Spectro-interferometrically adjustable measuring device and measuring method

Abstract

The application provides a kind of spectral interference adjustable measuring device and measuring method, belongs to optical interference detection field, method includes receiving the incident light emitted from multiple light sources;Multiple incident light is combined;The collimation of incident light;The incident light is split into reference beam and transmission beam;Reference beam is reflected to beam splitting unit;Transmission beam is transmitted to the surface of the object to be detected through phase shifter, optical lens, and optical lens reflects the measurement beam emitted by the object to be detected to beam splitting unit;Reference beam and measurement beam interfere at beam splitting unit, generate interference light;Real-time adjustment of the reflectivity of reference reflection unit so that the intensity values of reference beam and measurement beam are consistent or similar;Interference light is converged;Different wavelengths of light in the converging light are separated;In response to the converging light, the spectral information of the light is obtained. Through the processing scheme of the present application, the contrast of the interference fringes is improved, and the measurement accuracy of the device is improved.

Description

Technical Field

[0001] This invention relates to the field of optical interferometry, specifically to a measurement device and method with adjustable spectral interferometry. Background Technology

[0002] Coherent and incoherent measurements are two main methods in absolute distance measurement, characterized by large measurement range and high accuracy. Coherent measurement is based on the interference phenomenon of light, and the four typical two-beam interferometers include the Michelson interferometer, Mach-Zehnder interferometer, Seneca interferometer, and Fizeau interferometer. Coherent measurement techniques can be further divided into single-wavelength interferometry, dual-wavelength interferometry, and multi-wavelength interferometry (MWLI) techniques. Single-wavelength interferometry relies on guide rails, direction discrimination, and fringe counting techniques for measurement. Due to the limitations of half-cycle phase ambiguity, it is difficult to use for measuring the morphology of optical elements with large step differences (≥±600μm) and roughness (Ra≥3μm). Compared to single-wavelength interferometry, dual-wavelength interferometry expands the measurement range, but when the equivalent wavelength is very long, the error amplification effect makes it increasingly difficult to correct single-wavelength detection results with dual-wavelength detection results, affecting detection accuracy. Multi-wavelength interferometry utilizes multiple single wavelengths to form a series of synthetic wavelengths of different sizes. Based on the fractional part of the synthetic wavelength interferometry order, the measured displacement value can be solved through a step-by-step refinement algorithm. It does not require guide rails, orientation identification, or fringe counting, and the measurement accuracy is consistent with that of single-wavelength interferometry.

[0003] Multiwavelength interferometry has been used to measure object distance, vibration, and morphology (such as aspherical and spherical optical elements). It is applicable to the measurement of various optical materials, including polished, rough, specular, transparent, and opaque materials, and has broad technological and market prospects. However, when measuring the morphology of optical elements, different elements have different reflectivities. In the same interferometer, the beam splitter ratio is fixed, meaning the intensity of the reference light remains constant, while the intensity of the measurement light varies with the reflectivity of the object surface. However, when the intensity difference between the measurement light and the reference light is large, the contrast of the interference fringes obtained by the interferometric measurement device decreases, thus affecting the measurement accuracy to some extent. When the intensity of the measurement light and the reference light are equal, the fringe contrast is at its maximum of 1, resulting in the best measurement accuracy. When the intensity difference between the measurement light and the reference light is large, the interference fringe contrast deteriorates sharply, affecting the measurement accuracy. Summary of the Invention

[0004] Therefore, in order to overcome the shortcomings of the prior art, the present invention provides a spectral interferometric adjustable measurement device and a spectral interferometric adjustable measurement method that improves the contrast of interference fringes and enhances the measurement accuracy of the device.

[0005] To achieve the above objectives, the present invention provides a measurement device with tunable spectral interferometry, comprising a coupling optical unit, a first wavelength division multiplexer (WDM), a collimating optical unit, a beam splitting unit, a reference reflection unit with tunable reflectivity, a measurement reflection unit, a converging optical unit, a second WDM, and a detector. The plurality of coupling optical units respectively receive incident light emitted from multiple light sources and couple the incident light to the WDM; the first WDM combines the collimated incident light into a single beam; the collimating optical unit collimates the combined incident light; the beam splitting unit splits the collimated incident light into a reference beam and a transmitted beam; the reference reflection unit reflects the reference beam and reflects it back to the beam splitting unit; the measurement reflection unit includes a phase shifter and an optical lens, and the transmitted beam, after passing through the phase shifter, is... An optical lens transmits the light beam to the surface of the object to be tested, and then reflects the measurement beam emitted by the object to the beam splitting unit. The phase shifter modulates the phase of the transmitted beam to achieve interferometric measurement. The reference beam reflected by the reference reflection unit and the measurement beam meet and interfere at the beam splitting unit, generating interference light. The reference reflection unit has multiple regions with different reflectivities, and the reflectivity of the reference reflection unit is adjusted in real time to make the intensity values ​​of the reference beam and the measurement beam consistent or similar. The converging optical unit converges the interference light to obtain converged light. The second wavelength division multiplexer separates the light of different wavelengths in the converged light. Different lenses of the detector generate photoelectric responses to the separated converged light, and the photoelectric responses are processed to obtain the spectral information of the light.

[0006] In one embodiment, the reference reflection unit includes a reflector wheel, and different regions of the reflector wheel have different reflectivities of light.

[0007] In one embodiment, the reference reflection unit further includes an adjustable aperture, the aperture of which can be adjusted in real time as needed.

[0008] In one embodiment, a reflector is installed in different areas of the reflector wheel, and all the reflectors of the reflector wheel have different reflectivities.

[0009] In one embodiment, phase modulation can be achieved using a sinusoidal phase modulation method, which modulates the phase by modulating the optical path difference between two coherent beams. The theoretical formula for the intensity of the interference signal detected by the detector is as follows: In the formula, I(t) is the signal strength value of the detector. Let A(t) be the background intensity of the interference signal, φ be the amplitude of the interference signal, φ be the phase difference between the initial reference optical path and the measurement optical path, and zsin(ωt+θ) be the modulation function of the phase shifter on the interference signal, where z is the modulation degree, θ is the initial phase of the modulated signal, and t is time. Based on the theoretical formula for interference signal intensity, the phase value φ at each measurement point is calculated. Within a single sinusoidal signal modulation period, four sets of interference signals are acquired at equal time intervals, namely E1, E2, E3, and E4, which correspond to the integral values ​​of the interference signal intensity in the time intervals of 0~T / 4, T / 4~T / 2, T / 2~3T / 4, and 3T / 4~T, respectively. Then, the following formula is used to calculate: Calculate the phase value φ at sampling point 0, then the displacement value h at sampling point 0 is: In the formula, λ is the wavelength of the light source, and then the displacement value h of different sampling points is calculated sequentially according to the above method.

[0010] In one embodiment, a spatial modulator is further disposed between the collimating optical unit and the beam splitting unit. The spatial modulator is used to reflect the incident light onto the beam splitting unit and adjust the beam diameter of the incident light on the beam splitting unit.

[0011] In one embodiment, a reflector is disposed between the collimating optical unit and the beam splitting unit. The reflector is used to reflect the incident light onto the beam splitting unit, or to reflect the incident light onto the beam splitting unit and reflect the interference light back to the collimating optical unit.

[0012] In one embodiment, an adjustable coupler is further provided between the converging optical unit and the detector. The adjustable coupler can be moved in real time along the optical axis of the converging optical unit, thereby changing the amount of light energy entering the adjustable coupler.

[0013] A tunable spectral interferometry measurement method includes: using multiple coupling optical units to receive incident light emitted from multiple light sources, and coupling the incident light to a first wavelength division multiplexing (WDM) unit; using the first WDM unit to combine multiple collimated incident light beams; using a collimating optical unit to collimate the combined incident light beam; using a beam splitting unit to split the collimated incident light into a reference beam and a transmitted beam; using a reference reflection unit to reflect the reference beam and reflect the reference beam back to the beam splitting unit; using a measurement reflection unit to transmit the transmitted beam to a target object and reflect a measurement beam emitted from the target object back to the beam splitting unit. The beam splitter unit is used to generate interference light when the reference beam reflected by the reference reflection unit and the measurement beam meet at the beam splitter unit. The reference reflection unit has multiple regions with different reflectivities. The reflectivity of the reference reflection unit is adjusted in real time so that the intensity values ​​of the reference beam and the measurement beam are at the same or similar levels. The interference light is focused by a focusing optical unit to obtain focused light. The different wavelengths of light in the focused light are separated by a second wavelength division multiplexer. The focused light is generated by different lenses of the detector, and the photoelectric response is processed to obtain the spectral information of the light.

[0014] Compared with the prior art, the advantages of the present invention are: the reflectivity of the reference reflection unit is designed to be adjustable. When measuring surface shapes with different reflectivities, the reflectivity of the reference reflection unit can be adjusted in real time so that the intensity values ​​of the reference light intensity and the measured light intensity are consistent or similar, thereby improving the contrast of the interference fringes and improving the measurement accuracy of the device. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of the dual-beam interference optical path in existing technology; Figure 2 This is a schematic diagram of interference signals with different contrasts in the prior art; Figure 3 This is a schematic diagram of a spectral interference adjustable measuring device in one embodiment of the present invention; Figure 4 This is a schematic diagram of the integral of the interference signal intensity in one embodiment of the present invention; Figure 5This is a schematic diagram illustrating the relationship between depth of field and blur spot of lenses with different aperture sizes in one embodiment of the present invention; Figure 6 This is a schematic diagram of the beam diameter modulation operation of the optical spatial modulator in an embodiment of the present invention; Figure 7 This is a schematic diagram of the multi-channel reflector wheel module in an embodiment of the present invention; Figure 8 This is a schematic diagram of a spectral interference adjustable measuring device in another embodiment of the present invention; Figure 9 This is a schematic diagram of a spectral interference adjustable measuring device in another embodiment of the present invention; In the diagram: 1. Light source; 2. Light source; 3. Light source; 4. Lens; 5. Lens; 6. Lens; 7. Wavelength division multiplexer; 8. Collimating lens; 9. Mirror; 10. Spatial modulator; 11. Beam splitter; 12. Converging lens; 13. Mirror wheel; 14. Phase shifter; 15. Converging lens; 16. Object to be tested; 17. Converging lens; 18. Wavelength division multiplexer; 19. Lens; 20. Lens; 21. Lens; 22. Detector; 23. Detector; 24. Detector; 25. Control board; 26. Computer; 27. Surface under test; 28. Surface under test; 29. ​​Surface under test; 30. Reference mirror; 31. Measuring mirror; 32. Interference signal 1; 33. Interference signal 2; 34. Adjustable aperture; 35. Adjustable coupler. Detailed Implementation

[0017] The embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0018] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. This application can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application. It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments can be combined with each other. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0019] It should be noted that various aspects of embodiments within the scope of the appended claims are described below. It will be apparent that the aspects described herein can be embodied in a wide variety of forms, and any particular structure and / or function described herein is merely illustrative. Based on this application, those skilled in the art will understand that one aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number and aspects set forth herein can be used to implement the device and / or practice the method. Additionally, this device and / or method can be implemented using structures and / or functionalities other than one or more of the aspects set forth herein.

[0020] It should also be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of this application. The drawings only show the components related to this application and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0021] Furthermore, specific details are provided in the following description to facilitate a thorough understanding of the examples. However, those skilled in the art will understand that the described aspects can be practiced without these specific details.

[0022] The typical optical path principle of a Michelson interferometer is as follows: Figure 1 As shown, the light beam emitted from light source 1 is collimated by collimating lens 8, and then split by beam splitter 11. Part of the energy is reflected as reference light, which is reflected back to beam splitter 11 by reference mirror 30. Part of the energy is transmitted as measurement light, which is reflected back to beam splitter 11 by measurement mirror 31. The reference light and measurement light meet at beam splitter 11 and interfere. The interference signal is converged by converging lens 17 and reaches detector 22. Measurement mirror 31 can move back and forth in the horizontal direction, thus modulating the phase of the interference signal, while reference mirror 30 remains stationary. In practical applications, measurement mirror 31 may be made of materials with different transmittance, resulting in different energy intensities of the reflected measurement light. The fringe contrast after interference between this portion of the measurement light and the reference light will vary with the energy level of the measurement light. The formula for calculating the interference fringe contrast K is shown below: In the formula, The maximum intensity value of the interference signal. This represents the minimum intensity value of the interference signal.

[0023] like Figure 2As shown, when the fringe contrast is 1, the interference signal curve between the reference light and the measurement light is as shown in interference signal 1, which is called complete coherence. When the fringe contrast is < 1, the interference signal curve between the reference light and the measurement light is as shown in interference signal 2, which is called partial coherence. The amplitude of interference signal 1 is I. t1 The change is greater than the amplitude I of the interference signal. t2 The changes.

[0024] like Figure 3 As shown, this application provides a measurement device with adjustable spectral interferometry, including a coupling optical unit, a first wavelength division multiplexer, a collimating optical unit, a beam splitting unit, a reference reflection unit with adjustable reflectivity, a measurement reflection unit, a converging optical unit, a second wavelength division multiplexer, and a detector.

[0025] Light sources 1, 2, and 3 are light sources with three different wavelengths (the number of wavelengths can be ≥3, but only 3 are shown in the diagram). Three light sources. Multiple coupling optical units receive incident light emitted from multiple light sources and couple the incident light to the wavelength division multiplexer. Lenses 4, 5, and 6 in the figure couple the incident light into the optical fiber of the wavelength division multiplexer 7.

[0026] The first wave division multiplexer 7 combines multiple collimated incident beams into a single beam.

[0027] Collimating optical unit 8 collimates the incident light beam. The light emitted from light sources 1, 2, and 3 is coupled into the optical fiber of wavelength division multiplexer 7 by lenses 4, 5, and 6, and then the outgoing light is collimated by collimating lens 8.

[0028] exist Figure 3 In order to shorten the optical path, the spectral interference adjustable measurement device sets up an optical element with reflection function between the collimating optical unit and the beam splitting unit. The optical element can be a mirror 9 or a spatial modulator 10 with reflection function. There is an angle between the mirror 9 or the spatial modulator 10 and the optical path of the incident light.

[0029] The beam-splitting unit splits the collimated incident light into a reference beam and a transmitted beam. The beam-splitting unit can be a beam splitter 11 or other optical elements capable of splitting light beams. The beam splitter 11 is parallel to the reflecting mirror 9 or the spatial modulator 10. The beam splitter 11 reflects a portion of the light, which becomes the reference beam; the remaining light is transmitted through the beam splitter 11, becoming the transmitted beam. This transmitted beam can illuminate the surface of the object to be measured 16, and then the light is reflected to obtain the measurement beam.

[0030] The reference reflection unit reflects a reference beam and then reflects it to the beam splitting unit. The reference reflection unit has multiple regions with different reflectivities; real-time adjustment of the reflectivity of the reference reflection unit can bring the intensity values ​​of the reference beam and the measurement beam to the same or similar levels. The reference reflection unit may include a reflecting mirror wheel 13. In one embodiment, the reference reflection unit may include a reflecting mirror wheel 13 and a converging lens 12. The reference beam is converged by the converging lens 12 onto the reflecting mirror wheel 13 and then reflected by the reflecting mirror wheel 13. When the reference reflection unit does not include the converging lens 12, the reference beam is directly reflected by the reflecting mirror wheel 13. The reflecting mirror wheel 13 is rotatable; different regions on the wheel have different reflectivities. By rotating the wheel, surfaces with different reflectivities can be aligned with the beam, thereby adjusting the energy of the reflected light.

[0031] The reflector wheel 13 may contain only one reflector, and different areas of the reflector have different reflectivities of light; the reflector wheel 13 may also be equipped with multiple reflectors, and different reflectors have different reflectivities of light, while different areas of the same reflector may have different or the same reflectivities of light.

[0032] The measurement reflection unit transmits the transmitted light beam to the object under test and reflects the measurement beam emitted from the object under test back to the beam splitting unit. The measurement reflection unit includes a phase shifter 14 and an optical lens 15. After passing through the phase shifter 14, the transmitted light beam is transmitted to the surface of the object under test by the optical lens 15, which then reflects the measurement beam emitted from the object under test back to the beam splitting unit 11. The phase shifter 14 modulates the phase of the transmitted light beam to achieve interferometric measurement.

[0033] Phase shifter 14 modulates the phase of the measurement light beam to achieve interferometric measurement. Phase shifter 14 can be a module capable of phase modulation, such as an electro-optic modulation crystal. Since the purpose of phase shifter 14 is to create a phase difference between the light beams in the reference optical path and the measurement optical path, thereby achieving displacement measurement of the object under test 16, phase shifter 14 can be placed in either the reference optical path or the measurement optical path. Movement of the object under test 16 causes a corresponding change in the interference signal, thus enabling the measurement of the displacement, surface shape, etc., of the object under test 16.

[0034] The reference beam and the measurement beam reflected by the reference reflection unit meet and interfere at the beam splitter unit, generating interference light. The reference light reflected by the reflecting mirror wheel 13 and the measurement light reflected by the object under test 16 interfere at the beam splitter 11. The reflectivity of the reference reflection unit is adjustable, so that the intensity values ​​of the reference beam and the measurement beam are at the same or similar levels.

[0035] The converging optical unit converges the interference light to obtain converged light. The interference light is reflected by the reflecting mirror 9 to the converging lens 17.

[0036] The second wavelength division multiplexer 18 separates different wavelengths of light in the converged light.

[0037] Different lenses of the detector generate photoelectric responses to the separated converged light. The photoelectric responses are processed to obtain the spectral information of the light. The converged light is coupled into the optical fiber of wavelength division multiplexer 18. Wavelength division multiplexer 18 separates the three wavelengths of light, and then the light of different wavelengths is converged by lenses 19, 20, and 21 of the detector onto the corresponding sub-detectors 22, 23, and 24, respectively.

[0038] In one embodiment, the interference signal is processed on the control board 25. A certain relationship exists between the interference signal and the displacement value of the object to be detected 16. The displacement value of the object to be detected 16 can be calculated using a corresponding algorithm and then transmitted to the computer 26 for display. The control board 25 can be a chip with microprocessor capabilities, such as an MCU or SCU. The control board 25 can adjust the light intensity output by light sources 1, 2, and 3.

[0039] The aforementioned device designs the reflectivity of the reference reflection unit to be adjustable. When measuring surface shapes with different reflectivities, the reflectivity of the reference reflection unit can be adjusted in real time to make the intensity values ​​of the reference light intensity and the measured light intensity consistent or similar, thereby improving the contrast of the interference fringes and enhancing the measurement accuracy of the device.

[0040] In one embodiment, phase modulation can be achieved using a sinusoidal phase modulation method, which modulates the phase by modulating the optical path difference between two coherent beams. The theoretical formula for the intensity of the interference signal detected by the detector is as follows: In the formula, I(t) is the signal strength value of the detector. Let A(t) be the background intensity of the interference signal, φ be the amplitude of the interference signal, φ be the phase difference between the initial reference optical path and the measurement optical path, and zsin(ωt+θ) be the modulation function of the phase shifter on the interference signal, where z is the modulation degree, θ is the initial phase of the modulated signal, and t is time.

[0041] Based on the theoretical formula for interference signal intensity, the phase value φ at each measurement point is calculated. To reduce the influence of error, z is set to 2.45 and θ to 0.98. After parameter optimization, the phase value φ at each measurement point can be calculated. .

[0042] The intensity of the interference signal detected by the detector is as follows Figure 4As shown, within a single sinusoidal signal modulation period, four sets of interference signals, E1, E2, E3, and E4, are acquired at equal time intervals, corresponding to the integral values ​​of the interference signal intensity over the time intervals 0~T / 4, T / 4~T / 2, T / 2~3T / 4, and 3T / 4~T, respectively. The results are then calculated using the following formula: Calculate the phase value φ at sampling point 0, then the displacement value h at sampling point 0 is: In the formula, λ is the wavelength of the light source. Then, the displacement values ​​h at different sampling points are calculated sequentially according to the above method. Multi-wavelength interferometry can achieve large-range, high-precision measurement by using a step-by-step refinement algorithm to measure displacement.

[0043] In one embodiment, a spatial modulator 10 is further disposed between the collimating optical unit and the beam splitting unit. The spatial modulator is used to reflect the incident light and adjust the beam diameter of the incident light, and can be controlled in real time as needed. Since the spatial modulator 10 can adjust the beam diameter of the reflected light in real time, the beam diameter converged by the converging lens 15 will also change. Figure 5 The diagram illustrates beam diameters D1 and D2.

[0044] The beam diameter is modulated by the spatial modulator 10. When the beam diameter is D1, the light rays, after passing through the converging lens 15, focus on the object surface 28. Assuming the measurement range of the interferometer is L (when the object surface exceeds this measurement range, very little light will return to the converging lens 15, and the signal-to-noise ratio cannot meet the requirements for high-precision measurement), then the object surfaces 27 and 29 are the boundaries of the measurement range, and d1 is the diameter of the beam's blur at the measurement boundary. Similarly, when the incident beam diameter is D2 (D2 is less than D1), within the measurement range of L, the maximum blur diameter of the beam is d2.

[0045] According to optical theory, within the measurement range L, as the diameter of the beam's diffuse spot increases, the light energy coupled to the optical system decreases, leading to a reduction in the fringe contrast of the interference signal detected by the detector and affecting measurement accuracy. Therefore, within the measurement range L, a smaller beam diffuse spot diameter is better. However, the aperture in commonly used interferometric measurement devices is generally a fixed value. To obtain a smaller diffuse spot diameter, beam diameter D2 is more advantageous than D1 (D2 is smaller than D1). However, when the incident light diameter decreases, the light energy incident on the detector also weakens, resulting in the interferometric measurement device not achieving the overall optimal signal-to-noise ratio within the measurement range L. To simultaneously meet the requirements of a large measurement range and a high overall signal-to-noise ratio, the incident light beam diameter needs to be adjusted in real time according to the position of the measured object surface 28. When the measured object surface is at position 28, the beam diameter can be adjusted to D1 (adjusted by the spatial modulator 10 via servo control), at which point the incident energy is maximum, and the obtained fringe contrast and signal-to-noise ratio are optimal.

[0046] When the object being measured is at position 27 or 29, the control board 25 controls the spatial modulator 10 to modulate the beam diameter, adjusting it to D2. Although this sacrifices some incident light energy, it effectively improves the contrast of the fringes and suppresses interference from background light intensity, thus promoting improved measurement accuracy and signal-to-noise ratio. By adjusting the beam diameter of the incident light in real time according to the positional relationship between the object being measured and the focal plane of the lens, the optimal signal-to-noise ratio within the measurement range L can be obtained. However, the interferometer using only beam diameter D1 has a lower signal-to-noise ratio than the device of the invention when measuring objects with large defocus amounts, and the interferometer using only beam diameter D2 has a lower signal-to-noise ratio than the device in this embodiment when measuring objects with small defocus amounts. The device in this embodiment has better overall adaptability when measuring objects at the focal plane, in small defocus ranges, and in large defocus ranges.

[0047] like Figure 6As shown, the spatial modulator 10 can adjust the diameter of the reflected beam, and can be a liquid crystal spatial light modulator (SLM) or a digital micromirror device (DMD), etc. The figure illustrates three beam diameter modes, M1, M2, and M3, with M1 having the largest beam diameter, followed by M2, and M3 having the smallest. Assuming the distance to the measured object surface 28 is 0 when the interferometer measures it, and the measured object surface 28 is located on the optimal focal plane of the lens, the beam diameter is largest at this time, which is mode M1. The energy coupled by the interferometer is the largest, resulting in the highest signal-to-noise ratio. When the absolute value of the measured displacement reading of the interferometer is greater than 0, the beam diameter of the reflected light from the spatial modulator 10 needs to be reduced in real time according to the position of the measured object surface to obtain the optimal signal-to-noise ratio. The optimal matching parameter between the position of the measured object surface and the beam diameter needs to be pre-calibrated. When the interferometer is measuring online, the size of the reflected beam diameter of the spatial modulator 10 can be adjusted in real time according to the displacement reading of the interferometer, thereby solving to some extent the problems of low fringe contrast and measurement accuracy of the interferometer during large-scale measurements.

[0048] like Figure 7 As shown, in one embodiment, the reference reflection unit includes a reflector wheel, with different regions of the reflector wheel exhibiting different reflectivities. In one embodiment, a reflector is mounted on each region of the reflector wheel, and all the reflectors on the reflector wheel have different reflectivities. A reflector is mounted on the reflector wheel 13, and different regions of the reflector surface have different reflectivities. For example, R1 has a reflectivity of 90%, R2 80%, R3 70%, R4 60%, R5 50%, R6 40%, R7 30%, R8 20%, R9 10%, R10 5%, R11 1%, and R12 0.5%, covering most of the reflectivity range of the measured surface. Specific reflective surfaces can also be configured according to requirements. The rotation of the reflector wheel 13 can be controlled by a motor, moving regions with different reflectivities to the position where light is incident, thereby achieving the purpose of adjusting the intensity of the reflected light from the reference beam.

[0049] In actual measurements, the reflectivity of the object under test (16) varies depending on its material, film layer, and roughness, resulting in different energy intensities of the measurement light reflected by the object. When the difference between the measured light intensity and the reference light intensity is large, the contrast of the interference fringes deteriorates sharply, affecting the measurement accuracy. When the measured light intensity and the reference light intensity are equal, the fringe contrast is at its maximum of 1, and the measurement accuracy is relatively the best. Therefore, to enable the interferometer to be conveniently used for measuring objects with different reflectivities (without changing the measuring lens), it is necessary to adjust the reflectivity of the reference surface. When measuring a surface with known reflectivity, the region whose reflectivity is closest to that of the object being tested is directly rotated to the position of the incident beam. At this time, the contrast of the interference fringes obtained by the detector is relatively optimal. When measuring a surface with unknown reflectivity, the region with the lowest reflectivity is first rotated to the position of the incident beam. Then, the reflector wheel 13 is gradually rotated to rotate regions with different reflectivities to the position of the incident beam in turn. The detector detects the peak-to-peak value (amplitude) intensity of the interference signal, determines the reflection region when the peak-to-peak value of the interference signal is the largest, and rotates this region to the position of the incident beam to complete the subsequent surface measurement task. At this time, the contrast of the interference fringes obtained by the detector is relatively optimal.

[0050] In some embodiments, the spatial modulator 10 and the reflector wheel 13 can modulate the beam individually or in concert.

[0051] In some embodiments, such as Figure 8 As shown, the beam diameter is adjusted via an aperture adjustment mechanism. The light source module and detector module can be coupled together using optical fibers or other light-guiding elements, further enhancing the flexibility of the optical path configuration. The reference reflection unit also includes an adjustable aperture 34. The aperture of the adjustable aperture can be adjusted in real time as needed.

[0052] The light emitted from the light source is split into a reference beam and a transmitted beam after passing through the collimating lens 8, the reflecting mirror 9, and the beam splitter 11. The reference beam, reflected by the beam splitter 11, passes through the adjustable aperture 34 and reaches the reflecting mirror wheel 13. The aperture of the adjustable aperture 34 can be adjusted in real time as needed. The measurement beams reflected by the reflecting mirror wheel 13 and the object under test 16 interfere at the beam splitter 11. The interference signal passes through the reflecting mirror 9 and the collimating lens 8, enters the optical fiber, and then reaches the detector module. The control board 25 processes the interference signal and transmits the displacement value of the object under test 16 to the computer 26.

[0053] By adjusting the aperture of the adjustable aperture 34 in real time, the return energy of the reference optical path can be controlled in real time. When measuring objects with different defocusing amounts, the return energy of the reference optical path and the measurement optical path are kept at the same or similar levels, thereby improving the signal-to-noise ratio of the interferometer and increasing the measurement accuracy.

[0054] The peak-to-peak value and contrast of the interference signal can be analyzed by controlling the board 25. When the peak-to-peak value of the interference signal decreases or increases, it indicates that the light energy reflected from the object to be detected 16 decreases or increases. The aperture of the adjustable aperture 34 needs to be adjusted accordingly to reduce or increase the light energy reflected from the mirror wheel 13.

[0055] In one embodiment, such as Figure 9 As shown, an adjustable coupler is also provided between the converging optical unit and the detector. The adjustable coupler can be moved in real time along the optical axis of the converging optical unit, thereby changing the amount of light energy entering the adjustable coupler. The adjustable coupler 35 can adjust the effective numerical aperture of the light coupled into the detector module, thereby improving the contrast of interference fringes and increasing measurement accuracy. The adjustable coupler 35 can be located in the optical path between the converging lens 17 and the detectors 21-23. In the preferred embodiment, it is located near the focal plane of 17.

[0056] After passing through the reflector 9 and the converging lens 17, the interference beam reaches the adjustable coupler 35. Under the action of the control board 25, the adjustable coupler 35 can move in real time along the optical axis of the converging lens 17, changing the amount of light energy entering the adjustable coupler 35, thereby improving the contrast and signal-to-noise ratio when measuring different defocus surfaces and improving the measurement accuracy.

[0057] When the adjustable coupler 35 is located at the focal plane of the converging lens 17, the adjustable coupler 35 couples all the light energy into the optical fiber. When the peak-to-peak value of the interference signal decreases or increases, it indicates that the light energy reflected from the object to be detected 16 decreases or increases. It is necessary to perform servo adjustment through the control board 25 to move the adjustable coupler 35 in real time so that some of the light rays near the optical axis in the optical path enter the optical fiber or all of the light rays enter the optical fiber. This can also achieve the purpose of improving the contrast of the interference fringes.

[0058] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A multi-wavelength phase modulation interferometric measurement device, characterized in that, It includes a coupling optical unit, a first wavelength division multiplexer, a collimating optical unit, a beam splitter, a reference reflection unit, a measurement reflection unit, a converging optical unit, a second wavelength division multiplexer, and a detector. The plurality of coupled optical units respectively receive incident light emitted from the plurality of light sources and couple the incident light to the first wavelength division multiplexer; The first wavelength division multiplexer combines multiple collimated incident beams into a single beam; The collimating optical unit collimates the incident light after beam combining; The beam splitting unit splits the collimated incident light into a reference beam and a transmitted beam; The reference reflection unit reflects the reference beam and reflects the reference beam back to the beam splitting unit; The measurement reflection unit includes a phase shifter and an optical lens. After passing through the phase shifter, the transmitted light beam is transmitted to the surface of the object to be tested by the optical lens. The optical lens then reflects the measurement light beam emitted by the object to be tested back to the beam splitting unit. The phase shifter modulates the phase of the transmitted light beam to achieve interferometric measurement. The reference beam reflected by the reference reflection unit and the measurement beam meet and interfere at the beam splitting unit, generating interference light; The reference reflection unit has multiple regions with different reflectivities. The reflectivity of the reference reflection unit is adjusted in real time so that the intensity values ​​of the reference beam and the measurement beam are at the same or similar levels. The converging optical unit converges the interference light to obtain converged light; The second wavelength division multiplexer separates the different wavelengths of light in the converged light; Different lenses of the detector generate photoelectric responses to the separated converged light, and the photoelectric responses are processed to obtain spectral information of the light at different wavelengths. A spatial modulator is also provided between the collimating optical unit and the beam splitting unit. The spatial modulator is used to reflect the incident light onto the beam splitting unit and adjust the beam diameter of the incident light on the beam splitting unit. The reference reflection unit includes a reflector wheel, which is rotatable, and different areas of the reflector wheel have different reflectivities for light. The spatial modulator and the reflector wheel modulate the beam individually, or the two work together to modulate the beam.

2. The apparatus according to claim 1, characterized in that, The reference reflection unit also includes an adjustable aperture. The aperture of the adjustable aperture can be adjusted in real time as needed.

3. The apparatus according to claim 1, characterized in that, A reflector is installed in different areas of the reflector wheel, and all the reflectors on the reflector wheel have different reflectivities.

4. The apparatus according to claim 1, characterized in that, The phase modulation employs a sinusoidal phase modulation method, which achieves phase modulation by modulating the optical path difference between two coherent beams. The theoretical formula for the intensity of the interference signal detected by the detector is as follows: In the formula, I(t) is the signal strength value of the detector. Let A(t) be the background intensity of the interference signal, Φ be the amplitude of the interference signal, Φ be the phase difference between the initial reference optical path and the measurement optical path, and zsin(ωt+θ) be the modulation function of the phase shifter on the interference signal, where z is the modulation degree, θ is the initial phase of the modulation signal, and t is time. Based on the aforementioned theoretical formula for interference signal intensity, the phase difference Φ between the initial reference optical path and the measurement optical path at each measurement point is calculated. Within a single sinusoidal signal modulation period, four sets of interference signals, E1, E2, E3, and E4, are acquired at equal time intervals, corresponding to the integral values ​​of the interference signal intensity over the time intervals 0~T / 4, T / 4~T / 2, T / 2~3T / 4, and 3T / 4~T, respectively. The results are then calculated using the following formula: Calculate the phase difference Φ between the initial reference optical path and the measurement optical path at the sampling point, then the displacement value h at sampling point 0 is: In the formula, λ is the wavelength of the light source, and then the displacement value h of different sampling points is calculated sequentially according to the above process.

5. The apparatus according to claim 1, characterized in that, An adjustable coupler is also provided between the converging optical unit and the detector. The adjustable coupler can be moved in real time along the optical axis of the converging optical unit, thereby changing the amount of light energy entering the adjustable coupler.

6. A multi-wavelength phase modulation interferometry method, implemented based on the multi-wavelength phase modulation interferometry device according to any one of claims 1-5, characterized in that, include: Multiple coupled optical units are used to receive incident light emitted from multiple light sources and couple the incident light to a first wavelength division multiplexer. The first wavelength division multiplexer is used to combine multiple collimated incident beams; The incident light after beam combining is collimated using a collimating optical unit. The collimated incident light is split into a reference beam and a transmitted beam using a beam splitter unit. The reference beam is reflected by a reference reflection unit and then reflected back to the beam splitting unit. The transmitted light beam is transmitted to the object to be tested using a measurement reflection unit, and the measurement light beam emitted from the object to be tested is reflected back to the beam splitting unit. The reference beam reflected by the reference reflection unit and the measurement beam meet and interfere at the beam splitting unit, generating interference light; The reference reflection unit has multiple regions with different reflectivities. The reflectivity of the reference reflection unit is adjusted in real time so that the intensity values ​​of the reference beam and the measurement beam are at the same or similar levels. The interfering light is focused using a converging optical unit to obtain focused light; A second wavelength division multiplexer is used to separate the light of different wavelengths in the converged light; The photoelectric response is generated by using different lenses of the detector to separate the converging light, and the photoelectric response is processed to obtain the spectral information of the light.

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