Generalized Doppler effect measurement method and device

Abstract

The invention discloses a generalized Doppler effect measurement method and device, belongs to the technical field of photoelectric detection and motion sensing, and aims to solve the problem that the complete vector information of a moving target cannot be obtained at one time through single laser because the linear effect, the rotation effect and the vector effect are mutually independent in the existing laser Doppler measurement technology. The method comprises the following steps: generating and emitting a spin-dual orbital angular momentum coupling light field to a moving target; scattering signals are received and converted into time-domain electric signals after polarization analysis; performing spectrum analysis on the signal to obtain a generalized spectrum containing a traditional Doppler signal peak, a Doppler polarization signal peak and two Doppler polarization vortex signal peaks; calculating the frequency shift according to the spectrum peak position, and judging the motion direction according to the relative phase difference. The corresponding device comprises a narrow linewidth laser, a polarization modulation and coupling light field generation module, a 4F imaging system, a digital micromirror target simulation unit and a signal detection and analysis unit.

Description

Technical Field

[0001] This invention belongs to the field of photoelectric detection and motion sensing technology, specifically relating to a Doppler effect measurement method and device based on a special structured light field, and in particular a generalized measurement scheme that can unify and extend the traditional linear, rotational and vector Doppler effects. Background Technology

[0002] Laser Doppler measurement technology, with its high response speed, wide measurement range, excellent accuracy, and non-contact characteristics, plays an important role in fields such as fluid velocimetry, structural vibration monitoring, atmospheric wind field remote sensing, and moving target detection. Especially in real-time tracking and early warning scenarios for high-speed dynamic targets, this technology is less affected by changes in atmospheric conditions, supports continuous observation, and is well-suited to high-speed moving vehicles, demonstrating promising application prospects.

[0003] Traditional Doppler measurement techniques have evolved along two relatively independent directions. The first is the linear Doppler effect, which is based on plane wave detection. Since the energy flow direction of a plane wave is strictly parallel to the optical axis, this method is only sensitive to the velocity component of the target along the beam axis and is ineffective for lateral motion. The second is the rotational Doppler effect, which utilizes a beam with orbital angular momentum and a helical phase wavefront. The energy flow direction of this type of beam is at an angle to the optical axis, thus enabling the detection of target rotation or lateral translation. Based on this principle, researchers have developed various motion information inversion schemes suitable for different signal-to-noise ratios, working distances, and alignment conditions.

[0004] However, neither linear nor rotating Doppler methods can simultaneously determine the magnitude and direction of the Doppler frequency shift in a single measurement using only a single laser beam and a single detection channel. To distinguish whether the target is approaching or moving away, existing schemes typically require additional reference or comparison mechanisms. For example, heterodyne detection requires an independent reference optical path; dual-frequency vortex light necessitates complex frequency modulation of the light source; and rotating laser light sources rely on mechanical moving parts. These measures undoubtedly increase the complexity, cost, and instability of the system, deviating from the principle that measurement systems should strive for simplicity and robustness.

[0005] In recent years, the coupling phenomenon between spin angular momentum and orbital angular momentum in an optical field has become a research hotspot due to its high tunability and rich physical implications. Based on this, the vector Doppler effect has emerged. This technique utilizes a vector beam with a non-uniformly distributed polarization state in space (such as a cylindrical vector beam) as the probe light, achieving the ability to simultaneously acquire Doppler frequency shift magnitude and direction information with a single transmission and reception. This marks a significant step forward in Doppler measurement from scalar information acquisition to vector information acquisition. However, it is worth noting that the vector Doppler effect currently realized is still based on the coupling between spin and a single orbital angular momentum mode. Although the generated Doppler polarization signal contains direction information, it is still only one independent form among many Doppler effects, lacking an essential theoretical connection with classical linear Doppler signals and rotational Doppler signals. A higher-level, universal framework capable of encompassing and unifying these effects has not yet been formed.

[0006] In summary, while the field of laser Doppler measurement continues to advance, it also faces a fundamental challenge: the three effects of linear Doppler, rotational Doppler, and vector Doppler have long been developing independently and separately. Each employs different physical models and experimental setups for specific motion components. Current technology cannot yet organically integrate these three effects through a simple and unified principle and method, and unambiguously acquire complete vector information of a moving target in a single measurement using a single beam. Therefore, constructing a unified theoretical and technological system that can encompass existing Doppler effects and achieve truly comprehensive single-shot vector measurement has become a key scientific problem and technological bottleneck urgently needing to be solved for breakthroughs in this field. Summary of the Invention

[0007] To address the problem that existing laser Doppler measurement techniques suffer from independent linear, rotational, and vector effects, making it impossible to acquire complete vector information of a moving target using a single laser beam, this invention provides a generalized Doppler effect measurement method and apparatus.

[0008] In a first aspect, the present invention provides a method for measuring the generalized Doppler effect, comprising the following steps:

[0009] S1. Generate and emit a spin-dual orbital angular momentum coupled light field toward the moving target, the light field simultaneously carrying a non-zero polarization order. Non-zero orbital angular momentum order ;

[0010] S2. Receive signal light scattered or reflected by the moving target;

[0011] S3. The signal light is passed through an analytical polarizer with an adjustable transmission axis angle, and converted into a time-domain electrical signal by a photodetector. ;

[0012] S4. For the time-domain electrical signal Spectral analysis was performed to obtain the generalized Doppler spectrum containing four characteristic peaks, which correspond to: the conventional Doppler signal peak, the Doppler polarization signal peak, the first Doppler polarization vortex signal peak, and the second Doppler polarization vortex signal peak, respectively.

[0013] S5. Calculate the magnitude of the Doppler frequency shift based on the frequency position of the characteristic peak, and determine the direction of the Doppler frequency shift based on the relative phase difference between signals under different polarization analysis conditions.

[0014] Preferably, in step S1, the electric field of the spin-dual orbital angular momentum coupled optical field is in cylindrical coordinates. The Chinese character is represented as:

[0015]

[0016] in, The complex amplitude is related to the radial position. It is the azimuth angle. The initial polarization angle, and Let be the orders of the two orbital angular momentum, and satisfy . .

[0017] Preferably, in step S3, the time-domain electrical signal The expression is:

[0018]

[0019] in, The angle of the transmission axis of the analytical polarizer is [missing information]. or These correspond to right-handed circular polarization or left-handed circular polarization, respectively. The time-varying phase is introduced by the target motion. This represents a complex number of Doppler polarization vortex signal peaks, including the first Doppler polarization vortex signal peak and the second Doppler polarization vortex signal peak.

[0020] Preferably, when the target is rotating, ,in The rotational angular velocity of the target; for the time-domain electrical signal The Doppler frequency shifts corresponding to the four characteristic peaks obtained by performing time-phase differentiation or spectral analysis are as follows:

[0021]

[0022]

[0023]

[0024]

[0025] In the formula, For Doppler polarization frequency shift, For the first Doppler polarization vortex frequency shift, For traditional Doppler frequency shift, This is the frequency shift of the second Doppler polarization vortex.

[0026] Preferably, in step S5, the direction of the Doppler frequency shift can be determined by analyzing the initial polarization angle shift. or linear polarization angle difference The resulting relative phase difference distinguish:

[0027]

[0028] in, Represents a symbolic function. Doppler polarization frequency shift First Doppler polarization vortex frequency shift Or the second Doppler polarization vortex frequency shift Linear polarization angle difference To analyze the change in the angle of the polarizer.

[0029] Preferably, in step S1, the spin-dual orbital angular momentum coupled optical field is generated by cascading modulation of a spatial light modulator and a vortex half-wave plate; specifically, the spatial light modulator is first used to modulate and generate a dual orbital angular momentum optical field, and then the vortex half-wave plate is used to modulate it to generate the spin-dual orbital angular momentum coupled optical field.

[0030] In a second aspect, the present invention provides a generalized Doppler effect measurement device, comprising: arranged sequentially along the optical path:

[0031] Narrow linewidth laser 1, used to generate Gaussian mode beams;

[0032] A polarization modulation module is used to modulate the Gaussian beam into a horizontally linearly polarized state;

[0033] A coupled light field generation module is used to receive the horizontally linearly polarized light and generate the spin-dual orbital angular momentum coupled light field, which includes at least a spatial light modulator 4 and a vortex half-wave plate 6.

[0034] The first 4F imaging system is used to image the generated coupled light field onto the target surface;

[0035] The target simulation unit is disposed on the image plane of the first 4F imaging system and is used to simulate a target with set motion parameters;

[0036] The signal collection module is used to collect the signal light after it has been processed by the target simulation unit. It includes a non-polarizing beam splitter 7, a second 4F imaging system and a bandpass filter 11.

[0037] The polarization analysis and detection module is used to perform polarization screening on the signal light and convert it into an electrical signal. It includes an analysis polarizer 12 with an adjustable transmission axis angle and a photodetector 13.

[0038] The signal processing unit 14 is connected to the photodetector 13 and is used to acquire and analyze the electrical signal to obtain the generalized Doppler spectrum.

[0039] Preferably, the target simulation unit is a digital micromirror device 9, which controls the flipping state and refresh frequency of its reflective mirrors through programming to simulate moving targets with different angular velocities, angular accelerations and rotation directions.

[0040] Preferably, the polarization modulation module includes a half-wave plate 2 and a first linear polarizer 3 sequentially disposed in the optical path of the narrow linewidth laser 1; the analysis polarizer 12 is a second linear polarizer.

[0041] Preferably, the first 4F imaging system is composed of a first plano-convex lens 5 and a second plano-convex lens 8; the second 4F imaging system is composed of the second plano-convex lens 8 and a third plano-convex lens 10; the non-polarizing beam splitter 7 is placed at the confocal surface of the first 4F imaging system; the signal processing unit 14 is an oscilloscope with a fast Fourier transform function, used to transform the electrical signal from the time domain to the frequency domain and extract the four characteristic peaks.

[0042] The beneficial effects of this invention are:

[0043] 1. Achieving theoretical unification and revealing the physical essence: In traditional measurements, linear Doppler, rotational Doppler, and vector Doppler are three independent techniques, each employing different models and devices. This invention, for the first time, integrates these three types of effects into a single framework through a unified mathematical model. This is achieved by adjusting two key parameters of the light field (polarization order). and orbital angular momentum order This model can naturally degenerate into a specific case of the original technology. This reveals the intrinsic connection between different Doppler effects, establishing a more universal theoretical foundation for the field.

[0044] 2. Complete motion information can be obtained in a single measurement: Existing technologies typically require additional reference optical paths, dual-frequency lasers, or rotation of the light source itself to simultaneously measure the magnitude and direction (approaching or moving away), resulting in complex systems with poor stability. This invention only requires emitting a specially structured beam of light, which is reflected by the target and received by a single detector. By analyzing this signal, not only can the magnitude of the velocity be directly calculated from the four characteristic peaks of the spectrum, but the direction of motion can also be clearly determined by comparing the phase difference of the signal under different polarization settings. The entire process requires no additional references or mechanical moving parts, achieving the simplest and most direct full-vector measurement.

[0045] 3. Simple and reliable system structure: The device for realizing this invention mainly consists of standard components such as a laser, common optical lenses, polarization devices, spatial light modulators, and digital micromirrors. Its optical path design is based on a mature 4F imaging system, with a clear structure and convenient assembly and adjustment. Since there is no need to introduce heterodyne interference optical paths or mechanical rotation mechanisms, the entire system avoids the most error-prone complex links, thus possessing high stability and environmental adaptability, making it more suitable for practical applications.

[0046] 4. Adaptable to more complex motion states: This invention is not only suitable for measuring uniform motion, but also for effectively analyzing variable motion. By programming and controlling the digital micromirror device, the dynamic processes of target acceleration and deceleration can be simulated. Time-frequency analysis of the detected signal (such as short-time Fourier transform) can clearly observe the trajectory of velocity changes over time. This enables the technology to handle more complex motion detection scenarios in the real world.

[0047] 5. Providing direction for technological upgrading and integration: The light field manipulation method adopted in this invention (such as using a spatial light modulator) is highly compatible with the rapidly developing integrated photonics technology route. It demonstrates a technical path to obtain more information by designing the spatial structure of the light field itself (rather than relying solely on the frequency or intensity of light). This lays the theoretical foundation for the future development of smaller, smarter, and more integrable next-generation optical velocimetry sensors.

[0048] In summary, this invention achieves the unification and upgrading of Doppler measurement theory in principle, realizes more comprehensive measurement functions with a simpler system in terms of technology, and has good reliability and expansion potential, thus possessing significant scientific significance and practical value. Attached Figure Description

[0049] Figure 1 This is a schematic diagram of a generalized Doppler effect measurement method according to the present invention;

[0050] Figure 2 This invention relates to a generalized Doppler effect measurement device;

[0051] Figure 3 The present invention measures the generalized Doppler signal and spectrum of a uniformly rotating target; wherein, (a) is the time-domain signal measured by changing the polarizer angle, (b) is the corresponding spectrum, (c) is the time-domain signal after changing the optical field parameters, (d) is the corresponding spectrum, (e) is the time-domain signal measured by changing the initial polarization angle, and (f) is the corresponding spectrum.

[0052] Figure 4 To measure the generalized Doppler time-frequency signal and generalized Doppler time-frequency spectrum under uniformly accelerated motion using a generalized Doppler effect measurement method and device of the present invention; wherein, (a) is the preset angular velocity change curve, (b) is the DMD refresh frequency change curve, (c) is the spectrum during forward rotation, (d) is the spectrum during reverse rotation, (e) is the relative phase difference spectrum during forward rotation, and (f) is the relative phase difference spectrum during reverse rotation.

[0053] In the diagram, 1-narrow linewidth laser, 2-half-wave plate, 3-first linear polarizer, 4-spatial light modulator, 5-first plano-convex lens, 6-vortex half-wave plate, 7-unpolarized beam splitter, 8-second plano-convex lens, 9-digital micromirror device, 10-third plano-convex lens, 11-bandpass filter, 12-analytical polarizer, 13-photodetector, 14-oscilloscope. Detailed Implementation

[0054] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0055] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0056] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but this is not intended to limit the scope of the invention.

[0057] Specific Implementation Method 1: The following is combined with... Figures 1 to 4 This implementation method is described below.

[0058] The aforementioned generalized Doppler effect measurement device, see [link / reference]. Figure 2 As shown, the following components are arranged sequentially along the optical path:

[0059] Narrow linewidth laser 1: Used to generate Gaussian mode beams as the system light source. Single-frequency lasers with wavelengths of 1550nm or 632.8nm can be used to ensure good coherence.

[0060] Half-wave plate 2: placed behind laser 1, used to initially adjust the polarization state of the output laser and control the ratio of horizontal and vertical polarization components.

[0061] First linear polarizer 3: placed behind half-wave plate 2, used to modulate the beam into pure horizontally linearly polarized light.

[0062] Spatial Light Modulator 4 (SLM): Located behind the first linear polarizer 3. Its LCD screen displays a specific computer-generated hologram used to diffract and modulate the incident horizontally linearly polarized Gaussian beam into a beam carrying a pair of opposite orbital angular momentum (i.e., ... , The dual-orbital angular momentum light field.

[0063] The first plano-convex lens 5 and the second plano-convex lens 8 constitute the first 4F imaging system. The first plano-convex lens 5 is placed behind the spatial light modulator 4, and the second plano-convex lens 8 is placed behind it. The purpose of this system is to image the light field generated on the SLM surface onto the subsequent image plane without distortion.

[0064] The vortex half-wave plate 6 is positioned behind the first plano-convex lens 5. This device is a spatially variable waveplate whose fast axis azimuth varies linearly along the azimuth direction. It is used to apply different geometric phases to the left and right circularly polarized light components passing through it, thereby coupling the polarization state (spin) with different orbital angular momentum modes. After passing through this device, the desired "spin-dual orbital angular momentum coupled light field" is finally generated.

[0065] Unpolarized beam splitter 7: Located at the confocal surface (i.e., Fourier surface) of the first 4F system. Its function is to transmit the coupled light field from the front end, so that it illuminates the target; at the same time, it reflects the signal light that returns after being scattered / reflected by the target back to the detection optical path.

[0066] Digital Micromirror Device 9 (DMD): Located at the image plane of the first 4F system (i.e., the back focal plane of the second plano-convex lens 8), it serves as the target simulation unit. By controlling the flipping state and refresh rate of millions of micromirrors on the DMD through computer programming, it can accurately simulate an object moving at an angular velocity... (or linear velocity) The target surface can be rotated or moved, and the speed, acceleration and rotation direction can be flexibly set.

[0067] The third plano-convex lens 10 is placed in the reflected light path of the non-polarizing beam splitter 7. Together with the second plano-convex lens 8, it forms the second 4F imaging system, which is used to re-image the signal light field on the DMD surface onto the subsequent detection surface.

[0068] Bandpass filter 11: placed behind the third plano-convex lens 10, used to filter out ambient stray light and unwanted harmonics generated by DMD diffraction, allowing only the light signal of the laser wavelength to pass through, thereby improving the signal-to-noise ratio.

[0069] Analysis polarizer 12 (second linear polarizer): placed behind bandpass filter 11. Its transmission axis angle... It can rotate precisely. It is a key component for achieving polarization decoupling and direction discrimination, used to project polarization onto signal light in a specific direction.

[0070] Photodetector 13: Located behind the analytical polarizer 12, it is used to convert the polarization-selected light signal into a time-domain analog voltage signal proportional to its intensity. High-speed photodiodes or photomultiplier tubes are typically selected.

[0071] Oscilloscope 14: Connected to photodetector 13 via cable, it serves as a signal processing unit. It is responsible for acquiring and digitizing time-domain voltage signals. It utilizes its built-in Fast Fourier Transform (FFT) function to convert time-domain signals into frequency-domain spectra, thereby directly displaying and measuring the position (frequency) and relative intensity of each characteristic peak in the generalized Doppler spectrum.

[0072] A method for measuring the generalized Doppler effect is developed, based on the principle of cascaded liquid crystal devices to generate a spin-dual-orbit coupled light field, providing source mechanism and technical support for the study of the generalized Doppler effect. The interaction mechanism between the coupled light and the moving target is analyzed through electromagnetic wave phase modulation, and the measurement mechanism of the generalized Doppler effect is elucidated using polarization decoupling. The measurement mechanism and technology of the generalized Doppler frequency shift are revealed based on phase differentiation; ultimately, the measurement of the generalized Doppler effect is achieved.

[0073] Combination Figure 1 The schematic diagram shown illustrates the steps for measuring the generalized Doppler effect using the aforementioned device, which are as follows:

[0074] S1. Generate and emit a spin-dual orbital angular momentum coupled light field toward the moving target, the light field simultaneously carrying a non-zero polarization order. Non-zero orbital angular momentum order ;

[0075] The spin-dual orbital angular momentum coupled optical field is generated by cascading modulation of a spatial light modulator and a vortex half-wave plate. Specifically, the spatial light modulator is first used to modulate and generate a dual orbital angular momentum optical field, and then the vortex half-wave plate is used to modulate it to generate the spin-dual orbital angular momentum coupled optical field.

[0076] From a mathematical perspective, the electric field of the spin-dual orbital angular momentum coupled optical field in cylindrical coordinates... The Chinese character is represented as:

[0077]

[0078] in, The complex amplitude is related to the radial position. It is the azimuth angle. The initial polarization angle, and Let be the orders of the two orbital angular momentum, and satisfy . .

[0079] Subsequently, the light field was directly emitted at an angular velocity or linear velocity On a moving isotropic particle. The particle's motion introduces a frequency shift in the scattered light.

[0080] When the target is rotating ,in The rotational angular velocity of the target; for the time-domain electrical signal By performing time-phase differentiation or spectral analysis, the Doppler frequency shifts corresponding to the four characteristic peaks are respectively the Doppler polarization frequency shifts. First Doppler polarization vortex frequency shift Traditional Doppler frequency shift Second Doppler polarization vortex frequency shift .

[0081] S2. Receive signal light scattered or reflected by the moving target;

[0082] S3. The signal light is passed through an analytical polarizer with an adjustable transmission axis angle, and converted into a time-domain electrical signal by a photodetector. ;

[0083] To analyze the generalized Doppler vector signal, the scattered light is passed through an analytical polarizer 12 (a second linear polarizer) at an angle of θ and detected by a photodetector 13. The resulting generalized Doppler signal related to time t is:

[0084]

[0085] in, The angle of the transmission axis of the analytical polarizer is [missing information]. or These correspond to right-handed circular polarization or left-handed circular polarization, respectively. The time-varying phase is introduced by the target motion. This represents a complex number of Doppler polarization vortex signal peaks, including the first Doppler polarization vortex signal peak and the second Doppler polarization vortex signal peak.

[0086] In the formula, the phase related to time t can be expressed as that caused by translational motion: (Linear Doppler effect) or rotational motion triggers: (Used for the rotational Doppler effect). +1 or -1 indicates right-handed or left-handed circular polarization. From the above formula, we can see that when... , When the generalized Doppler signal degenerates into a traditional linear / rotational DS; when , At that time, it degenerates to the existing DPS. Only when and Only then will a new type of DPVS emerge, which can comprehensively characterize the Doppler effect. This formula unifies the traditional DS, DPS, and the new DPVS under one framework, and is therefore called the "generalized Doppler effect".

[0087] S4. For the time-domain electrical signal Spectral analysis was performed to obtain the generalized Doppler spectrum containing four characteristic peaks, which correspond to: the conventional Doppler signal peak, the Doppler polarization signal peak, the first Doppler polarization vortex signal peak, and the second Doppler polarization vortex signal peak, respectively.

[0088] Assuming time When the relevant phase is caused by rotational motion, i.e. The magnitude of the Doppler frequency shift can be obtained by differentiating the time phase of the generalized Doppler signal:

[0089]

[0090]

[0091]

[0092]

[0093] S5. Calculate the magnitude of the Doppler frequency shift based on the frequency position of the characteristic peak, and determine the direction of the Doppler frequency shift based on the relative phase difference between signals under different polarization analysis conditions.

[0094] Four Doppler peaks can be observed simultaneously in the generalized Doppler spectrum modulated by rotational motion. The direction of the Doppler frequency shift can be determined by analyzing the initial polarization angle shift. or linear polarization angle difference The resulting relative phase difference distinguish:

[0095]

[0096] in, Represents a symbolic function. Doppler polarization frequency shift First Doppler polarization vortex frequency shift Or the second Doppler polarization vortex frequency shift Linear polarization angle difference To analyze the change in the angle of the polarizer.

[0097] The following two embodiments briefly describe a generalized Doppler effect measurement method and apparatus of the present invention.

[0098] Example 1: Measuring the generalized Doppler signal and generalized Doppler spectrum under uniform motion of a target

[0099] In this embodiment, based on the generalized Doppler effect measurement method and device of the present invention, we will control the spin dual-orbit angular momentum optical field ( =1, =0, The device is launched onto a rotating target surface, which is programmed and controlled by a digital micromirror device 9. The rotational angular velocity is first preset. The value is 500 rad / s. Modulation analysis of polarizer 12 rotation angle, both before and after. The angles are denoted as follows: and In these two The generalized Doppler signals measured at the angle are denoted as follows: and ( Figure 3 (a)). A Fast Fourier Transform (FFT) of the signal reveals four distinct Doppler spectral peaks, corresponding to DS, DPS, and two new DPVS (DPVS1 and DPVS2). Figure 3 (b) The measured amplitude of the DPVS peak is approximately half that of DS and DPS, and the experimental results are in agreement with theoretical predictions, thus confirming the generalized Doppler effect. Further manipulation of the spin-dual orbital angular momentum optical field ( =8, The measured generalized Doppler signal and spectrum are as follows: Figure 3 As shown in (c) and 3(d), the ability to manipulate the spin-orbit coupled multi-generalized Doppler spectrum is demonstrated. Finally, the polarizer 12 is set in... Keeping it unchanged, changing the vortex half-wave plate 6 respectively in and At that time, the measured generalized Doppler signals were respectively and ( Figure 3 e), performing a Fast Fourier Transform on the signal, also reveals four distinct Doppler spectral peaks ( Figure 3 (f) This further confirms the generalized Doppler effect.

[0100] Example 2: Measurement of generalized Doppler time-frequency signal and generalized Doppler time spectrum under uniformly accelerated motion of a target

[0101] In this embodiment, we measure the generalized Doppler effect of a target with time-varying rotational speed. A DMD is programmed to simulate a rotating target that first accelerates and then decelerates; see [link to DMD simulation]. Figure 4 (a), in the figure The refresh rate of the digital micromirror device 9 is dynamically adjusted based on the preset time. Corresponding to the preset rotation speed See Figure 4 (b). Then, using a spin-double orbital angular momentum light field ( =8, Irradiate the target rotating in opposite directions (positive and negative Ω), while simultaneously passing through a vortex half-wave plate 6 (analytical polarizer 12 fixed on). Adjusting the initial polarization angle and Short-time Fourier transform analysis was performed on the acquired signal, in the positive ( Figure 4 (c) and negative ( Figure 4 (d) The rotating Doppler power spectrum revealed four distinct time-spectral plot trajectories, within which the intensity distribution clearly identified the DPVSs, DS, and DPS components. This confirmed the generalized Doppler effect under variable motion. Finally, the relative phase difference spectrum ( This enables Doppler frequency shift direction discrimination. For positive rotation ( Figure 4 e) and negative rotation ( Figure 4 (f) can be observed that DPS and DPVS have clear directional characteristics, and when rotating in the positive direction... When rotating in the negative direction In contrast, DS is not sensitive to direction, regardless of the direction of rotation. Always about This demonstrates the ability of the generalized Doppler effect to distinguish directions.

[0102] While the invention has been described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the invention. Therefore, it should be understood that many modifications can be made to the exemplary embodiments, and other arrangements can be designed without departing from the spirit and scope of the invention as defined by the appended claims. It should be understood that different dependent claims and features described herein can be combined in ways different from those described in the original claims. It is also understood that features described in conjunction with individual embodiments can be used in other described embodiments.

Claims

1. A method for measuring the generalized Doppler effect, characterized in that, Includes the following steps: S1. Generate and emit a spin-dual orbital angular momentum coupled light field toward the moving target, the light field simultaneously carrying a non-zero polarization order. Non-zero orbital angular momentum order ; S2. Receive signal light scattered or reflected by the moving target; S3. The signal light is passed through an analytical polarizer with an adjustable transmission axis angle, and converted into a time-domain electrical signal by a photodetector. ; S4. For the time-domain electrical signal Spectral analysis was performed to obtain the generalized Doppler spectrum containing four characteristic peaks, which correspond to: the conventional Doppler signal peak, the Doppler polarization signal peak, the first Doppler polarization vortex signal peak, and the second Doppler polarization vortex signal peak, respectively. S5. Calculate the magnitude of the Doppler frequency shift based on the frequency position of the characteristic peak, and determine the direction of the Doppler frequency shift based on the relative phase difference between signals under different polarization analysis conditions.

2. The method for measuring the generalized Doppler effect according to claim 1, characterized in that, In step S1, the electric field of the spin-dual orbital angular momentum coupled optical field in cylindrical coordinates... The Chinese character is represented as: in, The complex amplitude is related to the radial position. It is the azimuth angle. The initial polarization angle, and Let be the orders of the two orbital angular momentum, and satisfy . .

3. The method for measuring the generalized Doppler effect according to claim 2, characterized in that, In step S3, the time-domain electrical signal The expression is: in, The angle of the transmission axis of the analytical polarizer is [missing information]. or These correspond to right-handed circular polarization or left-handed circular polarization, respectively. The time-varying phase is introduced by the target motion. This represents a complex number of Doppler polarization vortex signal peaks, including the first Doppler polarization vortex signal peak and the second Doppler polarization vortex signal peak.

4. The method for measuring the generalized Doppler effect according to claim 3, characterized in that, When the target is rotating ,in The rotational angular velocity of the target; for the time-domain electrical signal By performing time-phase differentiation or spectral analysis, the Doppler frequency shifts corresponding to the four characteristic peaks are as follows: In the formula, For Doppler polarization frequency shift, For the first Doppler polarization vortex frequency shift, For traditional Doppler frequency shift, This is the frequency shift of the second Doppler polarization vortex.

5. A method for measuring the generalized Doppler effect according to claim 3 or 4, characterized in that, In step S5, the direction of the Doppler frequency shift can be determined by analyzing the initial polarization angle shift. or linear polarization angle difference The resulting relative phase difference distinguish: in, Represents a symbolic function. Doppler polarization frequency shift First Doppler polarization vortex frequency shift Or the second Doppler polarization vortex frequency shift Linear polarization angle difference To analyze the change in the angle of the polarizer.

6. The method for measuring the generalized Doppler effect according to claim 1, characterized in that, In step S1, the spin-dual orbital angular momentum coupled optical field is generated by cascading modulation of a spatial light modulator and a vortex half-wave plate; specifically, the spatial light modulator is first used to modulate and generate a dual orbital angular momentum optical field, and then the vortex half-wave plate is used to modulate it to generate the spin-dual orbital angular momentum coupled optical field.

7. A generalized Doppler effect measurement device, used to implement the method according to any one of claims 1 to 6, characterized in that, Including those arranged sequentially along the optical path: Narrow linewidth laser (1) is used to generate Gaussian mode beams; A polarization modulation module is used to modulate the Gaussian beam into a horizontally linearly polarized state; The coupled light field generation module is used to receive the horizontally linearly polarized light and generate the spin-dual orbital angular momentum coupled light field, which includes at least a spatial light modulator (4) and a vortex half-wave plate (6). The first 4F imaging system is used to image the generated coupled light field onto the target surface; A target simulation unit is disposed on the image plane of the first 4F imaging system and is used to simulate a target with set motion parameters. The signal collection module is used to collect the signal light after it has been processed by the target simulation unit. It includes a non-polarizing beam splitter (7), a second 4F imaging system and a bandpass filter (11). The polarization analysis and detection module is used to perform polarization screening on the signal light and convert it into an electrical signal. It includes an analysis polarizer (12) with an adjustable transmission axis angle and a photodetector (13). The signal processing unit (14) is connected to the photodetector (13) and is used to collect and analyze the electrical signal to obtain the generalized Doppler spectrum.

8. The generalized Doppler effect measurement device according to claim 7, characterized in that, The target simulation unit is a digital micromirror device (9), which controls the flipping state and refresh frequency of its reflective mirrors through programming to simulate moving targets with different angular velocities, angular accelerations and rotation directions.

9. A generalized Doppler effect measurement device according to claim 7, characterized in that, The polarization modulation module includes a half-wave plate (2) and a first linear polarizer (3) sequentially disposed in the optical path of the narrow linewidth laser (1); the analysis polarizer (12) is a second linear polarizer.

10. A generalized Doppler effect measurement device according to claim 7, characterized in that, The first 4F imaging system is composed of a first plano-convex lens (5) and a second plano-convex lens (8); the second 4F imaging system is composed of a second plano-convex lens (8) and a third plano-convex lens (10); the non-polarizing beam splitter (7) is placed at the confocal surface of the first 4F imaging system; the signal processing unit (14) is an oscilloscope with a fast Fourier transform function, used to transform the electrical signal from the time domain to the frequency domain and extract the four characteristic peaks.

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