Optical film reflectance measurement system and method based on optical interference

Abstract

The application provides an optical thin film reflectivity measurement system based on optical interference, comprising: a fiber end surface reflectivity test subsystem, which collects multiple sets of interference spectra by changing the cavity length distance between two fiber end surfaces and calculates the corresponding cavity length; fits the multiple sets of interference spectra based on a double-beam interference formula and calculates the measured reflectivity of the fiber end surface; compares the measured reflectivity with the standard reflectivity of the fiber end surface directly measured by a spectrometer, and obtains a relationship formula of the reflectivity compensation coefficient-cavity length through polynomial fitting; a graphene thin film reflectivity test subsystem, which collects multiple sets of interference spectra by changing the distance between the aligned single-mode optical fiber and the optical thin film, fits the interference spectra based on a double-beam interference formula, and thus calculates the measured reflectivity of the optical thin film; and a correction subsystem, which corrects the measured reflectivity of the optical thin film based on the expression of the reflectivity compensation coefficient to obtain the corrected reflectivity of the optical thin film. A corresponding measurement method is also disclosed.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical measurement technology, and in particular to an optical thin film reflectivity measurement system and method based on optical interference. BACKGROUND

[0002] Optical thin films are a kind of optical medium materials composed of thin layered media, which propagate light beams through interfaces. Optical thin films endow optical elements with various use properties and are widely used in numerous optical systems and devices. The performance and quality of optical thin films directly affect the application level of optical systems or devices.

[0003] Among them, reflectivity is one of the most basic and important optical properties of optical thin films, so the measurement of optical thin film reflectivity is also one of the key measurement techniques of optical thin films. Reflectivity refers to the ratio of reflected radiant flux or luminous flux to incident flux under given conditions (wavelength, polarization state and incident angle of incident light, etc.). The most commonly used optical interference reflectivity measurement method is to measure reflectivity by demodulating the interference spectrum, and according to the “GB / T 37412-2019 Laser and Laser Related Equipment Optical Cavity Ring-Down High Reflectivity Measurement Method” issued by the China National Standardization Management Committee, the reflectivity measurement result is independent of the cavity length, but other factors that can affect the reflectivity measurement result may be related to the cavity length, such as diffraction loss, limited instrument response time, etc. Therefore, in order to obtain high-precision optical thin film reflectivity, especially the low reflectivity value of ultra-thin optical thin film, a reasonable correction method needs to be introduced to improve the measurement precision.

[0004] In the late 1970s, to solve the problem of optical coating for laser gyroscopes, Academician Gao Bolong proposed a transmission / reflection measurement scheme using the differential principle. The transmission / reflection instrument prepared based on this principle is still widely used at present. Later, with the advent of the transmission / reflection rate integrating sphere, the measurement of transmission and reflectivity of various media was realized, but it was expensive and had high space occupancy, making it difficult to popularize. In 2020, a reflectivity measurement method for curved optical thin film elements was disclosed in Chinese patent document CN110646169, which provided a solution to the problem of difficult collection of light rays at different angles, ensuring the measurement precision of the reflectivity of curved optical thin film elements with different radii of curvature. However, this method still relies on an integrator, and the measurement precision of the reflectivity of planar optical thin films is not mentioned. In 2021, a high-precision optical thin film reflectivity measurement method was disclosed in Chinese patent document CN113008833A, which constructed a balanced detection light path and used the Fresnel formula and the differential principle to convert the reflectivity measurement problem of the measurement light beam into a reflectivity precision calibration problem of the reference light beam on the surface of the optical prism. However, the test system used in this method is complex, and the impact of optical path loss is not considered.

[0005] Therefore, the existing research shows that in the field of reflectivity measurement of optical thin films, there are the following technical defects:

[0006] (1) The light interference method is the most commonly used and most accurate measurement method, but the light interference method is inevitably affected by the light loss in the transmission process. The light loss will cause errors in the calculation of the reflectivity, further causing the measured optical thin film reflectivity to be inaccurate.

[0007] (2) The reflectivity testing instrument on the market has a complex structure, a high space occupancy rate, and great limitations in the testing method of ultra-thin optical thin films. SUMMARY

[0008] The present application provides an optical thin film reflectivity measurement system and method based on optical interference, which overcomes the defects of the prior art. The basic principle is to measure the reflectivity of the optical thin film. The measurement system and method in the present application perform double-beam interference fitting on the interference spectrum, and combine the calibration compensation of the standard reflectivity of the fiber end face to realize accurate calculation of the reflectivity of the optical thin film, thereby effectively reducing the problem of large measurement error of the reflectivity of the optical thin film, making the test system more resistant to interference, and having important practical significance and application value for the study of thin film optical properties.

[0009] According to one aspect of the present application, an optical thin film reflectivity measurement system based on optical interference is provided, comprising:

[0010] The fiber end face reflectivity testing subsystem, the optical thin film reflectivity testing subsystem, and the correction subsystem, wherein:

[0011] The fiber end face reflectivity testing subsystem is used to obtain a relationship between the reflectivity compensation coefficient and the cavity length, comprising: performing reflectivity data acquisition of the optical fiber, collecting multiple sets of interference spectra by changing the cavity length distance between the two fiber end faces, and calculating the corresponding cavity length; fitting the multiple sets of interference spectra based on the double-beam interference formula and calculating the measured reflectivity of the fiber end face; comparing the measured reflectivity with the standard reflectivity of the fiber end face directly measured by the spectrometer, and obtaining the relationship between the reflectivity compensation coefficient and the cavity length by polynomial fitting;

[0012] The optical thin film reflectivity testing subsystem is used to change the distance between the aligned single-mode optical fiber and the optical thin film, collect multiple sets of interference spectra using the fiber end face reflectivity testing subsystem, fit the interference spectra based on the double-beam interference formula, and thereby calculate the measured reflectivity of the optical thin film;

[0013] The correction subsystem corrects the measured reflectivity of the optical thin film based on the expression of the reflectivity compensation coefficient, thereby obtaining the corrected reflectivity of the optical thin film;

[0014] in:

[0015] The optical fiber end face reflectivity test subsystem comprises an incident single-mode optical fiber (1), a ferrule (2), a ferrule matching sleeve (3), epoxy resin glue (4), a reflective single-mode optical fiber (5), a spectrometer (6), a broadband light source (7), an optical circulator (8) and a three-dimensional optical fiber micro-motion platform; wherein, the incident single-mode optical fiber (1) has an incident single-mode optical fiber end face (11), and the reflective single-mode optical fiber (5) has a reflective single-mode optical fiber end face (51); one end of the ferrule (2) is a polished end face, which is a zirconium oxide ferrule; the bottom surface of the ferrule matching sleeve (3) is C-shaped, and the material is zirconium oxide, SiO2 or glass, The broadband light source (7) is used to provide an optical input signal, the spectrometer (6) is used to collect the interference spectrum of the incident single-mode optical fiber (1) and the reflected single-mode optical fiber (5), and the optical circulator (8) is used to transmit the optical signal. By changing the distance between the incident single-mode optical fiber end face (11) and the reflected single-mode optical fiber end face (51), the cavity length of the Fabry-Perot interferometer cavity is adjusted, and the interference spectrum of the incident single-mode optical fiber (1) and the reflected single-mode optical fiber (5) is processed to obtain the cavity length and the reflectivity of the reflected single-mode optical fiber end face (51) of the reflected single-mode optical fiber (5) to be measured, as well as the relationship between the reflectivity compensation coefficient and the cavity length;

[0016] The optical film reflectivity test subsystem comprises an incident single-mode optical fiber (1), a ferrule (2), a ferrule matching sleeve (3), an epoxy resin glue (4), a spectrometer (6), a broadband light source (7), an optical circulator (8), and a three-dimensional optical fiber micro-motion platform, which are shared with the optical fiber end face reflectivity test subsystem, and also comprises an optical film (9) and an electron microscope copper mesh (10); wherein the optical film (9) is covered on the electron microscope copper mesh (10); the broadband light source (7) provides an optical input signal, and the spectrometer (6) collects the interference light of the incident single-mode optical fiber (1) and the optical film (9). The optical circulator (8) is used for transmitting optical signals, the incident single-mode optical fiber (1) has an incident single-mode optical fiber end face (11), and the distance between the incident single-mode optical fiber end face (11) and the optical film (9) is adjusted by a three-dimensional optical fiber micro-motion platform to change the distance between the incident single-mode optical fiber end face (11) and the optical film (9), thereby adjusting the cavity length of the Fabry-Perot interferometer cavity, and performing data processing on the interference spectrum between the incident single-mode optical fiber end face (11) and the optical film (9) to obtain the cavity length and the reflectivity of the optical film, and after correction by the reflectivity compensation coefficient, obtain the corrected reflectivity of the optical film.

[0017] Preferably, the optical film (9) is a single-layer, few-layer or multi-layer film; the shape of the optical film (9) is circular, square, triangular or a combination of the above different shapes.

[0018] The present invention also aims to provide a method for measuring the reflectivity of an optical thin film based on optical interference, comprising:

[0019] Step 1, selecting components of the optical fiber end face reflectivity test subsystem and the optical film reflectivity test subsystem and assembling them respectively according to the test process, wherein the components include an incident single-mode optical fiber (1), a ferrule (2), a ferrule matching sleeve (3), epoxy resin glue (4), a reflective single-mode optical fiber (5), a spectrometer (6), a broadband light source (7), an optical circulator (8), an optical film (9), an electron microscope copper mesh (10), and a three-dimensional optical fiber micro-motion platform;

[0020] Step 2, pre-treating the incident single-mode optical fiber (1), the ferrule (2), the ferrule matching sleeve (3), and the reflective single-mode optical fiber (5), comprising: performing ultrasonic and deionized water cleaning on the ferrule (2) and the ferrule matching sleeve (3), then using a fiber cleaver to cut the tail ends of the incident single-mode optical fiber (1) and the reflective single-mode optical fiber (5), removing the coating layer and the cladding to expose a portion of the bare fiber, and inspecting the flatness of the end faces of the incident single-mode optical fiber (1) and the reflective single-mode optical fiber (5) using a microscope or an end face detector;

[0021] Step 3, obtaining an expression for a reflectivity compensation coefficient based on the optical fiber end face reflectivity testing subsystem;

[0022] Step 4: Based on the optical film reflectivity testing subsystem, by changing the distance between the aligned single-mode optical fiber and the optical film, using multiple sets of interference spectra collected by the optical fiber end face reflectivity testing subsystem, fitting the interference spectra based on a double-beam interference formula, thereby solving the measured reflectivity of the optical film;

[0023] Step 5: Correcting the measured reflectivity of the optical film based on the expression of the reflectivity compensation coefficient to obtain the corrected reflectivity of the optical film.

[0024] Preferably, the step 3 comprises:

[0025] Step 31, inserting the incident single-mode optical fiber (1) and the reflective single-mode optical fiber (5) pre-treated in step 2 into two different ferrules (2), fixing one of the single-mode optical fibers in the ferrule (2) using the epoxy resin glue (4), and then inserting the two ferrules (2) from both ends of the ferrule matching sleeve (3) respectively, so that the end faces of the incident single-mode optical fiber (1) and the reflective single-mode optical fiber (5) are parallel and on the same horizontal line, thereby forming a Fabry-Perot interferometer cavity;

[0026] Step 32, collecting reflectivity data of the end faces of the incident single-mode optical fiber (1) and the reflective single-mode optical fiber (5), adjusting the three-dimensional optical fiber micro-motion platform to change the cavity length distance between the end faces of the incident single-mode optical fiber (1) and the reflective single-mode optical fiber (5), changing the cavity length distance between the end faces of the incident single-mode optical fiber (1) and the reflective single-mode optical fiber (5), and collecting multiple sets of interference spectra under different cavity length conditions;

[0027] Step 33, calculating the cavity lengths corresponding to the multiple sets of interference spectra, and fitting the interference spectra based on a double-beam interference formula to obtain the measured reflectivity of the reflective single-mode fiber end face (51) of the reflective single-mode fiber (5) to be measured;

[0028] Step 34, comparing the measured reflectivity with the reflectivity of the reflective single-mode optical fiber (5) directly measured by a spectrometer, and fitting the relationship between the reflectivity compensation coefficient and the cavity length through a polynomial.

[0029] Preferably, step 4 includes:

[0030] Step 41, after cutting the optical film (9) to a size suitable for the electron microscope copper mesh, the optical film (9) is transferred to the mesh of the electron microscope copper mesh (10);

[0031] Step 42, aligning the incident single-mode optical fiber (1) with the optical film (9), adjusting the three-dimensional optical fiber micro-motion platform to change the cavity length distance between the incident single-mode optical fiber (1) and the end face of the optical film (9), changing the distance between the incident single-mode optical fiber (1) and the optical film (9), collecting multiple groups of interference spectra of the incident single-mode optical fiber end face (11) of the incident single-mode optical fiber (1) and the optical film (9), fitting the interference spectra based on the double-beam interference formula, and solving the measured reflectivity of the optical film.

[0032] Preferably, the step 33 of calculating the cavity lengths corresponding to the multiple sets of interference spectra includes:

[0033] The interference spectrum is demodulated by the optical signal double-peak phase demodulation method, and the calculated cavity length can be expressed as:

[0034]

[0035] Wherein, λ1 and λ2 are two adjacent peak-to-peak values ​​or minimum values ​​of the interference spectrum;

[0036] Preferably, the principle of directly measuring the reflectivity of the reflective single-mode optical fiber (5) by the spectrometer in step 34 is: collecting the reflection spectrum of the optical fiber end face, and calculating the reflectivity of the reflective single-mode optical fiber (5) according to the dimensionless relative light intensity The calculation formula is: r and I iare the reflected light intensity and the incident light intensity, I r / I i That is, the reflectivity of the optical fiber end face directly measured by the spectrometer.

[0037] Preferably, the step 41 of transferring the optical film (9) to the mesh of the electron microscope copper mesh (10) includes: dry transfer or wet transfer.

[0038] Preferably, the step 42 of aligning the incident single-mode optical fiber (1) with the optical film (9) includes: fixing the incident single-mode optical fiber end face (11) and the electron microscope copper mesh (10) at the center of the microscope; using a pump light source to emit colored light through an optical attenuator to the incident single-mode optical fiber (1), and adjusting the position of the electron microscope copper mesh (10) under the field of view of the microscope so that the colored light spot on the end face of the single-mode optical fiber is directly opposite to the small hole in the electron microscope copper mesh, thereby aligning the incident single-mode optical fiber (1) with the optical film (9) on the mesh of the electron microscope copper mesh (10).

[0039] Preferably, the step 42 of fitting the interference spectrum based on the double-beam interference formula to calculate the measured reflectivity of the optical film includes:

[0040] The double-beam interference is the interference of two reflected light intensities, and the generated reflected light intensity I r It can be expressed as:

[0041]

[0042] Where, I in is the incident light signal, R1 and R2 are the reflectivity of the two reflecting surfaces, ξ is the coupling coefficient of the Fabry-Perot interferometer cavity, is the phase difference of the light beam reflected from the fiber end face and the optical film, where L is the cavity length of the Fabry-Perot interferometer cavity, and λ is the wavelength of the incident laser.

[0043] The present invention has significant advantages and beneficial effects compared to the prior art. By utilizing the above technical solutions, the method and device provided by the present invention can achieve significant technological advancement and practicality, and have wide industrial application value. It has at least the following advantages:

[0044] (1) The measurement system consists of a broadband light source, a spectrometer, an optical circulator, etc. It has a simple structure, small space occupancy, high cost performance, and strong anti-interference ability. It can be applied to the reflectivity measurement of optical thin films and can solve the practical problems of the existing reflectivity test system with complex structure and high space occupancy;

[0045] (2) The measurement method has the advantages of high measurement accuracy and strong anti-interference capability, wherein the optical thin film reflectivity correction algorithm is based on optical interference method, and the reflectivity is calculated through formula fitting, which effectively reduces the problem of large error of measured optical thin film reflectivity, maximally eliminates the influence of optical transmission loss, increases the accuracy of calculation reflectivity, has practical significance for the study of optical properties of optical thin films, and is expected to serve the field of high-precision optical measurement.

[0046] The above description is only a summary of the technical solutions of the present application, in order to enable the technical means of the present application to be more clearly understood and implemented according to the content of the specification, and in order to enable the above and other purposes, characteristics and advantages of the present application to be more obvious and easy to understand, the following preferred embodiments are described in detail as follows, and the accompanying drawings are described in detail as follows. BRIEF DESCRIPTION OF DRAWINGS

[0047] Some specific embodiments of the present application will be described in detail hereinafter with reference to the accompanying drawings. The same reference signs in the drawings denote the same or similar components or parts. It should be understood by those skilled in the art that the drawings are not necessarily drawn to scale. The objects and features of the present application will become more apparent from the following description in conjunction with the accompanying drawings, in which:

[0048] Figure 1 The structure schematic diagram of the optical fiber end face reflectivity test subsystem according to the embodiment of the present application.

[0049] Figure 2 The structure schematic diagram of the optical thin film reflectivity test subsystem according to the embodiment of the present application.

[0050] Figure 3 The flow chart of the optical thin film reflectivity measurement method based on optical interference according to the embodiment of the present application. DETAILED DESCRIPTION

[0051] In order to further illustrate the technical means and effects adopted by the present application to achieve the predetermined purposes, the specific embodiments, methods, steps and effects according to the present application are described in detail below in conjunction with the drawings and preferred embodiments.

[0052] Through the description of the specific embodiments, a more in-depth and specific understanding of the technical means and effects adopted by the present application to achieve the predetermined purposes can be obtained, however, the accompanying drawings are provided for reference and illustration only, and are not used to limit the present application.

[0053] The embodiment provides an optical thin film reflectivity measurement system based on optical interference, taking graphene film as an example, and specifically comprising:

[0054] Optical fiber end face reflectivity test subsystem, graphene film reflectivity test subsystem and correction subsystem, including:

[0055] The fiber end face reflectivity test subsystem is used to obtain the reflectivity compensation coefficient-cavity length relationship, including: collecting optical fiber reflectivity data, collecting multiple sets of interference spectra and calculating the corresponding cavity length by changing the cavity length distance between the two optical fiber end faces; fitting the multiple sets of interference spectra based on the double-beam interference formula and solving the measured reflectivity of the optical fiber end face; comparing the measured reflectivity with the standard reflectivity of the optical fiber end face directly measured by the spectrometer, and obtaining the reflectivity compensation coefficient-cavity length relationship through polynomial fitting;

[0056] The graphene film reflectivity test subsystem is used to calculate the measured reflectivity of the graphene film by varying the distance between the aligned single-mode optical fiber and the graphene film and fitting the interference spectra based on the double-beam interference formula using multiple sets of interference spectra collected by the optical fiber end face reflectivity test subsystem.

[0057] The correction subsystem corrects the measured reflectivity of the graphene film based on the expression of the reflectivity compensation coefficient, thereby obtaining the corrected reflectivity of the graphene film.

[0058] like Figure 1 The optical fiber end face reflectivity test subsystem shown in the figure includes an incident single-mode optical fiber 1, a ferrule 2, a ferrule matching sleeve 3, epoxy resin glue 4, a reflective single-mode optical fiber 5, a spectrometer 6, a broadband light source 7, an optical circulator 8 and a three-dimensional optical fiber micro-motion platform; wherein, the incident single-mode optical fiber 1 has an incident single-mode optical fiber end face 11, and the reflective single-mode optical fiber 5 has a reflective single-mode optical fiber end face 51. In this embodiment, the outer diameter of the incident single-mode optical fiber 1 and the reflecting single-mode optical fiber 5 is 2.5 mm, the inner diameter is 125±0.7 μm, and the core is 10.4±0.5 μm; one end of the ferrule 2 is a polished end face, with an outer diameter of 2.5 mm and an inner diameter of 126±1 μm, and the ferrule 2 is a zirconia ferrule; the bottom surface of the ferrule matching sleeve 3 is C-shaped, with an outer diameter of 3.2±0.02 mm and an inner diameter of 2.45±0.02 mm, and its material can be zirconia, SiO2 or glass. Of course, those skilled in the art can also use other suitable materials, all of which are within the scope of protection of the present invention. The broadband light source 7 is used to provide an optical input signal, the spectrometer 6 is used to collect the interference spectrum of the incident single-mode optical fiber 1 and the reflected single-mode optical fiber 5, and the optical circulator 8 is used to transmit the optical signal. By changing the distance between the incident single-mode optical fiber end face 11 and the reflected single-mode optical fiber end face 51, the cavity length of the Fabry-Perot interferometer cavity is adjusted, and the interference spectrum of the incident single-mode optical fiber 1 and the reflected single-mode optical fiber 5 is processed to obtain the cavity length and the reflectivity of the reflected single-mode optical fiber end face 51 of the reflected single-mode optical fiber 5 to be measured, as well as the relationship between the reflectivity compensation coefficient and the cavity length.

[0059] Figure 2 Fig. 1 shows a schematic diagram of a graphene film reflectivity test subsystem of the present embodiment. The graphene film reflectivity test subsystem comprises an incident single-mode optical fiber 1, a ferrule 2, a ferrule matching sleeve 3, an epoxy glue 4, a spectrometer 6, a broadband light source 7, an optical circulator 8, and a three-dimensional optical fiber micro-motion platform, and further comprises a graphene film 9 and a copper mesh 10. The graphene film 9 is coated on the copper mesh 10. In the present embodiment, the copper mesh 10 has a specification including 100 mesh, 200 mesh, 300 mesh, 400 mesh, or 600 mesh. The broadband light source 7 provides an optical input signal, the spectrometer 6 collects an interference spectrum of the incident single-mode optical fiber 1 and the graphene film 9, and the optical circulator 8 is used for transmission of the optical signal. The incident single-mode optical fiber 1 has an incident single-mode optical fiber end face 11. The distance between the incident single-mode optical fiber end face 11 and the graphene film 9 can be adjusted by the three-dimensional optical fiber micro-motion platform. The distance between the incident single-mode optical fiber end face 11 and the graphene film 9 is changed to adjust the cavity length of a Fabry-Perot interference cavity. The interference spectrum of the incident single-mode optical fiber end face 11 and the graphene film 9 is processed to obtain the cavity length and the reflectivity of the graphene film. After correction by a reflectivity compensation coefficient, the corrected reflectivity of the graphene film is obtained.

[0060] As a preferred implementation, the graphene film 9 has a shape of a circle, a square, a triangle, or a combination of different shapes. The graphene film 9 is single-layer, few-layer, or multi-layer graphene.

[0061] As shown in Fig. 1, the present embodiment further provides a graphene film reflectivity measurement method based on optical interference, comprising: Figure 3

[0062] Step 1: Selecting components of the fiber end face reflectivity test subsystem and the graphene film reflectivity test subsystem and assembling them according to a test process. The components include the incident single-mode optical fiber 1, the ferrule 2, the ferrule matching sleeve 3, the epoxy glue 4, the reflective single-mode optical fiber 5, the spectrometer 6, the broadband light source 7, the optical circulator 8, the graphene film 9, the copper mesh 10, and the three-dimensional optical fiber micro-motion platform.

[0063] Step 2: Preprocessing the incident single-mode optical fiber 1, the ferrule 2, the ferrule matching sleeve 3, and the reflective single-mode optical fiber 5, including: ultrasonic cleaning the ferrule 2 and the ferrule matching sleeve 3, then cutting the tail ends of the incident single-mode optical fiber 1 and the reflective single-mode optical fiber 5 flat with an optical fiber cutter, removing the coating layer and the cladding layer to expose part of the bare fiber, and checking the flatness of the end faces of the incident single-mode optical fiber 1 and the reflective single-mode optical fiber 5 by a microscope or an end face detector.

[0064] Step 3: Obtaining an expression of the reflectivity compensation coefficient based on the fiber end face reflectivity test subsystem.

[0065] ​Step 4, based on the reflectivity test subsystem of the graphene film, by changing the distance between the aligned single-mode optical fiber and the graphene film, using the multiple sets of interference spectra collected by the fiber end reflectivity test subsystem, based on the double-beam interference formula fitting the interference spectrum, to solve the measured reflectivity of the graphene film;

[0066] Step 5, based on the expression of the reflectivity compensation coefficient, the measured reflectivity of the graphene film is corrected, and the corrected reflectivity of the graphene film is obtained.

[0067] As a preferred embodiment, step 3 comprises:

[0068] Step 31, the incident single-mode optical fiber 1 and the reflected single-mode optical fiber 5 preprocessed in step 2 are inserted into two different cores 2 respectively, one of the single-mode optical fibers is fixed in the core 2 by using epoxy resin glue 4, and then the two cores 2 are inserted into the two ends of the core matching sleeve 3 respectively, so that the end faces of the incident single-mode optical fiber 1 and the reflected single-mode optical fiber 5 are parallel and on the same horizontal line, forming a Fabry-Perot interference cavity.

[0069] Step 32, the reflectivity data of the end faces of the incident single-mode optical fiber 1 and the reflected single-mode optical fiber 5 are collected, the three-dimensional optical fiber micro-motion platform is adjusted to change the cavity length distance between the end faces of the incident single-mode optical fiber 1 and the reflected single-mode optical fiber 5, and multiple sets of interference spectra under different cavity lengths are collected.

[0070] Step 33, the cavity length corresponding to the multiple sets of interference spectra is calculated, and the interference spectrum is fitted based on the double-beam interference formula, and the measured reflectivity of the reflected single-mode optical fiber end face 51 of the reflected single-mode optical fiber 5 to be measured is solved.

[0071] Step 34, the measured reflectivity is compared with the reflectivity of the reflected single-mode optical fiber 5 directly measured by the spectrometer, and the relationship between the reflectivity compensation coefficient and the cavity length is fitted by a polynomial.

[0072] As a preferred embodiment, step 4 comprises:

[0073] Step 41, after the graphene film 9 is cut to a size suitable for the electron microscope copper mesh, the graphene film 9 is transferred to the mesh holes of the electron microscope copper mesh 10;

[0074] Step 42, the incident single-mode optical fiber 1 is aligned with the graphene film 9, the three-dimensional optical fiber micro-motion platform is adjusted to change the cavity length distance between the end faces of the incident single-mode optical fiber 1 and the graphene film 9, the distance between the incident single-mode optical fiber 1 and the graphene film 9 is changed, multiple sets of interference spectra of the incident single-mode optical fiber end face 11 of the incident single-mode optical fiber 1 and the graphene film 9 are collected, the interference spectrum is fitted based on the double-beam interference formula, and the measured reflectivity of the graphene film is solved.

[0075] As a preferred embodiment, the step 33 of calculating the cavity length corresponding to the plurality of sets of interference spectra comprises:

[0076] The calculated cavity length can be expressed as:

[0077]

[0078] In the formula, λ1 and λ2 are two adjacent peak-to-peak values or minimum values of the interference spectrum;

[0079] As a preferred embodiment, the step 34 of directly measuring the reflectivity of the reflection single-mode optical fiber 5 by the spectrometer is based on the principle of collecting the reflection spectrum of the end face of the optical fiber and calculating the dimensionless relative light intensity r i r i , i.e., the reflectivity of the end face of the optical fiber directly measured by the spectrometer.

[0080] As a preferred embodiment, the step 41 of transferring the graphene film 9 to the mesh of the electron microscope copper mesh 10 comprises dry transfer or wet transfer.

[0081] As a preferred embodiment, the step 42 of aligning the incident single-mode optical fiber 1 to the graphene film 9 comprises: fixing the end face 11 of the incident single-mode optical fiber and the electron microscope copper mesh 10 at the center of the microscope; emitting colored light from the pump light source through the optical attenuator to the incident single-mode optical fiber, adjusting the position of the electron microscope copper mesh 10 under the field of view of the microscope so that the colored light spot on the end face of the single-mode optical fiber is directly opposite the small hole in the electron microscope copper mesh, thereby aligning the incident single-mode optical fiber 1 to the graphene film 9 on the mesh of the electron microscope copper mesh 10.

[0082] As a preferred embodiment, the step 42 of fitting the interference spectrum based on the two-beam interference formula to calculate the measured reflectivity of the graphene film comprises:

[0083] The two-beam interference is the interference of two reflected light intensities, and the reflected light intensity I r can be expressed as:

[0084]

[0085] In the formula, I in is the incident light signal, R1 and R2 are the reflectivities of the two reflecting surfaces, ξ is the coupling coefficient of the Fabry-Perot interference cavity, is the phase difference of the light beams reflected from the end face of the optical fiber and the graphene film, wherein, L is the cavity length of the Fabry-Perot interference cavity, and λ is the wavelength of the incident laser.​​​​

[0086] The embodiment has the following advantages:

[0087] (1) The measurement system is composed of a broadband light source, a spectrometer, an optical circulator and the like, has simple structure, small space occupancy, high cost performance and strong anti-interference ability, can be applied not only to reflectivity measurement of graphene film but also to other two-dimensional materials or organic films, and can solve the practical problems of complex structure and high space occupancy of the existing reflectivity test system;

[0088] (2) The measurement method has the advantages of high measurement precision and strong anti-interference ability, wherein the graphene film reflectivity correction algorithm is based on optical interference method, the interference spectrum is solved by formula fitting to reflectivity, the problem of too large error of measured graphene film reflectivity is effectively reduced, the influence of optical transmission loss is maximally eliminated, the accuracy of the solved reflectivity is increased, the optical property research of graphene film has practical significance, and the method is expected to serve the field of high-precision optical measurement.

[0089] The above is only a preferred embodiment of the present application, and does not limit the present application in any form. Although the present application has been disclosed as above with a preferred embodiment, it is not intended to limit the present application. Any skilled person in the art can make some changes or modifications to the above disclosed technical content without departing from the technical solution of the present application, and the equivalent embodiments with equivalent changes are equivalent to the above embodiments. Any simple modification, equivalent change and modification made on the basis of the technical essence of the present application to the above embodiments are still within the scope of the technical solution of the present application.

Claims

1. An optical thin film reflectivity measurement system based on optical interference, characterized in that: include: Optical fiber end face reflectivity test subsystem, optical film reflectivity test subsystem and correction subsystem, including: The optical fiber end face reflectivity test subsystem is used to obtain a reflectivity compensation coefficient-cavity length relationship, including: collecting optical fiber reflectivity data, collecting multiple sets of interference spectra and calculating the corresponding cavity length by changing the cavity length distance between two optical fiber end faces; fitting the multiple sets of interference spectra based on a double-beam interference formula and solving the measured reflectivity of the optical fiber end face; comparing the measured reflectivity with the standard reflectivity of the optical fiber end face directly measured by a spectrometer, and obtaining a reflectivity compensation coefficient-cavity length relationship through polynomial fitting; The optical film reflectivity testing subsystem is used to calculate the measured reflectivity of the optical film by fitting the interference spectra based on a double-beam interference formula using multiple sets of interference spectra collected by the optical fiber end face reflectivity testing subsystem by changing the distance between the aligned single-mode optical fiber and the optical film; The correction subsystem corrects the measured reflectivity of the optical film based on the expression of the reflectivity compensation coefficient, thereby obtaining the corrected reflectivity of the optical film; in: The optical fiber end face reflectivity test subsystem comprises an incident single-mode optical fiber (1), a ferrule (2), a ferrule matching sleeve (3), epoxy resin glue (4), a reflective single-mode optical fiber (5), a spectrometer (6), a broadband light source (7), an optical circulator (8) and a three-dimensional optical fiber micro-motion platform; wherein, the incident single-mode optical fiber (1) has an incident single-mode optical fiber end face (11), and the reflective single-mode optical fiber (5) has a reflective single-mode optical fiber end face (51); one end of the ferrule (2) is a polished end face, which is a zirconium oxide ferrule; the bottom surface of the ferrule matching sleeve (3) is C-shaped, and the material is zirconium oxide, SiO2 or glass, The broadband light source (7) is used to provide an optical input signal, the spectrometer (6) is used to collect the interference spectrum of the incident single-mode optical fiber (1) and the reflected single-mode optical fiber (5), and the optical circulator (8) is used to transmit the optical signal. By changing the distance between the incident single-mode optical fiber end face (11) and the reflected single-mode optical fiber end face (51), the cavity length of the Fabry-Perot interferometer cavity is adjusted, and the interference spectrum of the incident single-mode optical fiber (1) and the reflected single-mode optical fiber (5) is processed to obtain the cavity length and the reflectivity of the reflected single-mode optical fiber end face (51) of the reflected single-mode optical fiber (5) to be measured, as well as the relationship between the reflectivity compensation coefficient and the cavity length; The optical film reflectivity test subsystem comprises an incident single-mode optical fiber (1), a ferrule (2), a ferrule matching sleeve (3), an epoxy resin glue (4), a spectrometer (6), a broadband light source (7), an optical circulator (8), and a three-dimensional optical fiber micro-motion platform, which are shared with the optical fiber end face reflectivity test subsystem, and also comprises an optical film (9) and an electron microscope copper mesh (10); wherein the optical film (9) is covered on the electron microscope copper mesh (10); the broadband light source (7) provides an optical input signal, and the spectrometer (6) collects the interference light of the incident single-mode optical fiber (1) and the optical film (9). The optical circulator (8) is used for transmitting optical signals, the incident single-mode optical fiber (1) has an incident single-mode optical fiber end face (11), and the distance between the incident single-mode optical fiber end face (11) and the optical film (9) is adjusted by a three-dimensional optical fiber micro-motion platform to change the distance between the incident single-mode optical fiber end face (11) and the optical film (9), thereby adjusting the cavity length of the Fabry-Perot interferometer cavity, and performing data processing on the interference spectrum between the incident single-mode optical fiber end face (11) and the optical film (9) to obtain the cavity length and the reflectivity of the optical film, and after correction by the reflectivity compensation coefficient, obtain the corrected reflectivity of the optical film.

2. The optical thin film reflectivity measurement system based on optical interference according to claim 1, characterized in that: The optical film (9) is a single-layer, few-layer or multi-layer film; the shape of the optical film (9) is circular, square, triangular or a combination of the above different shapes; the optical film (9) is a two-dimensional material or an organic film.

3. A method for measuring the reflectivity of an optical thin film based on optical interference according to any one of claims 1-2, characterized in that: include: Step 1, selecting the components of the optical fiber end face reflectivity test subsystem and the optical film reflectivity test subsystem and assembling them respectively according to the test process, wherein the components include an incident single-mode optical fiber (1), a ferrule (2), a ferrule matching sleeve (3), epoxy resin glue (4), a reflective single-mode optical fiber (5), a spectrometer (6), a broadband light source (7), an optical circulator (8), an optical film (9), and an electron microscope copper mesh (10). and a three-dimensional fiber-optic micro-motion platform; Step 2, pre-treating the incident single-mode optical fiber (1), the ferrule (2), the ferrule matching sleeve (3), and the reflective single-mode optical fiber (5), comprising: performing ultrasonic and deionized water cleaning on the ferrule (2) and the ferrule matching sleeve (3), then using a fiber cleaver to cut the tail ends of the incident single-mode optical fiber (1) and the reflective single-mode optical fiber (5), removing the coating layer and the cladding to expose a portion of the bare fiber, and inspecting the flatness of the end faces of the incident single-mode optical fiber (1) and the reflective single-mode optical fiber (5) using a microscope or an end face detector; Step 3, obtaining an expression for a reflectivity compensation coefficient based on the optical fiber end face reflectivity testing subsystem; Step 4: Based on the optical film reflectivity testing subsystem, by changing the distance between the aligned single-mode optical fiber and the optical film, using multiple sets of interference spectra collected by the optical fiber end face reflectivity testing subsystem, fitting the interference spectra based on a double-beam interference formula, thereby solving the measured reflectivity of the optical film; Step 5: Correcting the measured reflectivity of the optical film based on the expression of the reflectivity compensation coefficient to obtain the corrected reflectivity of the optical film.

4. The measuring method according to claim 3, characterized in that The step 3 includes: Step 31, inserting the incident single-mode optical fiber (1) and the reflective single-mode optical fiber (5) pre-treated in step 2 into two different ferrules (2), fixing one of the single-mode optical fibers in the ferrule (2) using the epoxy resin glue (4), and then inserting the two ferrules (2) from both ends of the ferrule matching sleeve (3) so that the end faces of the incident single-mode optical fiber (1) and the reflective single-mode optical fiber (5) are parallel and on the same horizontal line, thereby forming a Fabry-Perot interferometer cavity; Step 32, collecting reflectivity data of the end faces of the incident single-mode optical fiber (1) and the reflective single-mode optical fiber (5), adjusting the three-dimensional optical fiber micro-motion platform to change the cavity length distance between the end faces of the incident single-mode optical fiber (1) and the reflective single-mode optical fiber (5), changing the cavity length distance between the end faces of the incident single-mode optical fiber (1) and the reflective single-mode optical fiber (5), and collecting multiple sets of interference spectra under different cavity length conditions; Step 33, calculating the cavity lengths corresponding to the multiple sets of interference spectra, and fitting the interference spectra based on a double-beam interference formula to obtain the measured reflectivity of the reflective single-mode fiber end face (51) of the reflective single-mode fiber (5) to be measured; Step 34, comparing the measured reflectivity with the reflectivity of the reflective single-mode optical fiber (5) directly measured by a spectrometer, and fitting the relationship between the reflectivity compensation coefficient and the cavity length through a polynomial.

5. The measuring method according to claim 4, characterized in that The step 4 comprises: Step 41, after cutting the optical film (9) to a size suitable for the electron microscope copper mesh, the optical film (9) is transferred to the mesh of the electron microscope copper mesh (10); Step 42, aligning the incident single-mode optical fiber (1) with the optical film (9), adjusting the three-dimensional optical fiber micro-motion platform to change the cavity length distance between the incident single-mode optical fiber (1) and the end face of the optical film (9), changing the distance between the incident single-mode optical fiber (1) and the optical film (9), collecting multiple groups of interference spectra of the incident single-mode optical fiber end face (11) of the incident single-mode optical fiber (1) and the optical film (9), fitting the interference spectra based on the double-beam interference formula, and solving the measured reflectivity of the optical film.

6. The measuring method according to claim 5, characterized in that The calculation of the cavity lengths corresponding to the multiple sets of interference spectra in step 33 includes: The interference spectrum is demodulated by the optical signal double-peak phase demodulation method, and the calculated cavity length can be expressed as: Wherein, λ1 and λ2 are two adjacent peak-to-peak values ​​or minimum values ​​of the interference spectrum.

7. The measuring method according to claim 6, characterized in that The principle of directly measuring the reflectivity of the reflective single-mode optical fiber (5) by the spectrometer in step 34 is as follows: collecting the reflection spectrum of the optical fiber end face, and calculating the reflectivity of the reflective single-mode optical fiber (5) according to the dimensionless relative light intensity The calculation formula is: r and I i are the reflected light intensity and the incident light intensity, I r / I i That is, the reflectivity of the optical fiber end face directly measured by the spectrometer.

8. The measuring method according to claim 7, characterized in that The step 41 of transferring the optical film (9) to the mesh of the electron microscope copper mesh (10) includes: dry transfer or wet transfer.

9. The measuring method according to claim 8, characterized in that The step 42 of aligning the incident single-mode optical fiber (1) with the optical film (9) includes: fixing the incident single-mode optical fiber end face (11) and the electron microscope copper mesh (10) at the center of the microscope; using a pump light source to emit colored light through an optical attenuator to the incident single-mode optical fiber (1); and adjusting the position of the electron microscope copper mesh (10) under the field of view of the microscope so that the colored light spot on the end face of the single-mode optical fiber is directly opposite to the small hole in the electron microscope copper mesh, thereby aligning the incident single-mode optical fiber (1) with the optical film (9) on the mesh of the electron microscope copper mesh (10).

10. The measuring method according to claim 9, characterized in that The step 42 of fitting the interference spectrum based on the double-beam interference formula to calculate the measured reflectivity of the optical film includes: The double-beam interference is the interference of two reflected light intensities, and the generated reflected light intensity I r It can be expressed as: Where, I in is the incident light signal, R1 and R2 are the reflectivity of the two reflecting surfaces, ξ is the coupling coefficient of the Fabry-Perot interferometer cavity, is the phase difference of the light beam reflected from the fiber end face and the optical film, where L is the cavity length of the Fabry-Perot interferometer cavity, and λ is the wavelength of the incident laser.

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