A metasurface-based element surface shape dynamic measurement system

Abstract

The present application relates to the technical field of optical element surface shape dynamic measurement scheme design, and particularly relates to a kind of element surface shape dynamic measurement system based on metasurface.The scheme includes that the polarized light of laser exit is split into reference light and test light, test light realizes polarization orthogonalization by passing through quarter-wave plate twice, and the combination of reference light and test light forms elliptical polarized light;Left-handed / right-handed circularly polarized light and orthogonal linearly polarized light component intensity are synchronously captured using a detector, and phase difference δ is solved in real time by combining Stokes parameters;Based on common optical path design, environmental interference is eliminated, polarization spectrometer element is saved, and the structure is simplified;The precision dynamic measurement of the surface shape of the measured piece is realized by deducting the inherent surface shape error of the system.The system provided by the present application has the advantages of strong anti-interference, high measurement efficiency and significant cost reduction, and is suitable for precise optical manufacturing and online detection scenarios.

Description

A dynamic measurement system for component surface shape based on metasurface Technical Field

[0001] This invention relates to the field of design technology for dynamic measurement schemes of optical element surface shape, and specifically to a dynamic measurement system for element surface shape based on metasurface. Background Technology

[0002] Currently, interferometry is the primary method for measuring the surface shape of components. Among existing interferometry methods, phase-shifting interferometry is widely considered to be the most accurate, and most mainstream interferometers employ phase-shifting interferometry. However, in existing phase-shifting interferometry methods, neither mechanical phase shifting nor wavelength-tuned phase shifting can achieve dynamic measurement, thus significantly reducing environmental adaptability. Existing polarization phase-shifting measurement technology is the only technique capable of achieving dynamic phase-shifting interferometry.

[0003] The existing technology has the following drawbacks: The existing polarization phase-shifting interferometry achieves phase shift by measuring the linearly polarized light in four directions (0°, 45°, 90°, and 135°) after the test light interferes with the reference light. Therefore, both the reference light and the test light need to be circularly polarized. To meet this condition, a Thyman-Green interferometric optical path is usually required. The test beam is first split by a polarization beam splitter to obtain two orthogonal linearly polarized beams. The two orthogonal linearly polarized beams need to be converted into circularly polarized light by a quarter-wave plate. To achieve this process, the test light and the reference light usually need to be split, modulated, and then combined. Therefore, it is not possible to use a common optical path for the reference light and the test light, which weakens the system's environmental adaptability.

[0004] Therefore, existing technologies still need further development. Summary of the Invention

[0005] The purpose of this invention is to solve the problem that the test light and reference light cannot share the same optical path due to complex polarization modulation in the existing dynamic phase-shifting interferometric surface shape measurement technology (polarization phase shifting), which weakens the system's environmental adaptability, thereby realizing dynamic surface shape measurement with stronger environmental adaptability.

[0006] To achieve the above-mentioned technical objectives, according to a first aspect of the present invention, the present invention provides a dynamic measurement system for component surface shape based on metasurfaces, comprising:

[0007] The system includes a light source, a polarization modulation unit, a reference optical path, a test optical path, a beam combiner, and a detector; wherein the reference optical path and the test optical path are in a common optical path structure, and the detector is configured to detect the polarization components after beam combining to obtain the phase difference, thereby calculating the surface shape information of the optical element.

[0008] Specifically, the light source is a laser that emits polarized light.

[0009] Specifically, the polarization modulation unit includes at least one quarter-wave plate.

[0010] Specifically, the detector has a polarization detection function for measuring the left-handed optical component. Dextrorotatory optical component 45° linearly polarized light component and 135° linearly polarized light component .

[0011] Specifically, it also includes a computing unit configured to calculate the phase difference δ based on Stokes parameters.

[0012] Specifically, the phase difference δ is expressed by the formula calculate.

[0013] Specifically, the quarter-wave plate is placed in the test light path to rotate the polarization direction of the test light by 90 degrees.

[0014] Specifically, the reference light path is formed by reflecting the light from the standard mirror through a reflector, and the test light path includes the device under test. After passing through the device under test, the test light is combined with the reference light to form elliptically polarized light.

[0015] Specifically, the 90-degree rotation of the polarization direction is achieved by the test light passing through a quarter-wave plate twice.

[0016] Specifically, the system omits the polarization beam splitter (PBS) element compared to the existing Thyman Green polarization phase-shifting interferometry system, and the reference light and test light share the same optical path to enhance environmental adaptability.

[0017] Beneficial effects:

[0018] This invention provides a dynamic measurement system for component surface shape based on metasurfaces, which achieves significant performance breakthroughs through multi-dimensional innovative design:

[0019] 1. Significantly Enhanced Environmental Adaptability: The shared optical path structure ensures that the test and reference beams propagate strictly along the same path, completely eliminating the path difference sensitivity problem in traditional beam splitter designs. The effects of external vibrations and temperature gradient changes on the dual beams can be synchronously canceled out. Combined with a sealed nitrogen-filled housing design, the system maintains stable operation even under strong disturbances, and its measured anti-interference capability is on par with traditional solutions.

[0020] 2. Innovative Measurement Accuracy and Efficiency: A unique dynamic polarization state resolution mechanism replaces mechanical phase-shifting scanning. By simultaneously capturing the left-hand / right-hand circular polarization component difference and the 45° / 135° linear polarization component difference with a detector, the phase difference δ is directly calculated and the surface shape reconstructed, avoiding phase-shifting errors and increasing the sampling frequency to the millisecond level. This design enables high-resolution capture of micro- and nano-scale transient deformations.

[0021] 3. Significantly simplified system architecture: Compared to the existing Thyman Green polarization phase-shifting interferometry system, the polarization beam splitter (PBS) and the quarter-glass slide in the reference optical path are omitted, reducing the number of optical components. This not only reduces manufacturing costs but also simplifies the system and makes it more environmentally adaptable.

[0022] 4. Full-process error suppression: The computing unit innovatively adopts system surface shape calibration compensation technology to pre-subtract inherent surface shape errors from standard mirrors and waveplates; combined with anti-vibration algorithms to filter out low-frequency disturbances, ensuring the authenticity and repeatability of the surface shape reconstruction results. This technology provides a reliable tool for breaking through accuracy bottlenecks in high-end optical manufacturing, semiconductor testing, and other fields. Attached Figure Description

[0023] Figure 1 is a schematic diagram of the composition of the component surface dynamic measurement system based on metasurface provided in a specific embodiment of the present invention. Detailed Implementation

[0024] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Based on the embodiments in this application, other similar embodiments obtained by those skilled in the art without creative effort should all fall within the scope of protection of this application. Furthermore, directional terms mentioned in the following embodiments, such as "up," "down," "left," and "right," are only for reference to the directions in the accompanying drawings; therefore, the directional terms used are for illustrative purposes and not for limiting the invention.

[0025] The present invention will be further described below with reference to the accompanying drawings and preferred embodiments.

[0026] Please refer to Figure 1. This invention provides a dynamic measurement system for component surface shape based on metasurfaces, comprising:

[0027] The system includes a light source, a polarization modulation unit, a reference optical path, a test optical path, a beam combiner, and a detector; wherein the reference optical path and the test optical path are in a common optical path structure, and the detector is configured to detect the polarization components after beam combining to obtain the phase difference, thereby calculating the surface shape information of the optical element.

[0028] It should be further explained that the core implementation of the metasurface-based component surface dynamic measurement system provided by this invention includes a laser, a polarization modulation unit, and a polarization detection detector, wherein the reference light path and the test light path adopt a common optical path design. The linearly polarized light emitted by the laser is split by a reflector; part of it is reflected by a standard mirror as reference light, and the other part is used as test light, passing through a quarter-wave plate to illuminate the device under test. After being reflected by the device under test, the test light passes through the quarter-wave plate again, rotating its polarization direction by 90°, and finally interferes with the reference light in the beam combining unit to form elliptically polarized light. The detector measures the left-handed polarization component (…). ), right-handed optical component ( ), 45° linear polarization component ( ) and 135° linear polarization component ( Phase difference calculated using Stokes parameters This allows for the calculation of surface shape information. Its beneficial effects include:

[0029] (1) The common optical path structure significantly improves environmental adaptability and avoids temperature / vibration interference;

[0030] (2) Eliminating the traditional polarization beam splitter (PBS) simplifies the system architecture and reduces hardware costs.

[0031] As can be understood, as shown in Figure 1, the laser beam emitted is linearly polarized. After passing through the reflector, part of it is reflected by the standard mirror as a reference beam. The reflected beam is then reflected by the reflector and incident on the detector. The other part is used as a test beam, passing through the standard mirror and a quarter-wave plate. After being reflected by the device under test (DUT), it passes through the quarter-wave plate again. The two passes through the quarter-wave plate rotate the positive polarization direction of the original linearly polarized light by 90°, making it orthogonal to the original polarization direction. This test beam continues to pass through the standard mirror and the reflector before being combined with the reference beam. Since the phase of each point on the wavefront of the test beam is modulated after passing through the standard mirror, the wave plate, and the DUT, there is a phase difference between the test beam and the reference beam. This phase difference causes the reference beam and the test beam to be combined into elliptically polarized light. The phase difference can be obtained by measuring the left and right circular polarization information or linear polarization information. This phase difference is the surface shape of the system and the DUT. After subtracting the surface shape information of the system components such as the standard mirror and the wave plate, the surface shape information of the DUT can be obtained.

[0032] In the specific testing process, the reference photoelectric field intensity can be expressed as E. r =E r0 e iφr Among them, E r (Left side) represents the complex amplitude (including phase information) of the reference light at the detector position; E r0 (Before the exponent on the right) represents the real amplitude of the reference light (the peak value of the electric field intensity of the light wave), characterizing the magnitude of the light wave energy; e iφrLet φr represent the phase factor, where i is the imaginary unit and φr is the phase angle of the reference light at the probe point (in radians). It can be understood that this formula fully describes the wave characteristics (amplitude + phase) of the reference light in complex exponential form, providing a basis for subsequent interferometric calculations.

[0033] The electric field intensity of the test light can be expressed as: :

[0034] in:

[0035] (Left side) indicates the complex amplitude of the test light at the detector position.

[0036] (Before the exponent on the right) indicates the real amplitude of the test light.

[0037] Represents the phase factor. It is the phase angle of the test light modulated by the device under test.

[0038] Key difference: Compared to the reference light, It includes the phase delay introduced by the surface shape of the test piece (i.e., the micro-deformation information of the test piece).

[0039] According to the Stokes parameter, the difference between the left-handed and right-handed components of the combined beam can be expressed as:

[0040]

[0041] in:

[0042] The intensity of the left-hand circularly polarized component in the elliptically polarized light formed after beam combining (unit: optical power / area).

[0043] The intensity of the right-hand circularly polarized component.

[0044] The product of the real amplitudes of the reference light and the test light is proportional to the total energy of the interfering light.

[0045] : Sine function It is the phase difference between the test light and the reference light. This directly reflects the deviation between the surface shape of the measured part and the reference surface.

[0046] Core mechanism: This formula reveals the phase difference The sinusoidal relationship between the intensity difference of the circular polarization state and the surface shape is the core physical basis for dynamically solving the surface shape.

[0047] To facilitate the calculation of the phase difference, the intensity difference between a pair of orthogonally polarized linear components at 45° and 135° to the polarization direction of the reference light can be obtained. This difference can be expressed using the Stokes parameter as follows:

[0048]

[0049] in:

[0050] The intensity of the linearly polarized component at a 45° angle to the polarization direction of the reference light.

[0051] The intensity of the linearly polarized component at a 135° angle to the polarization direction of the reference light (and) (Components are orthogonal).

[0052] : cosine function, here The phase difference is defined in the same way as the formula for the difference between the left-handed and right-handed components after beam combining. ).

[0053] Key function: By measuring the intensity difference between a pair of orthogonally polarized light components, it is possible to independently obtain... The cosine value, thus combined with the formula for the difference between the left-handed and right-handed components after beam combining, enables the calculation of a larger wrap-around phase (2π) of the phase difference (e.g., calculating...). ).

[0054] Finally, the phase difference can be calculated as:

[0055]

[0056] in, , , , All of these can be obtained using a detector with polarization detection capabilities.

[0057] It should be further explained that in the design scheme of this invention:

[0058] 1. Phase difference :

[0059] The microscopic height difference between the surface profile of the test piece and the standard mirror is directly quantified. Based on wave optics, the surface profile height difference... and The relationship is ( (Where the laser wavelength is used).

[0060] 2. Elliptically polarized light:

[0061] It is a polarization state formed by the interference of two coherent beams (reference beam and phase-modulated test beam). Its left / right rotation and linear polarization components carry complete phase information and can be accurately characterized by Stokes parameters.

[0062] 3. Dynamic measurement principle:

[0063] Simultaneous detection using optical metasurface and CMOS camera The intensity of the four polarization components can be calculated in real time by substituting them into the formulas for the difference between the left-handed and right-handed polarization components after beam combining and the formula for the difference in intensity of the orthogonally polarized components. This enables dynamic surface shape measurement that is phase-shift-free and vibration-resistant.

[0064] Specifically, the light source is a laser that emits polarized light.

[0065] It should be further noted that the light source is a 635nm helium-neon laser, producing linearly polarized light with an output power of 5mW, and the polarization direction is at a 0° angle to the horizontal plane. This laser is maintained at a temperature stability of ±0.1℃ through a constant temperature control module, ensuring the stability of the output beam's polarization state. The beneficial effects are as follows:

[0066] (1) Matching the sensitivity of metasurface detectors with specific wavelengths and power improves the signal-to-noise ratio;

[0067] (2) The constant temperature control eliminates thermal polarization drift, so that the measurement accuracy reaches λ / 100 (λ=632.8nm).

[0068] Specifically, the polarization modulation unit includes at least one quarter-wave plate.

[0069] It should be further explained that the polarization modulation unit includes a 0.14mm thick quartz quarter-wave plate placed in the test light path. The fast axis of the wave plate forms a 45° angle with the polarization direction of the incident light, causing the test light to rotate a cumulative 90° in polarization direction after passing through twice. The surface of the wave plate is coated with an anti-reflection film (reflectivity less than 0.2%), and the support is equipped with a fine-tuning mechanism to achieve ±0.5° angle calibration. The beneficial effects are:

[0070] (1) The dual-wave plate design compensates for assembly errors and ensures polarization modulation accuracy;

[0071] (2) Antireflective coatings reduce light energy loss;

[0072] (3) Increases the effective signal strength by 40%.

[0073] Specifically, the detector has a polarization detection function for measuring the left-handed optical component. Dextrorotatory optical component 45° linearly polarized light component and 135° linearly polarized light component .

[0074] It should be further noted that the detector employs a CMOS polarization camera with a pixel size of 2.2μm, integrating a 45° / 135° linear polarization filter array and left / right circular polarization detection modules. The camera calculates the intensity of the four polarization components in real time via an FPGA, with a sampling frequency of 200fps. Beneficial effects include:

[0075] (1) Multi-channel synchronous detection avoids mechanical phase shift and realizes dynamic surface shape measurement;

[0076] (2) High-speed sampling captures transient deformation with a time resolution better than 5ms.

[0077] Specifically, it also includes a computing unit configured to calculate the phase difference δ based on Stokes parameters.

[0078] It should be further explained that the computing unit is equipped with an ARM processor and executes the Stokes parametric algorithm: firstly, for , , , Perform dark current correction, and then... The phase difference is calculated, and finally, the system surface shape error between the standard mirror and the waveplate is subtracted. An environmental vibration resistance module is added to the algorithm, and Zernike polynomial fitting is used to eliminate low-frequency disturbances. The beneficial effects are:

[0079] (1) Fully digital processing makes the surface reconstruction error less than 5nm RMS;

[0080] (2) The vibration compensation function maintains stable measurement even under 1-100Hz disturbance.

[0081] Specifically, the phase difference δ is expressed by the formula calculate.

[0082] It should be further explained that the phase difference calculation uses floating-point arithmetic optimization, and the formula is... The process can be broken down into three steps: First, calculate the numerator difference ΔA = - Difference from the denominator ΔB= - Then, calculate the ratio k = ΔA / ΔB, and finally obtain arctan(k) using a lookup table. A threshold condition is set so that the interpolation algorithm is enabled when |ΔB| is less than 0.01. The beneficial effects are:

[0083] (1) Avoid division by zero errors and improve system robustness;

[0084] (2) The calculation time is reduced to 0.8ms, which meets the real-time requirements.

[0085] Specifically, the quarter-wave plate is placed in the test light path to rotate the polarization direction of the test light by 90 degrees.

[0086] It should be further noted that the quarter-wave plate is mounted on a six-axis fine-tuning frame, and its 45° angle with the beam is calibrated using a laser interferometer, with a positioning accuracy of ±0.1°. The test optical path is set with an aperture to limit the beam diameter within the effective area of ​​the wave plate, resulting in an edge occlusion ratio of less than 1%. Beneficial effects include:

[0087] (1) High-precision positioning ensures the effectiveness of the polarization modulation theoretical model;

[0088] (2) The aperture design suppresses stray light;

[0089] (3) Make the interference contrast > 85%.

[0090] Specifically, the reference light path is formed by reflecting the light from the standard mirror through a reflector, and the test light path includes the device under test. After passing through the device under test, the test light is combined with the reference light to form elliptically polarized light.

[0091] It should be further explained that the reference light path guides the reflected light from the standard mirror to the beam combiner unit via a plane mirror. In the test light path, the device under test (DUT) is placed on a five-dimensional adjustment stage, enabling adaptive measurement of the off-axis angle from 0-30°. The beam combiner unit uses a non-polarizing beam splitter prism with a splitting ratio of 50:50 and a light-transmitting aperture of Φ25mm. The beneficial effects are:

[0092] (1) The common optical path design significantly improves the system’s anti-disturbance performance compared to the existing Thyman Green optical path.

[0093] Specifically, the 90-degree rotation of the polarization direction is achieved by the test light passing through a quarter-wave plate twice.

[0094] It should be further explained that the polarization rotation mechanism was verified through ray tracing: linearly polarized light is converted into circularly polarized light when it first passes through the waveplate, and after being reflected by the test object, it is converted into orthogonally linearly polarized light when it passes through the waveplate a second time. A Jones matrix model was established to verify that the rotation angle error is less than 0.5°, and this was further verified through actual measurements using a dual-frequency laser interferometer. The beneficial effects are as follows:

[0095] (1) The error between the theoretical model and the actual measurement is less than λ / 200;

[0096] (2) Ensure the accuracy of phase calculation.

[0097] Specifically, the system omits the polarization beam splitter (PBS), thus enhancing its environmental adaptability.

[0098] It should be further noted that this system omits the PBS and the quarter-glass slide in the reference optical path of existing polarization phase-shifting interferometry systems based on the Thyman-Green optical path, thus reducing the overall size and simplifying the system. The beneficial effects are:

[0099] (1) Simplifying the structure makes assembly and adjustment simpler;

[0100] (2) Environmental adaptability meets the requirements of mobile platforms such as vehicle-mounted and airborne platforms.

[0101] Specifically, the phase difference is used to obtain the surface shape of the measured component after subtracting the surface shape information of the system components.

[0102] It should be further explained that the system surface shape subtraction adopts a calibration mode: first, the measured part is removed, and the reference phase distribution δ_sys without the target is measured and stored as a compensation template. During the formal measurement, the true surface shape is obtained by δ_true = δ_measured - δ_sys. The calibration process is repeated 3 times and the average value is taken to eliminate random errors. Beneficial effects include:

[0103] (1) Eliminate standard mirror shape error (on the order of λ / 10);

[0104] (2) Compensation waveplate stress birefringence effect.

[0105] It is understood that the present invention splits the test light into two orthogonally linearly polarized beams. One beam is used as the test light and passes through the device under test. The other beam is used as the reference light and is combined with the test light. After the beam is combined, it is incident on a detector with corresponding polarization detection capability. Finally, the surface shape of the device under test can be obtained by solving the Stokes parameters.

[0106] It is understood that the technical effects or advantages of the present invention are as follows:

[0107] 1) This invention realizes dynamic optical element surface shape detection with reference light and test light sharing the same optical path, which improves the environmental adaptability of the detection system compared with the existing dynamic surface shape detection technology (polarization phase shift).

[0108] 2) Compared with existing dynamic surface shape detection technology (polarization phase shifting), this invention does not require the use of polarization beam splitter (PBS) or separation of reference optical path and test optical path, which greatly simplifies the system and reduces hardware cost.

[0109] The technical features described above can be combined arbitrarily. Although not all possible combinations of these technical features are described, any combination of these technical features should be considered to be covered by this specification, provided that such combination does not contain contradictions.

[0110] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A dynamic measurement system for component surface shape based on metasurfaces, characterized in that, The system includes a light source, a polarization modulation unit, a reference light path, a test light path, a beam combiner, and a detector. The reference light path and the test light path share a common optical path. The detector is configured to detect the polarization components after beam combining to obtain the phase difference, thereby calculating the surface shape information of the optical element. The polarization modulation unit includes at least one quarter-wave plate. The quarter-wave plate is disposed in the test light path to rotate the polarization direction of the test light by 90 degrees. The reference light path is formed by reflecting light from a standard mirror using a mirror, and the test light path includes the device under test (DUT). After the test light passes through the DUT... The test beam is combined with the reference beam to form elliptically polarized light. The 90-degree rotation of the polarization direction is achieved by the test beam passing through a quarter-wave plate twice. The light beam emitted from the light source is linearly polarized. After passing through the reflector, part of it is reflected by the standard mirror as reference light. The reflected light is then reflected by the reflector and enters the detector. The other part is used as test light and passes through the standard mirror and the quarter-wave plate. After being reflected by the test object, it passes through the quarter-wave plate again. The two passes through the quarter-wave plate rotate the positive polarization direction of the original linearly polarized light by 90°, making it orthogonal to the original polarization direction. The test light continues to pass through the standard mirror and the reflector before being combined with the reference beam.

2. The component surface dynamic measurement system based on metasurfaces according to claim 1, characterized in that, The light source is a laser that emits polarized light.

3. The component surface shape dynamic measurement system based on metasurfaces according to claim 1, characterized in that, The detector described above has a polarization detection function for measuring the left-handed optical component. Dextrorotatory optical component 45° linearly polarized light component and 135° linearly polarized light component 。 4. The component surface shape dynamic measurement system based on metasurfaces according to claim 1, characterized in that, It also includes a computing unit configured to calculate the phase difference δ based on Stokes parameters.

5. The component surface dynamic measurement system based on metasurfaces according to claim 3, characterized in that, The phase difference δ is obtained through the formula calculate.

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