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

Abstract

The invention discloses an optical fiber displacement sensing probe of a Michelson interferometer based on G-lens, in the optical fiber displacement sensing probe, fiber core offset welding is adopted, a measuring arm and a reference arm are generated, so that the structure is more compact, the interference influence of an external environment is small, the G-lens is placed on an emergent end face, emergent measuring light is focused, the coupling efficiency is improved, and the measurement precision is improved. The sensitivity is improved. The device has the advantages of being simple and compact in structure, high in sensitivity and high in precision, can meet the strict requirement of accurate measurement, and monitors and monitors some special environments.

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 G-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] The fiber optic displacement sensor probe is an important application of fiber optic displacement sensors in micro-measurement, and is widely used in the field of distance detection and measurement. Due to its excellent sensitivity, it can accurately measure the distance and displacement of the object to be measured. Due to its compact structure, small size, and excellent performance, it can perform high-sensitivity and high-precision measurements in some narrow specific areas, such as precision positioning in semiconductors. During the semiconductor processing, precision mechanical systems need to handle nano-level displacement adjustment and control. In bridge health monitoring, due to some factors, the bridge will produce tiny vibrations and displacements. These changes may indicate structural aging or potential damage. Monitor the vibration of precision mechanical equipment. In high-precision processing machinery (such as digital machine tools), tiny vibrations may affect the processing accuracy, and the vibration of the equipment needs to be monitored.

[0004] In order to solve the shortcomings of some current technologies, an innovative solution is proposed, namely, a fiber optic displacement sensing probe based on the G-lens Michelson interferometer. This probe uses a unique optical path design to achieve linear displacement measurement. It has the advantages of simple structure, compact structure, high sensitivity and high precision, and can meet the strict requirements of accurate measurement and monitor certain special environments. 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 with simple structure, compact structure, high sensitivity and high precision.

[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 G-lens, characterized in that it 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 air gap (7), an anti-reflection film (8) and a G-lens (9). The characteristics are:

[0008] 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 the G-lens (9) has an anti-reflection film (8), there is an air gap (7) between the single-mode optical fiber (5) and the G-lens (9), and the incident end face of the G-lens (9) has an inclination angle of 8°.

[0009] The working principle of the sensor probe is as follows: the light source (1) is input from the single-mode optical fiber (2). Since the single-mode optical fiber (2) is fused with the core offset of the single-mode optical fiber (5), a measuring arm and a reference arm are generated. A part of the light is incident into the single-mode optical fiber (5) according to the offset area ratio to generate the measuring light, and the other part is reflected by the high-reflection film (3) to generate the reference light. The light beam transmitted to the single-mode optical fiber (5) is transmitted to the G-lens (9), and after being collimated by the G-lens (9), it is transmitted to the surface to be measured and reflected. The measuring light reflected back to the single-mode optical fiber (2) by the surface to be measured interferes with the reference light in the single-mode optical fiber (2).

[0010] The measurement principle of this optical fiber displacement sensor probe is:

[0011] 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 (8) can be expressed as follows:

[0012]

[0013]

[0014] In the above formula, S1 is the area of ​​the single-mode optical fiber (2) and the single-mode optical fiber (5) where they are fused together, S2 is the area of ​​the single-mode optical fiber (2) coated with the high-reflection film (7), and S is the cross-sectional area of ​​the single-mode optical fiber.

[0015] The optical power coupling efficiency of the measured light reflected back to the single-mode optical fiber (5) through the measured surface is η, which can be expressed as follows:

[0016]

[0017] In the above formula, k is the wave number, w0 is the spot radius of the measurement light emitted from the single-mode optical fiber (5), and the coordinate system is established with (x, y, z). 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 s *(x, y, z) is the conjugate light field distribution. The coordinate system is established at the receiving end with (x', y', z'). r(x', y', z') is the light field distribution of the measurement light reflected from the surface to be measured back to the output end face of the single-mode optical fiber (5), E r *(x',y',z') is the conjugate light field distribution. The relationship between the (x,y,z) coordinate system and the (x',y',z') coordinate system can be expressed as follows:

[0018]

[0019]

[0020]

[0021] y=y′

[0022]

[0023] In the above formula, L is the optical path of the measuring light from the single-mode optical fiber (5) to the end face to be measured and reflected back to the exit end face of the single-mode optical fiber (5), λ is the wavelength of the light output by the light source (1), θ is the inclination angle of the surface to be measured, w(L) is the spot radius of the measuring light reflected back to the exit end face of the single-mode optical fiber (5), and R(L) is the curvature radius of the measuring light reflected back to the exit end face of the single-mode optical fiber (5), which can be expressed as follows:

[0024] L=2L air +2n0L g +2d

[0025]

[0026]

[0027] In the above formula, L air is the length of the air gap (7), n0 is the central refractive index of G-lens (9), L g is the length of G-lens (9), d is the distance from G-lens (9) to the surface to be measured, i.e., the working distance, and ABCD are the elements of the ray matrix M of the measuring light emitted from the exit end face, reflected by the surface to be measured, and returned to the exit end face, which are respectively expressed as follows:

[0028]

[0029] In the above formula, since in the design, L air is very small. At this time, the transmission matrix of G-lens (9) can be considered as the transmission matrix without tilt, and √A is the self-focusing constant.

[0030] The intensity of the measurement light reflected back to the single-mode optical fiber (2) by the surface to be measured can be expressed as:

[0031]

[0032] I1 and I 2r Interference occurs in the single-mode optical fiber (2), forming an interference light intensity I end， It can be expressed as follows:

[0033]

[0034] In the above formula, To measure the phase change of light emitted from the output end face of the single-mode optical fiber (2) and then reflected back to the single-mode optical fiber (2) by the surface to be measured, it can be expressed as follows:

[0035]

[0036] In the above formula, l smf is the length of the single-mode optical fiber (5).

[0037] This solution uses a core offset method to generate reference light and measurement light, which is different from a traditional Michelson interferometer, so that the design structure of the optical fiber displacement sensor probe is compact. A G-lens (9) is placed at the output end face of the single-mode optical fiber (5) to focus the output light, achieve higher coupling efficiency, and achieve high sensitivity.

[0038] This solution has the advantages of simple structure, compact structure, high sensitivity and high precision, etc. It can meet the strict requirements of accurate measurement and monitor certain special environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 A schematic diagram of the optical path of a fiber optic displacement sensing probe based on a G-lens Michelson interferometer described in the present invention;

[0040] Figure 2 The figure is a schematic diagram of the optical path structure of a fiber optic displacement sensing probe of a Michelson interferometer based on G-lens described in the present invention.

[0041] 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. air gap; 8. anti-reflection film; 9. G-lens; 10. 45° reflector; 11. matte paint. DETAILED DESCRIPTION

[0042] The drawings are merely illustrative and should not be construed as limiting the present patent;

[0043] In order to better illustrate the implementation cases, some elements in the drawings may be partially enlarged or reduced, and do not represent the sizes of actual products.

[0044] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments:

[0045] Example 1

[0046] Combined with Figure 1 , light source 1, single-mode optical fiber 2, high-reflection film 3, matte paint 4, single-mode optical fiber 5, anti-reflection film 6, air gap 7, anti-reflection film 8, G-lens 9;

[0047] Combined with Figure 1 The single-mode optical fiber 2 and the single-mode optical fiber 5 are core-offset 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 inclination angle of the single-mode optical fiber 5 is 8°, the output end face of the single-mode optical fiber 5 is coated with an anti-reflection film 6, the incident end face of the G-lens 9 is coated with an anti-reflection film 8, there is an air gap 7 between the single-mode optical fiber 5 and the G-lens 9, and the incident end face inclination angle of the G-lens 9 is 8°.

[0048] The specific working principle in this embodiment is as follows:

[0049] The light source 1 is input by the single-mode optical fiber 2, and the cores of the single-mode optical fiber 2 and the single-mode optical fiber 5 are offset and fused to generate a measuring arm and a reference arm. A part of the light is incident into the single-mode optical fiber 5 according to the offset area ratio to generate the measuring light, and the other part is reflected by the high-reflection film 3 to generate the reference light. The measuring light is transmitted to the G-lens 9 through the single-mode optical fiber (5), and after being collimated by the G-lens (9), it is transmitted to the surface to be measured and reflected. The measuring light reflected back to the single-mode optical fiber (2) from the surface to be measured interferes with the reference light in the single-mode optical fiber (2).

[0050] Example 2

[0051] Combined with Figure 2 , light source 1, single-mode optical fiber 2, high-reflection film 3, matte paint 4, single-mode optical fiber 5, anti-reflection film 6, air gap 7, anti-reflection film 8, G-lens 9, 45° reflector 10 and matte paint 11;

[0052] The specific working principle in this embodiment is as follows:

[0053] The light source 1 is input by the single-mode optical fiber 2, and the cores of the single-mode optical fiber 2 and the single-mode optical fiber 5 are offset and fused to generate a measuring arm and a reference arm. A part of the light is incident into the single-mode optical fiber 5 according to the offset area ratio to generate the measuring light, and the other part is reflected by the high-reflection film 3 to generate the reference light. The measuring light is transmitted to the G-lens 9 through the single-mode optical fiber 5, and the measuring light is focused by the G-lens 9. After being transmitted to the 45° reflector 10 through the G-lens 9, it is reflected to the surface to be measured. The measuring light reflected back to the single-mode optical fiber 2 from the surface to be measured and the reference light interfere in the single-mode optical fiber 2.

Claims

1. A fiber optic displacement sensing probe based on a Michelson interferometer of G-lens, characterized in that: It 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 air gap (7), an anti-reflection film (8) and a G-lens (9).

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

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

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