Polarization switchable geometric phase focusing laser radar telescope system and beam waist adjusting method

Abstract

The present application relates to the technical field of laser radar optical system, and discloses a polarization switchable geometric phase focusing laser radar telescope system and beam waist adjusting method.The system comprises a beam input interface, a telescope optical assembly, a polarization modulation assembly, a polarization related geometric phase focusing element, a polarization restoration assembly and a control module.The polarization modulation assembly is used to switch the incident circular polarization chirality, so that the geometric phase focusing element forms different optical power states, and together with the telescope optical assembly, different beam transmission states are formed, so that the outgoing Gaussian beam is discretely switched between multiple preset beam waist positions.When multiple polarization modulation units and geometric phase focusing elements are adopted, the number of beam waist gear positions can be further expanded, and multi-gear beam waist adjustment without mechanical movement is realized.

Description

Technical Field

[0001] This invention relates to the field of lidar optical system technology, and in particular to a polarization-switchable geometric phase-focusing lidar telescope system and a beam waist adjustment method. Background Technology

[0002] LiDAR typically requires collimation and beam expansion of the laser beam using a transmitting telescope to control the spot size, divergence, and energy distribution of the emitted Gaussian beam within the target range. When lidar needs to cover different detection distances, different operating distances often correspond to different suitable beam propagation states, thus requiring adjustment of the beam waist position emitted from the telescope.

[0003] Existing methods for adjusting the beam waist position mainly include mechanical focusing, liquid lens focusing, and liquid crystal variable focus lens focusing. Mechanical focusing typically changes the lens group spacing by moving the driven lens along the optical axis, thereby changing the system's equivalent focal length. This method requires the inclusion of a motor, transmission mechanism, or guide mechanism. While liquid lens and liquid crystal variable focus lenses can reduce mechanical movement, they generally still rely on continuously changing the optical power of the device as the primary focusing method, requiring the establishment of a continuous correspondence between the driving state and the focal length.

[0004] Pancharatnam-Berry geometric phase focusing elements can exhibit different geometric phase distributions depending on the chirality of the incident circularly polarized light, thus forming different optical power states. However, when directly applying these polarization-dependent optical power states to lidar telescopes, it is also necessary to consider the overall optical transmission relationship between the geometric phase focusing element and other optical components of the telescope, as well as the polarization transmission relationship between the emitted light and the target echo under coaxial transmission and reception conditions.

[0005] Especially when switching between multiple working distances, there is still room for improvement in how to stably convert different polarization states into different far-field Gaussian beam waist positions distributed along the beam propagation direction, and how to make each beam waist position selectable in a preset manner. Summary of the Invention

[0006] The purpose of this invention is to provide a polarization-switchable geometric phase focusing lidar telescope system and a beam waist adjustment method. By changing the circular polarization chirality of the incident polarization-related geometric phase focusing element, the polarization-related geometric phase focusing element can switch between different optical power states. The different optical power states, together with the telescope optical components, form different Gaussian beam transmission states, thereby enabling the outgoing Gaussian beam to be discretely switched between multiple preset beam waist positions spaced apart along the propagation direction.

[0007] To achieve the above objectives, the present invention provides a polarization-switchable geometric phase focusing lidar telescope system, including a beam input interface, telescope optical components, polarization modulation components, polarization-related geometric phase focusing elements, polarization restoration components, and a control module.

[0008] The telescope optical assembly includes at least one optical element, a polarization modulation component and a polarization-dependent geometric phase focusing element disposed in the optical path from the beam input interface to the target space, and the polarization-dependent geometric phase focusing element and the telescope optical assembly together form a Gaussian beam transmission optical path.

[0009] The specific composition of the telescope's optical components and their relative positions to the polarization-dependent geometrical phase (GEP) focusing element can be determined based on the input Gaussian beam parameters and the target beam waist position. For example, a collimating optical component can be placed before the GEP focusing element, or other optical components with positive or negative optical powers can be placed. Alternatively, an optical component can be omitted from the GEP focusing element, allowing the beam to be polarized before entering the GEP focusing element, and then the subsequent telescope optical components can form the desired beam transmission state.

[0010] The polarization modulation component is used to switch the incident beam onto the polarization-dependent geometric phase focusing element between a first circular polarization chirality and a second circular polarization chirality opposite to the first circular polarization chirality. The polarization-dependent geometric phase focusing element forms a first optical power state and a second optical power state that are different from each other when the two circular polarization chirities are incident.

[0011] The polarization-dependent geometric phase focusing element and the telescope optical components form different beam transmission states in the first optical power state and the second optical power state, respectively, so that the outgoing Gaussian beam forms a first preset beam waist position and a second preset beam waist position set at intervals along the propagation direction.

[0012] The polarization restoration component is located in the optical path from the polarization-dependent geometric phase focusing element to the target space. It is used to convert the circularly polarized light that has passed through the polarization-dependent geometric phase focusing element into predetermined linearly polarized light, so that the emitted light can enter the target space in a predetermined linear polarization state, and the echo component in the target echo that matches the emitted polarization state completes the corresponding polarization state conversion during the coaxial reverse propagation process.

[0013] The control module is electrically connected to the polarization modulation component. According to the beam waist position switching command, the working state of the polarization modulation component is changed, so that the light beam incident on the polarization-related geometric phase focusing element changes the circular polarization chirality, thereby realizing discrete selection between different optical power states and different preset beam waist positions.

[0014] Furthermore, the polarization modulation assembly may include a liquid crystal variable retarder and a quarter-wave plate. The liquid crystal variable retarder may be disposed on the incident side or the exit side of the quarter-wave plate; in another embodiment, the liquid crystal variable retarder can directly switch between a quarter-wave phase delay state and a three-quarter-wave phase delay state, thereby omitting the quarter-wave plate separately disposed in the polarization modulation assembly. When using a liquid crystal variable retarder to directly form circularly polarized light, the optical axis of the liquid crystal variable retarder can be set at 45° to the polarization direction of the incident linearly polarized light.

[0015] Furthermore, the polarization-dependent geometrical phase focusing element can be a Pancharatnam-Berry phase lens formed of a liquid crystal polymer, or a geometrical phase metasurface focusing element formed of a subwavelength dielectric microstructure array. When using a Pancharatnam-Berry phase lens, opposite circular polarization chirality can correspond to optical powers with opposite signs; when using a geometrical phase metasurface focusing element, opposite circular polarization chirality can correspond to different optical powers, and these different optical powers are not necessarily required to have opposite signs.

[0016] Furthermore, when more than two preset beam waist positions need to be formed, multiple polarization modulation units and multiple polarization-dependent geometric phase focusing elements can be set along the beam propagation direction. Each polarization modulation unit can independently control the incident circular polarization chirality of the corresponding geometric phase focusing element. Multiple combined optical power states are formed by combining different optical power states of multiple geometric phase focusing elements, and each corresponds to a different preset beam waist position. For two independent two-state polarization focusing stages, four polarization combinations can be formed; by setting the optical power and optical position of two polarization-dependent geometric phase focusing elements, the four combined optical power states can be made different from each other, corresponding to four preset beam waist positions.

[0017] This invention also provides a beam waist adjustment method for a polarization-switchable geometric phase-focusing lidar telescope system, comprising: acquiring a beam waist position switching command corresponding to a target beam waist position; determining a corresponding circular polarization chirality or a combination of circular polarization chirality according to the beam waist position switching command; controlling the corresponding polarization modulation component to output a corresponding polarization state; causing the polarization-related geometric phase-focusing element to form a corresponding optical power state; causing the corresponding optical power state and the telescope optical components to jointly form a corresponding beam transmission state; and causing the outgoing Gaussian beam to form a corresponding preset beam waist position, thereby completing the beam waist position switching.

[0018] Compared with existing technologies, this invention achieves the switching of optical power states of the geometric phase focusing element through polarization chirality selection, eliminating the need for mechanical movement of the focusing optical element along the optical axis. Different optical power states are converted into different far-field Gaussian beam waist positions by the telescope optical components, allowing each beam waist position to be predetermined and discretely selected. When multiple independently controlled polarization modulation units and multiple geometric phase focusing elements are used, multiple combined optical power states can be formed, thereby expanding the number of preset beam waist positions. In the coaxial transceiver structure, through the polarization restoration component in conjunction with the previous stage polarization modulation and geometric phase focusing process, the echo component matching the transmitted polarization state can also be made to return along the coaxial optical path. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of a specific structure of the polarization-switchable geometric phase-focusing lidar telescope system of the present invention; Figure 2 These are schematic diagrams illustrating different configurations of the polarization modulation component of the present invention, wherein: Figure 2 (a) is a schematic diagram of the configuration of the liquid crystal variable retarder on the incident side of the quarter-wave plate; Figure 2 (b) is a schematic diagram of a configuration where a quarter-wave plate is placed on the incident side of a liquid crystal variable retarder; Figure 2 (c) is a schematic diagram of the configuration of the liquid crystal variable retarder that directly switches between the quarter-wavelength phase delay state and the three-quarter-wavelength phase delay state; Figure 3 This is a schematic diagram illustrating different preset beam waist positions corresponding to different optical power states of the present invention, wherein: Figure 3 (a) in the diagram is a schematic diagram of the first preset waist position corresponding to the first optical power state; Figure 3 (b) in the diagram is a schematic diagram of the second preset waist position corresponding to the second optical power state; Figure 4 This is a schematic diagram of the polarization transmission relationship in the coaxial transmit / receive state of the present invention, wherein: Figure 4 (a) in the diagram is a schematic diagram of the polarization transmission relationship when the emitted light propagates in the forward direction; Figure 4 (b) in the diagram is a schematic diagram of the polarization transmission relationship when the target echo propagates in the reverse direction; Figure 5 This is a schematic diagram illustrating the cascading of multiple polarization-dependent geometric phase focusing elements to form multiple preset beam waist positions according to the present invention, wherein: Figure 5 (a) is a schematic diagram of the first beam transmission state corresponding to the preset beam waist position 10; Figure 5 (b) is a schematic diagram of the second beam transmission state corresponding to the preset beam waist position 11; Figure 5 (c) is a schematic diagram of the third beam transmission state corresponding to the preset beam waist position 12; Figure 6 This is a schematic diagram of the beam waist adjustment method for the polarization-switchable geometric phase-focusing lidar telescope system of the present invention.

[0020] In the figure: 1. Beam input interface; 2. Collimating optical component; 3. Polarization modulation component; 31. Liquid crystal variable delay device; 32. Quarter-wave plate; 4. Polarization-dependent geometric phase focusing element; 5. Beam expanding optical component; 6. Polarization restoration component; 7. Control module; 8. First preset beam waist position; 9. Second preset beam waist position; 3a. First polarization modulation unit; 3b. Second polarization modulation unit; 4a. First polarization-dependent geometric phase focusing element; 4b. Second polarization-dependent geometric phase focusing element; 10. First multi-stage preset beam waist position; 11. Second multi-stage preset beam waist position; 12. Third multi-stage preset beam waist position. Detailed Implementation

[0021] The embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0022] Example 1: As Figure 1 As shown, this embodiment provides a polarization-switchable geometric phase focusing lidar telescope system, including a beam input interface 1, a collimating optical component 2, a polarization modulation component 3, a polarization-dependent geometric phase focusing element 4, a beam expanding optical component 5, a polarization restoration component 6, and a control module 7. The beam input interface 1, collimating optical component 2, polarization modulation component 3, polarization-dependent geometric phase focusing element 4, beam expanding optical component 5, and polarization restoration component 6 are arranged sequentially along the beam propagation direction.

[0023] In this embodiment, the collimating optical component 2 and the beam expanding optical component 5 constitute a specific configuration of the telescope optical components. They are respectively matched with the polarization-dependent geometric phase focusing element 4 to form the corresponding Gaussian beam transmission state.

[0024] The beam input interface 1 is used to guide the Gaussian beam output from the lidar transmission link into the telescope system. Simultaneously, when using a coaxial transceiver structure, it serves as the optical interface for the target echo to return to the receiving link. The beam input interface 1 can employ a combination of a polarization-maintaining fiber endface, a fiber optic connector, and a collimation port, or it can be a free-space incident interface. Its specific structure can be determined based on the existing transmission and reception architecture of the lidar. The collimating optical component 2 is located on the output side of the beam input interface 1 and is used to convert the diverging Gaussian beam output from the beam input interface 1 into a near-parallel beam, ensuring that the beam entering the subsequent polarization modulation component 3 and the polarization-dependent geometric phase focusing element 4 has a smaller angular distribution range. The collimating optical component 2 can be a single spherical lens, an aspherical lens, or a collimating lens group composed of multiple lenses. The focal length, effective aperture, and distance between the collimating optical component 2 and the beam input interface 1 can be determined using existing Gaussian beam collimation methods based on the beam waist radius and divergence angle of the input Gaussian beam. The number, curvature, material, and fixing method of the collimating optical component 2 are not the focus of the improvement of this invention. They can be selected according to the working wavelength and input beam parameters using existing optical design methods.

[0025] Depending on the initial propagation state of the input Gaussian beam and the target beam waist position, other pre-stage optical configurations can be used. For example, an optical element with positive or negative optical power can be set in the incident optical path of the polarization-dependent geometric phase focusing element 4 to pre-shape the Gaussian beam; when the beam state output from the beam input interface 1 can meet the subsequent focusing requirements, the collimating optical component 2 can be omitted, and the beam can be directly fed into the polarization-dependent geometric phase focusing element 4 after passing through the polarization modulation component 3.

[0026] The polarization modulation component 3 is disposed on the exit side of the collimating optical component 2 and is electrically connected to the control module 7. It is used to change the circular polarization chirality of the incident polarization-dependent geometric phase focusing element 4 according to the control signal output by the control module 7.

[0027] like Figure 2 As shown in (a) of the diagram, in one embodiment, the polarization modulation component 3 includes a liquid crystal variable delay unit 31 and a quarter-wave plate 32 arranged sequentially along the beam propagation direction. Under different driving states output by the control module 7, the liquid crystal variable delay unit 31 applies different phase delays to the linearly polarized light passing through it, causing a change in its output polarization state. The fast axis of the quarter-wave plate 32 is set at 45° to the polarization direction of its incident linearly polarized light, causing the beam after passing through the quarter-wave plate 32 to form left-handed or right-handed circularly polarized light. The liquid crystal variable delay unit 31 can be an existing liquid crystal variable delay device, and its driving circuit and the correspondence between the driving voltage and the phase delay can be determined using existing liquid crystal delay unit calibration and control methods, as long as the desired polarization state can be formed according to the control signal.

[0028] like Figure 2 As shown in (b), in another embodiment, a quarter-wave plate 32 is disposed on the incident side of the liquid crystal variable retarder 31. The incident linearly polarized light is first converted into circularly polarized light by the quarter-wave plate 32 before entering the liquid crystal variable retarder 31. The liquid crystal variable retarder 31 can operate in a state with half-wave polarization conversion function, and by changing its driving state, the output circularly polarized light can be switched between two opposite circular polarization chiralities.

[0029] like Figure 2 As shown in (c), the quarter-wave plate 32 can be omitted from the polarization modulation assembly 3, and the conversion from linearly polarized light to circularly polarized light can be directly completed by the liquid crystal variable retarder 31. In this case, the optical axis of the liquid crystal variable retarder 31 is set at 45° to the polarization direction of the incident linearly polarized light, and it can switch between a quarter-wave phase retardation state and a three-quarter-wave phase retardation state. When the liquid crystal variable retarder 31 is in the quarter-wave phase retardation state, the incident linearly polarized light is converted into a chiral circularly polarized light; when the liquid crystal variable retarder 31 switches to the three-quarter-wave phase retardation state, the incident linearly polarized light is converted into another type of circularly polarized light with the opposite chirality to the aforementioned circularly polarized light. Which phase retardation state corresponds to left-handed circularly polarized light and which corresponds to right-handed circularly polarized light is determined by the optical axis orientation of the liquid crystal variable retarder 31 and the incident linear polarization direction.

[0030] Figure 2 Although different polarization modulation structures are used in (a) to 2(c) in the figure, they can all enable the beam incident on the polarization-dependent geometric phase focusing element 4 to switch between two opposite circular polarization chirality in a controlled manner.

[0031] A polarization-dependent geometric phase focusing element 4 is disposed on the emission side of the polarization modulation assembly 3. In this embodiment, the polarization-dependent geometric phase focusing element 4 can be a Pancharatnam-Berry phase lens. A Pancharatnam-Berry phase lens has an anisotropic optical axis orientation distribution that varies with aperture position, forming a geometric phase modulation related to the incident circular polarization chirality when circularly polarized light passes through it. Under paraxial conditions, the lens-type geometric phase distribution of the Pancharatnam-Berry phase lens can be expressed as: ; In the formula, The polarization-dependent geometric phase focusing element 4 is located in the radial position. The geometric phase formed at that point, The radial coordinates are relative to the optical axis. For the system's operating wavelength, This is the absolute value of the focal length corresponding to the polarization-dependent geometric phase focusing element 4.

[0032] The positive and negative signs in the formula are determined by the chirality of the incident circularly polarized light.

[0033] Therefore, without changing the mechanical position and physical structure of the polarization-dependent geometric phase focusing element 4, simply changing the chirality of the incident circularly polarized light can alter the sign of its geometric phase, resulting in different signed optical power states. For example, when the first circularly polarized chirality is incident, the polarization-dependent geometric phase focusing element 4 can generate positive optical power and converge the beam; when the circularly polarized chirality is reversed, it can generate negative optical power and diverge the beam. Which specific circularly polarized chirality corresponds to positive optical power and which corresponds to negative optical power can be determined based on the geometric phase orientation design of the polarization-dependent geometric phase focusing element 4.

[0034] When the polarization-dependent geometric phase focusing element 4 adopts a geometric phase metasurface focusing element, the spatial orientation and phase response design of the subwavelength dielectric microstructure array can make two opposite circular polarization chirals correspond to different optical power states, and the two optical power states are not required to have opposite signs.

[0035] The beam expanding optical component 5 is located on the exit side of the polarization-dependent geometric phase focusing element 4. It is used to expand the aperture of the exit beam and, together with the polarization-dependent geometric phase focusing element 4, determines the propagation state of the Gaussian beam after it leaves the telescope. The beam expanding optical component 5 can be a Galilean beam expander or a Keplerian beam expander. Its number of lenses, radius of curvature, material, magnification, and spacing between lenses can be determined using existing laser beam expanding optical design methods based on the required exit pupil aperture, operating wavelength, and target beam parameters.

[0036] In another optical path configuration, the beam input interface 1 can be an optical fiber output interface. After the beam is polarized into a corresponding circular polarization state by the polarization modulation component 3, it enters the polarization-dependent geometric phase focusing element 4, and then enters other positive lenses, negative lenses or mirror groups in the telescope. The polarization-dependent geometric phase focusing element 4 and the other optical elements together form the required Gaussian beam transmission state.

[0037] For the Gaussian beam propagation in this embodiment, the existing ABCD matrix transmission theory can be used to describe the beam transmission state formed by the polarization-dependent geometrical phase focusing element 4, the telescope optical components, and the free-space propagation between these optical components. When the polarization-dependent geometrical phase focusing element 4 is in the first optical power state, its optical power and the telescope optical components together form the first beam transmission state. When the polarization-dependent geometrical phase focusing element 4 switches to the second optical power state, its optical power changes, causing the ABCD transformation matrix corresponding to the entire telescope optical system to change accordingly, thereby changing the propagation state and far-field beam waist position of the emitted Gaussian beam. The method of establishing the ABCD matrix itself and the calculation method of determining the Gaussian beam propagation state and beam waist position based on the ABCD matrix can be implemented using existing Gaussian beam transmission methods in this field.

[0038] like Figure 3 As shown in (a), when the polarization modulation component 3 outputs the first circular polarization chirality, the polarization-dependent geometric phase focusing element 4 forms the first optical power state. The polarization-dependent geometric phase focusing element 4, together with the collimating optical component 2 and the beam expanding optical component 5 in this embodiment, forms the first beam transmission state, so that the outgoing Gaussian beam forms a beam waist at the first preset beam waist position 8.

[0039] like Figure 3 As shown in (b), when the control module 7 changes the driving state of the polarization modulation component 3, causing the circular polarization chirality of the incident polarization-dependent geometric phase focusing element 4 to switch, the polarization-dependent geometric phase focusing element 4 forms a second optical power state, and then forms a second beam transmission state, so that the outgoing Gaussian beam forms a beam waist at the second preset beam waist position 9.

[0040] The first preset beam waist position 8 and the second preset beam waist position 9 are spaced apart from each other along the beam propagation direction. Therefore, the system can discretely select between two different far-field beam waist positions by switching polarization states without mechanically moving the focusing optics in the telescope along the optical axis.

[0041] To further illustrate the correspondence between different optical power states of the polarization-dependent geometric phase focusing element 4 and the far-field beam waist position, this embodiment provides a set of specific optical design parameters.

[0042] Table 1 Optical parameters corresponding to different polarization focusing states ; Under the above design conditions, when the signed focal length of the polarization-dependent geometrical phase focusing element 4 is +258.671 mm, the corresponding system equivalent focal length is approximately -137.11 mm, the far-field beam waist position is approximately 200 m, the beam waist radius is approximately 5.877 mm, and the exit pupil diameter is approximately 47.24 mm. After switching the circular polarization chirality, the signed focal length of the polarization-dependent geometrical phase focusing element 4 becomes -258.671 mm, corresponding to a system equivalent focal length of approximately -82.12 mm, a far-field beam waist position of approximately 50 m, a beam waist radius of approximately 1.326 mm, and an exit pupil diameter of approximately 48.52 mm. Therefore, it can be seen that, while keeping the mechanical positions of all optical elements in the telescope unchanged, by changing the circular polarization chirality incident on the polarization-dependent geometrical phase focusing element 4, the optical power state and beam propagation state of the system can be changed, and the far-field beam waist position can be significantly altered.

[0043] The data listed in Table 1 correspond to Figure 1 The specific optical structure shown is one design configuration and does not constitute a limitation on the focal length of the polarization-dependent geometrical phase focusing element 4, the equivalent focal length of the telescope, the exit pupil aperture, the structure of the telescope optical components, or the preset beam waist position. For different lidar detection distances, existing Gaussian beam design and telescope optical design methods can be used to redetermine the corresponding preset beam waist position based on the input beam parameters, the optical power of the polarization-dependent geometrical phase focusing element 4, the optical parameters of other optical components of the telescope, and the optical distances between the various optical components.

[0044] The polarization restoration component 6 is disposed on the output side of the beam expander optical component 5. It converts the circularly polarized light, after passing through the polarization-dependent geometrical phase focusing element 4 and being transmitted through the beam expander optical component 5, into predetermined linearly polarized light, allowing the beam to enter the target space with a linearly polarized state suitable for lidar emission. In this embodiment, the polarization restoration component 6 can be a quarter-wave plate. The material, thickness, aperture, fast axis direction, and fixing method of the quarter-wave plate can be determined according to existing techniques in the field of polarization optics, based on the circularly polarized state entering the polarization restoration component 6 and the desired output linear polarization direction. The polarization restoration component 6 can also cooperate with the pre-stage polarization modulation component 3 and the polarization-dependent geometrical phase focusing element 4 to form a polarization transmission relationship suitable for coaxial transmission and reception.

[0045] Figure 4 In this context, H represents the linear polarization state along a predetermined reference direction, LCP represents the left-hand circular polarization state, and RCP represents the right-hand circular polarization state. For circularly polarized light, the chirality determination of LCP and RCP is based on the actual propagation direction of the corresponding beam. Therefore, when the emitted light propagates in the forward direction and the target echo propagates in the reverse direction, the respective propagation directions should be considered. Figure 4 The LCP and RCP states are shown in the diagram. Figure 4As shown in (a), the emitted light enters the telescope system through the beam input interface 1. After passing through the collimating optics 2, it remains linearly polarized. Then, it passes through the polarization modulation optics 3, where it is converted to either LCP or RCP circular polarization corresponding to the current beam waist position. When the circularly polarized light passes through the polarization-dependent geometric phase focusing element 4, the element modulates the geometric phase according to the current circular polarization chirality, simultaneously reversing the chirality—that is, a corresponding conversion occurs between LCP and RCP. The beam then passes through the beam expander optics 5 for beam expansion and, after being converted to a predetermined linear polarization state by the polarization restoration optics 6, enters the target space.

[0046] like Figure 4 As shown in (b), the target echo enters the telescope system in the opposite direction to the emitted light. For the echo component in the target echo that maintains its polarization state relative to the emitted light, this component first passes through the polarization restoration component 6 in a linear polarization state, forming an LCP or RCP circular polarization state corresponding to the reverse propagation direction. It then passes in the reverse direction through the beam expander component 5 and the polarization-dependent geometric phase focusing element 4. When the echo passes through the polarization-dependent geometric phase focusing element 4, the circular polarization chirality is converted again, i.e., it is converted between LCP and RCP according to its reverse propagation direction. Since the determination of circular polarization chirality is related to the beam propagation direction, the left-handed and right-handed circular polarization states under forward and reverse propagation conditions should be determined in conjunction with their respective propagation directions.

[0047] Subsequently, the echo component matching the received polarization state continues to pass through the polarization modulation component 3 and the collimating optical component 2, and forms an H-linear polarization state matching the received optical path before returning to the beam input interface 1, and then returns to the lidar receiving link through the beam input interface 1. Other depolarization components generated by target reflection can be processed using existing lidar polarization selection, filtering, or coherent reception methods; this invention does not impose any particular limitations on these methods.

[0048] The control module 7 is used to generate the control signals required by the polarization modulation component 3. The control module 7 can be a microcontroller, microprocessor, FPGA, DSP, or an existing main controller for the lidar. The storage circuit, LCD driving circuit, power supply circuit, and communication interface involved in the control module 7 can be implemented using existing control technologies. The control module 7 can pre-store the correspondence between different beam waist positions and polarization modulation states. When a first preset beam waist position 8 needs to be formed, the control module 7 controls the polarization modulation component 3 to form a first circular polarization chirality; when a second preset beam waist position 9 needs to be formed, the control module 7 changes the operating state of the polarization modulation component 3 to form a second circular polarization chirality opposite to the first circular polarization chirality.

[0049] Thus, by switching the polarization state, the polarization-related geometric phase focusing element 4 changes the optical power state, and then the telescope optical components change the Gaussian beam transmission state, ultimately causing the far-field beam waist position of the outgoing Gaussian beam to change discretely.

[0050] When it is necessary to create more than two preset waist-cinching positions, the following can be used: Figure 5 The multi-level structure shown.

[0051] like Figure 5 As shown, the first polarization modulation unit 3a, the first polarization-dependent geometrical phase focusing element 4a, the second polarization modulation unit 3b, and the second polarization-dependent geometrical phase focusing element 4b are sequentially arranged between the collimating optical component 2 and the beam expanding optical component 5 along the beam propagation direction. The control module 7 is electrically connected to the first polarization modulation unit 3a and the second polarization modulation unit 3b, respectively, thereby enabling control over the circular polarization chirality of the light incident on the first polarization-dependent geometrical phase focusing element 4a and the second polarization-dependent geometrical phase focusing element 4b.

[0052] The first polarization modulation unit 3a and the first polarization-dependent geometrical phase focusing element 4a constitute the first focusing stage, and the second polarization modulation unit 3b and the second polarization-dependent geometrical phase focusing element 4b constitute the second focusing stage. The first polarization-dependent geometrical phase focusing element 4a and the second polarization-dependent geometrical phase focusing element 4b can have the same absolute focal length, or they can use different absolute focal lengths according to the needs of setting multiple beam waist positions. By changing the optical power state of the two polarization-dependent geometrical phase focusing elements by the two polarization modulation units respectively, a variety of combined optical power states can be formed.

[0053] When two polarization-dependent geometric phase focusing elements are approximated by a thin lens with spacing, their combined equivalent focal length can be expressed as: ; In the formula, The combined equivalent focal length of the two polarization-dependent geometric phase focusing elements in the current state. The signed focal length of the first polarization-dependent geometric phase focusing element 4a. The signed focal length of the second polarization-dependent geometric phase focusing element 4b. This is the axial distance between the two focusing elements.

[0054] The aforementioned combined equivalent focal length is only used to characterize the equivalent optical power relationship between the two polarization-dependent geometric phase focusing elements. Since the actual telescope system also includes collimating optical component 2, beam expanding optical component 5, and free space propagation between each optical component, the final preset beam waist position needs to be determined in conjunction with the Gaussian beam propagation state of the entire telescope optical path.

[0055] like Figure 5 As shown in (a), when the first polarization modulation unit 3a and the second polarization modulation unit 3b are in the first polarization combination state, the first polarization-related geometric phase focusing element 4a and the second polarization-related geometric phase focusing element 4b form a first combined optical power state, causing the emitted Gaussian beam to form a corresponding first beam transmission state, and forming a beam waist at the first multi-stage preset beam waist position 10. Figure 5 As shown in (b), when the control module 7 changes the working state of at least one of the first polarization modulation unit 3a or the second polarization modulation unit 3b, the two polarization-related geometric phase focusing elements form a second combined optical power state, causing the emitted Gaussian beam to form a second beam transmission state, and forming a beam waist at the second multi-stage preset beam waist position 11. Figure 5 As shown in (c), when the first polarization modulation unit 3a and the second polarization modulation unit 3b form the third polarization combination state, the two polarization-related geometric phase focusing elements form the third combined optical power state, so that the outgoing Gaussian beam forms the third beam transmission state, and forms a beam waist at the third multi-stage preset beam waist position 12.

[0056] The first polarization modulation unit 3a and the second polarization modulation unit 3b each have two polarization control states, thus enabling the formation of four polarization combinations. Figure 5 The diagram illustrates the beam propagation states corresponding to three polarization combinations. For the fourth polarization combination (not shown), by setting the optical power and optical position of the first polarization-related geometric phase focusing element 4a and the second polarization-related geometric phase focusing element 4b, a fourth multi-position preset beam waist can be formed when its corresponding combined optical power state differs from the first three combined optical power states. Therefore, for two independent two-state polarization focusing stages, four different preset beam waist positions can be formed when the four combined optical power states are different from each other. In a multi-position design, multiple preset beam waist positions can be set at approximately 50m, 150m, 200m, and 250m according to application requirements.

[0057] The preset beam waist positions are not required to be equally spaced. Existing Gaussian beam design and telescope optical design methods can be used to determine the preset beam waist positions corresponding to each polarization combination state based on the focal length of the first polarization-related geometrical phase focusing element 4a and the second polarization-related geometrical phase focusing element 4b, the distance between them, the optical parameters of the beam expanding optical component 5, and the input beam parameters. In addition to using a Pancharatnam-Berry phase lens formed of liquid crystal polymer, the polarization-related geometrical phase focusing element 4a and the second polarization-related geometrical phase focusing element 4b can also use a geometrical phase metasurface focusing element. The geometrical phase metasurface focusing element can include a transparent substrate and an array of subwavelength dielectric microstructures formed on the transparent substrate. Each subwavelength dielectric microstructure is arranged according to a predetermined spatial orientation, so that it forms different geometrical phase responses when incident with opposite circularly polarized chiralities, and correspondingly forms different optical power states. Subwavelength dielectric microstructures can be formed using high-refractive-index, low-absorption dielectric materials suitable for the target operating wavelength. Their specific dimensions, period, thickness, material selection, and processing methods can be determined based on the operating wavelength using existing dielectric metasurface design and manufacturing technologies. This embodiment does not impose any particular limitations on these aspects.

[0058] Through the above structure, the control module 7 first controls the polarization modulation state, and the polarization modulation state further determines the optical power state of the polarization-related geometric phase focusing element. The optical power state, together with other optical components in the telescope, forms the corresponding beam transmission state, and finally makes the outgoing Gaussian beam form a beam waist at the preset far-field beam waist position.

[0059] Example 2: This example provides a beam waist adjustment method for a polarization-switchable geometric phase-focusing lidar telescope system. This method can be applied to... Figure 1 The dual-gear structure shown can also be applied to Figure 5 The multi-gear structure shown.

[0060] like Figure 6 As shown, when switching waist-gain positions, the switching command corresponding to the target waist-gain position is first obtained. The target waist-gain position can be determined by the upper-level control system of the lidar. Multiple waist-gain positions can be preset according to different working distances of the lidar. When the system needs to enter the corresponding working state, the upper-level control system sends the corresponding waist-gain position switching command to the control module 7. The specific method of generating the target waist-gain position is not the focus of this invention. It can be determined by manual control commands, or by the existing working mode control, distance judgment module, or task control module of the lidar. This part can be implemented using existing lidar control technology.

[0061] for Figure 1The single-stage structure shown has a pre-established correspondence between the target beam waist position and the target polarization state of the polarization modulation component 3 in the control module 7. When the target beam waist position corresponds to the first preset beam waist position 8, the control module 7 determines that the polarization modulation component 3 needs to output the first circular polarization chirality; when the target beam waist position corresponds to the second preset beam waist position 9, the control module 7 determines that the polarization modulation component 3 needs to output the second circular polarization chirality. The control module 7 outputs corresponding control signals to the polarization modulation component 3 according to the determined circular polarization chirality.

[0062] for Figure 2 As shown in (a), the liquid crystal variable delay device 31 changes the output linear polarization state, and then forms the corresponding circular polarization chirality through the quarter-wave plate 32.

[0063] for Figure 2 In the structure shown in (b), the incident linearly polarized light first passes through a quarter-wave plate 32 to form circularly polarized light, and then passes through a liquid crystal variable delay device 31 to change the circular polarization chirality.

[0064] for Figure 2 As shown in (c), the control module 7 controls the liquid crystal variable delay unit 31 to switch between a quarter-wavelength phase delay state and a three-quarter-wavelength phase delay state, so that the incident linearly polarized light is directly converted into the corresponding first circularly polarized chirality or second circularly polarized chirality.

[0065] Once the circular polarization chirality is determined, the beam enters the polarization-dependent geometric phase focusing element 4. The polarization-dependent geometric phase focusing element 4 forms a corresponding first optical power state or a second optical power state based on the current circular polarization chirality.

[0066] The current optical power of the polarization-dependent geometric phase focusing element 4, together with the telescope's optical components and the propagation distances between them, determines the current beam transmission state of the telescope system. For a specific optical system, the existing Gaussian beam ABCD matrix transmission method can be used to determine the far-field beam waist position corresponding to different optical power states.

[0067] When the current target beam waist position corresponds to the first preset beam waist position 8, the control module 7 enables the polarization-dependent geometrical phase focusing element 4 to form a first optical power state and enables the telescope system to form a first beam transmission state, thereby forming a beam waist at the first preset beam waist position 8. When the target beam waist position switches from the first position to the second position, the control module 7 changes the working state of the polarization modulation component 3, causing a change in the circular polarization chirality of the incident polarization-dependent geometrical phase focusing element 4. As the circular polarization chirality changes, the polarization-dependent geometrical phase focusing element 4 switches from the first optical power state to the second optical power state, and the telescope system further forms a second beam transmission state, causing the outgoing Gaussian beam to switch from the propagation state corresponding to the first preset beam waist position 8 to the propagation state corresponding to the second preset beam waist position 9.

[0068] During the aforementioned waist position switching process, it is not necessary to use a mechanical drive mechanism to displace the polarization-dependent geometric phase focusing element 4 or other focusing optical elements in the telescope along the optical axis.

[0069] for Figure 5 The multi-level structure shown in the control module 7 pre-establishes a correspondence between multiple target waist positions and the polarization state combinations of the first polarization modulation unit 3a and the second polarization modulation unit 3b.

[0070] When the target waist position corresponds to the first multi-level preset waist position 10, the control module 7 causes the first polarization modulation unit 3a and the second polarization modulation unit 3b to form a first polarization combination state, thereby causing the first polarization-related geometric phase focusing element 4a and the second polarization-related geometric phase focusing element 4b to form a first combined optical power state.

[0071] The first combined optical power state, together with the telescope optical components and the propagation relationship between each optical component, forms the corresponding first beam transmission state, so that the outgoing Gaussian beam forms a waist at the first multi-level preset waist position 10.

[0072] When the target waist position corresponds to the second multi-level preset waist position 11, the control module 7 changes the polarization modulation state of at least one of the first polarization modulation unit 3a and the second polarization modulation unit 3b, so that the two polarization-related geometric phase focusing elements form a second combined optical power state, thereby forming a waist at the second multi-level preset waist position 11 of the emitted Gaussian beam.

[0073] When the target waist position corresponds to the third multi-level preset waist position 12, the control module 7 controls the first polarization modulation unit 3a and the second polarization modulation unit 3b to form a third polarization combination state according to the pre-established position correspondence, so that the two polarization-related geometric phase focusing elements form a third combined optical power state, thereby forming a waist at the third multi-level preset waist position 12 of the emitted Gaussian beam.

[0074] For the fourth polarization combination, the control module 7 controls the first polarization modulation unit 3a and the second polarization modulation unit 3b to form a corresponding polarization combination state, so that the two polarization-related geometric phase focusing elements form a fourth combined optical power state, and when the fourth combined optical power state is different from the first three combined optical power states, the emitted Gaussian beam forms a fourth multi-level preset beam waist position.

[0075] The correspondence between multiple beam waist positions and different polarization combinations can be established in advance after the telescope's optical structure and parameters are determined. Specifically, existing Gaussian beam propagation calculation methods can be used to determine the optical power state corresponding to different polarization combinations and the far-field beam waist position corresponding to each optical power state, and establish a correspondence between the polarization combinations that meet the target working distance requirements and the corresponding beam waist positions.

[0076] The aforementioned correspondence can be stored in the control module 7 using a lookup table, or it can be implemented using other existing data mapping methods. The specific storage structure, programming language, and communication method of the control module 7 are not the focus of this invention and can be implemented using existing control technologies.

[0077] When the system is running, the control module 7 reads the corresponding polarization modulation state according to the target beam waist position and outputs a drive signal to the corresponding polarization modulation component or polarization modulation unit, so that the corresponding polarization-related geometric phase focusing element forms an optical power state or a combined optical power state corresponding to the target beam waist position.

[0078] At this optical power, the Gaussian beam passes through the telescope optical system to form a beam transmission state corresponding to the target waist position, and finally forms a waist at the corresponding preset waist position, thereby completing the waist position switching.

[0079] When the lidar needs to switch from the current working distance to another working distance, the upper control system re-outputs the target beam waist position. The control module 7 determines the new circular polarization chirality or combination of circular polarization chirality based on the new target beam waist position and updates the working status of the corresponding polarization modulation components.

[0080] Therefore, switching between multiple waist-cinching levels can be done directly according to the target waist-cinching level, without requiring sequential switching based on the spatial order of the preset waist-cinching positions.

[0081] The instruction reception, data storage, drive signal generation, liquid crystal driving, and electrical connection between the control module 7 and the liquid crystal variable delay device involved in the implementation of the method can be achieved using conventional control technologies of existing lidar control systems and liquid crystal polarization devices.

[0082] Using the above method, the target beam waist position is first converted into the corresponding polarization control state. The polarization control state further determines the optical power state of the polarization-related geometric phase focusing element. The optical power state, together with other optical components in the telescope, forms the corresponding Gaussian beam transmission state, ultimately enabling the outgoing Gaussian beam to form a far-field beam waist position corresponding to the target beam waist position, thereby achieving discrete adjustment of the beam waist position under single-level dual-position or multi-level multi-position conditions.

Claims

1. A polarization-switchable geometric phase-focusing lidar telescope system, characterized in that, It includes a beam input interface (1), a telescope optical assembly, a polarization modulation assembly (3), a polarization-dependent geometric phase focusing element (4), a polarization restoration assembly (6), and a control module (7); The telescope optical assembly includes at least one optical element. The polarization modulation assembly (3) and the polarization-dependent geometric phase focusing element (4) are disposed in the optical path from the beam input interface (1) to the target space. The polarization-dependent geometric phase focusing element (4) and at least one optical element together form a Gaussian beam transmission optical path. The beam input interface (1) is used to introduce a Gaussian beam into the telescope system; The polarization modulation component (3) is used to switch the beam incident on the polarization-dependent geometric phase focusing element (4) between a first circular polarization chirality and a second circular polarization chirality opposite to the first circular polarization chirality; The polarization-dependent geometric phase focusing element (4) is configured to form a first optical power state and a second optical power state that are different from each other when the first circularly polarized chirality and the second circularly polarized chirality are incident. The polarization-dependent geometric phase focusing element (4) and the telescope optical components form different beam transmission states in the first optical power state and the second optical power state, so that the Gaussian beam emitted from the telescope system forms a first preset beam waist position (8) and a second preset beam waist position (9), and the first preset beam waist position (8) and the second preset beam waist position (9) are set at intervals along the propagation direction of the emitted beam. The polarization restoration component (6) is used to convert circularly polarized light transmitted by the polarization-dependent geometric phase focusing element (4) into predetermined linearly polarized light; The control module (7) is electrically connected to the polarization modulation component (3) and is used to control the polarization modulation component (3) to switch the circular polarization chirality according to the beam waist position switching command, so that the beam waist position of the emitted Gaussian beam is discretely switched between at least a first preset beam waist position (8) and a second preset beam waist position (9).

2. The polarization-switchable geometric phase-focusing lidar telescope system according to claim 1, characterized in that: The polarization modulation component (3) includes a liquid crystal variable delay unit (31); The liquid crystal variable delay device (31) and the quarter-wave plate (32) are arranged sequentially along the beam propagation direction. The liquid crystal variable delay device (31) is used to change the polarization state of the incident beam polarized light so that the beam after passing through the quarter-wave plate (32) forms a first circular polarization chirality or a second circular polarization chirality. or, The quarter-wave plate (32) is disposed on the incident side of the liquid crystal variable delay device (31), which is used to perform chiral switching on the circularly polarized light formed by the quarter-wave plate (32).

3. The polarization-switchable geometric phase-focusing lidar telescope system according to claim 1, characterized in that: The polarization modulation component (3) includes a liquid crystal variable delay unit (31), the optical axis of which is set at 45° to the polarization direction of the incident linearly polarized light; The liquid crystal variable delay device (31) is configured to switch between a quarter-wavelength phase delay state and a three-quarter-wavelength phase delay state to convert incident linearly polarized light into first circularly polarized light and second circularly polarized light with opposite chirality, respectively.

4. The polarization-switchable geometric phase-focusing lidar telescope system according to claim 1, characterized in that: The polarization-dependent geometric phase focusing element (4) includes a Pancharatnam-Berry phase lens formed of a liquid crystal polymer, or a geometric phase metasurface focusing element formed of a subwavelength dielectric microstructure array. When the polarization-dependent geometric phase focusing element (4) is a Pancharatnam-Berry phase lens, it forms a first optical power and a second optical power with opposite signs when the first circular polarization chirality and the second circular polarization chirality are incident, respectively. One of the first optical power and the second optical power is a positive optical power and the other is a negative optical power. When the polarization-dependent geometric phase focusing element (4) is a geometric phase metasurface focusing element, it forms a first optical power and a second optical power that are different from each other when the first circular polarization chirality and the second circular polarization chirality are incident.

5. The polarization-switchable geometric phase-focusing lidar telescope system according to claim 1, characterized in that: The telescope optical components include a collimating optical component (2) and a beam expanding optical component (5). The beam input interface (1), collimating optical component (2), polarization modulation component (3), polarization-related geometric phase focusing element (4), beam expanding optical component (5) and polarization restoration component (6) are arranged sequentially along the direction of emitted light propagation. In coaxial transmit / receive mode, the emitted light passes sequentially through the beam input interface (1), collimating optical component (2), polarization modulation component (3), polarization-related geometric phase focusing element (4), beam expanding optical component (5) and polarization restoration component (6) before entering the target space; The target echo passes sequentially along the reverse optical path through the polarization restoration component (6), the beam expanding optical component (5), the polarization-related geometric phase focusing element (4), the polarization modulation component (3), and the collimating optical component (2) and returns to the beam input interface (1).

6. The polarization-switchable geometric phase-focusing lidar telescope system according to claim 5, characterized in that: The emitted light is linearly polarized before entering the polarization modulation component (3). After passing through the polarization modulation component (3), it becomes circularly polarized light with first or second circular polarization chirality. After passing through the polarization-dependent geometric phase focusing element (4), the circular polarization chirality is reversed. After passing through the polarization restoration component (6), it is restored to linearly polarized light. When the echo component in the target echo that matches the transmitted polarization state propagates along the reverse optical path, it undergoes a corresponding polarization state conversion through the polarization restoration component (6), the polarization-related geometric phase focusing element (4), and the polarization modulation component (3), and forms a linear polarization state that matches the receiving optical path before the return beam input interface (1).

7. The polarization-switchable geometric phase-focusing lidar telescope system according to claim 1, characterized in that: The polarization modulation component (3) includes a first polarization modulation unit (3a) and a second polarization modulation unit (3b); The polarization-dependent geometric phase focusing element (4) includes a first polarization-dependent geometric phase focusing element (4a) and a second polarization-dependent geometric phase focusing element (4b); The first polarization modulation unit (3a), the first polarization-related geometric phase focusing element (4a), the second polarization modulation unit (3b), and the second polarization-related geometric phase focusing element (4b) are arranged sequentially along the beam propagation direction; The control module (7) is electrically connected to the first polarization modulation unit (3a) and the second polarization modulation unit (3b) respectively, and is used to control the circular polarization chirality of the first polarization-related geometric phase focusing element (4a) and the second polarization-related geometric phase focusing element (4b) respectively, so that the first polarization-related geometric phase focusing element (4a) and the second polarization-related geometric phase focusing element (4b) form different combined optical power states, and correspondingly form multiple preset beam waist positions spaced apart along the propagation direction of the outgoing beam.

8. The polarization-switchable geometric phase-focusing lidar telescope system according to claim 7, characterized in that: The first polarization modulation unit (3a) and the second polarization modulation unit (3b) each have two polarization control states to form four circular polarization chiral combinations; By setting the optical power and optical position of the first polarization-dependent geometric phase focusing element (4a) and the second polarization-dependent geometric phase focusing element (4b), the four circular polarization chiral combinations correspond to four different combined optical power states, and the outgoing Gaussian beam forms a first multi-level preset waist position (10), a second multi-level preset waist position (11), a third multi-level preset waist position (12) and a fourth multi-level preset waist position, respectively.

9. A method for adjusting the beam waist of a polarization-switchable geometric phase-focusing lidar telescope system, characterized in that, The system applied to the polarization-switchable geometric phase-focusing lidar telescope system according to any one of claims 1-8 includes: Obtain the waist-cinching gear switching command corresponding to the target waist-cinching gear; The circular polarization chirality or combination of circular polarization chirality corresponding to the target waist setting is determined according to the waist setting switching command. Control the polarization modulation component (3) or polarization modulation unit corresponding to the target waist position to output the corresponding polarization state, so that the corresponding polarization-related geometric phase focusing element forms the corresponding optical power state or combined optical power state. The optical power state or combined optical power state, together with the telescope optical components, forms a beam transmission state corresponding to the target beam waist position, so that the Gaussian beam emitted from the telescope system forms the corresponding preset beam waist position. When switching between different target beam waist positions, the circular polarization chirality of the incident beam onto the corresponding polarization-dependent geometric phase focusing element is changed, thereby causing the beam transmission state to change discretely, and thus the beam waist position of the outgoing Gaussian beam to switch discretely between multiple preset beam waist positions.

10. The beam waist adjustment method for the polarization-switchable geometric phase-focusing lidar telescope system according to claim 9, characterized in that: When the polarization switchable geometric phase focusing lidar telescope system includes a first polarization modulation unit (3a), a first polarization-related geometric phase focusing element (4a), a second polarization modulation unit (3b), and a second polarization-related geometric phase focusing element (4b), the circular polarization chiral combination corresponding to the first polarization modulation unit (3a) and the second polarization modulation unit (3b) is determined according to the target beam waist position. The first polarization modulation unit (3a) and the second polarization modulation unit (3b) are controlled respectively to make the first polarization-related geometric phase focusing element (4a) and the second polarization-related geometric phase focusing element (4b) form a combined optical power state corresponding to the target beam waist position, and make the outgoing Gaussian beam form a first multi-level preset beam waist position (10), a second multi-level preset beam waist position (11), a third multi-level preset beam waist position (12) or a fourth multi-level preset beam waist position.

Images