A kind of super surface light modulator-based rotational speed measurement system and measurement method

Abstract

The application relates to a rotation speed measurement system and method based on a metasurface light modulator, and aims to solve the problems of a large number of optical elements, a complex structure and low optical efficiency of an existing rotating Doppler rotation speed measurement system. The application comprises a single-mode optical fiber laser, a metasurface light modulator, a half-wave plate and a polarization light splitting prism arranged on an outgoing light path of the single-mode optical fiber laser; a quarter-wave plate and a rotating target object to be measured are sequentially arranged on a transmission light path of the polarization light splitting prism, and a photodetector and a measurement terminal connected with an output end of the photodetector are arranged on a reflection light path. The metasurface light modulator is used to directly generate a vortex light beam carrying a topological charge conjugate superposition photon orbital angular momentum, and the rotation speed measurement of the rotating target is realized by using a rotating Doppler effect. Compared with the existing system, the application does not need an additional 4F optical filtering system or a ring interference light path, and has the characteristics of a simple light path, a compact structure and high optical efficiency.

Description

Technical Field

[0001] This invention relates to a rotational speed measuring device, specifically to a rotational speed measuring system and method based on a metasurface optical modulator. Background Technology

[0002] The rotational Doppler effect generated by the interaction between a vortex beam carrying photonic orbital angular momentum and a rotating target provides a new perspective for rotational speed measurement. Rotational speed measurement methods based on this principle feature fast response, wide measurement range, and non-contact operation, making them a research hotspot in recent years. Because rotating targets generate radial jitter or complex motion during detection, the process of detecting the reflected echo signal from the rotating target is inevitably affected by the linear Doppler effect, complicating the extraction of the rotational Doppler frequency shift. Therefore, the measurement requires the interaction of a vortex beam carrying a conjugate superposition of topological charges and photonic orbital angular momentum with the rotating target, generating the same linear Doppler frequency shift and an opposite rotational Doppler frequency shift. This allows the linear Doppler frequency shift to cancel out in the beat frequency signal, while the rotational Doppler frequency shift is multiplied in the beat frequency signal.

[0003] Many devices and methods for measuring rotational speed based on the rotating Doppler effect of topologically charged conjugate vortex beams have been proposed. However, spatial light modulators and digital micromirrors typically used to generate topologically charged conjugate vortex beams produce beams with multiple diffraction orders, requiring additional 4F optical filtering systems to extract the first-order beam and eliminate other uncorrelated terms. Using vortex waveplates and spiral phase plates can only generate single-topologically charged vortex beams, necessitating additional annular interference optical paths in practical applications. The optical paths of these existing conventional rotational speed measurement systems utilizing the rotating Doppler effect of topologically charged conjugate vortex beams are highly complex, requiring numerous optical components, hindering system integration, and easily leading to significant light intensity loss during measurement. This is particularly problematic when size and payload are limited, severely restricting the feasibility of existing rotational speed measurement systems in practical applications. Summary of the Invention

[0004] The main objective of this invention is to address the problems of existing rotational speed measurement systems based on topological charge conjugate vortex beams being overly complex, having low optical efficiency, and being unsuitable for integration and application. Instead, this invention provides a rotational speed measurement system and method based on a metasurface optical modulator.

[0005] The concept of this invention is to directly generate a photonic orbital angular momentum vortex light signal carrying a conjugate superposition of topological charges using a metasurface light modulator. The metasurface light modulator is an innovative two-dimensional optical element that can be used to manipulate the light field with high precision, thereby controlling the phase, amplitude, and polarization state of light at the subwavelength scale. At the same time, the metasurface light modulator can perform local phase control of the light beam through its internal nanopillar units, which can generate various special structured light fields, including the photonic orbital angular momentum vortex light signal carrying a conjugate superposition of topological charges required by this invention. Therefore, it does not require an additional 4F optical filtering system or a ring interference optical path for further extraction, which simplifies the optical path structure and reduces light intensity loss.

[0006] To achieve the above-mentioned objectives and complete the above-mentioned inventive concept, the present invention provides the following technical solution:

[0007] A rotational speed measurement system based on a metasurface optical modulator, characterized by:

[0008] It includes a single-mode fiber laser, and a metasurface light modulator, a half-wave plate, and a polarizing beam splitter sequentially arranged in the output optical path of the single-mode fiber laser; the polarizing beam splitter is used to transmit horizontally polarized light and reflect vertically polarized light.

[0009] It also includes a quarter-wave plate set in the transmission optical path of the polarizing beam splitter and a photodetector set in the reflection optical path of the polarizing beam splitter, as well as a measurement terminal connected to the output end of the photodetector; the rotating target object to be measured is set in the output optical path of the quarter-wave plate.

[0010] The operating mode of the metasurface optical modulator is set to the photonic orbital angular momentum conjugate output mode. The metasurface optical modulator is composed of silicon circular nanopillars and a silicon dioxide substrate. It has two metasurface structures designed by nesting each other using the finite-difference time-domain method. One metasurface structure modulates the topological charge number with +m, and the other metasurface structure modulates the topological charge number with -m. This enables the laser incident on the metasurface optical modulator to be modulated into a photonic orbital angular momentum vortex light signal carrying the conjugate superposition of topological charges. Its topological charge number is ±m, where m is a natural number greater than zero.

[0011] The operating wavelengths of both the half-wave plate and the quarter-wave plate are the same as the center wavelength of the laser emitted by the single-mode fiber laser. The half-wave plate is used to convert the incident photonic orbital angular momentum vortex light signal carrying the conjugate superposition of topological charges into a horizontally polarized photonic orbital angular momentum vortex light signal and incident it onto the polarizing beam splitter. The quarter-wave plate is used to convert the horizontally polarized photonic orbital angular momentum vortex light signal that has been fully transmitted through the polarizing beam splitter into a left-handed circularly polarized photonic orbital angular momentum vortex light signal, and to convert the right-handed circularly polarized photonic orbital angular momentum vortex light signal obtained after reflection from the rotating target object into a vertically polarized photonic orbital angular momentum vortex light signal and incident it onto the polarizing beam splitter.

[0012] The photodetector is used to receive the vertically polarized photon orbital angular momentum vortex light signal that has been completely reflected by the polarization beam splitter, and transmit it into the measurement terminal. The measurement terminal calculates the received vertically polarized photon orbital angular momentum vortex light signal to obtain the rotational speed Ω of the rotating target object to be measured.

[0013] Furthermore, the measurement terminal includes a Fourier transform unit and a calculation unit. The Fourier transform unit performs a fast Fourier transform on the received vertically polarized photon orbital angular momentum vortex light signal to obtain the spectrum Δf of the photon orbital angular momentum signal, and inputs the spectrum Δf into the calculation unit. The calculation unit calculates the spectrum Δf of the photon orbital angular momentum signal based on the relationship between the topological charge ±m and the rotational speed Ω. The rotational speed Ω of the rotating target object under test is obtained by calculation.

[0014] Furthermore, the laser emitted by the single-mode fiber laser is linearly polarized light with a center wavelength of 1550±10nm and a linewidth of less than 250Hz.

[0015] Furthermore, the half-wave plate represents a phase delay. A 1550nm polymer true zero-order half-wave plate, where λ1 is the working wavelength of the half-wave plate, λ1=1550nm.

[0016] Furthermore, the quarter-wave plate represents a phase delay. A 1550nm polymer true zero-order quarter-wave plate, where λ2 is the operating wavelength of the quarter-wave plate, λ2=1550nm.

[0017] Furthermore, the polarizing beam splitter is a near-infrared polarizing beam splitter cubic prism with an extinction ratio greater than 1000:1.

[0018] Furthermore, the photodetector is an indium gallium arsenide bias detector, used to receive light signals with wavelengths in the near-infrared range.

[0019] Meanwhile, the present invention also provides a rotational speed measurement method based on a metasurface optical modulator, which employs the aforementioned rotational speed measurement system based on a metasurface optical modulator, and is characterized by including the following steps:

[0020] Step 1: Turn on the single-mode fiber laser and level its optical path. The emitted laser is incident into the metasurface light modulator. The metasurface light modulator modulates the incident laser to obtain a photonic orbital angular momentum vortex light signal carrying a conjugate superposition of topological charges. Its topological charge number is ±m, where m is a non-zero natural number.

[0021] Step 2: The photonic orbital angular momentum vortex light signal carrying the conjugate superposition of topological charges is incident into a half-wave plate. The half-wave plate converts the polarization direction of the photonic orbital angular momentum vortex light signal carrying the conjugate superposition of topological charges into horizontal polarization, thus obtaining a horizontally polarized photonic orbital angular momentum vortex light signal.

[0022] Step 3: The horizontally polarized photonic orbital angular momentum vortex light signal is incident into a polarizing beam splitter. After being transmitted through the polarizing beam splitter, the horizontally polarized photonic orbital angular momentum vortex light signal is incident into a quarter-wave plate. The quarter-wave plate converts the polarization direction of the horizontally polarized photonic orbital angular momentum vortex light signal into left-hand circular polarization, thus obtaining a left-hand circularly polarized photonic orbital angular momentum vortex light signal.

[0023] Step 4: The left-hand circularly polarized photon orbital angular momentum vortex light signal is incident on the surface of the rotating target object to be tested. After reflection from the surface of the rotating target object, the right-hand circularly polarized photon orbital angular momentum vortex light signal is obtained.

[0024] Step 5: The rotating target object under test reflects the right-hand circularly polarized photonic orbital angular momentum vortex light signal back to the quarter-wave plate; the quarter-wave plate converts the polarization direction of the right-hand circularly polarized photonic orbital angular momentum vortex light signal into vertical polarization, thus obtaining the vertically polarized photonic orbital angular momentum vortex light signal.

[0025] Step 6: The vertically polarized photon orbital angular momentum vortex light signal is incident on a polarizing beam splitter and reflected by the polarizing beam splitter into a photodetector.

[0026] Step 7: The vertically polarized photon orbital angular momentum vortex light signal detected by the photodetector is transmitted to the measurement terminal; the measurement terminal calculates the vertically polarized photon orbital angular momentum vortex light signal to obtain the rotational speed Ω of the rotating target object under test, thus completing the rotational speed measurement based on the metasurface light modulator.

[0027] Furthermore, step 7 specifically includes:

[0028] Step 7.1: The photodetector transmits the vertically polarized photon orbital angular momentum vortex light signal to the measurement terminal.

[0029] Step 7.2: The Fourier transform unit in the measurement terminal performs a fast Fourier transform on the vertically polarized photon orbital angular momentum vortex light signal to obtain the spectrum Δf, and then inputs the spectrum Δf into the calculation unit.

[0030] Step 7.3: The calculation unit is used to determine the relationship between the spectrum Δf, the topological charge ±m, and the rotational speed Ω. The rotational speed Ω of the rotating target object under test is calculated, thus completing the rotational speed measurement based on the metasurface optical modulator.

[0031] Compared with the prior art, the beneficial effects of the present invention are:

[0032] This invention provides a rotational speed measurement system and method based on a metasurface optical modulator. The system uses a metasurface optical modulator to directly generate a vortex beam carrying the orbital angular momentum of conjugate superimposed photons with topological charges, and then uses the rotating Doppler effect to measure the rotational speed of a rotating target. Compared with the prior art, it does not require an additional 4F optical filtering system or a ring interference optical path, and has the characteristics of simple optical path, compact structure and high optical efficiency. It has important application value in the field of target rotational motion state sensing. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of an embodiment of the rotational speed measurement system based on a metasurface optical modulator according to the present invention;

[0034] Figure 2 Figure 1 is a schematic diagram of the working principle and process of a metasurface optical modulator in an embodiment of a rotation speed measurement system based on a metasurface optical modulator according to the present invention; wherein, Figure (a) is a schematic diagram of the superposition principle of two nested metasurface structures modulating beams; Figure (b) is a schematic diagram of the process of the metasurface optical modulator modulating the incident laser.

[0035] Explanation of reference numerals in the attached figures:

[0036] 1-Single-mode fiber laser; 2-Metasurface optical modulator; 3-Half-wave plate; 4-Polarizing beam splitter; 5-Quarter-wave plate; 6-Rotating target object to be measured; 7-Photodetector; 8-Measurement terminal. Detailed Implementation

[0037] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0038] A rotational speed measurement system based on a metasurface optical modulator, such as Figure 1As shown, it includes a single-mode fiber laser 1, and a metasurface light modulator 2, a half-wave plate 3, and a polarizing beam splitter 4 arranged sequentially on the output optical path of the single-mode fiber laser 1; a quarter-wave plate 5 is arranged on the transmission optical path of the polarizing beam splitter 4, and a photodetector 7 is arranged on the reflection optical path; the output end of the photodetector 7 is connected to a measurement terminal 8; the rotating target object 6 to be measured is arranged on the output optical path of the quarter-wave plate 5, and can be a rotating specular reflector or a diffuse reflector;

[0039] Among them, the center wavelength of the linearly polarized laser emitted by the single-mode fiber laser 1 is 1550±10nm, and the linewidth is less than 250Hz.

[0040] The metasurface optical modulator 2 operates in a photonic orbital angular momentum conjugate output mode; it employs two nested metasurface structures designed using the finite-difference time-domain method. The modulation principle and process are as follows: Figure 2 As shown, one of the metasurface structures modulates a topological charge of +m, and the other metasurface structure modulates a topological charge of -m. The incident laser is superimposed after being modulated by the two metasurface structures to obtain a photonic orbital angular momentum vortex light signal carrying a conjugate superposition of topological charges, with a topological charge of ±m, where m is a natural number greater than zero.

[0041] Half-wave plate 3 represents the phase delay. A 1550nm polymer true zero-order half-wave plate is used to convert the incident photonic orbital angular momentum vortex light signal carrying the conjugate superposition of topological charges into a horizontally polarized photonic orbital angular momentum vortex light signal and incident it onto the polarization beam splitter 4; the quarter-wave plate 5 is a phase delay. A 1550nm polymer true zero-order quarter-wave plate is used to convert the horizontally polarized photonic orbital angular momentum vortex light signal transmitted through the polarization beam splitter 4 into a left-handed circularly polarized photonic orbital angular momentum vortex light signal, and to convert the right-handed circularly polarized photonic orbital angular momentum vortex light signal obtained after reflection from the rotating target object 6 into a vertically polarized photonic orbital angular momentum vortex light signal, which is then incident on the polarization beam splitter 4; wherein λ1 and λ2 are the working wavelengths of the half-wave plate 3 and the quarter-wave plate 5, respectively, and both are the same as the center wavelength of the laser emitted from the single-mode fiber laser 1, i.e., λ1=λ2=1550nm;

[0042] The polarizing beam splitter 4 is a near-infrared polarizing beam splitter cubic prism with an extinction ratio greater than 1000:1, used to transmit horizontally polarized light and reflect vertically polarized light.

[0043] The photodetector 7 is an indium gallium arsenide bias detector, which can receive light signals with wavelengths in the near-infrared range. In this embodiment, the photodetector 7 is used to receive the vertically polarized photon orbital angular momentum vortex light signal reflected by the polarization beam splitter 4 and transmit it into the measurement terminal 8.

[0044] Measurement terminal 8 includes a Fourier transform unit and a calculation unit. The Fourier transform unit performs a fast Fourier transform on the received vertically polarized photon orbital angular momentum vortex light signal to obtain the spectrum Δf, and then inputs it into the calculation unit. The calculation unit calculates the spectrum Δf based on the relationship between the topological charge ±m and the rotational speed Ω. Calculations are performed to obtain the rotational speed Ω of the rotating target object 6 to be tested.

[0045] Meanwhile, based on the above-mentioned rotational speed measurement system based on a metasurface optical modulator, this embodiment also provides a rotational speed measurement method based on a metasurface optical modulator, including the following steps:

[0046] Step 1: Turn on the single-mode fiber laser 1 and level its optical path. The emitted laser is incident on the metasurface light modulator 2. The metasurface light modulator 2 modulates the incident laser to obtain a photonic orbital angular momentum vortex light signal carrying a conjugate superposition of topological charges. Its topological charge number is ±m, where m is a non-zero natural number.

[0047] Step 2: The photon orbital angular momentum vortex light signal carrying the conjugate superposition of topological charges is incident into the half-wave plate 3. The half-wave plate 3 converts the polarization direction of the photon orbital angular momentum vortex light signal carrying the conjugate superposition of topological charges into horizontal polarization, thus obtaining a horizontally polarized photon orbital angular momentum vortex light signal.

[0048] Step 3: The horizontally polarized photonic orbital angular momentum vortex light signal is incident into the polarizing beam splitter 4. After being transmitted through the polarizing beam splitter 4, the horizontally polarized photonic orbital angular momentum vortex light signal is incident into the quarter-wave plate 5. The quarter-wave plate 5 converts the polarization direction of the horizontally polarized photonic orbital angular momentum vortex light signal into left-hand circular polarization, thus obtaining the left-hand circularly polarized photonic orbital angular momentum vortex light signal.

[0049] Step 4: The left-hand circularly polarized photon orbital angular momentum vortex light signal is incident on the surface of the rotating target object 6 to be tested. After being reflected by the surface of the rotating target object 6, the right-hand circularly polarized photon orbital angular momentum vortex light signal is obtained.

[0050] Step 5: The rotating target object 6 reflects the right-hand circularly polarized photonic orbital angular momentum vortex light signal back into the quarter-wave plate 5; the quarter-wave plate 5 converts the polarization direction of the right-hand circularly polarized photonic orbital angular momentum vortex light signal into vertical polarization, thus obtaining the vertically polarized photonic orbital angular momentum vortex light signal.

[0051] Step 6: The vertically polarized photon orbital angular momentum vortex light signal is incident on the polarization beam splitter 4 and reflected by the polarization beam splitter 4 into the photodetector 7.

[0052] Step 7, Rotational speed measurement

[0053] Step 7.1: The photodetector 7 transmits the vertically polarized photon orbital angular momentum vortex light signal detected to the measurement terminal 8;

[0054] Step 7.2: The Fourier transform unit in the measurement terminal 8 is used to perform a fast Fourier transform on the vertically polarized photon orbital angular momentum vortex light signal to obtain the spectrum Δf, and the spectrum Δf is then input into the calculation unit.

[0055] Step 7.3: The calculation unit is used to determine the relationship between the spectrum Δf, the topological charge ±m, and the rotational speed Ω. The rotational speed Ω of the rotating target object 6 under test is obtained by calculation, and the rotational speed measurement based on the metasurface optical modulator is completed.

[0056] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. For those skilled in the art, modifications can be made to the specific technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. However, these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions protected by the present invention.

Claims

1. A rotational speed measurement system based on a metasurface optical modulator, characterized in that: It includes a single-mode fiber laser (1), and a metasurface light modulator (2), a half-wave plate (3), and a polarizing beam splitter (4) arranged sequentially on the output optical path of the single-mode fiber laser (1); the polarizing beam splitter (4) is used to transmit horizontally polarized light and reflect vertically polarized light. It also includes a quarter-wave plate (5) disposed on the transmission optical path of the polarizing beam splitter (4) and a photodetector (7) disposed on the reflection optical path of the polarizing beam splitter (4), as well as a measurement terminal (8) electrically connected to the output end of the photodetector (7); the rotating target object (6) to be measured is disposed on the outgoing optical path of the quarter-wave plate (5); The operating mode of the metasurface light modulator (2) is the photonic orbital angular momentum conjugate output mode. The metasurface light modulator (2) is composed of silicon circular nanopillars and a silicon dioxide substrate. It has two metasurface structures with a nested design. One metasurface structure modulates a topological charge of +m, and the other metasurface structure modulates a topological charge of -m. This enables the laser incident on the metasurface light modulator (2) to be modulated into a photonic orbital angular momentum vortex light signal carrying a topological charge conjugate superposition. Its topological charge is ±m, where m is a natural number greater than zero. The operating wavelengths of the half-wave plate (3) and the quarter-wave plate (5) are the same as the center wavelength of the laser emitted by the single-mode fiber laser (1). The half-wave plate (3) is used to convert the incident photonic orbital angular momentum vortex light signal carrying the conjugate superposition of topological charges into a horizontally polarized photonic orbital angular momentum vortex light signal and incident it onto the polarization beam splitter (4). The quarter-wave plate (5) is used to convert the horizontally polarized photonic orbital angular momentum vortex light signal transmitted through the polarization beam splitter (4) into a left-hand circularly polarized photonic orbital angular momentum vortex light signal, and to convert the right-hand circularly polarized photonic orbital angular momentum vortex light signal obtained after reflection from the rotating target object (6) into a vertically polarized photonic orbital angular momentum vortex light signal and incident it onto the polarization beam splitter (4). The photodetector (7) is used to receive the vertically polarized photon orbital angular momentum vortex light signal reflected by the polarization beam splitter (4) and transmit it into the measurement terminal (8). The measurement terminal (8) calculates the received vertically polarized photon orbital angular momentum vortex light signal to obtain the rotational speed Ω of the rotating target object (6) to be measured.

2. The rotational speed measurement system based on a metasurface optical modulator according to claim 1, characterized in that: The measurement terminal (8) includes a Fourier transform unit and a calculation unit. The Fourier transform unit performs a fast Fourier transform on the received vertically polarized photon orbital angular momentum vortex light signal to obtain the spectrum Δf, and inputs the spectrum Δf into the calculation unit. The calculation unit calculates the spectrum Δf based on the relationship between the topological charge ±m and the rotational speed Ω. The rotational speed Ω of the rotating target object (6) to be tested is obtained by calculation.

3. The rotational speed measurement system based on a metasurface optical modulator according to claim 2, characterized in that: The laser emitted by the single-mode fiber laser (1) is linearly polarized light with a center wavelength of 1550±10nm and a linewidth of less than 250Hz.

4. The rotational speed measurement system based on a metasurface optical modulator according to claim 3, characterized in that: The half-wave plate (3) is the phase delay. The 1550nm polymer true zero-order half-wave plate, where λ1 is the working wavelength of the half-wave plate (3), λ1=1550nm.

5. The rotational speed measurement system based on a metasurface optical modulator according to claim 4, characterized in that: The quarter-wave plate (5) is a phase delay. The 1550nm polymer true zero-order quarter-wave plate, where λ2 is the working wavelength of the quarter-wave plate (5), λ2=1550nm.

6. The rotational speed measurement system based on a metasurface optical modulator according to claim 1, characterized in that: The polarizing beam splitter (4) is a near-infrared polarizing beam splitter cubic prism with an extinction ratio greater than 1000:

1.

7. The rotational speed measurement system based on a metasurface optical modulator according to claim 5, characterized in that: The photodetector (7) is an indium gallium arsenide bias detector used to receive light signals with wavelengths in the near-infrared range.

8. A rotational speed measurement method based on a metasurface optical modulator, employing the rotational speed measurement system based on a metasurface optical modulator as described in any one of claims 1-7, characterized in that, Includes the following steps: Step 1: Turn on the single-mode fiber laser (1) and level its optical path. The emitted laser is incident into the metasurface light modulator (2). The metasurface light modulator (2) modulates the incident laser to obtain a photon orbital angular momentum vortex light signal carrying the conjugate superposition of topological charges. Its topological charge number is ±m, where m is a non-zero natural number. Step 2: The photon orbital angular momentum vortex light signal carrying the conjugate superposition of topological charges is incident into the half-wave plate (3). The half-wave plate (3) converts the polarization direction of the photon orbital angular momentum vortex light signal carrying the conjugate superposition of topological charges into horizontal polarization, thus obtaining a horizontally polarized photon orbital angular momentum vortex light signal. Step 3: The horizontally polarized photonic orbital angular momentum vortex light signal is incident into the polarization beam splitter (4). After being transmitted through the polarization beam splitter (4), the horizontally polarized photonic orbital angular momentum vortex light signal is incident into the quarter-wave plate (5). The quarter-wave plate (5) converts the polarization direction of the horizontally polarized photonic orbital angular momentum vortex light signal into left-hand circular polarization, thus obtaining the left-hand circularly polarized photonic orbital angular momentum vortex light signal. Step 4: The left-hand circularly polarized photon orbital angular momentum vortex light signal is incident on the surface of the rotating target object (6) to be tested. After being reflected by the surface of the rotating target object (6), the right-hand circularly polarized photon orbital angular momentum vortex light signal is obtained. Step 5: The rotating target object (6) reflects the right-hand circularly polarized photonic orbital angular momentum vortex light signal back to the quarter-wave plate (5); the quarter-wave plate (5) converts the polarization direction of the right-hand circularly polarized photonic orbital angular momentum vortex light signal into vertical polarization, thus obtaining the vertically polarized photonic orbital angular momentum vortex light signal. Step 6: The vertically polarized photon orbital angular momentum vortex light signal is incident into the polarization beam splitter (4), and reflected by the polarization beam splitter (4) into the photodetector (7); Step 7: The vertically polarized photon orbital angular momentum vortex light signal detected by the photodetector (7) is transmitted to the measurement terminal (8); the measurement terminal (8) calculates the received vertically polarized photon orbital angular momentum vortex light signal to obtain the rotational speed Ω of the rotating target object (6) to be measured, and completes the rotational speed measurement based on the metasurface light modulator.

9. The rotational speed measurement method based on a metasurface optical modulator according to claim 8, characterized in that, Step 7 specifically includes: Step 7.1: Transmit the vertically polarized photon orbital angular momentum vortex light signal detected by the photodetector (7) to the measurement terminal (8); Step 7.2: The Fourier transform unit in the measurement terminal (8) is used to perform a fast Fourier transform on the vertically polarized photon orbital angular momentum vortex light signal to obtain the spectrum Δf, and the spectrum Δf is then transmitted into the calculation unit. Step 7.3: The calculation unit is used to determine the relationship between the spectrum Δf, the topological charge ±m, and the rotational speed Ω. The rotational speed Ω of the rotating target object (6) to be measured is obtained by calculation, and the rotational speed measurement based on the metasurface light modulator is completed.

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