TW201816493A - Method for manufacturing a liquid-crystal electro-optical element - Google Patents

Abstract

A method for manufacturing a liquid-crystal electro-optical element is disclosed. The present application discloses a method to align liquid crystal in a non-contact way, which provide liquid-crystal molecules sealed in an electro-optical element a stable alignment with a defined pre-tilt angle and thereby prevent the liquid crystal under an external field from having defects caused by inverse tilts. The method comprising: providing an optical unit having at least one hollow space; injecting a liquid-crystal mixture into the at least one hollow space; and applying a gradient field with strength exhibiting a gradient distribution to the liquid-crystal mixture.

Description

 Method of manufacturing liquid crystal electro-optical components  

The invention relates to a method for manufacturing a liquid crystal electro-optical component, in particular to a liquid crystal alignment in a non-contact manner, and provides a liquid crystal molecule sealed in a liquid crystal electro-optical element to achieve a stable alignment effect, so that liquid crystal molecules have a definition at steady state. The pretilt angle can prevent the occurrence of defects caused by the reverse tilt of the liquid crystal molecules when the applied electric field tends to be dynamic.

When a liquid crystal (LC) material is combined with a hollow fiber, a photonic crystal or a closed structure to develop a novel electro-optical element, there is a problem that it is impossible to effectively control the liquid crystal molecules in a hollow column to form a stable arrangement, so that liquid crystal molecules In the case of an applied electric field, a disclination line (also referred to as a discontinuous line) may occur, which may seriously cause light scattering loss. The reason for the defect is that the closed surface of the hollow cylinder cannot be rubbed, so it is impossible to obtain an elastomer liquid crystal molecule in a closed cylinder (or structure) which is not rubbed. Stable and consistent alignment direction, and the orientation mechanism of liquid crystal molecules in the closed pores is quite complicated, not simple in the square structure of the traditional liquid-crystal cell; 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 a hollow fiber or a photonic crystal, since the rubbing alignment treatment cannot be performed on the wall of the cylindrical cavity to provide a preferred direction of the liquid crystal molecules, the thermal perturbation causes the optical axis direction of the liquid crystal molecules to be unstable. In the direction, when an electric field is applied to the liquid crystal (optical fiber) component, liquid crystal molecules may be rotated and tilted in two different directions, so that orientation defects occur at the boundary between the two regions that are oppositely inclined, such as Figure 1 shows. In Fig. 1, in the optical unit 11, the power source 19 drives the upper electrode 18a and the lower electrode 18b to generate an electric field applied therebetween to the liquid crystal mixture 13, so that the liquid crystal molecules 13a are tilted to cause a reverse tilt region, resulting in a disclination line. occur. This defect causes a difference in refractive index with the surrounding liquid crystal molecules to form an interface, which causes loss of optical signals of the liquid crystal/fiber element and deterioration of optical characteristics. Therefore, the application range of the liquid crystal fiber or electro-optical element will be limited.

The arrangement state of the liquid crystal molecules has a significant influence on the light propagation characteristics of the fiber element. In order to improve the optical characteristics of the liquid crystal fiber element, it is necessary to first solve the problem of orientation defects of the reverse tilt of the liquid crystal molecules. However, the arrangement of liquid crystal molecules permeated 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, and 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 a cylindrical hole is planar-aligned and splayed-aligned parallel to the axial direction of the fiber. Since the expanded liquid crystal molecules have no Fredericks transition threshold, there is no reverse tilt domain defects such as parallel alignment of liquid crystal molecules due to reverse tilt. Therefore, in the prior literature, it is proposed to avoid the occurrence of block defects, and it is necessary to use a light alignment technique or a liquid crystal material (such as a dual-frequency liquid crystal or a negative liquid crystal) which can exhibit an expanded arrangement in a hollow fiber, which will limit the liquid crystal material. Selectivity. Further, the dielectric anisotropy (Δε) of the negative liquid crystal material is smaller than that of the positive liquid crystal, so that the threshold voltage is high.

Although polymer stabilized alignment (PSA) technology has been proposed as early as 1998, it is mainly used for the improvement of the characteristics of liquid crystal displays. In recent years, due to its good characteristics and related technical improvements, gradually The land has received the attention of all parties. The technique of polymer-stabilized liquid crystal molecular alignment is mainly to obtain a polymer network structure by phase separation by phtopolymerization. Ultraviolet (UV) photopolymerization is carried out by a reactive liquid crystal or photo-sensitive monomers under an applied electric field (or a driving electric field) to generate a polymer network for controlling the pretilt direction of the liquid crystal molecules. Since the curing electric field guides the liquid crystal molecules to be aligned in a specific direction, the liquid crystal director (the direction indicated by the liquid crystal axis) in the hollow fiber has a specific direction characteristic. 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 stable alignment technology can provide a stable alignment, simple process, low cost, and Low threshold voltage, fast response, highly tuned and highly stable liquid crystal fiber or electro-optical components.

Polymer stable alignment technology is also applied in the liquid crystal panel industry. Here, the polymer stable alignment technique 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 a certain initial pre-light angle and a wide viewing angle display characteristic, it is necessary to use an oblique electric field so that the liquid crystal molecules are tilted toward the desired direction under the application of an external electric field, and the above oblique electric field is required. Special electrode pattern design is achieved. When the liquid crystal molecules are tilted in a desired direction due to the oblique electric field, an illuminating polymerization process is performed to polymerize the photosensitive monomers in the liquid crystal mixture into a surface polymer network. The polymer network can provide a direction of the pretilt angle of the liquid crystal molecules in the direction in which the liquid crystal molecules are tilted when performing the illumination polymerization process, and the angle of the pretilt angle depends in part on the oblique electric field at which the liquid crystal molecules are tilted when the photopolymerization process is performed. Strength. Although a polymer stable alignment technique is employed to provide an initial pretilt angle of liquid crystal molecules in a certain direction, the substrate still requires the presence of a vertical alignment layer before the surface polymer is formed by an illuminating polymerization procedure.

In general, in order to enable liquid crystal molecules to 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 the hollow fiber, the difficulty lies in the wall of the cylindrical hole. Perform rubbing alignment treatment. Although the liquid crystal molecules tend to be axially aligned due to the capillary flow force of the injection, they do not have a preferred alignment direction under the action of an applied electric field, so that local alignment defects of the reverse tilt alignment of the liquid crystal molecules are likely to occur. The occurrence of this defect causes loss of optical power, slow response speed, and deterioration of optical characteristics of the liquid crystal optical fiber element.

When the liquid crystal is filled into the hollow fiber, if the pore wall surface is not treated, since the liquid crystal molecules exhibit a rod-like structure, the flow force of the capillary phenomenon will cause the overall arrangement direction of the liquid crystal to be substantially parallel to the fiber axis, as shown in FIG. Shown in part (a). 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 inclinations in the direction of the optical fiber 21, so that the all black state cannot be observed under the orthogonal polarizing microscope, as shown in part (b) of Fig. 2 A slight light leakage was observed in which the optical fiber tube 21a was covered with the liquid crystal mixture 23, and symbols A and P indicate the axial directions of the polarizer and the light detecting sheet, respectively. Since the liquid crystal molecules are easily driven by the applied electric field to change the alignment direction, when an electric field is applied to the liquid crystal fiber, since the rubbing alignment treatment cannot be performed on the pore glass wall surface of the hollow fiber tube, the liquid crystal molecules exist in different directions in the unaligned cylindrical holes. The dip angles are arranged such that the action of the applied electric field causes the liquid crystal molecules to make a reverse tilt alignment response, and the discontinuity of the liquid crystal guide axis arrangement causes the disclination lines to be randomly generated, as shown in FIG. In Fig. 3, the optical fiber tube 31a of the optical fiber 31 covers 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 so that the liquid crystal molecules 33a are tilted. In addition, it is known from the theory of liquid crystal continuous elastomer that the alignment of liquid crystal molecules is affected by the disclination line, so that the multi-block liquid crystal alignment with the disclination line as the interface will be formed under the electric field drive, and this disclination line defect will be The optical signal loss of the liquid crystal fiber component, the hysteresis of the electro-optic response, and the response speed are slowed down.

In order to enable the successful combination of liquid crystal materials and hollow fibers and application to the development of highly tunable optical fibers or electro-optical components, it is necessary to solve the problem that it is difficult to align liquid crystal molecules in a narrow closed space (micrometer scale), thereby improving liquid crystals. The disclination line produced by the reverse tilt of the molecule occurs. Therefore, the present invention provides a liquid crystal molecule in a hollow fiber by a gradient field (electric field, magnetic field, temperature field or stress field, etc., but not limited thereto) and surface polymer stabilized alignment (SPSA) technology. The core can reach a stable alignment direction and have a pretilt angle distribution.

In more detail, the present invention mainly utilizes a gradient field to drive liquid crystal molecules in a uniform direction to eliminate the generation of a disclination defect, and then to fix the liquid crystal molecules in a desired direction and inclination by a surface polymer stable alignment technique. . The gradient field portion can use an electric field, a temperature field, a magnetic field, or a stress field to realize a gradient field to cause liquid crystal molecules to flow.

That is, in order to enable 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 provide liquid crystal molecules in an air column by using a combination of a gradient field and a surface polymer stable alignment technique. A pretilt angle is anchored in a certain direction, so that when the electric field acts, the liquid crystal molecules have a preferred stable direction to rearrange, thereby improving the phenomenon of the disclination line generated by the applied electric field.

Accordingly, the present invention provides a method of fabricating a liquid crystal electro-optical element comprising: providing an 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, The intensity of the gradient field presents a gradient distribution. Thus, the occurrence of a disclination defect of the liquid crystal electro-optical element of the present invention can be eliminated.

According to an embodiment of the 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 may be an optical fiber; the hollow space may extend parallel to the axis of the optical fiber; and the strength of the gradient field may be increased or decreased in the direction of the axis of the optical fiber.

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

According to another embodiment of the present invention, the optical unit may be an optical waveguide, and the optical waveguide may be composed of a substrate defining the hollow space; and the intensity of the gradient field may be increased or decreased in a direction parallel to the substrate. .

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

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

In order to further stabilize the direction and angle of the pretilt angle of the liquid crystal molecules, according to an embodiment of the present invention, the method of the present invention may further comprise: 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 invention, the photo-sensitive monomers can be polymerized into a surface polymer network on the interface of the hollow space when the irradiation-curing light is performed.

In order to modulate the direction and angle of the pretilt angle of the liquid crystal molecules, according to an embodiment of the invention, the method of the present invention may further comprise: applying a curing electric field to the liquid crystal mixture, wherein the applying a curing electric field is performed in the curing light Before the program, and the curing electric field can be a spatially uniform electric field.

Finally, the liquid crystal molecules in the liquid crystal electro-optical element manufactured according to the above aspect of the invention may have a steady state pretilt angle having a defined direction and angle.

11‧‧‧ Optical unit

13‧‧‧Liquid Crystal Mixture

13a‧‧‧liquid crystal molecules

18a‧‧‧Upper electrode

18b‧‧‧ lower electrode

19‧‧‧Power supply

21‧‧‧ fiber

21a‧‧‧Fiber tube

22‧‧‧ hollow space

23‧‧‧Liquid Crystal Mixture

23a‧‧‧liquid crystal molecules

31‧‧‧ fiber optic

31a‧‧‧Fiber tube

33‧‧‧Liquid Crystal Mixture

33a‧‧‧liquid crystal molecules

38a‧‧‧Upper electrode

38b‧‧‧ lower electrode

41‧‧‧Fiber

42‧‧‧ hollow space

41a‧‧‧Fiber tube

43‧‧‧Liquid Crystal Mixture

43a‧‧‧liquid crystal molecules

45‧‧‧Lighting monomer

46‧‧‧ Polymer

48a‧‧‧Upper electrode

48b‧‧‧ lower electrode

49‧‧‧Power supply

51‧‧‧ fiber optic

51A‧‧‧Fiber

51B‧‧‧Fiber

52‧‧‧heating station

57‧‧‧shims

Fig. 1 is a schematic view showing a reverse tilt region of a liquid crystal in a conventional liquid crystal electro-optical element.

Fig. 2 is a view showing the (a) molecular arrangement of a conventional liquid crystal in an optical fiber and (b) observation under a polarizing microscope.

Fig. 3 is a view showing the generation of (a) of the disclination line defects of the liquid crystal in the optical fiber and (b) the observation results under a polarizing microscope.

Fig. 4 is a schematic view showing a method of fabricating a liquid crystal electro-optical element according to a first embodiment of the present invention.

Fig. 5 is a view showing the elements of a liquid crystal fiber type Mach-Zehnder interferometer according to a first embodiment of the present invention.

Fig. 6 is a view showing the observation of a liquid crystal optical fiber according to the first embodiment of the present invention under a polarizing microscope.

Fig. 7 is a graph showing a transmission spectrum of a liquid crystal fiber type Mach-Zehnder interferometer driven by different applied voltages according to the first embodiment of the present invention.

Fig. 8 is a graph showing the resonance wavelength shift amount of the liquid crystal optical fiber type Mach-Zehnder interferometer driven at different applied voltages according to the first embodiment of the present invention.

Figure 9 is a schematic view showing a method of fabricating a liquid crystal electro-optical element according to a second embodiment of the present invention.

The embodiments of the present invention are disclosed herein to provide a further understanding of the principles and spirit of the invention.

The present invention provides a method of fabricating a liquid crystal electro-optical element comprising: providing an 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, the intensity of the gradient field exhibiting a gradient distribution. Thus, the occurrence of a disclination defect of the liquid crystal electro-optical element of the present invention can be eliminated. That is, the liquid crystal molecules of the liquid crystal cell fabricated by this method have a defined pretilt angle.

According to an embodiment of the 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 may be an optical fiber; the hollow space may extend parallel to the direction of the axis of the optical fiber; and the strength of the gradient field may be increased or decreased along the direction of the axis of the optical fiber, but is not limited thereto. . For example, the gradient vector of the gradient field can be parallel to the direction of the axis of the fiber, perpendicular to the axis of the fiber, or to any orientation in space.

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

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

According to another embodiment of the present invention, the optical unit may be a liquid crystal cell, and the liquid crystal cell may be composed of two substrates defining the hollow space; and the intensity of the gradient field may be enhanced in a direction parallel to one of the two substrates or Weakened, but not limited to this. 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 to any orientation in the space.

After the above-described application of the gradient field program is completed, the optical unit of the present invention does not exhibit a disclination line defect due to the reverse tilt driven by the applied 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 pretilt angle, so that the liquid crystal molecules of the liquid crystal mixture can be uniformly steered by the applied electric field, thereby preventing the tilt due to the reverse tilt. The resulting disclination line defect.

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

In addition, in order to further modulate the direction and angle of the liquid crystal molecule pretilt angle, in an embodiment of the invention, the method of the present invention may further comprise: irradiating a curing light to the liquid crystal mixture, wherein the liquid crystal mixture may include liquid crystal molecules and light. Sensitive monomer.

The photo-sensitive monomers may be polymerized into a surface polymer network at the interface of the hollow space to perform the irradiation-curing light to provide a pretilt angle defined by the liquid crystal molecules, but is not limited thereto. For example, the photo-sensitive monomers can be polymerized into a spatial polymer network in the hollow space, including the space between its interface and its interface.

In an embodiment of the invention, the method of the present invention may further comprise: applying a curing electric field to the liquid crystal mixture, wherein the applying a curing electric field is performed in the curing light. Before the program, and the curing electric field can be a spatially uniform electric field.

According to another embodiment of the present invention, the application of the gradient field program and the illumination curing light program can be performed simultaneously. In this case, the application of the gradient field program can be ended simultaneously at the end of the irradiation of the curing light program.

In more detail, according to another embodiment of the present invention, the illumination curing light program may be executed after the first time interval of applying the gradient field program and the execution of the applied gradient field program may be maintained, wherein the first time interval may be 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 to 15 minutes; more preferably, the first A time interval can be 8 to 12 minutes. After the first time interval of performing the irradiation curing light program, the liquid crystal mixture can be detected to have no disclination line defects due to the reverse tilt under the applied electric field. In this case, the application of the gradient field program can be continuously performed when the irradiation of the curing light program is started, and in this case, the application of the gradient field program can be ended simultaneously at the end of the irradiation of the curing light program.

The application of the curing electric field procedure described above can further modulate and stabilize the pretilt characteristics of the liquid crystal mixture by applying a gradient field program. That is, the above-described application of the solidified electric field program can modulate the magnitude and direction of the pretilt angle, and stabilize the size and direction of the pre-warp angle modulated by the polymerization of the photosensitive monomer.

According to an embodiment of the invention, the hollow space of the invention may have a spatial dimension between the range of 1-100 μm. In particular, 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 may be less than 100 μm, 50 μm, or 10 μm; and when the hollow core fiber is used as the optical unit of the present invention, the inner diameter of each hollow axis The cell gap may be less than 100 μm, 50 μm, or 10 μm when the liquid crystal cell is used as the optical unit of the present invention.

Hereinafter, more specific embodiments will be further disclosed.

[First Embodiment: Gradient Electric Field Experiment]

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

Step 2: first attaching an optical fiber or a photonic crystal fiber filled with a liquid crystal/photosensitive monomer mixture to an ITO glass substrate (lower electrode 48b), and then covering another upper ITO glass electrode (upper electrode 48a) at the upper end, as described in Figure 4 (a) shows.

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

Step 4: After applying a voltage, a gradient electric field may be formed between the upper electrode 48a and the lower electrode 48b. Subsequently, the gradient electric field is observed by a polarizing microscope (POM) to cause the liquid crystal molecules 43a to rotate; if a disclination line occurs (as shown in FIG. 3), the upper electrode 48a can be appropriately adjusted, and a voltage is applied until the disclination line is not The occurrence of defects. Alternatively, this experiment can use a system that can generate a precise gradient electric field, or directly use the coating technology on the component to fabricate the upper and lower conductive films on the optical fiber, so that the upper and lower electrodes are tapered to form a gradient structure, thereby applying a gradient electric field to achieve no Defective liquid crystal alignment.

Step 5: UV exposure was performed on the optical fiber 41 having an applied voltage without a disclination line defect, as shown in part (c) of Fig. 4, the exposure power was 1 mW, and the exposure time was 3 min. The light-sensitive monomer 45 in the optical fiber 41 is photopolymerized by UV exposure to form a network of the polymer 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, the photosensitive monomer 45 and the liquid crystal molecules 43a (having a positive Δ ε) injected into the liquid crystal mixture 44 of the hollow space 42 are substantially parallel to each other. The axial direction of the optical fiber 41 (part (a) of Fig. 4). When a gradient electric field is applied to the optical fiber 41 by driving the upper electrode 48a and the lower electrode 48b by the power source 49, the force will drive the liquid crystal molecules 43a to be aligned in a certain direction due to the gradient change of the electric field: if it is a positive liquid crystal material, The molecular axis direction tends to be parallel to the direction of the electric field; conversely, if it is a negative liquid crystal material, its molecular axis direction tends to be perpendicular to the direction of the electric field, as shown in part (b) of Fig. 4, wherein the length of the dotted arrow indicates the electric field. The size of the intensity.

In order to stabilize the alignment of the liquid crystal molecules 43a and impart a pretilt angle, an electric field is additionally applied, and then the liquid crystal fiber 41 sample is irradiated with UV light (part (c) of Fig. 4). Upon the action of the curing electric field and the curing of the UV light, the photosensitive monomer 45 is polymerized on the inner wall surface of the optical fiber tube 41a at a pretilt angle with respect to the surface of the substrate. Moreover, when the electric field is released, the liquid crystal is anchored by the arrangement of the network of the polymer 46, causing the liquid crystal molecules 43a to have an inclination angle and a certain arrangement direction in the initial state, and the pretilt angle will be permanently maintained, as in the fourth. Shown in part (d) of the figure.

Therefore, with this simple process, the pretilt angle and the alignment direction of the liquid crystal can be controlled by the polymer 46 network on the wall surface of the optical fiber 41 which is not subjected to the rubbing treatment. The polymer network can be regarded as providing a force for recovering or anchoring the boundary of the liquid crystal molecules 43a, so that the occurrence of defects and the relaxation (restoration) of the liquid crystal molecules 43a at a faster speed can be eliminated. However, the pretilt angle obtained by polymerization of the photosensitive monomer 45 and its surface topography are related to the concentration of the monomer 45, the exposure conditions, and the curing electric field.

The liquid crystal fiber processed through the above steps is bonded to the single mode fiber by a specific bonding parameter, and the joint end face is formed into a fiber cone. After joining the two ends, the components of the liquid crystal fiber type Mach-Zehnder Interferometer (as shown in Fig. 5) are completed.

Referring to Figure 5, when incident light is conducted from a single mode fiber to a first fiber cone, light in one portion of the fiber core is coupled into the fiber shell, and light from the other portion remains in the fiber core when light is conducted. When the second fiber cone is reached, the light in the fiber shell is coupled back to the fiber core, causing the two lights to form an interference, where the component interference formula is: λ _p = 2L( n _co - n _cl ) / (2 N +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, and 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 fiber is changed, and the affected values n _co , λ _p cause the value to be displaced.

As shown in Fig. 6, it can be observed from a polarizing microscope (POM) that the surface polymer stable alignment technique of the present invention can effectively eliminate the occurrence of disclination of liquid crystals. Since the change in the alignment of the liquid crystal molecules causes a change in the effective refractive index of the core, the resonance wavelength of the interferometer is changed. The present invention utilizes an optical spectrum analyzer to analyze the relationship between voltage and resonant wavelength variation. As shown in Fig. 7, the increase in voltage causes a red shift in the resonance wavelength. This is because the alignment direction of the positive liquid crystal tends to be parallel to the direction of the electric field when an electric field is applied, resulting in an increase in the effective refractive index of the entire core. The resonant wavelength shifts to a long wavelength with a liquid crystal fill length of 1400 μm.

Further finishing and analysis can obtain the correlation between the displacement of the wavelength and the voltage. As shown in Fig. 8, the voltage-induced wavelength change tends to conform to the physical properties of the liquid crystal. It was found from the experimental results that the threshold voltage for driving the liquid crystal molecules was about 30V. When the operating voltage is less than 30V, the amount of displacement of the resonant 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, and the degree of rotation of the liquid crystal driven by the electric field is very small, so the refractive index increase caused by the driving voltage shows only a slight change. When the applied voltage exceeds the threshold voltage (at 30-70V), the liquid crystal molecules have a large amount of rotation under the action of the high-voltage electric field, so the refractive index variation range is also large, so that more resonant wavelengths can be obtained. The amount of displacement. When the applied voltage is greater than 70V, the change in the resonance wavelength displacement caused by the voltage is not large because the liquid crystal molecules in the intermediate layer in the hollow fiber are almost parallel to the electric field direction and reach a steady state under the driving of a large voltage. Therefore, the relatively large voltage is mainly used to drive the rotation of the liquid crystal molecules near the boundary of the surface, thereby causing the refractive index to increase only slightly, and thus the variation of the resonance wavelength shift amount becomes smaller.

[Second embodiment: gradient temperature field experiment]

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

Step 2: In order to generate the gradient temperature field, the method is as follows: (1) Raising the right side of the optical fiber 51A by the insulating spacer 57 (~2 mm), so that the substrate is inclined and the further the right side is away from the heating surface of the heating stage 52. Then, the optical fiber 51A has a temperature gradient characteristic of temperature gradient because it is unevenly heated, as shown in part (a) of 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 side heated portion of the optical fiber 51B exhibits the highest temperature, and the temperature gradually decreases as the distance from the left heated portion increases. The lowest temperature is shown until the right side, as shown in part (b) of Figure 9.

Step 3: After heating for a period of time, a vertical curing electric field is applied to the liquid crystal fiber 51, the vertical solidified electric field is perpendicular to the axis of the liquid crystal fiber 51, and the uniform applied electric field is observed by a polarizing microscope POM to make the liquid crystal (having a positive Δ ε). The situation of rotation, 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 defect does not occur, the optical fiber 51 is exposed by using parameters required for the experiment. In this embodiment, the exposure power is 1 mW and the exposure time is 3 min. The photo-sensing monomer in the element is photopolymerized by UV exposure to form a polymer network, thereby stabilizing the alignment of the liquid crystal molecules.

Specifically, the liquid crystal sample is placed in a heating device, and the temperature on the liquid crystal sample exhibits a gradient change by an appropriate arrangement, and the temperature of the liquid crystal sample in the left and right portions of FIG. 9 is decremented from the left side to the right side, Therefore, this 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 technique is used to form a polymer network to stabilize the liquid crystal molecules in a specific direction, and the occurrence of no misalignment line defects. That is, the curing electric field and the UV exposure are applied to form the liquid crystal director to form an effect of stably aligning at a specific pretilt angle. However, the surface polymer stable alignment process is similar to the method disclosed in the above first embodiment, except that the electric field applied to the liquid crystal sample is a uniform electric field, and the electric field can be given a pretilt angle to the liquid crystal molecules as desired. Given that, the higher the applied electric field is, the larger the pretilt angle is, and the smaller the range of electronically controllable modulation of the liquid crystal element will be.

The polymer network in the SPSA fiber optic component 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 increase the response speed when the electric field is applied. Therefore, in the embodiment of the present invention, the key technology of the SPSA can effectively improve the shortcoming of the hollow fiber in the process and the hysteresis of the component. In addition, the polymer network utilizing SPSA technology provides stability and modulation alignment effect to liquid crystal molecules, and the polymer network type and structure depend on photopolymerization conditions, such as UV light intensity, exposure temperature, monomer concentration, electric field distribution, And the exposure time and other factors, the invention can achieve the diversified component characteristics of the liquid crystal optical fiber or the liquid crystal photoelectric element according to the design of the process conditions.

Finally, the liquid crystal molecules in the liquid crystal electro-optical element manufactured according to the above aspect of the invention may have a steady state pretilt angle having a defined direction and angle, thereby eliminating the occurrence of disclination defects of the liquid crystal electro-optical element of the present invention.

The present invention has been disclosed in the above-described embodiments, and is not intended to limit the scope of the invention, and various modifications and changes can be made without departing from the spirit and scope of the invention. Therefore, the scope of the invention should be determined by the scope of the appended claims.

Claims (10)

 A method of fabricating a liquid crystal electro-optical element, comprising: providing an 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 is Gradient distribution.    The method of claim 1, wherein the gradient field is a gradient electric field, a gradient temperature field, a gradient magnetic field, or a gradient stress field.    The method of claim 1, wherein the optical unit is an optical fiber; the hollow space extends in a direction parallel to an axis of the optical fiber; and the intensity of the gradient field increases or decreases in a direction of an axis of the optical fiber.    The method of claim 3, wherein the fiber is a photonic crystal fiber.    The method of claim 1, wherein the optical unit is an optical waveguide, the optical waveguide is composed of a substrate defining the hollow space; and the intensity of the gradient field is increased or decreased in a direction parallel to the substrate. .    The method of claim 1, wherein the optical unit is a liquid crystal cell composed of two substrates defining the hollow space; and the intensity of the gradient field is parallel to one of the two substrates. The direction is increased or decreased.    The method of claim 1, wherein the hollow space has a spatial dimension of less than 100 μm.    The method of any one 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 a photosensitive monomer.    The method of claim 8, wherein the photosensitive monomers are polymerized into a surface polymer network on the interface of the hollow space when the irradiation-curing light is performed.    According to 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.