CN107085309B - Method for generating various high-power column vector polarized light beams based on spiral wave plate - Google Patents

Method for generating various high-power column vector polarized light beams based on spiral wave plate Download PDF

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CN107085309B
CN107085309B CN201710304877.3A CN201710304877A CN107085309B CN 107085309 B CN107085309 B CN 107085309B CN 201710304877 A CN201710304877 A CN 201710304877A CN 107085309 B CN107085309 B CN 107085309B
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wave plate
lambda
plate
polarized light
spiral
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CN107085309A (en
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祁俊力
汪卫华
张辉
潘保国
杨锦宏
邓海飞
周先院
范炯
单会会
张连庆
史博
芦伟
王辉
杜昂
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COLLEGE OF CHINESE PEOPLE'S LIBERATION ARMY OFFICER ACADEMY
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    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/28—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for polarising
    • G02B27/286—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for polarising for controlling or changing the state of polarisation, e.g. transforming one polarisation state into another

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Abstract

The invention discloses a method for generating various high-power column vector polarized light beams based on a spiral wave plate, which is characterized in that high-power linearly polarized light in any polarization direction enters, the polarization direction of the linearly polarized light can be adjusted by rotating a lambda/2 wave plate, the linearly polarized light can become horizontal linearly polarized light through a horizontal analyzer, the horizontal linearly polarized light is amplified through a lens group, the horizontal linearly polarized light sequentially passes through a first lambda/4 wave plate, the spiral wave plate and a second lambda/4 wave plate to generate column vector polarized light beams, and the space phase compensation is realized through a spiral phase plate to generate synchronous column vector polarized light. And finally, the light beam is enlarged or reduced according to actual requirements through a light beam scaler. The invention realizes polarization state control by utilizing the combination of the wave plate and the spiral wave plate, has high damage threshold, can realize high-power column vector polarized light, can generate various light beams by simply rotating the wave plate, and has simple structure, easy operation and control and high stability.

Description

Method for generating various high-power column vector polarized light beams based on spiral wave plate
Technical Field
The invention relates to the technical field of space polarized beam shaping, in particular to a method for generating various high-power column vector polarized beams based on a spiral wave plate, which converts high-power linearly polarized beams into high-power column vector polarized beams, such as: radial polarized light, angular polarized light, phase-variable cylindrical vector polarized light beams, high-order cylindrical vector polarized light beams, vortex light beams and the like.
Background
Cylindrical vector polarized light is a special vector polarized light whose spatial polarization state distribution is not uniform but has a certain symmetry or similarity with respect to the optical axis. The axial-symmetric light beam belongs to one of cylindrical vector polarized light, including radial polarized light, angular polarized light and the like, and has unique optical characteristics and applications because the polarization and the phase are axially symmetrically distributed on the cross section of the light beam. In addition, a cylindrical symmetric light beam with adjustable phase, such as a radial polarization vortex light beam, a high-order radial polarized light beam with cylindrical symmetry or the like, and the like, have a plurality of special optical characteristics and applications due to special spatial polarization and phase distribution. A vortex beam is a beam with a helical phase distribution, expressed with a phase factor exp (il θ), each photon in the beam carrying
Figure BDA0001285345820000011
The orbital angular momentum of (a), wherein l is called topological charge, has the characteristic of hollowness, and plays an important role in the fields of optical micro-manipulation, biomedicine, information transmission and the like due to the special spatial phase distribution of the orbital angular momentum. Radial polarized light is taken as an example. The radial polarized light has perfect axisymmetric distribution and has significantly different characteristics compared with linearly polarized light and circularly polarized light. For example, radially polarized light has an electric field distribution that is symmetrical along the optical axis andan empty annular beam structure; the radial polarized light and the angular polarized light are both in polarization eigenstates, and crosstalk cannot occur when the light is transmitted in the C tangential crystal; when the high-numerical-aperture lens is focused, the radial polarized light can generate an extremely small focus exceeding the diffraction limit, the focus is much smaller than the focus points of linearly polarized light and circularly polarized light, and the longitudinal electric field of the focus area becomes very strong. So that it has advantages in drawing, capturing and accelerating metal particles, cutting metals, improving optical storage density and longitudinal resolution, etc.
The cylindrical vector polarized light and the vortex light beam have unique optical characteristics and great application potential. Because the generation of the column vector polarized light and the vortex light beam is difficult, most of domestic research is carried out by adopting a theoretical analysis method, and the research on the optical characteristics is insufficient and the application is limited because few experimental researches are carried out.
Foreign countries, the research on the generation method of radial polarized light is relatively more, and the method is mainly divided into two categories: i.e., intracavity (active) and external conversion (extracavity, passive). The intracavity method is that radial polarized light is directly generated in a laser, the structure of the laser needs to be correspondingly adjusted, and the intracavity method relates to a gain medium. The current intracavity method generally produces radial polarized light with the following types: the method comprises the steps of generating radial polarized light by utilizing crystal axis birefringence, generating radial polarized light by utilizing crystal dichroism, generating radial polarized light by utilizing crystal Brewster angle characteristics and generating radial polarized light by utilizing an interference method. However, it is not always feasible to place a special device in the cavity, since the redesign of existing lasers is a very complicated technique and its space is limited.
The external conversion method is to convert spatially uniform polarized light into radial polarized light by a certain phase device or by a decomposition and re-synthesis method outside a laser, and has great design flexibility but relatively low utilization efficiency because the laser does not need to be modified. Common external transformation methods are: the method comprises the steps of generating radial polarized light by a coherent polarization manipulation method, generating approximate radial polarized light by a block wave plate or an optical rotation crystal, generating radial polarized light by a spatial light modulator, generating radial polarized light by an optical fiber and the like.
Although the coherent polarization manipulation method can generate radial polarized light with higher purity, the coherent polarization manipulation method has higher requirements on the stability and the precision control of an experimental light path and is complex to operate and control; the column vector polarized light generated by the conventional block wave plate or the optical rotation crystal has single type, relatively low purity and limited application effect; the radial polarized light energy generated by the spatial light modulator or the optical fiber is small and has limited application.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: the defects of the prior art are overcome, the high-power column vector polarized light beam is generated by utilizing the spiral wave plate, one spiral phase plate can be used for space phase compensation, a plurality of column vector polarized light beams can be generated by simply rotating the two lambda/4 wave plates, and the high-power column vector polarized light beam generating device has the characteristics of simple structure, easiness in operation and control, good practicability, capability of obtaining various high-purity light beams and the like.
The technical scheme of the invention is as follows: the method for generating various high-power column vector polarized light beams based on the spiral wave plate comprises the following steps:
s1, setting an incident beam which is linearly polarized light and has any polarization direction;
s2, setting and adjusting a lambda/2 wave plate to enable the optical axis of the light beam to pass through the center of the lambda/2 wave plate and be parallel to the normal line, wherein the lambda/2 wave plate can be replaced and the main shaft can rotate and be adjusted along the optical axis;
s3, arranging a horizontal analyzer which can be a polaroid or a polarizing prism, making the optical axis of the light beam pass through the center of the horizontal analyzer and be parallel to the normal, and making the polarization transmission direction of the light beam be horizontal and have high extinction ratio to the light beam of a certain wave band;
s4, arranging a lens group to realize the light beam amplification, wherein the amplification factor is related to the size of the wave plate;
s5, arranging and adjusting two lambda/4 wave plates to enable the optical axis of the light beam to pass through the center of the lambda/4 wave plates and to be parallel to the normal line, wherein the lambda/4 wave plates can be replaced and the main shaft can rotate and be adjusted along the optical axis;
s6, arranging a spiral wave plate between two lambda/4 wave plates, wherein the whole spiral wave plate has the same fast axis, the fast axis direction is along the X-axis direction, the thickness of the spiral wave plate gradually changes along with the rotation angle clockwise, and the optical axis of the light beam passes through the center of the spiral wave plate and is parallel to the normal of the substrate;
s7, setting the spiral phase plate with isotropy to generate spiral phase delay, the spiral direction is opposite to the spiral wave plate, namely, the spiral wave plate rotates anticlockwise, and the optical axis of the light beam passes through the center and is parallel to the normal of the substrate;
s8, amplifying or reducing the light beam through the light beam scaler according to the requirement;
s9, the rotation of the space polarization state is realized after the horizontal linear polarization light passes through the two lambda/4 wave plates and the spiral wave plate, the modulation of the space phase is realized after the space phase plate, the synchronous regulation of the space light beam phase and the space polarization state is realized by combining the two lambda/4 wave plates, the space phase and the polarization state are considered, when the two lambda/4 wave plates are rotated, different types of column vector polarized light can be generated, and when the fast axes of the two lambda/4 wave plates are in the horizontal or vertical direction, vortex light beams can be generated.
In step S1, the incident beam is set to use a high-power laser light source, and a linearly polarized light beam is obtained after passing through a polarizer or a polarization splitting prism, and the spectral width is less than ± 3nm, or a linearly polarized light source can be directly used.
In the steps S2 and S3, the λ/2 wave plate can be replaced and rotated, and is consistent with the central wavelength λ of the light source, so as to improve the application range, and the polarization direction of the incident light can be adjusted by rotating the λ/2 wave plate; the horizontal analyzer ensures that the emergent light beam is horizontally linearly polarized light, and the horizontal analyzer is combined with the lambda/2 wave plate, so that the light intensity of the light beam can be adjusted by rotating the lambda/2 wave plate.
In the steps S5 and S9, the two λ/4 wave plates can be replaced and rotated, and are consistent with the central wavelength λ of the light source, the fast axis of the first λ/4 wave plate is initially set to form an angle of-45 ° -135 ° with the X axis (i.e., along the horizontal right direction of the optical path perpendicular to the optical axis), and the fast axis of the second λ/4 wave plate forms an angle of 45 ° with the X axis, and the fast axis direction can be changed by rotating the two λ/4 wave plates as required, so as to generate different cylindrical vector polarized lights, for example, by respectively rotating the two λ/4 wave plates by 90 °, 4 different cylindrical vector polarized lights can be generated, and when the two λ/4 wave plates are rotated so that the fast axis is in the horizontal or vertical direction, a vortex light beam can be generated.
In step S6, the fast axis of the spiral wave plate is along the X direction, and the thickness h of the spiral wave plate gradually changes clockwise with the rotation angle θ
Figure BDA0001285345820000031
Wherein the substrate thickness h0M is an integer, X-axis forward direction θ is 0, λ is incident light wavelength, n ise，noThe two principal refractive indices of the wave plate crystal, the beam optic axis is perpendicular to and through the center of the spiral wave plate substrate. Because the continuous spiral gradual change wave plate is difficult to manufacture, the continuous spiral gradual change wave plate can be replaced by a block gradual change fan-shaped wave plate, and the thickness of the kth wave plate is the same as that of the kth wave plate under the assumption that N fan-shaped wave plates form a circle
Figure BDA0001285345820000032
Wherein, in the step S7, the phase retardation of the spiral phase plate
Figure BDA0001285345820000033
With respect to the rotation angle theta
Figure BDA0001285345820000034
That is, the phase is rotated counterclockwise, θ is 0 in the X-axis forward direction, and the phase can be realized by plating with various isotropic media having different thicknesses, such as SiN, H-K9L, fused silica JGS1, and the like, and assuming that the refractive index of the medium is n and the refractive index of air is 1, the change of the plating thickness with the forward index angle θ is
Figure BDA0001285345820000035
l0The thickness of the substrate can be directly made by the processes of reverse mould cutting, grinding and the like, and the optical axis of the light beam is vertical to the substrate of the spiral phase plate and passes through the center of the substrate. When the block gradual change fan-shaped wave plate is used, the corresponding block gradual change fan-shaped phase plate also has N blocks, and the coating thickness of the kth block
Figure BDA0001285345820000041
In the steps S2, S5, S6 and S7, the λ/2 wave plate, the two λ/4 wave plates, the helical wave plate and the helical phase plate can all bear high-power laser, and parameters can be changed according to the wavelength of incident light.
The principle of the invention is that a helical wave plate is arranged between two lambda/4 wave plates, so that the rotation of the polarization direction of linearly polarized light can be realized. The fast axis direction of the first lambda/4 wave plate forms 135 degrees (-45 degrees) with the x axis, the fast axis of the spiral wave plate is parallel to the x axis, the thickness h of the spiral wave plate is gradually changed along with the rotation angle theta clockwise
Figure BDA0001285345820000042
The fast axis of the second lambda/4 plate is oriented at 45 deg. to the x-axis. The Jones matrix of the first and second lambda/4-wave plates is J1And J2The helicon wave plate can generate a space phase delay 2 theta with J matrix0Respectively expressed as:
Figure BDA0001285345820000043
wherein i is a complex number. The jones matrix of the system can be expressed as:
Figure BDA0001285345820000044
jones matrix J12The input light theta may be rotated clockwise by an angle but accompanied by a wavefront integral phase delay theta. Therefore, the system can compensate the space phase through a spiral phase plate, and the phase delay amount of the spiral phase plate
Figure BDA0001285345820000045
With respect to the rotation angle theta
Figure BDA0001285345820000046
When the X axis is positive, theta is 0, namely anticlockwise rotation, the X axis can be realized by plating certain isotropic mediums with different thicknesses, the refractive index of the medium is n, and the air refraction is assumedThe ratio is 1, the change of the coating thickness with the angle is
Figure BDA0001285345820000047
When the two lambda/4 wave plates are rotated by 90 degrees at the same time, the Jones matrix of the system can be expressed as follows:
Figure BDA0001285345820000048
jones matrix J21The input light theta may be rotated counterclockwise by an angle but with an overall phase retardation theta of the wavefront, it may also be spatially phase compensated by the helical phase plate.
When the second λ/4 plate is rotated by 90 °, the first λ/4 plate remains unchanged, and the jones matrix of the system can be expressed as:
Figure BDA0001285345820000049
jones matrix J11The input light may be made to rotate symmetrically about the y-x axis and then rotate counterclockwise by an angle of θ, but with an overall wavefront phase retardation of θ + π/2, it may be spatially phase compensated by a spiral phase plate.
When the first λ/4 plate is rotated by 90 °, and the second λ/4 plate remains unchanged, the jones matrix of the system can be expressed as:
Figure BDA0001285345820000051
jones matrix J22The input light can be made to rotate symmetrically about the y-x axis and then rotate clockwise by an angle theta, but the input light can be subjected to spatial phase compensation through a spiral phase plate along with a wave front integral phase delay quantity theta-pi/2.
When the two lambda/4 wave plates are rotated at other different angles, the system can generate other column vector polarized light, and when the two lambda/4 wave plates are rotated to enable the fast axis to be in the horizontal or vertical direction, or the two lambda/4 wave plates are directly removed, the system can also generate vortex light beams.
By replacing the wave plate, the helical wave plate and the helical phase plate, the multi-band light beam can be controlled, and high-order column vector polarized light can be generated by newly designing the helical wave plate and the helical phase plate, for example, when the thickness of the helical wave plate meets the requirement
Figure BDA0001285345820000052
And the spiral phase plate satisfies
Figure BDA0001285345820000053
In addition, the starting point of the thickness variation of the spiral wave plate is different, and the polarization direction of the generated cylindrical vector polarized light is also different, for example, when the thickness of the spiral wave plate satisfies the requirement
Figure BDA0001285345820000054
The polarization direction of the cylindrical vector polarized light is rotated by theta0And (4) an angle.
Compared with the prior art, the invention has the advantages that:
(1) the spiral wave plate and the spiral phase plate can generate high-power light beams and have stable performance.
(2) Through simply rotating two lambda/4 wave plates, various column vector polarized lights including vortex light beams can be generated, and the device is simple in structure, easy to operate and control and strong in functionality.
(3) The control of multiband light beams can be realized by replacing the wave plate, the helical wave plate and the helical phase plate, and high-order column vector polarized light can be generated by newly designing the helical wave plate and the helical phase plate.
Drawings
Fig. 1 is a schematic diagram of an optical path principle of a beam generation system utilized by a method for generating a plurality of high-power column vector polarized beams based on a helical wave plate according to the present invention, in which 1 is a high-power laser, 2 is a λ/2 wave plate, 3 is a horizontal analyzer, 4 is a first lens, 5 is a second lens, 6 is a first λ/4 wave plate, 7 is a helical wave plate, 8 is a second λ/4 wave plate, 9 is a helical phase plate, 10 is a beam pantograph, and 11 is column vector polarized light;
FIG. 2 is a schematic diagram of a helical waveplate and a helical phase plate;
FIG. 3 is a schematic diagram of the polarization direction rotation principle, which is composed of two λ/4 wave plates and a helical wave plate;
FIG. 4 is a schematic view of some of the cylindrical vector polarized beams produced by rotating two λ/4 plates by 90 °;
FIG. 5 shows some of the column vector polarized beams experimentally generated by the present invention.
Detailed Description
The technical scheme of the invention is explained in detail by taking the specific embodiment of the invention as the accompanying drawing.
As shown in fig. 1, the beam generation system includes a high power laser 1, a λ/2 wave plate 2, a horizontal analyzer 3, a lens group (including a first lens 4 and a second lens 5), a first λ/4 wave plate 6, a helical wave plate 7, a second λ/4 wave plate 8, a helical phase plate 9, and a beam scaler 10. The dashed and solid lines in fig. 1 represent the left and right portions of the beam, representing the spatial beam variation. Linearly polarized light with any polarization direction enters, the polarization direction of the linearly polarized light is adjusted through the lambda/2 wave plate 2, a horizontally polarized light beam is ensured to be obtained through the horizontal analyzer 3, and the intensity of the light beam can be adjusted through the combination of the lambda/2 wave plate 2 and the horizontal analyzer 3. Then the light beam is amplified through a lens group, the horizontal line polarized light beam sequentially passes through a first lambda/4 wave plate 6, a spiral wave plate 7 and a second lambda/4 wave plate 8 to realize the control of the polarization state of the space light beam, then the space phase compensation is realized through the space phase modulation after passing through a spiral phase plate 9, and finally the column vector polarized light beam 11 suitable for the requirement is generated after passing through a light beam scaler 10.
As shown in fig. 1, 2 and 3, the method of the present invention is specifically realized as follows:
step 101 sets the incident beam. The incident beam is linearly polarized light and can be obtained by a linearly polarized light source, or an unpolarized light source is obtained by a polarizing film or a polarizing prism, the polarization direction can be any direction, and horizontal linearly polarized light and a spectral width smaller than +/-3 nm are preferably selected in experiments (such as high-power femtosecond pulse laser);
step 102 sets a lambda/2 wave plate 2. The light beam vertically passes through the center of the lambda/2 wave plate 2, the main shaft of the lambda/2 wave plate 2 rotates along the optical axis and can be adjusted, the direction and the rotation angle of the main shaft can be read, and when the wavelength of the light source changes, the wave plate is replaced;
step 103 sets the horizontal analyzer 3. The light beam vertically passes through the center of the horizontal analyzer 3, and the transmission direction of the light beam is the horizontal direction;
step 104 sets a lens group. The two lenses with different focal lengths form a beam amplifier, the focal length of the first lens 4 is small, the focal length of the second lens 5 is large, beam amplification is achieved, and the amplification factor is related to the size of the wave plate;
step 105, arranging two lambda/4 wave plates, enabling the optical axis of a light beam to pass through the center of the lambda/4 wave plate to be parallel to a normal line, enabling a lambda/4 wave plate main shaft to rotate along the optical axis to be adjustable, reading the direction and the rotation angle of the main shaft, and replacing the lambda/4 wave plate when the wavelength of a light source changes; the fast axis of the first lambda/4 wave plate 6 and the X axis (namely the fast axis perpendicular to the horizontal right direction of the optical axis along the light path) are initially arranged to form an angle of-45 degrees, namely 135 degrees, and the fast axis of the second lambda/4 wave plate 8 and the X axis form an angle of 45 degrees, and the fast axis direction can be changed by rotating the wave plates according to requirements, so that different column vector polarized light is generated, for example, 4 different column vector polarized light can be generated by respectively rotating the two lambda/4 wave plates by 90 degrees, when the two lambda/4 wave plates are rotated to enable the fast axis to be in the horizontal or vertical direction, or the two lambda/4 wave plates are directly removed, and vortex light beams can be generated;
106, arranging the helical wave plate 7 between the two lambda/4 wave plates, wherein the whole helical wave plate 7 has the same fast axis, the fast axis direction is along the X-axis direction, and the thickness h of the helical wave plate 7 is gradually changed along with the rotation angle theta clockwise
Figure BDA0001285345820000071
Wherein the substrate thickness h0M is an integer, X-axis forward direction θ is 0, λ is incident light wavelength, n ise，noThe two main refractive indexes of the wave plate crystal are adopted, and the optical axis of a light beam is vertical to the substrate of the helical wave plate 7 and passes through the center of the substrate; because the continuous spiral gradual change wave plate is difficult to manufacture, the continuous spiral gradual change wave plate can be replaced by a block gradual change fan-shaped wave plate, and the thickness of the kth wave plate is the same as that of the kth wave plate under the assumption that N fan-shaped wave plates form a circle
Figure BDA0001285345820000072
Step 107, setting the spiral phase plate 9 to have isotropy and generate spiral phase delay, wherein the spiral direction is opposite to the spiral wave plate 7, realizing space phase compensation, and the phase delay amount of the spiral phase plate 9
Figure BDA0001285345820000073
With respect to the rotation angle theta (clockwise) of
Figure BDA0001285345820000074
That is, the phase is rotated counterclockwise, θ is 0 in the X-axis forward direction, and the phase can be realized by plating with various isotropic media having different thicknesses, such as SiN, H-K9L, fused silica JGS1, and the like, and assuming that the refractive index of the medium is n and the refractive index of air is 1, the change of the plating thickness with the forward index angle θ is
Figure BDA0001285345820000075
l0The thickness of the substrate can be directly manufactured by processes such as reverse die cutting and polishing, and the optical axis of the light beam passes through the center of the substrate and is parallel to the normal of the substrate; when the block gradual change fan-shaped wave plate is used, the corresponding block gradual change fan-shaped phase plate also has N blocks, and the coating thickness of the kth block
Figure BDA0001285345820000076
108, replacing the wave plates (including the lambda/2 wave plate 2, the first lambda/4 wave plate 6 and the second lambda/4 wave plate 8), the helical wave plate 7 and the helical phase plate 9, realizing the control of the multiband light beams, and generating high-order column vector polarized light from the newly designed helical wave plate 7 and the newly designed helical phase plate 9, for example, when the helical wave plate satisfies the requirement
Figure BDA0001285345820000077
And the spiral phase plate 9 satisfies
Figure BDA0001285345820000078
Then, second-order cylindrical vector polarized light can be generated;
step 109 may zoom the beam in or out as desired by the beam scaler 10, with the zoom factor being adjustable.
FIG. 4 is a schematic diagram of some of the column vector polarized light beams generated after two λ/4 wave plates are rotated by 90 °, wherein FIG. 4(a) is input horizontal linearly polarized light, and FIGS. 4(b) - (e) correspond to Jones matrix J, respectively12、J21、J11And J224 kinds of cylindrical vector polarized light beams are generated, wherein, FIGS. 4(b) and 4(e) are radial polarized light and angular polarized light; fig. 5 shows some of the column vector polarized light beams generated by the experiment of the present invention, fig. 5(a) - (d) show 4 column vector polarized light beams generated by the experiment, in which fig. 5(a1) - (d1) show the light field distribution of each light beam after passing through a horizontal linear polarizer, fig. 5(a2) - (d2) show the light field distribution of each light beam after passing through a 45 ° linear polarizer, fig. 5(a3) - (d3) show the light field distribution of each light beam after passing through a vertical linear polarizer, fig. 5(a4) - (d4) show the light field distribution of each light beam after passing through a-45 ° (135 °) polarizer, and the arrow direction shows the light transmission direction of the polarizer. The experimental result is consistent with the theoretical analysis result, and the correctness and the effectiveness of the method are proved.
In a word, the high-power column vector polarized light is generated based on the spiral wave plate, various light beams can be generated by simply rotating the two lambda/4 wave plates, and the system is simple in structure and easy to operate and control. In addition, multi-wavelength modulation and multi-type light beams can be realized by replacing the wave plate, the spiral wave plate and the spiral phase plate.
The invention has not been described in detail and is part of the common general knowledge of a person skilled in the art.
Although specific embodiments of the present invention have been described above, it will be appreciated by those skilled in the art that these are merely illustrative and that many changes or modifications may be made to these embodiments (e.g., selection of materials for the helical waveplate and the helical phase plate, changes in thickness of the helical waveplate, changes in position of the starting point, changes in angle of the starting point, changes in direction of rotation, selection of a horizontal analyzer, etc.) without departing from the principles and implementations of the present invention, and therefore the scope of the present invention is to be defined by the appended claims.

Claims (1)

1. The method for generating various high-power column vector polarized light beams based on the spiral wave plate is characterized by comprising the following steps of:
step S1, setting incident light beam with linear polarized light and arbitrary polarization direction;
step S2, setting and adjusting the lambda/2 wave plate (2), wherein the optical axis of the light beam is required to pass through the center of the lambda/2 wave plate (2) and be parallel to the normal line, the lambda/2 wave plate (2) can be replaced, and the main shaft can rotate and be adjusted along the optical axis;
step S3, setting a horizontal analyzer (3) which can be a polaroid or a polarizing prism, requiring the optical axis of the light beam to pass through the center of the horizontal analyzer (3) and be parallel to the normal, and the polarization transmission direction of the light beam to be the horizontal direction and have high extinction ratio to the light beam of a certain wave band;
step S4, a lens group is set, the light beam is required to be amplified, and the amplification factor is related to the size of the wave plate;
step S5, two lambda/4 wave plates are arranged and adjusted, the optical axis of the light beam is required to pass through the center of the lambda/4 wave plate and be parallel to the normal, the lambda/4 wave plate can be replaced, and the main shaft can rotate and be adjusted along the optical axis;
step S6, arranging a helical wave plate (7) between two lambda/4 wave plates, requiring the whole helical wave plate (7) to have the same fast axis, wherein the fast axis direction is perpendicular to the optical axis along the X-axis direction along the optical path and horizontally changes to the right, the thickness of the helical wave plate (7) changes gradually along with the rotation angle clockwise, and the optical axis of the light beam passes through the center of the helical wave plate and is parallel to the normal of the substrate of the helical wave plate;
step S7, setting a spiral phase plate (9) to require isotropy and generate spiral phase delay, wherein the spiral direction is opposite to the spiral wave plate (7), namely, the spiral wave plate rotates anticlockwise, and the optical axis of the light beam passes through the center of the spiral phase plate and is parallel to the normal of the base of the spiral phase plate;
step S8, the light beam is enlarged or reduced through the light beam scaler (10) according to the requirement;
step S9, the rotation of the space polarization state is realized after the horizontal linear polarized light passes through the two lambda/4 wave plates and the spiral wave plate (7), the modulation of the space phase is realized after the horizontal linear polarized light passes through the spiral phase plate (9), the synchronous adjustment of the space light beam phase and the space polarization state is realized by combining the two lambda/4 wave plates, the space phase and the polarization state are considered, when the two lambda/4 wave plates are rotated, different types of column vector polarized light can be generated, and when the fast axes of the two lambda/4 wave plates are in the horizontal or vertical direction, vortex light beams can be generated;
in the step S1, setting an incident beam to adopt a high-power laser light source (1), obtaining a linearly polarized light beam after passing through a polaroid or a polarization splitting prism, wherein the spectral width is less than +/-3 nm, and the linearly polarized light source can also be directly adopted;
in the steps S2 and S3, the lambda/2 wave plate (2) can be replaced and rotated, and is consistent with the central wavelength lambda of the light source so as to improve the application range, and the polarization direction of incident light can be adjusted by rotating the lambda/2 wave plate (2); the horizontal analyzer (3) ensures that the emergent light beam is horizontally linearly polarized light, the horizontal analyzer (3) is combined with the lambda/2 wave plate (2), and the light intensity of the light beam can be adjusted by rotating the lambda/2 wave plate (2);
in the steps S5 and S9, the two λ/4 wave plates can be replaced and rotated, and are consistent with the central wavelength λ of the light source, the fast axis of the first λ/4 wave plate (6) is initially set to form an angle of-45 °, that is, 135 °, with the X axis, and the fast axis of the second λ/4 wave plate (8) forms an angle of 45 ° with the X axis, and the fast axis direction can be changed by rotating the two λ/4 wave plates as required, so as to generate different column vector polarized light, for example, by respectively rotating the two λ/4 wave plates by 90 °, 4 different column vector polarized light can be generated;
in the step S6, the fast axis of the helical wave plate (7) is along the X direction, and the thickness h of the helical wave plate (7) is gradually changed clockwise along with the rotation angle θ
Figure FDA0002414790660000021
Wherein the substrate thickness h0M is an integer, X-axis forward direction θ is 0, λ is incident light wavelength, n ise，noThe two main refractive indexes of the wave plate crystal are adopted, the optical axis of a light beam is perpendicular to the substrate of the spiral wave plate (7) and passes through the center of the spiral wave plate, the continuous spiral gradually-changed wave plate is difficult to manufacture and can be replaced by a segmented gradually-changed fan-shaped wave plate, and the thickness of the kth wave plate is reduced on the assumption that N fan-shaped wave plates form a circle
Figure FDA0002414790660000022
In the step S7, the phase delay amount of the spiral phase plate (9)
Figure FDA0002414790660000029
With respect to the rotation angle theta
Figure FDA00024147906600000210
That is, the phase is rotated counterclockwise, θ is 0 in the X-axis forward direction, and the phase can be formed by plating various isotropic media having different thicknesses, and assuming that the refractive index of the medium is n and the refractive index of air is 1, the change in the thickness of the plating layer according to the angle θ of the forward pointer is
Figure FDA0002414790660000023
l0The thickness of the substrate can be directly made by the processes of reverse mould cutting, grinding and the like, the optical axis of a light beam is vertical to the substrate of the spiral phase plate (9) and passes through the center of the substrate, when a block gradual change fan-shaped wave plate is used, the corresponding block gradual change fan-shaped phase plate also has N blocks, and the coating thickness of the kth block
Figure FDA0002414790660000024
In the steps S2, S5, S6 and S7, the λ/2 wave plate, the two λ/4 wave plates, the helical wave plate (7) and the helical phase plate (9) can bear high-power laser, and parameters can be changed according to the wavelength of incident light;
the method arranges a spiral wave plate between two lambda/4 wave plates to realize the rotation of linearly polarized light polarization direction, the fast axis direction of the first lambda/4 wave plate forms 135 degrees (-45 degrees) with the x axis, the fast axis of the spiral wave plate is parallel with the x axis, the thickness h of the spiral wave plate is clockwise gradually changed with the rotation angle theta
Figure FDA0002414790660000025
The fast axis direction of the second lambda/4 wave plate forms 45 degrees with the x axis, and the Jones matrix of the first lambda/4 wave plate and the second lambda/4 wave plate is J1And J2The helical waveplate produces a spatial phase delay 2 theta, the Jones momentArray is J0Respectively expressed as:
Figure FDA0002414790660000026
where i is a complex number, the jones matrix of the system can be expressed as:
Figure FDA0002414790660000027
jones matrix J12The input light theta can be rotated clockwise by an angle but with an overall phase retardation theta of the wavefront, so that the system can be spatially phase compensated by a helical phase plate with a phase retardation
Figure FDA00024147906600000211
With respect to the rotation angle theta
Figure FDA0002414790660000028
When the X axis is positive, theta is equal to 0, namely anticlockwise rotation, the X axis can be realized by plating certain isotropic mediums with different thicknesses, the refractive index of the medium is n, and if the refractive index of air is 1, the change of the thickness of the plating layer along with the angle is
Figure FDA0002414790660000031
When the two lambda/4 wave plates are rotated by 90 degrees at the same time, the Jones matrix of the system can be expressed as follows:
Figure FDA0002414790660000032
jones matrix J21The angle of the input light theta can be rotated anticlockwise, but the input light theta is accompanied by a wave front integral phase delay quantity theta, and the input light theta can be subjected to spatial phase compensation through the spiral phase plate;
when the second λ/4 plate is rotated by 90 °, the first λ/4 plate remains unchanged, and the jones matrix of the system can be expressed as:
Figure FDA0002414790660000033
jones matrix J11The input light can be symmetrically rotated about the y-x axis and then rotated counterclockwise by an angle theta, but the input light can be subjected to spatial phase compensation through a spiral phase plate along with a wave front integral phase delay quantity theta + pi/2;
when the first λ/4 plate is rotated by 90 °, and the second λ/4 plate remains unchanged, the jones matrix of the system can be expressed as:
Figure FDA0002414790660000034
jones matrix J22The input light can be symmetrically rotated about the y-x axis and then clockwise rotated by an angle theta, but the input light can be subjected to spatial phase compensation through a spiral phase plate along with a wave front integral phase delay quantity theta-pi/2;
when the two lambda/4 wave plates are rotated at other different angles, the system can generate other column vector polarized light, and when the two lambda/4 wave plates are rotated to enable the fast axis to be in the horizontal or vertical direction, or the two lambda/4 wave plates are directly removed, the system can also generate vortex light beams;
by replacing the wave plate, the helical wave plate and the helical phase plate, the multi-band light beam can be controlled, and high-order column vector polarized light can be generated by newly designing the helical wave plate and the helical phase plate, for example, when the thickness of the helical wave plate meets the requirement
Figure FDA0002414790660000035
And the spiral phase plate satisfies
Figure FDA0002414790660000036
In addition, the starting point of the thickness variation of the spiral wave plate is different, and the polarization direction of the generated cylindrical vector polarized light is also different, for example, when the thickness of the spiral wave plate satisfies the requirement
Figure FDA0002414790660000037
The polarization direction of the cylindrical vector polarized light is rotated by theta0And (4) an angle.
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