CN115236786A - 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 148
- 238000002360 preparation method Methods 0.000 title abstract description 6
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- G—PHYSICS
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- 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
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- 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 embodiment of the invention discloses a liquid crystal phase plate, a preparation method and a double-sided vortex light 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 positioned between the first substrate and the second substrate, and spacing particles are arranged between the first substrate and the second substrate; the side, close to the liquid crystal layer, of the first substrate and the second substrate is provided with a light-operated orientation film, molecular directors of the light-operated orientation film are arranged according to a spiral phase control graph modulated by a circular cubic phase and a circular linear phase, and liquid crystal molecular directors in the liquid crystal layer are controlled to be arranged according to the control graph, so that a Gaussian beam irradiated on the liquid crystal phase plate is converted into a double-sided vortex beam with controllable polarization; the spiral phase control pattern modulated by the round cubic phase and the round linear phase is formed by superposing a round cubic phase pattern, a round linear phase pattern and a spiral phase pattern. According to the technical scheme of the embodiment of the invention, the polarization-controllable double-sided vortex light beam 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 light beam generation system.
Background
Vortex beams have been a focus of research in the field of optics in recent years. The vortex light beam has a spiral equiphase surface and carries orbital angular momentum; the presence of the phase singularity causes the vortex beam to appear as an annular spot centered on the dark field. Due to the unique property of the vortex light beam, the vortex light beam is 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 type of beam, the two-sided wave is also attracting attention of researchers. The two-sided wave has a "real" component and an "imaginary" component, respectively located at two symmetrical foci in opposite transmission directions. The virtual component can be introduced into the real space through the double-lens structure, so that the generation of a double-sided beam is realized. At present, research for generating double-sided vortex light beams based on double-sided wave regulation and control of vortex light beams is lacked at home and abroad, and related research can further expand application dimensions of the vortex light 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 light beam generation system.
According to an aspect of the present invention, there is provided a liquid crystal phase plate, including:
the liquid crystal display panel comprises a first substrate, a second substrate and a liquid crystal layer, wherein the first substrate and the second substrate are arranged oppositely, and the liquid crystal layer is positioned between the first substrate and the second substrate;
the side, close to the liquid crystal layer, of the first substrate and the second substrate is provided with a light-operated orientation film, molecular directors of the light-operated orientation film are arranged according to a spiral phase control graph modulated by a circular cubic phase and a circular linear phase, and the light-operated orientation film controls liquid crystal molecular directors in the liquid crystal layer to be arranged according to the spiral phase control graph modulated by the circular cubic phase and the circular linear phase, so that a Gaussian beam irradiated on the liquid crystal phase plate is converted into a double-sided vortex beam with controllable polarization;
the circular cubic phase and circular linear phase modulated 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 director of the photoalignment film satisfies:
wherein,
representing a circular cubic phase in the circular cubic phase pattern, the expression of which satisfies:
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 round cubic phase, and Λ is L Denotes the period of the circular linear phase in the radial direction, and m denotes the topological charge of the generated vortex beam.
Optionally, the circular cubic phase pattern includes a plurality of concentric circular cubic phase patterns, the phase period modulation amount of each circular cubic phase pattern is 2 pi, the phase modulation range of the circular cubic phase pattern is 0-16 pi, and the width of each circular cubic phase pattern gradually decreases from the central area of the circular cubic phase pattern along the radial direction;
the circular linear phase pattern comprises a plurality of concentric circular linear phase patterns, the phase period modulation amount of each circular linear phase pattern is 2 pi, the phase modulation range of the 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 amount 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 spiral phase control patterns of the circular cubic phase and circular linear phase modulation of the photoalignment film are erasable, and the material of the photoalignment film comprises azo dyes.
Optionally, the phase difference between the ordinary ray and the extraordinary ray in the liquid crystal phase plate satisfies:
where Δ n is a birefringence difference 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 described above;
the light source is positioned on the light incidence side of the liquid crystal phase plate 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 double-lens structure and the imaging device are located on the same straight line;
and controlling the intensity and the polarization state of the incident Gaussian beam by adjusting an included angle between the fast axis direction of the quarter-wave plate and the polarizing direction of the polarizing plate.
Optionally, when the incident gaussian beam generated by the light source 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 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, and the incident Gaussian beam generated by the light source is a left-handed polarized Gaussian beam or a right-handed circularly polarized Gaussian beam, the incident Gaussian beam is converted into a right-handed self-focused vortex Airy beam or a left-handed self-defocused vortex Airy beam through the liquid crystal phase plate.
According to another aspect of the present invention, there is provided a method of manufacturing a liquid crystal phase plate, including:
forming a photoalignment film on one side of the first substrate and the second substrate;
the spacer particles are arranged on the first substrate and are encapsulated with the second substrate, wherein one side of the light control orientation film of the first substrate is opposite to one side of the light control orientation film of the second substrate;
performing multi-step overlapping exposure on the photoalignment film to enable the molecular director direction of the photoalignment film to be arranged according to the gray value of 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 the circular cubic phase pattern, the circular linear phase pattern and the 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 modulated spiral phase control pattern of the photo-alignment film controls the arrangement of liquid crystal molecular directors in the liquid crystal layer according to the circular cubic phase and circular linear phase modulated spiral phase control pattern.
Optionally, the light control orientation film is subjected to multi-step overlapping exposure, so that the molecular director directions of the light control orientation film are 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 light control orientation film comprises:
adopting a miniature projection exposure system based on a numerical control micromirror array, selecting an exposure pattern corresponding to a phase value and a corresponding induced light polarization direction according to an exposure sequence, and sequentially exposing;
the exposure areas of the exposure patterns in the 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 that a circular cubic phase control pattern and a circular linear phase control pattern modulated by the circular cubic phase and the circular linear phase are formed by overlapping the circular cubic phase pattern, the circular linear phase pattern and the 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, and the liquid crystal layer is positioned between the first substrate and the second substrate; wherein, interval particles are arranged between the first substrate and the second substrate to support the first substrate or the second substrate; the side, close to the liquid crystal layer, of the first substrate and the second substrate is provided with a light-operated orientation film, molecular directors of the light-operated orientation film are arranged according to a spiral phase control graph modulated by a circular cubic phase and a circular linear phase, and liquid crystal molecular directors in the liquid crystal layer are controlled by the light-operated orientation film to be arranged according to the spiral phase control graph modulated by the circular cubic phase and the circular linear phase, so that a Gaussian beam irradiated on the liquid crystal phase plate is converted into a double-sided vortex beam with controllable polarization; the circular cubic phase and circular linear phase modulated spiral phase control pattern is formed by superposing a circular cubic phase pattern, a circular linear phase pattern and a spiral phase pattern. The light-operated orientation films are arranged on the first substrate and the second substrate which are oppositely arranged, molecular directors of the light-operated orientation films are arranged according to a spiral phase control graph modulated by a circular cubic phase and a circular linear phase, and the control graph of the light-operated orientation films controls liquid crystal molecular directors in the liquid crystal layer to be gradually distributed in a 0-180-degree mode according to the spiral phase control graph modulated by the circular cubic phase and the circular linear phase, so that a Gaussian beam irradiated on the liquid crystal phase plate is converted into a double-sided vortex beam with controllable polarization. The double-sided vortex light 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 light beam and the length of the focuses can realize customized design by changing spiral phase control graphic parameters of circular cubic phase and circular linear phase modulation according to requirements.
It should be understood that the statements in this section do not necessarily identify key or critical features of the embodiments of the present invention, nor do they necessarily limit the scope of the invention. Other features of the present invention will become apparent from the following description.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
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 the 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 illustrating a process of forming a spiral phase control pattern with circular cubic phase and circular linear phase modulation according to an embodiment of the present invention;
FIG. 5 is a microscopic view of a sample of a liquid crystal phase plate when the phase difference between ordinary and extraordinary rays is equal to an odd multiple of π;
FIG. 6 is a schematic structural diagram of a polarization-controllable double-sided vortex beam generation system according to an embodiment of the present invention;
FIG. 7 is a schematic diagram of a two-sided vortex beam spot profile generated by modulation with the liquid crystal phase plate of FIG. 5, a simulation diagram of transmission dynamics, and an experimental diagram;
FIG. 8 is a phase distribution simulation diagram and experimental measurement diagram of a double-sided vortex beam generated by a liquid crystal phase plate;
FIG. 9 is a diagram showing a simulation of polarization distribution and experimental measurements of a double-sided vortex beam generated by a liquid crystal phase plate;
FIG. 10 is a schematic flow chart illustrating 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 a multi-step overlay exposure process for a photo-alignment film according to an embodiment of the present invention.
Detailed Description
In order to make the technical solutions of the present invention better understood, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It should be noted that the terms "first," "second," and the like in the description and claims of the present invention and in the drawings described above are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the invention described herein are capable of operation in sequences other than those illustrated or described herein. Moreover, 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 this 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 located between the first substrate 11 and the second substrate 12; wherein, the spacer 14 is disposed between the first substrate 11 and the second substrate 12 to support the first substrate 11 or the second substrate 12 and form an accommodating space of the liquid crystal layer 13; the sides of the first substrate 11 and the second substrate 12 adjacent to the liquid crystal layer 13 are provided with photo-alignment films 15 and 16, molecular directors of the photo-alignment films 15 and 16 are arranged according to a spiral phase control pattern of circular cubic phase and circular linear phase modulation, and the photo-alignment films 15 and 16 control liquid crystal molecular directors in the liquid crystal layer 13 to be arranged according to a spiral phase control pattern of circular cubic phase and circular linear phase modulation, so that incident gaussian light beams irradiated on the liquid crystal phase plate are converted into double-sided vortex light beams with controllable polarization. The control patterns of the photo-alignment films 15 and 16 are the same, and the circular cubic phase and circular linear phase modulated 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 the liquid crystal director distribution corresponding to the structure of FIG. 1. Referring to fig. 2, under the anchoring action of the photoalignment film, since the molecular director directions of the photoalignment film are aligned according to the spiral phase control pattern of the circular cubic phase and the circular linear phase modulation, the photoalignment film causes the directors of the liquid crystal molecules in the liquid crystal layer to be correspondingly aligned from 0 ° to 180 ° in each period 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 forming process of 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 gray scale value gradation of 0-255 can be regarded as a simulated schematic diagram of the spatial gradation distribution of the liquid crystal director direction of 0-180 °, where the gradation of the liquid crystal director direction from 0 ° to 180 ° is represented by 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, where the circular cubic phase pattern indicates that the phase in each phase change period changes in a cubic law in the radial direction, the circular linear phase pattern indicates that the phase in each phase change period changes in a linear law in the radial direction, and the spiral phase pattern indicates that the phase in each phase change period changes in a linear law in the angular direction. The three patterns (a), (b) and (c) in fig. 4 are superposed to obtain the spiral phase control pattern including the circular cubic phase and the circular linear phase modulation shown in fig. 3.
According to the technical scheme of the embodiment of the invention, the light-operated orientation films are arranged on the first substrate and the second substrate which are oppositely arranged, and molecular directors of the light-operated orientation films are arranged according to the spiral phase control graph modulated by the circular cubic phase and the circular linear phase, and the control graph of the light-operated orientation films controls the liquid crystal molecular directors in the liquid crystal layer to be gradually distributed in a 0-180-degree mode according to the spiral phase control graph 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 double-sided vortex beams with controllable polarization. The double-sided vortex light 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 light beam and the length of the focuses can realize customized design by changing spiral phase control graphic parameters of circular cubic phase and circular linear phase modulation according to requirements.
On the basis of the above embodiment, optionally, the molecular director of the photoalignment film satisfies:
wherein,
representing the circular cubic phase in the circular cubic phase graph, and the expression satisfies:
wherein x and y represent coordinates in a rectangular coordinate system with the center of the liquid crystal phase plate as the origin, beta is a parameter for controlling the modulation amount of the round cubic phase, and Λ is L Representing the circumference of a circular linear phase in the radial directionAnd m represents the topological charge of the generated vortex beam.
It can be understood that different circular cubic phases and spiral phase control patterns of circular linear phase modulation can be designed according to requirements by changing the circular cubic phase modulation amount, the period of the circular linear phase, the order of the spiral phase and the like, so that different polarization-controllable double-sided vortex light beams can be generated.
Optionally, with reference to fig. 4 (a), the circular cubic phase pattern includes a plurality of concentric circular cubic phase patterns, the phase period modulation amount of each circular 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 cubic phase pattern gradually decreases from the central area of the circular cubic phase pattern along the radial direction; with continued reference to FIG. 4 (b), the circular linear phase pattern comprises a plurality of concentric circular ring linear phase patterns, the phase period modulation amount of each circular ring linear phase pattern is 2 π, the phase modulation range of the circular linear phase pattern is 0-30.8 π, the width of each circular ring linear phase pattern remains unchanged in the radial direction from the central region of the circular linear phase pattern, plotted with 1080 × 1080 resolution, corresponding Λ L Is 35 pixels; with reference to fig. 4 (c), the spiral phase pattern includes multiple spiral phase patterns, the phase period modulation amount of each spiral phase pattern is 2 pi, and the phase value of each spiral phase pattern changes uniformly with the azimuth angle, in this embodiment, the number of phase periods of the spiral phase pattern is 6, and the corresponding value m is 6.
It can be understood that the larger the value range of the circular cubic phase, the larger the cycle number of the circular cubic phase cycle pattern, the larger the focal length of the correspondingly generated double-sided vortex light beam, and the circular cubic phase range is set to be 0-16 pi in this embodiment. The larger the value range of the circular linear phase is, the smaller the period is, the more the period number of the circular linear phase period pattern is, 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 0-30.8 pi in the embodiment. The larger the m value of the spiral phase, the larger the number of periods of the spiral period pattern, the larger the topological charge of the correspondingly generated vortex light beam, and the larger the central dark spot, and the m value is set to 6 in this embodiment. In specific implementation, the ranges of the circular cubic phase and the circular linear phase and the magnitude of the topological load can be set according to actual requirements, which is not limited in the embodiment of the invention.
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 patterns of the round cubic phase and round linear phase modulation of the light-operated orientation film are erasable, and the material of the light-operated orientation film comprises azo dye.
It can be understood that the liquid crystal layer can be made of any one of nematic liquid crystal, dual-frequency liquid crystal or ferroelectric liquid crystal, and can be selected according to actual conditions during specific implementation, the photoalignment film is made of azo dye, so that the liquid crystal phase plate can be recycled, and the structure of the liquid crystal phase plate capable of generating the double-sided vortex light beams can be changed in real time by erasing and writing a spiral phase control pattern modulated by circular cubic phase and circular linear phase on the photoalignment film, so that the double-sided vortex light beams in various modes can be generated.
Optionally, the phase difference of the ordinary ray and the extraordinary ray in the liquid crystal phase plate satisfies:
where Δ n is a birefringence difference 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.
It can be understood that the thickness of the liquid crystal layer can be controlled such that the phase difference of the ordinary and extraordinary rays of the incident gaussian beam in the liquid crystal phase plate is equal to an odd multiple of pi by adjusting the distance between the first and second substrates by adjusting the size of the spacer. FIG. 5 is a schematic microscopic view of a sample of a liquid crystal phase plate in which the phase difference between ordinary and extraordinary rays is equal to an odd multiple of π, with the scale of 100 μm. The liquid crystal phase plate has the advantages that when the phase difference of the ordinary light and the extraordinary light of the incident Gaussian beam in the liquid crystal phase plate is equal to the odd multiple of pi, the light beam emitted after the incident Gaussian beam irradiates the liquid crystal phase plate is a double-sided vortex light beam with controllable polarization, and the use of electrodes is avoided.
Fig. 6 is a schematic structural diagram of a polarization-controllable double-sided vortex beam generation system according to an embodiment of the present invention. Referring to fig. 6, the polarization-controllable double-sided vortex beam generation system includes any one of the liquid crystal phase plates 21 provided in the above-described embodiments; a light source 22 located at 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 between the light source 22 and the liquid crystal phase plate 21; a double lens structure (lenses 23 and 24) and an imaging device 25 on the light exit side of the liquid crystal phase plate 21.
The light source 22 may be a laser light source, which has good collimation property, and the quality of the double-sided vortex light 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 incident gaussian beam with an arbitrary wavelength to a double-sided vortex beam can be realized. Illustratively, the wavelength may be set to be greater than 500nm, so as to avoid the influence of the incident gaussian beam emitted 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, a 671nm laser is used to irradiate the liquid crystal phase plate 21, and Fourier transform and focusing are performed through a double-lens structure composed of a lens 23 with a focal length of 100mm and a lens 24 with a focal length of 150mm, so that a double-sided vortex beam can be obtained. The embodiment of the present invention does not limit the focal lengths of the lenses 23 and 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 polarizer 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 located 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 polarizing direction of the polarizer 26.
The polarization-controllable double-sided vortex light beam generation system provided by the embodiment of the invention generates a preset incident polarization Gaussian beam through the light source, and converts the incident Gaussian beam into the double-sided vortex light beam through the liquid crystal phase plate capable of generating the double-sided vortex light beam. The double-sided vortex light 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 light beam and the length of the focal length can realize customized design by changing spiral phase control graphic parameters of circular cubic phase and circular linear phase modulation according to requirements.
Optionally, 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 through the liquid crystal phase plate 21; when one of the two lenses is removed, the incident gaussian beam generated by the light source 22 is left-handed polarized gaussian beam or right-handed circularly polarized gaussian beam, and the incident gaussian beam is converted into a right-handed self-focused vortex airy beam or a left-handed self-defocused vortex airy beam by the liquid crystal phase plate 21.
Fig. 7 is a schematic diagram of a two-sided vortex beam spot profile generated by modulation of the liquid crystal phase plate shown in fig. 5, and a simulation diagram and an experimental diagram of transmission dynamics. 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 transmission 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 radius of the main ring of the double-sided vortex light beam gradually decreases, the energy is gradually concentrated, the first focusing is carried out at 12cm, and then the radius of the main ring gradually increases, and the energy is gradually diffused. At a transmission distance of 15cm as shown in fig. 7 (e), i.e. at the focal plane of the second lens (lens 24) in the dual lens configuration, although the dark field at the center of the beam is reduced, this non-focused state is the result of the vector light field formed by the superposition of the vortex beams of opposite topological charge. With further increase in transmission distance, the main ring radius is again decreased from large to small, and the intensity is again increased until refocusing at 18 cm. After the transmission distance is larger than 18cm, the light beam is always divergent. Fig. 7 (j) is a dynamic experimental result of transmission of the double-sided vortex light beam generated after modulation by the liquid crystal phase plate, in which a hollow circle is the measured radius of the main ring of the double-sided vortex light beam at different transmission distances, and a curve is parabolic fit, representing the transmission trajectory of the double-sided vortex light beam. As can be seen from the figure, the light beam undergoes a process of focusing-diverging-focusing-diverging as the transmission distance increases. Fig. 7 (k) is a simulation diagram of a transmission trajectory of a double-sided vortex beam, and the experimental result of fig. 7 (j) is substantially identical to the simulation result of fig. 7 (k). When the incident Gaussian beam generated by the light source is in left-hand circular polarization, the incident Gaussian beam is converted into a single-focus vortex Airy beam in right-hand circular polarization through the liquid crystal phase plate, and the focus is at the position of 12cm of transmission distance; when the incident Gaussian beam generated by the light source is right-handed circularly polarized, the incident Gaussian beam is converted into a single-focus vortex Airy beam with left-handed circularly polarized through the liquid crystal phase plate, and the focus is at the position with the transmission distance of 18 cm. When one of the lenses in the dual-lens structure, such as lens 24, is removed, 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 transformed into a right-handed self-focused vortex airy beam or a left-handed self-defocused vortex airy beam by the lc phase plate, as shown in the simulated inner and outer ring beam transmission dynamics of fig. 7 (l), respectively.
FIG. 8 is a simulation diagram and experimental measurement diagram of the phase distribution of a double-sided vortex beam generated by 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 lens 24) and 18cm (at the second focal plane), respectively, with experimental results substantially in accordance with theoretical results. At the first focal plane shown in FIGS. 8 (a) and 8 (d), the helical phase that has undergone 6 counterclockwise changes from 0 to 2 π is detected, indicating that the double-sided vortex beam carries a topological charge of +6 or orbital angular momentum at this focal plane
In contrast, at the second focal plane shown in FIGS. 8 (c) and 8 (f), the helical phase was detected as having undergone 6 clockwise changes from 0 to 2 π, showing that the orbital angular momentum carried by the double-sided vortex beam at this focal plane is
The phase distribution at these two focal planes verifies the characteristics of the opposite helical phase or opposite orbital angular momentum distribution of the double-sided vortex beam at the dual focal points. At the focal plane position of the lens 24 in fig. 8 (b) and (e), the phase distribution of the light field exhibits 6 phase jumps of 0-pi, which characterizes a vector light beam with a polarization order of 6, and also verifies the analysis of the vector light field in fig. 7 at a transmission distance of 15 cm.
FIG. 9 is a simulation diagram and experimental measurement diagram of polarization distribution of a double-sided vortex beam generated by a liquid crystal phase plate. FIGS. 9 (a) - (b) and FIGS. 9 (c) - (d) are simulated and experimentally measured polarization distributions of the double-vortex light beam at the first and second focal planes, respectively, with background on the intensity distribution of the corresponding double-vortex light beam. Wherein, darker polarized ellipses in the images of fig. 9 (a) - (b) indicate that the double-sided vortex light beam at the corresponding focus is in a right-handed circular polarized state, and brighter polarized ellipses in the images of fig. 9 (c) - (d) indicate that the double-sided vortex light beam at the corresponding focus is in a left-handed circular polarized 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 the opposite spin angular momentum distribution of the double-sided vortex beam at the dual focal points.
It can be understood that different circular cubic phases and spiral phase control patterns of circular linear phase modulation can be designed according to requirements by changing the circular cubic phase modulation amount, the period of the circular linear phase, the order of the spiral phase and the like, so that different polarization-controllable double-sided vortex light beams can be generated.
Optionally, the structure of the liquid crystal phase plate capable of generating the double-sided vortex light beam can be changed in real time by erasing and writing a circle cubic phase control pattern of circle radial linearity and spiral phase modulation on the photo-alignment film, so that the double-sided vortex light beam in multiple modes can be generated.
Fig. 10 is a schematic flow chart illustrating 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:
step S110 of forming a photoalignment film on one side of the first substrate and the second substrate.
Optionally, the first substrate and the second substrate may be glass substrates, and before the formation of the photoalignment film, in order to increase wettability and adhesiveness of the photoalignment film with the first substrate and the second substrate, the glass substrates are ultrasonically cleaned with a cleaning solution (mixed reagent such as acetone and alcohol) for 30 minutes, and then ultrasonically cleaned with ultrapure water twice, each for 10 minutes. 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 a photoalignment material on one side of a first substrate and a second substrate, the spin coating parameters being: spin-coating at low speed for 5 seconds at 800 rpm, spin-coating at high speed for 40 seconds at 3000 rpm;
and annealing the first substrate and the second substrate which are coated with the light control orientation material in a spinning mode for 10 minutes at the annealing temperature of 100 ℃ to form the light control orientation film.
Step S120, disposing a spacer on the first substrate and encapsulating the spacer with the second substrate, wherein the photoalignment film side of the first substrate is disposed opposite to the photoalignment film side of the second substrate.
The size of the spacer particles can be selected according to specific needs, and the distance between the first substrate and the second substrate can be adjusted by selecting the spacer particles with different sizes, so that the phase difference of ordinary light and extraordinary light of an 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 ray and the extraordinary ray of the incident gaussian light beam in the liquid crystal phase plate is equal to an odd multiple of pi, the incident gaussian light beam irradiates the liquid crystal phase plate and then exits as a set double-sided vortex light beam, and the double-sided vortex light beam has polarization controllable characteristics.
Step S130, performing multi-step overlay exposure on the photo-alignment film to arrange the molecular director direction of the photo-alignment film according to the gray values of the circular cubic phase and circular linear phase modulated spiral phase control patterns, wherein the circular cubic phase and circular linear phase modulated spiral phase control patterns are formed by overlapping the circular cubic phase pattern, the circular linear phase pattern and the spiral phase pattern.
The molecular director in the photoalignment film can be set by inducing the polarization direction of light, specifically, a circular cubic phase and circular linear phase modulated spiral phase control pattern with the molecular director gradually distributed in a space gradient manner can be formed on the photoalignment film through a plurality of times of partially overlapped exposure patterns of 0-180 degrees, wherein the circular cubic phase pattern of the circular cubic phase and circular linear phase modulated spiral phase control pattern comprises a plurality of periods of circular arc structures, the periods of the circular arc structures gradually decrease from a central area to two sides, the circular linear phase pattern also comprises a plurality of periods of circular arc structures, and the periods of the circular arc structures are kept unchanged from the central area to the two sides.
Optionally, the light-control alignment film is subjected to multi-step overlapping exposure, so that the molecular director direction of the light-control alignment film is arranged according to a circular cubic phase and a 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 method includes:
adopting a miniature projection exposure system based on a numerical control micromirror array, selecting an exposure pattern corresponding to a phase value and a corresponding induced light polarization direction according to an exposure sequence, and sequentially exposing;
the exposure areas of the exposure patterns in the 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 that a circular cubic phase control pattern and a circular linear phase control pattern modulated by the circular cubic phase and the circular linear phase are formed by overlapping the circular cubic phase pattern, the circular linear phase pattern and the spiral phase pattern.
Fig. 11 is a schematic flow chart of a multi-step overlay exposure process for a photo-alignment film according to an embodiment of the present invention. Referring to fig. 11, illustratively, there are three exposures, in order of a first exposure, a second exposure, and a third exposure. Exposure by triple exposureThe light patterns have the same period, each exposure pattern is exemplarily set to have 3 periods T1, T2, T3, the width of each period gradually decreases from the central region of the exposure pattern to both sides, and exemplarily T1= T3<And T2. During the first exposure, a numerical control micro-mirror array exposure system is adopted to select a first exposure pattern, the induced light polarization direction corresponding to the first exposure is 0 degrees, each period is divided into 3 equal parts Tn1, tn2 and Tn3, n =1,2,3, and the exposure area of the first exposure pattern is T11 and T12 of T1, T21 and T22 of T2, and T31 and T32 of T3. After the first exposure is finished, the second exposure pattern is replaced, the corresponding induced light polarization direction is selected to be 60 degrees, each period is divided into 3 equal parts, and the exposure area of the second exposure pattern is T12 and T13 of T1, T22 and T23 of T2, and T32 and T33 of T3. And after the second exposure is finished, replacing a third exposure image, selecting the corresponding induced light polarization direction to be 120 degrees, dividing each period into 3 equal parts, and setting the exposure area of the third exposure image to be T11 and T13 of T1, T21 and T23 of T2 and T31 and T33 of T3. Therefore, the exposure region of the first exposure pattern overlaps with the exposure region of the second exposure pattern by T12, T22, T32; the exposure area of the second exposure pattern partially overlaps the exposure area of the third exposure pattern by T13, T23, T33. T11, T12, T13, T21, T22, T23, T31, T32 and T33 are exposed twice, the induced light polarization direction of each exposure is different, and the dose of each exposure is not enough to make the molecular director direction arrangement of the photoalignment film reach stable arrangement (for example, when the exposure dose is 5J/cm) 2 In the process, the molecular director direction arrangement of the light-operated orientation film can reach stable arrangement, and the exposure dose can be selected to be 1J/cm during step-by-step overlapping exposure 2 ) The sum of the multiple exposure doses is such that it is in a stable state and the molecular director direction of the photoalignment film is in an intermediate state of the polarization angle of the multiple exposures experienced, e.g., T12 is 0 ° at the first exposure, T12 is 60 ° at the second exposure, then the molecular director direction of the photoalignment film in the T12 region is between 0 ° and 60 °. Therefore, after multi-step overlapping exposure, a control pattern with a spatially gradually-changed molecular director direction is generated on the photoalignment film and is round and verticalEach period of the spiral phase control pattern of the square phase and circular linear phase modulation comprises a circular arc structure with the period gradually decreasing from the central area to two sides, a circular arc structure with the period unchanged from the central area to two sides and a structure with the phase gradually changing in a 0-pi rotation mode.
It should be noted that fig. 11 exemplarily selects three-step overlap exposure, and does not limit the embodiment of the present invention, and generally, the more the exposure times (i.e. the more polarization angles of 0-180 ° average), the more the number of average in each period in the exposure pattern, the finer the liquid crystal director direction is spatially gradually distributed, 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 actual needs.
Step S140, filling a liquid crystal layer between the first substrate and the second substrate, wherein the circular cubic phase and circular linear phase modulated spiral phase control pattern of the photoalignment film controls the 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.
The photoalignment film has an anchoring function, under the control function of the spiral phase control pattern of the circular cubic phase and circular linear phase modulation formed in step 130, the director of the liquid crystal molecules in the liquid crystal layer is in a gradual change distribution of 0-180 degrees in space, and incident Gaussian beams irradiated on the liquid crystal phase plate capable of generating the double-sided vortex beams are converted into the double-sided vortex beams.
The above-described embodiments should not be construed as limiting the scope of the invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions may be made in accordance with design requirements and other factors. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. A liquid crystal phase plate, comprising:
the liquid crystal display panel comprises a first substrate, a second substrate and a liquid crystal layer, wherein the first substrate and the second substrate are arranged oppositely, and the liquid crystal layer is positioned between the first substrate and the second substrate;
the side, close to the liquid crystal layer, of the first substrate and the second substrate is provided with a light-operated orientation film, molecular directors of the light-operated orientation film are arranged according to a spiral phase control graph modulated by a circular cubic phase and a circular linear phase, and the light-operated orientation film controls liquid crystal molecular directors in the liquid crystal layer to be arranged according to the spiral phase control graph modulated by the circular cubic phase and the circular linear phase, so that a Gaussian beam irradiated on the liquid crystal phase plate is converted into a double-sided vortex beam with controllable polarization;
the circular cubic phase and circular linear phase modulated 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 panel according to claim 1, wherein the molecular director of the photoalignment film satisfies:
wherein,
representing a circular cubic phase in the circular cubic phase pattern, the expression of which satisfies:
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 round cubic phase, and Λ is L Denotes the period of the circular linear phase in the radial direction, and m denotes the topological charge 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 cubic phase patterns, each of the circular cubic phase patterns has a phase period modulation amount of 2 pi, the circular cubic phase patterns has a phase modulation range of 0 to 16 pi, and a width of each of the circular cubic phase patterns gradually decreases in a radial direction from a central region of the circular cubic phase pattern;
the circular linear phase pattern comprises a plurality of concentric circular linear phase patterns, the phase period modulation amount of each circular linear phase pattern is 2 pi, the phase modulation range of the 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 amount 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 comprises any one of nematic liquid crystal, dual frequency liquid crystal, or ferroelectric liquid crystal;
the spiral phase control pattern of the round cubic phase and round linear phase modulation of the light-operated orientation film is erasable, and the material of the light-operated orientation film comprises azo dye.
5. The liquid crystal phase plate according to claim 1, wherein the phase difference of the ordinary ray and the extraordinary ray in the liquid crystal phase plate satisfies:
where Δ n is a birefringence difference 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 generating system, comprising:
a liquid crystal phase plate according to any one of claims 1 to 5;
the light source is positioned on the light incident side of the liquid crystal phase plate 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 of claim 6, wherein the optical axes of said light source, said polarizer, said quarter wave plate, said liquid crystal phase plate, said double lens structure and said imaging device are located on the same line;
and controlling the intensity and the polarization state of the incident Gaussian beam by adjusting an included angle between the fast axis direction of the quarter-wave plate and the polarizing direction of the polarizing plate.
8. The polarization-controllable double-sided vortex beam generating system of claim 6,
when the incident Gaussian beam generated by the light source is a linearly 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, and the incident Gaussian beam generated by the light source is a left-handed polarized Gaussian beam or a right-handed circularly polarized Gaussian beam, the incident Gaussian beam is converted into a right-handed self-focused vortex Airy beam or a left-handed self-defocused vortex Airy beam through the liquid crystal phase plate.
9. A method for preparing a liquid crystal phase plate, comprising:
forming a photoalignment film on one side of the first substrate and the second substrate;
the spacer particles are arranged on the first substrate and are encapsulated with the second substrate, wherein one side of the light control orientation film of the first substrate is opposite to one side of the light control orientation film of the second substrate;
performing multi-step overlapping exposure on the photoalignment film to enable the molecular director direction of the photoalignment film to be arranged according to the gray value of 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 the circular cubic phase pattern, the circular linear phase pattern and the 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 graph of the photoalignment film controls the arrangement of liquid crystal molecular directors in the liquid crystal layer according to the circular cubic phase and circular linear phase modulation spiral phase control graph.
10. The production method according to claim 9, wherein the photo-alignment film is subjected to multiple overlapping exposures such that the 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 in which a circular cubic phase and a circular linear phase modulated spiral phase control pattern are superimposed, and wherein the multiple overlapping exposures comprise:
adopting a miniature projection exposure system based on a numerical control micromirror array, selecting an exposure figure corresponding to a phase value and a corresponding induced light polarization direction according to an exposure sequence, and sequentially exposing;
the exposure areas of the exposure patterns in the 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 that a circular cubic phase control pattern and a circular linear phase control pattern modulated by the circular cubic phase and the circular linear phase are formed by overlapping the circular cubic phase pattern, the circular linear phase pattern and the spiral phase pattern.
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