Multi-channel surface shape detection apparatus and method based on wavelength-shifted interferometry

Abstract

This invention relates to a multi-channel surface shape detection device and method based on wavelength phase-shifting interferometry, belonging to the field of phase-shifting interferometry technology. The device includes a wavelength-tuned laser, a total incident fiber, a fiber beam splitter, a first-channel fiber, a Fizeau interferometer module, a second-channel fiber, and a Thyman Green interferometer module. The Fizeau interferometer module includes a beam splitter, a first collimating lens, a first standard lens, a first mirror under test, an imaging lens, and a first detector. The Thyman Green interferometer module includes a second collimating lens, a reflecting mirror, a beam splitter, a reference mirror, a second standard lens, a second mirror under test, an imaging system, and a second detector. The method includes steps such as stabilizing the light source, system adjustment, phase-shifting calibration, acquiring interferograms, calculating the surface shape phase, wrapping calculation, and system reset. This invention uses the output wavelength of the wavelength-tuned laser to complete the phase shift, achieving multi-channel parallel measurement with a single phase shift, reducing the number of devices, lowering application costs, and improving measurement efficiency.

Description

Technical Field

[0001] This invention belongs to the field of phase-shifting interferometry technology, specifically a multi-channel surface shape detection device and method based on wavelength phase-shifting interferometry. Background Technology

[0002] With the rapid development of modern science and technology, from smartphones to military and aerospace applications, higher demands are being placed on the precision and quantity of optical components. The widespread use of precision optical components has driven the development of optical components towards mass production, low cost, high efficiency, and ultra-precision machining, while simultaneously promoting the transformation of traditional optical component production and inspection technologies. The optical system is the core component of an optical product, composed of precision optical components such as lenses or mirrors. The surface quality of optical components is a crucial factor affecting the image quality or wavefront aberration of the optical system; the higher the surface quality of the optical components, the closer the optical system can be to the design values. Therefore, the efficient inspection and manufacturing of large quantities of ultra-precision optical components presents new challenges to current surface inspection technologies.

[0003] Surface shape inspection technology is crucial for ensuring the precision of optical component manufacturing. Traditional surface shape inspection methods include point-by-point scanning, Hartmann method, and knife-edge method. These methods carry the risk of damaging the mirror surface upon contact or have low accuracy. Laser interferometry (LIMA), on the other hand, is a digital precision testing method with nanometer-level accuracy and is currently recognized as one of the most effective and accurate techniques for inspecting the surface shape quality of optical components. The basic principle of laser interferometer technology is that two beams of light carrying information about the surface to be measured and a reference surface form an interference pattern. After phase shifting, a sequence of multiple frames of ordered phase differences in the interference pattern is obtained, thereby resolving the wavefront phase information of the surface to be measured and reconstructing the wavefront. Existing laser interferometers mostly employ mechanical phase shifting based on piezoelectric ceramics and polarization phase shifting based on polarization principles. Each interferometer requires a phase shifting unit. When inspecting the surface shape of multiple optical components online in real time, multiple interferometers and phase shifting units are needed, resulting in numerous devices, high costs, and low efficiency, which cannot meet the requirements of mass production of optical components. Summary of the Invention

[0004] To address the issues of requiring multiple interferometers and phase-shifting units for detecting the surface shape of multiple optical components, resulting in numerous devices, high costs, and low efficiency, this invention provides a multi-channel surface shape detection device and method based on wavelength phase-shifting interferometry. A wavelength-tuned laser serves as both a light source and a phase-shifting unit, using the output wavelength of the wavelength-tuned laser to perform phase shifting. Multiple interferometers are connected via fiber optic beam splitters, enabling parallel measurement of multiple channels in a single phase shift. This reduces the number of devices required, lowers application costs, and improves measurement efficiency.

[0005] The technical solution of the present invention is as follows:

[0006] On one hand, the present invention provides a multi-channel surface shape detection device based on wavelength phase-shifting interferometry, including a wavelength-tuned laser, a total incident fiber, a fiber beam splitter, a first channel fiber, a Fizeau interferometer module, a second channel fiber, and a Thyman Green interferometer module. The Fizeau interferometer module includes a beam splitter, a first collimating lens, a first standard lens, a first mirror under test, an imaging lens, and a first detector. The Thyman Green interferometer module includes a second collimating lens, a reflecting mirror, a beam splitter, a reference mirror, a second standard lens, a second mirror under test, an imaging system, and a second detector.

[0007] The laser emitted by the wavelength-tuned laser serves as the total light source and phase-shifting unit of the interferometer. It is incident on the fiber optic beam splitter via the main incident fiber, thereby splitting one laser beam into multiple laser beams. These beams are then connected to the Fiso interferometer module via the first fiber optic channel and to the Thyman Green interferometer module via the second fiber optic channel.

[0008] In the Fiso interferometer module, the first channel fiber incident light source passes through the beam splitter and the first collimating lens in sequence to form parallel light. The parallel light is partially reflected and partially transmitted through the first standard lens. The reflected light serves as the reference light, and the transmitted light serves as the test light. The test light is incident on the first mirror under test and reflected, carrying the surface shape information of the first mirror under test. It forms a first interferogram with the reference light and returns along the original path. It passes through the beam splitter and the imaging lens in sequence and is incident on the first detector. The first detector collects the first interferogram information to analyze and calculate the surface shape of the first mirror under test.

[0009] In the Thyman Green interferometer module, the second-channel fiber optic incident light source is transmitted sequentially through the second collimating lens and the reflecting mirror, and is incident parallel to the beam splitter, where it is split into transmitted light and reflected light. The transmitted light is reflected sequentially through the reference mirror and the beam splitter to form reference light. The reflected light is transmitted sequentially through the second standard lens and reflected by the second mirror under test, carrying the surface shape information of the second mirror under test. It is then transmitted sequentially through the second standard lens and the beam splitter, forming a second interferogram with the reference light. After being transmitted through the imaging system, it is incident on the second detector. The second detector collects the second interferogram information to analyze and calculate the surface shape of the second mirror under test.

[0010] Furthermore, the first-channel optical fiber and Fiso interferometer module are supplied as a set, which can be expanded to two or more sets; the second-channel optical fiber and Thyman Green interferometer module are supplied as a set, which can be expanded to two or more sets.

[0011] On the other hand, the present invention also provides a multi-channel surface shape detection method based on wavelength phase-shifting interferometry, comprising the following steps:

[0012] Step a: Stabilize the light source

[0013] Turn on the wavelength-tuned laser and wait for the wavelength and power to stabilize. Record the initial wavelength as λ0.

[0014] Step b, System Adjustment

[0015] The main incident fiber is connected to the fiber optic beam splitter. After splitting, the beam is incident on the Fiso interferometer module through the first fiber channel and on the Thyman Green interferometer module through the second fiber channel. The first mirror to be tested is placed in the Fiso interferometer module so that the first detector obtains a first interferogram with near-zero fringes. The second mirror to be tested is placed in the Thyman Green interferometer module so that the second detector obtains a second interferogram with near-zero fringes.

[0016] Step c, Phase shift calibration

[0017] Measure the cavity length h1 from the first mirror under test to the first standard lens, and calculate the wavelength tuning step Δλ of the wavelength-tuned laser as follows:

[0018]

[0019] Measure the optical path difference h2 between the second mirror under test and the front surface of the reference mirror, and calculate the wavelength tuning step Δλ of the wavelength-tuned laser as follows:

[0020]

[0021] Step d: Acquire interferograms

[0022] The wavelength tuning step size Δλ controls the wavelength-tuned laser to perform 13 phase shifts. At each phase shift, the first detector acquires one interferogram frame, for a total of 13 interferogram frames, denoted as I. 1,1 I 1,2 ... I 1,13 The second detector acquires one interferogram frame at each phase shift, for a total of 13 interferogram frames, denoted as I. 2,1 I 2,2 ... I 2,13 ;

[0023] Step e: Solve the surface phase

[0024] The surface phase is calculated using a 13-step phase-shifting algorithm, as shown in the following formula:

[0025]

[0026]

[0027] Step f, Package unpacking

[0028] The surface phase obtained in step e is unwrapped using an unwrapping algorithm to obtain a surface phase map. Then, the surface PV, RMS and Zernike coefficients are calculated to evaluate the surface quality of the first or second mirror under test.

[0029] Step g, System Reset

[0030] After each 13-step phase shift, the wavelength of the wavelength-tuned laser is restored to the initial wavelength λ0.

[0031] Beneficial effects:

[0032] This invention uses a wavelength-tuned laser as both a light source and a phase-shifting unit. The phase shift is accomplished by using the output wavelength of the wavelength-tuned laser. Multiple interferometers are connected through an optical fiber beam splitter to achieve multi-channel parallel measurement with a single phase shift, which reduces the number of devices, lowers the application cost, and improves the measurement efficiency. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the multi-channel surface shape detection device based on wavelength phase-shifting interference of the present invention.

[0034] Figure 2 This is a flowchart of the multi-channel surface shape detection method based on wavelength phase-shifting interference of the present invention.

[0035] In the diagram: 1 Wavelength-tuned laser, 2 Total incident fiber, 3 Fiber beam splitter, 4-1 First channel fiber, 4-2 Second channel fiber, 5 Fizeau interferometer module, 5-1 Beam splitter, 5-2 First collimating lens, 5-3 First standard lens, 5-4 First mirror under test, 5-5 Imaging lens, 5-6 First detector, 6 Thyman Green interferometer module, 6-1 Second collimating lens, 6-2 Reflector, 6-3 Beam splitter, 6-4 Reference mirror, 6-5 Second standard lens, 6-6 Second mirror under test, 6-7 Imaging system, 6-8 Second detector. Detailed Implementation

[0036] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings, but this should not be construed as limiting the scope of protection of the present invention.

[0037] Example 1:

[0038] A schematic diagram of a multi-channel surface shape detection device based on wavelength phase-shifting interferometry is shown below. Figure 1 As shown, the system includes a wavelength-tuned laser 1, a main incident fiber 2, a fiber beam splitter 3, a first channel fiber 4-1, a Fizeau interferometer module 5, a second channel fiber 4-2, and a Thyman Green interferometer module 6. The Fizeau interferometer module 5 includes a beam splitter 5-1, a first collimating lens 5-2, a first standard lens 5-3, a first mirror under test 5-4, an imaging lens 5-5, and a first detector 5-6. The Thyman Green interferometer module 6 includes a second collimating lens 6-1, a reflecting mirror 6-2, a beam splitter 6-3, a reference mirror 6-4, a second standard lens 6-5, a second mirror under test 6-6, an imaging system 6-7, and a second detector 6-8.

[0039] The laser emitted by the wavelength-tuned laser 1 serves as the total light source and phase-shifting unit of the interferometer. It is incident on the fiber beam splitter 3 via the total incident fiber 2, thereby splitting one laser beam into multiple laser beams. The beams are then connected to the Fiso interferometer module 5 via the first channel fiber 4-1 and to the Thyman Green interferometer module 6 via the second channel fiber 4-2.

[0040] In the Fiso interferometer module 5, the light source is incident on the first channel fiber 4-1, and after being transmitted through the beam splitter 5-1 and the first collimating lens 5-2, it forms parallel light. The parallel light is partially reflected and partially transmitted through the first standard lens 5-3. The reflected light is used as the reference light, and the transmitted light is used as the test light. The test light is incident on the first mirror under test 5-4 and reflected, carrying the surface shape information of the first mirror under test 5-4. It forms a first interference pattern with the reference light and returns along the original path. It is transmitted through the beam splitter 5-1 and the imaging lens 5-5, and then incident on the first detector 5-6. The first detector 5-6 collects the first interference pattern information to analyze and calculate the surface shape of the first mirror under test 5-4.

[0041] In the Thyman Green interferometer module 6, the second channel fiber 4-2 is the incident light source. It is transmitted through the second collimating lens 6-1 and the reflecting mirror 6-2 in sequence, and is incident parallel to the beam splitter 6-3 and split into transmitted light and reflected light. The transmitted light is reflected through the reference mirror 6-4 and the beam splitter 6-3 in sequence to form reference light. The reflected light is transmitted through the second standard lens 6-5 and reflected by the second test mirror 6-6 in sequence, carrying the surface shape information of the second test mirror 6-6. It is then transmitted through the second standard lens 6-5 and the beam splitter 6-3 in sequence, forming a second interferogram with the reference light. It is then transmitted through the imaging system 6-7 and incident on the second detector 6-8. The second detector 6-8 collects the second interferogram information to analyze and calculate the surface shape of the second test mirror 6-6. Specific Implementation Method Two

[0043] Example 2

[0044] Based on Embodiment 1, it is further specified that: the first channel optical fiber 4-1 and the Fiso interferometer module 5 appear as a set, which can be expanded to two or more sets; the second channel optical fiber 4-2 and the Thyman Green interferometer module 6 appear as a set, which can be expanded to two or more sets.

[0045] The first standard lens (5-3) and the second standard lens (6-5) of the interferometer can select lenses with appropriate parameters according to the characteristics of the mirror under test, or combine them with optical elements such as compensators and CGH to compensate for the mirror aberration of the mirror under test, so as to realize the measurement of the surface shape of optical elements with basic morphology of plane, spherical, aspherical and freeform surfaces.

[0046] The following is a specific implementation of the multi-channel surface shape detection method based on wavelength phase-shifting interferometry of the present invention, including the following steps:

[0047] Step a: Stabilize the light source

[0048] Turn on wavelength-tuned laser 1, and wait for the wavelength and power to stabilize. Record the initial wavelength as λ0.

[0049] Step b, System Adjustment

[0050] The main incident fiber 2 is connected to the fiber optic beam splitter 3. After splitting, the beam is incident on the Fieso interferometer module 5 through the first channel fiber 4-1 and on the Thyman Green interferometer module 6 through the second channel fiber 4-2. The first test mirror 5-4 is placed in the Fieso interferometer module 5 so that the first detector 5-6 obtains a first interferogram with near-zero fringes. The second test mirror 6-6 is placed in the Thyman Green interferometer module 6 so that the second detector 6-8 obtains a second interferogram with near-zero fringes.

[0051] Step c, Phase shift calibration

[0052] Measure the cavity length h1 from the first test mirror 5-4 to the first standard lens 5-3, and calculate the wavelength tuning step Δλ of the wavelength-tuned laser 1 as follows:

[0053]

[0054] Measure the optical path difference h2 between the front surface of the second test mirror 6-6 and the reference mirror 6-4, and calculate the wavelength tuning step Δλ of the wavelength-tuned laser 1 as follows:

[0055]

[0056] Step d: Acquire interferograms

[0057] The wavelength tuning step size Δλ controls the wavelength-tuned laser 1 to perform 13 phase shifts. Each phase shift involves the first detector 5-6 acquiring one interferogram frame, for a total of 13 interferogram frames, denoted as I. 1,1 I 1,2 ... I 1,13 Each phase-shifting step uses the second detector (6-8) to acquire one interferogram frame, for a total of 13 interferogram frames, denoted as I. 2,1 I 2,2 ... I 2,13 ;

[0058] Step e: Solve the surface phase

[0059] The surface phase is calculated using a 13-step phase-shifting algorithm, as shown in the following formula:

[0060]

[0061]

[0062] Step f, Package unpacking

[0063] The surface phase obtained in step e is unwrapped using the unwrapping algorithm to obtain the surface phase map. Then, the surface PV, RMS and Zernike coefficients are calculated to evaluate the surface quality of the first test mirror 5-4 or the second test mirror 6-6.

[0064] Step g, System Reset

[0065] After each 13-step phase shift is completed, the wavelength of wavelength-tuned laser 1 is restored to the initial wavelength λ0.

[0066] This invention uses a wavelength-tuned laser as both a light source and a phase-shifting unit. The phase shift is accomplished by using the output wavelength of the wavelength-tuned laser. Multiple interferometers are connected through an optical fiber beam splitter to achieve multi-channel parallel measurement with a single phase shift, which reduces the number of devices, lowers the application cost, and improves the measurement efficiency.

Claims

1. A multi-channel surface shape detection device based on wavelength phase-shifting interferometry, characterized in that, include: Wavelength tuned laser (1), total incident fiber (2), fiber beam splitter (3), first channel fiber (4-1), second channel fiber (4-2), ..., Nth channel fiber (4-N), and N≥2, and at least one set of Fiso interferometer module (5) and Thyman Green interferometer module (6); The wavelength-tuned laser (1) emits laser light, which serves as the total light source and phase-shifting unit of the interferometer. The laser light is incident on the fiber beam splitter (3) through the total incident fiber (2), thereby splitting one laser beam into N laser beams. These beams are then connected to the first group of Fiso interferometer module (5) and Thyman Green interferometer module (6) through the first channel fiber (4-1) and the second channel fiber (4-2), respectively. In the Fiso interferometer module (5), the light source is incident on the first channel optical fiber (4-1), and after being transmitted through the beam splitter (5-1) and the first collimating lens (5-2) in sequence, parallel light is formed. The parallel light is partially reflected and partially transmitted through the first standard lens (5-3). The reflected light is used as the reference light and the transmitted light is used as the test light. The test light is incident on the first mirror under test (5-4) and reflected, carrying the surface shape information of the first mirror under test (5-4). It forms a first interference pattern with the reference light and returns along the original path. After being transmitted through the beam splitter (5-1) and the imaging lens (5-5) in sequence, it is incident on the first detector (5-6). The first detector (5-6) collects the first interference pattern information to analyze and calculate the surface shape of the first mirror under test (5-4) and obtain an interference pattern with near-zero fringes. In the Thyman Green interferometer module (6), the second channel optical fiber (4-2) is incident on the light source, which is transmitted through the second collimating lens (6-1) and the reflecting mirror (6-2) in sequence, and is incident parallel to the beam splitter (6-3) and split into transmitted light and reflected light. The transmitted light is reflected through the reference mirror (6-4) and the beam splitter (6-3) in sequence to form reference light. The reflected light is transmitted through the second standard lens (6-5) and reflected by the second test mirror (6-6) in sequence, carrying the surface shape information of the second test mirror (6-6). It is then transmitted through the second standard lens (6-5) and the beam splitter (6-3) in sequence, and forms a second interferogram with the reference light. It is transmitted through the imaging system (6-7) and incident on the second detector (6-8). The second detector (6-8) collects the second interferogram information to analyze and calculate the surface shape of the second test mirror (6-6) and obtain an interferogram with near-zero fringes.

2. The multi-channel surface shape detection device based on wavelength phase-shifting interferometry according to claim 1, characterized in that, The first channel optical fiber (4-1) and the Fiso interferometer module (5) appear as a set, which can be expanded to two or more sets; the second channel optical fiber (4-2) and the Thyman Green interferometer module (6) appear as a set, which can be expanded to two or more sets.

3. A multi-channel surface shape detection method based on wavelength phase-shifting interferometry, characterized in that, Includes the following steps: Step a: Stabilize the light source Turn on the wavelength-tuned laser (1) to stabilize the wavelength and power, and denote the initial wavelength as λ0; Step b, System Adjustment The main incident fiber (2) is connected to the fiber beam splitter (3). After splitting, the fiber is incident on the Fiso interferometer module (5) through the first channel fiber (4-1) and on the Thyman Green interferometer module (6) through the second channel fiber (4-2). The first test mirror (5-4) is placed in the Fiso interferometer module (5) so that the first detector (5-6) obtains a first interference pattern with near-zero fringes. The second test mirror (6-6) is placed in the Thyman Green interferometer module (6) so that the second detector (6-8) obtains a second interference pattern with near-zero fringes. Step c, Phase shift calibration The cavity length h1 from the first test mirror (5-4) to the first standard lens (5-3) is measured, and the wavelength tuning step Δλ of the wavelength-tuned laser (1) is calculated as follows: Measure the optical path difference h2 between the front surface of the second test mirror (6-6) and the reference mirror (6-4), and calculate the wavelength tuning step Δλ of the wavelength-tuned laser (1): Step d: Acquire interferograms The wavelength tuning step size Δλ controls the wavelength-tuned laser (1) to perform 13 phase shifts. In each phase shift, the first detector (5-6) acquires one frame of interferogram, for a total of 13 frames of interferograms, denoted as I. 1,1 I 1,2 ... I 1,13 Each phase-shifting second detector (6-8) acquires one interferogram frame, for a total of 13 interferogram frames, denoted as I. 2,1 I 2,2 ... I 2,13 ; Step e: Solve the surface phase The surface phase is calculated using a 13-step phase-shifting algorithm, as shown in the following formula: Step f, Package unpacking The surface phase obtained in step e is unwrapped using the unwrapping algorithm to obtain the surface phase map. Then, the surface PV, RMS and Zernike coefficients are calculated to evaluate the surface quality of the first test mirror (5-4) or the second test mirror (6-6). Step g, System Reset After each 13-step phase shift is completed, the wavelength of the wavelength-tuned laser (1) is restored to the initial wavelength λ0.

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