FP sensor probe, absolute distance measuring device and absolute distance measuring method

Abstract

The present disclosure provides an FP sensor probe, an absolute distance measuring device and an absolute distance measuring method, which belong to the technical field of non-contact measurement of absolute distance. The structure includes a first N+1 core multimode optical fiber head (9), an optical fiber sleeve (10), an imaging lens group (11) and a standard lens (12), and the first N+1 core multimode optical fiber head (9), the imaging lens group (11) and the standard lens (12) are fixed in order inside the optical fiber sleeve (10) along a direction from the FP sensor probe to a sample (8), and the first N+1 core multimode optical fiber head (9) includes N first multimode optical fibers (16) and one second multimode optical fiber (17), where N satisfies N≧2, and the N first multimode optical fibers (16) are arranged around the second multimode optical fiber (17).

Description

[Technical field]

[0001] The present disclosure relates to the technical field of non-contact measurement of absolute distance, and in particular to an FP sensor probe, an absolute distance measuring device, and an absolute distance measuring method.

[0002] (CROSS REFERENCE TO RELATED APPLICATIONS) This application claims priority based on a Chinese application filed with the China Patent Office on December 1, 2022, bearing application number 202211534663.2 and entitled "FP sensor probe, absolute distance measuring device and absolute distance measuring method", the entire contents of which are incorporated by reference into this application. [Background technology]

[0003] Non-contact measurement of absolute distance is widely applied to precision work stage positioning, focus position detection, ultra-smooth surface appearance inspection, step height measurement, etc. In particular, in semiconductor processes, when nano patterns are processed using photolithography technology, it is necessary to monitor the focus position of the silicon wafer with high precision and in real time, and then feed back to the work stage for closed-loop control. In near-field optical storage technology, it is necessary to measure the distance between the head and disk of the near-field optical storage with high precision. In ultra-smooth surface appearance inspection technology, it is necessary to monitor the absolute distance between the standard lens and the surface to be measured in real time. In part geometric dimension detection, it is necessary to accurately measure the step contour.

[0004] Currently, commonly used measuring instruments include triangulation-type reflective laser sensors, chromatic confocal sensors, laser displacement sensors, and capacitance sensors. All of these measuring instruments can achieve high-precision measurement of displacement, but only chromatic confocal sensors and capacitance sensors can achieve direct measurement of absolute distance; other measuring instruments require the initial position to be determined in order to measure absolute distance, and have poor repeatability when turning off and restarting. Chromatic confocal sensors have relatively good repeatability when turning off and restarting, but have low measurement resolution, and capacitance sensors are easily affected by parasitic capacitance and are greatly affected by thermal drift. Summary of the Invention

[0005] In view of the above problems, the present disclosure provides a Fabry-Perot (FP) optical fiber sensor probe structure, an absolute distance measuring device, and an absolute distance measuring method.

[0006] A first aspect of the present disclosure provides an FP sensor probe, the FP sensor probe comprising a first N+1 core multimode optical fiber head, an optical fiber sleeve, an imaging lens group, and a standard lens, the first N+1 core multimode optical fiber head, the imaging lens group, and the standard lens being fixed in order inside the optical fiber sleeve along a direction from the FP sensor probe to a sample, the first N+1 core multimode optical fiber head including N first multimode optical fibers and one second multimode optical fiber, N satisfies N≧2, and the N first multimode optical fibers are arranged around the second multimode optical fiber.

[0007] In an embodiment of the present disclosure, when the reflectance of the surface of the sample is 40% or more, the FP sensor probe further includes a window film layer, and the window film layer is attached to the surface of the standard lens.

[0008] In an embodiment of the present disclosure, the window film layer is a metal film layer having a transmittance of 40%±5% and a reflectance of 15%±5%, and preferably, the metal film layer includes a metal chrome layer having a thickness of 4-8 nm.

[0009] In an embodiment of the present disclosure, the standard lens is made of quartz glass having a thickness of 5 mm or more and a surface roughness PV of PV≦λ / 20, where λ is the wavelength of an interferometer used to measure the surface roughness of the standard lens.

[0010] In an embodiment of the present disclosure, the second multimode optical fiber is disposed at a central position of the first N+1 core multimode optical fiber head, and N of the first multimode optical fibers are spaced apart from the second multimode optical fiber at intervals Δd 1 are arranged in a ring at equal intervals.

[0011] In an embodiment of the present disclosure, each of the N first multimode optical fibers is disposed so as to be in contact with the second multimode optical fiber. In the embodiment of the present disclosure, the core diameter d of the first multimode optical fiber 1 and the core diameter d of the second multimode optical fiber 2 are all standard core diameters, and d 2 ≧d 1 and the interval Δd between two adjacent first multimode optical fibers is 1 0≦Δd 1 ≦d 1 Satisfy / 2.

[0012] In an embodiment of the present disclosure, the number of the first multimode optical fibers is determined by the following formula: JPEG0007675868000001.jpg2168 N is the number of the first multimode optical fibers.

[0013] A second aspect of the present disclosure provides an absolute distance measuring device that uses the above-mentioned FP sensor probe. the first N+1 core multimode optical fiber head of the FP sensor probe is connected to the FP sensor connector, an end of the FP sensor connector remote from the FP sensor probe is connected to the second N+1 core multimode optical fiber and a first end of the 1×2 optical fiber coupler in that order, a second end of the 1×2 optical fiber coupler is connected to each of the N-core multimode optical fiber and the single-core multimode optical fiber, the N-core multimode optical fiber is connected to the projecting optical fiber connector, the single-core multimode optical fiber is connected to the receiving optical fiber connector, the projecting optical fiber connector is connected to a projecting light source, and the receiving optical fiber connector is connected to a demodulation system, the projecting light source is configured to project light, and the demodulation system is configured to determine an absolute distance between a sample and the FP sensor probe.

[0014] In an embodiment of the present disclosure, a first multimode optical fiber in the FP sensor probe is connected to the light emitting optical fiber connector, and a second multimode optical fiber in the FP sensor probe is connected to the light receiving optical fiber connector.

[0015] In an embodiment of the present disclosure, the flood light source includes a halogen lamp light source, an LED, an SLD, or a supercontinuum laser light source, and the demodulation system includes a spectrometer that acquires and analyzes interference light intensity signals at different distances, and an FP optical fiber demodulator.

[0016] A third aspect of the present disclosure provides an absolute distance measuring method using the above absolute distance measuring device, which includes a light incidence step in which light from a light projecting light source is joined and enters a branch path where a light projecting optical fiber connector is located, exits via N first multimode optical fibers in a first N+1 core multimode optical fiber head, enters the FP sensor probe, and is focused on an air gap between a standard lens and a sample, a light reflection step in which the light is reflected by the standard lens and a surface of the sample, passes through the FP sensor probe, is focused again by a second multimode optical fiber in the first N+1 core multimode optical fiber head, and finally arrives at a receiving optical fiber connector, and a distance determination step in which an absolute distance between the sample and the FP sensor probe is determined by analyzing an optical signal received by the receiving optical fiber connector.

[0017] In an embodiment of the present disclosure, the light incidence step includes a step in which light from a light projecting light source is merged and enters a light projecting optical fiber connector, and then sequentially passes through an N-core multimode optical fiber, a 1×2 optical fiber coupler and a second N+1-core multimode optical fiber to arrive at the FP sensor probe, and after exiting from N first multimode optical fibers in a first N+1-core multimode optical fiber head, passes through an imaging lens group and a standard lens, and is first focused on an air gap between the standard lens and a sample.

[0018] In an embodiment of the present disclosure, the light reflecting step includes a step in which the light reflected by the standard lens and the surface of the sample sequentially passes through the standard lens and the imaging lens group, is re-focused by the second multimode optical fiber in the first N+1 core multimode optical fiber head, and is merged and enters the second multimode optical fiber; and a step in which the optical signal having the absolute distance information of the air gap sequentially arrives at the receiving optical fiber connector via the second N+1 core multimode optical fiber, the 1×2 optical fiber coupler and the single-core multimode optical fiber.

[0019] In an embodiment of the present disclosure, the distance determining step includes receiving and analyzing the optical signal by a demodulation system to obtain the thickness of the air gap between the standard lens and the sample, thereby determining the absolute distance between the sample and the FP sensor probe.

[0020] In the embodiment of the present disclosure, the absolute distance between the sample and the FP sensor probe is obtained by the following method: based on the principle of multi-beam interference by a parallel plate, a standard lens and a sample are regarded as an FP cavity, a reflection coefficient of the FP cavity is calculated, a simulated reflectance of the FP cavity is calculated based on the reflection coefficient, a model base of the simulated reflectance of the FP cavity corresponding to air gaps of different thicknesses is constructed, an actual measured reflectance of the FP cavity is calculated, a cross-correlation operation is performed between the actual measured reflectance and a plurality of simulated reflectances in the model base, and the thickness of the air gap corresponding to the simulated reflectance with the highest correlation is determined as the absolute distance between the sample and the FP sensor probe.

[0021] In an embodiment of the present disclosure, the reflection coefficient of the FP cavity is calculated according to the following formula: JPEG0007675868000002.jpg21105 In the formula, s and p represent s-waves and p-waves, respectively. Warning 2: Image is smaller than 4cm wide and 3cm tall. JPEG0007675868000003.jpg139 represents the reflection coefficient at the interface between a standard lens and an air gap corresponding to a t-wave, JPEG0007675868000004.jpg118 represents the reflection coefficient at the interface between the air gap and the sample corresponding to the t-wave, JPEG0007675868000005.jpg1210 represents the phase shift of light due to changes in optical path length in a standard lens and an air gap, JPEG0007675868000006.jpg99 represents the reflection coefficient of the FP cavity corresponding to the t-wave, specifically, JPEG0007675868000007.jpg1251 is calculated using the following formula: JPEG0007675868000008.jpg38135 In the formula, n 0 , n 1 , n 2 are the refractive indices of the standard lens, the air gap, and the sample, respectively, and θ 0 , θ 1 represent the angle of incidence and the angle of refraction of the light incident on the lower surface of the standard lens from the first multimode optical fiber, respectively, and θ 2 represents the refraction angle of the incident light at the top surface of the sample, In JPEG0007675868000009.jpg1021, when the light beam is obliquely incident, the refractive index is n m-1 and n m represent the reflection coefficients of s-waves and p-waves at the interface of two media, respectively. In an embodiment of the present disclosure, JPEG0007675868000010.jpg128 is calculated using the following formula: JPEG0007675868000011.jpg1760 c 1 is the thickness of the air gap and λ is the spectral wavelength of the light from the measurement light source. In an embodiment of the present disclosure, a window film layer is attached to the surface of the standard lens, and the reflection coefficient of the FP cavity is calculated according to the following formula: In the formula JPEG0007675868000012.jpg17164, s and p represent s-waves and p-waves, respectively. JPEG0007675868000013.jpg118 represents the reflection coefficient at the interface between a standard lens and a window film layer corresponding to t-waves, JPEG0007675868000014.jpg118 represents the reflection coefficient at the interface between the window film layer and the air gap corresponding to the t-wave, JPEG0007675868000015.jpg118 represents the reflection coefficient at the interface between the air gap and the sample corresponding to the t-wave, JPEG0007675868000016.jpg1220 represents the phase shift of light due to changes in optical path length in the window film layer and in the air gap, respectively; JPEG0007675868000017.jpg108 represents the reflection coefficient of the FP cavity corresponding to the t-wave, specifically JPEG0007675868000018.jpg1362 is calculated using the following formula: JPEG0007675868000019.jpg39138 In the formula, n 0 , n 1 , n 2 , n 3 are the refractive indices of the standard lens, the window film layer, the air gap, and the sample, respectively, and θ 0 , θ 1 represent the angle of incidence and the angle of refraction of the light incident from the first multimode optical fiber at the top surface of the window film layer, respectively, and θ 2 represents the refraction angle of the incident light at the bottom surface of the window film layer, and θ 3 represents the refraction angle of the incident light at the top surface of the sample, In JPEG0007675868000020.jpg1122, when the light beam is obliquely incident, the refractive index is n m-1 and n m represent the reflection coefficients of s-waves and p-waves at the interface of two media, respectively.

[0022] In an embodiment of the present disclosure, JPEG0007675868000021.jpg1119 is calculated using the following formula: JPEG0007675868000022.jpg19104 c 1 , c 2 are the thicknesses of the window film layer and the air gap, respectively, and λ is the spectral wavelength of the light from the measurement light source. In the embodiment of the present disclosure, the simulated reflectance of the FP cavity is calculated according to the following formula: JPEG0007675868000023.jpg1685 R sim represents the simulated reflectance of the FP cavity, JPEG0007675868000024.jpg1020 represents the reflection coefficients of the FP cavity for s-waves and p-waves, respectively.

[0023] In the embodiment of the present disclosure, the measured reflectance of the FP cavity is calculated according to the following formula: JPEG0007675868000025.jpg1790 R exp represents the measured reflectivity of the FP cavity, and I sample represents the reflected light intensity of the sample, and I dark represents the stray light intensity, and I ref represents the reference light intensity, and R ref represents the reflectance correction factor, Specifically, R ref is calculated according to the following formula: JPEG0007675868000026.jpg1470 r 12、 t 12 are the reflection and transmission coefficients of a standard lens, respectively, JPEG0007675868000027.jpg43 represents the reflection coefficient at the interface between the air gap and the sample.

[0024] In an embodiment of the present disclosure, a window film layer is attached to the surface of the standard lens, and the measured reflectance of the FP cavity is calculated according to the following formula: JPEG0007675868000028.jpg1790 R exp represents the measured reflectivity of the FP cavity, and I sample represents the reflected light intensity of the sample, and I dark represents the stray light intensity, and I ref represents the reference light intensity, and R ref represents the reflectance correction factor, Specifically, R ref is calculated according to the following formula: JPEG0007675868000029.jpg1370 r 13、 t 13 represent the reflection and transmission coefficients of the window film layer, respectively, and r' represents the reflection coefficient at the interface between the air gap and the sample.

[0025] Compared with the prior art, the FP sensor probe, the absolute distance measuring device, and the absolute distance measuring method according to the present disclosure have at least the following beneficial effects.

[0026] The present disclosure realizes measurement of the absolute distance between a sensor probe and a measurement target surface based on the principle of optical fiber Fabry-Perot (FP) interferometry, and has features such as high accuracy, high resolution, excellent turn-off / restart repeatability, and non-contact, making it possible to measure absolute distance without the need for orientation.

[0027] The above and other objects, features, and advantages of the present disclosure will become more apparent from the following description of embodiments of the present disclosure with reference to the accompanying drawings. [Brief description of the drawings]

[0028] [Figure 1] 1 is a schematic diagram showing an entire FP sensor probe according to a first embodiment of the present disclosure. [Diagram 2] FIG. 11 is a schematic configuration diagram of an absolute distance measurement device according to a second embodiment of the present disclosure. [Diagram 3] 13 is a schematic flowchart of a method for determining an absolute distance according to a third embodiment of the present disclosure. [Figure 4] FIG. 13 is a schematic diagram illustrating the principle of a multilayer film structure according to a fourth embodiment of the present disclosure. [Diagram 5] 13 is a schematic flowchart of a method for determining an absolute distance according to a fourth embodiment of the present disclosure. [Figure 6]13 is a graph showing a comparison of spectral curves of measured reflectance and simulated reflectance according to a third embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] In order to make the objectives, technical solutions and advantages of the present disclosure more clear, the present disclosure will be described in more detail below with reference to the drawings using specific embodiments. The embodiments described are only some of the embodiments of the present disclosure, and are not all of the embodiments. Based on the embodiments in the present disclosure, all other embodiments obtained by those skilled in the art without using inventive ability also fall within the protection scope of the present disclosure.

[0030] The terms used herein are merely for the purpose of describing specific examples and are not intended to limit the disclosure. As used herein, the terms "comprises," "comprises," and the like refer to the presence of at least one of the applicable features, steps, operations, and components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0031] In this disclosure, unless otherwise specified, the terms "attached," "coupled," "connected," "fixed," and the like should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection. It may be a mechanical connection, an electrical connection, or a communication connection. It may also be a direct connection, an indirect connection via an intermediate object, or two elements may communicate with each other or interact with each other. Those skilled in the art can understand the specific meaning of the above terms in this disclosure according to the specific situation.

[0032] Unless otherwise specified, all terms (including technical and scientific terms) used herein have the meanings commonly understood by those of ordinary skill in the art. Terms used herein should be interpreted to have a meaning consistent with the context of this specification and should not be interpreted as ideal or absolute.

[0033] Example 1 FIG. 1 is a schematic diagram showing an entire FP sensor probe according to a first embodiment of the present disclosure.

[0034] 1, the FP sensor probe according to the first embodiment of the present disclosure includes a first N+1 core multimode optical fiber head 9, an optical fiber sleeve 10, an imaging lens group 11, and a standard lens 12. The FP sensor probe is installed between a sample 8 and an FP sensor connector 1, and is used to measure an absolute distance.

[0035] Along the direction from the FP sensor probe to the sample 8, a first N+1 core multimode optical fiber head 9, an imaging lens group 11, and a standard lens 12 are fixed in this order inside an optical fiber sleeve 10. The first N+1 core multimode optical fiber head 9 includes N first multimode optical fibers 16 and one second multimode optical fiber 17, where N satisfies N≧2, and the N first multimode optical fibers 16 are arranged around the second multimode optical fiber 17. The first N+1 core multimode optical fiber head 9 is connected to the FP sensor connector 1.

[0036] Usually, the surface of the standard lens 12 is flush with the outer end face of the optical fiber sleeve 10, and the distance between the sensor and the sample 8 to be measured can be adjusted by moving the FP sensor probe. However, due to the limit of the actual processing accuracy, it is not possible to realize absolute flushness between the standard lens 12 and the optical fiber sleeve 10. Preferably, the surface of the standard lens 12 protrudes from the outer end face of the optical fiber sleeve 10, thereby ensuring that there is no other extra air gap between the sample 8 and the standard lens 12, which is located between the surface of the standard lens 12 and the end face of the optical fiber sleeve 10, and is formed by the standard lens 12 being recessed from the end face of the optical fiber sleeve 10. Due to the extra air gap, the measurement accuracy of the sensor for the value of the air gap 18 to be measured is impaired.

[0037] In the embodiment of the present disclosure, the part between the sample 8 and the standard lens 12 is the air gap 18 to be measured for distance. When the reflectance of the surface of the sample 8 is 40% or more, the FP sensor probe further includes a window film layer 13, and the window film layer 13 is attached to the surface of the standard lens 12, and the air gap 18 is located between the sample 8 and the window film layer 13. In the measurement, different samples 8 have different reflectances, so the standard lens can be divided into a standard lens with a window film layer 13 and a standard lens without a window film layer 13, and the standard lens 12 can be selected according to the actual situation of the sample 8.

[0038] The window film layer 13 is attached to the surface of the standard lens 12 and is usually prepared by magnetron sputtering, and the optical parameters are determined by the reflectance of the surface of the sample 8 to be measured. Specifically, when the reflectance of the surface of the sample 8 is less than 40%, the window film layer 13 is usually not required, and when the reflectance of the surface of the sample 8 is 40% or more, the window film layer 13 is usually a metal film layer with a transmittance of 40%±5% and a reflectance of 15%±5%. Preferably, the metal film layer includes a metal chrome layer, for example, with a thickness of 4-8 nm.

[0039] In an embodiment of the present disclosure, the standard lens 12 is a quartz glass lens having a thickness of 5 mm or more and a surface roughness PV that satisfies PV≦λ / 20, and λ is the wavelength of the interferometer when measuring the surface roughness of the standard lens 12, and specifically, is the wavelength set in the interferometer when measuring the surface roughness of the quartz glass using the interferometer.

[0040] In the embodiment of the present disclosure, the second multimode optical fiber 17 is installed at the center position of the first N+1 core multimode optical fiber head 9, and the N first multimode optical fibers 16 are arranged around the second multimode optical fiber 17 at intervals Δd 1 are arranged in a ring at equal intervals.

[0041] Furthermore, each of the N first multimode optical fibers 16 is disposed so as to be in contact with a second multimode optical fiber 17 .

[0042] Typically, the core diameter d of the N first multimode optical fibers 16 1 and a core diameter d of one second multimode optical fiber 17 2 are all standard core diameters (e.g., 105 / 125 μm, 200 / 220 μm, etc.), and d 2 ≧d 1 In order to realize continuous circular light projection, the interval Δd between two adjacent first multimode optical fibers 16 is set to be 1 / 2. 1 0≦Δd 1 ≦d 1 Satisfy / 2.

[0043] Typically, the number N of the first multimode optical fibers 16 is d 1 , d 2 and Δd 1 Specifically, it can be calculated by the following formula: JPEG0007675868000030.jpg2265

[0044] For example, d 1 = 125 μm, d 2 = 220 μm, Δd 1 is Δd 1 If N is ≦62.5 μm, then by substituting this into the above formula, it becomes 8.47≧N≧5.47, which when converted into an integer becomes 8≧N≧6.

[0045] Example 2 FIG. 2 is a schematic configuration diagram of an absolute distance measurement device according to a second embodiment of the present disclosure.

[0046] As shown in Fig. 2, the second embodiment of the present disclosure provides an absolute distance measuring device using the FP sensor probe according to the above first embodiment, which includes an FP sensor probe, an FP sensor connector 1, a second N+1-core multimode optical fiber 4, a 1x2 optical fiber coupler 7, an N-core multimode optical fiber 5, a single-core multimode optical fiber 6, a light-emitting optical fiber connector 2, a light-receiving optical fiber connector 3, a light-emitting source, and a demodulation system.

[0047] A first N+1-core multimode optical fiber head 9 of the FP sensor probe is connected to the FP sensor connector 1, an end of the FP sensor connector 1 remote from the FP sensor probe is connected in turn to a second N+1-core multimode optical fiber 4 and a first end of a 1×2 optical fiber coupler 7, and a second end of the 1×2 optical fiber coupler 7 is connected to each of the N-core multimode optical fiber 5 and the single-core multimode optical fiber 6. The N-core multimode optical fiber 5 is connected to the projecting optical fiber connector 2, the single-core multimode optical fiber 6 is connected to the receiving optical fiber connector 3, the projecting optical fiber connector 2 is connected to a projecting light source, and the receiving optical fiber connector 3 is connected to a demodulation system. The projecting light source is configured to project light, and the demodulation system is configured to determine an absolute distance between the sample 8 and the FP sensor probe.

[0048] As shown in FIG. 2 , the first multimode optical fiber 16 in the FP sensor probe is connected to the light emitting optical fiber connector 2 via the second N+1 core multimode optical fiber 4, the 1×2 optical fiber coupler 7 and the N-core multimode optical fiber 5, in that order, and the second multimode optical fiber 17 in the FP sensor probe is connected to the light receiving optical fiber connector 3 via the second N+1 core multimode optical fiber 4, the 1×2 optical fiber coupler 7 and the single-core multimode optical fiber 6, in that order.

[0049] Specifically, the flood light source includes, but is not limited to, a halogen lamp light source, an LED, an SLD, and a supercontinuum laser light source. The demodulation system includes, but is not limited to, a spectrometer that acquires and analyzes interference light intensity signals at different distances, and an FP optical fiber demodulator.

[0050] According to the above embodiment, the present disclosure can realize the measurement of the absolute distance between the FP sensor probe and the sample 8. The light projecting optical fiber connector 2 is connected to a broad spectrum light projecting light source. The light receiving optical fiber connector 3 is connected to a demodulation system, so that interference light intensity signals at different distances can be acquired and analyzed.

[0051] Example 3 A third embodiment of the present disclosure provides an absolute distance measuring method using the absolute distance measuring device according to the above second embodiment. The absolute distance measuring method includes the following steps:

[0052] Light incidence step: The light from the light projecting light source is joined and enters the branch path where the light projecting optical fiber connector 2 is located, exits via the N first multimode optical fibers 16 in the first N+1 core multimode optical fiber head 9, enters the FP sensor probe, and is focused in the air gap 18 between the standard lens 12 and the sample 8.

[0053] Light reflection step: After the light beam is reflected by the standard lens 12 and the surface of the sample 8, it passes through the FP sensor probe, is refocused by the second multimode optical fiber 17 in the first N+1 core multimode optical fiber head 9, and finally arrives at the receiving optical fiber connector 3.

[0054] Distance determining step: The optical signal received by the receiving optical fiber connector 3 is analyzed to determine the absolute distance between the sample 8 and the FP sensor probe.

[0055] In the embodiment of the present disclosure, the light incidence step specifically includes the following steps:

[0056] The light from the light projecting light source is merged and enters the projecting optical fiber connector 2, and then sequentially passes through the N-core multimode optical fiber 5, the 1×2 optical fiber coupler 7 and the second N+1-core multimode optical fiber 4 to reach the FP sensor probe, and after being emitted from the N first multimode optical fibers 16 in the first N+1-core multimode optical fiber head 9, it passes through the imaging lens group 11 and the standard lens 12 in order, and is first focused on the air gap 18 between the standard lens 12 and the sample 8, and the reflected light 14 by the sample shown in FIG.

[0057] In the embodiment of the present disclosure, the light reflecting step specifically includes the following steps:

[0058] After the light beam is reflected by the standard lens 12 and the surface of the sample 8, it passes through the FP sensor probe again, see the reflected light beam 15 by the standard lens shown in Figure 1. It is then focused again by the second multimode optical fiber 17 in the first N+1 core multimode optical fiber head 9.

[0059] The optical signal having the absolute distance information of the air gap 18 sequentially travels through the second N+1 core multimode optical fiber 4 , the 1×2 optical fiber coupler 7 and the single-core multimode optical fiber 6 to arrive at the receiving optical fiber connector 3 .

[0060] In the embodiment of the present disclosure, the distance determining step specifically includes the following steps: Receive and analyze the optical signal through a demodulation system to obtain the thickness of the air gap 18, i.e., the absolute distance between the sample 8 and the FP sensor probe.

[0061] The specific process of the distance determination step will be described in detail below.

[0062] In the above step, to determine the thickness of the air gap 18 between the standard lens 12 and the sample 8, a multi-beam white light interferometry method using parallel plates is used to construct a multi-layer film system structure, which includes the standard lens 12, the air gap 18, and the sample 8, which are arranged in order from top to bottom.

[0063] Core diameter d 1 The incident light 19 from the first multimode optical fiber 16 reaches the top and bottom surfaces of the standard lens 12, a part of which is directly reflected to become the reflected light 20 by the standard lens 12, another part of which is transmitted to reach the top surface of the sample 8 via the air gap 18, and is then reflected again to reach the standard lens 12 to become the reflected light 21 by the sample. Finally, the incident light 19 reaches the top surface of the sample 8 via the air gap 18, and is reflected again to reach the standard lens 12 to become the reflected light 21 by the sample. 2 The light is received by the second multimode optical fiber 17 .

[0064] Based on the principle of multi-beam interference by a parallel plate, the standard lens 12 and the sample 8 form an FP cavity. The incidence angle and refraction angle of the incident light 19 on the lower surface of the standard lens 12 are respectively θ 0 and θ 1 Assume that the refraction angle of the incident light 19 on the upper surface of the sample is θ 2 The refractive indices of the standard lens 12, the air gap 18, and the sample 8 are n 0 , n 1 , n 2 year, In JPEG0007675868000031.jpg1222, when the light beam is obliquely incident, the refractive index is n m-1 and n m represent the reflection coefficients of s-waves and p-waves at the interface of two media with thicknesses of air gap 18 and c 1 In this way, a multilayer film structure was constructed.

[0065] Based on the multilayer film-based structure constructed as above, FIG. 3 is a schematic flow chart of a method for determining an absolute distance according to a third embodiment of the present disclosure.

[0066] As shown in FIG. 3, in the embodiment of the present disclosure, in the above distance determining step, the absolute distance between the sample 8 and the FP sensor probe is determined by the following steps S410 to S440.

[0067] Step S410: Based on the principle of multi-beam interference by a parallel plate, the standard lens 12 and the sample 8 are regarded as an FP cavity, and the reflection coefficient of the FP cavity is calculated.

[0068] In an embodiment of the present disclosure, the reflection coefficient of the FP cavity can be calculated by the following formula: JPEG0007675868000032.jpg19102 In the formula, s and p represent s-waves and p-waves, respectively. JPEG0007675868000033.jpg129 represents the reflection coefficient at the interface between the standard lens 12 and the air gap 18 corresponding to the t-wave, JPEG0007675868000034.jpg108 represents the reflection coefficient at the interface between the air gap 18 and the sample 8 corresponding to the t-wave, JPEG0007675868000035.jpg117 represents the phase shift of light due to the change in optical path length in a standard lens 12 and an air gap 1; JPEG0007675868000036.jpg109 represents the reflection coefficient of the FP cavity corresponding to the t-wave.

[0069] specifically, JPEG0007675868000037.jpg1351, calculated using the following formula. JPEG0007675868000038.jpg37133 In the formula, n 0 , n 1 , n 2 represent the refractive indices of the standard lens 12, the air gap 18 and the sample 8, respectively, and θ 0 , θ 1 represent the angle of incidence and the angle of refraction of the incident light 19 from the first multimode optical fiber 16 at the lower surface of the standard lens 12, respectively, and θ 2 represents the angle of refraction of the incident light 19 at the top surface of the sample 8, In JPEG0007675868000039.jpg1121, when the light beam is obliquely incident, the refractive index is n m-1 and nm represent the reflection coefficients of s-waves and p-waves at the interface of two media, respectively.

[0070] In an embodiment of the present disclosure, JPEG0007675868000040.jpg119 is calculated using the following formula. JPEG0007675868000041.jpg1661 c 1 is the thickness of the air gap 18 and λ is the spectral wavelength of the light from the measurement light source.

[0071] Step S420: Calculate the simulated reflectance of the FP cavity based on the reflection coefficient, and build a model base of the simulated reflectance of the FP cavity corresponding to the air gap 18 of different thicknesses.

[0072] In the embodiment of the present disclosure, the simulated reflectance of the FP cavity is calculated according to the following formula: JPEG0007675868000042.jpg1986 R sim represents the simulated reflectance of the FP cavity, JPEG0007675868000043.jpg921 represents the reflection coefficients of the FP cavity for s-waves and p-waves, respectively.

[0073] Based on the above formula, different thicknesses c 1 The simulated reflectivity R of the FP cavity corresponding to the air gap of 18 sim It is possible to build a model base of

[0074] Step S430: The actual reflectance of the FP cavity is calculated.

[0075] In the embodiment of the present disclosure, the measured reflectance of the FP cavity is calculated according to the following formula: JPEG0007675868000044.jpg1790 R exprepresents the measured reflectivity of the FP cavity, and I sample represents the reflected light intensity of the sample, and is typically the light intensity carrying absolute distance information of the air gap 18 output by the second multimode optical fiber 17. dark represents the stray light intensity, which is usually the light intensity of the stray light directly received by the second multimode optical fiber 17, and includes the environmental stray light intensity and the light intensity of the light from the first multimode optical fiber 16 that directly enters the environment without passing through the imaging lens group 11 and the standard lens 12. ref R represents the reference light intensity, which usually represents the light intensity of the output light of the second multimode optical fiber 17 when the air gap 18 between the standard lens 12 and the sample 8 exceeds the measurement range of the FP sensor probe (e.g., 2.5 times the measurement range, the specific value can be selected empirically and is not limited here). ref represents the reflectance correction factor, which is typically the reflectance coefficient when the air gap 18 between the standard lens 12 and the sample 8 exceeds the measurement range of the FP sensor probe.

[0076] Specifically, R ref can be calculated by the following formula: JPEG0007675868000045.jpg1471 r 12、 t 12 represent the reflection and transmission coefficients, respectively, of the standard lens 12. r′ represents the reflection coefficient at the interface between the air gap 18 and the sample 8.

[0077] Step S440: A cross-correlation calculation is performed between the measured reflectance and a plurality of simulated reflectances based on the model, and the thickness of the air gap 18 corresponding to the simulated reflectance with the highest correlation is determined as the absolute distance between the sample 8 and the FP sensor probe.

[0078] Example 4 The fourth embodiment of the present disclosure provides an absolute distance measuring method using the absolute distance measuring device according to the above second embodiment. In this embodiment, when the reflectance of the surface of the sample 8 is 40% or more, the FP sensor probe further includes a window film layer 13, and the measuring method includes the following steps:

[0079] Light incidence step: the light from the light projecting light source merges and enters the branch path where the light projecting optical fiber connector 2 is located, exits via the N first multimode optical fibers 16 in the first N+1 core multimode optical fiber head 9, then enters the FP sensor probe, and is focused in the air gap 18 between the window film layer 13 and the sample 8.

[0080] Light reflection step: After the light is reflected by the window film layer 13 and the surface of the sample 8, it passes through the FP sensor probe, is re-collected by the second multimode optical fiber 17 in the first N+1 core multimode optical fiber head 9, and finally arrives at the receiving optical fiber connector 3.

[0081] Distance determining step: The optical signal received by the receiving optical fiber connector 3 is analyzed to determine the absolute distance between the sample 8 and the FP sensor probe.

[0082] In the embodiment of the present disclosure, the light incidence step specifically includes the following steps:

[0083] The light from the light projecting light sources joins together and enters the projecting optical fiber connector 2, then passes through the N-core multimode optical fiber 5, the 1×2 optical fiber coupler 7 and the second N+1-core multimode optical fiber 4 in order to arrive at the FP sensor probe, and after exiting from the N first multimode optical fibers 16 in the first N+1-core multimode optical fiber head 9, passes through the imaging lens group 11, the standard lens 12 and the window film layer 13 in order, and is first focused on the air gap 18 between the window film layer 13 and the sample 8.

[0084] In the embodiment of the present disclosure, the light reflecting step specifically includes the following steps:

[0085] After the light is reflected by the window film layer 13 and the surface of the sample 8, it passes through the window film layer 13, the standard lens 12 and the imaging lens group 11 again, and is again focused by the second multimode optical fiber 17 in the first N+1 core multimode optical fiber head 9, and then merges and enters the second multimode optical fiber 17.

[0086] The optical signal having the absolute distance information of the air gap 18 sequentially travels through the second N+1 core multimode optical fiber 4 , the 1×2 optical fiber coupler 7 and the single-core multimode optical fiber 6 to arrive at the receiving optical fiber connector 3 .

[0087] In the embodiment of the present disclosure, the distance determination step specifically includes the following steps: receive and analyze the optical signal through a demodulation system to obtain the thickness of the air gap 18 between the standard lens 12 and the sample 8, and thereby determine the absolute distance between the sample 8 and the FP sensor probe.

[0088] The specific process of the distance determination step will be described in detail below.

[0089] FIG. 4 is a schematic diagram showing the principle of a multilayer film structure according to a fourth embodiment of the present disclosure.

[0090] In the above step, to determine the thickness of the air gap 18 between the window film layer 13 and the sample 8, a multi-beam white light interference measurement method using parallel plates is used to construct a multi-layer film structure as shown in FIG. 4, which includes a standard lens 12, a window film layer 13, an air gap 18 and a sample 8, which are arranged from top to bottom.

[0091] Core diameter d 1The incident light 19 from the first multimode optical fiber 16 reaches the upper and lower surfaces of the window film layer 13 via the standard lens 12, a part of which is directly reflected to become the reflected light 20 by the standard lens 12, another part of which is transmitted to reach the upper surface of the sample 8 via the air gap 18, and is then reflected again to reach the standard lens 12 via the window film layer 13 to become the reflected light 21 by the sample. Finally, the incident light 19 reaches the upper and lower surfaces of the window film layer 13 via the air gap 18, and finally reaches the upper surface of the sample 8 via the air gap 18 via the core diameter d 2 The light is received by the second multimode optical fiber 17 .

[0092] Based on the principle of multi-beam interference by a parallel plate, the window film layer 13 and the sample 8 form an FP cavity. The incidence angle and refraction angle of the incident light 19 on the upper surface of the window film layer 13 are respectively θ 0 and θ 1 Assume that the incident angle and the refraction angle of the incident light 19 on the lower surface of the window film layer 13 are θ 1 and θ 2 The incident angle and the refraction angle of the incident light 19 on the upper surface of the sample 8 are respectively θ 2 and θ 3 and the refractive indices of the standard lens 12, the window film layer 13, the air gap 18 and the sample 8 are n 0 , n 1 , n 2 and n 3 Let the reflection coefficient and transmission coefficient at the interface between the standard lens 12 and the window film layer 13 be r 1 and t 1 and the reflection and transmission coefficients at the interface between the window film layer 13 and the air gap 18 are r 2 and t 2 The reflection coefficient at the interface between the air gap 18 and the sample 8 is r 3 The thicknesses of the window film layer 13 and the air gap 18 are c 1 and c 2 As a result, we were able to construct a multilayer film structure.

[0093] Based on the multilayer film structure constructed as above, FIG. 5 is a schematic flow chart of a method for determining an absolute distance according to a fourth embodiment of the present disclosure.

[0094] As shown in FIGS. 4 and 5, in the embodiment of the present disclosure, in the above distance determining step, the absolute distance between the sample 8 and the FP sensor probe is determined by the following steps S510 to S540.

[0095] Step S510: Based on the principle of multi-beam interference by a parallel plate, the window film layer 13 and the sample 8 are regarded as an FP cavity, and the reflection coefficient of the FP cavity is calculated.

[0096] In an embodiment of the present disclosure, the reflection coefficient of the FP cavity can be calculated by the following formula: JPEG0007675868000046.jpg19164 In the formula, s and p represent s-waves and p-waves, respectively. JPEG0007675868000047.jpg148 represents the reflection coefficient at the interface between the standard lens 12 and the window film layer 13 corresponding to the t-wave, JPEG0007675868000048.jpg119 represents the reflection coefficient at the interface between the window film layer 13 and the air gap 18 corresponding to t-waves; JPEG0007675868000049.jpg128 represents the reflection coefficient at the interface between the air gap 18 and the sample 8 corresponding to the t-wave, JPEG0007675868000050.jpg1020 represents the phase shift of light due to changes in optical path length in the window film layer 13 and the air gap 18, respectively; JPEG0007675868000051.jpg97 represents the reflection coefficient of the FP cavity corresponding to the t-wave.

[0097] specifically, JPEG0007675868000052.jpg1361 is calculated using the following formula. JPEG0007675868000053.jpg37142 In the formula, n 0 , n 1 , n 2 , n 3 represent the refractive indices of the standard lens 12, the window film layer 13, the air gap 18 and the sample 8, respectively, and θ 0 , θ 1 represent the angle of incidence and the angle of refraction of the incident light 19 from the first multimode optical fiber 16 at the top surface of the window film layer 13, respectively, and θ 2 represents the refraction angle of the incident light 19 at the lower surface of the window film layer 13, and θ 3 represents the angle of refraction of the incident light 19 at the top surface of the sample 8, In JPEG0007675868000054.jpg1122, when the light beam is obliquely incident, the refractive index is n m-1 and n m represent the reflection coefficients of s-waves and p-waves at the interface of two media, respectively.

[0098] In an embodiment of the present disclosure, JPEG0007675868000055.jpg1020 is calculated using the following formula. JPEG0007675868000056.jpg15102 c 1 , c 2 are the thicknesses of the window film layer 13 and the air gap 18, respectively, and λ is the spectral wavelength of the light from the measurement light source.

[0099] Step S520: Calculate the simulated reflectance of the FP cavity based on the reflection coefficient, and build a model base of the simulated reflectance of the FP cavity corresponding to the air gap 18 of different thicknesses.

[0100] In the embodiment of the present disclosure, the simulated reflectance of the FP cavity is calculated according to the following formula: JPEG0007675868000057.jpg1684 R sim represents the simulated reflectance of the FP cavity, JPEG0007675868000058.jpg1020 represents the reflection coefficients of the FP cavity for s-waves and p-waves, respectively.

[0101] Using the above formula, different thicknesses c 2 The simulated reflectivity R of the FP cavity corresponding to the air gap of 18 sim It is possible to build a model base of

[0102] Step S530: The actual reflectance of the FP cavity is calculated.

[0103] In the embodiment of the present disclosure, the measured reflectance of the FP cavity is calculated according to the following formula: JPEG0007675868000059.jpg1992 R exp represents the measured reflectivity of the FP cavity, and I sample represents the reflected light intensity of the sample, and is typically the light intensity carrying absolute distance information of the air gap 18 output by the second multimode optical fiber 17. dark represents the stray light intensity, which is typically the light intensity of the stray light directly received by the second multimode optical fiber 17, and includes the environmental stray light intensity and the light intensity of the light from the first multimode optical fiber 16 that directly enters the environment without passing through the imaging lens group 11, the standard lens 12, and the window film layer 13. ref R represents the reference light intensity, which typically represents the light intensity of the output light of the second multimode optical fiber 17 when the air gap 18 between the window film layer 13 and the sample 8 exceeds the measurement range of the FP sensor probe (e.g., 2.5 times the measurement range, the specific value can be selected empirically and is not limited here). refrepresents the reflectance correction factor, which is typically the reflectance coefficient when the air gap 18 between the window film layer 13 and the sample 8 exceeds the measurement range of the FP sensor probe.

[0104] Specifically, R ref is calculated according to the following formula: JPEG0007675868000060.jpg1370 r 13、 t 13 represent the reflection and transmission coefficients, respectively, of the window film layer 13. r′ represents the reflection coefficient at the interface between the air gap 18 and the sample 8.

[0105] Step S540: A cross-correlation calculation is performed between the measured reflectance and a plurality of simulated reflectances based on the model, and the thickness of the air gap 18 corresponding to the simulated reflectance with the highest correlation is determined as the absolute distance between the sample 8 and the FP sensor probe.

[0106] FIG. 6 is a graph showing a comparison of spectral curves of measured reflectance and simulated reflectance according to a third embodiment of the present disclosure.

[0107] Through the above process of determining the absolute distance, the representative simulation value (i.e., the simulation reflectance) and the actual measurement value (i.e., the actual measurement reflectance) spectrum curves are as shown in Fig. 6. As can be seen from Fig. 6, the simulation value is extremely close to the actual measurement value, that is, the absolute distance measurement method using the above absolute distance measurement device according to the third embodiment of the present disclosure can realize the measurement of the absolute distance with high accuracy.

[0108] As can be seen from the above description, the FP sensor probe, the absolute distance measuring device, and the absolute distance measuring method according to the above embodiments of the present disclosure can achieve at least the following technical effects.

[0109] The present disclosure realizes measurement of the absolute distance between a sensor probe and a measurement target surface based on the principle of optical fiber Fabry-Perot (FP) interferometry, and has features such as high accuracy, high resolution, excellent turn-off / restart repeatability, and non-contact, making it possible to measure absolute distance without the need for orientation.

[0110] The specific order or inclusion of steps in the disclosed processes is an example of an exemplary method. As a design preference, the specific order or inclusion of steps in the processes may be recombined without departing from the scope of protection of the present disclosure. The accompanying method claims describe the elements of each step in an exemplary order, but are not meant to be limited to the specific order or inclusion.

[0111] In the description of the present disclosure, the directions or positional relationships expressed by terms such as "upper", "lower", "front", "rear", "left", and "right" are based on the drawings and are merely for the purpose of simply and concisely describing the present disclosure, and do not expressly or imply that the relevant devices or parts necessarily have a specific direction, or are constructed or operated in a specific direction, and therefore do not limit the present disclosure. In the drawings, similar elements are represented by the same or similar symbols. When there is a risk of interfering with the understanding of the present disclosure, a description of the general configuration or structure is omitted. Furthermore, the shape, dimensions, and positional relationship of each member shown in the drawings do not indicate the actual size, ratio, or positional relationship.

[0112] Similarly, in the above description of exemplary embodiments of the present disclosure, features of the present disclosure are grouped together in a single embodiment, figure, or description in order to simplify the present disclosure and facilitate understanding of one or more of the disclosed aspects. Descriptions using terms such as "one embodiment," "several embodiments," "examples," "particular examples," or "several examples" mean that the specific features, structures, materials, or characteristics described in the embodiment or example are included in at least one embodiment or example of the present disclosure. In this specification, exemplary expressions for the above terms do not necessarily refer to the same embodiment or example. And the specific features, structures, materials, or characteristics described can be appropriately combined in any one or more embodiments or examples.

[0113] Additionally, the terms "first" and "second" are merely for illustrative purposes and do not express or imply a relative importance or number of technical features. Thus, a feature qualified by "first" or "second" may expressly or imply that it includes one or more of the relevant features. In the description of this disclosure, unless otherwise specified, "plurality" means two or more, e.g., two, three, etc. Additionally, the term "1" or "one" preceding an element does not exclude the presence of a plurality of such elements. Unless otherwise specified, the expressions "approximately," "about," "essentially," and "about" mean within 10%, preferably within 5%.

[0114] The above specific examples further illustrate the objectives, technical solutions and beneficial effects of the present disclosure. The above are only specific examples of the present disclosure and do not limit the present disclosure. As long as they do not deviate from the spirit and principle of the present disclosure, any modifications, equivalent replacements, improvements, etc., fall within the scope of protection of the present disclosure. [Explanation of symbols]

[0115] 1 FP sensor connector 2-throw fiber optic connector 3 Receiving fiber connector 4. Second N+1 core multimode optical fiber 5 N-core multimode optical fiber 6 Single-core multimode optical fiber 7 1x2 Fiber Optic Coupler 8 Samples 9 First N+1 core multimode optical fiber head 10 Optical fiber sleeve 11 Imaging lens group 12 Standard Lens 13 Window Film Layers 14. Light reflected by sample 15 Reflected light from a standard lens 16 First multimode optical fiber 17 Second multimode optical fiber 18 Air gap 19 Incident light 20 Reflected light from a standard lens 21 Reflection from the sample

Claims

1. An FP sensor probe, A first N+1 core multimode optical fiber head (9), an optical fiber sleeve (10), an imaging lens group (11), and a standard lens (12), the first N+1 core multimode optical fiber head (9), an imaging lens group (11) and a standard lens (12) are fixed in order inside the optical fiber sleeve (10) along a direction from the F-P sensor probe to a sample (8); The first N+1 core multimode optical fiber head (9) includes N first multimode optical fibers (16) and one second multimode optical fiber (17), where N satisfies N≧2, and the N first multimode optical fibers (16) are arranged around the second multimode optical fiber (17). The FP sensor probe is characterized by:

2. When the reflectance of the surface of the sample (8) is 40% or more, the FP sensor probe further includes a window film layer (13), and the window film layer (13) is attached to the surface of the standard lens (12).

2. The FP sensor probe according to claim 1.

3. The window film layer (13) is a metal film layer having a transmittance of 40%±5% and a reflectance of 15%±5%, and the metal film layer includes a metal chrome layer having a thickness of 4-8 nm.

3. The FP sensor probe according to claim 2.

4. The standard lens (12) is made of quartz glass having a thickness of 5 mm or more and a surface roughness PV of the surface that satisfies PV≦λ / 20, where λ is the wavelength of an interferometer used to measure the surface roughness of the standard lens (12).

2. The FP sensor probe according to claim 1.

5. The second multimode optical fiber (17) is installed at the center position of the first N+1 core multimode optical fiber head (9), and N of the first multimode optical fibers (16) are arranged around the second multimode optical fiber (17) at intervals Δd １ are arranged in a ring at equal intervals.

2. The FP sensor probe according to claim 1.

6. Each of the N first multimode optical fibers (16) is disposed so as to be in contact with the second multimode optical fiber (17).

6. The FP sensor probe according to claim 5.

7. The core diameter d of the first multimode optical fiber (16) １ and the core diameter d of the second multimode optical fiber (17). ２ are all standard core diameters, and d ２ ≧d １ Fulfilling The distance Δd between two adjacent first multimode optical fibers (16) １ 0≦Δd １ ≦d １ / 2 is satisfied 2. The FP sensor probe according to claim 1.

8. The number of the first multimode optical fibers (16) is determined by the following formula: N is the number of the first multimode optical fibers (16).

8. The FP sensor probe according to claim 7.

9. 2. An absolute distance measuring device using the FP sensor probe according to claim 1, The present invention includes an F-P sensor probe, an F-P sensor connector (1), a second N+1 core multimode optical fiber (4), a 1×2 optical fiber coupler (7), an N-core multimode optical fiber (5), a single-core multimode optical fiber (6), a light projecting optical fiber connector (2), a light receiving optical fiber connector (3), a light projecting light source, and a demodulation system, The first N+1 core multimode optical fiber head (9) of the FP sensor probe is connected to the FP sensor connector (1); an end of the F-P sensor connector (1) remote from the F-P sensor probe is connected in turn to the second N+1 core multimode optical fiber (4) and a first end of a 1×2 optical fiber coupler (7), and a second end of the 1×2 optical fiber coupler (7) is connected to each of the N core multimode optical fiber (5) and the single-core multimode optical fiber (6); The N-core multimode optical fiber (5) is connected to a light projecting optical fiber connector (2), the single-core multimode optical fiber (6) is connected to a light receiving optical fiber connector (3), the light projecting optical fiber connector (2) is connected to a light projecting light source, and the light receiving optical fiber connector (3) is connected to a demodulation system, the light projecting light source is configured to project light, and the demodulation system is configured to determine an absolute distance between a sample (8) and an F-P sensor probe. Absolute distance measuring device.

10. A first multimode optical fiber (16) in the FP sensor probe is connected to the light emitting optical fiber connector (2); A second multimode optical fiber (17) in the FP sensor probe is connected to the receiving optical fiber connector (3).

10. An absolute distance measuring device according to claim 9.

11. The floodlight source includes a halogen lamp light source, an LED, an SLD, and a supercontinuum laser light source; The demodulation system includes a spectrometer that acquires and analyzes interference light intensity signals at different distances, and an FP optical fiber demodulator.

10. An absolute distance measuring device according to claim 9.

12. 10. An absolute distance measuring method using the absolute distance measuring device according to claim 9, comprising the steps of: a light input step in which light from a light projecting light source is joined and enters a branch path where a light projecting optical fiber connector (2) is located, exits via N first multimode optical fibers (16) in a first N+1 core multimode optical fiber head (9), enters the F-P sensor probe, and is focused in an air gap (18) between a standard lens (12) and a sample (8); a light reflection step, in which the light beam is reflected by a standard lens (12) and the surface of the sample (8), then passes through the F-P sensor probe, is refocused by a second multimode optical fiber (17) in the first N+1 core multimode optical fiber head (9), and finally arrives at the receiving optical fiber connector (3); and a distance determining step of determining an absolute distance between the sample (8) and the FP sensor probe by analyzing the optical signal received by the receiving optical fiber connector (3). Absolute distance measurement method.

13. The light incidence step includes: The method includes a step in which light from a light projection light source is joined and enters a projection optical fiber connector (2), and then sequentially passes through an N-core multimode optical fiber (5), a 1×2 optical fiber coupler (7), and a second N+1-core multimode optical fiber (4) to arrive at the F-P sensor probe, and after exiting from N first multimode optical fibers (16) in a first N+1-core multimode optical fiber head (9), the light passes through an imaging lens group (11) and a standard lens (12) in order, and is first focused on an air gap (18) between the standard lens (12) and the sample (8).

13. The method for measuring absolute distance according to claim 12.

14. The light reflecting step includes: The light reflected by the standard lens (12) and the surface of the sample (8) passes through the standard lens (12) and the imaging lens group (11) in order, and is re-focused by the second multimode optical fiber (17) in the first N+1 core multimode optical fiber head (9), and is merged and enters the second multimode optical fiber (17); the optical signal having the absolute distance information of the air gap (18) arrives at the receiving optical fiber connector (3) via the second N+1 core multimode optical fiber (4), the 1×2 optical fiber coupler (7) and the single-core multimode optical fiber (6).

13. The method for measuring absolute distance according to claim 12.

15. The distance determining step includes: receiving and analyzing the optical signal by a demodulation system to obtain a thickness of the air gap (18) between the standard lens (12) and the sample (8), thereby determining the absolute distance between the sample (8) and the FP sensor probe.

13. The method for measuring absolute distance according to claim 12.

16. The absolute distance between the sample (8) and the FP sensor probe is determined by the following method: Based on the principle of multi-beam interference by a parallel plate, the standard lens (12) and the sample (8) are regarded as an F-P cavity, and the reflection coefficient of the F-P cavity is calculated; Calculating a simulated reflectance of the FP cavity based on the reflection coefficient, and constructing a model base of simulated reflectance of the FP cavity corresponding to air gaps (18) of different thicknesses; Calculate the measured reflectivity of the FP cavity; A cross-correlation calculation is performed between the measured reflectance and a plurality of simulated reflectances based on the model, and the thickness of the air gap (18) corresponding to the simulated reflectance with the highest correlation is determined as the absolute distance between the sample (8) and the F-P sensor probe.

16. The method for measuring absolute distance according to claim 15.

17. The reflection coefficient of the FP cavity is calculated according to the following formula: In the formula, s and p represent s-waves and p-waves, respectively. represents the reflection coefficient at the interface between the standard lens (12) and the air gap (18) corresponding to the t-wave, represents the reflection coefficient at the interface between the air gap (18) and the sample (8) corresponding to the t-wave, represents the phase shift of light due to the change in optical path length in the standard lens (12) and the air gap (18); represents the reflection coefficient of the F-P cavity corresponding to the t wave, specifically, is calculated according to the following formula: In the formula, n ０ , n １ , n ２ represent the refractive indices of the standard lens (12), the air gap (18) and the sample (8), respectively, and θ ０ , θ １ represent the angle of incidence and the angle of refraction of the incident light (19) from the first multimode optical fiber (16) at the lower surface of the standard lens (12), respectively, and θ ２ represents the angle of refraction of the incident light (19) at the top surface of the sample (8); When the light beam is obliquely incident, the refractive index is n ｍ－１ and n ｍ represent the reflection coefficients of s-waves and p-waves at the interface of two media, respectively.

17. The method of claim 16, wherein the absolute distance is measured.

18. The above is calculated according to the following formula: c １ is the thickness of the air gap (18), and λ is the spectral wavelength of the light from the measurement light source.

18. The method for measuring absolute distance according to claim 17.

19. A window film layer (13) is attached to the surface of the standard lens (12), and the reflection coefficient of the FP cavity is calculated according to the following formula: In the formula, s and p represent s-waves and p-waves, respectively. represents the reflection coefficient at the interface between the standard lens (12) and the window film layer (13) corresponding to the t-wave, represents the reflection coefficient at the interface between the window film layer (13) and the air gap (18) corresponding to the t-wave, represents the reflection coefficient at the interface between the air gap (18) and the sample (8) corresponding to the t-wave, represent the phase shift of light due to the change in optical path length in the window film layer (13) and the air gap (18), respectively; represents the reflection coefficient of the F-P cavity corresponding to the t wave, specifically, is calculated according to the following formula: In the formula, n ０ , n １ , n ２ , n ３ represent the refractive indices of the standard lens (12), the window film layer (13), the air gap (18) and the sample (8), respectively, and θ ０ , θ １ represent the angle of incidence and the angle of refraction of the incident light (19) from the first multimode optical fiber (16) at the top surface of the window film layer (13), respectively, and θ ２ represents the refraction angle of the incident light (19) at the lower surface of the window film layer (13), and θ ３ represents the angle of refraction of the incident light (19) at the top surface of the sample (8); When the light beam is obliquely incident, the refractive index is n ｍ－１ and n ｍ represent the reflection coefficients of s-waves and p-waves at the interface of two media, respectively.

17. The method of claim 16, wherein the absolute distance is measured.

20. The above is calculated according to the following formula: c １ , c ２ are the thicknesses of the window film layer (13) and the air gap (18), respectively, and λ is the spectral wavelength of the light from the measurement light source.

20. The method of claim 19, wherein the absolute distance is measured.

21. The simulated reflectance of the FP cavity is calculated according to the following formula: R ｓｉｍ represents the simulated reflectance of the FP cavity, represent the reflection coefficients of the F-P cavity for s-waves and p-waves, respectively.

17. The method of claim 16, wherein the absolute distance is measured.

22. The measured reflectance of the FP cavity is calculated according to the following formula: R ｅｘｐ represents the measured reflectance of the FP cavity, and I ｓａｍｐｌｅ represents the reflected light intensity of the sample, and I ｄａｒｋ represents the stray light intensity, and I ｒｅｆ represents the reference light intensity, R ｒｅｆ represents the reflectance correction factor, Specifically, R ｒｅｆ is calculated according to the following formula: r １２、 t １２ are the reflection and transmission coefficients of the standard lens (12), respectively, and r′ is the reflection coefficient at the interface between the air gap (18) and the sample (8).

17. The method of claim 16, wherein the absolute distance is measured.

23. A window film layer (13) is attached to the surface of the standard lens (12), and the measured reflectance of the FP cavity is calculated according to the following formula: R ｅｘｐ represents the measured reflectance of the FP cavity, and I ｓａｍｐｌｅ represents the reflected light intensity of the sample, and I ｄａｒｋ represents the stray light intensity, and I ｒｅｆ represents the reference light intensity, R ｒｅｆ represents the reflectance correction factor, Specifically, R ｒｅｆ is calculated according to the following formula: r １３、 t １３ represent the reflection and transmission coefficients of the window film layer (13), respectively, and r′ represents the reflection coefficient at the interface between the air gap (18) and the sample (8).

17. The method of claim 16, wherein the absolute distance is measured.

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