Synchronous wavelength phase-shifting interference measurement system

Abstract

The invention relates to the technical field of optical interference measurement, in particular to a synchronous wavelength phase-shifting interference measurement system. According to the scheme, a laser set outputs multiple narrow-linewidth light beams with nm-level wavelength spacing, and the multiple narrow-linewidth light beams are combined through a wavelength division multiplexer and then enter an interference light path to generate multi-wavelength interference fringes. The metasurface achieves separation of interference fringes of all wavelengths through a sub-wavelength structure array, a detector synchronously captures light intensity data of the interference fringes of all the wavelengths in a single frame mode, and then phase distribution can be directly calculated through single-frame multi-wavelength light intensity. According to the system, mechanical phase shifting and polarization control assemblies are eliminated, the defects that a traditional wavelength phase shifting interference measurement technology is poor in environmental adaptability and a traditional synchronous phase shifting technology has polarization errors are overcome, and a high-precision and high-environmental-adaptability dynamic measurement scheme is provided for optical manufacturing.

Description

Technical Field

[0001] This invention relates to the field of optical interferometry technology, and more specifically to a synchronous wavelength phase-shifting interferometry system. Background Technology

[0002] Interferometry is currently the primary method for measuring the surface shape of planar devices such as optical elements and wafers. Among interferometric methods, phase-shifting interferometry is recognized as the most accurate, and most mainstream interferometers currently employ it. Phase-shifting interferometry techniques mainly include mechanical phase shifting, polarization phase shifting, and wavelength phase shifting. Mechanical phase shifting uses piezoelectric ceramics to shift a standard mirror to adjust the optical path difference, thus achieving phase shifting. Because this method is susceptible to environmental vibrations, it is only suitable for small-aperture interferometric systems; large-aperture systems typically do not use this technique. Polarization phase shifting is currently the only synchronous phase shifting technique; however, it is susceptible to polarization errors and cannot accurately measure birefringent crystals or crystals exhibiting significant stress birefringence, thus having significant limitations. Wavelength-tuned phase shifting achieves phase shifting by adjusting the wavelength of the test light and is the main phase shifting technique for large-aperture interferometric systems. Its environmental adaptability is better than mechanical phase shifting but less than polarization phase shifting, but it has no polarization error compared to polarization phase shifting.

[0003] The existing technology has the following technical defects: The existing wavelength phase shifting technology, namely wavelength tuning phase shifting, achieves phase shifting by adjusting the wavelength of the test light. This method is time-division phase shifting and cannot perform dynamic measurement, thereby reducing the system's environmental adaptability and making it difficult to meet the needs of field measurement.

[0004] Therefore, the existing technology still needs further development. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned technical deficiencies and provide a synchronous wavelength phase-shifting interferometry measurement system to solve the problems existing in the prior art, including: Laser array, used to provide laser sources of multiple wavelengths; A wavelength division multiplexer, whose input is connected to the laser array via an optical fiber, is used to combine laser beams of multiple wavelengths. An interference optical path, whose input end is connected to the output end of the wavelength division multiplexer via an optical fiber, is used to project the combined multi-wavelength beam onto the device under test and generate multi-wavelength interference fringes. A detector is used to receive the multi-wavelength interference fringe image output by the interference optical path; A wavelength-gated metasurface is attached to the target surface of the detector. The wavelength-gated metasurface is composed of several functional units arranged together. Each functional unit includes several wavelength-gated subwavelength structure arrays. Each subwavelength structure array is configured to have high transmittance for a specific wavelength beam and suppress other wavelength beams.

[0006] Specifically, the laser group comprises at least three lasers, with the center wavelength spacing of their output wavelengths less than 10 nm.

[0007] Specifically, the wavelength division multiplexer is a coupler-type wavelength division multiplexer.

[0008] Specifically, the functional units of the wavelength-gated metasurface are arranged in a periodic array, with each functional unit corresponding to a pixel of the detector.

[0009] Specifically, each functional unit contains the same number of subwavelength structure arrays as the number of lasers, and the peak transmittance wavelength of each subwavelength structure array is matched with the output wavelength of the laser group.

[0010] Specifically, the material and structural dimensions of the subwavelength structure array are determined through electromagnetic simulation optimization based on the target transmission wavelength.

[0011] Specifically, the wavelength-gated metasurface is a transmissive metasurface.

[0012] Specifically, the system is configured to simultaneously acquire at least three sets of phase-shifting interferograms to achieve synchronous phase-shifting measurement under dynamic conditions.

[0013] Beneficial effects: This invention innovatively combines a multi-wavelength light source, an interferometric measurement system, and a wavelength-gated metasurface to achieve synchronous wavelength phase shifting, thereby realizing a dynamic wavelength phase shifting measurement technology. This greatly improves the environmental adaptability of wavelength phase shifting technology, enabling its use in outdoor environments and other scenarios where only polarization phase shifting technology can handle the task. Furthermore, this invention significantly reduces the requirements for the light source in wavelength phase shifting, eliminating the need for the wavelength-tuned light source costing approximately 300,000 yuan required by existing technologies. Instead, it only requires coupling multiple wavelength lasers with a wavelength division multiplexer to meet the usage requirements, with a cost of less than 100,000 yuan, greatly reducing system costs. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the system composition of the synchronous wavelength phase-shifting interferometry measurement system provided in a specific embodiment of the present invention. Detailed Implementation

[0015] 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.

[0016] The present invention will be further described below with reference to the accompanying drawings and preferred embodiments.

[0017] It needs to be further explained that, such as Figure 1 As shown, the synchronous wavelength phase-shifting interferometric measurement system proposed in this invention consists of a laser array, a wavelength division multiplexer (WDM), an interferometric optical path, and a detector. The laser array provides multiple wavelengths of laser light, with the center wavelength spacing between the output wavelengths of each laser on the order of nanometers (compared to the method used in the existing patented technology "Multi-wavelength Coherent Imaging Device (Authorization Announcement No.: CN219122495U)" which employs a color camera to detect three wavelengths with a wavelength spacing of hundreds of nanometers, using similar wavelengths here can significantly reduce the influence of color difference on the measurement results). The output beams of the aforementioned multiple wavelengths of laser light are connected to the WDM via optical fiber. The WDM combines the beams of the aforementioned wavelengths and outputs them to the interferometric optical path via optical fiber. The interferometric optical path is used to load the surface shape information of the measured element into the interferometric image. Here, because simultaneously using… Since multiple wavelengths of test beams are used, interference fringes corresponding to multiple wavelengths will be generated. The fringe information is detected by a detector. For the detector, this invention enables it to simultaneously detect interference images corresponding to multiple wavelengths by attaching a wavelength-gated metasurface to its target surface. The wavelength-gated metasurface is an array of several functional units. Each functional unit has the ability to simultaneously gate multiple wavelength beams. Each functional unit consists of several wavelength-gated subwavelength structure arrays. Each subwavelength structure array can be adjusted to have high transmittance only for specific wavelengths by adjusting the size, shape, material, etc. of the subwavelength structure, while suppressing beams of other bands.

[0018] Please see Figure 1 The present invention provides a synchronous wavelength phase-shifting interferometry measurement system, comprising: A laser array is used to provide laser sources of multiple wavelengths, with the center wavelength spacing between the output wavelengths of each laser being on the order of nm. A wavelength division multiplexer, whose input is connected to the laser array via an optical fiber, is used to combine laser beams of multiple wavelengths. An interference optical path, whose input end is connected to the output end of the wavelength division multiplexer via an optical fiber, is used to project the combined multi-wavelength beam onto the device under test and generate multi-wavelength interference fringes. A detector is used to receive the multi-wavelength interference fringe image output by the interference optical path; A wavelength-gated metasurface is attached to the target surface of the detector. The wavelength-gated metasurface is composed of several functional units arranged together. Each functional unit includes several wavelength-gated subwavelength structure arrays. Each subwavelength structure array is configured to have high transmittance for a specific wavelength beam and suppress other wavelength beams.

[0019] It should be further explained that the synchronous wavelength phase-shifting interferometry system specifically includes: Laser array: Three distributed feedback (DFB) lasers are used to simultaneously provide light sources of different wavelengths. The center wavelength spacing between the three lasers is no more than 5 nm, the power stability requirement is less than ±0.5%, and constant temperature control is adopted. The linewidth y is preferably less than 1 MHz to ensure a coherence length >10 m. Wavelength division multiplexer: It adopts a 3-channel fiber coupler, with the input port connected to the laser group, the beam combining loss ≤0.3dB, and the channel isolation is preferably greater than 30dB; Interference optical path: The Fizeau interference structure is adopted, which includes a beam splitter, a reference mirror and a wafer carrier stage under test. The combined beam is collimated and then incident on the interference optical path. Detector: A CMOS area array detector is selected, with a preferred resolution of 4096×4096 and a preferred frame rate of 20fps (at full resolution). Wavelength-gated metasurface: attached to the CMOS target surface, its functional unit size matches the pixel size (5.5μm×5.5μm), and each functional unit contains 3 subwavelength structure arrays.

[0020] It should be further noted that the interference optical path proposed in this invention includes the following key components: Beam splitter: fused silica substrate, reflectance / transmittance ratio 50:50; Reference mirror: λ / 20 flatness, piezoelectric ceramic displacement stage (for initial calibration); Test platform: air-bearing vibration isolation platform, load capacity 5kg.

[0021] In a preferred embodiment of the present invention, the arrangement of functional units is preferably matched with CMOS pixels in a 1:1 ratio.

[0022] It is understood that the specific operation process of the synchronous wavelength phase-shifting interferometry measurement system proposed in this invention includes: 1. Three-wavelength laser beams are combined using a wavelength division multiplexer and then input into the Fizeau interference optical path; 2. The test light interferes with the reference light to form three sets of fringes; 3. Stripes are filtered by metasurface: subwavelength array A transmits λ1 (transmittance > 90%) and suppresses λ2 / λ3 (transmittance < 5%); arrays B / C are treated similarly for λ2 / λ3; 4. The detector captures a three-wavelength phase-shifting interferogram simultaneously in a single exposure.

[0023] Specifically, the laser array comprises 3-5 lasers, with the center wavelength spacing of their output wavelengths ranging from 0.1 nm to 10 nm.

[0024] In a preferred embodiment of the invention, the laser array is expanded to at least four: The wavelength division multiplexer was replaced with an arrayed waveguide grating (AWG) type multiplexer, with channel isolation >40dB.

[0025] Specifically, the wavelength division multiplexer is a coupler-type wavelength division multiplexer with a beam combining loss of less than 0.5 dB.

[0026] Specifically, the functional units of the wavelength-gated metasurface are arranged in a periodic array, with each functional unit corresponding to a pixel of the detector.

[0027] Specifically, each functional unit contains the same number of subwavelength structure arrays as the number of lasers, and the peak transmittance wavelength of each subwavelength structure array is matched with the output wavelength of the laser group.

[0028] Specifically, the material and structural dimensions of the subwavelength structure array are determined through electromagnetic simulation optimization based on the target transmission wavelength.

[0029] Specifically, the wavelength-gated metasurface is a transmissive metasurface with an average transmittance greater than 80% and crosstalk between adjacent wavelength channels less than -20dB.

[0030] In other preferred embodiments of the present invention, the wavelength-gated metasurface employs the following optimized design: 1. Structural layout: such as Figure 1 As shown in the dashed box, the functional units are arranged in a 4×4 periodic pattern, and each unit contains 4 subwavelength structure arrays (matching 4 wavelengths). 2. Materials and Design: The subwavelength structure is a silica nanopillar, optimized through FDTD simulation. It should be further noted that the present invention also provides a cost control implementation scheme, as shown in Table 1: Table 1 Cost Control Implementation Plan Specifically, the system is configured to simultaneously acquire at least three sets of phase-shifting interferograms to achieve synchronous phase-shifting measurement under dynamic conditions.

[0031] Specifically, the interference optical path is a Thyman-Green interference structure or a Fizeau interference structure, and does not contain mechanical phase-shifting elements.

[0032] Specifically, the system is suitable for measuring the surface shape of birefringent crystals and does not require a polarization phase shifting component.

[0033] It is understood that the synchronous wavelength phase-shifting interferometric measurement system proposed in this invention consists of a laser group, a wavelength division multiplexer (WDM), an interferometric optical path, and a detector. The laser array provides laser sources of multiple wavelengths, with the center wavelength spacing between the output wavelengths of each laser on the order of nm. The output beams of the lasers of these multiple wavelengths are connected to a wavelength division multiplexer (WDM) via optical fiber. The WDM combines the beams of each wavelength and outputs them to the interference optical path via optical fiber. The interference optical path is used to load the surface shape information of the device under test into the interference image. Since multiple wavelength test beams are used simultaneously, multiple interference fringes corresponding to the wavelengths are generated. The fringe information is detected by a detector. For the detector, this invention enables it to simultaneously detect interference images corresponding to multiple wavelengths by attaching a wavelength-gated metasurface to its target surface. The wavelength-gated metasurface is an array of several functional units. Each functional unit has the ability to simultaneously gate multiple wavelength beams. Each functional unit consists of several wavelength-gated subwavelength structure arrays. Each subwavelength structure array can be adjusted by changing the subwavelength structure material, size, shape, etc., so that it has high transmittance only for a specific wavelength while suppressing beams of other bands.

[0034] It should be noted that this invention innovatively combines a multi-wavelength light source, an interferometric measurement system, and a wavelength-gated metasurface to achieve synchronous wavelength phase shifting, thereby realizing a dynamic wavelength phase shifting measurement technology. This greatly improves the environmental adaptability of wavelength phase shifting technology, enabling its use in outdoor environments and other scenarios where only polarization phase shifting technology can handle the task. In addition, this invention significantly reduces the requirements for the light source in wavelength phase shifting, eliminating the need for the wavelength-tuned light source costing around 300,000 yuan required by existing technologies. Instead, it only requires coupling multiple wavelength lasers with a wavelength division multiplexer to meet the requirements, with a cost of less than 100,000 yuan, greatly reducing system costs.

[0035] It is understandable that the synchronous wavelength phase-shifting interferometry measurement system of the present invention breaks through the bottlenecks of traditional technology through multi-level innovative design: 1. A leap in environmental adaptability: By combining multi-wavelength laser synchronous beam combining with metasurface beam splitting, multiple phase-shifting interferograms can be captured in a single exposure, completely eliminating mechanical vibration errors. Wavelength-gated metasurfaces achieve pixel-level spectral separation on the detector target surface, suppressing the disruption of phase correlation caused by vibrations.

[0036] 2. Breakthrough in material compatibility: Wavelength phase shifting is used instead of polarization modulation to avoid polarization errors caused by birefringent materials; The metasurface channel-type beam-splitting synchronous wavelength phase-shifting mechanism eliminates polarization-dependent errors, significantly improving the measurement accuracy of crystals such as lithium niobate.

[0037] 3. System reliability optimization: The interference optical path design without mechanical phase shifting components reduces system complexity and failure rate, as well as the impact of environmental vibration on measurement accuracy; Wavelength division multiplexers and metasurfaces work together to replace traditional beam splitting and beam combining modules, reducing the number of optical components by more than 60%. The combination of all-fiber transmission and solidified metasurface enables module-level packaging to adapt to industrial scenarios.

[0038] 4. A revolution in measurement efficiency: The multi-wavelength parallel processing architecture transforms phase-shifting operations from a temporal mode to a spatial mode; The hardware-level integration of wavelength gating and phase calculation is an order of magnitude faster than tuned laser solutions.

[0039] 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.

[0040] 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 synchronous wavelength phase-shifting interferometric measurement system, characterized in that, include: Laser array, used to provide laser sources of multiple wavelengths; A wavelength division multiplexer, whose input is connected to the laser array via an optical fiber, is used to combine laser beams of multiple wavelengths. An interference optical path, whose input end is connected to the output end of the wavelength division multiplexer via an optical fiber, is used to project the combined multi-wavelength beam onto the device under test and generate multi-wavelength interference fringes. A detector is used to receive the multi-wavelength interference fringe image output by the interference optical path; A wavelength-gated metasurface is attached to the target surface of the detector. The wavelength-gated metasurface is composed of several functional units arranged together. Each functional unit includes several wavelength-gated subwavelength structure arrays. Each subwavelength structure array is configured to have high transmittance for a specific wavelength beam and suppress other wavelength beams.

2. The synchronous wavelength phase-shifting interferometric measurement system according to claim 1, characterized in that, The laser array comprises at least three lasers, the center wavelength spacing of which is less than [missing information]. 10nm.

3. The synchronous wavelength phase-shifting interferometric measurement system according to claim 2, characterized in that, The wavelength division multiplexer is a coupler-type wavelength division multiplexer.

4. The synchronous wavelength phase-shifting interferometric measurement system according to claim 1, characterized in that, The functional units of the wavelength-gated metasurface are arranged in a periodic array, with each functional unit corresponding to a pixel of the detector.

5. The synchronous wavelength phase-shifting interferometric measurement system according to claim 4, characterized in that, Each functional unit contains the same number of subwavelength structure arrays as the number of lasers, and the peak transmittance wavelength of each subwavelength structure array matches the output wavelength of the laser group.

6. The synchronous wavelength phase-shifting interferometric measurement system according to claim 5, characterized in that, The material and structural dimensions of the subwavelength structure array are determined through electromagnetic simulation optimization based on the target transmission wavelength.

7. The synchronous wavelength phase-shifting interferometric measurement system according to claim 1, characterized in that, The wavelength-gated metasurface is a transmissive metasurface.

8. The synchronous wavelength phase-shifting interferometric measurement system according to claim 1, characterized in that, The system is configured to simultaneously acquire at least three sets of phase-shifting interferograms to achieve synchronous phase-shifting measurement under dynamic conditions.

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