Adjustable liquid crystal optical differentiator, preparation method and dynamic edge imaging device

Abstract

The invention discloses an adjustable liquid crystal optical differentiator, a preparation method and a dynamic edge imaging device. A pattern is controlled to obey a first arcsine function to gradually change from-3pi / 8 to pi / 8 along a first direction, and is the same along a second direction; ferroelectric liquid crystal molecules form a layered spiral structure in an environment without an external electric field, a spiral shaft of the layered spiral structure is parallel to a plane where the first substrate is located, and an equivalent optical axis of the ferroelectric liquid crystal layer coincides with the spiral shaft of the layered spiral structure; in an environment without an external electric field, the ferroelectric liquid crystal molecules are arranged according to a control pattern of the orientation layer; and under the condition that an external electric field which is perpendicular to the first substrate and has a voltage value greater than or equal to a threshold voltage is applied between the first transparent electrode layer and the second transparent electrode layer, the layered spiral structure is unwound, and the equivalent optical axis synchronously rotates. The optical differentiator is provided with an electrically-controlled adjustable optical axis, high-speed switching between bright field imaging and edge imaging can be achieved by changing the polarity of an external electric field, the flexibility of the optical differentiator is improved, and dynamic imaging is assisted.

Description

Technical Field

[0001] The present invention relates to the technical field of optical edge imaging, and in particular to an adjustable liquid crystal optical differentiator, a preparation method and a dynamic edge imaging device. Background Art

[0002] With the growing demand for massive data processing, high-speed and efficient computing has become the core of modern information processing technology. Compared with traditional digital computing methods, optical analog computing has the advantages of ultra-high speed and real-time parallel processing, which is suitable for real-time processing of big data and is a strong candidate for the next generation of computing tools. Differentiation is a conventional means to achieve edge-enhanced imaging and has a wide range of applications in autonomous driving, biological imaging and other fields. Optical differentiation is a common and critical operation in optical analog computing. It has the advantages of fast speed, low energy consumption, parallel processing and large information capacity. It helps to enhance the readability of image information and maximize the simplification of data processing, thereby improving the efficiency of feature extraction, image segmentation, matching and recognition.

[0003] Conventional optical edge imaging technology is mainly based on the 4f system and combined with traditional filtering elements. The spectral information of the image is processed through various filtering methods, and then useful high-order information is extracted to enhance the edge contour of the object. With the rapid development of micro-nano structures and devices, optical differential devices such as photonic crystals, photonic chips and metasurfaces have broken through traditional amplitude filters and wavefront modulation methods, and have the advantages of being compact and easy to integrate. However, most devices and structures are fixed after manufacturing, usually do not have dynamic adjustment functions, and have single functions, which is an obvious shortcoming in application scenarios that require flexible adjustment of imaging states. Summary of the invention

[0004] The invention provides an adjustable liquid crystal optical differentiator, a preparation method and a dynamic edge imaging device. The adjustable liquid crystal optical differentiator has an electrically controlled adjustable optical axis, and can achieve high-speed switching between output bright field imaging and edge imaging by changing the polarity of an external electric field, thereby improving the flexibility of the optical differentiator.

[0005] In a first aspect, an embodiment of the present invention provides an adjustable liquid crystal optical differentiator, comprising a first substrate and a second substrate arranged opposite to each other, and a ferroelectric liquid crystal layer located between the first substrate and the second substrate;

[0006] A first transparent electrode layer is disposed on a side of the first substrate close to the second substrate, and a second transparent electrode layer is disposed on a side of the second substrate close to the first substrate;

[0007] An alignment layer is disposed on a side of the first transparent electrode layer close to the second substrate, the alignment layer having a control pattern, the control pattern gradually changes from -3π / 8 to π / 8 in accordance with a first inverse sine function along a first direction, and is the same along a second direction; wherein the first direction and the second direction are orthogonal, and both the first direction and the second direction are parallel to the plane where the first substrate is located;

[0008] The ferroelectric liquid crystal layer includes ferroelectric liquid crystal molecules, which form a layered spiral structure in the absence of an external electric field, the spiral axis of the layered spiral structure is parallel to the plane where the first substrate is located, and the equivalent optical axis of the ferroelectric liquid crystal layer coincides with the spiral axis of the layered spiral structure;

[0009] In an environment without an external electric field, the ferroelectric liquid crystal molecules are arranged gradually from -3π / 8 to π / 8 along the first direction in accordance with the control pattern of the alignment layer and obey the first inverse sine function, and are arranged in the same manner along the second direction;

[0010] When an external electric field perpendicular to the first substrate and having a voltage value greater than or equal to a threshold voltage is applied between the first transparent electrode layer and the second transparent electrode layer, the layered spiral structure is untwisted and the equivalent optical axis rotates synchronously.

[0011] Optionally, the first inverse sine function is α=0.5arcsin(x)-π / 8;

[0012] When no power is applied between the first transparent electrode layer and the second transparent electrode layer, the distribution of the equivalent optical axis obeys the first inverse sine function;

[0013] When a positive electric field is applied between the first transparent electrode layer and the second transparent electrode layer, the distribution of the equivalent optical axis obeys a second inverse sine function: α=0.5arcsin(x)-π / 8+θ, and the adjustable liquid crystal optical differentiator realizes edge imaging;

[0014] When a negative electric field is applied between the first transparent electrode layer and the second transparent electrode layer, the distribution of the equivalent optical axis obeys a third inverse sine function: α=0.5arcsin(x)-π / 8-θ, and the adjustable liquid crystal optical differentiator realizes bright field imaging;

[0015] Among them, α is the angle between the equivalent optical axis and the first direction, x is the coordinate of the first direction, and the value of θ is the angle between the long axis of the ferroelectric liquid crystal molecules and the layer normal when no power is applied between the first transparent electrode layer and the second transparent electrode layer.

[0016] Optionally, when an external electric field perpendicular to the first substrate and with a voltage value greater than or equal to a threshold voltage is applied, the director of the ferroelectric liquid crystal molecule rotates to a side of the spiral cone surface parallel to the first substrate according to the polarity of the electric field, and the distribution of the director of the ferroelectric liquid crystal molecule along the first direction after untwisting is still related to the first inverse sine function, and the equivalent optical axis rotates synchronously;

[0017] After power is applied, the overall optical axis distribution undergoes a rotational transformation. When positive power is applied, the equivalent optical axis distribution satisfies the second inverse sine function; when negative power is applied, the equivalent optical axis distribution satisfies the third inverse sine function.

[0018] Optionally, a spacer is arranged between the first substrate and the second substrate, and the spacer is used to support the first substrate and the second substrate to form a accommodating space for the ferroelectric liquid crystal layer, so that the thickness of the ferroelectric liquid crystal layer in a third direction is greater than or equal to the pitch of the layered spiral structure; wherein the third direction is perpendicular to the plane where the first substrate is located.

[0019] Optionally, the ferroelectric liquid crystal layer includes a ferroelectric liquid crystal in a chiral smectic C phase. Under the boundary condition that the orientation layer has a parallel orientation, the layer normal of the smectic layer in the ferroelectric liquid crystal is always parallel to the plane where the first substrate is located, and the ferroelectric liquid crystal molecules present a spiral structure when no external electric field is applied. The spiral axis of the ferroelectric liquid crystal molecules is always parallel to the plane where the first substrate is located, and the pitch of the spiral axis is less than or equal to the distance between the first substrate and the second substrate.

[0020] Optionally, the material of the alignment layer includes at least one of a photo-crosslinking material, a photo-degradable material or a photo-induced cis-trans isomerization material.

[0021] In a second aspect, an embodiment of the present invention further provides a method for preparing an adjustable liquid crystal optical differentiator, which is used to prepare the adjustable liquid crystal optical differentiator described in any embodiment of the first aspect, and the preparation method comprises:

[0022] Providing a first substrate having a first transparent electrode layer on one side and a second substrate having a second transparent electrode layer on one side;

[0023] forming an alignment layer on a side of the first transparent electrode layer away from the first substrate;

[0024] The first substrate and the second substrate are arranged opposite to each other, and a spacer is arranged between the first transparent electrode layer and the second transparent electrode layer to form a space for accommodating the ferroelectric liquid crystal molecules;

[0025] Orienting the alignment layer to form a control pattern; wherein the control pattern gradually changes from -3π / 8 to π / 8 in accordance with a first inverse sine function along a first direction and is the same along a second direction; the first direction and the second direction are orthogonal, and both the first direction and the second direction are parallel to the plane where the first substrate is located;

[0026] forming a ferroelectric liquid crystal layer between the alignment layer and the second transparent electrode layer to form the adjustable liquid crystal optical differentiator;

[0027] Wherein, the ferroelectric liquid crystal layer includes ferroelectric liquid crystal molecules, and the ferroelectric liquid crystal molecules form a layered spiral structure in the absence of an external electric field, the spiral axis of the layered spiral structure is parallel to the plane where the first substrate is located, and the equivalent optical axis of the ferroelectric liquid crystal layer coincides with the spiral axis of the layered spiral structure; in the absence of an external electric field, the ferroelectric liquid crystal molecules are arranged in a gradual manner from -3π / 8 to π / 8 along the first direction in accordance with the control pattern of the orientation layer and are arranged in the same manner along the second direction;

[0028] When an external electric field perpendicular to the first substrate and having a voltage value greater than or equal to a threshold voltage is applied between the first transparent electrode layer and the second transparent electrode layer, the layered spiral structure is untwisted and the equivalent optical axis rotates synchronously.

[0029] Optionally, a ferroelectric liquid crystal layer is formed between the alignment layer and the second transparent electrode layer to form the adjustable liquid crystal optical differentiator, comprising:

[0030] Performing ultraviolet light alignment on an empty box consisting of the first substrate, the second substrate, and the spacer, so that the alignment direction of the alignment layer is consistent with the control pattern;

[0031] At a temperature at or above the clearing point of the ferroelectric liquid crystal, the ferroelectric liquid crystal in an isotropic state is filled into the containing space. After the filling is completed, the temperature is lowered to room temperature using a hot plate to form the layered spiral structure, thereby manufacturing the adjustable liquid crystal optical differentiator.

[0032] In a third aspect, an embodiment of the present invention further provides a dynamic edge imaging device, comprising an external electric field control unit and a laser arranged on the same optical axis as the target object, a beam expansion system, a first lens, a first adjustable liquid crystal optical differentiator, a second adjustable liquid crystal optical differentiator, a Mach-Zehnder interference system, a second lens and an imaging device; wherein the first adjustable liquid crystal optical differentiator and the second adjustable liquid crystal optical differentiator are both the adjustable liquid crystal optical differentiators described in any embodiment of the first aspect;

[0033] The Mach-Zehnder interferometer system comprises a first polarization beam splitter, a first reflector, a second reflector and a second polarization beam splitter, and the first adjustable liquid crystal optical differentiator and the second adjustable liquid crystal optical differentiator are respectively located in two arms of the Mach-Zehnder interferometer system;

[0034] The beam expansion system includes a third lens and a fourth lens;

[0035] The light beam output by the laser passes through the beam expansion system, illuminates the target object, is transmitted from the first lens, enters the Mach-Zehnder interference system, first passes through the first polarization beam splitter, obtains horizontal linear polarized light in the transmission path, and is incident from the first substrate side of the first adjustable liquid crystal optical differentiator. The first adjustable liquid crystal optical differentiator performs geometric phase modulation on the incident linear polarized light beam. The outgoing light beam passes through the first reflector and enters the second polarization beam splitter, and is reflected by the second polarization beam splitter. At the same time, the vertical linear polarized light reflected from the first polarization beam splitter passes through the second reflector. The light is incident from the first substrate side of the second adjustable liquid crystal optical differentiator, and the second adjustable liquid crystal optical differentiator performs geometric phase modulation on the incident linear polarized light beam, and the outgoing light beam enters the second polarization beam splitter; the two-way combined light emitted from the second polarization beam splitter leaves the Mach-Zehnder interference system, passes through the second lens and is received by the imaging device; the imaging device receives a bright field image or a two-dimensional first-order edge image of the target object; the external electric field control unit is used to control the external electric field environment of the adjustable liquid crystal optical differentiator; and the polarity of the external electric field is changed to achieve switching between a bright field image and an edge image.

[0036] The invention discloses an adjustable liquid crystal optical differentiator, a preparation method and a dynamic edge imaging device. The adjustable liquid crystal optical differentiator comprises a first substrate, a second substrate and a ferroelectric liquid crystal layer located between the first substrate and the second substrate. A first transparent electrode layer is arranged on a side of the first substrate close to the second substrate, and a second transparent electrode layer is arranged on a side of the second substrate close to the first substrate. An orientation layer is arranged on a side of the first transparent electrode layer close to the second substrate, and the orientation layer has a control pattern. The control pattern gradually changes from -3π / 8 to π / 8 in accordance with a first inverse sine function along a first direction and is the same along a second direction. The first direction and the second direction are orthogonal, and the first direction and the second direction are both perpendicular to the first direction. The plane where the substrate is located is parallel; the ferroelectric liquid crystal layer includes ferroelectric liquid crystal molecules, and the ferroelectric liquid crystal molecules form a layered spiral structure in the absence of an external electric field. The spiral axis of the layered spiral structure is parallel to the plane where the first substrate is located, and the equivalent optical axis of the ferroelectric liquid crystal layer coincides with the spiral axis of the layered spiral structure; in the absence of an external electric field, the ferroelectric liquid crystal molecules are arranged in a first direction in accordance with the control pattern of the orientation layer, and are arranged in the same manner along the second direction; when an external electric field perpendicular to the first substrate and having a voltage value greater than or equal to the threshold voltage is applied between the first transparent electrode layer and the second transparent electrode layer, the layered spiral structure is untwisted, and the equivalent optical axis rotates synchronously. The adjustable liquid crystal optical differentiator provided in the embodiment of the present invention can realize bright field imaging and edge imaging respectively, and switching the polarity of the electric field can realize dynamic switching of the two imaging modes. Therefore, the adjustable liquid crystal optical differentiator provided in the embodiment of the present invention can realize optical image edge imaging and bright field imaging at high speed and high efficiency, and realize rapid switching between the two states, effectively improving the limitations of traditional optical differentiators such as non-adjustability and fixed functions.

[0037] It should be understood that the contents described in this section are not intended to identify the key or important features of the embodiments of the present invention, nor are they intended to limit the scope of the present invention. Other features of the present invention will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0039] Figure 1 A schematic diagram of the structure of an adjustable liquid crystal optical differentiator provided by an embodiment of the present invention;

[0040] Figure 2 A schematic top view of a ferroelectric liquid crystal layer structure provided by an embodiment of the present invention;

[0041] Figure 3 A schematic diagram of the distribution of an equivalent optical axis provided by an embodiment of the present invention;

[0042] Figure 4 A schematic diagram of the distribution of directors of a ferroelectric liquid crystal layer under different external electric field environments provided by an embodiment of the present invention;

[0043] Figure 5 A flow chart of a method for preparing an adjustable liquid crystal optical differentiator provided by an embodiment of the present invention;

[0044] Figure 6 A flow chart of another method for preparing an adjustable liquid crystal optical differentiator provided by an embodiment of the present invention;

[0045] Figure 7 A schematic structural diagram of a dynamic edge imaging device provided by an embodiment of the present invention;

[0046] Figure 8 A diagram showing the dynamic imaging results of an adjustable liquid crystal optical differentiator provided by an embodiment of the present invention;

[0047] Fig. 9 A switching response time diagram of an adjustable liquid crystal optical differentiator provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0048] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0049] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0050] Figure 1A schematic diagram of a structure of an adjustable liquid crystal optical differentiator provided by an embodiment of the present invention, referring to Figure 1 The adjustable liquid crystal optical differentiator comprises a first substrate 10 and a second substrate 20 which are arranged opposite to each other, and a ferroelectric liquid crystal layer 30 between the first substrate 10 and the second substrate 20. A first transparent electrode layer is arranged on the side of the first substrate 10 close to the second substrate 20, and a second transparent electrode layer is arranged on the side of the second substrate 20 close to the first substrate 10 (the first transparent electrode layer and the second transparent electrode layer are not shown in the drawings of the specification). An orientation layer 40 is arranged on the side of the first transparent electrode layer close to the second substrate 20, and the orientation layer 40 has a control pattern (the control pattern is not shown in the drawings of the specification), and the control pattern gradually changes from -3π / 8 to π / 8 in accordance with a first inverse sine function along a first direction x, and is the same along a second direction y; wherein the first direction x and the second direction y are orthogonal, and the first direction x and the second direction y are both parallel to the plane where the first substrate 10 is located.

[0051] Figure 2 A schematic top view of a ferroelectric liquid crystal layer structure provided by an embodiment of the present invention, referring to Figure 2 The ferroelectric liquid crystal layer 30 includes ferroelectric liquid crystal molecules 31. The ferroelectric liquid crystal molecules 31 form a layered spiral structure in the absence of an external electric field. In the embodiment of the present invention, the spiral axis of the layered spiral structure is parallel to the plane where the first substrate 10 is located, and the equivalent optical axis of the ferroelectric liquid crystal layer 30 coincides with the spiral axis of the layered spiral structure; in the absence of an external electric field, the ferroelectric liquid crystal molecules 31 are arranged gradually from -3π / 8 to π / 8 along the first direction x in accordance with the control pattern of the orientation layer 40, and are arranged in the same manner along the second direction y; when an external electric field perpendicular to the first substrate 10 and having a voltage value greater than or equal to the threshold voltage is applied between the first transparent electrode layer and the second transparent electrode layer, the layered spiral structure is untwisted and the equivalent optical axis rotates synchronously.

[0052] The first substrate 10 and the second substrate 20 may be flexible substrates, such as polyimide substrates, or may be rigid substrates, such as quartz substrates or glass substrates.

[0053] Optionally, the material of the orientation layer 40 includes at least one of a photo-crosslinking material, a photodegradable material or a photoinduced cis-trans isomerization material. For example, the photosensitive azo material SD1. These materials are photo-controlled orientation materials, which can undergo physical or chemical reactions under the irradiation of linear polarized ultraviolet light to generate anisotropic surface forces, thereby inducing the directional arrangement of liquid crystal molecules. Under the anchoring effect of the orientation layer 40, the ferroelectric liquid crystal layer 30 exhibits a layered spiral topological structure. In the absence of an external electric field, the equivalent optical axis of the ferroelectric liquid crystal layer 30 presents a gradual arrangement from -3π / 8 to π / 8 along the first direction x in accordance with the first inverse sine function, and is the same along the second direction, wherein the first inverse sine function is α=0.5arcsin(x)-π / 8, α is the angle between the equivalent optical axis and the first direction x, and x is the coordinate of the first direction x.

[0054] It should be noted that the applied electric field polarity is different, the rotation direction of the equivalent optical axis is different, and the resulting geometric phase modulation is different. When voltages of different polarities are applied between the first transparent electrode layer and the second transparent electrode layer, the adjustable liquid crystal optical differentiator can realize edge imaging or bright field imaging respectively.

[0055] The adjustable liquid crystal optical differentiator provided by the embodiment of the present invention has an electrically controlled adjustable optical axis, which can realize bright field imaging and edge imaging respectively, and the switching of the electric field polarity can realize the dynamic switching of the two imaging modes. Therefore, the adjustable liquid crystal optical differentiator provided by the embodiment of the present invention can realize optical image edge imaging and bright field imaging at high speed and high efficiency, and realize rapid switching between the two states, which effectively improves the limitations of traditional optical differentiators such as non-adjustability and fixed functions.

[0056] Optionally, based on the above embodiment, the first inverse sine function is α=0.5arcsin(x)-π / 8; when no power is applied between the first transparent electrode layer and the second transparent electrode layer, the distribution of the equivalent optical axis obeys the first inverse sine function; when a positive electric field is applied between the first transparent electrode layer and the second transparent electrode layer, the distribution of the equivalent optical axis obeys the second inverse sine function: α=0.5arcsin(x)-π / 8+θ, and the adjustable liquid crystal optical differentiator realizes edge imaging; when a negative electric field is applied between the first transparent electrode layer and the second transparent electrode layer, the distribution of the equivalent optical axis obeys the third inverse sine function: α=0.5arcsin(x)-π / 8-θ, and the adjustable liquid crystal optical differentiator realizes bright field imaging; wherein α is the angle between the equivalent optical axis and the first direction x, x is the coordinate of the first direction x, and the value of θ is the angle between the long axis of the ferroelectric liquid crystal molecule 31 and the layer normal when no power is applied between the first transparent electrode layer and the second transparent electrode layer, and θ is π / 8 for the best effect.

[0057] Optionally, on the basis of the above embodiment, when an external electric field perpendicular to the first substrate 10 and with a voltage value greater than or equal to the threshold voltage is applied, the pointing vector of the ferroelectric liquid crystal molecule 31 rotates to the side of the spiral cone surface parallel to the first substrate 10 according to the polarity of the electric field, and the distribution of the pointing vector of the untwisted ferroelectric liquid crystal molecule 31 along the first direction x is still related to the first inverse sine function, and the equivalent optical axis rotates synchronously; after power is applied, the overall optical axis distribution undergoes a rotational transformation, and when positive power is applied, the equivalent optical axis distribution satisfies the second inverse sine function; when negative power is applied, the equivalent optical axis distribution satisfies the third inverse sine function.

[0058] For example, Figure 3 A schematic diagram of the distribution of an equivalent optical axis provided by an embodiment of the present invention, specifically a schematic diagram of the distribution of the equivalent optical axis of the ferroelectric liquid crystal layer 30 of the adjustable liquid crystal optical differentiator when there is no external electric field, and a schematic diagram of the distribution of the equivalent optical axis of the ferroelectric liquid crystal layer 30 under external electric fields of different polarities, refer to Figure 3 , the ferroelectric liquid crystal layer 30, under the influence of the control pattern of the orientation layer 40, forms a layered spiral structure that is arranged in a first direction x in accordance with a first inverse sine function from -3π / 8 to π / 8, and arranged in the same manner in a second direction y. Without external electric field stimulation, the equivalent optical axis distribution of the ferroelectric liquid crystal layer 30 satisfies α=0.5arcsin(x)-π / 8. The ferroelectric liquid crystal layer 30 changes under an external electric field environment. When an external electric field with a voltage greater than or equal to a threshold voltage is applied, the equivalent optical axis of the ferroelectric liquid crystal layer 30 will rotate by an angle of θ, where θ is the tilt angle of the ferroelectric liquid crystal molecules (the angle between the long axis of the ferroelectric liquid crystal molecules and the layer normal when no power is applied). Exemplarily, when a positive external electric field is applied, the equivalent optical axis distribution of the ferroelectric liquid crystal layer satisfies α=0.5arcsin(x)-π / 8+θ, and when a negative external electric field is applied, the equivalent optical axis distribution of the ferroelectric liquid crystal layer satisfies α=0.5arcsin(x)-π / 8-θ. When a ferroelectric liquid crystal material with a tilt angle of 22.5° is selected, the equivalent optical axis distribution satisfies α=0.5arcsin(x)-π / 8 when there is no external electric field. When a positive external electric field is applied, the optical axis distribution of the ferroelectric liquid crystal layer satisfies α=0.5arcsin(x). When a negative external electric field is applied, the optical axis distribution of the ferroelectric liquid crystal layer satisfies α=0.5arcsin(x)-π / 4.

[0059] For example, in the embodiment of the present invention, the tilt angle of the selected ferroelectric liquid crystal material is 25°, and the design of the equivalent optical axis is modified and adjusted, referring to Figure 3 When θ is 25°, when there is no external electric field, the optical axis distribution of the ferroelectric liquid crystal layer satisfies α=0.5arcsin(x)-25°, when a positive external electric field is applied, the optical axis distribution of the ferroelectric liquid crystal layer satisfies α=0.5arcsin(x), and when a negative external electric field is applied, the optical axis distribution of the ferroelectric liquid crystal layer satisfies α=0.5arcsin(x)-50°.

[0060] It should be noted that Figure 3 The figure only shows the equivalent optical axis distribution of the ferroelectric liquid crystal layer 30 when there is no external electric field in the adjustable liquid crystal optical differentiator and the distribution diagram of the equivalent optical axis under the external electric fields of different polarities, but it is not a limitation on the ferroelectric liquid crystal material used in the present invention. In other embodiments, ferroelectric liquid crystal materials with other optical properties can be selected according to actual needs.

[0061] Optionally, based on the above embodiment, continue to refer to Figure 1 A spacer 50 is arranged between the first substrate 10 and the second substrate 20, and the spacer 50 is used to support the first substrate 10 and the second substrate 20 to form a accommodating space for the ferroelectric liquid crystal layer 30, so that the thickness of the ferroelectric liquid crystal layer 30 in the third direction y is greater than or equal to the pitch of the layered spiral structure; wherein the third direction y is perpendicular to the plane where the first substrate 10 is located.

[0062] The spacer 50 may be a quartz microsphere or a quartz column, and may be disposed at the boundary between the first substrate 10 and the second substrate 20 to support the first substrate 10 and the second substrate 20 to form a filling space for the ferroelectric liquid crystal layer 30. In a specific implementation, the height of the spacer 50 in the third direction y may be much greater than the pitch of the layered spiral structure. It is understandable that Figure 1 The spacer 50 is used to support the positional relationship between the first substrate 10 and the second substrate 20, but not the actual size and proportion. For example, in a certain embodiment of the present invention, the selected ferroelectric liquid crystal material has a pitch of 245nm, a spontaneous polarization of 110nC / cm2, and a ferroelectric liquid crystal layer thickness of 1.5μm. It should be noted that the above-mentioned ferroelectric liquid crystal material pitch and ferroelectric liquid crystal layer thickness are only exemplary descriptions, not limitations of the embodiments of the present invention. In other embodiments, other pitches and thicknesses may be used according to specific needs.

[0063] Optionally, on the basis of the above embodiment, the ferroelectric liquid crystal layer 30 includes a ferroelectric liquid crystal in a chiral smectic C phase, and under the boundary condition that the orientation layer 40 has a parallel orientation, the layer normal of the smectic layer in the ferroelectric liquid crystal is always parallel to the plane of the first substrate 10, and the ferroelectric liquid crystal molecules 31 present a spiral structure when no external electric field is applied, and the spiral axis of the ferroelectric liquid crystal molecules 31 is always parallel to the plane of the first substrate 10, and the pitch of the spiral axis is less than or equal to the spacing between the first substrate 10 and the second substrate 20.

[0064] Figure 4 A schematic diagram of the distribution of directors of a ferroelectric liquid crystal layer under different external electric field environments provided by an embodiment of the present invention. Figure 4When an external electric field perpendicular to the first substrate 10 and the second substrate 20 and having a voltage value greater than or equal to the threshold voltage is applied between the first transparent electrode layer and the second transparent electrode layer, the spiral structure of the ferroelectric liquid crystal layer 30 is untwisted, and the directors of the ferroelectric liquid crystal molecules 31 will be uniformly rotated to the side of the spiral cone parallel to one substrate according to the polarity of the electric field; when the polarity of the external electric field is reversed, the directors of the ferroelectric liquid crystal molecules will be uniformly rotated to the corresponding other side. The corresponding equivalent optical axes rotate synchronously, and the electric field polarity is different, the rotation direction is different, and the resulting geometric phase modulation is different.

[0065] Figure 5 A flowchart of a method for preparing an adjustable liquid crystal optical differentiator provided in an embodiment of the present invention, the method is used to prepare the adjustable liquid crystal optical differentiator of any of the above embodiments, with reference to Figure 5 , the preparation method comprises:

[0066] S510, providing a first substrate having a first transparent electrode layer on one side and a second substrate having a second transparent electrode layer on one side.

[0067] The first substrate and the second substrate may be flexible substrates or rigid substrates with high light transmittance (greater than or equal to 85%). For example, the first substrate and the second substrate may be made of glass, and the thickness of the substrate may be 1 mm to 2 mm. The first transparent electrode layer and the second transparent electrode layer may be indium tin oxide ITO.

[0068] S520, forming an alignment layer on a side of the first transparent electrode layer away from the first substrate.

[0069] Wherein, step S520 includes spin coating a solution containing an orientation material on a side of the first transparent electrode layer away from the first substrate, and after the spin coating is completed, annealing the first substrate to form an orientation layer. Exemplarily, in this embodiment, the orientation material is selected from a photosensitive azo material SD1, and the spin coating solution contains 0.35% SD1 and 99.65% dimethylformamide.

[0070] Exemplarily, the spin coating process may include: first adjusting the rotation speed to 600-900 rpm, controlling the first stage spin coating time to 5s-10s, so that the material is evenly distributed on the surface of the first transparent electrode layer; then adjusting the rotation speed to 2500-3500 rpm, controlling the second stage spin coating time to 30s-50s, so that the material is coated according to a specific thickness. Optionally, the thickness of the alignment layer can be 30nm-50nm.

[0071] Exemplarily, the annealing process may include: an annealing atmosphere of air, an annealing temperature of 80° C. to 120° C., and an annealing time of 8 min to 12 min.

[0072] It should be noted that the above-mentioned spin coating solution composition, spin coating parameters, and annealing parameters are only exemplary descriptions, and in other embodiments, they can be adjusted according to actual needs.

[0073] S530, disposing the first substrate and the second substrate opposite to each other, and disposing a spacer between the first transparent electrode layer and the second transparent electrode layer to form a space for accommodating ferroelectric liquid crystal molecules.

[0074] The spacers may be quartz microspheres or quartz columns, and may be disposed at the boundary between the first substrate and the second substrate.

[0075] S540 , aligning the alignment layer to form a control pattern.

[0076] The control pattern gradually changes from -3π / 8 to π / 8 in accordance with the first inverse sine function along the first direction and is the same along the second direction; the first direction and the second direction are orthogonal, and both the first direction and the second direction are parallel to the plane where the first substrate is located;

[0077] S550, forming a ferroelectric liquid crystal layer between the alignment layer and the second transparent electrode layer to form an adjustable liquid crystal optical differentiator.

[0078] Among them, the ferroelectric liquid crystal layer includes ferroelectric liquid crystal molecules, and the ferroelectric liquid crystal molecules form a layered spiral structure in the absence of an external electric field. The spiral axis of the layered spiral structure is parallel to the plane where the first substrate is located, and the equivalent optical axis of the ferroelectric liquid crystal layer coincides with the spiral axis of the layered spiral structure; in the absence of an external electric field, the ferroelectric liquid crystal molecules are arranged gradually from -3π / 8 to π / 8 along the first direction in accordance with the control pattern of the orientation layer and obey the first inverse sine function, and are arranged in the same way along the second direction; when an external electric field perpendicular to the first substrate and with a voltage value greater than or equal to a threshold voltage is applied between the first transparent electrode layer and the second transparent electrode layer, the layered spiral structure is untwisted and the equivalent optical axis rotates synchronously.

[0079] Specifically, the process of forming a ferroelectric liquid crystal layer between the first substrate and the second substrate includes: filling the ferroelectric liquid crystal in an isotropic state between the first substrate and the second substrate, slowly cooling it to a chiral smectic C phase, and making an adjustable liquid crystal optical differentiator.

[0080] Exemplarily, the ferroelectric liquid crystal material selected in the embodiment of the present invention transforms from isotropic to chiral smectic A phase at 78°C, and transforms from chiral smectic A phase to chiral smectic C phase at 72°C. The cooling process may include a cooling rate of 0.1°C / min within the range of ±2°C of the phase transition temperature, wherein the ferroelectric liquid crystal layer is oriented according to the control pattern.

[0081] Figure 6 A flowchart of another method for preparing an adjustable liquid crystal optical differentiator provided in an embodiment of the present invention, referring to Figure 6, the method comprises the following steps:

[0082] S610 , providing a first substrate having a first transparent electrode layer on one side and a second substrate having a second transparent electrode layer on one side.

[0083] S620, forming an alignment layer on a side of the first transparent electrode layer away from the first substrate.

[0084] S630, disposing the first substrate and the second substrate opposite to each other, and disposing a spacer between the first transparent electrode layer and the second transparent electrode layer to form a space for accommodating ferroelectric liquid crystal molecules.

[0085] S640 , aligning the alignment layer to form a control pattern.

[0086] The control pattern gradually changes from -3π / 8 to π / 8 in the first direction following the first inverse sine function and is the same in the second direction; the first direction and the second direction are orthogonal, and both the first direction and the second direction are parallel to the plane where the first substrate is located.

[0087] S651, performing ultraviolet light alignment on an empty box composed of a first substrate, a second substrate and a spacer, so that the alignment direction of the alignment layer is consistent with the control pattern.

[0088] Optionally, the ultraviolet light alignment includes: using a digital micromirror projection system, according to an exposure sequence, synchronously controlling an exposure pattern and an angle of a polarizing plate, and performing ultraviolet exposure treatment on a region where the alignment layer is located, so that the alignment layer forms a control pattern.

[0089] S652. At a temperature at or above the clearing point of the ferroelectric liquid crystal, fill the ferroelectric liquid crystal in an isotropic state into the containing space. After the filling is completed, cool it down to room temperature using a hot plate to form a layered spiral structure, thereby making an adjustable liquid crystal optical differentiator.

[0090] Optional, Figure 1 Step S550 in may include step S651 and step S652.

[0091] Figure 7 A schematic diagram of a dynamic edge imaging device according to an embodiment of the present invention is provided. Figure 7The device comprises external electric field control units 14 and 15, a laser 1 arranged coaxially with a target object 4, a beam expansion system, a first lens 5, a first adjustable liquid crystal optical differentiator 7, a second adjustable liquid crystal optical differentiator 10, a Mach-Zehnder interference system, a second lens 12 and an imaging device 13; wherein the first adjustable liquid crystal optical differentiator 7 and the second adjustable liquid crystal optical differentiator 10 are both adjustable liquid crystal optical differentiators provided in the above-mentioned embodiment; the Mach-Zehnder interference system comprises a first polarization beam splitter 6, a first reflector 8, a second reflector 9 and a second polarization beam splitter 11, and the first adjustable liquid crystal optical differentiator 7 and the second adjustable liquid crystal optical differentiator 10 are respectively located in the two arms of the Mach-Zehnder interference system; the beam expansion system comprises a third lens 2 and a fourth lens 3; the light beam output by the laser 1 passes through the beam expansion system, illuminates the target object 4, is transmitted from the first lens 5, enters the Mach-Zehnder interference system, first passes through the first polarization beam splitter 6, obtains horizontal linear polarized light in the transmission path, and then passes through the first adjustable liquid crystal differentiator 8. The first adjustable liquid crystal optical differentiator 7 performs geometric phase modulation on the incident linear polarized light beam, and the outgoing light beam passes through the first reflector 8 and enters the second polarization beam splitter 11, and is reflected by the second polarization beam splitter 11; at the same time, the vertical linear polarized light reflected from the first polarization beam splitter 6 passes through the second reflector 9 and is incident from the first substrate side of the second adjustable liquid crystal optical differentiator 10, and the second adjustable liquid crystal optical differentiator 10 performs geometric phase modulation on the incident linear polarized light beam, and the outgoing light beam enters the second polarization beam splitter 11; the two-way combined light emitted from the second polarization beam splitter 11 leaves the Mach-Zehnder interference system, passes through the second lens 12 and is received by the imaging device 13; the imaging device 13 receives the bright field image or the two-dimensional first-order edge image of the target object 4; the external electric field control units 14 and 15 are used to control the external electric field environment of the adjustable liquid crystal optical differentiator; and the polarity of the external electric field is changed to realize the switching of the bright field image or the edge image.

[0092] Exemplarily, a mask is used to form the target object 4, a charge coupled device (CCD) camera is used as the imaging device 13, and a signal generator is used as the external field control unit 14 and 15. The signal generator is used to adjust and switch the polarity of the external electric field to control the output to be a bright field image or an edge image.

[0093] The specific implementation can be designed according to the actual situation. By adjusting the external electric field, the output light field of the adjustable liquid crystal optical differentiators 7 and 10 can be changed, so that after exiting from the Mach-Zehnder interference system, a bright field image or an edge image is output. Exemplarily, voltages of +5V and -5V can be used as the external electric field. By changing the polarity of the external electric field, the bright field image or the edge image will be switched.

[0094] The first lens 5 and the second lens 12 form a 4f system; the first adjustable liquid crystal optical differentiator 7 and the second adjustable liquid crystal optical differentiator 10 are both placed on the 4f system spectrum plane, that is, the confocal plane of the first lens 5 and the second lens 12, to perform frequency domain modulation on the incident object light; the target object 4 is placed on the front focal plane of the first lens 5; and the CCD camera is placed on the rear focal plane of the second lens 12 to obtain a clear edge image or a bright field image.

[0095] For example, Figure 8 This is a diagram showing the dynamic imaging results of an adjustable liquid crystal optical differentiator provided by an embodiment of the present invention. The adjustable liquid crystal optical differentiator has linear modulation on the amplitude. The linear modulation on the spectrum plane enables the adjustable liquid crystal optical differentiator to produce a first-order differential effect, which can achieve edge imaging of the target pattern. Under a negative external electric field, the adjustable liquid crystal optical differentiator has no obvious modulation effect on the amplitude and phase, and can achieve bright field imaging of the target pattern. Reference Figure 8 When 630nm light is incident, the first column is the bright field image obtained under the -5V external field voltage environment, and the second column is the edge image obtained under the +5V external field voltage environment.

[0096] For example, Fig. 9 A switching response time diagram of an adjustable liquid crystal optical differentiator provided by an embodiment of the present invention. The switching time between the edge image and bright field image states is defined as the duration of the intensity change between 10% and 90%. When an AC square wave signal of 10Vpp and 1kHz is applied, the response time from edge image to bright field image and vice versa is measured to be 62μs. Reference Fig. 9 The adjustable liquid crystal optical differentiator still maintains ultra-fast response speed and good stability and reversibility after more than 1.8 million cycles.

[0097] It should be noted that the embodiment of the present invention only exemplarily shows the dynamic edge imaging effect corresponding to the incident light of 630nm, but does not limit the working band of the adjustable liquid crystal optical differentiator provided by the present invention. In other embodiments, the device is still applicable, and according to actual needs, by selecting appropriate ferroelectric liquid crystal and appropriate electric field environment, the adjustable liquid crystal optical differentiator provided by the embodiment of the present invention can have different response times.

[0098] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An adjustable liquid crystal optical differentiator, characterized in that: It comprises a first substrate and a second substrate which are arranged opposite to each other, and a ferroelectric liquid crystal layer located between the first substrate and the second substrate; A first transparent electrode layer is disposed on a side of the first substrate close to the second substrate, and a second transparent electrode layer is disposed on a side of the second substrate close to the first substrate; An alignment layer is disposed on a side of the first transparent electrode layer close to the second substrate, the alignment layer having a control pattern, the control pattern gradually changes from -3π / 8 to π / 8 in accordance with a first inverse sine function along a first direction, and is the same along a second direction; wherein the first direction and the second direction are orthogonal, and both the first direction and the second direction are parallel to the plane where the first substrate is located; The ferroelectric liquid crystal layer includes ferroelectric liquid crystal molecules, which form a layered spiral structure in the absence of an external electric field, the spiral axis of the layered spiral structure is parallel to the plane where the first substrate is located, and the equivalent optical axis of the ferroelectric liquid crystal layer coincides with the spiral axis of the layered spiral structure; In an environment without an external electric field, the ferroelectric liquid crystal molecules are arranged gradually from -3π / 8 to π / 8 along the first direction in accordance with the control pattern of the alignment layer and obey the first inverse sine function, and are arranged in the same manner along the second direction; When an external electric field perpendicular to the first substrate and having a voltage value greater than or equal to a threshold voltage is applied between the first transparent electrode layer and the second transparent electrode layer, the layered spiral structure is untwisted and the equivalent optical axis rotates synchronously.

2. The adjustable liquid crystal optical differentiator according to claim 1, characterized in that: The first inverse sine function is α=0.5arcsin(x)-π / 8; When no power is applied between the first transparent electrode layer and the second transparent electrode layer, the distribution of the equivalent optical axis obeys the first inverse sine function; When a positive electric field is applied between the first transparent electrode layer and the second transparent electrode layer, the distribution of the equivalent optical axis obeys a second inverse sine function: α=0.5arcsin(x)-π / 8+θ, and the adjustable liquid crystal optical differentiator realizes edge imaging; When a negative electric field is applied between the first transparent electrode layer and the second transparent electrode layer, the distribution of the equivalent optical axis obeys a third inverse sine function: α=0.5arcsin(x)-π / 8-θ, and the adjustable liquid crystal optical differentiator realizes bright field imaging; Among them, α is the angle between the equivalent optical axis and the first direction, x is the coordinate of the first direction, and the value of θ is the angle between the long axis of the ferroelectric liquid crystal molecules and the layer normal when no power is applied between the first transparent electrode layer and the second transparent electrode layer.

3. The adjustable liquid crystal optical differentiator according to claim 2, characterized in that: When an external electric field perpendicular to the first substrate and having a voltage value greater than or equal to a threshold voltage is applied, the director of the ferroelectric liquid crystal molecule rotates to the side of the spiral cone surface parallel to the first substrate according to the polarity of the electric field, and the distribution of the director of the ferroelectric liquid crystal molecule along the first direction after untwisting is still related to the first inverse sine function, and the equivalent optical axis rotates synchronously; After power is applied, the overall optical axis distribution undergoes a rotational transformation. When positive power is applied, the equivalent optical axis distribution satisfies the second inverse sine function; when negative power is applied, the equivalent optical axis distribution satisfies the third inverse sine function.

4. The adjustable liquid crystal optical differentiator according to claim 1, characterized in that: A spacer is arranged between the first substrate and the second substrate, and the spacer is used to support the first substrate and the second substrate to form a accommodating space for the ferroelectric liquid crystal layer, so that the thickness of the ferroelectric liquid crystal layer in a third direction is greater than or equal to the pitch of the layered spiral structure; wherein the third direction is perpendicular to the plane where the first substrate is located.

5. The adjustable liquid crystal optical differentiator according to claim 1, characterized in that: The ferroelectric liquid crystal layer includes a ferroelectric liquid crystal in a chiral smectic C phase. Under the boundary condition that the orientation layer has a parallel orientation, the layer normal of the smectic layer in the ferroelectric liquid crystal is always parallel to the plane where the first substrate is located. The ferroelectric liquid crystal molecules present a spiral structure when no external electric field is applied. The spiral axis of the ferroelectric liquid crystal molecules is always parallel to the plane where the first substrate is located, and the pitch of the spiral axis is less than or equal to the spacing between the first substrate and the second substrate.

6. The adjustable liquid crystal optical differentiator according to claim 1, characterized in that: The material of the alignment layer includes at least one of a photo-crosslinking material, a photo-degradable material or a photo-induced cis-trans isomerization material.

7. A method for preparing an adjustable liquid crystal optical differentiator, used for preparing the adjustable liquid crystal optical differentiator according to any one of claims 1 to 6, characterized in that: The preparation method comprises: Providing a first substrate having a first transparent electrode layer on one side and a second substrate having a second transparent electrode layer on one side; forming an alignment layer on a side of the first transparent electrode layer away from the first substrate; The first substrate and the second substrate are arranged opposite to each other, and a spacer is arranged between the first transparent electrode layer and the second transparent electrode layer to form a space for accommodating the ferroelectric liquid crystal molecules; Orienting the alignment layer to form a control pattern; wherein the control pattern gradually changes from -3π / 8 to π / 8 in accordance with a first inverse sine function along a first direction and is the same along a second direction; the first direction and the second direction are orthogonal, and both the first direction and the second direction are parallel to the plane where the first substrate is located; A ferroelectric liquid crystal layer is formed between the orientation layer and the second transparent electrode layer to form the adjustable liquid crystal optical differentiator; wherein the ferroelectric liquid crystal layer includes ferroelectric liquid crystal molecules, and the ferroelectric liquid crystal molecules form a layered spiral structure in the absence of an external electric field, the spiral axis of the layered spiral structure is parallel to the plane where the first substrate is located, and the equivalent optical axis of the ferroelectric liquid crystal layer coincides with the spiral axis of the layered spiral structure; in the absence of an external electric field, the ferroelectric liquid crystal molecules are arranged in a gradual manner from -3π / 8 to π / 8 along the first direction in accordance with the control pattern of the orientation layer and are arranged in the same manner along the second direction; When an external electric field perpendicular to the first substrate and having a voltage value greater than or equal to a threshold voltage is applied between the first transparent electrode layer and the second transparent electrode layer, the layered spiral structure is untwisted and the equivalent optical axis rotates synchronously. The first substrate and the second substrate are arranged opposite to each other, and a spacer is arranged between the first transparent electrode layer and the second transparent electrode layer to form a space for accommodating the ferroelectric liquid crystal molecules.

8. The preparation method according to claim 7, characterized in that: A ferroelectric liquid crystal layer is formed between the alignment layer and the second transparent electrode layer to form the adjustable liquid crystal optical differentiator, comprising: Performing ultraviolet light alignment on an empty box consisting of the first substrate, the second substrate, and the spacer, so that the alignment direction of the alignment layer is consistent with the control pattern; At a temperature at or above the clearing point of the ferroelectric liquid crystal, the ferroelectric liquid crystal in an isotropic state is filled into the containing space. After the filling is completed, the temperature is lowered to room temperature using a hot plate to form the layered spiral structure, thereby manufacturing the adjustable liquid crystal optical differentiator.

9. A dynamic edge imaging device, characterized in that: The invention comprises an external electric field control unit, a laser arranged on the same optical axis as the target object, a beam expansion system, a first lens, a first adjustable liquid crystal optical differentiator, a second adjustable liquid crystal optical differentiator, a Mach-Zehnder interference system, a second lens and an imaging device; wherein the first adjustable liquid crystal optical differentiator and the second adjustable liquid crystal optical differentiator are both the adjustable liquid crystal optical differentiators according to any one of claims 1 to 6; The Mach-Zehnder interferometer system comprises a first polarization beam splitter, a first reflector, a second reflector and a second polarization beam splitter, and the first adjustable liquid crystal optical differentiator and the second adjustable liquid crystal optical differentiator are respectively located in two arms of the Mach-Zehnder interferometer system; The beam expansion system includes a third lens and a fourth lens; The light beam output by the laser passes through the beam expansion system, illuminates the target object, is transmitted from the first lens, enters the Mach-Zehnder interference system, first passes through the first polarization beam splitter, obtains horizontal linear polarized light in the transmission path, and is incident from the first substrate side of the first adjustable liquid crystal optical differentiator. The first adjustable liquid crystal optical differentiator performs geometric phase modulation on the incident linear polarized light beam. The outgoing light beam passes through the first reflector and enters the second polarization beam splitter, and is reflected by the second polarization beam splitter. At the same time, the vertical linear polarized light reflected from the first polarization beam splitter passes through the second reflector. The light is incident from the first substrate side of the second adjustable liquid crystal optical differentiator, and the second adjustable liquid crystal optical differentiator performs geometric phase modulation on the incident linear polarized light beam, and the outgoing light beam enters the second polarization beam splitter; the two-way combined light emitted from the second polarization beam splitter leaves the Mach-Zehnder interference system, passes through the second lens and is received by the imaging device; the imaging device receives a bright field image or a two-dimensional first-order edge image of the target object; the external electric field control unit is used to control the external electric field environment of the adjustable liquid crystal optical differentiator; and the polarity of the external electric field is changed to achieve switching between a bright field image and an edge image.

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