CN109709708B - Liquid crystal Dammann cubic phase plate, preparation method and generation system - Google Patents
Liquid crystal Dammann cubic phase plate, preparation method and generation system Download PDFInfo
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- CN109709708B CN109709708B CN201910180816.XA CN201910180816A CN109709708B CN 109709708 B CN109709708 B CN 109709708B CN 201910180816 A CN201910180816 A CN 201910180816A CN 109709708 B CN109709708 B CN 109709708B
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Abstract
The embodiment of the invention discloses a liquid crystal Dammann cubic phase plate, a preparation method and a generation system. The liquid crystal Dammann cubic 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, 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 liquid crystal layer; 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 Dammann cubic phase control graph, and the light-operated orientation film controls liquid crystal molecular directors in the liquid crystal layer to be arranged according to the Dammann cubic phase control graph, so that incident light irradiated on the liquid crystal Dammann cubic phase plate is converted into a polarization-controllable Airy light beam array; the Dammann cubic phase control pattern is formed by superposing a cubic phase pattern and a Dammann grating pattern. According to the technical scheme of the embodiment of the invention, the Airy beam array with equal energy distribution and controllable polarization can be generated.
Description
Technical Field
The embodiment of the invention relates to a liquid crystal phase plate design and orientation control technology, in particular to a liquid crystal Dammann cubic phase plate, a preparation method and a generation system.
Background
Diffraction is the basic characteristic of a light beam, and due to diffraction, the light beam gradually increases in spot and gradually disperses energy in the transmission process. With the continuous expansion and deepening of the application of laser in the long-distance transmission fields such as communication, military and the like, people increasingly hope to eliminate diffraction and reduce the transmission dissipation of laser beams.
The non-diffraction, self-acceleration and self-healing characteristics of the Airy beams cause the Airy beams to be widely concerned in the field of space structure light fields, and the singular characteristics can cause the Airy beams to be applied to the aspects of particle manipulation, generation of a bent plasma channel, transmission in atmospheric turbulence, biological microscopic imaging and the like. If the array of Airy beams can be generated, the application of the Airy beams in the fields of optical tweezers, atmospheric science, biomedicine and the like can be greatly expanded.
Disclosure of Invention
The invention provides a liquid crystal Dammann cubic phase plate, a preparation method and a generation system, which are used for generating an equal-energy-distribution polarization-controllable Airy beam array.
In a first aspect, an embodiment of the present invention provides a liquid crystal dammann cubic phase plate, including a first substrate and a second substrate that are disposed opposite to each other, and a liquid crystal layer located between the first substrate and the second substrate; wherein a spacer is disposed between the first substrate and the second substrate to support the liquid crystal layer;
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 Dammann cubic phase control pattern, and the light-operated orientation film controls liquid crystal molecular directors in the liquid crystal layer to be arranged according to the Dammann cubic phase control pattern, so that incident light irradiating the liquid crystal Dammann cubic phase plate is converted into a polarized Airy light beam array;
the Dammann cubic phase control graph is formed by overlapping a cubic phase graph and a Dammann grating graph.
Optionally, the molecular director of the photoalignment film satisfies:
wherein the content of the first and second substances,
representing the cubic phase of the cubic phase pattern, the expression of which satisfies:
wherein x and y represent coordinates of a rectangular coordinate system with the center of the liquid crystal Dammann cubic phase plate as an origin, the function u () is a step function, u (t ≧ 0) ═ 1, u (t < 0) ═ 0, and xn、xn+1Is the phase jump point.
Optionally, the cubic phase pattern includes a cubic phase periodic pattern formed by a plurality of arcs, and a cubic phase range of the cubic phase periodic pattern is-15 pi to 15 pi;
the width of each of the cubic phase period patterns gradually decreases from the central region of the cubic phase period pattern toward both sides.
Optionally, the material of the liquid crystal layer is any one of nematic liquid crystal, dual-frequency liquid crystal or ferroelectric liquid crystal;
the Dammann cubic phase control graph of the light control orientation film is erasable, and the material of the light control orientation film is azo dye.
Optionally, the phase difference between the ordinary ray and the extraordinary ray in the liquid crystal Dammann cubic phase plate satisfies:
where Δ n is the birefringence difference of the liquid crystal molecules, d is the liquid crystal layer thickness, λ is the wavelength of incident light, and k is a natural number.
In a second aspect, an embodiment of the present invention further provides a polarization-controllable airy beam array generating system, including:
the liquid crystal dammann cubic phase plate according to the first aspect;
the light source is positioned on the light incidence side of the liquid crystal Dammann cubic phase plate to generate incident light;
the lens and the imaging device are positioned on the light-emitting side of the liquid crystal Dammann cubic phase plate;
wherein the optical axes of the light source, the liquid crystal Dammann cubic phase plate, the lens and the imaging device are positioned on the same straight line.
Optionally, the method further includes:
the polarizer and the quarter-wave plate are positioned between the light source and the liquid crystal Dammann cubic phase plate, and the optical axes of the light source, the polarizer, the quarter-wave plate, the liquid crystal Dammann cubic phase plate, the lens and the imaging device are positioned on the same straight line; and controlling the polarization state of the incident light by adjusting the included angle between the fast axis direction of the quarter-wave plate and the polarizing direction of the polarizing plate.
Optionally, the Dammann grating pattern in the liquid crystal Dammann cubic phase plate is a two-dimensional Dammann grating pattern;
the duty ratio of the two-dimensional Dammann grating pattern is 1:1, phase jump point x1When the value is 0.5:
when the incident light generated by the light source is a circularly polarized Gaussian beam, the incident light is converted into 2 multiplied by 2 array Airy beams with equal energy distribution through the liquid crystal Dammann cubic phase plate;
when the incident light generated by the light source is a linearly polarized Gaussian beam, the incident light is converted into a 2 x 2 array of Airy beams with equal energy distribution through the liquid crystal Dammann cubic phase plate.
In a third aspect, an embodiment of the present invention further provides a method for preparing a liquid crystal dammann cubic 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 a Dammann cubic phase control pattern, wherein the Dammann cubic phase control pattern is formed by overlapping a cubic phase pattern and a Dammann grating pattern;
and a liquid crystal layer is poured between the first substrate and the second substrate, and the Dammann cubic phase control pattern of the light control orientation film controls the arrangement of liquid crystal molecular directors in the liquid crystal layer according to the Dammann cubic phase control pattern.
Optionally, the light control alignment film is subjected to multi-step overlapping exposure so that the molecular director directions of the light control alignment film are arranged according to a dammann cubic phase control pattern, wherein the dammann cubic phase control pattern is formed by superimposing a cubic phase pattern and a dammann grating pattern, and includes:
adopting a numerical control micro-mirror array photoetching system, selecting an exposure figure corresponding to a phase value and a corresponding induced light polarization direction according to an exposure sequence, and sequentially exposing;
wherein, the exposure area of the exposure pattern of the adjacent step is partially overlapped, the polarization direction of the induced light is monotonically increased or monotonically decreased along with the exposure sequence, so as to form a Darman cubic phase control pattern formed by overlapping the cubic phase pattern and the Darman grating pattern.
The liquid crystal Dammann cubic 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 liquid crystal layer; 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 Dammann cubic phase control graph, and the light-operated orientation film controls liquid crystal molecular directors in the liquid crystal layer to be arranged according to the Dammann cubic phase control graph, so that incident light irradiated on the liquid crystal Dammann cubic phase plate is converted into a polarized Airy light beam array; the Dammann cubic phase control pattern is formed by superposing a cubic phase pattern and a Dammann grating pattern. 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 Dammann cubic phase control pattern, the control pattern of the light-operated orientation films controls liquid crystal molecular directors in the liquid crystal layer to be distributed in a gradient manner of 0-180 degrees according to the Dammann cubic phase control pattern, so that incident light irradiating the liquid crystal Dammann cubic phase plate is converted into an Airy light beam array. The Airy beam array generated by the embodiment of the invention has the characteristics of equal energy distribution and controllable polarization, and the array structure can realize customized design by changing the Dammann cube phase control graph according to requirements.
Drawings
Fig. 1 is a schematic structural diagram of a liquid crystal dammann cubic phase plate according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a Dammann cube phase control diagram according to an embodiment of the present invention;
FIG. 3 is a schematic top view of a liquid crystal director distribution corresponding to the structure of FIG. 1;
FIG. 4 is a microscopic view of a sample of a liquid crystal Dammann cube phase plate with the phase difference between ordinary and extraordinary rays equal to an odd multiple of π;
FIG. 5 is a schematic structural diagram of a polarization-controllable Airy beam array generating system according to an embodiment of the present invention;
FIGS. 6-8 are schematic views of the light spot profile of an Airy beam array generated by the Dammann cube phase control scheme of FIG. 2;
FIG. 9 is a graph of a periodic distribution of the Ali beam array spot profile after reducing the Dammann grating pattern;
FIG. 10 is a schematic diagram of another Dammann cube phase control scheme provided by an embodiment of the present invention;
FIG. 11 is a schematic microscopic view of a sample of liquid crystal Dammann cubic phase plate corresponding to FIG. 10;
FIG. 12 is a schematic diagram of the airy beam array spot profile produced by the Dammann cube phase control diagram of FIG. 10;
FIG. 13 is a schematic diagram of yet another Dammann cube phase control scheme provided by an embodiment of the present invention;
FIG. 14 is a schematic microscopic view of a sample of liquid crystal Dammann cubic phase plate corresponding to FIG. 13;
FIG. 15 is a schematic diagram of the airy beam array spot profile produced by the Dammann cube phase control diagram of FIG. 13;
FIG. 16 is a schematic diagram of yet another Dammann cube phase control scheme provided by an embodiment of the present invention;
FIG. 17 is a schematic microscopic view of a sample of liquid crystal Dammann cubic phase plate corresponding to FIG. 16;
FIG. 18 is a schematic representation of the Airy beam array spot profile produced by the Dammann cube phase control scheme of FIG. 16;
FIG. 19 is a schematic flow chart of a method for preparing a liquid crystal Dammann cubic phase plate according to an embodiment of the present invention;
fig. 20 is a schematic flow chart of a multi-step overlapping exposure process for a photo-alignment film according to an embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting of the invention. It should be further noted that, for the convenience of description, only some of the structures related to the present invention are shown in the drawings, not all of the structures.
Fig. 1 is a schematic structural diagram of a liquid crystal dammann cubic phase plate according to an embodiment of the present invention. Referring to fig. 1, the liquid crystal dammann cubic phase plate provided by the present embodiment includes a first substrate 11 and a second substrate 12 disposed opposite to each other, and a liquid crystal layer 13 disposed 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 liquid crystal layer 13; the sides, close to the liquid crystal layer 13, of the first substrate 11 and the second substrate 12 are provided with light-operated orientation films 15 and 16, molecular directors of the light-operated orientation films 15 and 16 are arranged according to a Dammann cubic phase control pattern, and the light-operated orientation films 15 and 16 control liquid crystal molecular directors in the liquid crystal layer 13 to be arranged according to the Dammann cubic phase control pattern, so that incident light irradiating the liquid crystal Dammann cubic phase plate is converted into a polarized Airy light beam array; the Dammann cubic phase control pattern is formed by superposing a cubic phase pattern and a Dammann grating pattern.
Fig. 2 is a schematic diagram of a dammann cubic phase control diagram according to an embodiment of the present invention. Referring to fig. 2, the darman cubic phase control pattern is exemplarily formed by superimposing a cubic phase pattern (an arc profile in the figure) and a darman grating pattern (a square grid), in which gradation can be regarded as a simulated schematic diagram of a spatial gradation distribution in which the liquid crystal director direction is gradually changed from 0 ° to 180 °, and the liquid crystal director direction is gradually changed from 0 ° to 180 ° as indicated by dark to light.
FIG. 3 is a schematic top view of the liquid crystal director distribution corresponding to the structure of FIG. 1. Referring to fig. 3, under the anchoring action of the photoalignment film, since the molecular director direction of the photoalignment film is aligned according to the dammann cubic phase control pattern, i.e., gradually changes from 0 ° to 180 ° according to the gray scale value of 0 to 255, the photoalignment film causes the director of the liquid crystal molecules in the liquid crystal layer to be correspondingly aligned according to 0 ° to 180 °. Wherein the area between the two dashed lines in fig. 1 and 3 corresponds to a square in fig. 2.
According to the technical scheme of the embodiment, 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 the Dammann cubic phase control graph, 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 range of 0-180 degrees according to the Dammann cubic phase control graph, so that incident light irradiating the liquid crystal Dammann cubic phase plate is converted into the Airy light beam array. The Airy beam array generated by the embodiment of the invention has the characteristics of equal energy distribution and controllable polarization, and the array structure can realize customized design by changing the Dammann cube phase control graph according to requirements.
On the basis of the above technical solution, optionally, the molecular director of the photoalignment film satisfies:
wherein the content of the first and second substances,
the cubic phase of the cubic phase graph is represented, and the expression of the cubic phase graph satisfies:
wherein x and y represent coordinates of a rectangular coordinate system with the center of the liquid crystal Dammann cubic phase plate as an origin, the function u () is a step function, u (t ≧ 0) ═ 1, u (t < 0) ═ 0, and xn、xn+1Is the phase jump point.
It can be understood that different Dammann cubic phase control patterns can be designed according to requirements by changing different Dammann grating patterns, so that different polarization-controllable Airy beam arrays can be generated, and the application requirements of the polarization-controllable Airy beam arrays in a plurality of research fields such as optical particle control, military optical bullets, biomedical science, atmospheric science and the like can be met.
Optionally, with continued reference to fig. 2, the cubic phase pattern includes a cubic phase periodic pattern formed by a plurality of arcs, the cubic phase of the cubic phase periodic pattern ranges from-15 pi to 15 pi; the width of each cubic phase period pattern gradually decreases from the central region of the cubic phase period pattern to both sides.
It can be understood that the larger the value range of the cubic phase is, the more the cycles of the cubic phase periodic pattern are, the cubic phase range is set to be-15 pi to 15 pi in this embodiment, and the range of the cubic phase may be set according to actual requirements in specific implementation, which is not limited in the embodiment of the present invention.
Optionally, the material of the liquid crystal layer is any one of nematic liquid crystal, dual-frequency liquid crystal or ferroelectric liquid crystal; the Dammann cubic phase control graph of the light-operated orientation film is erasable, and the material of the light-operated orientation film is 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 actual conditions in specific implementation, the material of the photoalignment film is azo dye, so that the liquid crystal Dammann cubic phase plate can be recycled, and the structure of the liquid crystal Dammann cubic phase plate can be changed in real time by erasing and writing a Dammann cubic phase control pattern on the photoalignment film, so that the Airy beam array with multiple modes can be generated.
Optionally, the phase difference between the ordinary ray and the extraordinary ray in the liquid crystal Dammann cubic phase plate satisfies:
where Δ n is the birefringence difference of the liquid crystal molecules, d is the liquid crystal layer thickness, λ is the wavelength of incident light, and k is a natural number.
It can be understood that the thickness of the liquid crystal layer can be controlled by adjusting the distance between the first substrate and the second substrate by adjusting the size of the spacer such that the phase difference between the ordinary light and the extraordinary light of the incident light in the liquid crystal dammann cubic phase plate is equal to an odd multiple of pi, and fig. 4 is a microscopic view of a sample of the liquid crystal dammann cubic phase plate where the phase difference between the ordinary light and the extraordinary light is equal to an odd multiple of pi, as shown on a scale of 100 μm. The advantage of this setting is that when the phase difference of ordinary ray and extraordinary ray of incident light in the liquid crystal Dammann cube phase plate is equal to odd times of pi, the emergent light beam after the incident light irradiates the liquid crystal Dammann cube phase plate is equal energy and controllable 2 x 2 Airy light beam array of polarization, has avoided the use of electrode.
Fig. 5 is a schematic structural diagram of a polarization-controllable airy beam array generating system according to an embodiment of the present invention. Referring to fig. 5, the polarization controllable airy beam array generating system includes: the liquid crystal dammann cubic phase plate 21 provided in the above embodiment; a light source 22 located at the light incident side of the liquid crystal Dammann cubic phase plate 21 to generate incident light; a lens 23 and an imaging device 24 positioned on the light-emitting side of the liquid crystal Dammann cubic phase plate 21; wherein the optical axes of the light source 22, the liquid crystal Dammann cube phase plate 21, the lens 23 and the imaging device 24 are positioned on the same straight line.
Optionally, the light source 22 may be a laser light source, which has good collimation property, and the airy beam array converted by the liquid crystal dammann cubic phase plate 21 has high quality. In addition, the wavelength range of the light source 22 is not limited, and the conversion of the airy beam array of incident light with any wavelength can be realized. Illustratively, the wavelength may be set to be longer than 500nm to avoid the influence of the incident light from the light source 22 on the Darman cubic phase control pattern in the liquid crystal Darman cubic phase plate 21. For example, a laser beam of 671nm is irradiated onto a liquid crystal Dammann cubic phase plate 21, and Fourier transform is performed by a lens 23 having a focal length of 125mm to obtain an Airy beam array. The embodiment of the present invention does not limit the focal length of the lens 23. The imaging device 24 may be a charge coupled device CCD or the like.
According to the polarization-controllable Airy beam array generation system provided by the embodiment of the invention, the preset incident polarized light is generated through the light source, and the incident light is converted into the Airy beam array through the liquid crystal Dammann cubic phase plate. The Airy beam array generated by the embodiment of the invention has the characteristics of equal energy distribution and controllable polarization, and the array structure can realize customized design by changing the Dammann cube phase control graph according to requirements.
Based on the above embodiment, optionally, with continued reference to fig. 5, the polarization-controllable airy beam array generating system further includes: the polarizing plate 25 and the quarter-wave plate 26 are positioned between the light source 22 and the liquid crystal Dammann cubic phase plate 21, and the optical axes of the light source 22, the polarizing plate 25, the quarter-wave plate 26, the liquid crystal Dammann cubic phase plate 21, the lens 23 and the imaging device 24 are positioned on the same straight line; the polarization state of the incident light is controlled by adjusting the angle between the fast axis direction of the quarter-wave plate 26 and the polarizing direction of the polarizer 25.
Optionally, the two-dimensional duty cycle of the dammann grating pattern is 1:1, phase jump point x10.5; when the incident light generated by the light source is a circularly polarized Gaussian beam, the incident light passes through the liquid crystalConverting the Dammann cubic phase plate into 2 multiplied by 2 array Airy beams with equal energy distribution; when the incident light generated by the light source is a linearly polarized Gaussian beam, the incident light is converted into a 2 × 2 × 2 array of Airy beams with equal energy distribution through the liquid crystal Dammann cubic phase plate.
Fig. 6-8 are schematic views of airy beam array spot shapes generated by the dammann cube phase control diagram of fig. 2. And for different polarization states of incident light, an array of airy beams of different polarization modes can be produced. Referring to fig. 6, when the incident light generated by the light source is linearly polarized, the incident light is converted into a 2 × 2 array of two airy beams through the liquid crystal dammann cubic phase plate, which are in a left-handed circular polarization state and a right-handed circular polarization state, respectively, and the intensity of the light of each two airy beams is the same, that is, 2 × 2 × 2 airy beams are generated in total. Referring to fig. 7 and 8, when the incident light generated by the light source is circularly polarized, the incident light is converted into a single 2 × 2 airy beam array through the liquid crystal dammann cubic phase plate, wherein the incident light in fig. 7 is right-handed circularly polarized and is converted into a left-handed circularly polarized airy beam array through the liquid crystal dammann cubic phase plate; in fig. 8, incident light is left-handed circularly polarized and is converted into a single-branch right-handed circularly polarized airy beam array by the liquid crystal dammann cubic phase plate. The liquid crystal Dammann cubic phase plate provided by the embodiment of the invention has polarization selectivity, and by selecting different incident light polarization properties, Airy beam arrays with different polarization states and different quantities can be obtained, so that the application requirements of the liquid crystal Dammann cubic phase plate in a plurality of research fields such as optical particle control, military optical bullets, biomedical science, atmospheric science and the like can be met.
Optionally, the structure of the liquid crystal Dammann cubic phase plate can be changed in real time by erasing and writing the Dammann cubic phase control pattern on the light-operated orientation film, so that the Airy beam array with multiple modes can be generated.
Illustratively, the period of the Dammann grating pattern of the Dammann cube phase control pattern is adjustable to vary the distance between the Airy beams in the array. Fig. 9 shows the speckle pattern of the airy beam array after a period of reducing the pattern of the dammann grating, and as can be seen from fig. 9, the separation between the airy beams is increased.
Alternatively to this, the first and second parts may,different arrays of airy beam array structures can be produced by varying the position of the phase jump point of the dammann grating pattern in the dammann cube phase control pattern. Fig. 10 is a schematic diagram showing another darmann cubic phase control pattern provided by an embodiment of the present invention, and fig. 11 is a schematic diagram of a microscope of a sample of a liquid crystal darmann cubic phase plate corresponding to fig. 10. Referring to fig. 10, the phase jump point is changed to x1＝0.03863，x2＝0.39084，x30.65552. The effect of the arrangement is that the light beams emitted after the incident light irradiates the liquid crystal Dammann cubic phase plate are 5 multiplied by 5 Airy light beam arrays with equal energy and controllable polarization. FIG. 12 is a schematic diagram of the airy beam array spot profile produced by the Dammann cube phase control diagram of FIG. 10. Referring to fig. 12, from left to right are respectively the 5 × 5 double-branched (or 5 × 5 × 2 single-branched left-handed and right-handed), 5 × 5 single-branched right-handed and 5 × 5 single-branched left-handed circularly polarized isoenergetic airy beam arrays obtained when the incident light is in the linear polarization, left-handed circularly polarized and right-handed circularly polarized states.
Alternatively, fig. 13 is a schematic diagram of another raman cubic phase control pattern provided by an embodiment of the present invention, and fig. 14 is a schematic diagram of a microscope of a liquid crystal raman cubic phase plate sample corresponding to fig. 13. Referring to fig. 13, the position of the phase jump point of the dammann grating pattern in the dammann cubic phase control pattern is x1＝0.23191，x2＝0.42520，x30.52571, the light beam emitted after the incident light irradiates the liquid crystal Dammann cubic phase plate is a 7 × 7 Airy light beam array with equal energy and controllable polarization. FIG. 15 is a schematic diagram of the airy beam array spot profile produced by the Dammann cube phase control diagram of FIG. 13. Referring to fig. 15, from left to right are respectively the 7 × 7 two-branch (or 7 × 7 × 2 single-branch left-hand and right-hand), 7 × 7 single-branch right-hand and 7 × 7 single-branch left-hand circularly polarized isoenergetic airy beam arrays obtained when the incident light is in the linear polarization, left-hand circular polarization and right-hand circular polarization states, respectively.
Alternatively, fig. 16 is a schematic diagram of another dammann cubic phase control pattern provided by an embodiment of the present invention, and fig. 17 is a schematic diagram of a microscope corresponding to the liquid crystal dammann cubic phase plate sample of fig. 16. Referring to fig. 16, a dammann grating pattern of a dammann cubic phase control pattern may be disposed with three phase transition points x having an included angle of 60 °1The structure of the one-dimensional grating superposition of 0.5 can generate a hexagonal Airy beam array with equal energy and controllable polarization. FIG. 18 is a schematic diagram of the airy beam array spot profile produced by the Dammann cube phase control diagram of FIG. 16. Referring to fig. 18, from left to right, the obtained hexagonal double-branched, hexagonal single-branched right-handed circular polarized and hexagonal single-branched left-handed circular polarized isoenergetic airy beam arrays are obtained when the incident light is in the states of linear polarization, left-handed circular polarization and right-handed circular polarization, respectively.
Fig. 19 is a schematic flow chart of a method for manufacturing a liquid crystal dammann cubic phase plate according to an embodiment of the present invention. Referring to fig. 19, 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 the photoalignment material on one side of the first substrate and the second substrate, wherein the spin coating parameters are as follows: 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 incident light in the liquid crystal Dammann cubic phase plate is equal to odd times of pi; the liquid crystal Dammann cubic phase plate has the advantages that when the phase difference of the ordinary light and the extraordinary light of the incident light in the liquid crystal Dammann cubic phase plate is equal to odd times of pi, the light beams emitted after the incident light irradiates the liquid crystal Dammann cubic phase plate are set Airy light beam arrays, the Airy light beam arrays have equal energy distribution and polarization controllable characteristics.
And step S130, carrying out multi-step overlapping exposure on the light control orientation film to ensure that the molecular director direction of the light control orientation film is arranged according to a Dammann cubic phase control pattern, wherein the Dammann cubic phase control pattern is formed by overlapping a cubic phase pattern and a Dammann grating pattern.
The molecular director in the light-operated orientation film can be set through the polarization direction of the induced light, specifically, a Dammann cubic phase control pattern with the molecular director direction in a spatially gradient distribution is formed on the light-operated orientation film through a plurality of times of partially overlapped exposure patterns with the angle of 0-180 degrees, wherein the cubic phase control pattern of the Dammann cubic phase control pattern comprises a plurality of periodic arc structures, the period of the arc structures is gradually reduced from a central area to two sides, the Dammann grating pattern comprises a two-dimensional Dammann grating pattern, the duty ratio of the two-dimensional Dammann grating pattern is 1:1, and a phase transition point x is a grating structure with a preset value. Illustratively, the phase jump point may be x1The incident light is converted into a 2 × 2 airy beam array by a liquid crystal dammann cubic phase plate (0.5); may also be x1＝0.03863，x2＝0.39084，x30.65552, converting incident light into a 5 × 5 airy beam array through a liquid crystal dammann cubic phase plate; can also be x1＝0.23191，x2＝0.42520，x30.52571, converting incident light into a 7 × 7 airy beam array through a liquid crystal dammann cubic phase plate; when the grating structure is changed into three phase jump points x with 60 degrees included angle1When 0.5 one-dimensional grating is superposed, incident light passes through liquid crystal DammannThe cubic phase plate is converted into a hexagonal airy beam array.
Step S140, a liquid crystal layer is poured between the first substrate and the second substrate, and the Dammann cubic phase control graph of the light control orientation film controls the arrangement of liquid crystal molecule directors in the liquid crystal layer according to the Dammann cubic phase control graph.
The photoalignment film has an anchoring function, and under the control function of the dammann cubic phase control pattern formed in step S130, the director of the liquid crystal molecules in the liquid crystal layer is spatially distributed in a gradual manner from 0 ° to 180 °, and the incident light irradiated on the liquid crystal dammann cubic phase plate is converted into an airy beam array.
On the basis of the above technical solution, optionally, the light control alignment film is subjected to multi-step overlapping exposure to arrange the molecular director direction of the light control alignment film according to a dammann cubic phase control pattern, wherein the dammann cubic phase control pattern is formed by superimposing a cubic phase pattern and a dammann grating pattern, and includes:
adopting a numerical control micro-mirror array photoetching system, selecting an exposure figure corresponding to a phase value and a corresponding induced light polarization direction according to an exposure sequence, and sequentially exposing;
wherein, the exposure area of the exposure pattern of the adjacent steps is partially overlapped, the polarization direction of the induced light is monotonically increased or monotonically decreased along with the exposure sequence, so as to form a Darman cubic phase control pattern formed by overlapping the cubic phase pattern and the Darman grating pattern.
Fig. 20 is a schematic flow chart illustrating a multi-step overlay exposure process for a photo-alignment film according to an embodiment of the present invention. Referring to fig. 20, illustratively, there are three exposures in total, in order of a first exposure, a second exposure, and a third exposure. The exposure patterns of the three exposures have the same period, each exposure pattern is exemplarily set to have 3 periods T1, T2, and T3, the width of each period gradually decreases from the central region of the exposure pattern to both sides, and an exemplary T1 is T3<T2. When the first exposure is carried out, 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 of Tn1, Tn2 and Tn3, n is 1, 2 and 3, and the first exposure is carried outThe exposure areas of the patterns were T11 and T12 for T1, T21 and T22 for T2, and T31 and T32 for T3. After the first exposure, the second exposure pattern was changed, the corresponding induced light polarization direction was selected to be 60 °, each period was divided into 3 equal parts, and the exposure area of the second exposure pattern was 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 corresponding induced light polarization direction is selected to be 120 degrees, each period is divided into 3 equal parts, and the exposure area of the third exposure image is T11 and T13 of T1, T21 and T23 of T2, and T31 and T33 of T3. Thus, the exposure region of the first exposure pattern partially overlaps the exposure region of the second exposure pattern by T12, T22, T32; the exposure region of the second exposure pattern partially overlaps the exposure region 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 light control orientation film reach stable arrangement (for example, when the exposure dose is 5J/cm)2In 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 exposure2) 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 intermediate to the polarization angle of the multiple exposures experienced, e.g., T12 at a first exposure with a polarization angle of 0 °, T12 at a second exposure with a polarization angle of 60 °, 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 each period of the Dammann cube phase control pattern comprises an arc-shaped structure, a two-dimensional duty ratio of 1:1, and a phase transition point of x1The period of the arc-shaped structure gradually decreases from the central region to both sides, which is a 0.5 grating structure.
It should be noted that, although fig. 20 exemplarily selects three-step overlap exposure, and does not limit the embodiment of the present invention, generally, the more the exposure times (i.e. the more polarization angles of the 0 ° to 180 ° averages), the more the number of averages per period in the exposure pattern is, the finer the liquid crystal director direction is spatially gradually distributed, and the better the quality of the final airy beam array is. In other embodiments, the number of exposures, and the number of averages per cycle, may be selected according to actual requirements.
It is to be noted that the foregoing is only illustrative of the preferred embodiments of the present invention and the technical principles employed. It will be understood by those skilled in the art that the present invention is not limited to the particular embodiments described herein, but is capable of various obvious changes, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, although the present invention has been described in greater detail by the above embodiments, the present invention is not limited to the above embodiments, and may include other equivalent embodiments without departing from the spirit of the present invention, and the scope of the present invention is determined by the scope of the appended claims.
Claims (8)
1. The liquid crystal Dammann cubic 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, and the liquid crystal layer is positioned between the first substrate and the second substrate; wherein a spacer is disposed between the first substrate and the second substrate to support the liquid crystal layer; the method is characterized in that:
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 Dammann cubic phase control pattern, and the light-operated orientation film controls liquid crystal molecular directors in the liquid crystal layer to be arranged according to the Dammann cubic phase control pattern, so that incident light irradiating the liquid crystal Dammann cubic phase plate is converted into a polarization-controllable Airy light beam array;
the Dammann cubic phase control graph is formed by superposing a cubic phase graph and a Dammann grating graph;
the Dammann grating pattern of the Dammann cube phase control pattern comprises three phase jump points x with an included angle of 60 degrees1The structure of one-dimensional grating superposition is 0.5, and the Airy light beam array is hexagonal AiryAn array of light beams.
2. The liquid crystal Dammann cubic phase plate of claim 1, wherein said cubic phase pattern includes a cubic phase period pattern formed by a plurality of arcs, a cubic phase of said cubic phase period pattern being in a range of-15 pi to 15 pi;
the width of each of the cubic phase period patterns gradually decreases from the central region of the cubic phase period pattern toward both sides.
3. The liquid crystal Dammann cubic phase plate of claim 1, wherein the material of the liquid crystal layer is any one of nematic liquid crystal, dual frequency liquid crystal or ferroelectric liquid crystal;
the Dammann cubic phase control graph of the light control orientation film is erasable, and the material of the light control orientation film is azo dye.
4. The liquid crystal Dammann cubic phase plate of claim 1, wherein a phase difference of the ordinary ray and the extraordinary ray in the liquid crystal Dammann cubic phase plate satisfies:
where Δ n is the birefringence difference of the liquid crystal molecules, d is the liquid crystal layer thickness, λ is the wavelength of incident light, and k is a natural number.
5. A polarization-controllable airy beam array generating system, comprising:
a liquid crystal Dammann cubic phase plate as set forth in any one of claims 1 to 4;
the light source is positioned on the light incidence side of the liquid crystal Dammann cubic phase plate to generate incident light;
the lens and the imaging device are positioned on the light-emitting side of the liquid crystal Dammann cubic phase plate;
wherein the optical axes of the light source, the liquid crystal Dammann cubic phase plate, the lens and the imaging device are positioned on the same straight line.
6. The polarization-controllable airy beam array generating system of claim 5, further comprising:
the polarizer and the quarter-wave plate are positioned between the light source and the liquid crystal Dammann cubic phase plate, and the optical axes of the light source, the polarizer, the quarter-wave plate, the liquid crystal Dammann cubic phase plate, the lens and the imaging device are positioned on the same straight line; and controlling the polarization state of the incident light by adjusting the included angle between the fast axis direction of the quarter-wave plate and the polarizing direction of the polarizing plate.
7. A method for preparing a liquid crystal Dammann cubic phase plate, which is used for preparing the liquid crystal Dammann cubic phase plate as claimed in any one of claims 1 to 4, 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 form a molecular director direction which is arranged according to the gray value of a Dammann cubic phase control pattern, wherein the Dammann cubic phase control pattern is formed by overlapping a cubic phase pattern and a Dammann grating pattern;
and a liquid crystal layer is poured between the first substrate and the second substrate, and the Dammann cubic phase control pattern of the light control orientation film controls the arrangement of liquid crystal molecular directors in the liquid crystal layer according to the Dammann cubic phase control pattern.
8. The production method according to claim 7, wherein the light control alignment film is subjected to multiple overlapping exposures such that the molecular director directions of the light control alignment film are aligned in accordance with a Dammann cubic phase control pattern, wherein the Dammann cubic phase control pattern is a superposition of a cubic phase pattern and a Dammann grating pattern, and comprises:
adopting a numerical control micro-mirror array photoetching system, selecting an exposure figure corresponding to a phase value and a corresponding induced light polarization direction according to an exposure sequence, and sequentially exposing;
wherein, the exposure area of the exposure pattern of the adjacent step is partially overlapped, the polarization direction of the induced light is monotonically increased or monotonically decreased along with the exposure sequence, so as to form a Darman cubic phase control pattern formed by overlapping the cubic phase pattern and the Darman grating pattern.
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| CN110989180B (en) * | 2019-11-19 | 2021-10-01 | 中国科学技术大学 | Compact Airy beam phase plate and manufacturing method thereof |
| CN111812893B (en) * | 2020-07-13 | 2021-04-16 | 西北工业大学 | Liquid crystal beam splitter of round Airy beam, preparation method and generation system |
| CN115236786B (en) * | 2022-08-02 | 2024-02-02 | 西北工业大学 | Liquid crystal phase plate, preparation method and double-sided vortex light beam generation system |
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