KR100582990B1 - Polarization Grating Device Using Liquid Crystals And Its Manufacturing Method - Google Patents

Abstract

The present invention discloses an electro-optically adjustable polarization diffraction grating element and its manufacturing method using liquid crystals. According to the present invention, resin networks formed by periodically photocuring inside the specimen provide different alignment conditions depending on the resin density formed in the liquid crystal. When the specimen is irradiated with a single controlled incident light corresponding to the absorption wavelength of the azo dye, the azo dye mixed in the liquid crystal periodically forms different liquid crystal alignment depending on the resin density. The direction of the liquid crystal rearranged by photo alignment is determined by the density of the resin and the polarization direction of the single incident light.

Accordingly, the present invention provides a liquid crystal polarization diffraction grating element capable of easily adjusting the polarization of transmitted light and diffracted light electro-optically by a resin network formed in a liquid crystal and an azo dye.

Description

Polarization Diffraction Device Using Liquid Crystal and Its Manufacturing Method {Polarization Grating Device Using Liquid Crystals And Its Manufacturing Method}

1A and 1B are cross-sectional views and a plan view, respectively, of the polarization diffraction element according to the present invention, showing a structure in which the liquid crystal is periodically redirected by the dye when irradiating a single control light.

2A and 2B are cross-sectional views and a plan view of a specimen in which a mixture of a liquid crystal, an azo dye, and a photocurable resin is injected, illustrating a uniform liquid crystal alignment state before forming the resin network in a lattice form.

3A and 3B are views illustrating the configuration of an optical mask for forming a resin network at predetermined cycles and the alignment state of liquid crystals after the formation of the network structure in order to manufacture the polarization diffraction element according to the present invention.

FIG. 4 is a pattern of the photomask shown in FIG. 3A.

5 is a schematic configuration diagram of a measuring device for measuring optical control, transmission, and diffracted light of a polarization diffraction element according to the present invention.

6 is a graph showing the real-time diffraction efficiency according to the optical control of the polarization diffraction element according to the present invention.

7A and 7B are micrographs of two regions different in the liquid crystal realignment state in the polarization diffraction element according to the present invention.

8A and 8B are graphs showing transmission and diffraction polarization characteristics according to incident polarization of the polarization diffraction element according to the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarization grating device in which a photocurable resin network is periodically formed inside a liquid crystal and azo dye mixture. More specifically, the liquid crystals having a photo-alignment characteristic of the liquid crystal by the azo dye appear differently according to the resin density, so that the liquid crystal director in the specimen can be periodically modified to control the efficiency and polarization of transmitted light and diffracted light electro-optically. It relates to a polarization diffraction element using the same and a method of manufacturing the same.

In general, a diffraction grating element is an amplitude grating having a light-transmitting portion and a non-light-transmitting portion periodically arranged according to its shape, and a phase-type diffraction element having a refractive index periodically formed on a high-transmissive material. (phase grating), and a polarization diffraction element periodically formed in the direction of the optical axis in the anisotropic material. Among these, the polarization diffraction element can control the efficiency and polarization of the transmitted light and the diffracted light according to the polarization, so that the polarization diffraction element can be used for various purposes such as a beam splitter, an optical switch, and a spectral photopolarimeter. It is utilized.

The polarization diffraction grating structure can generally be manufactured into a desired grating structure by electrically controlling the liquid crystal by a spatial light modulator. However, this method requires an active element and an electrode structure for individually controlling all pixels, and thus, there is a disadvantage in that the manufacturing process is complicated and expensive.

In order to overcome this, methods for periodically modifying the alignment of liquid crystals by optically controlling the alignment of azo dyes have been proposed. This interferes with the two control lights and periodically modifies the intensity or polarization of the control light in space, thereby obtaining a periodic alignment of the liquid crystal molecules.

When a dye is included in the liquid crystal material, the dye may apply torque to the liquid crystal molecules to control the orientation of the liquid crystal molecules. However, in this case, since the liquid crystal molecules are temporarily redirected, they operate as polarized diffraction grating elements only when both control lights are irradiated at the same time.

Alternatively, the dye may constitute a liquid crystal alignment film adjacent to the liquid crystal, in which case the reorientation of the dye of the alignment film and the liquid crystal adjacent thereto is more sustained. However, in this case, only one substrate can be controlled, and the liquid crystal orientation on the other substrate is fixed, so that uniform liquid crystal reorientation cannot be obtained throughout the specimen, and only a twisted molecular structure is possible. Therefore, the use of the polarization diffraction element is limited and there is a difficulty in predicting its characteristics.

Recently, polymer dispersed liquid crystals containing thermally reactive or photocurable resins containing dyes have been proposed as polarization diffraction elements. The polarization diffraction element is capable of sustaining the reorientation of the liquid crystal by the interaction between the resin structure formed in the liquid crystal and the redirected dye. However, the liquid crystal structure in which the resin is dispersed has a disadvantage in that it has a diffusion loss due to disordered liquid crystal drops.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and the present inventors have a single control in the case of a polarization diffraction element including a liquid crystal, a dye, and a resin formed in a network structure every predetermined period between an upper substrate and a lower substrate. By irradiating light, it was confirmed that the polarization state of transmitted light or diffracted light can be easily controlled, and this invention was completed.

Accordingly, an object of the present invention is to provide a polarization diffraction element that can easily control not only diffraction efficiency but also polarization state of transmitted light or diffraction light in various optical information processing fields requiring polarization diffraction elements such as display and optical communication.

Still another object of the present invention is to control the photoreactive properties of the liquid crystals to the photoreactive dye periodically by using a resin network formed periodically.

Another object of the present invention is to simplify and control the control of the diffraction efficiency of the polarization diffraction element and the polarization state of the diffracted light with only a single light without depending on the interference of two light sources.

The present invention relates to a polarization diffraction element comprising a liquid crystal, a dye and a resin between an upper substrate and a lower substrate provided with an electrode.

More specifically, the present invention is a liquid crystal, an azo dye, and photocurable on a specimen in which an alignment layer is laminated on an inner surface and two glass substrates (ie, an upper substrate and a lower substrate) rubbed in parallel with each other are bonded to face each other. Or it relates to a polarization diffraction element comprising a thermally reactive resin.

In the present invention, the resin is preferably formed in a resin network structure periodically. As the resin, a photocurable resin that absorbs an ultraviolet region and transmits a visible ray region is used, and after forming a photomask pattern on the resin, the resin network structure can be easily formed by irradiating ultraviolet rays. The period and shape of the diffraction grating formed by the resin network structure can be controlled by adjusting the pattern of the photomask used.

In order to form the resin network, a thermally reactive resin may be used in addition to the photocurable resin. That is, the network structure similar to the said photocurable resin can be formed by adding heat more than reaction temperature to a thermally reactive resin.

In the case of using a photocurable resin, a photomask pattern is required to form a periodic structure, whereas in the case of using a thermosetting resin, a periodic network structure may be formed by applying a periodic electric field pattern during thermal curing.

The photocurable or thermally reactive resin is preferably mixed in a weight ratio of 10% or less with respect to the mixture of the liquid crystal and the dye in order to maintain a uniform liquid crystal phase and to eliminate the diffusion loss. In the embodiment of the present invention described below it was mixed in a weight ratio of 1%.

In addition, the present invention,

(A) injecting a liquid crystal, a dye, and an ultraviolet photocurable resin between the upper substrate and the lower substrate;

(B) forming a photomask pattern having a predetermined period on the substrate; And

And a step (c) of irradiating the substrate with ultraviolet rays so that the resin exposed to the ultraviolet rays forms a network structure.

In addition, the present invention,

(A) injecting a liquid crystal, a dye, and a thermally reactive resin between the upper substrate and the lower substrate; And

It relates to a method of manufacturing a polarization diffraction device comprising the step (b) of applying a periodic electric field while applying heat to the substrate to form a network structure every predetermined period.

Moreover, this invention relates to the polarization control method of the said diffraction element which irradiates the said polarization diffraction element with the single control light of the absorption wavelength range of the said azo dye, and adjusts the orientation direction of the said liquid crystal. In order to periodically form the density of the resin network structure and thereby induce a change in the periodic liquid crystal director, a single control light corresponding to the absorption wavelength of the dye is irradiated. The polarization diffraction characteristic of the polarization diffraction element can be adjusted by the polarization and energy of a single control light. At this time, the absorption wavelength region of the resin is preferably different from the absorption wavelength region of the dye so that the resin is not deformed by the single control light.

Hereinafter, a polarization diffraction element and a method of manufacturing the same according to the present invention will be described in detail with reference to the accompanying drawings. The same code | symbol is attached | subjected to the part of the same structure and the same effect | action.

1A and 1B show a polarization diffraction grating element according to the present invention, respectively. FIG. 1A illustrates a cross section of a lattice element, and FIG. 1B is an orientation view of a liquid crystal viewed from the top of the specimen.

In the drawing, the polarization diffraction element according to the present invention comprises a resin formed of an upper substrate 1, a lower substrate 2, a liquid crystal 3, an azo dye 4, and a resin network 5 at predetermined intervals. Include. A horizontal alignment layer 6 was formed on the inner side of the upper substrate 1 and subjected to rubbing treatment in the R ₁ direction. Further, a horizontal alignment film 7 was formed on the inner surface of the lower substrate 2 and subjected to rubbing treatment in the R ₂ direction. The upper substrate and the lower substrates 1 and 2 are bonded so that the upper alignment layer 6 and the lower alignment layer 7 face each other, and the rubbing direction R ₁ of the upper alignment layer 6 and the lower alignment layer 7 The rubbing directions R ₂ are parallel to each other.

After the single control light 8 corresponding to the absorption wavelength band of the dye 4 is irradiated onto the specimen in which the resin network 5 is formed at predetermined intervals, the region 9 in which the resin network is formed and the non-formation region are formed. At 10, the optical axis direction of the liquid crystal is changed.

In the region 10 where the resin network is not formed, the reorientation of the dye 4 mixed in the liquid crystal 3 appears instantaneously, and after the control light is turned off, the initial rubbing direction R ₁ of the alignment film is caused by the elastic energy of the liquid crystal. , Return to R ₂ .

On the other hand, in the region 9 where the resin network is formed, even after the control light 8 is turned off, the reorientation of the liquid crystal 3 is maintained by the interaction between the resin network 5 and the redirected dye 4. . The sustained reorientation of the liquid crystal 3 is perpendicular to the polarization E of the control light 8 by trans-cis photoisomerization of the dye 4 mixed in the liquid crystal space. Direction, and the reorientation characteristics of the liquid crystal vary depending on the angle θ formed between the polarization E of the control light 8 and the rubbing directions R ₁ and R ₂ .

In this embodiment, the polarized light E of the control light 8 was irradiated to form 45 degrees with the rubbing directions R ₁ and R ₂ of the alignment film so that the optical torque by the dye 4 is maximized.

Therefore, after the single control light 8 is irradiated, two different liquid crystal alignment regions 9 and 10 appear depending on the presence or absence of the resin network 5. Since the alignment regions 9 and 10 of the two liquid crystals each maintain a uniform horizontal alignment, the total phase retardation in the two regions is the same, but because they have different optical paths depending on the polarization of the incident light, the diffraction grating The characteristic as a purely polarization diffraction grating element is shown.

FIG. 2A shows a cross-sectional view of a specimen before the resin is cured after injecting the liquid crystal 3, the dye 4, and the photocurable resin 11 mixture, and FIG. 2B shows the orientation of the liquid crystal 3 viewed from the top of the specimen. It is shown. The liquid crystal 3 and the dye 4 are uniformly oriented along the rubbing directions R ₁ and R ₂ of the alignment film, and the resin 11 is uniformly spread throughout the specimen.

In this embodiment, polyvinyl alcohol was used as the horizontal alignment layers 6 and 7 for determining the initial alignment of the liquid crystal, and the upper substrate and the lower substrate were bonded to each other with a spacer having a thickness of 6 μm.

As the liquid crystal 3, all kinds of liquid crystals having birefringence may be used, and in this embodiment, the nematic liquid crystal 3 is used.

In addition, in order to form the resin network 5 at predetermined intervals, various kinds of photocurable resins can be used. In this embodiment, ultraviolet photocurable resins (NOA65, Norland Products Inc.) are used for the liquid crystals 3 and azo. Mix with dye (4). In order to react independently with the azo dye 4, the photocurable resin 11 should have an absorption wavelength band different from the absorption wavelength of the azo dye 4 used and should have high transmittance in the visible light region. The azo dye (MR, Sigma-Aldrich, Inc.) used in this example shows the largest absorption at 488 nm, and the photocurable resin NOA65 absorbs only in the ultraviolet region of 400 nm or less. The resin 11 was mixed in a weight ratio of about 1% with respect to the mixture of the liquid crystal 3 and the dye 4 to eliminate the diffusion loss of the specimen and to obtain a uniform alignment of the liquid crystal.

It is preferable that the refractive index of the resin 11 is as similar as possible to the refractive index of the liquid crystal 3. Specifically, the difference in refractive index between the liquid crystal and the resin is preferably 10% or less. In this embodiment, the refractive index of the resin is 1.52, the normal refractive index of the nematic liquid crystal (ZLI-2293, E. Merk Industries Co., Ltd.) is 1.499, and the extraordinary refractive index is 1.631. The refractive index difference of resin is 2% or less.

3A illustrates a process of forming the photocurable resin network 5 at predetermined intervals within a specimen according to the present invention. By irradiating ultraviolet rays through the photomask 12 to the specimen into which the liquid crystal 3, the azo dye 4, and the photocurable resin mixture were injected between the upper and lower substrates 1 and 2 on which the alignment layers 6 and 7 were formed. The resin network 5 was formed every predetermined period. The size and the period of the light transmitting portion in the photomask 12 can be adjusted according to the desired diffraction grating characteristics, the size used in this embodiment is X = 200㎛, Y = 100㎛.

In addition, although the lattice direction and the rubbing directions R ₁ and R ₂ of the alignment layer may generally have any angles, they are formed to be orthogonal to each other in this embodiment. In addition, the manufactured resin network 5 exhibits a binary polarization grating, but in practice, a continuous polarization grating and an asymmetric polarization grating in order to obtain various diffraction characteristics. It is also possible to manufacture such as.

A cross-sectional view of the photomask 12 of FIG. 3A from above the substrate is shown in FIG.

The ultraviolet light source used in this embodiment emits ultraviolet light in the absorption wavelength region suitable for curing the resin as an Xe-Hg lamp.

FIG. 3B is an orientation view of the liquid crystal 3 viewed from the top of the specimen 16 in which the resin network 5 is periodically formed by the method shown in FIG. 3A. Before the single control light corresponding to the absorption wavelength of the dye 4 is irradiated, the liquid crystal 3 and the dye 4 of the specimen are uniformly oriented in the rubbing directions R ₁ and R ₂ of the alignment film. Since the resin network 5 periodically formed inside the specimen is mixed at a mass ratio of 1%, the difference between the normal refractive index of the liquid crystal 3 and the refractive index of the resin 5 is less than 2%. There is almost no difference in effective refractive index between the formed region 23 and the unformed region 24. Therefore, in the present embodiment, the specimen 16 before the control light is irradiated shows low diffraction efficiency, and in particular, exhibits no polarization control characteristic.

5 is a schematic configuration diagram showing an apparatus for measuring polarization control characteristics of transmitted light and diffracted light of a polarization diffraction grating element according to the present invention. As a single control light source 8, an Ar-ion laser having a 488 nm wavelength component which is the maximum absorption wavelength band of the dye 4 was used. The control light is enlarged while passing through a beam expander 12 and can be arbitrarily adjusted to a desired polarization by a combination of a variable wave plate 13 and a polarizer 14. . The control light has a diameter of 4 mm while passing through a light shutter 15, and is incident perpendicularly to the liquid crystal specimen 16. The measurement light source 17 used a helium-neon laser (He-Ne laser), and has a wavelength component of 633 nm in which absorption is not caused by the dye 4. The polarization of the measurement light can be adjusted to arbitrary polarizations by the variable wavelength retardation plate 18 and the polarizer 19. The power and polarization of the transmitted light passing through the liquid crystal specimen 16 are measured by a zero-order diffractometer 20, and the + 1st and -1st diffraction light are +1 and -1st diffractometers 21 and 22, respectively. The power and polarization are measured by

Here, the liquid crystal specimen 16 is uniform in the direction of the liquid crystal 3 and the refractive index difference between the cured resin and the liquid crystal is weak, as shown in FIG. It does not have the characteristic as a polarization diffraction element.

While the control light 8 was irradiated onto the liquid crystal specimen 16, the first diffraction efficiency was measured in real time with a first diffractometer, and the results are shown in FIG. 6. While the control light is irradiated, the liquid crystals are rearranged by the dye in both the region where the resin network is formed and the region where the resin network is not formed, but some diffracted light appears because the degree of rearrangement in the space varies depending on the density of the resin network. . On the other hand, after the control light irradiation off, the liquid crystal rearrangement in the region where the resin network is not formed does not persist and returns to the initial alignment state by the alignment film, and the liquid crystal rearrangement in the region where the resin network is formed is carried out by the resin network structure and recrystallization. Interactions between the arrayed dyes are maintained. Due to this difference in liquid crystal rearrangement, the diffracted light increases rapidly immediately after the control light irradiation off and then stabilizes.

7A and 7B are micrographs of the polarization diffraction element fabricated in the present example between the orthogonal polarizers. FIG. 7A illustrates a case where an optical axis of one of the orthogonal polarizers is parallel to the initial rubbing direction, and FIG. 7B illustrates a case where the optical axis and the initial rubbing direction of one of the orthogonal polarizers have an angle of 35 degrees. As shown in the photograph of FIG. 7A, the region 10 in which the resin network is not formed is completely dark, and the region 9 in which the resin network is formed is bright. On the other hand, in the photograph of FIG. 7B, the region 10 in which the resin network is not formed is bright and the region 9 in which the resin network is formed is completely dark.

As a result, the liquid crystal is oriented in the initial rubbing direction after the control light irradiation is turned off in the region 10 in which the resin network is not formed, and in the region 9 in which the resin network is formed, the liquid crystal is oriented in the direction rotated 35 degrees from the initial rubbing direction. Because it stabilized. At this time, the rearrangement of the liquid crystal in the resin network structure is uniformly rearranged throughout the specimen.

8a and 8b show the transmission and diffraction characteristics of the polarization diffraction grating device according to the present invention measured in the experimental apparatus shown in FIG. 8A shows a result of measuring polarization of transmitted light according to incident polarization of measurement light. In this embodiment, since the specimen was manufactured so that the total phase retardation of the liquid crystal was close to 2π × m (m is an integer), the polarization of the transmitted light was almost the same as the incident polarization of the measurement light. On the other hand, as shown in Fig. 8B, the polarization of the first diffracted light tends to change inversely with respect to the change in the incident polarization. That is, it can be seen that when the incident polarization rotates in the left line, the polarization of the diffracted light rotates in the preferential form.

Therefore, by using the polarization diffraction element according to the present invention, it is possible to obtain the transmitted light which is the same as the incident polarization and the diffraction light which is changed in the opposite direction. The polarization diffraction grating device can obtain various transmission and diffraction characteristics different from those of the present embodiment by electrically and optically adjusting the structure of the optical mask, the polarization of the control light, and the phase delay of the liquid crystal.

As described above, the present invention can be used as a polarization diffraction element with respect to incident light by periodically changing the director of the liquid crystal. Therefore, the present invention can easily adjust the light efficiency and polarization state of the diffracted light electrically or optically.

In this case, the present invention can spontaneously adjust the optical alignment angle with respect to the control light by forming different densities of the resin network structure in the specimen periodically.

In addition, according to the present invention, since the oriented liquid crystal is formed in the resin network structure, the thermal stability of the produced polarization diffraction element can be significantly improved.

Furthermore, since the present invention uses nematic liquid crystals having dielectric anisotropy and dyes capable of optically redirecting such liquid crystals, the diffraction efficiency and polarization state of the diffracted light of the manufactured polarizing diffraction elements are electrically or optically controlled. This can be widely applied in various optical information processing fields such as displays and optical communication systems requiring polarization control.

On the other hand, the present invention has been described by showing one specific embodiment, it is obvious that the present invention may be variously modified and implemented by those skilled in the art. Such modified embodiments should not be understood individually from the spirit or point of view of the present invention and these modified embodiments should be understood as falling within the scope of the appended claims of the present invention.

Claims (11)

Between the upper substrate and the lower substrate provided with an electrode, comprising a liquid crystal, a dye and a resin, wherein the resin is a polarization diffraction element, characterized in that formed in a network structure every predetermined period. The polarization diffraction element according to claim 1, wherein the dye is an azo dye, and the resin is a photocurable resin or a thermally reactive resin. delete The polarization diffraction element according to claim 1, wherein the resin absorbs an ultraviolet region and transmits a visible region. The polarization diffraction element according to claim 1, wherein an absorption wavelength region of the resin is different from an absorption wavelength region of the dye. The polarization diffraction element according to claim 1, wherein the resin is contained in a weight ratio of 10% or less with respect to the sum of the weights of the liquid crystal and the dye. The polarization diffraction element according to claim 1, wherein a difference between the refractive index of the resin and the refractive index of the liquid crystal is 10% or less. 4. The polarization diffraction device of claim 3, wherein rubbing is formed on inner surfaces of the upper substrate and the lower substrate in a direction parallel to each other, and the rubbing direction and the forming direction of the network structure are orthogonal to each other. (A) injecting a liquid crystal, a dye, and an ultraviolet photocurable resin between the upper substrate and the lower substrate; (B) forming a photomask pattern having a predetermined period on the substrate; And And (c) causing the resin exposed to the ultraviolet rays to form a network structure by irradiating the substrate with ultraviolet rays. (A) injecting a liquid crystal, a dye, and a thermally reactive resin between the upper substrate and the lower substrate; And (b) applying a periodic electric field while applying heat to the substrate to cause the resin to form a network structure every predetermined period. The polarization control method of the polarization diffraction element which adjusts the orientation direction of the said liquid crystal by irradiating the polarization diffraction element of Claim 1 to the single control light which has the absorption wavelength of the said azo dye.

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