System and method for comprehensive doppler shift measurement of a vortex beam

Abstract

This invention discloses a system and method for measuring the combined Doppler frequency shift of a vortex beam. The system includes, in sequence, a frequency-modulated light source module, a superimposed vortex beam generation module, a mode selection and purification module, a moving target module, and a signal receiving and processing module. This invention, by constructing a suitable vortex beam measurement system, measures the combined Doppler frequency shift of a complex moving object with linear and rotational velocities by changing the topological charge and light frequency, based on the Doppler frequency shift formula, thereby obtaining the linear and angular velocities of the target object. Based on the combined Doppler effect of vortex beams, the measurement light consists of superimposed vortex beams with opposite topological charges. By fully extracting motion information from the structured light interference field, the multidimensional motion information of a class of objects undergoing complex motion is determined. The extraction method is simple, direct, and highly operable. The optical path design of this invention is simple, using fewer complex optical components and equipment, making it easy to operate and highly integrateable.

Description

Technical Field

[0001] This invention relates to the field of Doppler frequency shift measurement technology, and in particular to a system and method for vortex beam integrated Doppler frequency shift measurement. Background Technology

[0002] Optical vortices (OVs) contain a helical phase factor and possess a novel degree of freedom—orbital angular momentum (OAM). Theoretically, the topological charge of OAM can take any integer value, so photons have infinitely many OAM orthogonal eigenstates, meaning vortex beams possess high-dimensional properties. Currently, due to the vortex and high-dimensional properties of OAMs, OAM modes are applied in numerous classical and quantum fields, such as quantum entanglement, quantum teleportation, optical tweezers, super-resolution microscopy, and detecting the angular velocity of rotating particles or physical objects.

[0003] A vortex beam carrying OAM (Optical Angle Modulation) can produce a rotational Doppler shift proportional to the topological charge and rotational speed when irradiated by a rotating object. This property allows for the acquisition of richer and more unique target attribute information in target detection, such as precise measurement of the (rotational) motion of a target perpendicular to the line-of-sight; and the acquisition of a description of the target's surface properties by measuring its orbital angular momentum spectrum.

[0004] Traditional target measurement and identification methods are mostly centralized, independent (translational or rotational), and unidirectional measurements, such as translational measurements corresponding to the linear Doppler effect and angular velocity measurements corresponding to the rotational Doppler effect. However, in real-world environments, the trajectories of moving objects are generally multi-dimensional. How to extract and measure this multi-dimensional information of a target to obtain its physical data remains a bottleneck in current research. Summary of the Invention

[0005] In view of this, the purpose of this invention is to propose a system and method for measuring vortex beam combined Doppler frequency shift, which can be used to measure the multidimensional motion information of an object, including the magnitude and direction of translational velocity and the magnitude and direction of rotational velocity in helical motion.

[0006] According to one aspect of the present invention, a system for measuring the Doppler frequency shift of a vortex beam is provided, comprising, sequentially arranged, a frequency-modulated light source module, a superimposed vortex beam generation module, a mode selection and purification module, a moving target module, and a signal receiving and processing module; the frequency-modulated light source module generates laser radiation of different wavelengths to the superimposed vortex beam generation module; the superimposed vortex beam generation module receives the laser and generates a superimposed vortex beam with positive and negative topological charges, which is then reflected to the mode selection and purification module; the mode selection and purification module selects the superimposed vortex beam mode and removes stray light, then radiates the purified superimposed vortex beam to the moving target module; the moving target module simulates a complex moving target with linear velocity and angular velocity, and the purified superimposed vortex beam radiates to the moving target module, generating a scattered rebound wave; the signal receiving and processing module captures the scattered rebound wave and performs signal processing for feature extraction and target recognition based on the linear Doppler and rotational Doppler effects.

[0007] According to another aspect of the present invention, a method for measuring the combined Doppler frequency shift of a vortex beam is provided, wherein the method measures the combined Doppler frequency shift of the scattered rebound waves acquired by the aforementioned system for measuring the combined Doppler frequency shift of a vortex beam; the method includes:

[0008] The scattered rebound wave signal collected by the signal receiving and processing module is converted into a time-domain light intensity signal. After the time-domain light intensity signal is subjected to a fast Fourier transform, the Doppler frequency shift is obtained.

[0009] By using vortex light with different topological charge numbers and frequencies, calculations were performed to measure complex moving targets with rotational Doppler shift and linear Doppler shift.

[0010] It can be observed that the above scheme, by constructing a suitable vortex beam measurement system and based on the Doppler frequency shift formula, measures the comprehensive Doppler frequency shift of complex moving objects with linear and rotational velocities by changing the topological charge and light frequency, thereby obtaining the linear and angular velocities of the target object. The frequency-tunable light source module has a large tuning range, making the frequency change caused by the Doppler effect more significant, and the inversion of the target's motion characteristics more accurate. This invention is based on the comprehensive Doppler effect of vortex beams. The measurement light consists of superimposed vortex beams with opposite topological charges. By fully extracting motion information from the structured light interference field, it determines the multidimensional motion information of a class of objects' composite motion. The extraction method is simple, direct, and highly operable. The optical path design of this invention is simple, uses fewer complex optical components and equipment, is easy to operate, has strong subsequent integration capabilities, is applicable to many scenarios, and has broad application prospects. Attached Figure Description

[0011] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0012] Figure 1 This is a schematic diagram of the system connection of an embodiment of the vortex beam integrated Doppler frequency shift measurement system of the present invention;

[0013] Figure 2 This is a schematic diagram of the optical path of an embodiment of the vortex beam integrated Doppler frequency shift measurement system of the present invention;

[0014] Figure 3 This is a phase loading diagram of a spatial light modulator for a vortex beam integrated Doppler frequency shift measurement system and method;

[0015] Figure 4 This is a measured image of a vortex beam with superimposed positive and negative topological charges, representing a vortex beam integrated Doppler frequency shift measurement system and method.

[0016] Figure 5 This is a simulation diagram of a vortex beam with superposition of positive and negative topological charges, representing a vortex beam integrated Doppler frequency shift measurement system and method.

[0017] Figure 6 This is a flowchart illustrating an embodiment of the vortex beam integrated Doppler frequency shift measurement method of the present invention. Detailed Implementation

[0018] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be particularly noted that the following embodiments are for illustrative purposes only and do not limit the scope of the invention. Similarly, the following embodiments are only some, not all, embodiments of the present invention, and all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] This invention provides a system for measuring vortex beam combined with Doppler frequency shift, which can be used to measure multidimensional motion information of an object, including the magnitude and direction of translational velocity and the magnitude and direction of rotational velocity in helical motion.

[0020] Please see Figure 1 , Figure 1This is a schematic diagram of the system connection of an embodiment of the vortex beam integrated Doppler frequency shift measurement system of the present invention. It includes a frequency-modulated light source module, a superimposed vortex light generation module, a mode selection and purification module, a moving target module, and a signal receiving and processing module arranged sequentially. The frequency-modulated light source module generates laser radiation of different wavelengths to the superimposed vortex light generation module. After receiving the laser, the superimposed vortex light generation module generates superimposed vortex light with positive and negative topological charges and reflects it to the mode selection and purification module. The mode selection and purification module selects the superimposed vortex light mode, removes stray light, and then radiates the purified superimposed vortex light to the moving target module. The moving target module simulates a complex moving target with linear and angular velocities. After the purified superimposed vortex light radiates to the moving target module, it generates a scattered rebound wave. The signal receiving and processing module captures the scattered rebound wave and performs signal processing for feature extraction and target recognition based on the linear Doppler and rotational Doppler effects.

[0021] The frequency-modulated light source module generates lasers of different wavelengths to facilitate subsequent signal processing and analysis based on linear and rotational Doppler effects. The superimposed vortex light generation module generates superimposed vortex light with positive and negative topological charges for measurement. The mode selection and purification module selects one or more specific modes of superimposed vortex light and removes stray light to make the measurement beam purer. The moving target module simulates complex moving targets with linear and angular velocities. The signal receiving and processing module receives the scattered rebound waves from the measurement vortex light hitting the moving target and performs signal processing for feature extraction and target recognition based on linear and rotational Doppler effects.

[0022] It can be observed that the above scheme, by constructing a suitable vortex beam measurement system and based on the Doppler frequency shift formula, measures the comprehensive Doppler frequency shift of complex moving objects with linear and rotational velocities by changing the topological charge and light frequency, thereby obtaining the linear and angular velocities of the target object. The frequency-tunable light source module has a large tuning range, making the frequency change caused by the Doppler effect more significant, and the inversion of the target's motion characteristics more accurate. This invention is based on the comprehensive Doppler effect of vortex beams. The measurement light consists of superimposed vortex beams with opposite topological charges. By fully extracting motion information from the structured light interference field, it determines the multidimensional motion information of a class of objects' composite motion. The extraction method is simple, direct, and highly operable. The optical path design of this invention is simple, uses fewer complex optical components and equipment, is easy to operate, has strong subsequent integration capabilities, is applicable to many scenarios, and has broad application prospects.

[0023] For further details, please refer to Figure 2 , Figure 2 This is a schematic diagram of the optical path of an embodiment of the vortex beam integrated Doppler frequency shift measurement system of the present invention.

[0024] In this embodiment, the frequency-modulated light source module includes: a tunable laser 101, a half-wave plate 102, an attenuator 103, a first collimating lens 104, and a beam expander 105 arranged sequentially along the first optical path direction A and coaxially. The tunable laser 101 generates lasers of different wavelengths that radiate along the first optical path direction A, are polarized by the half-wave plate 102, attenuated by the attenuator 103, collimated by the first collimating lens 104, and expanded by the beam expander 105 before radiating to the superimposed vortex light generation module. The tunable laser 101 adjusts the output power and wavelength of the beam according to the measurement needs of complex moving targets. A half-wave plate 102 adjusts the polarization properties of the laser output from the tunable laser 101, matching the polarization direction with that of the superimposed vortex light generation module. An attenuator 103 prevents damage to the photodetector caused by excessive light intensity. A first collimating lens 104 collimates the laser emitted from the tunable laser. A beam expander 105 expands the collimated laser beam, matching the laser spot size with the vortex light generation template to achieve phase matching. Specifically, the half-wave plate matches the polarization direction of the laser with that of the superimposed vortex light generation module. Generally, the emitted laser is linearly polarized with a fixed polarization direction; the polarization of the superimposed vortex light generation module also has a fixed polarization orientation. Only when these two directions match can effective phase modulation be achieved. The half-wave plate can change the polarization direction of the laser; by rotating the half-wave plate, the laser finds and matches the polarization direction of the superimposed vortex light generation module, which is considered a match.

[0025] In this embodiment, the superimposed vortex light generation module includes: a superimposed vortex light device 106 and a loading server 107 electrically connected to the superimposed vortex light device 106; the loading server 107 generates a phase map of ±18 topological charges; the superimposed vortex light device 106 uses the phase map of ±18 topological charges to modulate the laser into a superimposed vortex light of positive and negative topological charges, and radiates the superimposed vortex light of positive and negative topological charges along the second optical path direction B to the mode selection and purification module.

[0026] The superimposed vortex light method of the superimposed vortex light device includes one or more of the following: geometric mode conversion method, spiral phase plate, computational holography method, and spatial light modulator method. In this embodiment, the spatial light modulator method is used to generate complex vortex light. Specifically, the superimposed vortex light device 106, i.e., the spatial light modulator, loads the computational phase map generated by the server 107 to simulate the spatial field of the light beam, thereby generating positive and negative superimposed vortex light with opposite topological charges.

[0027] After loading a phase diagram (such as a phase diagram with ±18 topological loads), the topological loads can remain unchanged, or different phase diagrams such as ±30 or ±5 topological loads can be switched and loaded. This embodiment does not limit this, and the phase diagram with ±18 topological loads is only for explanation.

[0028] In this embodiment, please refer to Figure 3 , Figure 4 , Figure 5 , Figure 3 This is a phase loading diagram of a spatial light modulator, representing a system and method for measuring Doppler frequency shift using a vortex beam synthesis. Figure 4 This is a measured image of a vortex beam with superimposed positive and negative topological charges, representing a vortex beam integrated Doppler frequency shift measurement system and method. Figure 5 A simulation diagram of a vortex beam with superposition of positive and negative topological charges, representing a vortex beam synthesis Doppler frequency shift measurement system and method; a phase diagram of ±18 topological charges generated by server 107 is shown below. Figure 3 As shown, the generated positive and negative superimposed vortex light is as follows: Figure 4 As shown, the superimposed vortex light in the simulation is as follows: Figure 5 The results are almost identical.

[0029] In this embodiment, the mode selection and purification module includes: a mode selector 108 and a purifier arranged sequentially along the third optical path direction C and coaxially. The mode selector 108 selects a specific mode of the superimposed vortex light and reflects it to the third optical path direction C. The purifier includes a first lens 109, an aperture 110, and a second lens 111 arranged sequentially along the third optical path direction C and coaxially. The first lens 109 and the second lens 111 have equal focal lengths, and the aperture 110 is used to filter out stray light from the superimposed vortex light. The first lens 109 and the second lens 111 have equal focal lengths. As a telescope system, the aperture 110 is located in the middle of the telescope system and its function is to filter out stray light, ensuring the uniformity and purity of the measurement light. The mode selector 108 includes one or more of a blazed grating, a lens, and a mirror. The blazed grating uses a sawtooth-shaped groove cross-section to focus the energy of the incident light in a certain direction, thus maximizing the light intensity of a certain mode. The lens will manually select a specific mode according to the measurement needs. The selection of a specific mode for superimposed vortex light here refers to the fact that after the superimposed vortex light device generates vortex light, different modules or orders of vortex light will appear during the emission process. Among so many orders of light, a mode selector selects a vortex light whose intensity and light pattern meet the requirements of the subsequent test system for subsequent system testing. In short, it means that there are too many orders and modes of vortex light emitted after the superimposed vortex light device, and a better one is selected. The purpose of multiple modes is to provide variety: multiple lens groups can be combined to form optical device combinations or systems to achieve mode selection, such as lens + mirror or grating + mirror, etc., to meet different mode selection needs.

[0030] The mode selection and purification module is an optimized beam-shrinking system. After passing through the beam expander group, the laser spot size increases; therefore, it needs beam shrinking and optimization before being reflected to the subsequent motor simulating the rotation of a moving target. The aperture stop acts as an aperture stop, performing beam shaping and optimization. In simpler terms, it cuts off the portion of the beam outside the aperture stop, achieving shaping and stray removal. The purpose of the telescope system is to reduce the spot size, i.e., beam shrinking, because after passing through the previous beam expander, the spot size increases, which is not conducive to subsequent Doppler shift measurements. In short, it's about making the spot size suitable for the requirements of the subsequent system.

[0031] In this embodiment, the moving target module includes: a motor 112 simulating the rotation of a moving target and a translation stage 113 simulating the movement of the moving target, which is movably connected to the motor; the motor 112 is equipped with rotating plates of different roughness; after superimposed vortex light is radiated onto the rotating plates, the rotating plates generate scattered rebound waves, which are captured by the signal receiving and processing module. The motor 112 provides the rotational speed of the simulated moving target, and the motor is equipped with rotating plates of different roughness. The translation stage 113 provides the linear velocity of the moving target, and the linear velocity can be adjusted.

[0032] The rotating plate can be a rough optical lens or other rough plate that can reflect and scatter rebound waves; this is not limited here. The degree of roughness is not specifically specified; generally, rougher material may produce better results. It is sufficient that the rotating plate rotates at an angular velocity to overcome the impulse moment, causing a change in the optical frequency of the energy transferred to the return photons, thus generating a measured Doppler frequency shift. This embodiment does not impose any limitations on this.

[0033] In this embodiment, the signal receiving and processing module includes: a photodetector 116 and a signal acquisition card 117 electrically connected to the photodetector 116. The photodetector 116 is used to capture the scattered rebound wave reflected from the moving target module, and the signal acquisition card 117 is used to record the scattered rebound wave captured by the photodetector. The front end of the photodetector 116 also includes a beam reducer 114 and a collimator 115 arranged sequentially along the fourth optical path direction D and coaxially. The beam reducer 114 is used to reduce the beam reflected from the moving target module; the collimator 115 is used to collimate the reduced beam. The photodetector 116 detects the optical signal of the reflected light and transmits it to the signal acquisition card 117. The signal acquisition card 117 performs analog-to-digital conversion on the received photoelectric analog signal, thereby transmitting the digital signal to the server 107 for subsequent analysis and processing.

[0034] It can be observed that the above scheme, by constructing a suitable vortex beam measurement system and based on the Doppler frequency shift formula, measures the comprehensive Doppler frequency shift of complex moving objects with linear and rotational velocities by changing the topological charge and light frequency, thereby obtaining the linear and angular velocities of the target object. The frequency-tunable light source module has a large tuning range, making the frequency change caused by the Doppler effect more significant, and the inversion of the target's motion characteristics more accurate. This invention is based on the comprehensive Doppler effect of vortex beams. The measurement light consists of superimposed vortex beams with opposite topological charges. By fully extracting motion information from the structured light interference field, it determines the multidimensional motion information of a class of objects' composite motion. The extraction method is simple, direct, and highly operable. The optical path design of this invention is simple, uses fewer complex optical components and equipment, is easy to operate, has strong subsequent integration capabilities, is applicable to many scenarios, and has broad application prospects.

[0035] This invention also proposes a method for measuring the combined Doppler frequency shift using a vortex beam; please refer to [link to relevant documentation]. Figure 6 , Figure 6 This is a schematic flowchart of an embodiment of the vortex beam combined Doppler frequency shift measurement method of the present invention. It should be noted that if substantially the same result is obtained, the method of the present invention is not necessarily identical. Figure 6 The sequence of processes shown is limited.

[0036] like Figure 6 As shown, the method includes the following steps:

[0037] S101. The rebound wave signal scattered by the moving target module collected by the signal receiving and processing module is converted into a time-domain light intensity signal. After the time-domain light intensity signal is subjected to fast Fourier transform, the Doppler frequency shift is obtained.

[0038] The formula for calculating the linear Doppler frequency shift is as follows:

[0039]

[0040] Where f represents the frequency of the measured light, ν represents the linear velocity of the moving target, and c represents the speed of light.

[0041] The formula for calculating the rotational Doppler frequency shift is:

[0042]

[0043] Where l represents the topological charge and Ω is the angular velocity of the moving target.

[0044] Therefore, the formula for calculating the overall Doppler frequency shift of a complex moving target is:

[0045]

[0046] S102. Using vortex light with different topological charge numbers and frequencies, calculations are performed to measure complex moving targets with rotational Doppler frequency shift and linear Doppler frequency shift.

[0047] The collected scattered rebound wave signal is the time-domain intensity or power signal of the vortex beam. The actual measurement is in the Doppler frequency domain, so a simple Fourier transform is performed to convert it into a frequency domain signal for easier subsequent processing. The reflected signals from vortex beams of different frequencies and topological charges incident on rotating and translating target objects are received and demodulated. Using the frequency and charge, complex moving targets with rotational and linear Doppler frequency shifts are calculated. The principle behind this method is that rotational Doppler is independent of the beam frequency but depends on the mode, while translational Doppler is dependent on the beam frequency but independent of the mode.

[0048] It can be observed that the above scheme, by constructing a suitable vortex beam measurement system and based on the Doppler frequency shift formula, measures the comprehensive Doppler frequency shift of complex moving objects with linear and rotational velocities by changing the topological charge and light frequency, thereby obtaining the linear and angular velocities of the target object. The frequency-tunable light source module has a large tuning range, making the frequency change caused by the Doppler effect more significant, and the inversion of the target's motion characteristics more accurate. This invention is based on the comprehensive Doppler effect of vortex beams. The measurement light consists of superimposed vortex beams with opposite topological charges. By fully extracting motion information from the structured light interference field, it determines the multidimensional motion information of a class of objects' composite motion. The extraction method is simple, direct, and highly operable. The optical path design of this invention is simple, uses fewer complex optical components and equipment, is easy to operate, has strong subsequent integration capabilities, is applicable to many scenarios, and has broad application prospects.

[0049] The above description is only a part of the embodiments of the present invention and does not limit the scope of protection of the present invention. Any equivalent device or equivalent process transformation made based on the content of the present invention specification and drawings, or direct or indirect application in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A system for measuring Doppler frequency shift using a vortex beam synthesis, characterized in that, It includes, in sequence, a frequency modulation light source module, a superimposed vortex light generation module, a mode selection and purification module, a moving target module, and a signal receiving and processing module; The frequency-modulated light source module includes a tunable laser that generates laser radiation of different wavelengths to the superimposed vortex light generation module. The superimposed vortex light generation module receives laser light and generates superimposed vortex light with positive and negative topological charges, which is then reflected to the mode selection and purification module. The mode selection and purification module selects the superimposed vortex light mode and removes stray light before radiating the purified superimposed vortex light to the moving target module. The moving target module simulates a complex moving target with linear and angular velocities. The purified superimposed vortex light radiates to the moving target module and generates a scattered rebound wave. The scattered rebound wave signal from the moving target module collected by the signal receiving and processing module is converted into a time-domain light intensity signal. After the time-domain light intensity signal undergoes a fast Fourier transform, the Doppler frequency shift is obtained. Using vortex light with different topological charges and different frequencies, calculations are performed to measure the complex moving target with rotational Doppler frequency shift and linear Doppler frequency shift. The frequency-modulated light source module includes: a tunable laser, a half-wave plate, an attenuator, a first collimating lens, and a beam expander arranged sequentially along the first optical path direction and on the same optical axis; The tunable laser generates lasers of different wavelengths that radiate along the first optical path, are polarized by a half-wave plate, attenuated by an attenuator, collimated by a first collimating lens, and expanded by a beam expander before radiating to the superimposed vortex light generation module.

2. The system for vortex beam combined Doppler frequency shift measurement as described in claim 1, characterized in that, The half-wave plate is used to match the polarization direction of the laser with the polarization direction of the superimposed vortex light generation module.

3. The system for measuring Doppler frequency shift using a vortex beam as described in claim 1, characterized in that, The superimposed vortex light generation module includes: a superimposed vortex light device and a loading server electrically connected to the superimposed vortex light device; the loading server generates a phase map of the topological charge; the superimposed vortex light device uses the phase map to modulate the laser into a superimposed vortex light of positive and negative topological charges, and radiates the superimposed vortex light of positive and negative topological charges along the second optical path direction to the mode selection and purification module.

4. The system for measuring vortex beam combined Doppler frequency shift as described in claim 3, characterized in that, The superimposed vortex light method of the superimposed vortex light device includes one or more of the following: geometric mode conversion method, spiral phase plate, computational holography method, and spatial light modulator method.

5. The system for vortex beam combined Doppler frequency shift measurement as described in claim 1, characterized in that, The mode selection and purification module includes: a mode selector and a purifier arranged sequentially along the third optical path direction and on the same optical axis; the mode selector selects a specific mode of the superimposed vortex light and reflects it to the third optical path direction; the purifier includes a first lens, an aperture, and a second lens arranged sequentially along the third optical path direction and on the same optical axis; the first lens and the second lens have equal focal lengths, and the aperture is used to filter out stray light from the superimposed vortex light.

6. The system for measuring vortex beam combined with Doppler frequency shift as described in claim 5, characterized in that, The mode selector includes one or more of the following: blazed grating, lens, and mirror.

7. The system for vortex beam combined Doppler frequency shift measurement as described in claim 1, characterized in that, The moving target module includes: a motor simulating the rotation of a moving target and a translation stage simulating the movement of the moving target connected to the motor; the motor is equipped with rotating plates of different roughness; after the superimposed vortex light is radiated to the rotating plates, the rotating plates generate scattered rebound waves, which are captured by the signal receiving and processing module.

8. The system for measuring vortex beam combined with Doppler frequency shift as described in claim 1, characterized in that, The signal receiving and processing module includes: a photodetector and a signal acquisition card electrically connected to the photodetector. The photodetector is used to capture the scattered rebound wave reflected from the moving target module, and the signal acquisition card is used to record the scattered rebound wave captured by the photodetector.

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