Method and device for regulating and controlling high-order Poincare sphere beam

Abstract

The invention discloses a method and a device for regulating and controlling a high-order Poincare spherical beam, and provides a method for effectively regulating and controlling the high-order Poincare spherical beam with complex vector polarization distribution in multiple dimensions such as angular momentum, light intensity distribution, polarization state and the like by using a nonlinear optical crystal based on a nonlinear effect of second harmonic. And different phase matching conditions in the second harmonic generation process are set, so that the regulation and control results of the second harmonic of the high-order Poincare spherical beam are enriched. According to the method and the device, a good effect is achieved during nonlinear regulation and control of the high-order Poincare spherical beam, the structure is simple, the cost is low, regulation and control of multi-dimensional optical properties are achieved, and the method and the device are suitable for design of optical nonlinear polarization imaging elements.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of light field regulation, and particularly relates to a method and device for regulating a high-order Poincare sphere light beam. BACKGROUND

[0002] A high-order Poincare sphere (HOPS) light beam, or a generalized vector vortex light beam, is a structured light beam with more complex polarization characteristics and phase characteristics compared to a general Gaussian light beam.

[0003] The prior art uses a metasurface to perform multi-dimensional nonlinear regulation on a high-order Poincare sphere light beam, but when regulating the polarization state and light intensity distribution, only one regulation result can be achieved, and the metasurface manufacturing process is complex, needs to be precisely designed, and is high in cost.

[0004] Therefore, the prior art needs to be further improved. SUMMARY

[0005] In view of the deficiencies in the above related art, the purpose of the present application is to provide a method and device for regulating a high-order Poincare sphere light beam, overcoming the defects of the prior art method that the regulation result of the high-order Poincare sphere is single and the cost is high.

[0006] The technical solution adopted by the present application to solve the technical problems is as follows: In a first aspect, the present application provides a method for regulating a high-order Poincare sphere light beam, comprising: receiving the high-order Poincare sphere light beam by using a nonlinear optical crystal to generate a second harmonic wave in the nonlinear optical crystal and obtain a target structured light field.

[0007] Optionally, the nonlinear optical crystal is a BBO crystal.

[0008] Optionally, the step of receiving the high-order Poincare sphere light beam by using a nonlinear optical crystal to generate a second harmonic wave in the nonlinear optical crystal and obtain a target structured light field comprises: setting the nonlinear optical crystal optical axis as a horizontal direction, inputting the Poincare sphere light beam into the nonlinear optical crystal, and setting the phase matching condition as type I phase matching when the high-order Poincare sphere light beam generates a second harmonic wave in the nonlinear optical crystal, generating a light intensity distribution inherited from the horizontal polarization component of the fundamental light, and a target structured light field with a vertical polarization state.

[0009] Optionally, the step of receiving the high-order Poincare sphere light beam by using a nonlinear optical crystal to generate a second harmonic wave in the nonlinear optical crystal and obtain a target structured light field comprises: The optical axis of the nonlinear optical crystal is set as a horizontal direction, the high-order Poincare sphere light beam is input into the nonlinear optical crystal, and when the second harmonic wave is generated in the nonlinear optical crystal, the phase matching condition is type II phase matching, and a target structured light field is generated, the light intensity distribution of which inherits the horizontal and vertical polarization components of the fundamental light.

[0010] Optionally, the step of receiving the high-order Poincare sphere light beam by the nonlinear optical crystal to generate a second harmonic wave in the nonlinear optical crystal to obtain a target structured light field comprises: The high-order Poincare sphere light beam is input into two nonlinear optical crystals arranged orthogonally, and when the second harmonic wave is generated in the two nonlinear optical crystals, the phase matching condition is type I phase matching, and a target structured light field is generated, the light intensity distribution of which inherits the horizontal and vertical polarization components of the fundamental light.

[0011] Optionally, the target structured light field corresponds to a control parameter, which comprises: light intensity distribution, polarization characteristics and phase structure.

[0012] In a second aspect, the present application provides a device for controlling a high-order Poincare sphere light beam, which comprises: a Poincare sphere light beam generation module, configured to output a high-order Poincare sphere light beam; a nonlinear optical crystal, arranged on the light path of the high-order Poincare sphere light beam, configured to receive the high-order Poincare sphere light beam to control the high-order Poincare sphere light beam, generate a second harmonic wave, and obtain a target structured light field.

[0013] Optionally, the number of the nonlinear optical crystals is one, and when the second harmonic wave is generated in the nonlinear optical crystal, the phase matching condition is type I phase matching; or the number of the nonlinear optical crystals is one, and when the second harmonic wave is generated in the nonlinear optical crystal, the phase matching condition is type II phase matching; or the number of the nonlinear optical crystals is two, and the two nonlinear optical crystals are arranged orthogonally, and when the second harmonic wave is generated in the two nonlinear optical crystals arranged orthogonally, the phase matching condition is type I phase matching.

[0014] Optionally, the nonlinear optical crystal is a BBO crystal.

[0015] Optionally, the Poincare sphere light beam generation module comprises a laser, a polarizer, a quarter-wave plate and a vortex wave plate. The laser beam emitted by the laser passes through the polarizer, the quarter-wave plate and the vortex wave plate in sequence, and the high-order Poincare sphere light beam is obtained.

[0016] Advantages: The application discloses a method and device for regulating high-order Poincare sphere light beams, and based on the nonlinear effect of second harmonic, the method and device are used for effectively regulating high-order Poincare sphere light beams with complex vector polarization distribution in multiple dimensions of angular momentum, light intensity distribution and polarization state by using a nonlinear optical crystal. The method and device enrich the regulation results of the second harmonic of the high-order Poincare sphere light beams by controlling different phase matching conditions in the generation of the second harmonic. The method and device have good effects in the nonlinear regulation of the high-order Poincare sphere light beams, have simple structure and low cost, can realize the regulation of multiple-dimensional optical properties, and are suitable for the design of optical nonlinear polarization imaging elements. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 The figure is a high-order Poincare sphere light beam disclosed by the application, the topological charge number n=2, and three points respectively represent a circularly polarized vortex light beam, a cylindrical vector light beam and an elliptically polarized vortex light beam. Figure 2 The figure is a structure schematic diagram of a first embodiment of the device for regulating high-order Poincare sphere light beams disclosed by the application. Figure 3 The figure is a structure schematic diagram of a second embodiment of the device for regulating high-order Poincare sphere light beams disclosed by the application. Figure 4 The figure is the light intensity distribution and polarization state regulation result of the high-order Poincare sphere light beam with the topological charge number n=2 in the embodiment and the second harmonic thereof. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical scheme and advantages of the application more clear and understandable, the application is further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the application and do not limit the application.

[0019] The physical quantities of light, such as amplitude, frequency, phase, polarization and angular momentum, can be used to transmit information, and reasonable selection and regulation of these physical quantities can realize efficient, high-capacity and high-precision information transmission. High-order Poincare sphere (HOPS) is a high-order generalization of the classical Poincare sphere, which is used to describe a light beam with non-uniform polarization state (such as a cylindrical vector light beam). The classical Poincare sphere parameterizes the uniform polarization state (linear polarization, circular polarization, elliptical polarization) by the spherical coordinate, and the high-order Poincare sphere extends this model by introducing the topological charge to describe the spatially varying polarization structure. Compared with general Gaussian light beams, the high-order Poincare sphere light beam, or the generalized vector vortex light beam, has the following advantages: Figure 1The structure beam has more complex polarization characteristics and phase characteristics, can be divided into circularly polarized vortex beams, cylindrical vector beams and elliptically polarized vortex beams, and the complex structure itself can theoretically enable the structure beam to carry more information in the transmission process, and has great development prospects in the field of optical communication, but how to accurately control the structure beam in multiple dimensions in the process is still a difficult problem to be studied.

[0020] In order to overcome the problem that the high-order Poincare sphere light beam cannot be flexibly controlled in the prior art, the present application provides a method and device for controlling a high-order Poincare sphere light beam, which realizes multi-dimensional control of the high-order Poincare sphere light beam based on the nonlinear effect generated by the light beam in a nonlinear photonic crystal. The method provided by the present application not only has better light beam control effect, but also is easy to implement and low in cost, and is suitable for the design of an optical nonlinear polarization imaging element.

[0021] Nonlinear optics is a discipline studying the interaction between strong light and matter, and is an important branch of modern optics. Common nonlinear optical effects include second harmonic generation, third harmonic generation, optical Kerr effect, two-photon absorption, etc., which can control the properties of light in frequency, polarization, refractive index, angular momentum, etc. Therefore, the method and device for controlling a high-order Poincare sphere light beam disclosed by the present application are realized based on nonlinear effects in nonlinear optics.

[0022] The method and device for controlling a high-order Poincare sphere light beam disclosed in the present embodiment will be further described below with reference to the accompanying drawings.

[0023] In a first aspect, the present application discloses a method for controlling a high-order Poincare sphere light beam, comprising: Receiving the high-order Poincare sphere light beam by using a nonlinear optical crystal to generate a second harmonic wave in the nonlinear optical crystal, and obtaining a target structure light field.

[0024] In the present embodiment, the high-order Poincare sphere light beam is input into the nonlinear optical crystal to generate a second harmonic wave in the nonlinear optical crystal, so as to realize the control of physical quantities such as phase, polarization and angular momentum of the Poincare sphere light beam. In an implementation manner, the nonlinear optical crystal is a BBO crystal. Since the BBO crystal has a high nonlinear coefficient, a wide phase matching wavelength range, strong chemical and thermal stability, and a lower cost than some high-end crystals, the BBO crystal is used as the nonlinear optical crystal for control, which not only meets a more extensive light beam control range, but also is low in cost and easy to implement.

[0025] Further, if the high-order Poincare sphere beams are directly modulated by nonlinear optical crystals, the nonlinear effect has a linear polarization dependent property, which easily leads to the loss of the complex structure of the high-order Poincare sphere beams. Therefore, in the embodiment, phase matching is used to achieve high-efficiency energy conversion in the second harmonic generation. Without phase matching, the phase of the second harmonic light will quickly mismatch the phase of the fundamental light, resulting in ineffective energy accumulation. Temperature phase matching requires precise temperature control to change the refractive index of the crystal, and the equipment is complex; quasi-phase matching requires the introduction of a periodic polarization structure in the crystal, and the manufacturing process is complex and costly. Compared with the above, the use of type I and type II phase matching of the BBO crystal is low in cost and convenient to operate. In type I phase matching, the ordinary light of the fundamental frequency interacts to generate the extraordinary light of the second harmonic (o + o→ e); in type II phase matching, the ordinary light of the fundamental frequency interacts with the extraordinary light of the fundamental frequency to generate the extraordinary light of the second harmonic (o + e→ e). The selection of the polarization of the second harmonic generation under different phase matching conditions can interact well with the complex structure of the HOPS beam, generate interesting light field structures, realize the multi-dimensional light field modulation of the spot morphology distribution, polarization state, and topological charge, and explore the significance of this effect for the development of vector nonlinear optics, the application in the fields of nonlinear polarization imaging and communication, etc.

[0026] In the embodiment, based on the phase matching conditions and placement of the BBO crystal, three second harmonic generation paths are designed to modulate the light intensity distribution, polarization characteristics, and angular momentum of the high-order Poincare sphere beams and other multi-dimensional physical quantities.

[0027] In a first implementation, the step of receiving the high-order Poincare sphere beams by the nonlinear optical crystal to generate a second harmonic in the nonlinear optical crystal to obtain a target structured light field includes: The optical axis of the nonlinear optical crystal is set to be horizontal, the Poincare sphere beams are input into the nonlinear optical crystal, and the phase matching condition is set to be type I phase matching when the Poincare sphere beams generate a second harmonic in the nonlinear optical crystal, to generate a target structured light field whose light intensity distribution inherits the horizontal polarization component of the fundamental light and whose polarization state is vertical polarization.

[0028] In this implementation, the ordinary light of the fundamental frequency interacts to generate the extraordinary light of the second harmonic (o + o→ e), the ordinary light is set to be horizontally polarized, and the extraordinary light is set to be vertically polarized. Therefore, the light intensity distribution of the second harmonic inherits the horizontal polarization component of the fundamental light, and the polarization state is vertical polarization, while the vertical polarization component of the fundamental light does not participate in the action under this condition.

[0029] In a second implementation, the step of receiving the high-order Poincare sphere beams by the nonlinear optical crystal to generate a second harmonic in the nonlinear optical crystal to obtain a target structured light field includes: Set the optical axis of the nonlinear optical crystal as a horizontal direction, input the high-order Poincare sphere light beam into the nonlinear optical crystal, and set the phase matching condition as type II phase matching when generating the second harmonic wave in the nonlinear optical crystal, to generate a target structured light field whose light intensity distribution is inherited from the horizontal polarization component and the vertical polarization component of the fundamental light.

[0030] Under the type II phase matching condition, the ordinary light of the fundamental frequency and the extraordinary light of the fundamental frequency interact to generate the extraordinary light of the second harmonic wave (o+e→e), and the light intensity distribution of the second harmonic wave is inherited from the vertical polarization and the horizontal polarization of the fundamental light, and the two polarization components are the same.

[0031] In a third implementation, the step of using a nonlinear optical crystal to receive a high-order Poincare sphere light beam to generate a second harmonic wave in the nonlinear optical crystal to obtain a target structured light field includes: Input the Poincare sphere light beam into two nonlinear optical crystals arranged orthogonally, and set the phase matching condition as type I phase matching when the Poincare sphere light beam generates a second harmonic wave in the two nonlinear optical crystals, to generate a target structured light field whose light intensity distribution is inherited from the horizontal and vertical polarization components of the fundamental light.

[0032] Considering that the vertical polarization component is not used in the type I phase matching process, two orthogonally arranged BBO crystals are used to generate a second harmonic wave, so that the horizontal polarization component of the fundamental light participates in the action in the first BBO crystal, the vertical polarization component of the fundamental light participates in the action in the second BBO crystal, and then the two are combined in the subsequent optical path. The obtained second harmonic wave spot pattern is similar to that obtained in the type II phase matching, but its polarization state retains the complex distribution of the original high-order Poincare sphere light beam, which can be detected by a polarizer.

[0033] Since the above three different implementations all involve the generation of a second harmonic wave, according to the conservation of angular momentum, the topological charge number changes from n to 2n.

[0034] The above three implementations will be further described in more detail in combination with the implementation principle of the method and device of the application.

[0035] In specific implementation, the polarization state of the light beam can be characterized based on a Jones matrix, and the Jones matrix of the high-order Poincare sphere light beam with an arbitrary polarization state generated by a vortex half-wave plate and a quarter-wave plate is: ; where ω represents the frequency of the light beam, a and b represent the long axis and the short axis of the polarization ellipse, respectively, and their values depend on the polarization state of the light. For linearly polarized light, a = 1, b = 0; for circularly polarized light, a = 1, b = 1. exp(inφ) represents the vortex phase of the light beam, n represents the topological charge, which characterizes the angular momentum of the high-order Poincare sphere beam, φ is the azimuth angle of the vortex wave plate, and Φ is the polarization direction angle, is the intensity distribution function of the initial light beam, which presents the characteristics of the Gaussian beam.

[0036] In the second harmonic generation process, two photons of the same frequency interact to generate a new frequency photon, and the steady-state coupled wave equation is: ; wherein and are the second harmonic and fundamental light, respectively, z represents the transmission distance, c, , are the speed of light, the refractive index, and the angular frequency, respectively, and is the effective nonlinear coefficient of the material, which determines the strength of the nonlinear interaction. In addition, represents the phase mismatch of the frequency doubling process. The phase matching of the frequency doubling process requires that the propagation speed of the fundamental light and the frequency-doubled light in the BBO crystal be consistent, so as to reduce the destructive interference and maximize the frequency doubling efficiency.

[0037] The type I phase-matched second harmonic generation process (o+o→e) only has the ordinary light component with the polarization direction parallel to the optical axis of the crystal, and the type II phase-matched second harmonic generation process (o+e→e) has two light components with different polarization directions. Equation (2) can be rewritten as: ; ; wherein , represent the horizontal polarization components of the frequency-doubled light obtained by type I and type II phase matching, , represent the vertical and horizontal polarization components of the fundamental light. The Jones matrix of the high-order Poincare sphere beam is substituted into the above equation, and then integrated. Finally, the expression of the second harmonic under the corresponding condition can be obtained, i.e. ① Type I phase matching: ; ② Type II phase matching: ; ③ Using two orthogonally placed BBO crystals:

[0038] }; Its expression contains or After frequency multiplication, it becomes or By calculating the corresponding Stokes vector, it can be seen that the intensity of the frequency-doubled light obtained by type I phase matching is... or The intensity of the frequency-doubled light obtained by type II phase matching is directly proportional to the intensity of the frequency-doubled light. or The intensity distribution of the second harmonic is directly proportional to the polarization. If the incident fundamental light is a cylindrical vector beam, the intensity distribution of the second harmonic is petal-shaped, with 4 and 8 peaks and valleys. If the incident fundamental light is an elliptically polarized vortex beam, the second harmonic is similar to the former, but the peak intensity position is rotated by a certain angle. If the incident fundamental light is a circularly polarized vortex beam, the second harmonic is donut-shaped with a dark nucleus at the center. Regarding polarization state manipulation, the first two methods yield vertically polarized light. Frequency doubling using two BBO crystals produces a complex polarization distribution, and the polarization components in each direction can be detected by a polarizer. Regarding angular momentum manipulation, the topological charge changes from n to 2n, and the angular momentum changes from n... up to 2n .

[0039] The method disclosed in this embodiment utilizes phase-matching conditions and the placement of the BBO crystal to design three different second-harmonic generation paths, thereby achieving multi-dimensional manipulation of a high-order Poincaré sphere beam. The target structured light field is obtained after manipulation of the high-order Poincaré sphere beam. The physical quantities corresponding to the manipulated target structured light field include multiple dimensions such as light intensity distribution, polarization characteristics, and phase structure. This invention has the advantages of simple implementation and low cost.

[0040] Secondly, this application also provides a device for controlling higher-order Poincaré sphere beams, such as... Figure 2 As shown, it includes: The Poincaré sphere beam generation module is used to output a Poincaré sphere beam.

[0041] Specifically, the Poincaré sphere beam generation module includes a laser 101, a first polarizer 104, a quarter-wave plate 105, and a vortex wave plate 106. To allow for more angle adjustments to the position of the laser beam emitted by the laser, a reflector 102 is provided in the optical path of the laser beam to change the transmission direction of the laser.

[0042] The laser beam emitted by the laser is modulated sequentially by a first polarizer 104, a quarter-wave plate 105, and a vortex wave plate 106 to obtain a high-order Poincaré sphere beam. To prevent excessive laser power from damaging the BBO crystal, a filter 103 is placed between the reflector 102 and the first polarizer 104 to reduce the laser power.

[0043] In a specific implementation, a high-power laser (Carbide CB5-06) with a wavelength of 1030 nm, a repetition frequency of 60 kHz, and a pulse width of 225 fs is used as a pump light source, and the average power is set to a maximum of 6 W. To prevent damage to the crystal caused by excessive laser power, a neutral density filter is set after the laser output as an attenuation system to control the power of the laser. Then, the laser power controlled laser is input to the polarizer, polarized by the first polarizer, and then an arbitrary polarization state is generated by the quarter-wave plate. Then, the angle between the optical axis direction of the vortex wave plate and the polarization direction of the light beam is adjusted, and the 0-order polarized light is converted into a Poincare sphere light beam with an order of n=2 through the vortex wave plate.

[0044] A nonlinear optical crystal is arranged on the light path of the high-order Poincare sphere light beam to receive the high-order Poincare sphere light beam, to regulate the high-order Poincare sphere light beam, to generate a second harmonic wave, and to obtain a target structured light field. In a specific implementation, the nonlinear optical crystal is a BBO crystal.

[0045] The BBO crystal is arranged on the light path of the high-order Poincare sphere light beam output by the vortex wave plate to receive the high-order Poincare sphere light beam. The high-order Poincare sphere light beam generates a second harmonic wave in the BBO crystal to output one or more target structured light fields with regulated physical quantities.

[0046] Further, as shown in Figure 2 the number of nonlinear optical crystals is one, referred to as a first BBO crystal 1071, and the phase matching condition is type I phase matching when the nonlinear effect occurs in the nonlinear optical crystal; or the number of nonlinear optical crystals is one, and the phase matching condition is type II phase matching when the nonlinear effect occurs in the nonlinear optical crystal; or, as shown in Figure 3 the number of nonlinear optical crystals is two, and the two BBO crystals are arranged orthogonally, and the two orthogonally arranged BBO crystals are used as a BBO crystal assembly 1072, and the phase matching condition is type I phase matching when the nonlinear effect occurs in the two orthogonally arranged nonlinear optical crystals.

[0047] In detail, the above three paths are respectively: (1) a single BBO, type I phase matching; (2) a single BBO, type II phase matching; and (3) two orthogonally arranged BBOs, type I phase matching. As shown in Figure 2 or Figure 3 As shown in the wavelength of the fundamental light is 1030 nm, the wavelength of the second harmonic light is 515 nm, a 600 nm short-wave pass filter 108 is arranged to filter the fundamental light, and the second harmonic light is observed in a charge-coupled device 110 after polarization state adjustment by a second polarizer 109.

[0048] like Figure 4 The image shows the intensity distribution and polarization state modulation results of a high-order Poincaré sphere beam with a topological charge number of n=2 and its second harmonic. The black arrows indicate the polarization states. From... Figure 4 It can be seen that the beams (or second harmonic beams) of the target structured light field obtained after different modulation methods are all distributed in a petal shape. Figure 4 From (a1), (b1), (c1), and (d1), we know that the beam obtained by type-I phase matching has 4 lobes, while the beam obtained by type-II phase matching and using orthogonal type-I BBO has 8 lobes. The number of lobes is determined by the order n, which is contained in the above Jones matrix expression. or After frequency multiplication, it becomes or By calculating the corresponding Stokes vector, it can be seen that the intensity of the frequency-doubled light obtained by type I phase matching is... or Proportional. Figure 4 From (a2), (b2), (c2), and (d2), it can be seen that the intensity of the frequency-doubled light obtained by type II phase matching is... or The light intensity is directly proportional to the light intensity, therefore the light intensity distribution corresponds to 4 and 8 peaks and troughs. Figure 4 As shown in (a3), (b3), (c3), and (d3), the second harmonics of the circularly polarized vortex beam are basically the same in terms of spot morphology, all being donut-shaped, with only slight differences in light intensity. The second harmonics of the elliptically polarized vortex beam are also distributed in a petal shape, but the peak position of the light intensity has a certain angle of rotation.

[0049] This invention, based on the BBO crystal in nonlinear optical crystals, utilizes second harmonics to design a simple, low-cost, and multi-dimensional nonlinear control scheme for high-order Poincaré sphere beams. Experimental verification and theoretical derivation demonstrate that this method can achieve effective control of three different optical properties of high-order Poincaré sphere beams in the same nonlinear optical crystal, including intensity distribution, polarization state, and angular momentum.

[0050] The application discloses a method and device for regulating high-order Poincare sphere light beams, and based on the nonlinear effect of second harmonic, the method is used for effectively regulating high-order Poincare sphere light beams with complex vector polarization distribution in multiple dimensions such as angular momentum, light intensity distribution and polarization state by using nonlinear optical crystals.

[0051] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example" or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or N embodiments or examples in a suitable manner. In addition, the person skilled in the art can combine and combine the different embodiments or examples described in the present specification and the features of the different embodiments or examples without contradiction.

[0052] The above-described embodiments only express several implementation manners of the present application, the description is more specific and detailed, but it cannot be understood as the limitation of the patent scope of the application. It should be pointed out that for the person skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A method for controlling a high-order Poincaré sphere beam, characterized in that, include: A high-order Poincaré sphere beam is received using a nonlinear optical crystal to generate a second harmonic in the nonlinear optical crystal, thereby obtaining the target structured light field.

2. The method for controlling a higher-order Poincaré sphere beam according to claim 1, characterized in that, The nonlinear optical crystal is a BBO crystal.

3. The method for controlling a higher-order Poincaré sphere beam according to claim 1 or 2, characterized in that, The step of using a nonlinear optical crystal to receive a high-order Poincaré sphere beam, thereby generating a second harmonic in the nonlinear optical crystal and obtaining the target structured light field, includes: The optical axis of the nonlinear optical crystal is set to the horizontal direction. The Poincaré sphere beam is input into the nonlinear optical crystal. When the higher-order Poincaré sphere beam generates a second harmonic in the nonlinear optical crystal, the phase matching condition is set to type I phase matching. The generated light intensity distribution inherits the horizontal polarization component of the fundamental light, and the polarization state is vertically polarized target structure light field.

4. The method for controlling a higher-order Poincaré sphere beam according to claim 1 or 2, characterized in that, The step of using a nonlinear optical crystal to receive a high-order Poincaré sphere beam, thereby generating a second harmonic in the nonlinear optical crystal and obtaining the target structured light field, includes: The optical axis of the nonlinear optical crystal is set to the horizontal direction. The higher-order Poincaré sphere beam is input into the nonlinear optical crystal. When the second harmonic is generated in the nonlinear optical crystal, the phase matching condition is set to type II phase matching. The target structured light field is generated, and the light intensity distribution inherits the horizontal polarization component and the vertical polarization component of the fundamental frequency light.

5. The method for controlling a higher-order Poincaré sphere beam according to claim 1 or 2, characterized in that, The step of using a nonlinear optical crystal to receive a high-order Poincaré sphere beam, thereby generating a second harmonic in the nonlinear optical crystal and obtaining the target structured light field, includes: The higher-order Poincaré sphere beam is input into two orthogonally arranged nonlinear optical crystals, and the phase matching condition is set to type I phase matching when the higher-order Poincaré sphere beam generates second harmonics in the two nonlinear optical crystals, generating a target structured light field whose light intensity distribution inherits the horizontal and vertical polarization components of the fundamental frequency light.

6. The method for controlling a higher-order Poincaré sphere beam according to claim 1, characterized in that, The control parameters corresponding to the target structured light field include: light intensity distribution, polarization characteristics, and phase structure.

7. A device for controlling a high-order Poincaré sphere beam, characterized in that, include: Poincaré sphere beam generation module, used to output high-order Poincaré sphere beams; A nonlinear optical crystal is placed in the optical path of the higher-order Poincaré sphere beam to receive the higher-order Poincaré sphere beam, so as to modulate the higher-order Poincaré sphere beam, generate second harmonics, and obtain the target structured optical field.

8. The device for controlling a higher-order Poincaré sphere beam according to claim 7, characterized in that, The nonlinear optical crystal is one in number, and when a high-order Poincaré sphere beam generates a second harmonic in the nonlinear optical crystal, the phase matching condition is type I phase matching; or, the nonlinear optical crystal is one in number, and when a high-order Poincaré sphere beam generates a second harmonic in the nonlinear optical crystal, the phase matching condition is type II phase matching; or, the nonlinear optical crystal is two in number and orthogonally arranged, and when a high-order Poincaré sphere beam generates a second harmonic in the two orthogonally arranged nonlinear optical crystals, the phase matching condition is type I phase matching.

9. The device for controlling a higher-order Poincaré sphere beam according to claim 7, characterized in that, The nonlinear optical crystal is a BBO crystal.

10. The device for controlling a higher-order Poincaré sphere beam according to claim 7, characterized in that, The Poincaré sphere beam generation module includes a laser, a polarizer, a quarter-wave plate, and a vortex wave plate; The laser beam emitted by the laser is modulated sequentially by a polarizer, a quarter-wave plate, and a vortex plate to obtain a higher-order Poincaré sphere beam.

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