A nonlinear frequency conversion device based on vector beam

Abstract

A nonlinear frequency conversion device based on a vector beam includes an optical processing component for processing seed light into circularly polarized light; an angular momentum module for increasing orbital angular momentum of the input circularly polarized light, and then outputting a beam having a superposition state of polarization and orbital angular momentum; and a nonlinear frequency conversion module for performing nonlinear frequency conversion on the input beam, and then outputting the beam after nonlinear frequency conversion. The present invention can realize the operation of vector beams and nonlinear frequency conversion, and can be used to broaden the available frequency range of beams. It has strong effectiveness and robustness, uses fewer optical elements, is flexible to adjust, and has strong application prospects. The device can realize frequency doubling operation of vector beams, and the device is also applicable to other second-order nonlinear processes, such as sum-frequency and difference-frequency conversion processes, and can be extended to the quantum state of single photons.

Description

Technical Field

[0001] The invention relates to the fields of laser technology, nonlinear optical physics technology and atomic physics technology, and in particular to a nonlinear frequency conversion device based on vector light beams. Background Art

[0002] Since the birth of lasers, the development of laser technology in the past few decades has mainly focused on spatially uniform polarization states. In recent years, laser beams with spatially inhomogeneous polarization states (such as vector beams) have received increasing attention. Vector beams have special light intensity and polarization distribution, which can be used in many fields such as large numerical aperture focusing, optical trapping, laser processing, optical cages, super-resolution imaging, high-capacity communications, and quantum information science.

[0003] As an important laser technology, nonlinear frequency conversion has also been studied by people. When it is difficult to directly generate a beam of a suitable frequency band, nonlinear frequency conversion provides an important method to expand the available frequency range of the beam.

[0004] Until now, the manipulation of vectored beams and nonlinear frequency conversion have remained very challenging because most nonlinear processes are polarization sensitive. Summary of the invention

[0005] In order to solve the problem of how to apply the technology of nonlinear frequency conversion to a laser beam with an uneven polarization state, the present invention provides a nonlinear frequency conversion device based on a vector beam. The present invention adopts the following technical solutions:

[0006] A nonlinear frequency conversion device based on vector beam, comprising:

[0007] A light processing component, used for processing the seed light into circularly polarized light;

[0008] An angular momentum module is used to increase orbital angular momentum of input circularly polarized light, and then output a light beam having a superposition state of polarization and orbital angular momentum;

[0009] The nonlinear frequency conversion module is used to perform nonlinear frequency conversion on the input light beam and then output the light beam after the nonlinear frequency conversion.

[0010] A first solution of a nonlinear frequency conversion module, the nonlinear frequency conversion module includes a first dichroic mirror, a third polarization beam splitter, a first dichroic half-wave plate, a first crystal, and a first parabolic reflector and a second parabolic reflector symmetrically arranged on both sides of the first crystal; an input light beam passes through the first dichroic mirror and enters the third polarization beam splitter, and the third polarization beam splitter separates horizontal polarized light and vertical polarized light, the horizontal polarized light passes through the first dichroic half-wave plate, the first polished surface reflector, the first crystal, the second polished surface reflector, and the third polarization beam splitter in sequence; the vertical polarized light passes through the second polished surface reflector, the first crystal, the first polished surface reflector, the first dichroic half-wave plate, and the third polarization beam splitter in sequence, and the horizontal polarized light and the vertical polarized light are output by the third polarization beam splitter and then merged to form a light beam for nonlinear frequency conversion.

[0011] A second solution of a nonlinear frequency conversion module, the nonlinear frequency conversion module includes a first focusing lens, a second dichroic mirror, a fourth dichroic polarization beam splitter, a second dichroic half-wave plate, a seventh reflector, a second crystal, an eighth reflector, and a first collimating lens. The input light beam passes through the first focusing lens, the second dichroic mirror, and the fourth dichroic polarization beam splitter in sequence and is divided into horizontal polarized light and vertical polarized light. The horizontal polarized light passes through the second dichroic half-wave plate, the seventh reflector, the second crystal, the eighth reflector, and the fourth dichroic polarization beam splitter in sequence and is used as a first output. The vertical polarized light passes through the eighth reflector, the second crystal, the seventh reflector, the second dichroic half-wave plate, and the fourth dichroic polarization beam splitter in sequence and is used as a second output. The first output and the second output are mixed and then pass through the first collimating lens as the output of the nonlinear frequency conversion module.

[0012] A third solution of the nonlinear frequency conversion module, the nonlinear frequency conversion module comprises a second focusing lens, a third crystal group, a second collimating lens, and a filter which are arranged in sequence.

[0013] Specifically, the crystal is a periodically polarized KTP crystal, and vertically polarized light and horizontally polarized light are focused at the center of the crystal from two opposite directions of the crystal respectively.

[0014] Definition of the angular momentum module, the angular momentum module includes a second polarization beam splitter, a second reflector, a third reflector, a vortex phase plate, and a fourth reflector. The light beam input to the angular momentum module is divided into horizontal polarized light and vertical polarized light by the second polarization beam splitter. The horizontal polarized light passes through the second reflector, the third reflector, the vortex phase plate, and the fourth reflector in sequence, and then is output through the second polarization beam splitter; the vertical polarized light passes through the fourth reflector, the vortex phase plate, the third reflector, and the second reflector in sequence, and then enters the second polarization beam splitter for output. The two light beams output by the second polarization beam splitter are mixed as the output light beam of the angular momentum module.

[0015] Definition of the first measurement module: a first measurement module is also arranged between the angular momentum module and the nonlinear frequency conversion module, the first measurement module includes a third quarter wave plate, a fifth reflector, a fourth quarter wave plate, a sixth reflector, and a first CCD element, the third quarter wave plate, the fifth reflector, and the fourth quarter wave plate are sequentially arranged on the optical path between the angular momentum module and the nonlinear frequency conversion module, and the light reflected by the fifth reflector is reflected onto the first CCD element through the sixth reflector.

[0016] Definition of the second measurement module: the output end of the nonlinear frequency conversion module is further provided with a second measurement module, and the second measurement module comprises a fifth quarter wave plate and a second CCD element which are arranged on the output optical path of the nonlinear frequency conversion module.

[0017] Definition of the light processing component: the light processing component includes a circularly polarized light acquisition module, and the circularly polarized light acquisition module includes a second half-wave plate and a second quarter-wave plate arranged in sequence.

[0018] Further limitation of the light processing component is that the light processing component also includes a light generating module and a light regulating module arranged in sequence at the front end of the circularly polarized light acquisition module, and the light regulating module includes a first half-wave plate, a first quarter-wave plate, and a first polarization beam splitter arranged in sequence along the light path.

[0019] The advantages of the present invention are:

[0020] (1) The present invention can realize the operation of vector light beams and nonlinear frequency conversion, and can be used to broaden the available frequency range of light beams. It has strong effectiveness and robustness, uses fewer optical components, is flexible to adjust, and has strong application prospects. The device can realize the frequency doubling operation of vector light beams, and the device is also applicable to other second-order nonlinear processes, such as sum-frequency and difference-frequency conversion processes, and can be extended to the quantum state of single photons.

[0021] (2) The nonlinear frequency conversion module can double the frequency of vector beams, but it requires that the pumped vector beams be first converted into exponentially mixed polarized vector beams by the angular momentum module. The device can obtain vector beams with arbitrary polarization distribution by operating and nonlinearly converting vector beams with different topological charges.

[0022] (3) This application discloses three schemes of nonlinear frequency conversion modules, all of which can realize the function of nonlinear frequency conversion.

[0023] (4) The angular momentum module adds orbital angular momentum to the input circularly polarized light beam, and then outputs a light beam with a superposition state of polarization and orbital angular momentum.

[0024] (5) The second measurement module detects and records the light beam after the nonlinear frequency conversion.

[0025] (6) The function of the first measurement module is to ensure that the light beam input by the nonlinear frequency conversion module meets the requirements. If the requirements are not met, the relevant parameters of the light processing component and the angular momentum module can be adjusted.

[0026] (7) The light processing component converts the linearly polarized light generated by the light generating module into circularly polarized light, wherein the light regulating module controls the intensity and polarization angle of the linearly polarized light. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a modular connection diagram of the present invention.

[0028] Figure 2 This is a structural diagram of the light generation module.

[0029] Figure 3 This is a structural diagram of the light adjustment module.

[0030] Figure 4 This is a structural diagram of the circularly polarized light acquisition module.

[0031] Figure 5 This is the structural diagram of the angular momentum module.

[0032] Figure 6 This is a structural diagram of the first detection module.

[0033] Figure 7 This is the structural diagram of the first solution of the nonlinear frequency conversion module.

[0034] Figure 8 This is the structural diagram of the second solution of the nonlinear frequency conversion module.

[0035] Fig. 9 This is the structural diagram of the third solution of the nonlinear frequency conversion module.

[0036] Fig.10 It is a structural diagram of the second detection module.

[0037] The meanings of the symbols in the figure are as follows:

[0038] 1-Light processing components

[0039] 111- semiconductor laser 112- first half-wave plate 113- first quarter-wave plate

[0040] 12- first polarization beam splitter 13- first reflector

[0041] 141-second half-wave plate 142-second quarter-wave plate

[0042] 2- angular momentum module 21- second polarization beam splitter 22- second reflector 23- third reflector

[0043] 24- vortex phase plate 25- fourth reflector

[0044] 3-first measurement module 31-third quarter wave plate 32-fifth reflector

[0045] 33- fourth quarter wave plate 34- sixth reflector 35- first horizontal polarizer

[0046] 36-First CCD element

[0047] 4- nonlinear frequency conversion module 411- first dichroic mirror 412- third polarization beam splitter

[0048] 413-first two-color half-wave plate 414-first polished reflector 415-first crystal

[0049] 416-Second polished mirror

[0050] 421-first focusing lens 422-second dichroic mirror 423-fourth dichroic polarization beam splitter

[0051] 424-second two-color half-wave plate 425-seventh reflector 426-second crystal

[0052] 427-eighth reflector 428-first collimating lens

[0053] 431 - second focusing lens 432 - third crystal group 433 - second collimating lens

[0054] 434-Filter

[0055] 5- second measurement module 51- ninth reflector 52- fifth quarter wave plate

[0056] 53- second horizontal polarizing plate 54- second CCD element DETAILED DESCRIPTION

[0057] like Figure 1 As shown, a nonlinear frequency conversion device based on vector beams includes

[0058] A light processing component 1, used for processing the seed light into circularly polarized light;

[0059] Angular momentum module 2, used to increase orbital angular momentum of input circularly polarized light, and then output a beam with both polarization and orbital angular momentum superposition state

[0060] The nonlinear frequency conversion module 4 is used to perform nonlinear frequency conversion on the input light beam, and then output the light beam after the nonlinear frequency conversion.

[0061] The first measurement module 3 is arranged between the angular momentum module 2 and the nonlinear frequency conversion module 4, and is used to measure the light beam output by the angular momentum module 2. If the monitoring results cannot meet the requirements of the subsequent optical path system, the relevant parameters of the optical processing component 1 can be adjusted to make the light beam Can meet the requirements of subsequent optical path systems;

[0062] The second measurement module 5 is arranged at the output end of the nonlinear frequency conversion module 4 and is used to detect and record the light beam after the nonlinear frequency conversion.

[0063] The following is a detailed description of each module:

[0064] Specifically, the light processing assembly 1 includes a light generating module, a light regulating module, and a circularly polarized light acquiring module which are arranged in sequence. The specific description is as follows:

[0065] 11. Light generating module

[0066] like Figure 2 As shown, the optical generation module includes a semiconductor laser 111, which is a continuous laser amplified by a semiconductor seed light through a fiber amplifier, and provides an initial light beam for the entire system. The central wavelength of the seed light is 1560nm, the line width is less than 10MHz, and the output power after the amplifier is greater than 1W, and the line width is less than 100MHz.

[0067] 12. Light adjustment module

[0068] like Figure 3 As shown, the light adjustment module includes a first half-wave plate 112, a first quarter-wave plate 113, and a first polarization beam splitter 12 arranged in sequence along the optical path. The first half-wave plate 112 and the first quarter-wave plate 113 work together to control and adjust the intensity of the input laser, and the working wavelength is 1560nm. The first polarization beam splitter 12 is used to obtain a horizontally polarized light beam. The first polarization beam splitter 12 reflects and refracts the light multiple times. The vertical polarized light separated by the first polarization beam splitter 12 is emitted in the vertical direction, and the horizontal polarized light separated is transmitted in the horizontal direction to form It can be expressed by the following formula:

[0069]

[0070] In this embodiment, the first reflector 13 reflects the horizontally polarized light The light is reflected into the circularly polarized light acquisition module, and the coating parameters of the first reflector 13 are HR@1560nm and 45° incidence.

[0071] 13.Circularly polarized light acquisition module

[0072] like Figure 4 As shown, the circular polarization acquisition module includes a second half-wave plate 141 and a second quarter-wave plate 142 arranged in sequence. The working wavelength of the second half-wave plate 141 is 1560nm, and its fast axis is set to be aligned with the horizontal polarization light. The polarization direction angle is α, and different α values ​​can be obtained by rotating and adjusting the second half-wave plate 141. Its effect on the light beam can be expressed by the following formula:

[0073]

[0074] The second quarter wave plate 142 has an operating wavelength of 1560 nm and its fast axis is set to align with the horizontal polarized light. The polarization direction angle is -π / 4, which can convert the polarized light emitted from the second half-wave plate 141 into circularly polarized light. Its effect on the light beam can be expressed by the following formula:

[0075]

[0076] 2. Angular momentum module 2

[0077] like Figure 5 As shown, the angular momentum module 2 includes a second polarization beam splitter 21, a second reflector 22, a third reflector 23, a vortex phase plate 24, and a fourth reflector 25. The surface of the second polarization beam splitter 21 is coated with AR@1560nm, and the incidence is 0°. It is used to separate circularly polarized light into horizontally polarized light and vertically polarized light, wherein the horizontally polarized light is transmitted along the propagation direction of the original optical path, and then reflected to the vortex phase plate 24 by the second reflector 22 and the third reflector 23. The vertically polarized light is folded 90 degrees compared with the original optical path, and is reflected to the vortex phase plate 24 by the fourth reflector 25.

[0078] The working wavelength of the vortex phase plate 24 is 1560nm. The light beam passing through the vortex phase plate 24 will be added with orbital angular momentum, and the horizontally polarized light will be added with orbital angular momentum. Orbital angular momentum is added to vertically polarized light The horizontally polarized light with increased orbital angular momentum is reflected back to the second polarization beam splitter 21 via the fourth reflector 25, and is transmitted from the second polarization beam splitter 21. The vertically polarized light with increased orbital angular momentum is reflected back to the second polarization beam splitter 21 via the third reflector 23 and the second reflector 22, and is turned 90 degrees in the second polarization beam splitter 21, and then emitted therefrom. It should be pointed out that the vortex phase plate 24 needs to be placed in the middle of the annular structure composed of all components of the angular momentum module 2, specifically, between the third reflector 23 and the fourth reflector 25, so as to ensure that the light field at the output end of the annular structure contains both and

[0079] The surfaces of the second reflector 22 , the third reflector 23 , and the fourth reflector 25 are all coated with HR@1560nm film, and their functions are all to fold the light path.

[0080] The horizontal polarized light with increased orbital angular momentum and the vertical polarized light with increased orbital angular momentum are superimposed into a mixed light after being emitted from the second polarization beam splitter 21. The combined effect of the second polarization beam splitter 21, the second reflector 22, the third reflector 23, the vortex phase plate 24, and the fourth reflector 25 on the light beam can be accurately described by the following matrix:

[0081]

[0082] Wherein, Δ1 is the phase difference formed by the mirror reflection and the double refraction of the second polarization beam splitter 21 in the loop. l is the topological charge, which is an integer and is determined by the characteristics of the vortex phase plate 24.

[0083] Overlay Mixed Light The superposition mode, which includes the beam polarization and orbital angular momentum, can be expressed as:

[0084]

[0085] 3. First measurement module 3

[0086] like Figure 6 As shown, the first measurement module 3 includes a third quarter wave plate 31, a fifth reflector 32, a fourth quarter wave plate 33, a sixth reflector 34, and a first CCD element 36. The third quarter wave plate 31, the fifth reflector 32, and the fourth quarter wave plate 33 are sequentially arranged on the optical path between the angular momentum module 2 and the nonlinear frequency conversion module 4. The light reflected by the fifth reflector 32 is reflected onto the first CCD element 36 through the sixth reflector 34.

[0087] The working wavelength of the third quarter wave plate 31 is 1560nm, and the angle between its fast axis and the polarization direction of the horizontal polarized light is set to π / 4. Its effect on the light beam is expressed by the following formula:

[0088]

[0089] Overlay Mixed Light After reaching the third quarter wave plate 31, it becomes linearly polarized light with orbital angular momentum The light is then deflected by the fifth reflector 32 and the sixth reflector 34 and reaches the first CCD element 36. It can be expressed as follows:

[0090]

[0091] Wherein, θ=2(α+Δ1 / 4).

[0092] The first CCD element 36 has an operating band of 1.5 μm. First, it records the state 1 of the light beam. Then, after placing the first horizontal polarizer 35 in front of the first CCD element 36, it records the state 2 of the light beam. State 1 and state 2 reflect the state of the light beam before nonlinear frequency conversion. The working wavelength of the first horizontal polarizer 35 is 1560nm.

[0093] The fifth reflector 32 and the sixth reflector 34 are coated with HR@1560nm and the incident angle is 45°. They are used to fold the light path. After the first CCD element 36 records state 1 and state 2, the fifth reflector 32 will be removed. As a pump beam enters the nonlinear frequency conversion process.

[0094] The working wavelength of the fourth quarter wave plate is 1560nm, and the angle between its fast axis and the polarization direction of the horizontal polarized light is set to -π / 4. Its function is to convert the pump beam Restore

[0095] If the monitoring results (state 1 and state 2 of the light beam) cannot meet the requirements of the subsequent optical path system, the relevant parameters of the light processing component 1 can be adjusted to make the light beam The requirements of the subsequent optical path system can be met, and then the light beam is output from the angular momentum module 2.

[0096] 4.1. Nonlinear frequency conversion module 4 The first solution

[0097] like Figure 7As shown, the nonlinear frequency conversion module 4 includes a first dichroic mirror 411, a third polarization beam splitter 412, a first dichroic half-wave plate 413, a first crystal 415, and a first parabolic reflector and a second parabolic reflector 416 symmetrically arranged on both sides of the first crystal 415; the input light beam passes through the first dichroic mirror 411 and enters the third polarization beam splitter 412, and the third polarization beam splitter 412 separates the horizontal polarized light and the vertical polarized light, and the horizontal polarized light passes through the first dichroic half-wave plate 413, the first polished surface reflector 414, the first crystal 415, the second polished surface reflector 416, and the third polarization beam splitter 412 in sequence; the vertical polarized light passes through the second polished surface reflector 416, the first crystal 415, the first polished surface reflector 414, the first dichroic half-wave plate 413, and the third polarization beam splitter 412 in sequence, and the horizontal polarized light and the vertical polarized light are output by the third polarization beam splitter 412 and then merged to form a beam of nonlinear frequency conversion.

[0098] The first dichroic mirror 411 is coated with AR@1560nm on the incident surface corresponding to the light beam of the nonlinear frequency conversion module 4, and AR@1560nm, HR@780nm on the exit surface, with an incident angle of 45°. It can be smoothly transmitted through. And the frequency-doubled light beam after nonlinear frequency conversion will be deflected after reaching its surface and output from the nonlinear frequency conversion module 4.

[0099] The surface coating of the third polarization beam splitter 412 is AR@1560nm, AR@780nm, and the incident angle is 0°. Its function is to It is divided into horizontal polarized light and vertical polarized light. The horizontal polarized light is transmitted from the horizontal direction, and the vertical polarized light is folded 90° and emitted. Another function is to transmit the frequency-doubled horizontal polarized light from the horizontal direction, and the frequency-doubled vertical polarized light is folded 90° and emitted. The two are then emitted to form a mixed light after frequency doubling.

[0100] The λ / 2 of the first two-color half-wave plate 413 is @1560nm & 780nm, and the angle between its fast axis and the polarization direction of the horizontal polarized light is π / 4. Its first function is to convert the pumped horizontal polarized light into vertical polarized light. Its second function is to convert the frequency-doubled vertical polarized light into horizontal polarized light.

[0101] The first polished reflector 414 has a size of 1 inch, an off-axis angle of 45°, a focal length of 101.6 mm, and a silver-coated film to focus the pump beam at the center of the first crystal 415. It is worth noting that the above parameters are applicable to this embodiment. In other similar embodiments, these parameters will be adapted and adjusted, but they all fall within the protection scope of the present invention.

[0102] The first crystal 415 is a periodically polarized KTP crystal, specifically PPKTP, Type-0 (ZZZ) phase matching, with a geometric size of 1mm×2mm×8mm, a polarization period of 25.01μm, and a phase matching temperature of 45°C. It is only sensitive to vertically polarized light. After being acted upon, the relationship between the generated frequency-doubled beam and the pump beam can be expressed by the following formula:

[0103] E 2ω ∝(E ω ) 2

[0104] The comprehensive effect of the nonlinear frequency conversion module 4 on the polarization state of the light beam can be expressed by the following formula:

[0105]

[0106] Wherein, Δ2 is the phase difference mainly caused by the asymmetry of the first crystal 415 in the above nonlinear frequency conversion module 4 .

[0107] Taking the frequency doubling effect of the first crystal 415 into consideration, the overall process can be approximately expressed by the following formula:

[0108] E 2ω ∝T(E ω ) 2

[0109] The frequency-doubled light beams generated above are combined by the third polarization beam splitter 412 , reflected by the first dichroic mirror 411 , and then output from the nonlinear frequency conversion module 4 .

[0110] 4.2. Nonlinear frequency conversion module 4 Second solution

[0111] like Figure 8 As shown, the nonlinear frequency conversion module 4 includes a first focusing lens 421, a second dichroic mirror 422, a fourth dichroic polarization beam splitter 423, a second dichroic half-wave plate 424, a seventh reflector 425, a second crystal 426, an eighth reflector 427, and a first collimating lens 428. The input light beam passes through the first focusing lens 421, the second dichroic mirror 422, and the fourth dichroic polarization beam splitter 423 in sequence and is divided into horizontal polarized light and vertical polarized light. The horizontal polarized light passes through the second dichroic half-wave plate 424, the seventh reflector 425, the second crystal 426, the eighth reflector 427, and the fourth dichroic polarization beam splitter 423 in sequence and is output as a first path. The vertical polarized light passes through the eighth reflector 427, the second crystal 426, the seventh reflector 425, the second dichroic half-wave plate 424, and the fourth dichroic polarization beam splitter 423 in sequence and is output as a second path. The first path output and the second path output are mixed and then pass through the first collimating lens 428 as the output of the nonlinear frequency conversion module 4.

[0112] The surface of the first focusing lens 421 is coated with AR@1560nm and has a focal length of f1@1560nm. Its function is to focus the incident light beam at the center of the second crystal 426 .

[0113] The second dichroic mirror 422 is coated with AR@1560nm on the incident surface corresponding to the light beam entering the nonlinear frequency conversion module 4, and AR@1560nm, HR@780nm on the exit surface, with an incident angle of 45°. It can be smoothly transmitted through, and the frequency-doubled light beam after nonlinear frequency conversion is deflected after reaching its surface and enters the first collimating lens 428 .

[0114] The surface coating of the fourth two-color polarization beam splitter 423 is AR@1560nm, AR@780nm, and the incident angle is 0°. It is divided into horizontal polarized light and vertical polarized light. The horizontal polarized light is transmitted from the horizontal direction, and the vertical polarized light is folded 90° and emitted. Its second function is to transmit the frequency-doubled horizontal polarized light from the horizontal direction, and the frequency-doubled vertical polarized light is folded 90° and emitted. The two are then emitted to form a mixed light after frequency doubling.

[0115] The λ / 2 of the second two-color half-wave plate 424 is @1560nm & 780nm, and the angle between its fast axis and the polarization direction of the horizontal polarized light is π / 4. Its first function is to convert the horizontally polarized light of the pump into vertically polarized light. Its second function is to convert the vertically polarized light after frequency doubling into horizontally polarized light.

[0116] The surface of the seventh reflector 425 is coated with HR@1560nm and HR@780nm, and its function is to refract the light path.

[0117] The second crystal 426 is a periodically polarized KTP crystal, specifically PPKTP, Type-0 (ZZZ) phase matching, with a geometric size of 1mm×2mm×8mm, a polarization period of 25.01μm, and a phase matching temperature of 45°C. It is only sensitive to vertically polarized light. After its action, the relationship between the generated frequency-doubled beam and the pump beam can be expressed by the following formula:

[0118] E 2ω ∝(E ω ) 2

[0119] The surfaces of the eighth reflector 427 are coated with HR@1560nm and HR@780nm, and their function is to refract the light path.

[0120] The surface of the first focusing lens 421 is coated with AR@780nm, the focal length is f2@780nm, f2=f1, and its function is to collimate the converged light beam.

[0121] The comprehensive effect of the nonlinear frequency conversion module 4 on the polarization state of the light beam can be expressed by the following formula:

[0122]

[0123] Here, Δ2 is the phase difference in the above loop caused mainly by the asymmetry of the crystal.

[0124] Taking the frequency doubling effect of the second crystal 426 into consideration, the overall process can be approximately expressed by the following formula:

[0125] E 2ω ∝T(E ω ) 2

[0126] The frequency-doubled light beams generated above are combined by the fourth two-color polarization beam splitter 423 , reflected by the second dichroic mirror 422 , collimated by the first collimating lens 428 , and output from the nonlinear frequency conversion module 4 .

[0127] 4.3. Nonlinear frequency conversion module 4 The third solution

[0128] like Fig. 9 As shown, the nonlinear frequency conversion module 4 includes a second focusing lens 431 , a third crystal group 432 , a second collimating lens 433 , and a filter 434 which are arranged in sequence.

[0129] The surface coating of the second focusing lens 431 is AR@1560nm, and the focal length is f1@1560nm. The function of the second focusing lens 431 is to focus the incident light beam at the center of the third crystal group 432 .

[0130] The third crystal group 432 is composed of two identical periodically polarized KTP crystals. The second periodically polarized KTP crystal is rotated 90° relative to the first periodically polarized KTP crystal, and the angle between the optical axes of the two is 90°. The parameters of the two periodically polarized KTP crystals are: Type-0 (ZZZ) phase matching, geometric dimensions of 1mm×2mm×8mm, polarization period of 25.01μm, phase matching temperature of 45°C, and they are only sensitive to vertically polarized light. After its action, the relationship between the generated frequency-doubled beam and the pump beam can be expressed by the following formula:

[0131] E 2ω ∝T(E ω ) 2

[0132] The surface coating of the second collimating lens 433 is AR@780nm, the focal length is f2@780nm, f2=f1, and its function is to collimate the converged light beam.

[0133] The surface of the filter 434 is coated with HR@1560nm and AR@780nm, and its function is to filter out the light that has not been nonlinearly converted, while the light beam that has been nonlinearly converted can pass smoothly.

[0134] The comprehensive effect of the nonlinear frequency conversion module 4 on the polarization state of the light beam can be expressed by the following formula:

[0135]

[0136] Here, Δ2 is the phase difference in the above loop caused mainly by the asymmetry of the crystal.

[0137] Taking the frequency doubling effect of the third crystal group 432 into consideration, the overall process can be approximately expressed by the following formula:

[0138] E 2ω ∝T(E ω ) 2

[0139] The frequency-doubled light beam generated above passes through the second collimating lens 433 and the filter 434 and is output from the nonlinear frequency conversion module 4 .

[0140] 5. Second measurement module 5

[0141] like Fig.10 As shown, the second measuring module 5 includes a ninth reflector 51 , a fifth quarter wave plate 52 , a second horizontal polarizing plate 53 , and a second CCD element 54 , which are arranged on the output light path of the nonlinear frequency conversion module 4 .

[0142] The surface coating of the ninth reflector 51 is HR@780nm, and the incident angle is 45°. The function of the ninth reflector 51 is to fold the light path and fold the frequency-doubled light beam to the fifth quarter-wave plate 52 .

[0143] The λ / 4 of the fifth quarter wave plate 52 is @780nm, and the angle between its fast axis and the polarization direction of the horizontal polarized light is set to π / 4. Its effect on the light beam can be expressed as:

[0144]

[0145] The frequency-doubled light beam after being acted upon by the fifth quarter-wave plate 52 reaches the second CCD element 54, which By comparison, the frequency is doubled, which can be expressed as:

[0146]

[0147] Among them, Θ=4α+Δ1+Δ2 / 2-π / 4

[0148] The working wavelength of the second CCD element 54 is 780nm, and the working wavelength of the second horizontal polarizer 53 is 780nm, which can filter out the light with other polarization directions and only allow the light with horizontal polarization direction to pass.

[0149] The second CCD element 54 will record the frequency-doubled beam Then, a second horizontal polarizer 53 is placed in front of the second CCD element 54 to record the state 4 of the light beam. State 3 and state 4 reflect the light beam after frequency doubling (nonlinear frequency conversion). Characteristics, state 4 is the result of projection measurement in the horizontal polarization direction.

[0150] At present, the bottleneck of many research status is to directly convert the above Direct frequency doubling, this operation cannot obtain the ideal frequency doubling speed of light, the theoretical analysis is as follows:

[0151] Will The theoretical expression of direct frequency doubling is as follows:

[0152]

[0153] In the above equation, the constant term 1 / 2 represents a Gaussian beam, and the other term represents an orbital angular momentum beam superimposed by linear polarization, which is not the desired result.

[0154] By using the device of the present invention, before frequency doubling the vector beam, the pump vector beam can be first converted into an exponential mixed polarization vector beam. The frequency-doubled beam obtained in this way is as described above. As shown, it is compared to, In addition to the vector beam frequency-doubled component (l→2l), it also has a Gaussian mode without topological charge. It is not an ideal vector beam, so an ideal frequency-doubled vector beam can be obtained through this device.

[0155] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A nonlinear frequency conversion device based on vector beam, characterized in that: include A light processing component (1) is used to process the seed light into circularly polarized light; The angular momentum module (2) is used to increase the orbital angular momentum of the input circularly polarized light, and then output a light beam having a superposition state of polarization and orbital angular momentum. A nonlinear frequency conversion module (4) is used to convert the input light beam Performing nonlinear frequency conversion and then outputting a light beam after nonlinear frequency conversion; The angular momentum module (2) comprises a second polarization beam splitter (21), a second reflector (22), a third reflector (23), a vortex phase plate (24), and a fourth reflector (25); a light beam input into the angular momentum module (2) is split into horizontal polarization light and vertical polarization light by the second polarization beam splitter (21); the horizontal polarization light sequentially passes through the second reflector (22), the third reflector (23), the vortex phase plate (24), and the fourth reflector (25), and then is output by the second polarization beam splitter (21); the vertical polarization light sequentially passes through the fourth reflector (25), the vortex phase plate (24), the third reflector (23), and the second reflector (22), and then enters the second polarization beam splitter (21) for output; the two light beams output by the second polarization beam splitter (21) are mixed and used as the output light beam of the angular momentum module (2); The output end of the nonlinear frequency conversion module (4) is also provided with a second measurement module (5), and the second measurement module (5) comprises a fifth quarter-wave plate (52) and a second CCD element (54) arranged on the output light path of the nonlinear frequency conversion module (4).

2. The nonlinear frequency conversion device based on vector beam according to claim 1, characterized in that: The nonlinear frequency conversion module (4) comprises a first dichroic mirror (411), a third polarization beam splitter (412), a first two-color half-wave plate (413), a first crystal (415), and a first parabolic reflector and a second parabolic reflector symmetrically arranged on both sides of the first crystal (415); the input light beam passes through the first dichroic mirror (411) and enters the third polarization beam splitter (412); the third polarization beam splitter (412) generates horizontal polarized light and vertical polarized light, and the horizontal polarized light passes through the first dichroic mirror in sequence. A half-wave plate (413), a first polished surface reflector (414), a first crystal (415), a second polished surface reflector (416), and a third polarization beam splitter (412); the vertically polarized light sequentially passes through the second polished surface reflector (416), the first crystal (415), the first polished surface reflector (414), the first dichroic half-wave plate (413), and the third polarization beam splitter (412); the horizontally polarized light and the vertically polarized light are outputted by the third polarization beam splitter (412) and then merged to form a light beam with nonlinear frequency conversion.

3. The nonlinear frequency conversion device based on vector beam according to claim 1, characterized in that: The nonlinear frequency conversion module (4) comprises a first focusing lens (421), a second dichroic mirror (422), a fourth dichroic polarization beam splitter (423), a second dichroic half-wave plate (424), a seventh reflector (425), a second crystal (426), an eighth reflector (427), and a first collimating lens (428). The input light beam passes through the first focusing lens (421), the second dichroic mirror (422), and the fourth dichroic polarization beam splitter (423) in sequence and is then divided into horizontally polarized light and vertically polarized light. The horizontally polarized light passes through the second dichroic mirror in sequence. The half-wave plate (424), the seventh reflector (425), the second crystal (426), the eighth reflector (427), and the fourth two-color polarization beam splitter (423) are used as the first output; the vertical polarized light sequentially passes through the eighth reflector (427), the second crystal (426), the seventh reflector (425), the second two-color half-wave plate (424), and the fourth two-color polarization beam splitter (423) as the second output; the first output and the second output are mixed and then pass through the first collimating lens (428) as the output of the nonlinear frequency conversion module (4).

4. The nonlinear frequency conversion device based on vector beam according to claim 1, characterized in that: The nonlinear frequency conversion module (4) comprises a second focusing lens (431), a third crystal group (432), a second collimating lens (433), and a filter (434) which are arranged in sequence.

5. A nonlinear frequency conversion device based on a vector beam according to any one of claims 2 to 4, characterized in that: The crystal is a periodically polarized KTP crystal, and vertically polarized light and horizontally polarized light are focused at the center of the crystal from two opposite directions of the crystal respectively.

6. The nonlinear frequency conversion device based on vector beam according to claim 1, characterized in that: A first measurement module (3) is also arranged between the angular momentum module (2) and the nonlinear frequency conversion module (4); the first measurement module (3) comprises a third quarter wave plate (31), a fifth reflector (32), a fourth quarter wave plate (33), a sixth reflector (34), and a first CCD element (36); the third quarter wave plate (31), the fifth reflector (32), and the fourth quarter wave plate (33) are arranged in sequence on an optical path between the angular momentum module (2) and the nonlinear frequency conversion module (4); and the light reflected by the fifth reflector (32) is reflected onto the first CCD element (36) via the sixth reflector (34).

7. The nonlinear frequency conversion device based on vector beam according to claim 1, characterized in that: The light processing component (1) comprises a circularly polarized light acquisition module, and the circularly polarized light acquisition module comprises a second half-wave plate (141) and a second quarter-wave plate (142) which are arranged in sequence.

8. The nonlinear frequency conversion device based on vector beam according to claim 7, characterized in that: The light processing component (1) also includes a light generating module and a light regulating module arranged in sequence at the front end of the circularly polarized light acquisition module, and the light regulating module includes a first half-wave plate (112), a first quarter-wave plate (113), and a first polarization beam splitter (12) arranged in sequence along the light path.

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