CN108020960B - Method of manufacturing liquid crystal electro-optical components - Google Patents

Abstract

The present invention provides a method for manufacturing a liquid crystal electro-optical component, which performs liquid crystal alignment in a non-contact manner, provides a liquid crystal molecule sealed in the liquid crystal electro-optical component with a stable alignment, so that the liquid crystal molecule has a defined pre-tilt angle in a steady state, thereby preventing defects caused by reverse tilt of the liquid crystal when an external field tends to a dynamic state. The method comprises: providing an optical unit, the optical unit comprising a hollow space; injecting a liquid crystal mixture into the hollow space; and applying a gradient field to the liquid crystal mixture, wherein the intensity of the gradient field presents a gradient distribution.

Description

Method of manufacturing liquid crystal electro-optical components

technical field

The invention relates to a method for manufacturing a liquid crystal electro-optical component, in particular to a non-contact method for liquid crystal alignment to provide the effect of stable alignment of liquid crystal molecules sealed in the liquid crystal electro-optical component, so that the liquid crystal molecules have The defined pre-tilt angle can prevent the occurrence of defects caused by the reverse tilt of the liquid crystal molecules when the applied electric field becomes dynamic.

Background technique

When combining liquid crystal (LC) materials with hollow optical fibers, photonic crystals or closed structures to develop novel electro-optical components, there is a problem that the liquid crystal molecules cannot be effectively controlled into a stable arrangement in the hollow column. In the presence of an external electric field, a disclination line (disclination line, also called a discontinuous line) of alignment defect will occur, and this defect will seriously cause light scattering loss. The reason for the defect is that the closed surface of the hollow cylinder cannot be subjected to the rubbing process, so the elastomer liquid crystal molecules confined in a closed cylinder (or structure) without rubbing treatment cannot obtain a Stable and consistent alignment direction, and the orientation mechanism of liquid crystal molecules in closed pores is quite complex, not as simple as in the square structure of traditional liquid-crystal cells; therefore, the problem of alignment defects is severely limited Development of liquid crystal optical fibers or electro-optical components.

On the cylindrical hole wall of the hollow fiber or photonic crystal, the rubbing alignment treatment cannot be performed on the cylindrical cavity wall to provide a preferred direction of the liquid crystal molecules, so that the thermal disturbance will cause the optical axis direction of the liquid crystal molecules to be unstable. Therefore, when an electric field is applied to the liquid crystal (optical fiber) component, it may cause the liquid crystal molecules to rotate and tilt in two different directions, resulting in alignment defects at the boundary between the two oppositely inclined regions, as shown in the figure 1 shown. In FIG. 1, in the optical unit 11, the power supply 19 drives the upper electrode 18a and the lower electrode 18b to generate an electric field therebetween to apply an electric field to the liquid crystal mixture 13, so that the liquid crystal molecules 13a turn to tilt and cause a reverse tilt region, resulting in the occurrence of disclination lines . This defect causes a difference in refractive index with surrounding liquid crystal molecules to form an interface, which will lead to loss of optical signals of liquid crystal or optical fiber components, and deterioration of optical properties. Therefore, the application range of liquid crystal optical fibers or electro-optical components will be limited.

The arrangement state of liquid crystal molecules has a significant effect on the light propagation characteristics of optical fiber components. In order to improve the optical properties of the liquid crystal optical fiber assembly, the problem of the orientation defect of the reverse tilt of the liquid crystal molecules must be solved first. However, the arrangement of liquid crystal molecules in the hollow fiber is affected by many factors, such as liquid crystal elastic constant, liquid crystal dielectric anisotropy, dipole moment and rigidity of liquid crystal molecules, surface tension of liquid crystal and glass, glass air column Parameters such as the flatness of the pipe wall and the presence or absence of defects. Therefore, the arrangement of liquid crystal molecules in the cylindrical pores is quite complicated.

The common arrangement of liquid crystal molecules in the cylindrical hole includes a parallel arrangement (planar-aligned) and a splayed-aligned arrangement (splayed-aligned) parallel to the axis of the optical fiber. Since the liquid crystal molecules in the expansion alignment have no threshold voltage (Fredericks transition threshold), there will be no reverse tilt domain defects like the liquid crystal molecules in the parallel alignment. Therefore, in order to avoid the generation of block defects, it is proposed in the existing literature that photo-alignment technology or liquid crystal materials (such as dual-frequency liquid crystal or negative liquid crystal) that can exhibit expansion alignment in the hollow fiber must be used, which will limit the liquid crystal material. of selectivity. In addition, the dielectric anisotropy (Δε) of the negative-type liquid crystal material is smaller than that of the positive-type liquid crystal material, so its threshold voltage is higher.

Although polymer stabilized alignment (PSA) technology has been proposed as early as 1998, it is mainly used in the improvement of the characteristics of liquid crystal displays. In recent years, due to its good characteristics and the improvement of related technologies, it has gradually has received attention from all sides. The technology of polymer-stabilized liquid crystal molecular alignment is mainly to obtain a polymer network structure by phase separation caused by photopolymerization. Ultraviolet (UV) photopolymerization of reactive liquid crystals or photo-sensitive monomers under the action of an external electric field (or driving electric field) is used to generate a polymer network for controlling the pretilt direction of liquid crystal molecules. Since the curing electric field can guide the liquid crystal molecules to align in a specific direction, the liquid crystal director (direction, the direction of the liquid crystal axis) in the hollow fiber has the characteristic of a specific direction. Moreover, the pretilt angle (the angle between the liquid crystal axis and the interface) caused by the polymer network can control the tendency of the liquid crystal molecules to rotate, so the polymer stabilized alignment technology can provide a stable alignment, a simple process, low cost, and Liquid crystal fiber or electro-optical components with low threshold voltage, fast response, high tuning and high stability.

Polymer-stabilized alignment technology is also used in the LCD panel industry. Here, the polymer-stabilized alignment technology can be applied to a vertical alignment mode. That is, the liquid crystal used in the vertical alignment mode is a negative liquid crystal, the original pretilt angle is 90° but no specific direction, and the electric field for driving is a vertical electric field (perpendicular to the substrate). In order to make the liquid crystal molecules in the liquid crystal panel have the initial light angle and wide viewing angle display characteristics in a certain direction, it is necessary to use an oblique electric field to make the liquid crystal molecules tilt in the required direction under the driving of an external electric field, and the above oblique electric field requires Special electrode pattern design to achieve. When the liquid crystal molecules are tilted toward the desired direction due to the oblique electric field, the photopolymerization procedure is performed to polymerize the photosensitive monomers in the liquid crystal mixture into a surface polymer network. The polymer network can provide the direction of the pretilt angle of the liquid crystal molecules consistent with the direction in which the liquid crystal molecules fall when the photopolymerization process is performed, and the angle of the pretilt angle partly depends on the oblique electric field that causes the initial liquid crystal molecules to fall when the photopolymerization process is performed. strength. Although the polymer-stabilized alignment technology is used to provide the liquid crystal molecules with an initial pretilt angle of a certain direction, the substrate still needs the presence of a vertical alignment layer before the surface polymer is formed by the photopolymerization process.

Generally speaking, in order to make the liquid crystal molecules have a certain alignment direction on the surface of the substrate (glass), alignment treatment is usually performed on the surface of the substrate, but for hollow fibers, the difficulty lies in the alignment of the cylindrical hole wall A friction alignment treatment is performed. Although the liquid crystal molecules tend to be aligned axially in the fiber due to the injected capillary force, they do not have a preferred alignment direction under the action of the applied electric field, so it is easy to cause local alignment defects of the anti-tilt alignment of the liquid crystal molecules. The occurrence of this defect will cause the optical power loss of the liquid crystal fiber assembly, the slow response speed, and the deterioration of the optical properties.

After the liquid crystal is filled into the hollow fiber, if the pore wall surface is not treated, the liquid crystal molecules have a rod-like structure, and the flow force of the capillary phenomenon will cause the overall arrangement direction of the liquid crystal to be roughly parallel to the fiber axis, as shown in Figure 2(a) points shown. From a microscopic point of view, the liquid crystal molecules 23a are arranged in the hollow space 22 inside the optical fiber 21 at different inclination angles, so a completely black state cannot be observed under a crossed polarized light microscope, as shown in Fig. 2(b) A little light leaks, wherein the optical fiber tube 21a is covered with the liquid crystal mixture 23, and the symbols A and P represent the axial directions of the polarizer and the photodetector, respectively. Because the liquid crystal molecules are easily driven by an external electric field to change the alignment direction, when an external electric field is applied to the liquid crystal fiber, since the rubbing alignment treatment cannot be performed on the glass wall of the hole in the hollow fiber tube, the liquid crystal molecules in the unaligned cylindrical holes have different directions. The liquid crystal molecules are arranged at a tilt angle, so that the action of the applied electric field will cause the liquid crystal molecules to respond to the reverse tilt, and then the discontinuity of the liquid crystal guide axis arrangement causes the random generation of disclination lines, as shown in Figure 3(a) and Figure 3(b) Show. 3(a) and 3(b), the fiber tube 31a of the optical fiber 31 coats the liquid crystal mixture 33, and the upper electrode 38a and the lower electrode 38b apply an electric field E to the liquid crystal mixture 33 to make the liquid crystal molecules 33a rotate and tilt. In addition, it is known from the liquid crystal continuous elastomer theory that the arrangement of liquid crystal molecules is affected by the disclination line, so under the driving of the electric field, a multi-block liquid crystal arrangement with the disclination line as the interface will be formed, and the disclination line defect will Causes the loss of optical signal of the liquid crystal fiber assembly, the hysteresis of electro-optical response, and the slowing of the response speed.

SUMMARY OF THE INVENTION

In order to successfully combine liquid crystal materials with hollow fibers and apply them to the development of highly tuned optical fibers or electro-optical components, it is necessary to solve the problem that it is difficult to align liquid crystal molecules in a small enclosed space (micrometer scale), and then improve the liquid crystal molecules. A disclination line generated by the reverse tilt of the molecule occurs. Therefore, the present invention uses gradient field (electric field, magnetic field, temperature field or stress field, etc., but not limited thereto) and surface polymer stabilized alignment (SPSA) technology to provide liquid crystal molecules in the hollow fiber core. It can achieve a stable arrangement direction and have a pre-tilt angle distribution.

In more detail, the present invention mainly uses the gradient field to drive the liquid crystal molecules to align in a consistent direction to eliminate the generation of dislocation defects, and then uses the surface polymer stable alignment technology to fix the liquid crystal molecules in the desired direction and tilt angle. . The gradient field part can use an electric field, a temperature field, a magnetic field or a stress field to realize the gradient field to cause the liquid crystal molecules to flow.

That is, in order to allow various positive and negative liquid crystal materials to be widely used in the development of electronically controlled liquid crystal optical fibers or electro-optical components, the present invention proposes to use the combination of gradient field and surface polymer stable alignment technology to provide liquid crystal molecules in the air column. A pre-tilt angle can be obtained and anchored in a certain direction, so that when an electric field acts, the liquid crystal molecules have a preferred stable direction to rearrange, thereby improving the phenomenon of disclination lines driven by an external electric field.

Accordingly, the present invention provides a method of manufacturing a liquid crystal electro-optical device, comprising: providing an optical unit, the optical unit including a hollow space; injecting a liquid crystal mixture into the hollow space; and applying a gradient field to the liquid crystal mixture, The intensity of the gradient field exhibits a gradient distribution. In this way, the generation of disclination defects in the liquid crystal electro-optical device of the present invention can be eliminated.

According to an embodiment of the present invention, the gradient field may be a gradient electric field, a gradient temperature field, a gradient magnetic field, or a gradient stress field.

According to an embodiment of the invention, the optical unit can be an optical fiber; the hollow space can extend parallel to the axis of the optical fiber; and the intensity of the gradient field can be enhanced or weakened along the axis of the optical fiber.

According to another embodiment of the present invention, the optical fiber may be a photonic crystal fiber.

According to another embodiment of the present invention, the optical unit can be an optical waveguide, the optical waveguide can be composed of a substrate defining the hollow space; and the intensity of the gradient field can be enhanced or weakened along a direction parallel to the substrate .

According to another embodiment of the present invention, the optical unit can be a liquid crystal cell, and the liquid crystal cell can be composed of two substrates defining the hollow space; and the intensity of the gradient field can be enhanced along a direction parallel to one of the two substrates or weaken.

According to an embodiment of the present invention, the hollow space has a spatial dimension less than 100 μm.

In order to further stabilize the direction and angle of the pretilt angle of liquid crystal molecules, according to an embodiment of the present invention, the method of the present invention may further include: irradiating a curing light to the liquid crystal mixture, wherein the liquid crystal mixture may include liquid crystal molecules and photosensitive monomers.

According to an embodiment of the present invention, the photosensitive monomers can be polymerized into a surface polymer network at the interface of the hollow space when the irradiation of a curing light is performed.

In order to modulate the direction and angle of the pretilt angle of liquid crystal molecules, according to an embodiment of the present invention, the method of the present invention may further include: applying a curing electric field to the liquid crystal mixture, wherein the process of applying a curing electric field may be performed during the irradiation of a curing light prior to the procedure, and the curing electric field may be a spatially uniform electric field.

Finally, the liquid crystal molecules in the liquid crystal electro-optical device manufactured according to the above method of the present invention can have a stable pretilt angle with a defined direction and angle.

Description of drawings

FIG. 1 is a schematic diagram of a liquid crystal reverse tilt region in a conventional liquid crystal electro-optical module.

FIG. 2( a ) is a schematic diagram of the molecular arrangement of conventional liquid crystals in an optical fiber.

Fig. 2(b) is the observation result of the existing liquid crystal in the optical fiber under a polarizing microscope.

Fig. 3 (a) is a schematic diagram of the generation of a disclination line defect of liquid crystal in an optical fiber;

Figure 3(b) is the observation result of the disclination line defect of the liquid crystal in the optical fiber under a polarizing microscope.

4 is a schematic diagram illustrating a method for fabricating a liquid crystal electro-optical device according to the first embodiment of the present invention.

5 is a schematic diagram illustrating components of a liquid crystal fiber type Mach-Zander interferometer according to the first embodiment of the present invention.

FIG. 6 shows the observation results of the liquid crystal fiber according to the first embodiment of the present invention under a polarizing microscope.

FIG. 7( a ) is a graph 1 showing the transmission spectrum of the liquid crystal fiber Mach-Zander interferometer driven by different applied voltages according to the first embodiment of the present invention.

7( b ) is a second graph showing the transmission spectrum of the liquid crystal fiber Mach-Zander interferometer driven by different applied voltages according to the first embodiment of the present invention.

8 is a graph showing the amount of resonant wavelength shift of the liquid crystal fiber type Mach-Zander interferometer driven by different applied voltages according to the first embodiment of the present invention.

9 is a schematic diagram illustrating a method for fabricating a liquid crystal electro-optical device according to a second embodiment of the present invention.

[Description of reference numerals]

11-optical unit, 13-liquid crystal mixture, 13a-liquid crystal molecule, 18a-upper electrode, 18b-lower electrode, 19-power supply, 21-optical fiber, 21a-fiber tube, 22-hollow space, 23-liquid crystal mixture, 23a- Liquid crystal molecule, 31-fiber, 31a-fiber tube, 33-liquid crystal mixture, 33a-liquid crystal molecule, 38a-upper electrode, 38b-lower electrode, 41-fiber, 42-hollow space, 41a-fiber tube, 43-liquid crystal mixture , 43a-liquid crystal molecule, 45-photosensitive monomer, 48a-upper electrode, 48b-lower electrode, 49-power supply, 51-fiber, 51A-fiber, 51B-fiber, 52-heating table, 57-gasket.

Detailed ways

The embodiments of the present invention are disclosed herein to provide further understanding of the principles and spirit of the present invention, but the implementation or embodiment thereof is not limited thereto.

The invention provides a method for manufacturing a liquid crystal electro-optical component, comprising: providing an optical unit, the optical unit includes a hollow space; injecting a liquid crystal mixture into the hollow space; and applying a gradient field to the liquid crystal mixture, the intensity of the gradient field exhibits a gradient distribution. In this way, the generation of disclination defects in the liquid crystal electro-optical device of the present invention can be eliminated. That is, the liquid crystal molecules of the liquid crystal optoelectronic device fabricated by this method have a defined pretilt angle.

According to an embodiment of the present invention, the gradient field may be a gradient electric field, a gradient temperature field, a gradient magnetic field, or a gradient stress field.

According to an embodiment of the present invention, the optical unit can be an optical fiber; the hollow space can extend in a direction parallel to the axis of the optical fiber; and the intensity of the gradient field can be enhanced or weakened along the axis of the optical fiber, but not limited thereto . For example, the gradient vector of the gradient field may be oriented parallel to the axis of the fiber, oriented perpendicular to the axis of the fiber, or pointing to any orientation in space.

According to another embodiment of the present invention, the optical fiber may be a photonic crystal fiber.

According to another embodiment of the present invention, the optical unit can be an optical waveguide, and the optical waveguide can be composed of a substrate defining the hollow space; and the intensity of the gradient field can be enhanced or weakened along a direction parallel to the substrate, but not limited to this. For example, the gradient vector of the gradient field may be parallel to the substrate, perpendicular to the substrate, or point in any orientation in space.

According to another embodiment of the present invention, the optical unit can be a liquid crystal cell, and the liquid crystal cell can be composed of two substrates defining the hollow space; and the intensity of the gradient field can be enhanced along a direction parallel to one of the two substrates or weakened, but not limited to. For example, the gradient vector of the gradient field can be parallel to one of the two substrates, perpendicular to one of the two substrates, or point to any orientation in space.

After the above procedure of applying the gradient field is completed, the optical unit of the present invention will not have the disclination line defect caused by the reverse tilt under the driving of the external electric field. That is, the application of the gradient field enables the liquid crystal mixture in the optical unit of the present invention to have a defined pre-tilt angle, so that the liquid crystal molecules of the liquid crystal mixture can be turned uniformly under the driving of the applied electric field, thereby preventing the reverse tilt. Caused by the disclination line defect.

In order to meet various application requirements and types, according to an embodiment of the present invention, the liquid crystal mixture may include liquid crystal molecules and photosensitive monomers, wherein the liquid crystal molecules may include a plurality of liquid crystals, such as positive-type liquid crystal, negative-type liquid crystal, and dual-frequency liquid crystal .

In addition, in order to further modulate the direction and angle of the pre-tilt angle of the liquid crystal molecules, in an embodiment of the present invention, the method of the present invention may further include: irradiating a curing light to the liquid crystal mixture, wherein the liquid crystal mixture may include liquid crystal molecules and light single sense.

When performing the irradiation of a curing light, the photosensitive monomers can be polymerized into a surface polymer network at the interface of the hollow space, so as to provide a pretilt angle defined by the liquid crystal molecules, but not limited thereto. For example, these photosensitive monomers can polymerize into a space-type polymer network in the hollow space (including its interface and the space between its interfaces).

In order to modulate the direction and angle of the pre-tilt angle of liquid crystal molecules, in an embodiment of the present invention, the method of the present invention may further include: applying a curing electric field to the liquid crystal mixture, wherein the process of applying a curing electric field may be performed during the irradiation of a curing light prior to the procedure, and the curing electric field may be a spatially uniform electric field.

According to another embodiment of the present invention, the process of applying the gradient field and the process of irradiating the curing light can be performed simultaneously. In this case, the process of applying the gradient field may be ended simultaneously with the end of the process of irradiating the curing light.

In more detail, according to another embodiment of the present invention, the irradiating curing light process can be performed after the first time interval of the gradient field application process is performed, and the execution of the gradient field application process can be maintained at the same time, wherein the first time interval can be between 1- within 90 minutes. Specifically, the first time interval may be 1 minute, 5 minutes, 10 minutes, 15 minutes, 30 minutes, 60 minutes or 90 minutes; preferably, the first time interval may be 5-15 minutes; A time interval may be 8 to 12 minutes. After the first time interval of the irradiation curing light procedure, the liquid crystal mixture can be detected as having no disclination line defects caused by reverse tilting under the action of an applied electric field. In this case, the gradient field applying procedure may be continuously performed when the irradiation curing light procedure starts to be performed, and in this case, the gradient field applying procedure may be simultaneously ended when the irradiation curing light procedure ends.

The above application of the curing electric field procedure can further modulate and stabilize the pretilt angle characteristic of the liquid crystal mixture by applying the gradient field procedure. That is, the above procedure of applying the curing electric field can modulate the magnitude and direction of the pretilt angle, and stabilize the modulated magnitude and direction of the pretilt angle through the polymerization of the photosensitive monomer.

According to an embodiment of the present invention, the hollow space of the present invention may have a spatial dimension in the range of 1-100 μm. Specifically, the hollow space of the present invention may have a spatial dimension of less than 100 μm, 50 μm, or 10 μm. For example, when a hollow-core fiber is used as the optical unit of the present invention, the inner diameter of the fiber tube can be less than 100 μm, 50 μm, or 10 μm; when a multi-hollow-core optical fiber is used as the optical unit of the present invention, the inner diameter of each hollow core can be less than 100 μm, 50 μm, or 10 μm. 100 μm, 50 μm, or 10 μm; or when a liquid crystal cell is used as the optical unit of the present invention, the cell gap can be smaller than 100 μm, 50 μm, or 10 μm.

Hereinafter, more specific implementations will be further disclosed.

[First Embodiment: Gradient Electric Field Experiment]

Step 1: In order to generate a gradient electric field in the experiment, the ITO film of the ITO (indium tin oxide, indium tin oxide) glass substrate is directly used as the electrode plate for supplying the applied voltage.

Step 2: First attach the optical fiber or photonic crystal fiber filled with the liquid crystal/photosensitive monomer mixture on the ITO glass substrate (lower electrode 48b), and then cover the upper end with another piece of ITO glass substrate (upper electrode 48a), as shown in the figure. 4, part (a).

Step 3: In order to generate a gradient electric field between the electrode plates, the upper electrode 48a is slightly inclined so that it forms a small angle with the lower electrode 48b, as shown in part (b) of FIG. 4 .

Step 4: After the voltage is applied, a gradient electric field may be formed between the upper electrode 48a and the lower electrode 48b. Then, use a polarizing microscope (POM) to observe how the gradient electric field rotates the liquid crystal molecules 43a; if a disclination line occurs (as shown in Fig. 3(a) and Fig. 3(b) ), the upper electrode 48a can be adjusted appropriately. And a voltage is applied until no disclination line defect occurs. Alternatively, in this experiment, a system that can generate a precise gradient electric field can be used, or a coating technology can be used directly on the component to fabricate the upper and lower conductive films on the optical fiber, so that the distance between the upper and lower electrodes becomes a gradual structure, so as to apply a gradient electric field to achieve no Defective liquid crystal alignment.

Step 5: UV exposure is performed on the optical fiber 41 with applied voltage and no disclination line defect, as shown in part (c) of FIG. 4 , the exposure power is 1 mW, and the exposure time is 3 min. The photosensitive monomers 45 in the optical fiber 41 are photopolymerized by UV exposure to form a network of polymers 46, thereby stabilizing the arrangement of the liquid crystal molecules 43a, as shown in part (d) of FIG. 4 .

Specifically, as shown in FIG. 4 , in the absence of an applied electric field, both the photosensitive monomer 45 and the liquid crystal molecules 43 a (having a positive Δε) injected into the liquid crystal mixture 44 in the hollow space 42 are substantially parallel to the optical fiber 41 the axial direction (part (a) of Fig. 4). When the upper electrode 48a and the lower electrode 48b are driven by the power source 49 to apply a gradient electric field to the optical fiber 41, the force will drive the liquid crystal molecules 43a to align in a certain direction due to the gradient change of the electric field: if it is a positive liquid crystal material, its The direction of the molecular axis tends to be parallel to the direction of the electric field; on the contrary, if it is a negative liquid crystal material, the direction of the molecular axis tends to be perpendicular to the direction of the electric field, as shown in part (b) of Figure 4, where the length of the dashed arrow represents the strength of the electric field the size of.

In order to stabilize the alignment of the liquid crystal molecules 43a and give a pretilt angle, this applied electric field is maintained, and then the sample of the liquid crystal fiber 41 is irradiated with UV light (part (c) of FIG. 4 ). Through the action of the curing electric field and the curing of UV light, the photosensitive monomer 45 is polymerized on the inner sidewall surface of the optical fiber tube 41a at a pretilt angle relative to the surface of the substrate. Moreover, when the electric field is removed, the liquid crystal will be anchored by the arrangement of the polymer network 46, so that the liquid crystal molecules 43a have a tilt angle and a certain alignment direction in the initial state, and the pre-tilt angle will be permanently maintained, as shown in Figure 4 shown in part (d).

Therefore, the pretilt angle and the alignment direction of the liquid crystal can be controlled by the polymer network 46 on the wall surface of the optical fiber 41 that has not been rubbed by using this simple process. The polymer network can be regarded as a force that provides the liquid crystal molecules 43a to restore or anchor the boundaries, thereby eliminating the occurrence of defects and leading to faster relaxation (recovery) of the liquid crystal molecules 43a. However, the pretilt angle obtained by the polymerization of the photosensitive monomer 45 and its surface morphology are related to the concentration of the monomer 45, the exposure conditions, and the curing electric field.

With specific splicing parameters, the liquid crystal fiber processed in the above steps is spliced with the single-mode optical fiber, and the spliced end face is formed into a fiber taper. After splicing the two ends, the assembly of the liquid crystal fiber type Mach-Zehnder Interferometer (Mach-Zehnder Interferometer) is completed (as shown in FIG. 5 ).

Referring to Figure 5, when incident light is conducted from a single-mode fiber to the first fiber taper, a portion of the light in the fiber core is coupled into the fiber shell, while another portion of the light remains in the fiber core. In the second fiber taper, the light in the fiber shell will be coupled back to the fiber core, causing the two lights to form interference, where the component interference formula is: λ _p =2L(n _co –n _cl )/(2N+1), where n _co is the effective refractive index of the fiber core of the liquid crystal fiber, n _cl is the effective refractive index of the fiber shell, L is the filling length of the liquid crystal, N is a constant term (N=1, 2, 3...), and λ _p is The resonance wavelength that satisfies the minimum light intensity. When an electric field is applied to the liquid crystal fiber, the alignment direction of the liquid crystal molecules in the hollow-core fiber will change, and then the values of _nco and _λp will be affected and the values will be shifted.

As shown in FIG. 6 , it can be observed by polarizing microscope (POM) that the surface polymer-stabilized alignment technology of the present invention can effectively eliminate the occurrence of disclination lines of liquid crystals. Changes in the resonant wavelength of the interferometer are caused by changes in the effective refractive index of the fiber core due to changes in the arrangement of the liquid crystal molecules. Here, the present invention utilizes an optical spectrum analyzer to analyze the relationship between voltage and resonance wavelength. As shown in Fig. 7(a) and Fig. 7(b), the increase of the voltage will cause the red shift of the resonance wavelength. The effective refractive index of the entire core increases, so the resonance wavelength shifts to a longer wavelength, and the liquid crystal filling length is 1400 μm.

After further sorting and analysis, the correlation between the displacement of the wavelength and the voltage can be obtained. As shown in FIG. 8 , the trend of the voltage-induced wavelength change is consistent with the physical properties of liquid crystals. From the experimental results, it is found that the threshold voltage for driving the liquid crystal molecules is about 30V. When the working voltage is less than 30V, the displacement of the resonance wavelength caused by the voltage is very small. The main reason is that the liquid crystal is limited by the anchoring effect of the polymer network, resulting in a very small degree of rotation of the liquid crystal driven by the electric field, so the increase in the refractive index caused by the driving voltage only shows a very slight change. When the applied voltage exceeds the critical voltage (at 30-70V), the liquid crystal molecules have a large amount of rotation under the action of this high-voltage electric field, so the range of refractive index changes will also be large, so more resonance wavelengths can be obtained. displacement. When the applied voltage is greater than 70V, the reason for the small change in the resonant wavelength shift caused by the voltage is: under the driving of the large voltage, the liquid crystal molecules in the middle layer in the hollow-core fiber are almost parallel to the electric field direction and reach a stable state, Therefore, the relatively large voltage is mainly used to drive the rotation of the liquid crystal molecules near the surface boundary, so that the refractive index increases only slightly, which in turn leads to a smaller change in the resonant wavelength shift.

[Second Embodiment: Gradient Temperature Field Experiment]

Step 1: The liquid crystal fiber 51 is fixed between two electrode plates (not shown in the figure), and placed on the heating table 52, as shown in FIG. 9 .

Step 2: In order to generate the gradient temperature field, the method is as follows:

(1) The right side of the optical fiber 51A is raised (~2 mm) by the insulating spacer 57, so that the substrate is inclined and the farther the right side is from the heating surface of the heating stage 52, the more the optical fiber 51A will be heated unevenly. The temperature distribution characteristic with a temperature gradient is shown in FIG. 9 . Alternatively, (2) the right side of the optical fiber 51B is vacated and only the left side contacts the heating stage 52 (~70°C), so that the left heated part of the optical fiber 51B exhibits the highest temperature, and the temperature increases with the distance from the left heated part And gradually decreased until the right side showed the lowest temperature, as shown in Figure 9.

Step 3: After continuous heating for a period of time, a vertical curing electric field is applied to the liquid crystal fiber 51. The vertical curing electric field is a direction perpendicular to the axis of the liquid crystal fiber 51, and then the liquid crystal (with a positive Δε) is rotated by using a polarizing microscope POM to observe the uniformly applied electric field. , and observe whether there is a phenomenon of disclination.

Step 4: If there is a disclination line defect, repeat steps 2-3 until no disclination line is observed at all.

Step 5: After the disclination line defect does not appear, the optical fiber 51 is exposed by using the parameters required for the experiment. In this embodiment, the exposure power is 1 mW, and the exposure time is 3 min. The photosensitive monomer in the component is photopolymerized by UV exposure to form a polymer network, thereby stabilizing the arrangement of liquid crystal molecules.

Specifically, the liquid crystal sample is placed in the heating device, and the temperature on the liquid crystal sample exhibits a gradient change by appropriate arrangement. The temperature of the liquid crystal sample in the left and right parts of FIG. 9 decreases from the left to the right. Therefore, the temperature field causes the liquid crystal molecules to perturb in a certain direction.

In order to stabilize the alignment direction of the liquid crystal molecules, the surface polymer stable alignment technology is used to form a polymer network to stabilize the liquid crystal molecules in a specific direction without the occurrence of disclination line defects. That is, by adding a curing electric field and UV exposure, the liquid crystal directors can be stably aligned at a specific pre-tilt angle. However, the surface polymer-stabilized alignment process is similar to the method disclosed in the above-mentioned first embodiment, the only difference is that the electric field applied to the liquid crystal sample is a uniform electric field, and the electric field can be given to the liquid crystal molecules according to the desired pretilt angle. And given, when the applied electric field is higher, the pretilt angle caused by it is larger, and the range of the liquid crystal device that can be electrically controlled and modulated is also smaller.

The polymer network in the SPSA fiber assembly can affect the alignment of the liquid crystal, and give the liquid crystal an anchoring force, so that the liquid crystal molecules can rotate faster and improve their response speed when an electric field is applied. Therefore, in the embodiment of the present invention, the key technology of the SPSA can effectively improve the defect that the hollow fiber cannot be rubbed aligned in the manufacturing process and the magnetic hysteresis of the component. In addition, the present invention utilizes the polymer network of SPSA technology to provide stabilization and modulation of alignment for liquid crystal molecules, and the type and structure of the polymer network depend on photopolymerization conditions, such as UV light intensity, exposure temperature, monomer concentration, electric field distribution, and exposure time and other factors, the present invention can achieve diversified component characteristics of liquid crystal optical fibers or liquid crystal optoelectronic components according to the design of process conditions.

Finally, the liquid crystal molecules in the liquid crystal electro-optical device manufactured according to the present invention can have a stable pretilt angle with a defined direction and angle, thereby eliminating the occurrence of disclination defects in the liquid crystal electro-optical device of the present invention.

The present invention has been disclosed above by embodiments, but it is not intended to limit the present invention; without departing from the spirit and scope of the present invention, any person with ordinary knowledge in the field to which the present invention pertains can make various equivalent changes and modifications. Therefore, the protection scope of the present invention should be defined by the above claims.

Claims (10)

1. A method of fabricating a liquid crystal electro-optic assembly, comprising:

providing an optical unit, wherein the optical unit comprises a hollow space;

injecting a liquid crystal mixture into the hollow space; and

applying a gradient field to the liquid crystal mixture, wherein the intensity of the gradient field is in a gradient distribution;

wherein the hollow space has an axis; the strength of the gradient field increases along the axis or decreases along the axis; and the direction of the gradient field is consistent in the hollow space into which the liquid crystal mixture is injected.

2. The method of claim 1, wherein the gradient field is an electric gradient field, a temperature gradient field, a magnetic gradient field, or a stress gradient field.

3. The method of claim 1, wherein the optical unit is an optical fiber; the hollow space extends in a direction parallel to the axis of the optical fiber; and the strength of the gradient field is increased or decreased in the direction of the axis of the optical fiber.

4. The method of claim 3, wherein the optical fiber is a photonic crystal fiber.

5. The method of claim 1, wherein the optical element is an optical waveguide comprised of a substrate defining the hollow space; and the strength of the gradient field is increased or decreased along the direction parallel to the substrate.

6. The method of claim 1, wherein the optical unit is a liquid crystal cell comprised of two substrates defining the hollow space; and the strength of the gradient field is increased or decreased along the direction parallel to one of the two substrates.

7. The method of claim 1, wherein the hollow space has a spatial dimension of less than 100 μ ι η.

8. The method of any of claims 1 to 7, further comprising: irradiating a curing light to the liquid crystal mixture, wherein the liquid crystal mixture comprises liquid crystal molecules and photosensitive monomers.

9. The method of claim 8, wherein the photo-monomers are polymerized into a surface polymer network at the interface of the hollow space when the irradiating a curing light is performed.

10. The method of claim 8, further comprising, prior to the step of irradiating a curing light: applying a curing electric field to the liquid crystal mixture.

Images