JP2006215186A - Diffraction element, manufacturing method of the same, and polarization selecting device using diffraction element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a diffraction element having high diffraction efficiency and a simple structure, switching presence or absence of the diffraction state by applying an electric field as required, and produced inexpensively, and also to provide a method for manufacturing the element, and a polarization selecting device using the diffraction element. <P>SOLUTION: The diffraction element is characterized in that: a liquid crystal layer having uniform chemical composition and comprising a single phase is disposed between a pair of transparent substrates; the liquid crystal layer is composed of a first region having optical anisotropy and a second region having different optical anisotropy from that of the first region; and each region has an arrayed structure with a predetermined period. For example, a material having variable critical surface tension by addition of energy is used to form a surface layer having two surface patterns with different critical surface tensions on the surface of a transparent substrate. If necessary, a transparent electrode is disposed on each opposing surface of the pair of transparent substrates. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a diffractive element using liquid crystal, and more particularly to a diffractive element that achieves good diffraction efficiency with a simple structure, a manufacturing method thereof, and a polarization selection device using the diffractive element.

At present, the development of a projection display using a liquid crystal light valve as an optical switching element has been actively carried out, and in particular, the commercialization of a projection large screen display using a small liquid crystal device is rapidly progressing. However, since the liquid crystal devices used in the past are mainly transmissive, the situation is insufficient in terms of resolution and light utilization efficiency.
In order to deal with such problems, research and development for applying a reflective light valve excellent in characteristics such as resolution and light utilization efficiency to a projection display has been activated. However, since the reflection type light valve operates by polarization conversion, means for carrying out polarization separation such as a polarization beam splitter is required in the optical system.

At present, the polarization beam splitter used as the polarization separation means has a drawback that it is heavy and bulky because it is a glass prism in addition to an insufficient extinction ratio and light utilization efficiency in the entire visible range.
In addition, in a polarization separation element using a prism, in order to secure a high degree of polarization separation, it is necessary to form multiple layers of dielectric multilayer films, so that the manufacturing cost is high, and the thickness and size are reduced. There is a problem that it is difficult.
As a solution to this problem, several new elements that replace the current polarization beam splitter have been proposed.

  For example, a pattern layer having a first optical anisotropy and a filler layer having a second optical anisotropy that fills the space between the pattern layers are provided. A diffraction grating element in which either one of the refractive indexes with respect to a light beam is equal has been proposed (for example, see Patent Document 1). This proposal is said to provide an inexpensive, thin and light diffraction grating element that can realize a high degree of polarization separation.

  That is, the above proposal is a diffraction grating element obtained by pattern exposure of a mixed material of polymerizable liquid crystal and non-polymerizable liquid crystal aligned in one direction, and a portion polymerized by ultraviolet pattern exposure or two-beam interference exposure. Since diffractive elements are produced by regularly producing unpolymerized sites, the manufacturing process is complicated, and there are limitations on the combinations of materials used to achieve a high degree of polarization separation. Further, the obtained diffractive element has a limitation that it cannot switch between a state where light is diffracted and a state where light is not diffracted.

  In addition, the first transparent electrode provided in a plurality of lines on one substrate surface and the second transparent electrode provided in a plurality of lines on the other substrate surface to correspond to the first transparent electrode. A diffractive element has been proposed in which a pair of transparent substrates are arranged so as to face each other, and a gap between the substrates is filled with a substance whose refractive index changes when a voltage is applied (see, for example, Patent Document 2). With this proposal, it is possible to switch between a diffracting state and a non-diffracting state.

The above proposal utilizes the fact that the direction of the liquid crystal corresponding to the linear electrode portion is changed by applying a voltage, thereby causing a difference in refractive index. Thus, in the case of a structure in which the diffraction grating is composed only of liquid crystal and a plurality of transparent electrodes are linearly formed and an electric field is applied, there is an advantage that the presence or absence of diffraction can be switched. Since electric field leakage occurs in the meantime, there is a problem that the liquid crystal responds even in a portion where there is no linear electrode.
For this reason, it is difficult to increase the refractive index modulation of the diffractive element, and the performance of the obtained diffractive element is limited. That is, it is difficult to form a fine pitch by a method such as forming a linear transparent electrode and applying a linear alignment treatment thereto, and it is difficult to obtain an efficient diffraction element.

The present applicant has previously proposed an optical functional element having a diffraction function in which a liquid crystal is sandwiched between two transparent substrates (see, for example, Patent Document 3).
However, since this element cannot be arbitrarily switched between the diffracted state and the non-diffracted state, there is a restriction in the application field.

JP 2003-232910 A Japanese Patent Laid-Open No. 2001-4773 JP 2004-219750 A

  The present invention has been made in view of the above prior art, and provides a diffraction element that has a simple structure and good diffraction efficiency, can be produced simply and at low cost, and a method for manufacturing the same. With the goal. In addition, a diffraction element having a structure in which the presence or absence of a diffraction state can be switched by applying an electric field is provided. Furthermore, a polarization selection device using a diffraction element is provided.

  As a result of intensive studies, the present inventors have provided a liquid crystal layer having a uniform chemical composition and the same phase between a pair of transparent substrates, and this liquid crystal layer is periodically formed by two regions having optical anisotropy. The present invention has been found out that the above-mentioned problems can be solved by configuring.

That is, the present invention is a diffraction element provided with a liquid crystal layer having a uniform chemical composition and the same phase between a pair of transparent substrates,
In the liquid crystal layer, a first region (first region) having optical anisotropy and a second region (second region) having optical anisotropy different from the first region have a predetermined period. It is a diffraction element characterized by being arranged with.

Here, in the vicinity of one substrate interface constituting the pair of transparent substrates, the major axis direction of the liquid crystal in the first region is aligned substantially horizontally with respect to the substrate interface, and the major axis direction of the liquid crystal in the second region Is oriented substantially perpendicular to the substrate interface,
In the vicinity of the other substrate interface forming the pair of transparent substrates, the major axis direction of the liquid crystal in the first region and the second region is aligned substantially perpendicular to the substrate interface.

Also, in the vicinity of one substrate interface constituting the pair of transparent substrates, the major axis direction of the liquid crystal in the first region is aligned substantially horizontally with respect to the substrate interface, and the major axis direction of the liquid crystal in the second region is Oriented substantially perpendicular to the substrate interface,
In the vicinity of the other substrate interface forming the pair of transparent substrates, the major axis direction of the liquid crystal in the first region and the second region is aligned substantially horizontally with respect to the substrate interface.

  Further, in the vicinity of the interface between both substrates constituting the pair of transparent substrates, the major axis direction of the liquid crystal in the first region is aligned substantially horizontally with respect to each substrate interface, and the major axis direction of the liquid crystal in the second region Is characterized by being oriented substantially perpendicularly to each substrate interface.

  In the diffraction element, each major axis direction of the liquid crystal in the first region is aligned in substantially the same direction in the extending direction that is a plane horizontal to the substrate interface and orthogonal to the periodic direction of the first region. It is desirable that

  Here, each major axis direction of the liquid crystal in the first region is preferably substantially parallel or substantially perpendicular to the extending direction of the first region.

Furthermore, in any one of the above diffraction elements, a surface layer in which two surface patterns having different critical surface tensions are arranged with a predetermined period is provided on at least one transparent substrate surface in contact with the pair of transparent substrates and the liquid crystal layer,
The predetermined period of the surface pattern corresponds to the predetermined period of the first region and the second region, and the major axis direction of the liquid crystal in the first region and the second region corresponds to the critical surface tension of the surface pattern interface, respectively. It is characterized by being oriented horizontally or substantially vertically.

  In the diffractive element, the surface layer is preferably a layer formed using a material whose critical surface tension is changed by energy application.

  Here, the material whose critical surface tension is changed by the application of energy is preferably made of a polymer material having a hydrophobic group in a side chain.

  Further, it is preferable that the polymer material having a hydrophobic group in the side chain is made of a polymer material containing a polyimide skeleton.

  In any one of the above diffraction elements, it is preferable that the application of energy for changing the critical surface tension is by ultraviolet irradiation.

  The surface layer is preferably composed of two types of materials having different critical surface tensions.

  Furthermore, in any one of the above diffraction elements, a transparent electrode is provided on each of the opposing substrate surfaces of the pair of transparent substrates, and the orientation of the liquid crystal in the major axis direction can be controlled by applying an electric field.

Furthermore, the present invention includes a step of forming a surface layer on one or both of the pair of transparent substrates using a material whose critical surface tension is changed by applying energy;
Applying energy to the surface layer to form two surface patterns having a small critical surface tension region and a large region with a predetermined period;
A process of assembling a cell by subjecting the surface layer on which the surface pattern is formed to an alignment treatment and arranging a pair of transparent substrates so that the surface layer is on the inside,
Filling the cell with a liquid crystal material;
And a step of heating the cell filled with the liquid crystal material to a temperature at which the liquid crystal material is in an isotropic phase and then cooling the cell.

  Here, it is preferable that the application of energy for changing the critical surface tension is by ultraviolet irradiation.

Further, according to the present invention, two surface patterns composed of a region having a small critical surface tension and a region having a large critical surface tension are formed with a predetermined period on one or both of a pair of transparent substrates using two kinds of materials having different critical surface tensions. Process,
A process of assembling a cell by subjecting the surface layer on which the surface pattern is formed to an alignment treatment and arranging a pair of transparent substrates so that the surface layer is on the inside,
Filling the cell with a liquid crystal material;
And a step of heating the cell filled with the liquid crystal material to a temperature at which the liquid crystal material is in an isotropic phase and then cooling the cell.

  In any one of the above-described diffraction element manufacturing methods, when surface layers are provided on both of the pair of transparent substrates, the critical surface tensions of two surface patterns having different critical surface tensions in each surface layer are equal. It is characterized in that a certain pattern is arranged so as to be substantially opposed to each other.

Further, the present invention is a polarization selection device configured to selectively transmit or diffract incident light according to a polarization direction using a diffraction element,
The diffractive element is a diffractive element according to any one of claims 1 to 13, and relates to a polarization selection device.

  Here, the incident light is reflected and separated in different directions according to the polarization direction.

The structure having a liquid crystal layer composed of a periodic structure of different optically anisotropic regions (first region and second region) in the present invention has a simple diffraction structure and a good diffraction efficiency. In addition, a diffraction element that can be produced at low cost can be provided.
In particular, by controlling the orientation state of the first region and the second region, it is possible to further improve the diffraction efficiency and simplify the manufacture of the diffraction element.

Control of the orientation state can be realized by forming a surface layer having two surface patterns having different critical surface tensions on the surface of the transparent substrate, and the critical surface tension of such a surface layer is changed by applying energy. It is formed by using materials or two kinds of materials having different critical surface tensions. As a material, a polymer material having a hydrophobic group in a side chain capable of producing a pattern corresponding to an arbitrary critical surface tension, particularly polyimide is preferable from the viewpoint of reliability.
Further, if the transparent substrate is provided on each counter substrate surface of the pair of transparent substrates, it is possible to provide a diffractive element capable of switching between a diffracted state and a non-diffracted state.

  Furthermore, according to the manufacturing method of the present invention, it is possible to manufacture a diffraction element with excellent productivity, simple and low cost.

  In addition, according to the polarization selection device of the present invention, the projection type display has excellent polarization selectivity, and can reflect and separate incident light in different directions according to the polarization direction, and can be manufactured thin, small and low cost. It can be used as a polarization beam splitting element.

As described above, in the diffraction element of the present invention, a liquid crystal layer having a uniform chemical composition and the same phase is provided between a pair of transparent substrates. This liquid crystal layer has a first optical anisotropy. A region (abbreviated as the first region) and a second region (abbreviated as the second region) having optical anisotropy different from the first region are repeatedly arranged with a predetermined period. It is a feature.
In addition, the above-mentioned “chemical composition is uniform and the same phase” may be hereinafter referred to as “single phase”. That is, that the liquid crystal layer is composed of a single phase means that materials constituting the liquid crystal layer have a substantially uniform chemical composition and exhibit the same phase.

FIG. 1 is a cross-sectional view and a top view schematically showing the configuration of a diffraction element in the present invention.
In FIG. 1, a liquid crystal layer (2) is filled between a pair of transparent substrates (1a, 1b). The liquid crystal layer (2) includes a first region having optical anisotropy (first region (3a)) and a second region having optical anisotropy (second region (3b)). Has been.
Thus, the first region (3a) and the second region (3b) have a periodic structure arranged with a predetermined period, and are horizontal to the substrate surface and perpendicular to the periodic direction (the upper surface of FIG. 1). It is formed in a structure extending in the extending direction in the figure. Although the periodic pitch of the periodic structure varies depending on the wavelength of incident light and a desired diffraction angle, it is about 0.2 to 10 μm. Light rays incident on the diffractive element are diffracted by the difference in refractive index between the first region and the second region.

  As shown in FIG. 1, the diffraction element of the present invention has a simple structure in which the liquid crystal layer 2 is composed of a single phase, and the first region and the second region are repeatedly arranged at a predetermined period. Good diffraction efficiency can be realized.

  In the present invention, the type of liquid crystal used may be nematic, smectic, or cholesteric, and a conventionally known material alone or a mixture may be used. In order to increase the refractive index modulation of the diffractive element, it is preferable to select a material having a large refractive index anisotropy, that is, a difference between the ordinary light refractive index and the extraordinary light refractive index.

  As the transparent substrate, a glass or plastic substrate used as a substrate of a liquid crystal display element can be used.

  The thickness of the liquid crystal layer is controlled by a spacer not shown. As the spacer member, the same spherical spacer, fiber spacer, post spacer, film spacer and the like as those used in conventional liquid crystal elements can be used. The height of the spacer member is appropriately set according to the wavelength of the diffracted light and the optical characteristics of each region of the liquid crystal layer.

  As long as the first region and the second region have different optical anisotropies, there is no limitation on the internal form thereof, but in order to achieve the object of realizing better diffraction efficiency A preferred embodiment will be described in detail below.

In the schematic diagram of FIG. 2, the example (I) of the 1st area | region and 2nd area | region of the diffraction element in this invention is shown.
In FIG. 2, in the vicinity of the interface of one substrate (21a) constituting the pair of transparent substrates (21a, 21b), the major axis direction of the liquid crystal in the first region (23a) is substantially horizontal with respect to the interface of the substrate (21a). The major axis direction of the liquid crystal in the second region (23b) is aligned substantially perpendicular to the interface of the substrate (21a), and in the vicinity of the interface of the other substrate (21b), the first region (23a) The major axis direction of the liquid crystal in the middle and second regions (23b) is aligned substantially perpendicular to the interface of the substrate (21b).
Hereinafter, the “major axis direction of liquid crystal” may be referred to as “liquid crystal director”.

  That is, in the first region (23a), the liquid crystal director adopts a hybrid alignment state in which the liquid crystal director continuously changes from horizontal alignment to vertical alignment between the upper and lower substrates, and the second region (23b) takes a homeotropic alignment state. Therefore, a diffractive element in which two regions having different refractive indexes are periodically arranged is obtained, and light incident on this element is diffracted.

With such a diffraction element structure, better diffraction efficiency can be achieved with a simple structure.
In addition, when manufacturing by the method described later, precise alignment is not required in the bonding process of the upper and lower substrates, so that one transparent substrate is subjected to line-shaped horizontal alignment processing and vertical alignment processing at a predetermined cycle, and the other transparent substrate is transparent. The substrate can be easily manufactured simply by performing a vertical alignment treatment.

The schematic diagram of FIG. 3 shows another example (II) of the first region and the second region of the diffraction element in the present invention.
In FIG. 3, in the vicinity of the interface of one substrate (31a) constituting the pair of transparent substrates (31a, 31b), the major axis direction of the liquid crystal in the first region (33a) is aligned substantially horizontally with respect to the substrate interface. The major axis direction of the liquid crystal in the second region (33b) is aligned substantially perpendicular to the substrate interface, and in the vicinity of the other substrate (31b) interface, the first region (33a) and the second region ( The major axis direction of the liquid crystal in 33b) is aligned substantially horizontally with respect to the substrate interface.

  That is, in the first region (33a), the liquid crystal director takes a horizontal alignment state between the upper and lower substrates, and in the second region (33b), the hybrid alignment continuously changes from the vertical alignment to the horizontal alignment between the upper and lower substrates. In order to take a state, it becomes a diffraction element in which two regions having different refractive indexes are periodically arranged, and light incident on this element is diffracted.

  The structure of such a diffractive element is a simple structure as in FIG. 1, and better diffraction efficiency can be realized. In addition, when manufacturing by the method described later, precise alignment is not required in the bonding process of the upper and lower substrates, so that one transparent substrate is subjected to line-shaped horizontal alignment processing and vertical alignment processing at a predetermined cycle, and the other transparent substrate is transparent. The substrate can be easily manufactured simply by performing a horizontal alignment treatment.

The schematic diagram of FIG. 4 shows another embodiment (III) of the first region and the second region of the diffraction element in the present invention.
In FIG. 4, the major axis direction of the liquid crystal in the first region (33a) is substantially horizontal to the interface of each substrate (31a, 31b) in the vicinity of the interface between both substrates (31a, 31b) constituting the pair of transparent substrates. The major axis direction of the liquid crystal in the second region (33b) is aligned substantially perpendicular to the interface of each substrate (31a, 31b).

  That is, in the first region (33a), the liquid crystal director adopts a horizontal alignment state, and in the second region (33b), a homeotropic alignment state is adopted. Therefore, two regions having different refractive indexes are periodically arranged. A diffractive element is formed, and light incident on the element is diffracted. In this case, the substantial refractive index of the first region (33a) is close to the extraordinary refractive index (ne) of the liquid crystal molecules, and the substantial refractive index of the second region (33b) is the ordinary refractive index of the liquid crystal molecules. Since the value is close to (no), the difference in refractive index between the two regions becomes large.

  Therefore, such a diffractive element has a simple structure as in FIG. 1, and has a refractive index modulation larger than that of the diffractive element shown in FIGS. be able to. When the diffraction element having such a structure is manufactured by a method described later, it can be easily manufactured by performing a linear alignment process and a vertical alignment process in a predetermined cycle on both transparent substrates. However, at the time of bonding the upper and lower substrates, it is necessary to perform proper alignment in order to obtain a desired structure.

The schematic diagram of FIG. 5 shows an example of the orientation of the first region of the diffractive element in FIGS.
As shown in FIG. 5, each major axis direction of the liquid crystal in the first region (33a) oriented substantially horizontally with respect to the interface of the transparent substrate (31a, 31b) is the extension of the first region (33a). It is preferable that they are aligned in substantially the same direction in the present direction.
A diffractive element having such a structure can be produced by performing a horizontal alignment process on the upper and lower substrates so that the alignment process directions are antiparallel when bonded.

By adopting such a configuration, a diffraction element in which the liquid crystal director is in a homogeneous alignment state that is aligned horizontally and in the same direction with respect to the substrate in the first region, and a homeotropic alignment state in the second region (33b). It becomes.
In this case, the polarization component of the incident light that vibrates in the same direction as the liquid crystal director direction in the first region has a high diffraction efficiency because it feels a large difference in refractive index between the two regions, and conversely, the liquid crystal in the first region. Since the polarization component that vibrates in the direction orthogonal to the director direction feels the difference in refractive index between the two regions to be particularly small, the diffraction efficiency decreases. By utilizing such an effect, polarization selectivity can be imparted to the diffraction element of the present invention.

Furthermore, it is preferable that the liquid crystal directors in the first region (33a) in the vicinity of both substrates in FIG. 5 are aligned substantially parallel or substantially perpendicular to the extending direction of the first region.
In the schematic diagram of FIG. 6, the liquid crystal director in the first region (33a) in FIG. 5 is oriented substantially parallel (a) or substantially perpendicular (b) to the extending direction of the first region. Show.

  In the case of FIG. 6A in which the liquid crystal directors are oriented substantially parallel to the extending direction of the first region in the first region, the refractive indexes of the first region (33a) and the second region (33b) are Both are almost equal to the ordinary light refractive index (no) of the liquid crystal. For this reason, the difference in refractive index between the two regions is not perceived with respect to p-polarized incident light, so that diffraction does not occur. The diffraction is performed by feeling the difference between the refractive index (abnormal light refractive index ne) and the refractive index (ordinary light refractive index no) of the second region (33b). With such an effect, a diffraction element that selectively diffracts s-polarized light is obtained.

  In the case of FIG. 6B in which the liquid crystal directors are aligned substantially perpendicular to the extending direction of the first region in the first region, the first region (33a) is used for incident light of s-polarized light. ) And the second region (33b) are almost equal to the ordinary refractive index (no) of the liquid crystal, so that no difference in refractive index between the two regions is felt, so that no diffraction occurs, whereas p-polarized light Is diffracted by feeling the difference between the refractive index (abnormal light refractive index ne) of the first region (33a) and the refractive index (ordinary light refractive index no) of the second region (33b). By such an effect, a diffractive element that selectively diffracts p-polarized light is obtained.

  For a diffractive element that selectively diffracts either s-polarized light or p-polarized light, the thickness of the element can be reduced by selecting a liquid crystal that has a large refractive index anisotropy Δn. By reducing the thickness of the element, the angle dependency of diffraction efficiency is further reduced, and the light utilization efficiency for practical non-parallel light is further improved.

  In addition, as a method for aligning the liquid crystal in the first region and the second region in FIGS. 2 to 6, conventionally known methods can be used, for example, rubbing method, chemical treatment, SiO oblique deposition, etc. can be applied. However, a rubbing method capable of simple and low-cost treatment is particularly preferable.

As a configuration of the diffraction element of the present invention, a surface layer in which two surface patterns having different critical surface tensions are arranged with a predetermined period can be provided on at least one transparent substrate surface where a pair of transparent substrates and a liquid crystal layer are in contact with each other. .
The schematic diagram of FIG. 7 shows an example of a diffraction element having a surface layer in which two surface patterns having different critical surface tensions are arranged with a predetermined period in the present invention.

In FIG. 7, the surface pattern A (74) and the surface pattern B having different critical surface tensions are formed on at least one transparent substrate (for example, 71b) surface where the pair of transparent substrates (71a, 71b) and the liquid crystal layer (72) are in contact. A surface layer in which (75) is arranged with a predetermined period is provided.
The predetermined periods of the surface pattern A and the surface pattern B are adjusted so as to correspond to the predetermined periods of the first region (73a) and the second region (73b) having optical anisotropy, respectively. Then, the major axis direction of the liquid crystal in the first region and the second region is aligned substantially horizontally or substantially vertically corresponding to the interface between the surface pattern A and the surface pattern B.

That is, a portion of a surface layer (for example, surface pattern A) having a large critical surface tension and a surface layer (for example, surface pattern B) having a smaller critical surface tension than surface pattern A are formed.
Thereby, in the vicinity of the surface pattern A having a large critical surface tension, that is, so-called high wettability, the liquid crystal director is oriented substantially horizontally on the substrate, and the so-called wettability having a smaller critical surface tension than the surface pattern A is obtained. In the vicinity of the low surface pattern B, the liquid crystal director is aligned in a direction close to perpendicular to the substrate.

For this reason, the liquid crystal director in the vicinity of the substrate is controlled by forming the surface pattern A in the portion where the liquid crystal is to be horizontally aligned and the surface pattern B in the portion where the liquid crystal is vertically aligned on at least one transparent substrate side. be able to. In addition, by increasing the difference in critical surface tension between the surface pattern A and the surface pattern B, the difference in refractive index between two regions having different optical anisotropies can be increased. It can be.
By providing a surface layer in which two surface patterns having different critical surface tensions are arranged in this way, the diffraction element having the first region and the second region shown in FIGS. 2 to 6 can be precisely manufactured. In addition, an element having better diffraction efficiency and polarization selectivity can be obtained.

Furthermore, the present inventors use a material whose critical surface tension is changed by applying energy (for example, irradiation with an energy beam such as ultraviolet rays), and a critical pattern arranged on a transparent substrate with a predetermined period, for example, a predetermined period. It has been found that the diffraction element of the present invention can be produced by providing a surface layer composed of two surface patterns having different surface tensions.
That is, by controlling the energy to be applied, two surface patterns having different critical surface tensions can be formed, so that a diffractive element can be manufactured easily and at low cost. Further, a preferable energy application method is the above-described ultraviolet irradiation. If energy is applied by this method, a surface pattern can be efficiently formed, and a diffraction element with high definition can be obtained. Excellent productivity.

If the material whose critical surface tension is changed by the application of energy is a polymer material having a hydrophobic group in the side chain, a pattern corresponding to an arbitrary critical surface tension can be produced as the surface layer of the diffraction element. Therefore, it is more preferable.
Specifically, as such a polymer material having a hydrophobic group in the side chain, as shown in the conceptual diagram of FIG. 8, it is directly or illustrated in the main chain L having a skeleton such as polyimide or (meth) acrylate. Examples thereof include those in which a side chain R having a hydrophobic group is bonded via a bonding group that is not bonded.

As the hydrophobic group of the side chain R in the figure, the terminal structure is —CF ₂ CH ₃ , —CF ₂ CF ₃ , —CF (CF ₃ ) ₂ , —C (CF ₃ ) ₃ , —CF ₂ H, — Examples include groups such as CFH ₂ . In order to facilitate the orientation of molecular chains, a group having a long carbon chain length is preferable, and a group having 4 or more carbon atoms is more preferable. Furthermore, a polyfluoroalkyl group in which two or more of the hydrogen atoms of the alkyl group are substituted with fluorine atoms (hereinafter referred to as “Rf group”) is preferable, and an Rf group having 4 to 20 carbon atoms is particularly preferable. The Rf group having 6 to 12 carbon atoms is preferred. The Rf group may have a linear structure or a branched structure, but a linear structure is preferred. Further, the hydrophobic group is preferably a perfluoroalkyl group in which substantially all of the hydrogen atoms of the alkyl group are substituted with fluorine atoms. The perfluoroalkyl group is preferably a group represented by C _n F _{2n + 1} — (where n is an integer of 4 to 16), particularly preferably when n is an integer of 6 to 12. The perfluoroalkyl group may have a linear structure or a branched structure, and a linear structure is preferred.

  The above materials are well described in detail in JP-A-3-178478, etc., and are lyophilic when brought into contact with a liquid or solid in a heated state and become lyophobic when heated in air. Have For example, the critical surface tension can be changed by selecting a contact medium and applying thermal energy.

Furthermore, examples of the hydrophobic group include groups having a terminal structure such as —CH ₂ CH ₃ , —CH (CH ₃ ) ₂ , and —C (CH ₃ ) ₃ that do not contain a fluorine atom. Also in this case, in order to facilitate the orientation of molecular chains, a group having a long carbon chain length is preferable, and a group having 4 or more carbon atoms is more preferable. The hydrophobic group may have a linear structure or a branched structure, but a linear structure is preferred.

  The alkyl group may contain a halogen atom, a cyano group, a phenyl group, a hydroxyl group, a carboxyl group, or a phenyl group substituted with a linear, branched or cyclic alkyl group having 1 to 12 carbon atoms or an alkoxy group. Good. It is considered that the more R binding sites, the lower the surface energy (the smaller the critical surface tension) and the more lyophobic. It is presumed that, due to ultraviolet irradiation or the like, a part of the bond is broken or the orientation state changes, so that the critical surface tension increases and becomes lyophilic.

  As the polymer material having a hydrophobic group in the side chain, a polymer material containing a polyimide skeleton is suitable as described above. Since polyimide is excellent in chemical resistance and heat resistance, it is difficult to be damaged during the manufacturing process, and a highly reliable surface layer can be formed. Furthermore, since it is excellent in electrical insulation, for example, in a diffraction element in which an electrode is provided on the surface of a transparent substrate and the orientation direction of liquid crystals in the first region and the second region is controlled by applying an electric field. In particular, a polymer material containing polyimide is preferably used, and a more reliable diffraction element can be obtained.

In the present invention, the surface layer having two surface patterns having different critical surface tensions may be composed of two types of materials having different critical surface tensions.
As a method of forming a surface pattern having different critical surface tensions using two kinds of materials, for example, referring to FIG. 7, after forming the surface pattern A on the entire surface of the transparent substrate by the spin coating method, The surface pattern B can be formed by a flexographic printing method using a plate having a predetermined pattern.

In addition to the combination of the spin coating method and the flexographic printing method, a surface pattern can be formed by appropriately combining coating methods such as a dipping method, an ink jet method, a casting method, and a bar coating method.
The method using these two kinds of materials is disadvantageous when a high-definition pattern is formed as compared with the case where a material whose critical surface tension is changed by applying the energy, but does not require a large amount of energy for forming the surface pattern. It is advantageous in terms of energy and has the advantage that it can be produced at low cost.

In addition, a transparent electrode is provided on each opposing substrate surface of the pair of transparent substrates in the diffraction element of the present invention, and an electric field is applied to the transparent electrode, whereby the first region and the second region having the optical anisotropy are provided. A diffractive element capable of controlling the alignment in the major axis direction of the liquid crystal contained therein and switching between a state where light is diffracted and a state where light is not diffracted can be obtained.
In addition, as an electrode, transparent electrodes, such as an ITO thin film normally used for a display element, can be used.
The schematic diagram of FIG. 9 shows a liquid crystal alignment state of a diffraction element in which a transparent electrode is provided on each counter substrate surface of a transparent substrate and a liquid crystal having positive dielectric anisotropy is used. (A): Voltage non-application state, (b): Voltage application state.

As shown in FIG. 9A, when no electric field is applied between the electrodes (94, 95), a first region having optical anisotropy (first region (93a)), a first region, The light is diffracted by the refractive index difference of the second region (second region (93b)) having different optical anisotropy.
When an electric field is applied between the electrodes (94, 95), as shown in FIG. 9B, the orientation of the liquid crystal director is aligned with the electric field direction in both the first region and the second region. The refractive index is also equal, and the light is not diffracted. Similarly, in a diffractive element having optical anisotropy other than that illustrated in FIG. 9A, the direction of the liquid crystal director is aligned by applying an electric field, and light is not diffracted. In this way, an element that can control the diffraction and non-diffraction of light by an electric field can be obtained.

  As described above, the diffraction element of the present invention selects either the case where a material whose critical surface tension is changed by applying energy (I) or the case where two kinds of materials having different critical surface tensions are used (II). Can be manufactured. The manufacturing process of each diffraction element (I) and (II) is as follows.

<In the case of (I)>
Step (1): A surface layer is formed on one or both of the pair of transparent substrates by using a material whose critical surface tension is changed by applying energy.
Step (2): Energy is applied to the formed surface layer, and two surface patterns composed of a region having a small critical surface tension and a region having a large critical surface tension are formed with a predetermined period.
Step (3): An orientation process is performed on the surface layer on which the surface pattern is formed, and a pair of transparent substrates are arranged to face each other so that the surface layer is on the inside, thereby assembling the cell.
Step (4): The assembled cell is filled with a liquid crystal material.
Step (5): The cell filled with the liquid crystal material is heated to a temperature at which the liquid crystal material becomes isotropic, and then cooled.

  Through a series of steps including the above steps (1) to (5), a surface pattern having a predetermined periodic structure consisting of a region having a small critical surface tension and a region having a large critical surface tension can be formed. Moreover, it can be manufactured at low cost.

  If energy for changing the critical surface tension is applied by ultraviolet irradiation, a higher-definition surface pattern can be efficiently formed, and a diffraction element with higher definition can be obtained. Also excellent.

<(II)>
Step (1): Two surface patterns composed of a region having a small critical surface tension and a region having a large critical surface tension are formed on one or both of the pair of transparent substrates with a predetermined period using two kinds of materials having different critical surface tensions.
Step (2): The surface layer on which the surface pattern is formed is subjected to an orientation treatment, and a pair of transparent substrates are arranged to face each other so that the surface layer is on the inside, and a cell is assembled.
Step (3): The assembled cell is filled with a liquid crystal material.
Step (4): The cell filled with the liquid crystal material is heated to a temperature at which the liquid crystal material becomes isotropic, and then cooled.

  Through a series of steps including the above steps (1) to (4), a surface pattern having a predetermined periodic structure consisting of a region having a small critical surface tension and a region having a large critical surface tension can be formed in an energetically advantageous manner, and has a simple structure and diffraction efficiency. Can be manufactured with good productivity.

  In the above (I) and (II), the diffraction efficiency is improved by arranging the two surface patterns having different critical surface tensions in the surface layer so that the patterns having the same critical surface tension are substantially opposed to each other. A diffractive element that is even better and has polarization selectivity can be manufactured with high productivity.

  In addition, if the diffractive element is used to selectively transmit or diffract incident light in accordance with the polarization direction, the polarization selection device is excellent in polarization selectivity and can be manufactured thin, small, and at low cost. It can be. Here, it can also be configured to reflect and separate incident light in different directions depending on the polarization direction.

The schematic diagram of FIG. 10 shows a configuration example of the polarization selection device in the present invention.
10 includes the diffraction grating (102) of the present invention and a reflective liquid crystal element (103). The reflective liquid crystal element is disposed on the side opposite to the incident light side. This is an example. Note that the present invention is not limited to this.

An example in which the diffractive element in FIG. 10 has the structure shown in FIG. 6B will be described below.
When incident light (L) is incident on the polarization selection device (101), the s-polarized light component Ls travels straight without being diffracted and passes therethrough. On the other hand, the p-polarized light component Lp is diffracted by the diffractive element (102), and enters the reflective liquid crystal element (103) perpendicularly. The reflected light Lp1 that has not been converted to s-polarized light by the reflective liquid crystal element is diffracted again by the diffraction element and returns to the original incident light direction, and the reflected light Lp2 that has been converted to s-polarized light by the reflective liquid crystal element is It goes straight without being diffracted and passes through.
As described above, the above-described diffraction element (grating) functions as a polarization selection device that transmits s-polarized light and diffracts p-polarized light in incident light. Using this, incident light incident from the same direction is used. Can be used as a polarization selection device for separating the reflected light Lp1 and Lp2 in different directions. Therefore, the polarization selection device of the present invention can be used as a polarization separation element in a projection display or the like.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further more concretely, this invention is not limited to this.
Example 1
First, PIA-X491 (made by Chisso Petrochemical Co., Ltd.) containing a polyimide resin having an alkyl moiety in the structure was prepared as a material whose critical surface tension changes due to energy application. Next, PIA-X491 was formed into a film with a thickness of about 80 nm by spin coating on the electrode formation surface side of each of the pair of glass substrates with a transparent electrode serving as the upper and lower substrates, and then baked at 210 ° C.
The light intensity at 250 nm is 5 mW / cm through a quartz substrate photomask having a stripe-shaped pattern in which the widths of the light-shielding part and the transmission part are both 4 μm on each substrate on which PIA-X491 is formed. ^The ultraviolet rays controlled to ² were irradiated for 30 minutes. The irradiation dose corresponds to 9 J / cm ² .
By this ultraviolet irradiation, a substrate with an electrode provided with a surface layer having a surface pattern with a critical surface tension of about 40 mN / m and a stripe-like critical surface tension pattern composed of a surface pattern with a critical surface tension of about 24 mN / m was produced. . Subsequently, the surface layers of both substrates were rubbed in a direction parallel to the extending direction of the stripe pattern having a critical surface tension (a direction perpendicular to the periodic direction of the stripe pattern).

One substrate on which the surface pattern is formed is coated with a sealant containing an amine curable epoxy resin as a component, and the other substrate is made of resin beads having a particle diameter of 25 μm with isopropyl alcohol as a solvent for about 100. It sprayed with the density of the piece / mm < ² >. Next, the parts with high critical surface tension of the surface pattern are made to face each other, the substrates are stacked and bonded so that the rubbing direction is antiparallel, and the adhesive is cured in this state to produce an empty cell did.
After nematic liquid crystal TL-203 manufactured by Merck Co., Ltd. was sealed in this empty cell, it was placed on a hot plate and heated to 100 ° C. to make the liquid crystal isotropic phase, and then cooled to room temperature at a sufficiently slow cooling rate. Thus, a diffraction element was produced.

The diffraction efficiency of the produced diffraction element was measured under the following conditions.
For measuring the diffraction efficiency, a He—Cd laser having a wavelength of 442 nm and an output of 93 V was used.
The diffraction efficiency at the incident light angle at which the first-order diffracted light intensity is maximized, that is, the ratio of the first-order diffracted light intensity to the incident light intensity, was determined as the diffraction efficiency.
In addition, a linearly polarizing plate and a half-wave plate are arranged in the incident optical path, and the polarization direction (p-polarized light, s-polarized light) incident on the hologram element can be switched by rotating the optical axis of the half-wave plate by 45 degrees. The polarization selectivity of the first-order diffraction efficiency was compared.

  As a result of the measurement, the first-order diffraction efficiency of s-polarized light was 21%, and the first-order diffraction efficiency of p-polarized light was 0.4%, indicating good polarization selectivity. Furthermore, when an electric field of 10 V is applied between the upper and lower substrates, the diffraction efficiency is 0% for both s-polarized light and p-polarized light, and the state of diffracting light and the state of not diffracting (presence / absence of diffraction) are satisfactorily switched by applying the electric field. I was able to.

  The absolute value of the diffraction efficiency of s-polarized light is about 21%. This is because the thickness of the liquid crystal layer is not optimized with respect to the amount of refractive index modulation in the liquid crystal layer, and the substrate bonding accuracy is sufficient. It is estimated that there is a possibility that the surface patterns having the same critical surface tension are not exactly opposed to each other. Therefore, by optimizing the thickness of the liquid crystal layer and improving the bonding accuracy, it is possible to produce a diffraction element with better polarization selectivity and higher diffraction efficiency.

(Example 2)
In Example 1, a diffractive element was produced in the same manner as in Example 1 except that the rubbing treatment was performed in the direction perpendicular to the extending direction of the stripe pattern having the critical surface tension.
When the produced diffraction element was evaluated in the same manner as in Example 1, the first-order diffraction efficiency of s-polarized light was 0.4%, and the first-order diffraction efficiency of p-polarized light was 19%, indicating good polarization selectivity. It was.
Furthermore, when an electric field of 10 V was applied between the upper and lower substrates, the diffraction efficiency was 0% for both s-polarized light and p-polarized light, and it was possible to satisfactorily switch between the state of diffracting light and the state of not diffracting.

  The absolute value of the diffraction efficiency of p-polarized light is about 19%. This is because the thickness of the liquid crystal layer is not optimized with respect to the amount of refractive index modulation in the liquid crystal layer, as in Example 1. It is estimated that there is a possibility that the surface patterns with insufficient substrate bonding accuracy and the same critical surface tension are not exactly facing each other. Therefore, as in Example 1, by optimizing the thickness of the liquid crystal layer and improving the bonding accuracy, it is possible to manufacture a diffraction element with better polarization selectivity and higher diffraction efficiency.

(Example 3)
As a material whose critical surface tension is changed by energy application, a mixed solution in which a precursor that becomes a polymer structure represented by the following formula (1) and the following formula (2) is dissolved after firing is used. After being applied to the electrode forming surface side of the attached glass substrate by a spin coating method, it was baked at 200 ° C. The film thickness was about 80 nm.

The light intensity at 250 nm is applied to one of the deposited substrates through a quartz substrate photomask having a stripe pattern in which both the light-shielding portion and the transmission portion have a width of 4 μm, as in Example 1. Ultraviolet rays controlled to 5 mW / cm ² were irradiated for 30 minutes (irradiation amount: 9 J / cm ² ).

  By this ultraviolet irradiation, a substrate with an electrode provided with a surface layer having a surface pattern with a critical surface tension of about 40 mN / m and a stripe-like critical surface tension pattern consisting of a surface pattern with a critical surface tension of about 24 mN / m was produced. . Subsequently, a rubbing treatment was performed in a direction parallel to the extending direction of the stripe pattern having a critical surface tension (a direction perpendicular to the periodic direction of the stripe pattern).

  Next, a thin film made of polyimide resin was formed at a thickness of 60 nm on the electrode forming surface side of the other transparent glass substrate with electrodes using AL-3046 (manufactured by JSR), and then a rubbing treatment was performed. .

As in Example 1, a sealing material containing an amine curable epoxy resin as a component was applied to a substrate having a striped critical surface tension pattern with a dispenser, and resin beads having a particle diameter of 30 μm were applied to the other substrate with isopropyl. Alcohol was sprayed at a density of about 100 pieces / mm ² as a solvent. Two substrates were made to face each other, the substrates were stacked and bonded so that the rubbing direction was antiparallel, and in this state, the adhesive was cured to produce an empty cell.
After nematic liquid crystal TL-203 manufactured by Merck Co., Ltd. was sealed in this empty cell, it was placed on a hot plate and heated to 100 ° C. to make the liquid crystal isotropic phase, and then cooled to room temperature at a sufficiently slow cooling rate. Thus, a diffraction element was produced.

  When evaluated in the same manner as in Example 1, the first-order diffraction efficiency of s-polarized light was 18%, and the first-order diffraction efficiency of p-polarized light was 0.5%, indicating good polarization selectivity.

Example 4
A diffraction element was produced in the same manner as in Example 1 except that a glass substrate without a transparent electrode was used in Example 1, and the diffraction efficiency of the diffraction element produced in the same manner as in Example 1 was evaluated.
As a result of the measurement, the first-order diffraction efficiency of s-polarized light was 21%, and the first-order diffraction efficiency of p-polarized light was 0.4%, indicating good polarization selectivity.

(Example 5)
A diffraction element was produced in the same manner as in Example 3 except that a glass substrate without a transparent electrode was used in Example 3, and the diffraction efficiency of the diffraction element produced in the same manner as in Example 1 was evaluated.
As a result of the measurement, the first-order diffraction efficiency of s-polarized light was 18%, and the first-order diffraction efficiency of p-polarized light was 0.5%, indicating good polarization selectivity.

  From the results of Examples 1 to 5, the diffractive element of the present invention has a simple structure and good diffraction efficiency, and can be produced easily and at low cost.

(Example 6)
As in the case of FIG. 10, a polarization selection device composed of the diffraction grating of the present invention and a reflective liquid crystal element was produced.
As a result of evaluating this polarized light selection device, it has a polarization selectivity that transmits s-polarized light and diffracts p-polarized light in incident light, and has a function of separating incident light as reflected light Lp1 and Lp2 in different directions. confirmed. From these evaluations, it was found that it can be used as a polarization separation element in a projection display or the like.

It is sectional drawing and the top view which show typically the structure of the diffraction element in this invention. It is a schematic diagram which shows the example (I) of the 1st area | region and 2nd area | region of a diffraction element in this invention. It is a schematic diagram which shows another example (II) of the 1st area | region and 2nd area | region of a diffraction element in this invention. It is a schematic diagram which shows another example (III) of the 1st area | region and 2nd area | region of a diffraction element in this invention. FIG. 5 is a schematic diagram illustrating an example of orientation of a first region of the diffraction element in FIGS. It is a schematic diagram which shows the state which the liquid crystal director of the 1st area | region in FIG. 5 has orientated substantially parallel (a) or substantially right angle (b) with respect to the extending direction of a 1st area | region. It is a schematic diagram which shows an example of the diffraction element which has a surface layer in which two surface patterns from which critical surface tension differs in this invention were arranged with the predetermined period. It is a conceptual diagram for demonstrating the polymeric material which has a hydrophobic group in the side chain in this invention. It is a schematic diagram which shows the liquid crystal orientation state by the voltage non-application (a) and voltage application (b) of the diffraction element which provided the transparent electrode in each opposing board | substrate surface of a transparent substrate, and used the liquid crystal with positive dielectric anisotropy. It is a schematic diagram which shows the structural example of the polarization | polarized-light selection apparatus in this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1a, 1b Transparent substrate 2 Liquid crystal layer 3a 1st area | region 3b 2nd area | region 21a, 21b Transparent substrate 22 Liquid crystal layer 23a 1st area | region 23b 2nd area | region 31a, 31b Transparent substrate 32 Liquid crystal layer 33a 1st area | region 33b 2nd area | region 71a, 71b Transparent substrate 72 Liquid crystal layer 73a First region 73b Second region 74 Surface pattern A
75 Surface pattern B
91a, 91b Transparent substrate 92 Liquid crystal layer 93a First region 93b Second region 94, 95 Electrode 101 Polarization selector 102 Diffraction element 103 Reflective liquid crystal element

Claims (19)

A diffractive element in which a liquid crystal layer having a uniform chemical composition and the same phase is provided between a pair of transparent substrates,
In the liquid crystal layer, a first region (first region) having optical anisotropy and a second region (second region) having optical anisotropy different from the first region have a predetermined period. A diffractive element characterized by being arranged. In the vicinity of one substrate interface constituting the pair of transparent substrates, the major axis direction of the liquid crystal in the first region is aligned substantially horizontally with respect to the substrate interface, and the major axis direction of the liquid crystal in the second region is the substrate interface. Is oriented substantially perpendicular to the
The major axis direction of the liquid crystal in the first region and the second region is aligned substantially perpendicular to the substrate interface in the vicinity of the other substrate interface forming the pair of transparent substrates. The diffraction element according to 1. In the vicinity of one substrate interface constituting the pair of transparent substrates, the major axis direction of the liquid crystal in the first region is aligned substantially horizontally with respect to the substrate interface, and the major axis direction of the liquid crystal in the second region is the substrate interface. Is oriented substantially perpendicular to the
The major axis direction of the liquid crystal in the first region and the second region is aligned substantially horizontally with respect to the substrate interface in the vicinity of the other substrate interface forming the pair of transparent substrates. The diffraction element according to 1.   In the vicinity of both substrate interfaces constituting the pair of transparent substrates, the major axis direction of the liquid crystal in the first region is aligned substantially horizontally with respect to each substrate interface, and the major axis direction of the liquid crystal in the second region is The diffraction element according to claim 1, wherein the diffraction element is oriented substantially perpendicular to the substrate interface.   Each major axis direction of the liquid crystal in the first region is aligned in substantially the same direction in an extending direction that is a plane parallel to the substrate interface and orthogonal to the periodic direction of the first region. The diffraction element according to claim 3 or 4, characterized in that   The diffraction element according to claim 5, wherein each major axis direction of the liquid crystal in the first region is substantially parallel or substantially perpendicular to the extending direction of the first region. A surface layer in which two surface patterns having different critical surface tensions are arranged with a predetermined period on at least one transparent substrate surface in contact with the pair of transparent substrates and the liquid crystal layer,
The predetermined period of the surface pattern corresponds to the predetermined period of the first region and the second region, and the major axis direction of the liquid crystal in the first region and the second region corresponds to the critical surface tension of the surface pattern interface, respectively. The diffraction element according to claim 2, wherein the diffraction element is oriented horizontally or substantially vertically.   The diffraction element according to claim 7, wherein the surface layer is a layer formed using a material whose critical surface tension is changed by applying energy.   9. The diffraction element according to claim 8, wherein the material whose critical surface tension is changed by the application of energy is a polymer material having a hydrophobic group in a side chain.   The diffraction element according to claim 9, wherein the polymer material having a hydrophobic group in the side chain is a polymer material containing a polyimide skeleton.   The diffraction element according to any one of claims 8 to 10, wherein the application of energy for changing the critical surface tension is by ultraviolet irradiation.   The diffraction element according to claim 7, wherein the surface layer is made of two kinds of materials having different critical surface tensions.   The diffraction element according to any one of claims 1 to 12, wherein a transparent electrode is provided on each of the opposing substrate surfaces of the pair of transparent substrates, and the orientation in the major axis direction of the liquid crystal can be controlled by applying an electric field. . Forming a surface layer on one or both of the pair of transparent substrates using a material whose critical surface tension is changed by applying energy;
Applying energy to the surface layer to form two surface patterns having a small critical surface tension region and a large region with a predetermined period;
A process of assembling a cell by subjecting the surface layer on which the surface pattern is formed to an alignment treatment and arranging a pair of transparent substrates so that the surface layer is on the inside,
Filling the cell with a liquid crystal material;
And a step of heating the cell filled with the liquid crystal material to a temperature at which the liquid crystal material is in an isotropic phase and then cooling the cell.   The method for producing a diffraction element according to claim 14, wherein the application of energy for changing the critical surface tension is by ultraviolet irradiation. Forming two surface patterns having a small critical surface tension region and a large region with a predetermined period using two kinds of materials having different critical surface tensions on one or both of a pair of transparent substrates;
A process of assembling a cell by subjecting the surface layer on which the surface pattern is formed to an alignment treatment and arranging a pair of transparent substrates so that the surface layer is on the inside,
Filling the cell with a liquid crystal material;
And a step of heating the cell filled with the liquid crystal material to a temperature at which the liquid crystal material is in an isotropic phase and then cooling the cell.   When surface layers are provided on both of the pair of transparent substrates, the two surface patterns having different critical surface tensions in each surface layer are arranged so that the patterns having the same critical surface tension are substantially opposed to each other. The method for producing a diffraction element according to claim 14, wherein: A polarization selection device configured to selectively transmit or diffract incident light according to a polarization direction using a diffraction element,
The diffractive element is the diffractive element according to any one of claims 1 to 13, wherein the polarization selecting device. 19. The polarization selection apparatus according to claim 18, wherein the incident light is reflected and separated in different directions according to the polarization direction.

Images