System and method for measuring thickness of ultrathin metal foil based on Mach-Zehnder interference

Abstract

The invention discloses an ultrathin metal foil thickness measuring system and method based on Mach-Zehnder interference, and relates to the technical field of ultrathin metal thickness measuring methods. The system comprises a super-luminescent diode wide-spectrum light source SLD, the SLD emits a beam of white light, the white light is divided by a 50: 50 first optical fiber coupler into a light beam I and a light beam II with the same intensity, and the light beam I and the light beam II enter two Mach-Zehnder interference modules with the same structure respectively; the two Mach-Zehnder interference modules are symmetrically arranged along the upper side and the lower side of the sample to be tested, the output ends of the two Mach-Zehnder interference modules are connected with the input end of the second optical fiber coupler, and the output end of the second optical fiber coupler is connected with the input end of the spectrograph. The system and the method have the advantages of high real-time performance, high measurement precision, low cost and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of measuring methods of ultra-thin metal thickness, and particularly relates to a system and method for measuring the thickness of an ultra-thin metal foil based on Mach-Zehnder interference. BACKGROUND

[0002] A metal foil refers to a very thin sheet-shaped product of a metal material such as gold, aluminum, copper, or the like, which is manufactured by hammering or rolling, and an ultra-thin metal foil refers to a metal foil with a thickness of several micrometers to 100 micrometers. The ultra-thin metal foil has certain hardness and corrosion resistance, good electrical conductivity, excellent mechanical properties, and the like, and is widely used in the field of precision manufacturing (e.g., lithium battery electrode foil, semiconductor packaging, electronic component manufacturing, etc.) due to its ultra-thin thickness and smooth surface.

[0003] In a modern industrial system, precision machining and detection technology have become a bottleneck for the development of the industry. Precision machining determines the manufacturing capability of a part, and detection technology is the most important link for evaluating the quality of precision machining. Whether it is the semiconductor industry, optical instruments, or precision machinery equipment, the quality of the products cannot be guaranteed without the support of these technologies, and the technologies are also an important driving force for the technological innovation and upgrading of related industries. In the detection of various parameters of a material, the thickness and uniformity of a metal foil are key parameters that determine the performance and yield of a final product. Accurate, fast, and non-destructive online or offline measurement of the thickness has high industrial value.

[0004] Currently, thickness measurement techniques are mainly divided into contact and non-contact measurement. Contact thickness gauges such as micrometers and micrometers have the advantages of simple measurement principle and relatively high precision (up to micrometers). However, the disadvantages are that pressure needs to be applied during measurement, which may cause indentation, deformation, or even damage to the product surface, destroy the sample, or affect subsequent processing. In addition, manual operation is required, which is low in efficiency and difficult to meet the needs of rapid, high-precision, and large-area measurement in industrial production. Non-contact measurement methods mainly include laser triangulation displacement method / coherent focusing method, optical interference method, ultrasonic thickness gauge, and eddy current thickness gauge. The most significant advantage of non-contact measurement is that it can achieve non-destructive testing without damaging the sample. However, each of the above methods has its own limitations in measurement. For example, the laser triangulation displacement method / coherent focusing method requires a reference plane or a complex optical path design, and is sensitive to the reflectivity, roughness, and inclination of the metal surface. In particular, the diffuse reflection of a rough surface can seriously affect the measurement accuracy. Traditional monochromatic laser interference methods are limited by the existence of monochromatic light The phase ambiguity of the white light interferometry, the thickness value of the sample with a thickness greater than half a wavelength cannot be uniquely determined, a complex phase unwrapping algorithm is required, and the error is caused by the influence of noise and environmental vibration. The ultrasonic thickness gauge measures the ultrathin metal material of the order of 100 microns, which requires ultrasonic waves with very high frequency (tens or even hundreds of megahertz). After the high-frequency sound wave penetrates the material, the attenuation is large, the resolution is limited, and the signal-to-noise ratio is low. The eddy current thickness gauge is highly dependent on the conductivity and permeability of the measured metal material. In the scene where the material properties change, the accuracy and reliability are limited.

[0005] For the high-precision, fast, non-contact, and lossless absolute thickness measurement of independent ultrathin metal with a thickness of about 100 microns, the existing technology has many limitations. The existing technology proposes a white light interferometry (WLI) thickness measurement technology. Due to its absolute measurement capability and extremely high resolution, it has become an important means of ultrathin material thickness measurement. In 1996, Schnell et al. used a dispersive white light interferometer to measure the absolute distance between the two surfaces of the dielectric multilayer system on the object target. In 2006, the team of Kim Young-jeong proposed a dispersive white light interferometry measurement double-branch detection scheme, which realized the refractive index and thickness scanning view of the single-layer, nanometer range thin film layer. In 2022, Lin Yuan, Guo Tong, etc. proposed a constrained nonlinear fitting method for simultaneously measuring the thickness and refractive index of the thin film, achieving an error of within 1%. In 2025, Zhu Min-hao et al. proposed a double-probe interferometry system, which realized point-to-point measurement of the thickness of opaque samples, and was successfully applied to the thickness measurement of double-polished and single-polished silicon wafers. In summary, although the white light thickness measurement technology has gradually expanded from transparent materials to opaque metal measurement, its development has always been limited by the lack of information caused by the single-reflection interface of opaque metal, signal distortion caused by metal optical properties, and the difficulty in balancing anti-interference ability and fast measurement. Therefore, there is an urgent need to invent a real-time, high-precision, and low-cost thickness measurement system for independent ultrathin metal foil. SUMMARY

[0006] The technical problem to be solved by the present application is to provide a real-time, high-precision, and low-cost ultrathin metal foil thickness measurement device and method.

[0007] To solve the above technical problems, the technical solution adopted by the present application is: a Mach-Zehnder interferometry-based ultrathin metal foil thickness measurement system, comprising: The superluminescent diode wide spectrum light source SLD emits a white light beam which is divided into two light beams I and II with equal intensity by a first 50:50 optical fiber coupler, the light beams I and II enter two Mach-Zehnder interference modules respectively, the two Mach-Zehnder interference modules are symmetrically arranged along the upper and lower sides of a sample to be measured, the output ends of the two Mach-Zehnder interference modules are connected with the input end of a second optical fiber coupler, and the output end of the second optical fiber coupler is connected with the input end of a spectrometer.

[0008] Further, the first Mach-Zehnder interference module comprises a third optical fiber coupler, one output end of the first optical fiber coupler is connected with the input end of the third optical fiber coupler, one output end of the third optical fiber coupler is connected with one input end of a first optical fiber attenuator, the other output end of the third optical fiber coupler is connected with one input end of a first optical fiber circulator, one output end of the first optical fiber circulator is connected with a first collimating mirror, the output end of the first optical fiber attenuator is connected with one input end of a fourth optical fiber coupler, the other output end of the first optical fiber circulator is connected with the other input end of the fourth optical fiber coupler, and the output end of the fourth optical fiber coupler is connected with one input end of the second optical fiber coupler.

[0009] Further, the second Mach-Zehnder interference module comprises a fifth optical fiber coupler, the other output end of the first optical fiber coupler is connected with the input end of the fifth optical fiber coupler, one output end of the fifth optical fiber coupler is connected with one input end of a second optical fiber attenuator, the other output end of the fifth optical fiber coupler is connected with one input end of a second optical fiber circulator, one output end of the second optical fiber circulator is connected with a second collimating mirror, the output end of the second optical fiber attenuator is connected with one input end of a sixth optical fiber coupler, the other output end of the second optical fiber circulator is connected with the other input end of the sixth optical fiber coupler, and the output end of the sixth optical fiber coupler is connected with the other input end of the second optical fiber coupler.

[0010] The application further discloses a measurement method of the thickness of an ultrathin metal foil based on Mach-Zehnder interference. The superluminescent diode wide spectrum light source SLD emits a white light beam which is divided into two light beams I and II with equal intensity by a first optical fiber coupler; The light beams I and II enter two Mach-Zehnder interference modules respectively, and are divided into two light beams I1, I2 and II1, II2 with equal intensity by third and fifth optical fiber couplers in the Mach-Zehnder interference modules respectively. The light beams I1 and I2 enter the reference arm and the measurement arm of the first Mach-Zehnder interference module respectively, the light beam I2 enters the first optical fiber ring from the port 1, is emitted from the first collimating mirror connected with the port 2 of the first optical fiber ring and irradiates on the upper surface of the sample to be measured, the reflected light is collected by the first collimating mirror and transmitted to the port 3 of the first optical fiber ring, then meets the reference light I1 in the reference arm after passing through the adjustable first optical fiber attenuator and interferes in the fourth optical fiber coupler to generate the interference light beam I'; The light beams II1 and II2 enter the reference arm and the measurement arm of the second Mach-Zehnder interference module respectively, the light beam II2 enters the second optical fiber ring from the port 1, is emitted from the second collimating mirror connected with the port 2 of the optical fiber ring and irradiates on the lower surface of the sample to be measured, the reflected light is collected by the second collimating mirror and transmitted to the port 3 of the second optical fiber ring, then meets the reference light II1 in the reference arm after passing through the adjustable second optical fiber attenuator and interferes in the sixth optical fiber coupler to generate the interference light beam II'; The interference light beams I' and II' are transmitted to the second optical fiber coupler through optical fibers to superimpose the light intensity incoherently; The spectrometer receives the total interference light intensity after superposition, and the spectrum obtained by computer processing is calculated to obtain the thickness of the sample.

[0011] The beneficial effects generated by the above technical scheme are that the ultra-thin metal foil thickness measurement system uses differential design, through the upper and lower symmetrical Mach-Zehnder interference module structure and the standard gauge block calibration process, the internal optical path difference of the optical fiber is eliminated The influence on the measurement result. Through the Fourier phase analysis method of the phase information of the interference light beam, the optical path difference information can be accurately obtained. The problems such as the need for a reference plane, complex optical path design, tedious phase unwrapping, easy to be affected by the environment and insufficient precision in the traditional laser thickness measurement method when measuring opaque samples are avoided. The system can measure independent ultra-thin metal foils without relying on a reference plane, the differential structure of the system can suppress the drift of the intrinsic optical path of the optical fiber, has strong anti-interference ability, multi-material compatibility and is suitable for online dynamic detection.

[0012] The present application effectively meets the needs of high precision, fast real-time and strong anti-interference ability of opaque ultra-thin metal foil thickness measurement in industrial production, and obtains a practical and low-cost ultra-thin metal foil thickness measurement technology. BRIEF DESCRIPTION OF DRAWINGS

[0013] The present application will be further described in detail below in combination with the drawings and specific embodiments.

[0014] Figure 1 is the principle block diagram of the system described in the embodiments of the present application; Figure 2is a diagram of the measurement principle of the method according to an embodiment of the present invention; Among them: 1. Superluminescent laser diode (SLD) broadband light source; 2. First fiber coupler; 3. Third fiber coupler; 4. First fiber attenuator; 5. First fiber circulator; 6. First collimator; 7. Fourth fiber coupler; 8. Fifth fiber coupler; 9. Second collimator; 10. Second fiber circulator; 11. Second fiber attenuator; 12. Sixth fiber coupler; 13. Second fiber coupler; 14. Spectrometer; 15. Standard gauge block. DETAILED DESCRIPTION

[0015] The following is a clear and complete description of the technical solutions in the embodiments of the present invention, in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts are within the scope of protection of the present invention.

[0016] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0017] like Figure 1 As shown, an embodiment of the present invention discloses a system for measuring the thickness of an ultrathin metal foil based on Mach-Zehnder interferometry. The system comprises a superluminescent diode (SLD) broadband light source (SLD1). Preferably, the broadband light source (SLD) has a central wavelength of 846 nm, an output spectral width of 26 nm, a power of 12.6 mW, and a coherence length of 27.5 microns, meeting the requirements for ultrathin sample measurement. The high power also ensures that reflected light of sufficient intensity can be recovered from the sample surface for subsequent interference, ensuring sufficient interference contrast. The SLD emits a beam of white light, which is split into two beams of equal intensity, beam I and beam II, by a 50:50 1×2 first fiber coupler (2). Beams I and II enter two identical and symmetrically arranged Mach-Zehnder interferometer modules, respectively. The two Mach-Zehnder interferometer modules are symmetrically arranged along the upper and lower sides of the sample to be measured. The outputs of the two Mach-Zehnder interferometer modules are connected to the inputs of a 50:50 2×1 second fiber coupler (13). The output of the second fiber coupler (13) is connected to the input of a spectrometer (14).

[0018] Further, such as Figure 1As shown, the first Mach-Zehnder interferometer module in the system includes a 50:50 1×2 third fiber coupler 3. One output end of the first fiber coupler 2 is connected to the input end of the third fiber coupler 3. One output end of the third fiber coupler 3 is connected to an input end of a first fiber attenuator 4. Another output end of the third fiber coupler 3 is connected to an input end of a first fiber circulator 5. One output end of the first fiber circulator 5 is connected to a first collimator 6. The output end of the first fiber attenuator 4 is connected to an input end of a 50:50 2×1 fourth fiber coupler 7. Another output end of the first fiber circulator 5 is connected to another input end of the fourth fiber coupler 7. The output end of the fourth fiber coupler 7 is connected to an input end of a second fiber coupler 13.

[0019] Further, such as Figure 1 As shown, the second Mach-Zehnder interferometer module in the system includes a 50:50 1×2 type fifth fiber coupler 8, the other output end of the first fiber coupler 2 is connected to the input end of the fifth fiber coupler 8, one output end of the fifth fiber coupler 8 is connected to an input end of a second fiber attenuator 11, the other output end of the fifth fiber coupler 8 is connected to an input end of a second fiber circulator 10, one output end of the second fiber circulator 10 is connected to a second collimator 9, the output end of the second fiber attenuator 10 is connected to an input end of a 50:50 2×1 type sixth fiber coupler 12, the other output end of the second fiber circulator 10 is connected to the other input end of the sixth fiber coupler 12, and the output end of the sixth fiber coupler 12 is connected to the other input end of the second fiber coupler 13. Preferably, in the system described in the present application, the light output deflection angle of the first collimator 6 and the second collimator 9 is ≤0.3°, and they are coaxially mounted vertically on both sides of the upper and lower surfaces of the sample to be tested.

[0020] Furthermore, an embodiment of the present invention also discloses a method for measuring the thickness of an ultra-thin metal foil using the aforementioned system, the method comprising the following steps: A superluminescent diode broad spectrum light source SLD1 emits a beam of white light which is split into two beams of equal intensity, beam I and beam II, by a first fiber coupler 2; Light beam I and light beam II enter two Mach-Zehnder interferometer modules with the same structure respectively, and are respectively split into two light beams I1 and I2 and light beams II1 and II2 with equal intensity by the third fiber coupler 3 and the fifth fiber coupler 8 in the Mach-Zehnder interferometer module; The light beams I1 and I2 enter the reference arm and the measuring arm of the first Mach-Zehnder interference module respectively, the light beam I2 enters the port 1 of the first fiber ring 5, and is emitted from the first collimating mirror 6 connected with the port 2 of the first fiber ring 5 to irradiate on the upper surface of the sample to be measured, the reflected light is collected by the first collimating mirror 6 and transmitted to the port 3 of the first fiber ring 5, and then meets the reference light I1 in the reference arm after passing through the adjustable first fiber attenuator 4 to interfere with each other in the fourth fiber coupler 7 to generate the interference light beam I'; The light beams II1 and II2 enter the reference arm and the measuring arm of the second Mach-Zehnder interference module respectively, the light beam II2 enters the port 1 of the second fiber ring 10, and is emitted from the second collimating mirror 9 connected with the port 2 of the second fiber ring 10 to irradiate on the lower surface of the sample to be measured, the reflected light is collected by the second collimating mirror 9 and transmitted to the port 3 of the second fiber ring 10, and then meets the reference light II1 in the reference arm after passing through the adjustable second fiber attenuator 11 to interfere with each other in the sixth fiber coupler 12 to generate the interference light beam II'; The interference light beams I' and II' are transmitted to the second fiber coupler 13 through the optical fiber to superimpose the light intensity in a non-coherent manner; The spectrometer 14 receives the total interference light intensity after superposition, and the computer processes the spectrum to calculate the thickness of the sample.

[0021] Further, in the method described in the application: The two white light beams I and II divided by the first fiber coupler 2 are the light source beams of two Mach-Zehnder interference modules which are completely identical and symmetrical in structure. The reflected light intensity collected by the first collimating mirror 6 is weaker than the reference light I1 in the reference arm, so the adjustable fiber attenuator is used to control the intensity of the reference light I1 to ensure that the intensities of the two light beams for interference are approximately equal, thereby ensuring that the interference contrast is maximum.

[0022] In the first Mach-Zehnder interference module, the first fiber ring 5 can ensure that the fiber coupler 7 only receives the reflected light from the upper surface of the sample to be measured, and the reflected light carries the distance information between the first collimating mirror 6 and the upper surface of the standard gauge block with a known thickness The optical path difference between the measuring arm and the reference arm in the fiber of the Mach-Zehnder interference module is regarded as a constant The total optical path difference of the first Mach-Zehnder interference module is The optical path difference information is contained in the phase information of the interference light beam I'; The second Mach-Zehnder interference module is completely identical and symmetrical with the first Mach-Zehnder interference module, so the total optical path difference is The optical path difference information is contained in the phase information of the interference light beam II', wherein is the distance information between the second collimating mirror 9 and the lower surface of the standard gauge block with a known thickness. The superimposed interference beams I' and II' including the standard gauge block upper and lower surface distance information from the first collimating mirror 6 and the second collimating mirror 9, the spectral information received by the spectrometer 14 contains and Two information components, Fourier phase analysis method is performed on the spectrum to obtain and Two peak values, and the average value is recorded as ; Through the upper and lower symmetrical design and the thickness The calibration process of the known standard gauge block, the distance of the first collimating mirror 6 and the second collimating mirror 9 in the optical path is obtained , and then the measured sample is replaced and the measurement is repeated, and the spectral information of the measured sample is analyzed to obtain: , and the thickness of the measured sample is ; Wherein, is the distance information from the first collimating mirror 6 to the upper surface of the measured sample, wherein is the distance information from the second collimating mirror 9 to the lower surface of the measured sample, is the total optical path difference of the first Mach-Zehnder interference module when testing the measured sample, is the total optical path difference of the second Mach-Zehnder interference module when testing the measured sample.

[0023] Further, in the method described in the application, the Fourier phase analysis method includes: Removing the direct current component from the superimposed spectrum; Fourier transform to extract the main frequency phase ; The optical path difference is calculated as , and the wave number range is .

[0024] The system described in the application is divided into two stages during measurement: (1) Calibration stage, first, the collimating mirrors of the two interference modules need to be coaxial to ensure that the output beams of the upper and lower collimating mirrors vertically irradiate on the upper and lower surface thickness corresponding points of the sample. The coaxial alignment step can be adjusted by optimizing the coupling of the light beams emitted by the opposite collimating mirrors to the maximum light intensity without placing the measured sample. Then, a standard gauge block with a known thickness is used for measurement to obtain the Fourier transform spectrum of two peaks except the fundamental frequency, and through the two peak values of the Fourier transform spectrum, the ; (2) Measurement stage, a standard gauge block with a thickness of The sample to be measured is measured, during which the thickness measurement system element is fixed, the distance L between the two collimating mirrors is kept unchanged, the same data processing mode is carried out, and "reading out" is performed. The thickness value of the sample to be measured is obtained through computer calculation .

[0025] The application solves the limitations of the existing non-contact thickness measurement technology in measuring opaque ultra-thin metal foil. The optical fiber optical path drift is eliminated by a double-path Mach-Zehnder interference module, the air gap optical path difference is extracted by combining Fourier phase analysis, and the thickness absolute value is solved by using a calibration block , which is suitable for online detection of metal foil with a thickness of 1-100 mu m.

Claims

1. A system for measuring the thickness of ultra-thin metal foil based on Mach-Zehnder interferometry, characterized in that include: A superluminescent diode broad spectrum light source SLD (1) emits a beam of white light which is divided into two beams of equal intensity, beam I and beam II, by a 50:50 first optical fiber coupler (2). The beam I and beam II respectively enter two Mach-Zehnder interference modules with the same structure. The two Mach-Zehnder interference modules are symmetrically arranged along the upper and lower sides of a sample to be measured. The output ends of the two Mach-Zehnder interference modules are connected to the input ends of a second optical fiber coupler (13), and the output end of the second optical fiber coupler (13) is connected to the input end of a spectrometer (14).

2. The ultra-thin metal foil thickness measurement system based on Mach-Zehnder interferometry according to claim 1, characterized in that: The first Mach-Zehnder interferometer module includes a third fiber coupler (3), an output end of the first fiber coupler (2) is connected to an input end of the third fiber coupler (3), an output end of the third fiber coupler (3) is connected to an input end of a first fiber attenuator (4), another output end of the third fiber coupler (3) is connected to an input end of a first fiber circulator (5), an output end of the first fiber circulator (5) is connected to a first collimator (6), an output end of the first fiber attenuator (4) is connected to an input end of a fourth fiber coupler (7), another output end of the first fiber circulator (5) is connected to another input end of a fourth fiber coupler (7), and an output end of the fourth fiber coupler (7) is connected to an input end of a second fiber coupler (13).

3. The ultra-thin metal foil thickness measurement system based on Mach-Zehnder interferometry according to claim 2, characterized in that: The second Mach-Zehnder interferometer module includes a fifth fiber coupler (8), the other output end of the first fiber coupler (2) is connected to the input end of the fifth fiber coupler (8), one output end of the fifth fiber coupler (8) is connected to an input end of a second fiber attenuator (11), the other output end of the fifth fiber coupler (8) is connected to an input end of a second fiber circulator (10), one output end of the second fiber circulator (10) is connected to a second collimator (9), the output end of the second fiber attenuator (10) is connected to an input end of a sixth fiber coupler (12), the other output end of the second fiber circulator (10) is connected to the other input end of the sixth fiber coupler (12), and the output end of the sixth fiber coupler (12) is connected to the other input end of the second fiber coupler (13).

4. The ultra-thin metal foil thickness measurement system based on Mach-Zehnder interferometry according to claim 3, characterized in that: The central wavelength of the broadband light source SLD is 846 nm, the output spectrum width is 26 nm, the power is 12.6 mW, and the coherence length is 27.5 microns.

5. The ultra-thin metal foil thickness measurement system based on Mach-Zehnder interferometry according to claim 3, characterized in that: The first optical fiber coupler (2), the third optical fiber coupler (3) and the fifth optical fiber coupler (8) use 50:50 1×2 type optical fiber couplers.

6. The ultra-thin metal foil thickness measurement system based on Mach-Zehnder interferometry according to claim 3, characterized in that The second optical fiber coupler (13), the fourth optical fiber coupler (7) and the sixth optical fiber coupler (12) use 50:50 2×1 type optical fiber couplers.

7. The ultra-thin metal foil thickness measurement system based on Mach-Zehnder interferometry according to claim 3, wherein: The first collimating mirror (6) and the second collimating mirror (9) have a light output angle of ≤0.3° and are coaxially and vertically mounted on both sides of the upper and lower surfaces of the sample to be tested.

8. A method for measuring the thickness of ultra-thin metal foil based on Mach-Zehnder interferometry, characterized in that The method comprises the following steps: A superluminescent diode broad spectrum light source SLD (1) emits a beam of white light which is divided into two beams I and II of equal intensity by a first optical fiber coupler (2); Light beam I and light beam II enter two Mach-Zehnder interferometer modules with the same structure respectively, and are respectively divided into two light beams I1 and I2 and light beams II1 and II2 with equal intensities by the third fiber coupler (3) and the fifth fiber coupler (8) in the Mach-Zehnder interferometer module; Light beams I1 and I2 enter the reference arm and the measurement arm of the first Mach-Zehnder interferometer module respectively. Light beam I2 enters from port 1 of the first optical fiber circulator (5), and is emitted from the first collimator (6) connected to port 2 of the first optical fiber circulator (5) to illuminate the upper surface of the sample to be measured. After the reflected light is collected by the first collimator (6) and transmitted to port 3 of the first optical fiber circulator (5), it meets the reference light I1 in the reference arm after passing through the adjustable first optical fiber attenuator (4) at the fourth optical fiber coupler (7) and interferes, generating an interference beam I'. Light beams II1 and II2 enter the reference arm and the measurement arm of the second Mach-Zehnder interferometer module respectively. Light beam II2 enters from port 1 of the second optical fiber circulator (10), and is emitted from the second collimator (9) connected to port 2 of the second optical fiber circulator (10) to illuminate the lower surface of the sample to be measured. The reflected light is collected by the second collimator (9) and transmitted to port 3 of the second optical fiber circulator (10). It then meets the reference light II1 in the reference arm after passing through the adjustable second optical fiber attenuator (11) at the sixth optical fiber coupler (12) and interferes with it. The interference beam generated is II'. The interference light beam I' and the interference light beam II' are transmitted to the second optical fiber coupler (13) via the optical fiber to generate incoherent superposition of light intensity; The spectrometer (14) receives the total interference light intensity after superposition, and the spectrum obtained by computer processing is used to calculate the sample thickness.

9. The method for measuring the thickness of an ultra-thin metal foil based on Mach-Zehnder interferometry according to claim 8, wherein: The sample thickness calculation method includes the following steps: In the first Mach-Zehnder interferometer module, the first fiber circulator (5) is used to enable the fourth fiber coupler (7) to receive only the reflected light from the upper surface of the sample to be measured, and the reflected light carries information about the distance between the first collimator (6) and the upper surface of the standard block of known thickness. The optical path difference between the measuring arm and the reference arm in the optical fiber in the Mach-Zehnder interferometer module is considered to be a constant. , the total optical path difference of the first Mach-Zehnder interferometer module is , the optical path difference information is contained in the phase information of the interference beam I' spectrum; The second Mach-Zehnder interferometer module is identical and symmetrical to the first one, so the total optical path difference is , the optical path difference information is contained in the phase information of the interference beam II' spectrum, where is the distance information between the second collimating mirror (9) and the lower surface of the standard gauge block of known thickness; After the interference beams I' and II' including the distance information of the upper and lower surfaces of the standard block from the first collimator (6) and the second collimator (9) are superimposed, the spectrum information received by the spectrometer (14) includes and Two information components, the spectrum is analyzed by Fourier phase analysis to obtain and The two peak values ​​are averaged and recorded as ; Through the design of upper and lower symmetry and known thickness The distance between the first collimator (6) and the second collimator (9) in the optical path is obtained by calibrating the standard gauge block. Then, replace the sample to be measured and repeat the above steps. By analyzing the spectral information of the sample to be measured, we can obtain: , then the thickness of the sample to be measured is ; in, is the distance information between the first collimating mirror (6) and the upper surface of the sample to be measured, where is the distance information between the second collimating mirror (9) and the lower surface of the sample to be measured, The total optical path difference of the first Mach-Zehnder interferometer module when testing the sample to be tested is: The total optical path difference of the second Mach-Zehnder interferometer module when testing the sample to be tested.

10. The method for measuring the thickness of an ultra-thin metal foil based on Mach-Zehnder interferometry according to claim 8, wherein: The Fourier phase analysis method includes: Remove the DC component from the superimposed spectrum; Fourier transform to extract the main frequency phase ; according to Calculate the optical path difference, is the wave number range.

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