CN115236786B - Liquid crystal phase plate, preparation method and double-sided vortex light beam generation system - Google Patents
Liquid crystal phase plate, preparation method and double-sided vortex light beam generation system Download PDFInfo
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- 239000004973 liquid crystal related substance Substances 0.000 title claims abstract description 145
- 238000002360 preparation method Methods 0.000 title abstract description 6
- 239000000758 substrate Substances 0.000 claims abstract description 93
- 230000010287 polarization Effects 0.000 claims abstract description 44
- 125000006850 spacer group Chemical group 0.000 claims abstract description 11
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- 239000004988 Nematic liquid crystal Substances 0.000 claims description 4
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- 239000005262 ferroelectric liquid crystals (FLCs) Substances 0.000 claims description 4
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Classifications
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B5/00—Optical elements other than lenses
- G02B5/30—Polarising elements
- G02B5/3016—Polarising elements involving passive liquid crystal elements
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- G—PHYSICS
- 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
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B5/00—Optical elements other than lenses
- G02B5/30—Polarising elements
- G02B5/3083—Birefringent or phase retarding elements
Abstract
The embodiment of the invention discloses a liquid crystal phase plate, a preparation method and a double-sided vortex beam generation system. The liquid crystal phase plate comprises a first substrate, a second substrate and a liquid crystal layer, wherein the first substrate and the second substrate are oppositely arranged, the liquid crystal layer is arranged between the first substrate and the second substrate, and spacer particles are arranged between the first substrate and the second substrate; one side of the first substrate and the second substrate, which is close to the liquid crystal layer, is provided with a photo-alignment film, molecular directors of the photo-alignment film are arranged according to a spiral phase control pattern modulated by a circular cubic phase and a circular linear phase, and the liquid crystal molecular directors in the liquid crystal layer are controlled to be arranged according to the control pattern, so that Gaussian beams irradiated on the liquid crystal phase plate are converted into double-sided vortex beams with controllable polarization; the spiral phase control pattern of the circular cubic phase and the circular linear phase modulation is formed by superposing a circular cubic phase pattern, a circular linear phase pattern and a spiral phase pattern. According to the technical scheme provided by the embodiment of the invention, the double-sided vortex light beam with controllable polarization can be generated.
Description
Technical Field
The invention relates to the technical field of optics, in particular to a liquid crystal phase plate, a preparation method and a double-sided vortex beam generation system.
Background
Vortex beams have been a research hotspot in the optical field in recent years. The vortex beam has a spiral equiphase surface and carries orbital angular momentum; the presence of the phase singularities causes the swirling beam to assume a circular spot centered at the dark field. The unique property of vortex light beams enables the vortex light beams to be widely applied to the fields of optical tweezers, super-resolution microscopic imaging, image edge enhancement, image encryption, optical communication, quantum computation, astronomical observation and the like.
On the other hand, as a new proposed type of beam, a double sided wave is also attracting attention of researchers. The duplex wave has a "real" component and an "imaginary" component, located at two symmetrical focal points in opposite transmission directions, respectively. The imaginary component can be introduced into the real space by the double lens structure, thereby realizing the generation of double-sided wave beams. At present, research on generating double-sided vortex beams based on double-sided wave regulation vortex beams is not available at home and abroad, and related research can further expand the application dimension of the vortex beams in optics and other fields, so that the method has very important significance.
Disclosure of Invention
The embodiment of the invention provides a liquid crystal phase plate, a preparation method and a double-sided vortex beam generation system.
According to an aspect of the present invention, there is provided a liquid crystal phase plate comprising:
the liquid crystal display comprises a first substrate, a second substrate and a liquid crystal layer, wherein the first substrate and the second substrate are oppositely arranged, and spacer particles are arranged between the first substrate and the second substrate so as to support the first substrate or the second substrate;
one side of the first substrate and the second substrate, which is close to the liquid crystal layer, is provided with a photo-alignment film, molecular directors of the photo-alignment film are arranged according to a circular-cubic phase and circular-linear phase modulated spiral phase control pattern, and the photo-alignment film controls liquid crystal molecular directors in the liquid crystal layer to be arranged according to the circular-cubic phase and circular-linear phase modulated spiral phase control pattern, so that Gaussian beams irradiated on the liquid crystal phase plate are converted into polarization-controllable double-sided vortex beams;
the circular-cubic phase and circular-linear phase modulation spiral phase control pattern is formed by superposing a circular-cubic phase pattern, a circular-linear phase pattern and a spiral phase pattern.
Optionally, the molecular directors of the photoalignment film satisfy:
wherein,representing the circular-cubic phase in the circular-cubic phase graph, the expression of which satisfies:
representing the circular linear phase in the circular linear phase pattern, the expression of which satisfies:
representing the vortex phase in the spiral phase pattern, the expression of which satisfies:
θ＝arctan(y/x)；
wherein x and y represent coordinates in a rectangular coordinate system with the center of the liquid crystal phase plate as an origin, beta is a parameter for controlling the modulation amount of the circular cubic phase, and lambda L Representing the period of the circular linear phase in the radial direction, m represents the topological charge number of the generated vortex beam.
Optionally, the circular cube phase patterns include a plurality of concentric circular cube phase patterns, the phase period modulation amount of each circular cube phase pattern is 2 pi, the phase modulation range of each circular cube phase pattern is 0-16 pi, and the width of each circular cube phase pattern gradually decreases along the radial direction from the central area of the circular cube phase pattern;
the circular linear phase patterns comprise a plurality of concentric circular linear phase patterns, the phase period modulation quantity of each circular linear phase pattern is 2 pi, the phase modulation range of each circular linear phase pattern is 0-30.8 pi, and the width of each circular linear phase pattern is kept unchanged along the radial direction from the central area of the circular linear phase pattern;
The spiral phase patterns comprise multi-order spiral phase patterns, the phase period modulation quantity of each spiral phase pattern is 2 pi, and the phase value of each spiral phase pattern is uniformly changed along with the azimuth angle.
Optionally, the material of the liquid crystal layer includes any one of nematic liquid crystal, dual-frequency liquid crystal or ferroelectric liquid crystal;
the circular-cubic phase and circular-linear phase modulated spiral phase control pattern of the photo-alignment film can be erasable, and the photo-alignment film material comprises azo dye.
Optionally, the phase difference between the ordinary light and the extraordinary light in the liquid crystal phase plate satisfies:
wherein Δn is a difference in birefringence of liquid crystal molecules, d is a thickness of the liquid crystal layer, λ is a wavelength of an incident gaussian beam, and k is a natural number.
According to another aspect of the present invention, there is provided a polarization controllable double-sided vortex beam generating system comprising:
the liquid crystal phase plate;
a light source positioned on the light incident side of the liquid crystal phase plate so as to generate an incident Gaussian beam;
a polarizer and a quarter wave plate between the light source and the liquid crystal phase plate;
the double-lens structure and the imaging device are positioned on the light emitting side of the liquid crystal phase plate.
Optionally, the optical axes of the light source, the polarizer, the quarter-wave plate, the liquid crystal phase plate, the dual-lens structure and the imaging device are positioned on the same straight line;
and controlling the intensity and the polarization state of the incident Gaussian beam by adjusting the included angle between the fast axis direction of the quarter wave plate and the polarization direction of the polaroid.
Optionally, when the incident gaussian beam generated by the light source is a linear polarized gaussian beam, the incident gaussian beam is converted into a double-sided vortex beam by the liquid crystal phase plate;
when the incident Gaussian beam generated by the light source is a left-handed circularly polarized Gaussian beam or a right-handed circularly polarized Gaussian beam, the incident Gaussian beam is converted into a right-handed circularly polarized single-focus vortex Airy beam or a left-handed circularly polarized single-focus vortex Airy beam through the liquid crystal phase plate;
when one lens in the double-lens structure is removed, the incident Gaussian beam generated by the light source is a left-handed polarized Gaussian beam or a right-handed circularly polarized Gaussian beam, and the incident Gaussian beam is converted into a right-handed self-focusing vortex Airy beam or a left-handed self-defocusing vortex Airy beam through the liquid crystal phase plate.
According to still another aspect of the present invention, there is provided a method of manufacturing a liquid crystal phase plate, comprising:
forming a photo-alignment film on one side of the first substrate and the second substrate;
spacer particles are arranged on the first substrate and are encapsulated with the second substrate, wherein one side of the photo-alignment film of the first substrate is arranged opposite to one side of the photo-alignment film of the second substrate;
performing multi-step overlapping exposure on the photo-alignment film so that the molecular director direction of the photo-alignment film is arranged according to gray values of circular cubic phase and circular linear phase modulation spiral phase control patterns, wherein the circular cubic phase and circular linear phase modulation spiral phase control patterns are formed by overlapping a circular cubic phase pattern, a circular linear phase pattern and a spiral phase pattern;
and a liquid crystal layer is poured between the first substrate and the second substrate, and the circular cubic phase and circular linear phase modulation spiral phase control pattern of the photo-alignment film controls the arrangement of liquid crystal molecule directors in the liquid crystal layer according to the circular cubic phase and circular linear phase modulation spiral phase control pattern.
Optionally, performing multi-step overlapping exposure on the photoalignment film to enable the molecular director direction of the photoalignment film to be arranged according to a circular-cubic phase and circular-linear phase modulation spiral phase control pattern, wherein the circular-cubic phase and circular-linear phase modulation spiral phase control pattern is formed by overlapping a circular-cubic phase pattern, a circular-linear phase pattern and a spiral phase pattern, and the method comprises the following steps:
Adopting a micro projection exposure system based on a numerical control micro mirror array, and selecting an exposure pattern corresponding to a phase value and a corresponding induced light polarization direction according to an exposure sequence to sequentially expose;
wherein the exposure areas of the exposure patterns of adjacent steps are partially overlapped, and the polarization direction of the induced light is monotonically increased or monotonically decreased along with the exposure sequence, so as to form a circular cubic phase and circular linear phase modulated spiral phase control pattern formed by overlapping a circular cubic phase pattern, a circular linear phase pattern and a spiral phase pattern.
The liquid crystal phase plate provided by the embodiment of the invention comprises a first substrate, a second substrate and a liquid crystal layer, wherein the first substrate and the second substrate are oppositely arranged; spacer particles are arranged between the first substrate and the second substrate to support the first substrate or the second substrate; one side of the first substrate and the second substrate, which is close to the liquid crystal layer, is provided with a photo-alignment film, molecular directors of the photo-alignment film are arranged according to a spiral phase control pattern modulated by a circular cubic phase and a circular linear phase, and the photo-alignment film controls the liquid crystal molecular directors in the liquid crystal layer to be arranged according to the spiral phase control pattern modulated by the circular cubic phase and the circular linear phase, so that Gaussian beams irradiated on the liquid crystal phase plate are converted into polarized controllable double-sided vortex beams; the spiral phase control pattern of the circular cubic phase and the circular linear phase modulation is formed by superposing a circular cubic phase pattern, a circular linear phase pattern and a spiral phase pattern. The first substrate and the second substrate are arranged oppositely, molecular directors of the photo-alignment films are arranged according to a circular cubic phase and a circular linear phase modulation spiral phase control pattern, and the control patterns of the photo-alignment films control liquid crystal molecular directors in a liquid crystal layer to be distributed in a gradual change mode according to the circular cubic phase and the circular linear phase modulation spiral phase control pattern at 0-180 degrees, so that Gaussian beams irradiated on the liquid crystal phase plate are converted into polarization-controllable double-sided vortex beams. The double-sided vortex beam generated by the embodiment of the invention has the characteristic of controllable polarization, and the distance between two focuses of the double-sided vortex beam and the length of the focal length can be customized by changing the parameters of the spiral phase control graph modulated by the circular cubic phase and the circular linear phase according to the requirements.
It should be understood that the description in this section is not intended to identify key or critical features of the embodiments of the invention or to delineate the scope of the invention. Other features of the present invention will become apparent from the description that follows.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly described below, and it is apparent that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a schematic structural diagram of a liquid crystal phase plate according to an embodiment of the present invention;
FIG. 2 is a schematic top view of a liquid crystal director distribution corresponding to the structure of FIG. 1;
FIG. 3 is a schematic diagram of a spiral phase control pattern for circular cubic phase and circular linear phase modulation according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of a process for forming a spiral phase control pattern for circular cubic phase and circular linear phase modulation according to an embodiment of the present invention;
FIG. 5 is a microscopic schematic of a sample of a liquid crystal phase plate with a phase difference between the ordinary and extraordinary rays equal to an odd multiple of pi;
FIG. 6 is a schematic diagram of a polarization-controllable double-sided vortex beam generating system according to an embodiment of the present invention;
FIG. 7 is a schematic diagram of the appearance of a double-sided vortex beam spot generated by modulating the liquid crystal phase plate shown in FIG. 5, and a transmission dynamic simulation diagram and an experimental diagram;
FIG. 8 is a simulated plot and experimental plot of the phase distribution of a double-sided vortex beam generated by a liquid crystal phase plate;
FIG. 9 is a simulation and experimental measurement of the polarization distribution of a double-sided vortex beam generated by a liquid crystal phase plate;
fig. 10 is a schematic flow chart of a method for manufacturing a liquid crystal phase plate according to an embodiment of the present invention;
fig. 11 is a schematic flow chart of performing multi-step overlapped exposure on a photo-alignment film according to an embodiment of the present invention.
Detailed Description
In order that those skilled in the art will better understand the present invention, a technical solution in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in which it is apparent that the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present invention without making any inventive effort, shall fall within the scope of the present invention.
It should be noted that the terms "first," "second," and the like in the description and the claims of the present invention and the above figures are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used may be interchanged where appropriate such that the embodiments of the invention described herein may be implemented in sequences other than those illustrated or otherwise described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
Fig. 1 is a schematic structural diagram of a liquid crystal phase plate according to an embodiment of the present invention. Referring to fig. 1, the liquid crystal phase plate provided in the present embodiment can convert a gaussian beam into a double-sided vortex beam, and includes a first substrate 11, a second substrate 12, and a liquid crystal layer 13 between the first substrate 11 and the second substrate 12, which are disposed opposite to each other; wherein, spacer particles 14 are arranged between the first substrate 11 and the second substrate 12 to support the first substrate 11 or the second substrate 12, forming an accommodation space of the liquid crystal layer 13; the first substrate 11 and the second substrate 12 are provided with photo-alignment films 15 and 16 on the sides adjacent to the liquid crystal layer 13, the molecular directors of the photo-alignment films 15 and 16 are arranged in accordance with a spiral phase control pattern of circular-cubic phase and circular-linear phase modulation, and the photo-alignment films 15 and 16 control the alignment of the liquid crystal molecular directors in the liquid crystal layer 13 in accordance with the spiral phase control pattern of circular-cubic phase and circular-linear phase modulation, so that an incident gaussian beam irradiated on the liquid crystal phase plate is converted into a polarization-controllable double-sided vortex beam. Wherein the control patterns of the photo-alignment films 15 and 16 are identical, and the circular-cubic phase and circular-linear phase modulation spiral phase control pattern is formed by superposing a circular-cubic phase pattern, a circular-linear phase pattern and a spiral phase pattern.
Fig. 2 is a schematic top view of a liquid crystal director profile corresponding to the structure of fig. 1. Referring to fig. 2, under the anchoring action of the photoalignment film, since the molecular directors of the photoalignment film are aligned according to a spiral phase control pattern modulated by a circular cubic phase and a circular linear phase, the photoalignment film causes directors of liquid crystal molecules in a liquid crystal layer to be also aligned correspondingly from 0 ° to 180 ° per cycle according to the control pattern.
Fig. 3 is a schematic diagram of a spiral phase control pattern of circular cubic phase and circular linear phase modulation according to an embodiment of the present invention, and fig. 4 is a schematic diagram of a process of forming a spiral phase control pattern of circular cubic phase and circular linear phase modulation according to an embodiment of the present invention. Referring to fig. 3 and 4, the gradation value of 0-255 can be regarded as a simulated schematic of the liquid crystal director direction having a spatially graded distribution of 0 ° -180 °, where the gradation of the liquid crystal director direction from 0 ° to 180 ° is indicated from dark to light. In fig. 4, (a), (b), and (c) are respectively a circular cubic phase pattern, a circular linear phase pattern, and a spiral phase pattern, the circular cubic phase pattern refers to a regular change of the phase in each phase change period along the radial direction, the circular linear phase pattern refers to a regular change of the phase in each phase change period along the radial direction, and the spiral phase pattern refers to a regular change of the phase in each phase change period along the angular direction. The spiral phase control pattern shown in fig. 3, which includes a circular cubic phase and a circular linear phase modulation, can be obtained by superimposing the three patterns (a), (b), and (c) shown in fig. 4.
According to the technical scheme, the photo-alignment films are arranged on the first substrate and the second substrate which are arranged oppositely, molecular directors of the photo-alignment films are arranged according to the spiral phase control patterns modulated by the circular cubic phase and the circular linear phase, the control patterns of the photo-alignment films control liquid crystal molecular directors in the liquid crystal layer to be distributed in a gradual change mode at 0-180 degrees according to the spiral phase control patterns modulated by the circular cubic phase and the circular linear phase, and Gaussian beams irradiated on the liquid crystal phase plate are converted into double-sided vortex beams with controllable polarization. The double-sided vortex beam generated by the embodiment of the invention has the characteristic of controllable polarization, and the distance between two focuses of the double-sided vortex beam and the length of the focal length can be customized by changing the parameters of the spiral phase control graph modulated by the circular cubic phase and the circular linear phase according to the requirements.
On the basis of the above embodiments, optionally, the molecular directors of the photoalignment film satisfy:
wherein,the expression of the circular-cubic phase in the circular-cubic phase graph is expressed as follows:
the expression of the circular linear phase in the circular linear phase graph is expressed as follows:
representing the vortex phase in the spiral phase pattern, the expression satisfies:
θ＝arctan(y/x)；
Wherein x and y represent coordinates in a rectangular coordinate system with the center of the liquid crystal phase plate as an origin, beta is a parameter for controlling the modulation amount of the circular cubic phase, and lambda L Representing the period of the circular linear phase in the radial direction, m represents the topological charge number of the generated vortex beam.
It can be appreciated that by changing the amount of circular-cubic phase modulation, the period of circular linear phase, the order of spiral phase, etc., different spiral phase control patterns of circular-cubic phase and circular linear phase modulation can be designed according to the requirements, thereby generating different polarization-controllable double-sided vortex beams.
Optionally, with continued reference to fig. 4 (a), the circular-cubic phase patterns include a plurality of concentric circular-ring-cubic phase patterns, each of which has a phase period modulation amount of 2pi and a phase modulation range of 0 to 16pi, and the width of each of which gradually decreases in a radial direction from the central region of the circular-cubic phase pattern; with continued reference to FIG. 4 (b), the circular linear phase pattern comprises a plurality of concentric circular ring linear phase patterns, each circular ring linear phase pattern having a phase period modulation of 2 pi, a phase modulation range of 0-30.8 pi, each circular ring linear phase pattern having a width that remains unchanged radially from a central region of the circular linear phase pattern, plotted at 1080×1080 resolution, and a corresponding Λ L 35 pixels; with continued reference to fig. 4 (c), the spiral phase pattern includes multiple-order spiral phase patterns, the phase period modulation amount of each spiral phase pattern is 2pi, the phase value of each spiral phase pattern uniformly changes along with the azimuth angle, and in this embodiment, the set phase period number of the spiral phase pattern is 6, and the corresponding m value is 6.
It can be understood that the larger the range of the value of the circular-cubic phase is, the larger the number of periods of the circular-cubic phase periodic pattern is, and the larger the focal length of the correspondingly generated double-sided vortex beam is, and the range of the circular-cubic phase is set to be 0-16 pi in the embodiment. The larger the range of the circular linear phase value is, the smaller the period is, the larger the period number of the circular linear phase period pattern is, and the larger the radius of the correspondingly generated double-sided vortex beam on the initial plane is, and the circular cubic phase range is set to be 0-30.8pi in the embodiment. The larger the value of m for the spiral phase, the more the number of periods of the spiral periodic pattern, the larger the topological load of the correspondingly generated vortex beam, and the larger the central dark spot, the value of m is set to be 6 in the embodiment. In the specific implementation, the range of the circular cubic phase and the circular linear phase can be set according to the actual requirement, and the embodiment of the invention is not limited to the range.
Optionally, the material of the liquid crystal layer includes any one of nematic liquid crystal, dual-frequency liquid crystal or ferroelectric liquid crystal; the spiral phase control pattern modulated by the circular cubic phase and the circular linear phase of the photo-alignment film can be erasable, and the material of the photo-alignment film comprises azo dye.
It can be understood that the material of the liquid crystal layer can be any one of nematic liquid crystal, dual-frequency liquid crystal or ferroelectric liquid crystal, and can be selected according to practical conditions when in implementation, the material of the photo-alignment film is azo dye, so that the liquid crystal phase plate can be reused, and the structure of the liquid crystal phase plate capable of generating double-sided vortex beams can be changed in real time by erasing and writing a circular cubic phase and circular linear phase modulation spiral phase control pattern on the photo-alignment film, thereby realizing the generation of double-sided vortex beams in multiple modes.
Alternatively, the phase difference between the ordinary light and the extraordinary light in the liquid crystal phase plate satisfies:
where Δn is the difference in birefringence of the liquid crystal molecules, d is the thickness of the liquid crystal layer, λ is the wavelength of the incident gaussian beam, and k is a natural number.
It will be appreciated that by adjusting the distance between the first and second substrates by adjusting the size of the spacer particles, the thickness of the liquid crystal layer can be controlled such that the phase difference between the ordinary and extraordinary rays of the incident gaussian beam in the liquid crystal phase plate is equal to an odd multiple of pi. FIG. 5 is a microscopic schematic of a sample of a liquid crystal phase plate with a phase difference between ordinary and extraordinary rays equal to an odd multiple of pi, and the scale is 100. Mu.m. The arrangement has the advantages that when the phase difference between the ordinary light and the extraordinary light of the incident Gaussian beam in the liquid crystal phase plate is equal to odd times of pi, the emergent beam after the incident Gaussian beam irradiates the liquid crystal phase plate is a double-sided vortex beam with controllable polarization, and the electrode is avoided.
Fig. 6 is a schematic structural diagram of a polarization-controllable double-sided vortex beam generating system according to an embodiment of the present invention. Referring to fig. 6, the polarization-controllable double-sided vortex beam generating system includes any one of the liquid crystal phase plates 21 provided in the above-described embodiments; a light source 22 located on the light incident side of the liquid crystal phase plate 21 to generate an incident gaussian beam; a polarizing plate 26 and a quarter wave plate 27 located between the light source 22 and the liquid crystal phase plate 21; a two-lens structure (lenses 23 and 24) and an imaging device 25 on the light-emitting side of the liquid crystal phase plate 21.
The light source 22 may be a laser light source, which has good collimation, and the quality of the double-sided vortex beam converted by the liquid crystal phase plate 21 is high. In addition, the wavelength range of the light source 22 is not limited, and conversion from an arbitrary wavelength incident gaussian beam to a double-sided vortex beam can be achieved. For example, wavelengths longer than 500nm may be provided to avoid the effect of the incident gaussian beam from the light source 22 on the helical phase control pattern of the circular cubic phase and circular linear phase modulation in the liquid crystal phase plate 21. For example, the liquid crystal phase plate 21 is irradiated with a 671nm laser beam, and a double-sided vortex beam is obtained by fourier transform and focusing with a double-lens structure composed of a lens 23 having a focal length of 100mm and a lens 24 having a focal length of 150 mm. The embodiment of the present invention does not limit the focal length of the lenses 23, 24 of the dual lens structure. The imaging device 25 may be a charge coupled device CCD or the like.
Alternatively, the optical axes of the light source 22, the polarizing plate 26, the quarter-wave plate 27, the liquid crystal phase plate 21, the two-lens structure (lenses 23 and 24), and the imaging device 25 are on the same straight line; the intensity and polarization state of the incident gaussian beam are controlled by adjusting the angle between the fast axis direction of the quarter wave plate 27 and the polarization direction of the polarizer 26.
According to the polarization-controllable double-sided vortex beam generation system provided by the embodiment of the invention, the preset incident polarized Gaussian beam is generated by the light source, and the incident Gaussian beam is converted into the double-sided vortex beam by the liquid crystal phase plate capable of generating the double-sided vortex beam. The double-sided vortex beam generated by the embodiment of the invention has the characteristic of controllable polarization, and the distance between two focuses of the double-sided vortex beam and the length of the focal length can be customized by changing the parameters of the spiral phase control patterns modulated by the circular cubic phase and the circular linear phase according to the requirements.
Alternatively, when the incident gaussian beam generated by the light source 22 is a linearly polarized gaussian beam, the incident gaussian beam is converted into a double-sided vortex beam by the liquid crystal phase plate; when the incident gaussian beam generated by the light source 22 is a left-handed circularly polarized gaussian beam or a right-handed circularly polarized gaussian beam, the incident gaussian beam is converted into a right-handed circularly polarized single-focus vortex Airy beam or a left-handed circularly polarized single-focus vortex Airy beam by the liquid crystal phase plate 21; when one of the lenses in the dual-lens structure is removed, the incident gaussian beam generated by the light source 22 is a left-hand polarized gaussian beam or a right-hand circularly polarized gaussian beam, and the incident gaussian beam is converted into a right-hand self-focusing vortex Airy beam or a left-hand self-defocusing vortex Airy beam by the liquid crystal phase plate 21.
Fig. 7 is a schematic diagram of the appearance of a double-sided vortex beam spot generated by modulating the liquid crystal phase plate shown in fig. 5, and a transmission dynamic simulation diagram and an experimental diagram. When the incident Gaussian beam generated by the light source is linearly polarized, the incident Gaussian beam is converted into a double-sided vortex beam through a liquid crystal phase plate capable of generating the double-sided vortex beam, and the double-sided vortex beam is respectively in a right-handed circular polarization state and a left-handed circular polarization state. Fig. 7 (a) - (i) correspond to transport distances of 9, 10, 12, 14, 15, 16, 18, 19 and 20cm, respectively. As can be seen from the figure, as the transmission distance increases, the primary ring radius of the double-sided vortex beam gradually decreases, the energy gradually concentrates, the first focusing at 12cm, and then the primary ring radius gradually increases, and the energy gradually spreads. At a transmission distance of 15cm to fig. 7 (e), i.e. at the focal plane of the second lens (lens 24) in the two-lens configuration, the dark field at the center of the beam is reduced, but in the unfocused state, the result is a vector light field formed by superposition of the vortex beams of opposite topological charges. With further increases in the transmission distance, the primary ring radius again becomes smaller from large to small, and the intensity again increases until refocusing at 18 cm. After a transmission distance of more than 18cm, the beam diverges. Fig. 7 (j) shows the transmission dynamic experimental result of the double-sided vortex beam generated after the modulation of the liquid crystal phase plate, wherein the hollow circle is the measured radius of the main ring of the double-sided vortex beam at different transmission distances, and the curve is parabolic fit, and characterizes the transmission track of the double-sided vortex beam. As can be seen from the figure, as the transmission distance increases, the beam undergoes a focus-divergence-focus-divergence process. Fig. 7 (k) is a simulation diagram of a double-sided vortex beam transmission trajectory, and the experimental result of fig. 7 (j) substantially coincides with the simulation result of fig. 7 (k). When the incident Gaussian beam generated by the light source is in left-handed circular polarization, the incident Gaussian beam is converted into a single-focus vortex Airy beam in right-handed circular polarization through the liquid crystal phase plate, and the focal point is positioned at a transmission distance of 12 cm; when the incident Gaussian beam generated by the light source is in right-handed circular polarization, the incident Gaussian beam is converted into a left-handed circular polarized single-focus vortex Airy beam through the liquid crystal phase plate, and the focal point is located at the transmission distance of 18 cm. When one of the lenses in the dual-lens structure, such as the lens 24, is removed, the incident gaussian beam generated by the light source is a left-hand circularly polarized gaussian beam or a right-hand circularly polarized gaussian beam, and the incident gaussian beam is converted into a right-hand self-focusing vortex Airy beam or a left-hand self-defocusing vortex Airy beam by the liquid crystal phase plate, as shown in the simulated inner-ring and outer-ring beam transmission dynamics of FIG. 7 (l), respectively.
Fig. 8 is a simulation diagram and an experimental measurement diagram of the phase distribution of a double-sided vortex beam generated through a liquid crystal phase plate. Fig. 8 (a) - (c) are theoretical simulations and fig. (d) - (f) are experimentally measured phase distributions of the double-sided vortex beam at transmission distances of 12cm (at the first focal plane), 15cm (at the focal plane of the lens 24) and 18cm (at the second focal plane), respectively, with experimental results substantially consistent with theoretical results. In the first focal plane shown in FIGS. 8 (a) and 8 (d), a spiral phase that has undergone 6 counterclockwise changes from 0 to 2π is detected, indicating that the double-sided vortex beam carries a topological charge of +6 or orbital angular momentum at this focal planeIn contrast, in the second focal plane shown in fig. 8 (c) and 8 (f), a spiral phase having undergone 6 clockwise changes from 0 to 2 pi was detected, showing that the orbital angular momentum carried by the double-sided vortex beam in this focal plane was ∈>The phase distribution at these two focal planes verifies the characteristics of the opposite spiral phase or opposite orbital angular momentum distribution of the double sided vortex beam at the bifocal point. At the focal plane position of the lens 24 of fig. 8 (b) and (e), the phase distribution of the light field exhibits 6 phase jumps of 0-pi, which are characteristic of a vector light beam with a polarization order of 6, and the analysis of the vector light field of fig. 7 at a transmission distance of 15cm is also verified.
Fig. 9 is a simulation diagram and an experimental measurement diagram of the polarization distribution of a double-sided vortex beam generated through a liquid crystal phase plate. Fig. 9 (a) - (b) and fig. 9 (c) - (d) are polarization distributions of the double-sided vortex beam at the first focal plane and the second focal plane, respectively, as measured by simulation and experiment, with the background being the intensity distribution of the corresponding double-sided vortex beam. Wherein darker ellipses in the images of fig. 9 (a) - (b) indicate that the double-sided vortex beam at the corresponding focus is in a right-handed circular polarization state, and lighter ellipses in the images of fig. 9 (c) - (d) indicate that the double-sided vortex beam at the corresponding focus is in a left-handed circular polarization state. The experimental results of fig. 9 (b) and 9 (d) are substantially identical to the simulation results in fig. 9 (a) and 9 (c), except for some measurement errors. The polarization distribution at these two focal planes verifies the characteristics of the orthogonal circular polarization or opposite spin angular momentum distribution of the double sided vortex beam at the bifocal point.
It can be appreciated that by changing the amount of circular-cubic phase modulation, the period of circular linear phase, the order of spiral phase, etc., different spiral phase control patterns of circular-cubic phase and circular linear phase modulation can be designed according to the requirements, thereby generating different polarization-controllable double-sided vortex beams.
Optionally, by erasing the circular radial linear and spiral phase modulation circular-cubic phase control patterns on the photo-alignment film, the structure of the liquid crystal phase plate capable of generating double-sided vortex beams can be changed in real time, so that double-sided vortex beams in multiple modes can be generated.
Fig. 10 is a schematic flow chart of a method for manufacturing a liquid crystal phase plate according to an embodiment of the present invention. Referring to fig. 10, the preparation method includes:
and step S110, forming photo-alignment films on one sides of the first substrate and the second substrate.
Alternatively, the first substrate and the second substrate may be glass substrates, and before forming the photoalignment film, in order to increase wettability and adhesiveness between the photoalignment film and the first substrate and the second substrate, the glass substrates are ultrasonically cleaned for 30 minutes by using a cleaning solution (mixed reagent of acetone, alcohol, etc.), and then ultrasonically cleaned twice by using ultrapure water for 10 minutes each. After drying in an oven at 120 ℃ for 40 minutes, UVO (ultraviolet ozone) cleaning was performed for 30 minutes.
Alternatively, the photoalignment film may be formed on one side of the first substrate and the second substrate in the following manner:
spin-coating photo-alignment materials on one side of a first substrate and one side of a second substrate, wherein spin-coating parameters are as follows: spin coating at low speed for 5 seconds at a rotational speed of 800 rpm, spin coating at high speed for 40 seconds at a rotational speed of 3000 rpm;
And annealing the first substrate and the second substrate which are spin-coated with the photoalignment material for 10 minutes at the annealing temperature of 100 ℃ to form the photoalignment film.
Step S120, spacer particles are arranged on the first substrate and packaged with the second substrate, wherein one side of the photo-alignment film of the first substrate is opposite to one side of the photo-alignment film of the second substrate.
The size of the spacer can be selected according to specific requirements, and the distance between the first substrate and the second substrate can be adjusted by selecting the spacer with different sizes so as to realize that the phase difference between the ordinary light and the extraordinary light of the incident Gaussian beam in the liquid crystal phase plate is equal to odd times of pi; the advantage of this arrangement is that when the phase difference between the ordinary and extraordinary rays of the incident gaussian beam in the liquid crystal phase plate is equal to an odd multiple of pi, the beam emitted after the incident gaussian beam irradiates the liquid crystal phase plate is a set double-sided vortex beam, and the double-sided vortex beam has polarization controllable characteristics.
And S130, performing multi-step overlapped exposure on the photo-alignment film so that the molecular director directions of the photo-alignment film are arranged according to gray values of circular cubic phase and circular linear phase modulation spiral phase control patterns, wherein the circular cubic phase and circular linear phase modulation spiral phase control patterns are formed by overlapping the circular cubic phase patterns, the circular linear phase patterns and the spiral phase patterns.
The molecular directors in the photo-alignment film can be set by inducing the polarization direction of light, and particularly, a circular cubic phase and circular linear phase modulation spiral phase control pattern with the molecular directors in a spatially gradual distribution can be formed on the photo-alignment film by exposing an exposure pattern of 0-180 degrees by a plurality of times of partial overlapping, wherein the circular cubic phase and circular linear phase modulation spiral phase control pattern comprises a circular arc-shaped structure with a plurality of periods, the period of the circular arc-shaped structure gradually decreases from a central area to two sides, the circular linear phase pattern also comprises a circular arc-shaped structure with a plurality of periods, and the period of the circular arc-shaped structure remains unchanged from the central area to two sides.
Optionally, the photo-alignment film is subjected to multi-step overlapping exposure, so that the molecular director direction of the photo-alignment film is arranged according to a circular-cubic phase and circular-linear phase modulated spiral phase control pattern, wherein the circular-cubic phase and circular-linear phase modulated spiral phase control pattern is formed by overlapping a circular-cubic phase pattern, a circular-linear phase pattern and a spiral phase pattern, and the photo-alignment film comprises:
adopting a micro projection exposure system based on a numerical control micro mirror array, and selecting an exposure pattern corresponding to a phase value and a corresponding induced light polarization direction according to an exposure sequence to sequentially expose;
Wherein, the exposure areas of the exposure patterns of adjacent steps are partially overlapped, and the polarization direction of the induced light is monotonically increased or monotonically decreased along with the exposure sequence, so as to form a circular cubic phase and circular linear phase modulated spiral phase control pattern formed by overlapping a circular cubic phase pattern, a circular linear phase pattern and a spiral phase pattern.
Fig. 11 is a schematic flow chart of performing multi-step overlapped exposure on a photo-alignment film according to an embodiment of the present invention. Referring to fig. 11, there are three exposures, a first exposure, a second exposure, and a third exposure in this order, as an example. The three exposure patterns have the same period, and exemplary settings have 3 periods T1, T2, T3 per exposure pattern, with the width of each period gradually decreasing from the center region of the exposure pattern to both sides, exemplary t1=t3<T2. In the first exposure, a numerical control micro-mirror array exposure system is adopted to select a first exposure pattern, the polarization direction of induced light corresponding to the first exposure is 0 degrees, each period is divided into 3 equal parts Tn1, tn2 and Tn3, n=1, 2 and 3, and the exposure areas of the first exposure pattern are T11 and T12 of T1, T21 and T22 of T2 and T31 and T32 of T3. After the first exposure is completed, the second exposure pattern is replaced, the polarization direction of the corresponding induced light is selected to be 60 degrees, each period is divided into 3 equal parts, and the exposure areas of the second exposure pattern are T12 and T13 of T1, T22 and T23 of T2 and T32 and T33 of T3. After the second exposure is completed, the third exposure image is replaced, the polarization direction of the corresponding induced light is selected to be 120 degrees, each period is divided into 3 equal parts, and the exposure areas of the third exposure image are T11 and T13 of T1, T21 and T23 of T2 and T31 and T33 of T3. Therefore, the exposure area of the first exposure pattern is partially overlapped with the exposure area of the second exposure pattern, and the overlapped parts are T12, T22 and T32; the exposure area of the second exposure pattern is partially overlapped with the exposure area of the third exposure pattern, and the overlapped parts are T13, T23 and T33. T11, T12, T13, T21, T22, T23, T31, T32 and T33 are all exposed twice, the induced light polarization direction of each exposure is different, and the molecular director direction arrangement of the photo-alignment film is stable due to insufficient dose of each exposure (for example, when the exposure dose is 5J/cm 2 In the step of overlapping exposure, the molecular director direction arrangement of the photo-alignment film can be stably arranged, and the exposure dose can be selected to be 1J/cm 2 ) The sum of the doses of the multiple exposures is such that it is in a steady state and the molecular director direction of the photoalignment film is intermediate to the polarization angle of the multiple exposures experienced, e.g. T12 at the first exposureThe degree is 0 DEG, the polarization angle of T12 is 60 DEG in the second exposure, and then the molecular director direction of the photo-oriented film in the T12 region is between 0 DEG and 60 deg. Therefore, after multi-step overlapping exposure, a control pattern with a spatially gradual distribution of molecular directors is generated on the photoalignment film, and each period of the circular cubic phase and circular linear phase modulated spiral phase control pattern comprises a circular arc structure with a period gradually decreasing from a central area to two sides, a circular arc structure with a period kept unchanged from the central area to two sides, and a structure with a phase 0-pi rotation gradual change.
It should be noted that, fig. 11 illustrates three-step overlapping exposure, and is not limited to the embodiment of the present invention, generally, the more the number of exposure times (i.e. the more the polarization angles are equally divided by 0 ° -180 °), the more the number of equal division per period in the exposure pattern, the finer the spatial gradient distribution of the liquid crystal director direction, and the better the quality of the finally obtained double-sided vortex beam. In other embodiments, the number of exposures and the number of averages per cycle may be selected according to the actual requirements.
And step S140, a liquid crystal layer is poured between the first substrate and the second substrate, and the circular cubic phase and circular linear phase modulation spiral phase control patterns of the photo-alignment film control the alignment of liquid crystal molecule directors in the liquid crystal layer according to the circular cubic phase and circular linear phase modulation spiral phase control patterns.
The photoalignment film has an anchoring function, and under the control function of the circular cubic phase and circular linear phase modulation spiral phase control pattern formed in the step 130, liquid crystal molecular directors in the liquid crystal layer are distributed gradually in a space of 0-180 degrees, and incident Gaussian beams irradiated on a liquid crystal phase plate capable of generating double-sided vortex beams are converted into double-sided vortex beams.
The above embodiments do not limit the scope of the present invention. It will be apparent to those skilled in the art that various modifications, combinations, sub-combinations and alternatives are possible, depending on design requirements and other factors. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of the present invention.
Claims (10)
1. A liquid crystal phase plate, comprising:
the liquid crystal display comprises a first substrate, a second substrate and a liquid crystal layer, wherein the first substrate and the second substrate are oppositely arranged, and spacer particles are arranged between the first substrate and the second substrate so as to support the first substrate or the second substrate;
One side of the first substrate and the second substrate, which is close to the liquid crystal layer, is provided with a photo-alignment film, molecular directors of the photo-alignment film are arranged according to a circular cubic phase and a circular linear phase modulation spiral phase control pattern, the photo-alignment film controls liquid crystal molecular directors in the liquid crystal layer to be arranged according to the circular cubic phase and the circular linear phase modulation spiral phase control pattern, so that Gaussian beams irradiated on the liquid crystal phase plate are converted into polarization-controllable double-sided vortex beams, and the double-sided vortex beams have double-focus characteristics and have the characteristics of opposite spiral phases or opposite orbital angular momentum distribution at double focuses;
the circular-cubic phase and circular-linear phase modulation spiral phase control pattern is formed by superposing a circular-cubic phase pattern, a circular-linear phase pattern and a spiral phase pattern.
2. The liquid crystal phase plate of claim 1, wherein the molecular directors of the photoalignment film satisfy:
wherein,representing the circular-cubic phase in the circular-cubic phase graph, the expression of which satisfies:
representing the circular linear phase in the circular linear phase pattern, the expression of which satisfies:
Representing the vortex phase in the spiral phase pattern, the expression of which satisfies:
θ＝arctan(y/x)；
wherein x and y represent coordinates in a rectangular coordinate system with the center of the liquid crystal phase plate as an origin, beta is a parameter for controlling the modulation amount of the circular cubic phase, and lambda L Representing the period of the circular linear phase in the radial direction, m represents the topological charge number of the generated vortex beam.
3. The liquid crystal phase plate according to claim 1, wherein the circular-cubic phase pattern comprises a plurality of concentric circular-ring-cubic phase patterns, the phase period modulation amount of each circular-ring-cubic phase pattern is 2 pi, the phase modulation range of the circular-cubic phase pattern is 0 to 16 pi, and the width of each circular-ring-cubic phase pattern is gradually decreased in the radial direction from the central area of the circular-cubic phase pattern;
the circular linear phase patterns comprise a plurality of concentric circular linear phase patterns, the phase period modulation quantity of each circular linear phase pattern is 2 pi, the phase modulation range of each circular linear phase pattern is 0-30.8 pi, and the width of each circular linear phase pattern is kept unchanged along the radial direction from the central area of the circular linear phase pattern;
the spiral phase patterns comprise multi-order spiral phase patterns, the phase period modulation quantity of each spiral phase pattern is 2 pi, and the phase value of each spiral phase pattern is uniformly changed along with the azimuth angle.
4. The liquid crystal phase plate according to claim 1, wherein the material of the liquid crystal layer includes any one of nematic liquid crystal, dual-frequency liquid crystal, or ferroelectric liquid crystal;
the circular-cubic phase and circular-linear phase modulated spiral phase control pattern of the photo-alignment film can be erasable, and the photo-alignment film material comprises azo dye.
5. The liquid crystal phase plate according to claim 1, wherein a phase difference between ordinary light and extraordinary light in the liquid crystal phase plate satisfies:
wherein Δn is a difference in birefringence of liquid crystal molecules, d is a thickness of the liquid crystal layer, λ is a wavelength of an incident gaussian beam, and k is a natural number.
6. A polarization controllable double-sided vortex beam generation system, comprising:
a liquid crystal phase plate according to any one of claims 1 to 5;
a light source positioned on the light incident side of the liquid crystal phase plate so as to generate an incident Gaussian beam;
a polarizer and a quarter wave plate between the light source and the liquid crystal phase plate;
the double-lens structure and the imaging device are positioned on the light emitting side of the liquid crystal phase plate.
7. The polarization controllable double sided vortex beam generating system according to claim 6 wherein the optical axes of the light source, the polarizer, the quarter wave plate, the liquid crystal phase plate, the double lens structure and the imaging device are on the same straight line;
And controlling the intensity and the polarization state of the incident Gaussian beam by adjusting the included angle between the fast axis direction of the quarter wave plate and the polarization direction of the polaroid.
8. The polarization-controllable double-sided vortex beam generating system of claim 6, wherein,
when the incident Gaussian beam generated by the light source is a linear polarized Gaussian beam, the incident Gaussian beam is converted into a double-sided vortex beam through the liquid crystal phase plate;
when the incident Gaussian beam generated by the light source is a left-handed circularly polarized Gaussian beam or a right-handed circularly polarized Gaussian beam, the incident Gaussian beam is converted into a right-handed circularly polarized single-focus vortex Airy beam or a left-handed circularly polarized single-focus vortex Airy beam through the liquid crystal phase plate;
when one lens in the double-lens structure is removed, the incident Gaussian beam generated by the light source is a left-handed polarized Gaussian beam or a right-handed circularly polarized Gaussian beam, and the incident Gaussian beam is converted into a right-handed self-focusing vortex Airy beam or a left-handed self-defocusing vortex Airy beam through the liquid crystal phase plate.
9. A method of manufacturing a liquid crystal phase plate, comprising:
forming a photo-alignment film on one side of the first substrate and the second substrate;
Spacer particles are arranged on the first substrate and are encapsulated with the second substrate, wherein one side of the photo-alignment film of the first substrate is arranged opposite to one side of the photo-alignment film of the second substrate;
performing multi-step overlapping exposure on the photo-alignment film so that the molecular director direction of the photo-alignment film is arranged according to gray values of circular cubic phase and circular linear phase modulation spiral phase control patterns, wherein the circular cubic phase and circular linear phase modulation spiral phase control patterns are formed by overlapping a circular cubic phase pattern, a circular linear phase pattern and a spiral phase pattern;
and a liquid crystal layer is poured between the first substrate and the second substrate, and the circular cubic phase and circular linear phase modulation spiral phase control pattern of the photo-alignment film controls the arrangement of liquid crystal molecule directors in the liquid crystal layer according to the circular cubic phase and circular linear phase modulation spiral phase control pattern.
10. The method of manufacturing according to claim 9, wherein the photo-alignment film is subjected to multi-step overlapping exposure so that molecular director directions of the photo-alignment film are arranged in accordance with a circular-cubic phase and circular-linear phase modulated spiral phase control pattern formed by overlapping a circular-cubic phase pattern, a circular-linear phase pattern, and a spiral phase pattern, comprising:
Adopting a micro projection exposure system based on a numerical control micro mirror array, and selecting an exposure pattern corresponding to a phase value and a corresponding induced light polarization direction according to an exposure sequence to sequentially expose;
wherein the exposure areas of the exposure patterns of adjacent steps are partially overlapped, and the polarization direction of the induced light is monotonically increased or monotonically decreased along with the exposure sequence, so as to form a circular cubic phase and circular linear phase modulated spiral phase control pattern formed by overlapping a circular cubic phase pattern, a circular linear phase pattern and a spiral phase pattern.
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| 偏振方向对涡旋光束产生的影响;黄石明;聂建业;张蓉竹;;强激光与粒子束(第07期);全文 * |
| 光学涡旋产生方法的分析与研究;陈君;胡承忠;;泰山学院学报(第06期);全文 * |
| 基于光取向液晶的光场调控技术;陈鹏;徐然;胡伟;陆延青;;光学学报(第10期);全文 * |
| 基于双环形旋涡相位调制的多焦点产生;谭志华;翁晓羽;隋国荣;郭汉明;;光学仪器(第05期);全文 * |
| 基于液茹光控取向技木实现光场调控;魏冰研;中国博士学位论文全文数据库 工程科技I辑;全文 * |
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