AU2021105963A4 - Optical switch array based on chiral liquid crystals, preparation method thereof and method for beam steering - Google Patents
Optical switch array based on chiral liquid crystals, preparation method thereof and method for beam steering Download PDFInfo
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- 239000007788 liquid Substances 0.000 claims description 7
- 238000000137 annealing Methods 0.000 claims description 5
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Classifications
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/29—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the position or the direction of light beams, i.e. deflection
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
- G02B26/08—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/35—Optical coupling means having switching means
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/35—Non-linear optics
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K19/00—Liquid crystal materials
- C09K19/52—Liquid crystal materials characterised by components which are not liquid crystals, e.g. additives with special physical aspect: solvents, solid particles
- C09K19/58—Dopants or charge transfer agents
- C09K19/586—Optically active dopants; chiral dopants
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- Physics & Mathematics (AREA)
- Nonlinear Science (AREA)
- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Liquid Crystal (AREA)
Abstract
The invention provides a beam steering system based on chiral liquid crystals, a preparation
method thereof and a method for beam steering. The steering system comprises a
photoalignment flm and a chiral liquid crystals film arranged on one side of the
photoalignment film; the director direction of the photoalignment film is periodically and
gradually distributed; the director distribution of the chiral liquid crystals film close to the
photoalignment flm is the same as that of the photoalignment film. The optical switch is
prepared by forming a photoalignment film on one side of a transparent substrate, then
performing alignment treatment to form a preset molecular director distribution, and finally
coating a chiral liquid crystals material and self-assembling into a helical liquid crystals film.
The optical switch array provided by the invention has the advantages of low driving optical
power, non-contact and dynamic control, stable adjustment, high switching efficiency and good
integration degree.
-1/7
11
___ ___ __ ___ __ _'___ 12
' 13
Figure 1
T - H
TI T2 T3 T10 T17 T18
Horizontal direction
Figure 2
Description
-1/7
11
___ __ ___ ___ __ _'___ 12 ' 13
Figure 1
TI T2 T3 T10 T17 T18
Horizontal direction
Figure 2
Optical switch array based on chiral liquid crystals, preparation method thereof
and method for beam steering
The invention belongs to the technical field of optical switches, and particularly relates to
a beam steering system based on chiral liquid crystals, a preparation method thereof and a
method for beam steering.
With the continuous development of optical communication technology, optical switch
technology has been fully developed. All-optical network coverage technology has become
the future development trend. As an important device to control the connection and
disconnection of optical path, optical switch is becoming more and more important. The
optical switch itself has developed from the original low speed, high loss and low
integration to the direction of high speed, low loss and high integration. As the core device
of optical information exchange, optical switch is mainly responsible for mode conversion
or logic operation of optical signals in optical system or integrated optical path, and plays
an important role in realizing dynamic optical path management, fault protection of optical
network, and dynamic wavelength allocation, which can effectively improve the flexibility
of optical system.
Optical switches can be divided into electro-optical switches, magneto-optical switches and
thermo-optical switches according to their structural principles. Although the traditional
electro-optical switch is widely used as for can realize ultra-high-speed regulation and
control, but it is limited by the use environment, especially in the waveguide, wherein the electro-optical effect is weak, and generally speaking, the equipment occupies more space and the device is longer; traditional mechanical optical switch has the advantages of being unaffected by light wavelength, relatively small dielectric loss and unaffected by polarization. Magneto-optical switch is second only to electro-optical switch in response speed and has small crosstalk, but it is not easy to be integrated, which limits its wide application; other optical switches have some similar problems such as complex process, high manufacturing cost and poor thermal conductivity. Therefore, the research, improvement and optimization of optical switch has increasingly become a hot spot in the field of optical communication.
In view of the shortcomings of the prior art, the invention aims to provide a beam steering
system based on chiral liquid crystals, a preparation method thereof and a method for beam
steering, which has the advantages of low driving optical power, dynamic control and
stable adjustment, high switching efficiency and good integration.
To achieve this purpose, the invention adopts the following technical scheme:
In a first aspect, the invention provides a beam steering system based on chiral liquid
crystals, which comprises a photoalignment film and a chiral liquid crystals film arranged
on one side of the photoalignment film;
The molecular director direction of the photoalignment film is periodically and gradually
distributed;
The director distribution of the chiral liquid crystals film close to the photoalignment film
is the same as that of the photoalignment film.
The beam steering system based on chiral liquid crystals creatively utilizes the principle
that the photosensitive chiral liquid crystals generates different diffraction distributions
during the photoisomerization process to realize the function of beam steering. Chiral
liquid crystals have a layered structure with a helical pitch, and the layers rotate at a fixed
angle with preferential orientation along the helical axis, thus forming a spiral arrangement
structure. When different light bands are used for irradiation, the liquid crystal molecules
rotate to wind or unwind the helical structure, and then the diffracted light can be
modulated. By further orienting the liquid crystal molecules, the continuous regulation and
manipulation of light in two-dimensional space can be realized, and thus the light control
can be realized. The optical switch keeps high sensitivity to the exposure light, and at the
same time, the required driving force is small and the sample preparation is simple.
In the optical switch provided by the invention, liquid crystal molecules close to the
photoalignment film are anchored by the photoalignment film, so that the director
distribution is the same as that of the photoalignment film; liquid crystal molecules near
the air will be arranged perpendicular to the film surface due to the strong anchoring effect
of air; the middle liquid crystal molecules are self-assembled and arranged in a distorted
helical manner under the action of liquid crystal molecules at both ends.
As a preferred technical scheme of the present invention, the optical switch comprises a
transparent substrate, a photoalignment film arranged on one side of the transparent
substrate, and a chiral liquid crystals film arranged on the side of the photoalignment film
far away from the transparent substrate.
As a preferred technical scheme of the present invention, the thickness of the
photoalignment film is in the range of 2.2-50 [m.
Preferably, the thickness of the chiral liquid crystals film is 10-25 m according to the spin
coating rate.
In an embodiment of the present invention, the molecular director direction of the
photoalignment film periodically changes along the horizontal direction and remains
unchanged along the vertical direction, showing a one-dimensional grating structure.
It should be noted that the horizontal direction and the vertical direction are perpendicular
to each other, which is not a direction determined in thefield, but a direction artificially
defined for convenience of describing the molecular director distribution of the
photoalignment film.
The molecular director direction of the photoalignment film gradually deflects along the
horizontal direction, and every 180° of deflection is a period, and the area of each period
can be divided into a plurality of continuously deflected sub-areas, the molecular director
direction in each sub-area is the same, and the molecular director direction in two adjacent
sub-areas deflects at a certain angle. The number of sub-regions divided in each period can
be any integer >3, such as 3, 5, 6, 8, 10, 12, 15, 18, 21, 25, 30, etc. The larger the number,
the finer the structure of the obtained optical switch.
In another embodiment of the present invention, the photoalignment film has periodically
arranged circular areas, and the molecular director directions in the circular areas gradually
change in the radial direction from the center of the circle to the edge, and the molecular
director directions at the same distance from the center of the circle are the same, showing
a circular grating array structure.
In the above-mentioned circular region, the molecular director direction gradually deflects
from the center to the edge in the radial direction, and every 180 deflection is a period.
Each period can be divided into a plurality of continuous circular sub-regions with equal
width (the center is a circular sub-region whose width is its radius). The molecular director
direction in each circular sub-region is the same, and the molecular director direction in
two adjacent circular sub-regions deflects at a certain angle. The number of circular sub
regions divided in each period can be any integer >3, such as 3, 5, 6, 8, 10, 12, 15, 18, 21,
, 30, etc. The larger the number, the finer the structure of the obtained optical switch.
In a second aspect, the present invention provides a preparation method of the optical
switch, which comprises the following steps:
(1) Forming a photoalignment film on one side of a transparent substrate;
(2) Carrying out orientation treatment on the photoalignment film to make the molecular
directors of the photoalignment film present a preset distribution;
(3) Coating chiral liquid crystals material on the photoalignment film after the alignment
treatment, wherein molecules of the chiral liquid crystals material are aligned under the
control of the photoalignment film and self-assembled into a chiral liquid crystals film, and
removing or not removing the transparent substrate to obtain the optical switch.
As a preferred technical scheme of the present invention, the preparation method further
comprises: before step (1), cleaning the transparent substrate, so as to increase the
wettability and adhesion between the photoalignment film and the transparent substrate.
Preferably, the cleaning method is as follows: the transparent substrate is ultrasonically
cleaned with washing solution (acetone, alcohol and other mixed reagents) for 20-40
minutes, then ultrasonically cleaned with ultra-pure water twice, each time for 8-10
minutes, then dried in an oven at 100-120°C for 40-60 minutes, and finally cleaned with
ultraviolet ozone for 30-45 minutes.
Among them, the substrate is preferably a flexible substrate or a rigid substrate with high
light transmittance (for example, >85%); illustratively, the substrate material can be quartz
glass or ordinary glass.
As the preferred technical scheme of the present invention, the method for forming the
photoalignment film described in step (1) is to spin coat the photoalignment agent on one
side of the transparent substrate and anneal to form the photoalignment film.
The material of the photoalignment film can be selected from at least one of photo
crosslinked materials, photo-degradable materials and photo-induced cis-trans isomeric
materials; illustratively, the material of the photoalignment film can be azo material.
There are no special restrictions on the method of spin coating the photoalignment agent in
the present invention. For example, the following method can be adopted: spin coating at
a low speed of 800 rpm for 5 seconds, and then spin coating at a high speed of 3,000 rpm
for 40 seconds.
Preferably, the annealing temperature is 100-110C, and the annealing time is 10-20
minutes.
As the preferred technical scheme of the present invention, the alignment treatment method
in step (2) is multi-step overlapping exposure, and the multi-step overlapping exposure
method is as follows:
Adopting a numerical control micro mirror array lithography system, according to the
exposure sequence, selecting the corresponding exposure pattern and the corresponding
induced light polarization direction, and sequentially exposing;
-'7
The exposure areas of the exposure patterns of adjacent steps partially overlap, and the
polarization direction of the induced light gradually deflects clockwise or counterclockwise
with the exposure sequence.
Under the influence of induced polarization information during continuous exposure, the
molecules of photoalignment materials will be arranged along the direction perpendicular
to induced polarization.
There are no special restrictions on the method of coating chiral liquid crystals materials in
the present invention. For example, the following method can be adopted: controlling the
temperature to 65°C, first spin coating at a low speed of 800 rpm for 5 seconds, then spin
coating at a high speed of 2,400 rpm for 30 seconds, and then naturally cooling to room
temperature.
There are no special restrictions on the materials of chiral liquid crystals in the present
invention. For example, nematic/smectic liquid crystals and chiral agent can be mixed, for
example, composed of nematic liquid crystals E7 and chiral agent Chad-S in a mass ratio
of 99:1, or nematic liquid crystals E7 and chiral agent Chad-R in a mass ratio of 99:1.
In a third aspect, the present invention provides a method for steering the light direction,
which comprises the following steps: adopting the optical switch described in the first
aspect, and changing the molecular structure of the chiral liquid crystals film in the optical
switch under the irradiation of external light, thereby realizing the switching of the optical
path.
Wherein, the external light is used for transforming the conformation of optically active
groups in chiral liquid crystal molecules, which is different from the probe light beam for
optical switching. The external light is usually the light of two bands corresponding to the strongest absorption peaks of chiral liquid crystal molecules. By irradiating the light of these two bands respectively, the optically active groups can be transformed between two different conformations.
Compared with the prior art, the invention has the following beneficial effects:
According to the invention, the principle that the photosensitive chiral liquid crystals
generates different diffraction distributions in the photoisomerization process is creatively
utilized, and a beam steering system based on chiral liquid crystals is provided, and the
beam steering function can be realized by irradiating the beam steering system with
external light which changes the conformation of chiral liquid crystal molecules. The
optical switch has the advantages of low driving optical power, dynamic control and stable
adjustment, high switching efficiency, good integration, simple preparation process and
low cost.
Figure 1 is a schematic cross-sectional structure diagram of a beam steering system based
on chiral liquid crystals provided by an embodiment of the present invention;
Among them, 11 is chiral liquid crystals film, 12 is photoalignment film, and 13 is
transparent substrate.
Figure 2 is a schematic diagram of molecular director distribution of the photoalignment
film in the optical switch provided in embodiment 1 of the present invention;
Figure 3 is a schematic structural diagram of a chiral liquid crystals film in an optical switch
provided in embodiment 1 of the present invention;
Figure 4 is a flowchart of a method for manufacturing an optical switch provided by an
embodiment of the present invention;
Figure 5 is a schematic diagram of a multi-step overlapping exposure method adopted in
an embodiment of the present invention;
Figure 6 is an exposure pattern used for multi-step overlapping exposure in embodiment 1
of the present invention;
Among them, a, b, c and d are the exposure patterns used for the first, second, third and
fourth exposures respectively;
Figure 7 is a schematic diagram of molecular director distribution of the photoalignment
film in the optical switch provided in embodiment 2 of the present invention;
Wherein A represents any circular area;
Figure 8 is a schematic diagram of molecular director distribution in a circular area on the
photoalignment film in the optical switch provided in embodiment 2 of the present
invention;
Figure 9 is an exposure pattern used for multi-step overlapping exposure in embodiment 2
of the present invention;
Among them, a, b, c and d are the exposure patterns used for the first, second, third and
fourth exposures respectively;
Figure 10 is a diffraction image received after ultraviolet irradiation for different times in
embodiment 3 of the present invention;
Figure 11 is a graph showing the variation of light intensity of one of the first-order
diffraction spots of a diffraction image received in embodiment 3 of the present invention
with ultraviolet irradiation time;
Figure 12 is a diffraction image received after ultraviolet irradiation for different times in
embodiment 4 of the present invention.
The technical scheme of the present invention will be further explained with reference to
the figures and specific embodiments. It should be clear to those skilled in the art that the
detailed description is only to help understand the present invention, and should not be
regarded as a specific limitation of the present invention.
Embodiment 1
This embodiment provides a beam steering system based on chiral liquid crystals. Figure
1 is a schematic diagram of its structure. As shown in figure 1, the optical switch includes
a transparent substrate 13, a photoalignment film 12 disposed on one side of the transparent
substrate 13, and a chiral liquid crystals film 11 disposed on the side of the photoalignment
film 12 away from the transparent substrate 13.
Figure 2 is a schematic diagram of molecular director distribution of the photoalignment
film 12. As shown in figure 2, the molecular director direction of the photoalignment film
12 periodically changes along the horizontal direction and remains unchanged along the
vertical direction, showing a grating structure; among them, every 180° deviation of the
molecular director direction of the photoalignment film 12 is a period T with a width of
100 m, and each period is divided into 18 sub-regions with equal width (denoted as TI,
T2, T3, T4... T18 in turn), and the molecular director direction of two adjacent sub-regions
in the horizontal direction is deviated by 10;
Figure 3 is a schematic structural diagram of chiral liquid crystals film 11. as shown in
figure 3, chiral liquid crystals film 11 has a layered structure, in which the liquid crystal
molecules in the same layer have the same direction, and the directors of interlayer liquid
crystal molecules are sequentially twisted at a certain angle to form a helicoid structure.
Among them, the director distribution of a layer of liquid crystal molecules near the
photoalignment film 12 is the same as that of the photoalignment film 12, and the liquid
crystal molecules near the air tend to be perpendicular to the substrate 13 due to the strong
anchoring effect of the air. Actually, the helical layers near the LC-air interface are
distorted periodically.
The embodiment also provides a preparation method of the optical switch, and figure 4 is
a flowchart of the preparation method. As shown infigure 4, it includes the following steps:
Si: Providing a transparent substrate
Specifically, a piece of quartz glass with light transmittance above 85% is ultrasonically
cleaned with washing liquor for 30 minutes, and then ultrasonically cleaned with ultra-pure
water twice, each time for 10 minutes, then dried in an oven at 120°C for 40 minutes, and
finally cleaned with ultraviolet ozone for 30 minutes, so as to serve as a transparent
substrate.
S2: Forming a photoalignment film on one side of the transparent substrate
Specifically, the method for forming the photoalignment film is as follows: azo material is
used as the photoalignment material, and is spin-coated on one side of the transparent
substrate obtained in step S1, and the spin-coating parameters are as follows: spin-coating
at a low speed for 5 seconds at a rotating speed of 800 rpm; then spin-coating at high speed
for 40 seconds at a rotating speed of 3,000 rpm; the transparent substrate spin-coated with photoalignment material is annealed at 100°C for 10 minutes to form a photoalignment film with a thickness of 50 nm.
S3: Performing alignment treatment on the photoalignment film
Specifically, the alignment processing method is multi-step overlapping exposure: using a
numerical controlled micromirror array lithography system, according to the exposure
order, selecting the corresponding exposure pattern and the corresponding induced light
polarization direction, and sequentially exposing; wherein the exposure areas of the
exposure patterns of adjacent steps partially overlap, and the polarization direction of the
induced light gradually deflects clockwise with the exposure sequence; influenced by the
polarization information of induced light, the molecules of photo-controlled orientation
materials will be arranged along the direction perpendicular to induced polarized light;
Figure 5 is a schematic diagram of the multi-step overlapping exposure method adopted in
this embodiment. As shown in figure 5, taking any period T as an example, it is divided
into 18 sub-regions (denoted as TI, T2, T3, T4..., T18 in turn). Taking any five continuous
sub-regions as an example, (it should be noted that the region TI and region T18 in the
same period are not continuous in space, while, the region Ti and region T18 are treated
as continuous in order to illustrate the multi-step overlapping exposure method). The
photoalignment film is exposed for 18 times by using the numerical control micromirror
array lithography system, and the exposure area of the exposure pattern used for each
exposure moves by one sub-area compared with the previous exposure pattern (when it
reaches the region T18, it returns to the region T1), and the polarization direction of induced
light is shifted clockwise by 10 compared with the previous exposure.
Specifically, during the first exposure, the exposure areas of the first exposure pattern are
T1, T2, T3, T17 and T18, and the polarization direction of induced light corresponding to
the first exposure is 0°.
In the second exposure, the exposure areas of the second exposure pattern are T18, T1, T2,
T3 and T4, and the polarization direction of induced light corresponding to the second
exposure is 10.
In the third exposure, the exposure areas of the third exposure pattern are TI, T2, T3, T4
and T5, and the polarization direction of induced light corresponding to the third exposure
is 20.
By analogy, during the 18t exposure, the exposure areas of the 18t exposure pattern are
T1, T2, T16, T17 and T18, and the induced light polarization direction corresponding to
the 1 8 th exposure is 170'.
Figure 6 is an exposure pattern used for multi-step overlapping exposure in this
embodiment. a, b, c and d are the exposure patterns used for the first, second, third and
fourth exposures, respectively, in which black stripes are light shielding areas, white stripes
are exposure areas, and a group of adjacent black stripes and white stripes are one cycle;
After 18 exposures, each sub-region is exposed five times, so that the molecular directors
of the photoalignment film form a preset continuous distribution pattern.
S4: Forming a chiral liquid crystals film on the photoalignment film after alignment
treatment
Specifically, the method of forming chiral liquid crystals film is: mixing nematic liquid
crystals E7 and chiral agent Chad-S according to the mass ratio of 99:1 as chiral liquid
crystals material, and then spin-coated on the photoalignment film after alignment treatment, the spin-coating parameters are: control the temperature at 65°C, spin-coat at low speed for 5 seconds, wherein the rotating speed is 800 rpm, then spin coating at high speed for 30 seconds at a rotating speed of 3,000 rpm; then naturally cooled to room temperature, the chiral liquid crystals material is aligned under the control of the photoalignment film, and self-assembled into a chiral liquid crystals film (thickness of 15 pm), thus obtaining the optical switch of this embodiment.
Embodiment 2
This embodiment provides a beam steering system based on chiral liquid crystals, which is
different from Embodiment 1 in that the molecular director distribution of the
photoalignment film 12 is different, specifically as follows:
Figure 7 is a schematic diagram of the molecular director distribution pattern of the
photoalignment film 12 in the optical switch provided by this embodiment. As shown in
figure 7, the photoalignment film 12 has circular areas A arranged periodically; figure 8 is
a schematic diagram of molecular director distribution in any circular area A, as shown in
figure 8, the direction of molecular directors in circular area A gradually changes from the
center of the circle to the edge in the radial direction, and the molecular directors at the
same distance from the center of the circle have the same direction, showing a circular
grating array structure;
Specifically, the molecular director direction in the circular area A gradually deflects in the
radial direction from the center of the circle to the edge, and every 180° of deflection is a
period T (the width of one period is 100 m), and each period is divided into 18 continuous
circular sub-regions with equal width (the center is a circular sub-region whose width is its
radius), and the circular sub-regions in one period are sequentially denoted as TI, T2, T3,
T4...T18 in turn from the center of the circle. The direction of the molecular director in
each ring-shaped sub-region is the same, and two circles are adjacent to each other in the
radial direction. The director of the molecule in the circular sub-region is deflected by 10°
counterclockwise.
The steps of preparing the optical switch in this embodiment are basically the same as those
in Embodiment 1, with the only difference being the exposure pattern. Figure 9 is an
exposure pattern used for multi-step overlapping exposure in this embodiment, wherein a,
b, c and d are the exposure patterns used for the first, second, third and fourth exposures,
respectively, in which black rings are light shielding areas, white rings are exposure areas,
and a group of adjacent black rings and white rings are one cycle. Other exposure patterns
can be deduced by those skilled in the art according to the multi-step overlapping exposure
method in Embodiment 1 and the molecular director distribution of the photoalignment
film in this embodiment.
Embodiment 3
This embodiment provides a method for steering optical path, which uses the optical switch
provided in Embodiment 1 to irradiate external light to change the molecular structure of
the chiral liquid crystals film in the optical switch, thereby realizing the switching state of
the optical path;
Specifically, a 633 nm laser is used, which is first formed into a 633 nm laser with linear
polarization information after passing through a polarizer; then, after passing through
quarter-wave plate, the laser beam becomes a 633 nm laser beam with circular polarization
information; the 633 nm circularly polarized laser beam is used as the probe light, which
is incident from the substrate 13 of the optical switch provided in Embodiment 1, diffracted after passing through the photoalignment film 12 and the chiral liquid crystals film 11 in turn, and the diffracted image is received on the receiving screen.
Then, 365 nm ultraviolet light (optical power is 0.83 [w/cm 2) is used as external light to
irradiate the chiral liquid crystals film 11, so that the photoisomerization occurs and liquid
crystal molecules in the chiral liquid crystals film 11 start to rotate in a fixed direction. The
incident 633 nm circularly polarized laser beam is modulated by the liquid crystals
molecules at different times, and the phase changes correspondingly with the rotation of
the liquid crystal molecules, thus realizing the on-off state conversion of the outgoing light.
By observing the change of diffraction image received on the receiving screen with the
irradiation time of ultraviolet light, the switching state of the optical switch can be known,
and the results are shown in Figure 10 and Figure 11.
Figure 10 is a diffraction image received after UV irradiation for different times, in which
the direction indicated by the arrow is the UV irradiation time direction, and the irradiation
time is 0 min, 3 min, 3.2 min, 3.5 min, 6 min and 7 min in turn. The curve in the figure is
the diffraction spot intensity curve. Figure 11 is a graph showing the variation of light
intensity of positive first-order diffraction spots with ultraviolet irradiation time.
It can be seen from figure 10 and figure 11 that with the continuous incidence of ultraviolet
light at 365 nm, the diffraction images received on the receiving screen are diffraction
spots, in which the zero-order diffraction spots always exist, while the first-order
diffraction spots continuously change from bright to dark and then bright with the
irradiation of ultraviolet light, indicating that the beam steering system based on chiral
liquid crystals provided in embodiment 1 can realize the optical switch function. It can be
seen from figure 11 that when the irradiation time reaches 5 min, the intensity of diffraction spot continues to increase; after illumination time of about 10 min, the photoisomerization reaction in chiral liquid crystals films has tended to equilibrium, and the structure is no longer changed, so the intensity of diffraction spot remains stable. At this time, the 365 nm ultraviolet light is replaced by 450-490 nm blue light, and the chiral liquid crystal molecules can be restored to the initial state. One-dimensional control and logic conversion of beam steering system based on chiral liquid crystals are realized by Embodiment 3.
Embodiment 4
This embodiment provides a method for beam steering, which is different from
Embodiment 3 in that the optical switch provided in Embodiment 1 is replaced by the
optical switch provided in Embodiment 2. Observe the change of diffraction image
received on the receiving screen with ultraviolet irradiation time, and the result is shown
in Figure 12, in which the direction indicated by arrow is the direction of ultraviolet
irradiation time, and the irradiation time is 3 min, 3.2 min, 3.5 min, 4.3 min, 6 min and 7
min in turn, and the curve in the figure is the light intensity curve of diffraction ring.
It can be seen from figure 12 that the zero-order diffraction spot always exists in the
diffraction image, while the first-order diffraction rings continuously change from bright
to dark and then bright with the irradiation of ultraviolet light; the curve in figure 12 shows
the change of light intensity, and it can be intuitively seen that the light intensity of the
first-order diffraction rings continuously changes from large to small and then from small
to large with the increase of irradiation time of 365 nm ultraviolet light. It shows that the
beam steering system based on chiral liquid crystals provided in Embodiment 2 can realize
the function of optical switch. Two-dimensional control and logic conversion of beam
steering system based on chiral liquid crystals are realized by Embodiment 4.
The applicant declares that the above is only a specific embodiment of the present
invention, but the protection scope of the present invention is not limited to this. It should
be clear to those skilled in the technical field that any change or substitution that can be
easily thought of by those skilled in the technical field within the technical scope disclosed
by the present invention falls within the protection scope and disclosure scope of the
present invention.
Claims (10)
1. A beam steering system based on chiral liquid crystals, characterized in that the optical
switch comprises a photoalignment film and a chiral liquid crystals film arranged on one
side of the photoalignment film;
The molecular director direction of the photoalignment film is periodically and gradually
distributed;
The director distribution of a layer of liquid crystal molecules in the chiral liquid crystals
film close to the photoalignment film is the same as that of the photoalignment film.
2. The optical switch according to claim 1, wherein the optical switch comprises a
transparent substrate, a photoalignment film arranged on one side of the transparent
substrate, and a chiral liquid crystals film arranged on the side of the photoalignment film
far away from the transparent substrate.
3. The optical switch according to claim 1 or 2, wherein the thickness of the photoalignment
film is in the range of 2.2-50 [m;
Preferably, the thickness of the chiral liquid crystals film is 10-25 m according to the spin
coating rate.
4. The optical switch according to any one of claims 1-3, characterized in that the molecular
director direction of the photoalignment film gradually changes periodically along the
horizontal direction and remains unchanged along the vertical direction, showing a grating
structure.
5. The optical switch according to any one of claims 1-3, characterized in that the
photoalignment film has periodically arranged circular areas, and the direction of molecular
directors in the circular areas gradually changes in the radial direction from the center of the circle to the edge, and the molecular directors at the same distance from the center of the circle have the same direction, showing a circular grating array structure.
6. The preparation method of the optical switch according to any one of claims 1-5, wherein
the preparation method comprises the following steps:
(1) Forming a photoalignment film on one side of a transparent substrate;
(2) Carrying out orientation treatment on the photoalignment film to make the molecular
directors of the photoalignment film present a preset distribution;
(3) Coating chiral liquid crystals material on the photoalignment film after the alignment
treatment, wherein molecules of the chiral liquid crystals material are aligned under the
control of the photoalignment film and self-assembled into a chiral liquid crystals film, and
removing or not removing the transparent substrate to obtain the optical switch.
7. The preparation method according to claim 6, further comprising: cleaning the
transparent substrate before step (1);
Preferably, the cleaning method is as follows: the transparent substrate is ultrasonically
cleaned with washing liquid for 20-40 minutes, and then ultrasonically cleaned with ultra
pure water twice, each time for 8-10 minutes, then dried in an oven at 100-120°C for 40
minutes, and finally cleaned with ultraviolet ozone for 30-45 minutes.
8. The preparation method according to claim 6 or 7, wherein the method for forming the
photoalignment film in step (1) comprises spin coating a photoalignment agent on one side
of the transparent substrate and annealing to form the photoalignment film;
Preferably, the annealing temperature is 100-110C, and the annealing time is 10-20
minutes.
9. The preparation method according to any one of claims 6-8, characterized in that the
orientation treatment method in step (2) is multi-step overlapping exposure, and the multi
step overlapping exposure method is as follows:
Adopting a numerical controlled micro mirror array lithography system, according to the
exposure sequence, selecting the corresponding exposure pattern and the corresponding
induced light polarization direction, and sequentially exposing;
The exposure areas of the exposure patterns of adjacent steps partially overlap, and the
polarization direction of the induced light gradually deflects clockwise or counterclockwise
with the exposure sequence.
10. A method for beam steering, characterized in that the optical switch according to any
one of claims 1-5 is used, and the molecular structure of the chiral liquid crystals film in
the optical switch is changed under the irradiation of external light, thereby realizing the
switching of the optical path.
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Figure 1
Figure 2
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Figure 3
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Figure 4
Figure 5
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Figure 6
Figure 7
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Figure 8
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Figure 9
Figure 10
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Figure 11
Figure 12
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| CN114690479A (en) * | 2022-04-14 | 2022-07-01 | 南京大学 | Liquid crystal geometric phase device, preparation method thereof and detection device |
| CN114690479B (en) * | 2022-04-14 | 2024-04-30 | 南京大学 | Liquid crystal geometric phase device, preparation method thereof and detection device |
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