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

Abstract

The application discloses a tunable liquid crystal optical differentiator, a preparation method and a dynamic edge imaging device. A control pattern along a first direction is subject to a first arcsine function from-3pi / 8 to pi / 8, and the same along a second direction. Ferroelectric liquid crystal molecules form a layered helical structure in a non-external electric field environment. The helical axis of the layered helical structure is parallel to the plane of the first substrate. The equivalent optical axis of the ferroelectric liquid crystal layer coincides with the helical axis of the layered helical structure. In the non-external electric field environment, the ferroelectric liquid crystal molecules are arranged according to the control pattern of the orientation layer. In the case that 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 helical structure is disentangled, and the equivalent optical axis is synchronously rotated. The application has an electrically controllable optical axis. By changing the polarity of the external electric field, the high-speed switching of bright field imaging and edge imaging can be realized, the flexibility of the optical differentiator is improved, and the dynamic imaging is facilitated.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of optical edge imaging, and in particular to a tunable liquid crystal optical differentiator, a preparation method and a dynamic edge imaging device. BACKGROUND

[0002] With the growing demand for mass 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, and is suitable for real-time processing of big data, and is a strong candidate for the next generation of computing tools. Differentiation is a common means to achieve edge enhancement imaging, and has wide applications in automatic driving, biological imaging and other fields. Optical differentiation is a common and key operation in optical analog computing, which has the advantages of fast speed, low energy consumption, parallel processing and large information capacity, helps to enhance the readability of image information and simplify the data processing process to the maximum extent, and thus improves the efficiency of feature extraction, image segmentation, matching and recognition.

[0003] Conventional optical edge imaging technology is mainly based on a 4f system combined with traditional filter elements, and the spectral information of the image is processed by various filtering methods to extract useful high-order information to enhance the edge profile of the object. With the rapid development of micro-nano structures and devices, such as photonic crystals, photonic chips and superstructured surfaces, optical differentiation devices have broken through traditional amplitude filters and wavefront modulation means, and have the advantages of compactness, easy integration and the like. However, most of the devices and structures are fixed after manufacturing, and usually do not have dynamic adjustment function, and the function is single, which is a obvious shortcoming in application scenarios that require flexible adjustment of imaging state. SUMMARY

[0004] The present application provides a tunable liquid crystal optical differentiator, a preparation method and a dynamic edge imaging device, the tunable liquid crystal optical differentiator has an electrically controllable optical axis, and by changing the polarity of the applied electric field, the high-speed switching of the outgoing bright field imaging and edge imaging is realized, and the flexibility of the optical differentiator is improved.

[0005] In a first aspect, the present application provides a tunable liquid crystal optical differentiator, comprising a first substrate, a second substrate arranged opposite to each other and a ferroelectric liquid crystal layer located between the first substrate and the second substrate.

[0006] The first substrate is provided with a first transparent electrode layer on the side close to the second substrate, and the second substrate is provided with a second transparent electrode layer on the side close to the first substrate.

[0007] The first transparent electrode layer is provided with an orientation layer on the side close to the second substrate, and the orientation layer is provided with a control pattern which is subject to a first arcsine function from -3π / 8 to π / 8 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 comprises ferroelectric liquid crystal molecules which form a layered helical structure in the absence of an external electric field, and the helical axis of the layered helical 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 helical axis of the layered helical structure;

[0009] In the absence of an external electric field, the ferroelectric liquid crystal molecules are arranged in accordance with the control pattern of the orientation layer, and the arrangement along the first direction is subject to the first arcsine function from -3π / 8 to π / 8, and the arrangement along the second direction is the same;

[0010] In the case that 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 helical structure is disentangled, and the equivalent optical axis is synchronously rotated.

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

[0012] When no voltage is applied between the first transparent electrode layer and the second transparent electrode layer, the distribution of the equivalent optical axis is subject to the first arcsine 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 is subject to a second arcsine 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 is subject to a third arcsine function: α=0.5arcsin(x)-π / 8-θ, and the adjustable liquid crystal optical differentiator realizes bright field imaging;

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

[0016] Optionally, under the condition of applying an external electric field perpendicular to the first substrate and having a voltage value greater than or equal to a threshold voltage, the director of the ferroelectric liquid crystal molecules rotates to one side of the heliconical cone parallel to the first substrate according to the polarity of the electric field, and the distribution of the director of the ferroelectric liquid crystal molecules after unwinding is still related to the first arcsine function, and the equivalent optical axis rotates synchronously.

[0017] After power-on, the overall optical axis distribution is rotated and transformed, when a positive voltage is applied, the equivalent optical axis distribution satisfies the second arcsine function; when a negative voltage is applied, the equivalent optical axis distribution satisfies the third arcsine function.

[0018] Optionally, a spacer is arranged between the first substrate and the second substrate, the spacer is used to support the first substrate and the second substrate to form a containing space of the ferroelectric liquid crystal layer, so that the thickness of the ferroelectric liquid crystal layer in the third direction is greater than or equal to the pitch of the layered helical 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 chiral smectic C phase ferroelectric liquid crystal, under the boundary condition that the alignment layer has parallel alignment, 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 exhibit a helical structure under the condition of no external electric field, the helical axis of the ferroelectric liquid crystal molecules is always parallel to the plane where the first substrate is located, and the pitch of the helical 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 photo-crosslinking material, photo-degradable material or photoisomerization material.

[0021] In a second aspect, the embodiments of the present application further provide a preparation method of an adjustable liquid crystal optical microdifferentiator, used for preparing the adjustable liquid crystal optical microdifferentiator in any of the embodiments of the first aspect, and the preparation method comprises:

[0022] providing a first substrate with a first transparent electrode layer on one side and a second substrate with a second transparent electrode layer on one side;

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

[0024] arranging the first substrate and the second substrate oppositely, arranging a spacer between the first transparent electrode layer and the second transparent electrode layer to form a containing space of the ferroelectric liquid crystal molecules;

[0025] The orientation layer is oriented to form a control pattern; wherein the control pattern is subject to a first arcsine function from -3π / 8 to π / 8 along a first direction and 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] A ferroelectric liquid crystal layer is formed between the orientation layer and the second transparent electrode layer to form the adjustable liquid crystal optical micro-differentiator;

[0027] The ferroelectric liquid crystal layer comprises ferroelectric liquid crystal molecules, the ferroelectric liquid crystal molecules form a layered helical structure in the absence of an external electric field, the helical axis of the layered helical 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 helical axis of the layered helical structure; in the absence of an external electric field, the ferroelectric liquid crystal molecules are arranged in accordance with the control pattern of the orientation layer, and are arranged in the same manner along the first direction subject to the first arcsine function from -3π / 8 to π / 8 and along the second direction;

[0028] In the case that 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 helical structure is disentangled, and the equivalent optical axis is synchronously rotated.

[0029] Optionally, forming the adjustable liquid crystal optical micro-differentiator by forming a ferroelectric liquid crystal layer between the orientation layer and the second transparent electrode layer comprises:

[0030] The empty box composed of the first substrate, the second substrate and the spacer is subjected to ultraviolet orientation so that the orientation direction of the orientation layer is consistent with the control pattern;

[0031] At a temperature equal to or higher than the clearing point of the ferroelectric liquid crystal, the ferroelectric liquid crystal in an isotropic state is filled into the containing space, and after the filling is completed, the hot stage is cooled to room temperature to form the layered helical structure, thereby manufacturing the adjustable liquid crystal optical micro-differentiator.

[0032] In a third aspect, the embodiments of the present application also provide a dynamic edge imaging device, comprising an external electric field control unit, a laser, a beam expansion system, a first lens, a first adjustable liquid crystal optical micro-differentiator, a second adjustable liquid crystal optical micro-differentiator, a Mach-Zehnder interference system, a second lens and an imaging device arranged in a common optical axis with a target object; wherein the first adjustable liquid crystal optical micro-differentiator and the second adjustable liquid crystal optical micro-differentiator are both the adjustable liquid crystal optical micro-differentiator of any one of the embodiments of the first aspect;

[0033] The Mach-Zehnder interference system comprises a first polarization beam splitter, a first mirror, a second mirror and a second polarization beam splitter, and the first adjustable liquid crystal optical differential device and the second adjustable liquid crystal optical differential device are respectively located in two arms of the Mach-Zehnder interference system.

[0034] The beam expanding system comprises a third lens and a fourth lens.

[0035] The light beam output by the laser passes through the beam expanding 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, and transmits a horizontal linearly polarized light, is incident from the first substrate side of the first adjustable liquid crystal optical differential device, the first adjustable liquid crystal optical differential device performs geometric phase modulation on the incident linearly polarized light beam, the emitted light beam enters the second polarization beam splitter after passing through the first mirror, and is reflected via the second polarization beam splitter; meanwhile, the vertical linearly polarized light reflected from the first polarization beam splitter passes through the second mirror, is incident from the first substrate side of the second adjustable liquid crystal optical differential device, the second adjustable liquid crystal optical differential device performs geometric phase modulation on the incident linearly polarized light beam, and the emitted light beam enters the second polarization beam splitter; the two combined light beams emitted from the second polarization beam splitter leave the Mach-Zehnder interference system, are received by the imaging device after passing through the second lens; the imaging device receives the bright field image or the two-dimensional first-order edge image of the target object; the external electric field control unit is used for controlling the external electric field environment of the adjustable liquid crystal optical differential device; changing the polarity of the external electric field can realize the switching of the bright field image or the edge image.

[0036] The application discloses a tunable liquid crystal optical differentiator, a preparation method and a dynamic edge imaging device.

[0037] It should be understood that the description in this section is not intended to identify key or critical features of embodiments of the application or to limit the scope of the application. Other features of the application will become apparent from the following description. BRIEF DESCRIPTION OF DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the application, the following will briefly introduce the drawings needed to be used in the embodiment description. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can also be obtained by those skilled in the art without any creative effort based on these drawings.

[0039] Figure 1 A structure schematic diagram of a tunable liquid crystal optical differentiator provided by the embodiment of the application;

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

[0041] Figure 3 A distribution diagram of an equivalent optical axis provided by an embodiment of the present application is shown in the figure;

[0042] Figure 4 A distribution diagram of a director of a ferroelectric liquid crystal layer in different applied electric field environments provided by an embodiment of the present application is shown in the figure;

[0043] Figure 5 A flow chart of a preparation method of a tunable liquid crystal optical differentiator provided by an embodiment of the present application is shown in the figure;

[0044] Figure 6 A flow chart of a preparation method of another tunable liquid crystal optical differentiator provided by an embodiment of the present application is shown in the figure;

[0045] Figure 7 A structure diagram of a dynamic edge imaging device provided by an embodiment of the present application is shown in the figure;

[0046] Figure 8 A dynamic imaging result diagram of a tunable liquid crystal optical differentiator provided by an embodiment of the present application is shown in the figure;

[0047] Figure 9 A switching response time diagram of a tunable liquid crystal optical differentiator provided by an embodiment of the present application is shown in the figure. DETAILED DESCRIPTION

[0048] In order to make the person skilled in the art better understand the present application scheme, the technical scheme in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by the person skilled in the art without creative labor should belong to the scope of protection of the present application.

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

[0050] Figure 1A structure schematic diagram of an adjustable liquid crystal optical differentiator provided by an embodiment of the present application is shown in FIG. 1. Figure 1 The adjustable liquid crystal optical differentiator includes a first substrate 10, a second substrate 20 arranged oppositely, 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 a side of the first substrate 10 close to the second substrate 20, and a second transparent electrode layer is arranged on a 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). An alignment layer 40 is arranged on a side of the first transparent electrode layer close to the second substrate 20, and the alignment layer 40 is provided with a control pattern (the control pattern is not shown in the drawings). The control pattern gradually changes from -3π / 8 to π / 8 along a first direction x and is the same along a second direction y; the first direction x and the second direction y are orthogonal, and both the first direction x and the second direction y are parallel to a plane in which the first substrate 10 is located.

[0051] Figure 2 A top view schematic diagram of a ferroelectric liquid crystal layer structure provided by an embodiment of the present application is shown in FIG. 2. Figure 2 The ferroelectric liquid crystal layer 30 includes ferroelectric liquid crystal molecules 31, and the ferroelectric liquid crystal molecules 31 form a layered helical structure in the absence of an external electric field. In the embodiment of the present application, a helical axis of the layered helical structure is parallel to a plane in which the first substrate 10 is located, and an equivalent optical axis of the ferroelectric liquid crystal layer 30 coincides with the helical axis of the layered helical structure. In the absence of an external electric field, the ferroelectric liquid crystal molecules 31 are arranged in a manner that gradually changes from -3π / 8 to π / 8 along the first direction x and is the same along the second direction y according to the control pattern of the alignment layer 40. In the case that an external electric field perpendicular to the first substrate 10 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 helical structure is disentangled, and the equivalent optical axis is synchronously rotated.

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

[0053] Optionally, the material of the orientation layer 40 comprises at least one of photo-crosslinking material, photo-degradable material or photo-isomerization material, such as photosensitive azo material SD1. These materials are photo-controllable orientation materials, which can physically or chemically react under the irradiation of linearly polarized ultraviolet light, generate anisotropic surface force, and then induce the directional arrangement of liquid crystal molecules. The ferroelectric liquid crystal layer 30 exhibits a layered helical topological structure under the anchoring effect of the orientation layer 40. When no external electric field is applied, 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 subjecting to a first arcsine function, and the same along the second direction, wherein the first arcsine function is α=0.5arcsin(x)-π / 8, and α is the included 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 rotation direction of the equivalent optical axis is different when the polarity of the applied electric field is different, and the 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 tunable liquid crystal optical differentiator can realize edge imaging or bright field imaging, respectively.

[0055] The tunable liquid crystal optical differentiator provided by the embodiments of the present application has an electrically controllable adjustable optical axis, can realize bright field imaging and edge imaging, respectively, and can realize dynamic switching of the two imaging modes by switching the polarity of the electric field. Therefore, the tunable liquid crystal optical differentiator provided by the embodiments of the present application can realize optical image edge imaging and bright field imaging at high speed and high efficiency, and can realize rapid switching in the two states, thereby effectively improving the limitations of traditional optical differentiators, such as non-adjustability and fixed function.

[0056] Optionally, on the basis of the above embodiments, the first arcsine function is α=0.5arcsin(x)-π / 8; when no electric field is applied between the first transparent electrode layer and the second transparent electrode layer, the distribution of the equivalent optical axis is subject to the first arcsine 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 is subject to a second arcsine function: α=0.5arcsin(x)-π / 8+θ, and the tunable 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 is subject to a third arcsine function: α=0.5arcsin(x)-π / 8-θ, and the tunable liquid crystal optical differentiator realizes bright field imaging; wherein α is the included angle between the equivalent optical axis and the first direction x, x is the coordinate of the first direction x, θ has the best effect when the value of θ is the included angle between the long axis of the ferroelectric liquid crystal molecule 31 and the layer normal when no electric field is applied between the first transparent electrode layer and the second transparent electrode layer, and θ is π / 8.

[0057] Optionally, on the basis of the above embodiment, in the case of applying an external electric field perpendicular to the first substrate 10 and having a voltage value greater than or equal to a threshold voltage, the director of the ferroelectric liquid crystal molecules 31 rotates to one side parallel to the first substrate 10 on the helical cone according to the polarity of the electric field, and the distribution of the director of the ferroelectric liquid crystal molecules 31 after unwinding along the first direction x is still related to the first arcsine function, and the equivalent optical axis rotates synchronously; the overall optical axis distribution is rotated and transformed after being powered on, when a positive electric is applied, the equivalent optical axis distribution satisfies the second arcsine function; when a negative electric is applied, the equivalent optical axis distribution satisfies the third arcsine function.

[0058] Exemplarily, Figure 3 An equivalent optical axis distribution diagram is provided for the embodiment of the present application, specifically, the equivalent optical axis distribution of the ferroelectric liquid crystal layer 30 of the adjustable liquid crystal optical differentiator in the absence of an external electric field, and the equivalent optical axis distribution of the ferroelectric liquid crystal layer 30 under different polarity external electric fields, refer to Figure 3 , the ferroelectric liquid crystal layer 30 forms a layered helical structure arranged gradually from -3π / 8 to π / 8 along the first direction x and the same arrangement along the second direction y under the influence of the control pattern of the alignment layer 40, in the absence of an 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 the external electric field environment, when an external electric field with a voltage greater than or equal to the threshold voltage is applied, the equivalent optical axis of the ferroelectric liquid crystal layer 30 will rotate by an angle θ, wherein 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 not powered on). Exemplarily, when a positive polarity 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 negative polarity 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 the 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 in the absence of an external electric field, the ferroelectric liquid crystal layer optical axis distribution satisfies α=0.5arcsin(x) when a positive polarity external electric field is applied, and the ferroelectric liquid crystal layer optical axis distribution satisfies α=0.5arcsin(x)-π / 4 when a negative polarity external electric field is applied.

[0059] Exemplarily, in the embodiment of the present application, the tilt angle of the selected ferroelectric liquid crystal material is 25°, and the design of the equivalent optical axis is corrected and adjusted, refer to Figure 3 When θ is 25°, the ferroelectric liquid crystal layer optical axis distribution satisfies α=0.5arcsin(x)-25° in the absence of an external electric field, the ferroelectric liquid crystal layer optical axis distribution satisfies α=0.5arcsin(x) when a positive polarity external electric field is applied, and the ferroelectric liquid crystal layer optical axis distribution satisfies α=0.5arcsin(x)-50° when a negative polarity external electric field is applied.

[0060] It should be noted that, Figure 3 The equivalent optical axis distribution of the ferroelectric liquid crystal layer 30 without an external electric field and the equivalent optical axis distribution under different polar external electric fields are only exemplarily shown in the embodiment, but not a limitation on the ferroelectric liquid crystal material used in the present application. In other embodiments, the ferroelectric liquid crystal material with other optical properties can be selected according to actual needs.

[0061] Optionally, based on the above embodiment, continuing 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 containing space of 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 helical structure; wherein the third direction y is perpendicular to the plane where the first substrate 10 is located.

[0062] The spacer 50 can be a quartz microsphere or a quartz column, and can be arranged at the boundary position of the first substrate 10 and the second substrate 20, and is used to support the first substrate 10 and the second substrate 20 to form a filling space of the ferroelectric liquid crystal layer 30. In specific implementation, the height of the spacer 50 in the third direction y can be set to be much greater than the pitch of the layered helical structure. It can be understood that, Figure 1 The position relationship of the spacer 50 for supporting the first substrate 10 and the second substrate 20 is only exemplarily shown in the embodiment, but not the actual size and proportion. Exemplarily, in an embodiment of the present application, the pitch of the selected ferroelectric liquid crystal material is 245 nm, the spontaneous polarization is 110 nC / cm2, and the thickness of the ferroelectric liquid crystal layer is 1.5 μm. It should be noted that the pitch of the ferroelectric liquid crystal material and the thickness of the ferroelectric liquid crystal layer are only exemplarily described, but not a limitation on the embodiment of the present application. In other embodiments, other pitches and thicknesses can be used according to specific needs.

[0063] Optionally, based on the above embodiment, the ferroelectric liquid crystal layer 30 includes a chiral smectic C phase ferroelectric liquid crystal. Under the boundary condition that the alignment layer 40 has parallel alignment, the layer normal of the smectic layer in the ferroelectric liquid crystal is always parallel to the plane where the first substrate 10 is located. The ferroelectric liquid crystal molecules 31 exhibit a helical structure without an external electric field, and the helical axis of the ferroelectric liquid crystal molecules 31 is always parallel to the plane where the first substrate 10 is located. The pitch of the helical axis is less than or equal to the distance between the first substrate 10 and the second substrate 20.

[0064] Figure 4 The distribution of the director of a ferroelectric liquid crystal layer under different external electric field environments is provided for the embodiment of the present application. Referring to Figure 4In the case that an external electric field is applied between the first transparent electrode layer and the second transparent electrode layer, which is perpendicular to the first substrate 10 and the second substrate 20 and has a voltage value greater than or equal to a threshold voltage, the helical structure of the ferroelectric liquid crystal layer 30 is disentangled, and the director of the ferroelectric liquid crystal molecules 31 will rotate to one side of the helical cone surface parallel to one substrate according to the polarity of the electric field; when the polarity of the applied electric field is reversed, the director of the ferroelectric liquid crystal molecules will rotate to the corresponding other side. The corresponding equivalent optical axis rotates synchronously, the electric field polarity is different, the rotation direction is different, and the geometric phase modulation produced is different.

[0065] Figure 5 A flowchart of a preparation method of a tunable liquid crystal optical differentiator provided by an embodiment of the present application is provided, which is used to prepare the tunable liquid crystal optical differentiator of any of the above embodiments, with reference to Figure 5 The preparation method comprises the following steps:

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

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

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

[0069] The step S520 comprises spin-coating a solution containing an alignment material on the side of the first transparent electrode layer away from the first substrate, and performing annealing on the first substrate after the spin-coating to form the alignment layer. In this embodiment, the alignment material is a photosensitive azo material SD1, and the spin-coating solution contains 0.35% of SD1 and 99.65% of dimethylformamide.

[0070] The spin-coating process can comprise the following steps: first, adjusting the rotation speed to 600-900rpm, and controlling the first-stage spin-coating time to 5s-10s to make the material uniformly distributed on the surface of the first transparent electrode layer; and then adjusting the rotation speed to 2500-3500rpm, and controlling the second-stage spin-coating time to 30s-50s to make the material spread to a specific thickness. Optionally, the thickness of the alignment layer can be 30nm-50nm.

[0071] The annealing process can comprise the following steps: the annealing atmosphere is air, the annealing temperature is 80℃-120℃, and the annealing time is 8min-12min.

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

[0073] S530, the first substrate and the second substrate are arranged oppositely, the spacer is arranged between the first transparent electrode layer and the second transparent electrode layer, and the accommodation space of the ferroelectric liquid crystal molecules is formed.

[0074] The spacer can be a quartz microsphere or a quartz column, and can be arranged at the boundary position of the first substrate and the second substrate.

[0075] S540, the orientation layer is oriented to form a control pattern.

[0076] The control pattern gradually changes from-3π / 8 to π / 8 along the first direction according to the first arcsine function, and 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 of the first substrate;

[0077] S550, the ferroelectric liquid crystal layer is formed between the orientation layer and the second transparent electrode layer, and the tunable liquid crystal optical microdifferentiator is formed.

[0078] The ferroelectric liquid crystal layer includes ferroelectric liquid crystal molecules, the ferroelectric liquid crystal molecules form a layered helical structure in the absence of an external electric field, the helical axis of the layered helical structure is parallel to the plane of the first substrate, and the equivalent optical axis of the ferroelectric liquid crystal layer coincides with the helical axis of the layered helical structure; in the absence of an external electric field, the ferroelectric liquid crystal molecules are arranged according to the control pattern of the orientation layer, and the arrangement gradually changes from-3π / 8 to π / 8 along the first direction according to the first arcsine function, and the same along the second direction; in the case of applying an external electric field perpendicular to the first substrate and having a voltage value greater than or equal to a threshold voltage between the first transparent electrode layer and the second transparent electrode layer, the layered helical structure is disentangled, and the equivalent optical axis is rotated synchronously.

[0079] Specifically, the process of forming the ferroelectric liquid crystal layer between the first substrate and the second substrate includes: filling the ferroelectric liquid crystal in the isotropic state between the first substrate and the second substrate, slowly cooling to the chiral smectic C phase state, and manufacturing the tunable liquid crystal optical microdifferentiator.

[0080] For example, the ferroelectric liquid crystal material selected by the embodiment of the present application is converted from isotropic to chiral smectic A phase at 78℃, and from chiral smectic A phase to chiral smectic C phase at 72℃, so that the cooling process can include using a cooling rate of 0.1℃ / min within a phase transition temperature range of ±2℃, wherein the ferroelectric liquid crystal layer is oriented according to the control pattern.

[0081] Figure 6 Another flowchart of the preparation method of the tunable liquid crystal optical microdifferentiator provided by the embodiment of the present application is shown in Figure 6The method comprises the following steps:

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

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

[0084] S630, oppositely arranging the first substrate and the second substrate, arranging a spacer between the first transparent electrode layer and the second transparent electrode layer, and forming a containing space for ferroelectric liquid crystal molecules.

[0085] S640, orienting the orientation layer to form a control pattern.

[0086] The control pattern gradually changes from -3π / 8 to π / 8 along the first direction and the same along the second direction, the first direction and the second direction are orthogonal, and the first direction and the second direction are parallel to the plane where the first substrate is located.

[0087] S651, ultraviolet orientation is performed on the empty box composed of the first substrate, the second substrate and the spacer, so that the orientation direction of the orientation layer is consistent with the control pattern.

[0088] Optionally, the ultraviolet orientation comprises: using a digital micromirror projection system, synchronously controlling an exposure pattern and a polarizer angle according to an exposure order, and performing ultraviolet exposure processing on the area where the orientation layer is located, so that the orientation layer forms a control pattern.

[0089] S652, at a temperature above the clearing point of the ferroelectric liquid crystal, the isotropic state ferroelectric liquid crystal is filled into the containing space, after the filling is completed, the temperature is reduced to room temperature by using a hot stage, a layered spiral structure is formed, and an adjustable liquid crystal optical microdifferentiator is manufactured.

[0090] Optionally, Figure 1 The step S550 in the method can comprise the steps S651 and S652.

[0091] Figure 7 A structural schematic diagram of a dynamic edge imaging device provided by an embodiment of the present application is shown in FIG. 1. Figure 7The device comprises external electric field regulating units 14 and 15, and a laser 1, a beam expander system, a first lens 5, a first adjustable liquid crystal optical differential device 7, a second adjustable liquid crystal optical differential device 10, a Mach-Zehnder interference system, a second lens 12 and an imaging device 13 arranged on the same optical axis as the target object 4; wherein the first adjustable liquid crystal optical differential device 7 and the second adjustable liquid crystal optical differential device 10 are both the adjustable liquid crystal optical differential device provided in the above embodiment; the Mach-Zehnder interference system comprises a first polarization beam splitter 6, a first mirror 8, a second mirror 9 and a second polarization beam splitter 11, and the first adjustable liquid crystal optical differential device 7 and the second adjustable liquid crystal optical differential device 10 are respectively arranged in the two arms of the Mach-Zehnder interference system; the beam expander system comprises a third lens 2 and a fourth lens 3; the light beam output by the laser 1 passes through the beam expander 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, transmits the horizontal linearly polarized light, is incident from the first substrate side of the first adjustable liquid crystal optical differential device 7, the first adjustable liquid crystal optical differential device 7 performs geometric phase modulation on the incident linearly polarized light beam, the emitted light beam enters the second polarization beam splitter 11 after passing through the first mirror 8, and is reflected by the second polarization beam splitter 11; at the same time, the vertical linearly polarized light reflected from the first polarization beam splitter 6 passes through the second mirror 9, is incident from the first substrate side of the second adjustable liquid crystal optical differential device 10, the second adjustable liquid crystal optical differential device 10 performs geometric phase modulation on the incident linearly polarized light beam, and the emitted light beam enters the second polarization beam splitter 11; the two combined light beams emitted from the second polarization beam splitter 11 exit the Mach-Zehnder interference system, are received by the imaging device 13 after passing through the second lens 12; 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 regulating units 14 and 15 are used to regulate the external electric field environment of the adjustable liquid crystal optical differential device; changing the polarity of the external electric field can switch the bright field image or the edge image.

[0092] For example, a mask plate 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 regulating units 14 and 15, which is used to adjust the polarity of the external electric field to control the output of the bright field image or the edge image.

[0093] In specific implementation, it can be designed according to actual conditions. By regulating the external electric field, the emitted light field of the adjustable liquid crystal optical differential device 7 and 10 can be changed, so that the bright field image or the edge image is output after being emitted from the Mach-Zehnder interference system. For example, +5V and -5V voltages can be used as the external electric field. Changing the polarity of the external electric field can switch the bright field image or the edge image.

[0094] The first lens 5 and the second lens 12 constitute 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 frequency spectrum plane of the 4f system, i.e., the common focal plane of the first lens 5 and the second lens 12, to modulate the incident light in the frequency domain; the target object 4 is placed on the front focal plane of the first lens 5; and the CCD camera is placed at the back focal plane of the second lens 12 to obtain a clear edge image or bright field image.

[0095] Exemplarily, Figure 8 A dynamic imaging result diagram of an adjustable liquid crystal optical differentiator provided in an embodiment of the present application is shown. The adjustable liquid crystal optical differentiator has linear modulation on amplitude, and the linear modulation on the frequency spectrum plane makes the adjustable liquid crystal optical differentiator have a first-order differentiation effect, so that edge imaging of a target pattern can be realized. Under a negative polarity external electric field, the adjustable liquid crystal optical differentiator has no obvious modulation effect on amplitude and phase, so that bright field imaging of the target pattern can be realized. Reference Figure 8 When incident light of 630 nm is used, the first column shows a bright field image obtained under a -5 V external electric field, and the second column shows an edge image obtained under a +5 V external electric field.

[0096] Exemplarily, Figure 9 A switching response time diagram of the adjustable liquid crystal optical differentiator provided in the embodiment of the present application is shown. The switching time between the edge image and the bright field image is defined as the duration when the intensity changes between 10% and 90%. When an AC square wave signal of 10 Vpp and 1 kHz is applied, the response time of the edge image to the bright field image and vice versa is measured as 62 μs. Reference Figure 9 The adjustable liquid crystal optical differentiator still has superfast response speed and good stability and reversibility after more than 1.8 million cycles.

[0097] It should be noted that the dynamic edge imaging effect corresponding to incident light of 630 nm is only exemplarily shown, and the working waveband of the adjustable liquid crystal optical differentiator provided in the present application is not limited. In other embodiments, the device still has applicability, and according to actual requirements, a suitable ferroelectric liquid crystal and a suitable electric field environment can be selected to make the adjustable liquid crystal optical differentiator provided in the embodiment of the present application have different response times.

[0098] The above specific embodiments do not constitute a limitation on the protection scope of the present application. 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 replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. An adjustable liquid crystal optical differentiator, characterized by, The display device comprises a first substrate, a second substrate and a ferroelectric liquid crystal layer between the first substrate and the second substrate; The first substrate is provided with a first transparent electrode layer on the side close to the second substrate, and the second substrate is provided with a second transparent electrode layer on the side close to the first substrate; The first transparent electrode layer is provided with an orientation layer on the side close to the second substrate, and the orientation layer is provided with a control pattern, which is subject to a first arcsine function from -3π / 8 to π / 8 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 of the first substrate; The ferroelectric liquid crystal layer comprises ferroelectric liquid crystal molecules, which form a layered helical structure in the absence of an external electric field, and the helical axis of the layered helical structure is parallel to the plane of the first substrate, and the equivalent optical axis of the ferroelectric liquid crystal layer coincides with the helical axis of the layered helical structure; In the absence of an external electric field, the ferroelectric liquid crystal molecules are arranged in accordance with the control pattern of the orientation layer, and the arrangement along the first direction is subject to the first arcsine function from -3π / 8 to π / 8, and the arrangement along the second direction is the same; In the case of applying an external electric field perpendicular to the first substrate and with a voltage value greater than or equal to a threshold voltage between the first transparent electrode layer and the second transparent electrode layer, the layered helical structure is disentangled, and the equivalent optical axis rotates synchronously.

2. The tunable liquid crystal optical differentiator of claim 1, wherein, The first arcsine function is α=0.5arcsin(x)-π / 8; When no voltage is applied between the first transparent electrode layer and the second transparent electrode layer, the distribution of the equivalent optical axis is subject to the first arcsine 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 is subject to a second arcsine 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 is subject to a third arcsine function: α=0.5arcsin(x)-π / 8-θ, and the adjustable liquid crystal optical differentiator realizes bright field imaging; Wherein, α is the included 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 included angle between the long axis of the ferroelectric liquid crystal molecule and the layer normal when no voltage is applied between the first transparent electrode layer and the second transparent electrode layer.

3. The tunable liquid crystal optical differentiator according to claim 2, wherein, In the case of applying an external electric field perpendicular to the first substrate and with a voltage value greater than or equal to a threshold voltage, the director of the ferroelectric liquid crystal molecule rotates to the side parallel to the first substrate on the helical cone according to the electric field polarity, and the distribution of the director of the disentangled ferroelectric liquid crystal molecule along the first direction is still related to the first arcsine function, and the equivalent optical axis rotates synchronously; After applying voltage, the overall optical axis distribution is rotated and transformed, and when a positive voltage is applied, the distribution of the equivalent optical axis satisfies the second arcsine function; and when a negative voltage is applied, the distribution of the equivalent optical axis satisfies the third arcsine function.

4. The tunable liquid crystal optical differentiator of claim 1, wherein, A spacer is arranged between the first substrate and the second substrate to support the first substrate and the second substrate to form a containing space for the ferroelectric liquid crystal layer, so that the thickness of the ferroelectric liquid crystal layer in the third direction is greater than or equal to the pitch of the layered helical structure; wherein the third direction is perpendicular to the plane in which the first substrate is located.

5. The tunable liquid crystal optical differentiator of claim 1, wherein, The ferroelectric liquid crystal layer includes a chiral smectic C phase ferroelectric liquid crystal, under the boundary condition that the alignment layer has parallel alignment, the layer normal of the smectic layer in the ferroelectric liquid crystal is always parallel to the plane in which the first substrate is located, the ferroelectric liquid crystal molecules exhibit a helical structure under no external electric field, the helical axis of the ferroelectric liquid crystal molecules is always parallel to the plane in which the first substrate is located, and the pitch of the helical axis is less than or equal to the distance between the first substrate and the second substrate.

6. The tunable liquid crystal optical differentiator of claim 1, wherein, 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 producing a tunable liquid crystal optical differentiator, for producing the tunable liquid crystal optical differentiator according to any one of claims 1 to 6, characterized by, The preparation method comprises: providing a first substrate with a first transparent electrode layer on one side and a second substrate with a second transparent electrode layer on one side; forming an alignment layer on the side of the first transparent electrode layer away from the first substrate; arranging the first substrate and the second substrate oppositely, arranging a spacer between the first transparent electrode layer and the second transparent electrode layer to form a containing space for the ferroelectric liquid crystal molecules; aligning the alignment layer to form a control pattern; wherein the control pattern gradually changes from -3π / 8 to π / 8 along a first direction according to a first inverse sine function, and 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 in which the first substrate is located; forming a ferroelectric liquid crystal layer between the alignment layer and the second transparent electrode layer to form the adjustable liquid crystal optical microdifferentiator; wherein the ferroelectric liquid crystal layer includes ferroelectric liquid crystal molecules, the ferroelectric liquid crystal molecules form a layered helical structure under no external electric field, the helical axis of the layered helical structure is parallel to the plane in which the first substrate is located, and the equivalent optical axis of the ferroelectric liquid crystal layer coincides with the helical axis of the layered helical structure; under no external electric field, the ferroelectric liquid crystal molecules are arranged according to the control pattern of the alignment layer to gradually change from -3π / 8 to π / 8 along the first direction according to the first inverse sine function, and the same along the second direction; under the condition that 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 helical structure is disentangled, and the equivalent optical axis is synchronously rotated; arranging the first substrate and the second substrate oppositely, arranging a spacer between the first transparent electrode layer and the second transparent electrode layer to form a containing space for the ferroelectric liquid crystal molecules.

8. The production method according to claim 7, characterized by, forming a ferroelectric liquid crystal layer between the alignment layer and the second transparent electrode layer to form the adjustable liquid crystal optical microdifferentiator, comprising: The empty box composed of the first substrate, the second substrate and the spacer is subjected to ultraviolet light orientation so as to make the orientation direction of the orientation layer consistent with the control pattern; At a temperature equal to or higher than the ferroelectric liquid crystal clearing point, the ferroelectric liquid crystal in an isotropic state is filled into the containing space, and after the filling is completed, the hot stage is cooled to room temperature to form the layered helical structure and to manufacture the adjustable liquid crystal optical micro-differentiator.

9. A dynamic edge imaging device, characterized by The external electric field regulating unit, a laser, a beam expander system, a first lens, a first adjustable liquid crystal optical micro-differentiator, a second adjustable liquid crystal optical micro-differentiator, a Mach-Zehnder interference system, a second lens and an imaging device are arranged on the same optical axis of the target object; wherein the first adjustable liquid crystal optical micro-differentiator and the second adjustable liquid crystal optical micro-differentiator are both the adjustable liquid crystal optical micro-differentiator of any one of claims 1-6; The Mach-Zehnder interference system comprises a first polarization beam splitter, a first mirror, a second mirror and a second polarization beam splitter, and the first adjustable liquid crystal optical micro-differentiator and the second adjustable liquid crystal optical micro-differentiator are respectively arranged in two arms of the Mach-Zehnder interference system; The beam expander system comprises a third lens and a fourth lens; The light beam output by the laser passes through the beam expander 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, and transmits a horizontally linearly polarized light; the horizontally linearly polarized light is incident from the first substrate side of the first adjustable liquid crystal optical micro-differentiator, the first adjustable liquid crystal optical micro-differentiator performs geometric phase modulation on the incident linearly polarized light beam, the emitted light beam enters the second polarization beam splitter after passing through the first mirror, and is reflected by the second polarization beam splitter; meanwhile, the vertically linearly polarized light reflected from the first polarization beam splitter passes through the second mirror, is incident from the first substrate side of the second adjustable liquid crystal optical micro-differentiator, the second adjustable liquid crystal optical micro-differentiator performs geometric phase modulation on the incident linearly polarized light beam, and the emitted light beam enters the second polarization beam splitter; the light emitted from the second polarization beam splitter and combined from two paths exits the Mach-Zehnder interference system, is received by the imaging device after passing through the second lens; the imaging device receives a bright field image or a two-dimensional first-order edge image of the target object; the external electric field regulating unit is used for regulating the external electric field environment of the adjustable liquid crystal optical micro-differentiator; changing the polarity of the external electric field can realize switching of the bright field image or the edge image.

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