-reflection film 7, and is then transmitted to the C-lens 8. The C-lens 8 focuses the measuring light, which is transmitted to the surface to be measured through the C-lens 8 and reflected. The measuring light reflected from the surface to be measured to the single-mode optical fiber 5 interferes with the reference light in the single-mode optical fiber 2.

[0044] Example 2

[0045] Combined with Figure 2 The optical fiber displacement sensor probe includes a light source 1, a single-mode optical fiber 2, a high-reflection film 3, a matte paint 4, a single-mode optical fiber 5, an anti-reflection film 6, an anti-reflection film 7, a C-lens 8, an air gap 9, a 45° reflector 10, and a matte paint 11;

[0046] The specific working principle in this embodiment is as follows:

[0047] Light source 1 enters single-mode optical fiber 2. Since the cores of single-mode optical fiber 2 and single-mode optical fiber 5 are offset and then fused, a measuring arm and a reference arm are formed. Part of the light is reflected by the high-reflection film 3 to generate reference light, and the other part of the light is incident on the single-mode optical fiber 5 in proportion to the offset area to generate measuring light. The light beam transmitted to the single-mode optical fiber 5 passes through the anti-reflection film 6, the air gap 9 and the anti-reflection film 7, and is then transmitted to the C-lens 8. The C-lens 8 focuses the measuring light, which is then transmitted to the 45° reflector 10 through the C-lens 8 for reflection. The measuring light is then reflected by the surface to be measured to the single-mode optical fiber 5 and interferes with the reference light in the single-mode optical fiber 2.

[0048] Obviously, the above embodiments of the present invention are only for the purpose of clearly explaining the examples of the present invention, and are not intended to limit the implementation methods of the present invention. Other different forms of changes can be made based on the above description. Therefore, all changes made according to the shape and principle of the present invention are protected by the present invention.

Claims

1. A fiber optic displacement sensing probe based on a C-lens Michelson interferometer, characterized in that: The invention comprises a light source (1), a single-mode optical fiber (2), a high-reflection film (3), a matte paint (4), a single-mode optical fiber (5), an anti-reflection film (6), an anti-reflection film (7), a C-lens (8) and an air gap (9).

2. The optical fiber displacement sensing probe based on the C-lens Michelson interferometer according to claim 1, characterized in that: A light source (1) is injected into a single-mode optical fiber (2), the cores of the single-mode optical fiber (2) and the single-mode optical fiber (5) are offset and fused, the end faces of the single-mode optical fiber (2) and the single-mode optical fiber (5) that are not in contact are coated with a high-reflection film (3), the end faces of the single-mode optical fiber (5) and the single-mode optical fiber (2) that are not in contact are coated with a matte paint (4), the output end face of the single-mode optical fiber (5) has an inclination angle of 8°, the output end face of the single-mode optical fiber (5) has an anti-reflection film (6), the incident end face of a C-lens (8) has an anti-reflection film (7), an air gap (9) is provided between the single-mode optical fiber (5) and the C-lens (8), and the incident end face of the C-lens (8) has an inclination angle of 8°.

3. The optical fiber displacement sensing probe based on a C-lens Michelson interferometer according to claim 2 is characterized in that: A light source (1) enters a single-mode optical fiber (2). Due to the core offset of the single-mode optical fiber (2) and the single-mode optical fiber (5), a measuring arm and a reference arm are generated. Part of the light is reflected by a high-reflection film (3) to generate reference light. Another part of the light is incident on the single-mode optical fiber (5) in proportion to the offset area to generate measuring light. The light beam transmitted to the single-mode optical fiber (5) passes through an anti-reflection film (6), an air gap (9) and an anti-reflection film (7) and is then transmitted to a C-lens (8). The C-lens (8) collimates the measuring light and transmits it to a surface to be measured through the C-lens (8) to be reflected. The measuring light reflected by the surface to be measured to the single-mode optical fiber (5) interferes with another part of the reference light that passes through the high-reflection film (3) in the single-mode optical fiber (2).

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