JP4999485B2 - Beam splitting element and beam splitting method - Google Patents

Description

  The present invention relates to a light beam splitting element and a light beam splitting method having a function of transmitting or diffracting an element by a polarization component of an incident light beam, and in particular, a light beam splitting element and a light beam splitting device that split an incident light beam from one light source into two or more light beams. Regarding the method.

  In recent years, multi-beam technology using a semiconductor laser has progressed, and these are being applied to, for example, electrophotographic image forming apparatuses used in laser printers, digital copying machines, plain paper fax machines, and the like. With respect to the electrophotographic image forming apparatus, colorization and speeding-up have progressed, and tandem-compatible image forming apparatuses having a plurality of (usually four) photoreceptors have become widespread.

  However, in the case of such a tandem method, with an increase in the number of light sources, problems such as an increase in the number of parts, a color shift due to a wavelength difference between a plurality of light sources, and a cost increase arise. In addition, the deterioration of the semiconductor laser is cited as a cause of the failure of the writing unit. When the number of light sources increases, the probability of failure increases and the recyclability deteriorates.

Therefore, in order to reduce the number of light sources and the number of parts and reduce the cost, a method of dividing a beam from a common light source has been proposed. In Patent Document 1, a light beam is divided by the following means.
1) A method using a half mirror prism 2) A method combining a half mirror and a mirror 3) A method of spatially dividing an emitted beam by providing a plurality of openings.
Here, since both the 1) and 2) systems use mirrors as the separating means, beam spot diameter deterioration is likely to occur due to the effects of variations in the surface accuracy of the mirrors and the effects of arrangement errors. Further, the half mirror prism used in 1) is very expensive and increases the cost. Further, the method of combining the half mirror and the mirror shown in 2) is difficult to arrange the layout, and has an opening angle in the polarization rotation plane, so that the optical characteristics such as the beam spot diameter deteriorate. The method of splitting a light beam by a plurality of openings uses the peripheral part of the beam from the light source, and therefore has a problem that the light amount is insufficient and the beam spot diameter is increased.

  Further, the optical path lengths of the divided light beams are different from each other in the methods 1) and 2), and there is a problem that the focal position in the optical axis direction fluctuates when a light beam having a lens action is incident. In addition, the following patent documents 1-4 are known as a technique regarding a polarization hologram element.

  Patent Document 2 discloses an optical anisotropic diffractive element in which a diffraction grating shape is formed on an isotropic substrate, and a groove having the diffraction grating shape is filled with an optically anisotropic material.

  In Patent Document 3, photopolymerizable liquid crystal is used and exposed by a method such as interference exposure in a horizontally aligned state. After the liquid crystal in the exposed portion is periodically polymerized and solidified, an external field is applied to the unexposed portion. A hologram element that reacts and solidifies in a vertically aligned state is disclosed.

  In Patent Document 4, two-beam interference exposure is performed by controlling an optical medium including a liquid crystal and a polymer to a specific temperature range corresponding to the N-I point of the liquid crystal. A hologram element having a structure oriented in various directions is disclosed.

As a technique related to light beam splitting, the invention of Patent Document 5 is known. In Patent Document 5, in the optical scanning apparatus and the image forming apparatus, a beam from a common light source is divided, the beam is incident on a reflecting mirror at a different stage, and different scanned surfaces are scanned. It is a patent and light splitting is realized by a half mirror prism and a combination of a half mirror and a mirror.
JP 2005-92129 A Japanese Patent Laid-Open No. 10-92004 Japanese Patent Laid-Open No. 11-271536 JP 2000-212465 A JP 2005-92129 A

  An object of the present invention is to provide a high-efficiency and low-cost light beam splitting element that solves the above-described problems in a method of splitting a beam from a common light source.

  Specifically, an object of the present invention is to provide a high-efficiency and low-cost light beam splitting element that splits one light beam into two light beams, in which the optical path lengths of the split light beams are the same. .

  The present invention can be applied to an optical scanning device, an image forming apparatus, a projection image forming apparatus, and the like used for a laser printer, a digital copying machine, a plain paper fax machine, and the like.

The invention of the light beam splitting element according to claim 1 is a light beam splitting element comprising a periodic structure element having a periodic structure in which two layers having different refractive indexes in at least one of an optically isotropic region or an optically anisotropic region are repeated. The beam splitting element includes a first periodic structure element that splits an incident beam into a transmitted beam of zero-order light and a diffracted beam of primary light, and diffracts the diffracted beam again to form a second split beam. A second periodic structure element; a third periodic structure element that diffracts the transmitted light beam; and a fourth periodic structure that diffracts the light beam from the third periodic structure element into a first light beam. The optical axis of the split light is adjusted by transmission and diffraction of the first to fourth periodic structure elements, the split light of the outgoing light is emitted substantially in parallel with the adjustment, and the adjustment is performed for each split of the outgoing light. The optical path difference length of light is made substantially the same .

According to a second aspect of the present invention, in the first aspect , the pitch p of the periodic structure of the first to fourth periodic structure elements and the grating inclination φ are substantially the same. Features.

Invention of the light beam splitting device according to claim 3, in claim 1 or 2, the gap between the first-periodical substrate film is a thickness of the fourth structure of the periodic structure elements are the same or different It is characterized by.

According to a fourth aspect of the present invention, there is provided the light beam splitting element according to any one of the first to third aspects, wherein the first to fourth periodic structure elements have a periodic structure, and the inter-substrate gap, which is the thickness of the element, is substantially constant. The first periodic structure element has the periodic structure formed in a direction substantially orthogonal to the periodic structure element in which the transmitted light is diffracted by dividing incident light into two light beams by diffraction and transmission, When the polarization in the direction substantially parallel to the arrangement direction of the periodic structure is p-polarization and the polarization in the direction substantially perpendicular to the arrangement direction of the periodic structure is s-polarization, the incident light flux to the periodic structure element is The p-polarized light component and the s-polarized light component are divided into substantially equal intensities and emitted.

According to a fifth aspect of the present invention, the light beam splitting element according to the fourth aspect is characterized in that the incident light beam is linearly polarized light.

According to a sixth aspect of the present invention, there is provided the light beam splitting element according to the fifth aspect , wherein the polarization direction of the incident light beam is based on the arrangement direction of the periodic structure of the periodic structure element, and the periodic structure element is periodic. It is characterized by being oriented at approximately + 45 ° or approximately −45 ° with respect to the arrangement direction of such a structure.

Invention of the light beam splitting device according to claim 7, in claim 4, wherein the polarization of the light beam the incident is circular or elliptical polarization.

The invention of the light beam splitting element according to claim 8 is the pitch of the first and second periodic structure elements or the third and fourth periodic structure elements according to any one of claims 1 to 7. p and each lattice inclination φ are substantially the same and the lattice inclination φ is arranged in the same direction, and the lattice inclination φ of the first periodic structure element and the third periodic structure element is arranged in the opposite direction or the same direction. It is characterized by.

The invention of a light beam splitting element according to a ninth aspect is the light beam splitting element according to any one of the first to eighth aspects, wherein each of the first and second periodic structural elements or the third and fourth periodic structural elements. The pitch p and each grating inclination φ are substantially the same, and the first and second periodic structure elements or the third and fourth periodic structure elements are arranged substantially in parallel.

From the invention of the light beam splitting device of claim 1 0, in any one of claims 1 to 9, the periodic structure of the periodic structure elements and the non-polymerizable liquid crystal, and the polymerizable monomer or prepolymer The composition is held between a pair of transparent substrates, and the composition is subjected to a multi-beam interference exposure of two or more light beams, thereby causing a periodic phase of a layer mainly composed of a polymer and a layer mainly composed of a non-polymerizable liquid crystal. It is a polymer dispersion type liquid crystal hologram element in which a separation structure is formed.

Invention of the light beam splitting device of claim 1 1, in any one of claims 1 to 9, wherein at least one region of the periodic structure of the periodic structure element is a region showing optical anisotropy And the region is made of a material having birefringence.

Invention of the light beam splitting device of claim 1 2, in any one of claims 1 to 1 1, the region shows optical anisotropy of the periodic structure element has a non-polymerizable liquid or the polymerizable liquid crystal It is characterized by that.

Invention of the light beam splitting device according to claim 1 3, in any one of claims 1 to 12, a region showing a different optical isotropic refractive index of the periodic structure element is obtained as photopolymers It is characterized by that.

Invention of the light beam splitting device according to claim 1 4, in claim 8, grating inclination between the said first periodic structure elements third periodic structure elements φ is reversed, the second period At least one of the structural element and the third periodic structural element is arranged in a stage subsequent to the first periodic structural element.

Invention of the light beam splitting device according to claim 1 5, in claims 1 to 4, in parallel to the next stage of the second periodic structure elements and said third periodic structure elements and said first periodic structure element It is characterized by being arranged.

The invention of the light beam splitting element according to claim 16 is characterized in that, in claims 1 to 15 , the split first light beam and the split second light beam are split vertically or horizontally.

The invention of the light beam splitting element according to claim 17 is a method of splitting one light beam using the light beam splitting element according to claims 1 to 16 , wherein an outgoing light beam split by the method is an incident light beam. It is characterized by being substantially parallel to.

The invention of the light beam splitting element according to claim 18 is a method of splitting one light beam using the light beam splitting element according to claims 1 to 16 , wherein the split outgoing split light is substantially the same light. It has strength.

In other words, the invention can be as follows.
(1) A light beam splitting element comprising a periodic structure element having a periodic structure in which two layers having different refractive indexes in at least one of an optically isotropic region or an optically anisotropic region are repeated,
The light beam splitting element includes first to fourth periodic structure elements arranged in multiple stages, light is split by transmission and diffraction of the first periodic structure element, and transmitted by the second to fourth periodic structure elements. And the optical axis of the divided light is adjusted by diffraction.
(2) The adjustment is characterized in that each split light of the emitted light is emitted substantially in parallel.
(3) The adjustment is characterized in that the optical path difference length of each divided light of the outgoing light is made substantially the same.
(4) In the above (1) to (3), each pitch p and each grating inclination φ of the periodic structure of the first to fourth periodic structure elements are substantially the same.
(5) In the above (1) to (4), the first periodic structure element is arranged on the light incident side, and the second periodic structure element and the fourth periodic structure element are arranged on the emission side. It is characterized by.
(6) In the above (1) to (5), the gap between the substrates, which is the film thickness of the periodic structure of the first to fourth periodic structure elements, is the same or different.
(7) In the above (1) to (6), the first to fourth periodic structure elements have a periodic structure, and the inter-substrate gap which is the film thickness of the elements is substantially constant, and the first hologram element The periodic structure is formed in a direction substantially orthogonal to the hologram element in which the transmitted light is diffracted by dividing the incident light into two light beams by diffraction and transmission,
Polarized light in a direction substantially parallel to the arrangement direction of the periodic structure is p-polarized light,
When polarized light in a direction substantially perpendicular to the arrangement direction of the periodic structure is s-polarized light,
A light beam incident on the hologram element is divided into a p-polarized component and an s-polarized component and emitted with substantially equal intensity.
(8) In (7), the polarized light of the incident light beam is linearly polarized light.
(9) In the above (8), the polarization direction of the incident light beam is based on the arrangement direction of the periodic structure of the first periodic structure element, and the periodic structure of the first periodic structure element It is approximately + 45 ° or approximately −45 ° with respect to the arrangement direction.
(10) In the above (7), the polarization of the incident light beam is circular or elliptical polarization.
(11) In any one of the above (1) to (10), the periodic structure element has a periodic structure in which a composition comprising a non-polymerizable liquid crystal and a polymerizable monomer or prepolymer is interposed between a pair of transparent substrates. A polymer dispersed liquid crystal in which a periodic phase separation structure of a layer mainly composed of a polymer and a layer mainly composed of a non-polymerizable liquid crystal is formed by multi-beam interference exposure in which the composition is held by two or more light beams. It is a hologram element.
(12) In any one of (1) to (10), at least one region of the periodic structure of the periodic structure element is a region exhibiting optical anisotropy, and the region is a material having birefringence. It is characterized by comprising.
(13) The light beam splitting element according to any one of (1) to (12), wherein the region showing the optical anisotropy of the periodic structure element has a non-polymerizable liquid crystal or a polymerizable liquid crystal.
(14) In any one of the above (1) to (13), a region showing optical isotropy having a different refractive index of the periodic structure element is obtained by a photosensitive polymer.
(15) In any one of (1) to (13), the divided first light beam and the divided second light beam are divided in a vertical direction or a horizontal direction.

  As beam splitting means, transmission and diffraction of periodic structure elements (for example, hologram elements) arranged in multiple stages are used as beam splitting means. Therefore, beam spot diameter degradation caused by variations in mirror surface accuracy due to conventional mirror splitting and placement errors. In addition, since the optical path lengths of the divided light beams are the same, the focal position in the optical axis direction can always be fixed even if they are arranged in the lens system. Compared to an expensive half-mirror prism exhibiting similar characteristics, a light beam splitting element having a low cost and a simple configuration can be provided.

  The layout range of the periodic structure elements (for example, hologram elements) constituting the light beam splitting element can be expanded, and a light beam splitting element having a wide range of optical axis positions of the split light beams can be provided.

  With the optimal layout of the periodic structure elements (for example, hologram elements) formed by the light beam splitting elements, a thin light beam splitting element for split light beams can be provided.

  By adopting a configuration using periodic structure elements having different film thicknesses, the polarization direction of the incident light is split by fixing the p-polarized light, so that it is not necessary to adjust the polarization direction incident on the element.

  Productivity can be improved by using a device having a constant film thickness.

  In a light splitting element having a multistage arrangement using a periodic structure element having a constant film thickness, the intensity balance between the p-polarized component and the s-polarized component can be realized by rotating the light source such as an LD and simply adjusting the phase difference plate. .

  In a light beam splitting element having a multistage arrangement using a periodic structure element having a constant film thickness, the setting value of the film thickness by the rotation of a light source such as an LD and a retardation plate is defined, so that the p-polarization component and the s-polarization component The strength balance accuracy is improved.

  In a light splitting element having a multi-stage arrangement using a periodic structure element having a constant film thickness, the intensity balance between the p-polarized component and the s-polarized component can be realized without rotation of a light source such as an LD and adjustment by a phase difference plate.

  Since the periodic structure element made of liquid crystal produced by interference exposure can be duplicated in the original, cost reduction can be realized. By arranging the periodic structure elements made of liquid crystal in multiple stages, a low-cost beam splitting element can be provided.

  The region exhibiting optical anisotropy is composed of a polymer birefringent film, and this polymer birefringent film is a polymer film having birefringence by stretching the polymer film and aligning the polymer chain. . Thereby, the polymer birefringent film can be easily mass-produced, so that the cost can be reduced. By arranging the polarization periodic structure elements in multiple stages, a low-cost beam splitting element can be provided.

  The region showing optical anisotropy is made of liquid crystal generally used for display devices and the like. Therefore, in terms of manufacturing, mass production is good at low cost. In addition, since the optical anisotropy (birefringence) of the liquid crystal is large, the diffraction efficiency can be improved relatively easily.

  Further, a periodic structure element (for example, a hologram element) made of a photopolymer can be manufactured by interference exposure and can be duplicated, so that the cost can be reduced. By arranging the periodic structure elements in multiple stages, a low-cost beam splitting element can be provided.

  Hereinafter, the configuration and function of the light beam splitting element of the present invention will be described in detail by embodiments.

  The light beam splitting element of the present invention is configured by arranging hologram elements in multiple stages as first to fourth periodic structure elements.

<First Embodiment>
A schematic configuration of the first embodiment of the light beam splitting element of the present invention is shown in FIGS.

  The light beam splitting element of the present invention is configured by arranging the first to fourth hologram elements in multiple stages, the first hologram element is disposed on the light incident side, and the second hologram and the fourth hologram are disposed on the exit side. A hologram is arranged and configured. As a function of such an element, an incident light beam can be divided into two light beams (0th-order diffracted light (transmitted light) and first-order diffracted light (sometimes simply referred to as “diffracted light”)) having the same optical path length.

  As a principle of such division, the incident light beam is divided into two light beams of diffracted (for example, polarized light: first-order diffracted light) and transmitted light (for example, straight travel: zero-order diffracted light (transmitted light)) by the first hologram element. Of the divided light, the polarized light by diffraction is diffracted again by the second hologram element to be polarized, and the straight light (0th order diffracted light) transmitted through the first hologram element is converted into the third hologram element. The light is diffracted and polarized, and the polarized light is further diffracted and polarized again by the fourth hologram element.

Hereinafter, in this specification, the straight light transmitted through the first hologram element is referred to as “first transmitted straight light”,
The polarized light diffracted by the first hologram element to the polarized light diffracted by the fourth hologram element are defined as “first diffracted polarized light” to “fourth diffracted polarized light”, respectively, and in more detail the light beam splitting element Will be described.

  As shown in FIG. 2, if the optical axes of the divided first light beam divided into two light beams and the divided second light beam are parallel to the optical axis of the incident light beam, the optical paths of the divided first light beam and the divided second light beam The length difference corresponds to the optical path length difference between the first diffracted polarized light and the third diffracted polarized light, respectively. In addition, in this specification, parallelism refers to 1 degrees or less. The angle is preferably 0.2 ° (12 minutes) or less, more preferably 0.08 (5 minutes) or less.

The optical path length ΔL ₁ of the first diffracted polarized light is determined by ΔL ₁ = L _1-2 / from the diffraction angle θ ₁ of the first hologram element, the distance L _1-2 between the position of the first hologram element and the position of the second hologram element. Further, the optical path length ΔL ₃ of the third diffracted polarized light is obtained by sin θ ₁ , and the distance L ₃₋ between the diffraction angle θ ₃ of the third hologram element, the position of the third hologram element, and the position of the fourth hologram element. ₄ is obtained by ΔL ₃ = L _3-4 / sin θ ₃ (here, the refractive index is 1 (or the refractive index in the optical path is the same)).

Therefore, by setting L _1-2 , sin θ ₁ , L _3-4 and sin θ ₃ so that ΔL ₁ = ΔL _{3 at the} position shown in the configuration as shown in FIG. 2, it is perpendicular to the incident optical axis. It is possible to generate two light beams (a divided first light beam and a divided second light beam) having the same optical path length on a flat surface (xy plane).

FIG. 3 is a model diagram schematically showing a cross-sectional structure of a hologram element which is an example of a periodic structure element used in the present invention. At its upper portion a refractive index distribution of the periodic structure which varies in width of the refractive index change n _H.

As shown in FIG. 3, the hologram element used in the present invention has a periodic structure in which two regions of an optically anisotropic region and an optically isotropic region are alternately formed, and the refractive index modulation amount of the periodic structure is set. Δn _H is defined, the thickness of the periodic structure is defined as T, the pitch of the periodic structure is defined as p, and the lattice inclination of the periodic structure is defined as φ. Here, the refractive index modulation amount Δn _H is the refractive index change amount (refractive index of sinusoidal refractive index modulation) of the refractive index distribution in the periodic structure of the hologram element, as shown on the upper side of the diagram showing the periodic structure of FIG. Modulation amplitude × 2).

In general, the diffraction angle θ of the hologram element can be expressed by θ = sin ⁻¹ (λ / p), and is determined by the wavelength λ of the incident light beam and the grating pitch p of the hologram element. That is, the diffraction angle can be set by the grating pitch p of the hologram element if the wavelength λ of the light used for the incident light beam is determined.

  Further, as shown in FIGS. 1 and 2, since the divided light beams are generated by two diffractions, the light intensity of each divided light beam can be set by the diffraction efficiency of each hologram element.

In general, the diffraction efficiency of a hologram element depends on the refractive index modulation amount Δn _H generated from the grating periodic structure and the film thickness T of the periodic structure. By optimizing these parameters, the ideal diffraction efficiency can be obtained. Will be obtained. Although the maximum diffraction efficiency that can be theoretically obtained varies depending on the type of hologram used, the volume hologram can obtain very high diffraction efficiency (theoretical value: 100%), Bragg diffraction conditions (nλ = psinθ; n is an integer, By setting the incident angle satisfying the wavelength of light used, λ is the diffraction angle, and p is the pitch) and the inclination φ of the grating, the efficiency of the diffracted light of a specific order (especially + 1st order or -1st order) can be set is there.

That is, in FIGS. 1 and 2, the first hologram element diffracted from the incident light beam is set by setting the grating inclinations φ ₁ and φ ₂ of the first hologram element and the second hologram element to be the same (satisfying the Bragg diffraction condition). Diffracted polarized light can be re-diffracted with high efficiency into second diffracted polarized light that is parallel to the incident optical axis. Similarly, by setting the grating tilts φ ₃ and φ ₄ of the third hologram element and the fourth hologram element to be the same (satisfying the Bragg diffraction condition), the first transmitted straight light (the incident light flux and the optical axis are The third diffracted polarized light diffracted from the same) can be re-diffracted with high efficiency into the fourth diffracted polarized light that is parallel to the optical axis of the first transmitted straight light (the incident light beam has the same optical axis) as the incident light. A split light beam that is parallel to the axis and highly efficient can be generated. As described above, in this embodiment, each of the light beams divided into the 0th-order beam and the 1st-order beam by the first hologram element uses two hologram elements that are substantially the same as the first hologram element, The direction of the periodic structure of these two hologram elements is antisymmetric with respect to the first hologram element, and the primary light beam has substantially the same hologram element as the first hologram as the direction of the periodic structure of the first hologram element. It is the structure arrange | positioned substantially the same.

Second Embodiment
Next, a second embodiment of the light beam splitting element of the present invention will be described with reference to FIG.

  In FIG. 1, the grating pitches and the grating inclinations of the first to second hologram elements and the third to fourth hologram elements are schematically shown as being substantially the same, but in this embodiment, FIG. As shown in FIG. 3, the first and second hologram elements and the third to fourth hologram elements have different pitches and inclinations. In this embodiment, the hologram elements are arranged so that the first and second light beams are separated (for example, symmetrically arranged) on the right side and the left side with respect to the incident optical axis.

  Thus, in the present embodiment, the first to second hologram elements and the third to fourth hologram elements are configured so that the grating pitch and the grating inclination are different. In the present embodiment, the grating tilts of the third to fourth hologram elements on the 0th-order beam side separated by the first hologram element into the 0th-order beam and the first-order beam and the first to second hologram elements are They are arranged in the opposite direction. Each split light beam in the present embodiment is split in the same manner as described in the first embodiment.

<Third Embodiment>
Next, a third embodiment of the light beam splitter according to the present invention will be described with reference to FIG.

  As shown in FIG. 5, in this embodiment, the first to second hologram elements and the third to fourth hologram elements have different pitches and tilts, and are separated by the first hologram elements. The transmitted light and the diffracted light are made to be on the same side (right side or left side with respect to the incident light) with respect to the incident light, and the divided first light beam and the divided second light beam are emitted.

  As described above, in the light beam splitting element configured by arranging the first to fourth hologram elements in multiple stages, when splitting the incident light beam, by appropriately setting the diffraction angle and the arrangement interval of each hologram element, The optical axis, optical path length, and light intensity of the divided light beam can be set. In particular, when the arrangement shown in FIGS. 1 to 2 is adopted, the grating pitch p and the grating inclination φ of the first hologram element and the second hologram element are made substantially the same, and the third hologram element and the fourth hologram element By adopting a configuration in which the grating pitch p and the grating tilt φ of the hologram element are substantially the same, the optical path length is the same on the plane parallel to the optical axis of the incident light beam and perpendicular to the optical axis (xy plane). It is possible to generate a split beam with high efficiency and the same light intensity. Unlike the second embodiment, the third embodiment shows an example using a periodic structure in which the grating directions of the first to fourth hologram elements are the same. However, this is an example in which the pitches of the first to second hologram elements and the third to fourth hologram elements are different. Therefore, the 0th-order light beam and the 1st-order light beam emitted from the first hologram element are then diffracted to become the divided first light beam and the divided second light beam of the emitted light, but are emitted substantially parallel to the incident light beam. The emission conditions are not symmetrical with respect to the incident light beam.

  In the above-described second to third embodiments, the first and second hologram elements and the third and fourth hologram elements have the same pitch, and in both embodiments, the first and second hologram elements have the same pitch. The pitch <the pitch of the third and fourth hologram elements (that is, the pitch of the third and fourth hologram elements is larger than the pitch of the first and second hologram elements) The reverse relationship (pitch of the first and second hologram elements> pitch of the third and fourth hologram elements) may be used. However, as shown in the Bragg reflection condition as described above, the smaller the pitch, the larger the diffraction angle. Therefore, the configuration (arrangement) as shown in FIGS. This is preferable in that the thickness can be made thinner. Note that the configuration in which the hologram element itself is arranged with the tilt angle φ in the opposite direction is equivalent to the arrangement in which the hologram element itself is arranged in the spatially opposite direction. In the present invention, both technical ideas are Used to mean including. Alternatively, holograms having the same pitch but different θ and φ are included in the meaning of substantially the same hologram in the present invention. However, in the present invention, these may be excluded in a narrow sense. This is because, when these θ, φ, etc. are clearly different, path alignment becomes complicated, or the possibility that the thinning of the light beam splitting element is extremely hindered increases. The specific range such as how much of these is permissible is appropriately determined depending on the use condition or application of the light beam splitting element.

<Fourth embodiment>
A schematic configuration showing another example of the light beam splitting element of the present invention is shown in FIGS.

  The light beam splitting element of the present invention is configured by arranging the first to fourth hologram elements in multiple stages, and has the first hologram element on the light incident side. For example, the second hologram element and the third hologram The elements are arranged in the order of the fourth hologram element. As described above, the grating pitch p and the grating inclination φ of the first hologram element and the second hologram element are made the same, and the grating pitch p and the grating inclination φ of the third hologram element and the fourth hologram element are set to be the same. By making the same, it becomes possible to generate a high-efficiency split two-beam with the same optical path length and the same light intensity on a plane (xy plane) parallel to the optical axis of the incident light flux and perpendicular to the optical axis. Furthermore, when such an arrangement is adopted, the distance A′-B ′ between the two split light beams can be narrowed. Even in such a case, the influence of interference due to the arrangement of the second hologram element and the third hologram element. Therefore, the degree of freedom in element layout design can be expanded. In the first embodiment, the first hologram element, the third hologram element, the second hologram element, and the fourth hologram element are arranged in this order with respect to the incident light beam. It arrange | positions in order of the 1st-4th hologram element with respect to the light beam. In this embodiment having such an arrangement, interference between elements can be further suppressed, and the degree of freedom can be increased in the arrangement design in the element arrangement.

<Fifth Embodiment>
A schematic configuration of another embodiment (fifth embodiment) of the light beam splitting element of the present invention is shown in FIGS. The light beam splitting element of this embodiment is configured by arranging first to fourth hologram elements in multiple stages, and from the light incident side, the first hologram element, the second hologram element, and the third hologram element (both holograms). Both elements are arranged in the order of the fourth hologram element in the order of the distance from the first hologram element being substantially the same. As described above, the grating pitch p and the grating inclination φ of the first hologram element and the second hologram element are substantially the same, and the grating pitch p and the grating inclination φ of the third hologram element and the fourth hologram element are the same. Are substantially the same, it is possible to generate a highly efficient split two-beam with the same optical path length and the same light intensity on a plane (xy plane) parallel to the optical axis of the incident light beam and perpendicular to the optical axis. Further, with such an arrangement, since the second hologram element and the third hologram element are arranged in parallel in a horizontal row, as shown in FIG. 9, the thickness in the optical axis direction ( (Spacing) A-B can be reduced and the light beam splitting element can be thinned.

<Method for forming periodic structure>
In each embodiment of the present invention, as long as the grating pitch and the grating inclination can be set as the hologram element used for the light beam splitting element having the above-described configuration, as shown in FIGS. A periodic structure composed of regions (see FIG. 10), a periodic structure composed of regions exhibiting different optical anisotropy (see FIG. 11), or a periodic structure composed of regions exhibiting optical anisotropy and regions exhibiting optical isotropy. The structure which has (refer FIG. 12) can be used.

  For example, the periodic structure used in the present embodiment is formed by forming a grating groove in an isotropic medium (a medium whose refractive index can be expressed by a real number) or a birefringent medium (a medium having a complex refractive index) and then forming the groove. In addition, a combination of periodic structures formed by embedding an isotropic medium or a birefringent medium different from these groove-formed bodies is possible. Further, the periodic structure may be a periodic structure in which air is used as an isotropic region in the lattice grooves. In other words, a lattice groove having a periodic structure can be formed by using an isotropic medium or a birefringent medium as a base material and using photolithography, etching, other cutting or molding techniques. The grating grooves are embedded with other materials having different refractive indexes, or air under a vacuum including a reduced pressure environment and under normal pressure is also included as a material having different refractive indexes. As a method for forming the periodic structure, a general mask exposure method (wet method, dry method) using a stepper on a hologram recording material, a direct writing method using an electron beam, a direct writing method using a laser beam, a two-beam interference exposure method And so on. As a method of forming a hologram recording photosensitive material, a general coating method can be applied, and a coating film can be formed by a coating method such as spin coating or dipping on a single substrate, or a pair of substrates can be used. For example, a method of inserting between the substrates using a capillary phenomenon or a vacuum injection method to a certain cell can be used. Further, an ODF (One Drop Fill) method in which a single substrate is further bonded and the material is narrowed between a pair of substrates after the material is dropped onto the single substrate can be applied.

As an isotropic medium for forming these periodic structures, for example, a transparent resin such as a photopolymer (after curing), an optical glass material such as quartz, BK7, or the like can be used. Well, it is not limited to these. As the birefringent medium, calcite (calcite), CdS, YVO ₄ , TeO ₂ , MgF ₂ , crystalline quartz, α-BBO, lithium niobate crystal, tantalum niobate crystal, titanium oxide crystal, polymer birefringent film ( Polymer film), liquid crystal, and the like can be used.

As a (hologram) recording material used when forming a periodic structure using a periodic structure forming method, the following general photosensitive materials can be used. For example, dichromated gelatin, photochromic material, photothermoplastic, electro-optic crystal (eg, ferroelectric oxide: LiNbO ₃ , BaTiO ₃ crystal, etc.), photoresist, photopolymer, polymer liquid crystal, polymer dispersed liquid crystal, etc. There is.

Particularly in the present invention, a highly versatile photopolymer (before curing (before polymerization)) or a photoresist material (particularly positive type) can record a refractive index modulation type hologram (form a hologram). A diffraction efficiency is obtained, and a hologram with low granularity, high resolution, and low noise (low SN ratio) is obtained. In addition, it is possible to select a wide range of exposure sensitivity and photosensitive wavelength band, and there is a degree of freedom with respect to the range of selection such as film thickness and size. Such photosensitive materials (especially liquid materials) such as photopolymers are composed of a wide variety of materials and can be roughly classified into photocrosslinking types and photopolymerization types. Some photopolymerization types require development and others do not. Materials that do not require a development step can be classified into (a) a polymer and a monomer, (b) a monomer and a monomer (two or more monomers), and (c) an inactive component (low molecule) and a monomer. Among these, the components (a) and (c) are selected so that a large difference in refractive index occurs between the monomer polymerization material and the polymer or low molecular weight compound. (B) is composed of two or more types of monomers (including prepolymers such as oligomers) that form a periodic structure having a different refractive index after exposure. For example, I.I. Two or more monomers having different photopolymerizabilities, II. Photopolymerizable and thermally polymerizable monomers III. Combinations such as photo radical polymerizable monomers and photo cationic polymerizable monomers (different photo polymerization modes) are possible.

  In the case of a refractive index modulation type hologram having a high diffraction efficiency, the optimum film thickness is reduced when the difference in refractive index modulation of the periodic structure in the recorded hologram region (that is, after photopolymerization by exposure) is large. (Thinning) is also possible. Accordingly, the change in diffraction efficiency depending on the wavelength variation and the incident angle can be reduced. That is, it is possible to realize a hologram (periodic structure) having a wide tolerance range with respect to wavelength variation and incident angle of high diffraction efficiency characteristics. Photosensitive materials that can increase the difference in refractive index modulation of the periodic structure include polymer birefringent materials exhibiting birefringence, polymer liquid crystals, and polymer dispersed liquid crystals.

  A polymer birefringent film is a polymer film having birefringence by stretching a polymer film and orienting polymer chains, and can be easily mass-produced by a stamper etc. There is an advantage that an element can be manufactured. Examples of the polymer material for the stretched polymer film include, but are not limited to, polyolefin, polyacrylate, polycarbonate (PC), polyvinyl alcohol (PVA), polymethyl methacrylate (PMMA), polystyrene, and the like. .

<Periodic structure element having liquid crystal phase>
As an element having a periodic structure (periodic structure element) used in the light beam splitting element of the present invention, a polymer liquid crystal and a polymer-dispersed liquid crystal are a polymerizable liquid crystal or a non-polymerizable liquid crystal. A periodic structure element having a periodic structure can also be prepared using a composition comprising a prepolymer such as a polymerizable monomer or oligomer and a photopolymerization initiator (one type or a combination of two or more types). As the polymerizable liquid crystal that can be used in such a composition, a liquid crystal acrylate monomer or the like can be used, and as the non-polymerizable liquid crystal, a general liquid crystal having refractive index anisotropy can be used. The phase structure may be any of nematic, cholesteric, and smectic types. In addition, as a prepolymer used for the said composition, prepolymers, such as a photopolymerization, a photocrosslinkable monomer, an oligomer, and mixtures thereof can be used.

  In addition to the above, a photosensitizer, a thermal polymerization inhibitor (such as MEHQ), and a plasticizer may be added. A light beam splitting element having a lattice-like periodic structure can be obtained by applying a composition comprising these on a substrate or by inserting between the substrates for exposure.

  A known material can be used as a photopolymerization initiator for curing by such exposure, and the addition amount depends on the absorbance of each material (initiator) with respect to the wavelength of light to be irradiated. It is adjusted as appropriate according to the exposure conditions.

  The composition comprising the above-described photosensitive material forms a periodic structure in which the refractive index distribution varies depending on the polarization direction (the amount of refractive index modulation in the periodic structure varies depending on the polarization direction) by appropriately setting the exposure conditions. Can do. Examples of compositions include holographic polymer dispersed liquid crystal (HPDLC) in which a non-polymerizable liquid crystal and a photopolymerization initiator are dispersed in a polymer monomer, or a mixture of a polymerizable liquid crystal and a photopolymerization initiator. There is a material for a beam splitting element such as a photo-polymerized liquid crystal (PPLC).

  The case where an interference fringe is exposed using the above-described composition will be described. FIG. 13 shows a cross-sectional configuration of HPDLC before interference exposure. 1 shows a configuration in which a composition in which a non-polymerizable liquid crystal molecule, a polymerizable monomer or prepolymer, and a photopolymerization initiator (not shown) are uniformly mixed is sandwiched between two transparent substrates. FIG. 14 schematically shows a process of forming a hologram by phase separation as shown in FIG. 13. The monomer moves in the bright part of the interference fringe (phase separation between the polymer and the liquid crystal) and cures, and the dark part of the interference fringe Remains in the liquid crystal and is pulled by the polymer cured in the bright part, and the liquid crystal is oriented in a specific direction. Because of this orientation, one of the incident polarized light beams orthogonal to each other transmits almost no refractive index change. In the polarization direction orthogonal to this, the liquid crystal is aligned and coincides with the direction in which the refractive index is large, so that the incident light is diffracted with a periodic refractive index change. Thus, HPDLC functions as a polarizing diffraction grating. In PPLC, a liquid crystal having a photopolymerizable sensitive group is sealed between a transparent electrode (ITO) and a substrate having an alignment layer for aligning liquid crystal to horizontally align the liquid crystal. When the interference fringes are exposed to this, liquid crystal molecules are polymerized and cured in the bright portions of the fringes. On the other hand, the dark portion of the stripe remains without the liquid crystal molecules being cured. Next, light is irradiated while applying a voltage between the transparent electrodes sandwiching the liquid crystal layer. At this time, the liquid crystal in the dark portion is oriented in the direction perpendicular to the substrate by applying a voltage and cured by light. As described above, the alignment of the liquid crystal has a horizontal / vertical periodic structure corresponding to the bright and dark interference fringes. When polarized light orthogonal to the diffraction grating recorded in this way is incident, in one polarization direction (coincident with the minor axis direction of the horizontally aligned liquid crystal molecules), no change in refractive index is felt even with horizontal / vertical alignment. In the direction orthogonal to this, the incident light almost diffracts in the direction perpendicular to this, feeling the change in the refractive index due to the horizontal / vertical alignment in line with the long axis direction of the horizontally aligned liquid crystal molecules. As described above, a polarization hologram having polarization selectivity can be produced by phase separation accompanying the polymerization reaction of the composition material, or a change in orientation due to the polymerization reaction and an external field.

  FIG. 15 shows a schematic configuration of a cross section of an HPDLC (polarization hologram) element. In the polarization hologram element, a region showing optical anisotropy (birefringence) and a region showing optical isotropy are periodically formed between a pair of substrates. As a functional operation of such a hologram element, for example, as shown in FIG. 16, the direction of polarization incident on the element is s-polarized light (here, it is assumed to be perpendicular to the periodic array direction which is the direction perpendicular to the paper surface), and isotropic region When the refractive index n and the refractive index of one of the birefringent regions (real refractive index (real part of refractive index)) no are n = no, the light is transmitted as it is. Further, the incident polarization direction is p-polarized light (here, parallel to the periodic array direction which is the left-right direction on the paper surface), and the refractive index n of the isotropic region and the other refractive index ne (imaginary) of the birefringent region. When the refractive index (imaginary part of the refractive index) is n ≠ ne, the light is diffracted. Thus, an element having a birefringence has a function of selecting transmission and diffraction depending on the polarization direction of incident light. In FIG. 16, the p-polarized light is diffracted and the s-polarized light is transmitted. However, the p-polarized light may be transmitted and the s-polarized light may be diffracted depending on the refractive index of the periodic structure.

  FIG. 15 shows a configuration in which a periodic structure of an optically anisotropic region and an optically isotropic region is sandwiched between a pair of substrates. However, the present invention is not limited to this. For example, these periodic structures are formed on a substrate. May be formed (for example, an element in which one surface is in contact with the substrate and the other surface is in contact with the outside), or may be an element composed of only a periodic structure (no substrate).

Here, the polarization hologram elements shown in FIGS. 15 and 16 are volume type refractive index modulation hologram elements. As described above, the diffraction efficiency is the product of the refractive index modulation amount Δn _H and the thickness T of the hologram. Depending on Δn _H · T, when the refractive index modulation amount Δn _H in a region showing optical anisotropy and a region showing optical isotropy in a specific polarization direction is constant, the thickness T ( The diffraction efficiency can be appropriately set by setting the same as the film thickness or the cell gap. Φ shown in FIG. 15 is a vector perpendicular to the grating periodic structure, and the relation (45 ° <φ <135 °) is assumed with the periodic structure arrangement surface as a reference (0 °).

  FIG. 17 shows the relationship between the diffraction efficiency and transmittance of a volume type refractive index modulation hologram element and the film thickness. As described above, the volume type refractive index modulation hologram element theoretically has a diffraction efficiency of 100% at maximum, and when the diffraction efficiency and the transmittance are added, it becomes 100% (100% when the diffraction efficiency and the transmittance are added). Become).

Here, when the polarization hologram elements having the same film thickness (cell gap) are arranged in multiple stages as the first hologram element and the second hologram element, and the incident polarization direction is parallel to the arrangement direction of the hologram periodic structure, As shown in FIG. 18, at T ₂ where the film thickness (cell gap) of the element obtains the maximum diffraction efficiency, all incident light is diffracted by the first hologram element and re-diffracted by the second hologram element. That is, the first transmitted straight light is not generated, only the optical axis is shifted, and the light beam is not divided. Further, as shown in FIG. 19, at T ₁ where the film thickness (cell gap) of the element obtains half of the maximum diffraction efficiency, the first hologram element is equally divided into the first transmitted straight light and the first diffracted polarized light. In the second hologram element, since the second diffracted polarized light is evenly divided, the light emitted from the elements arranged in multiple stages becomes three luminous fluxes, and the intensity of these three luminous fluxes varies.

In the present invention, for example, in a configuration in which holograms having different film thicknesses (cell gaps) are arranged in multiple stages as a first hologram element and a second hologram element, the incident polarization direction is parallel to the arrangement direction of the hologram periodic structure, When the film thickness of the hologram element is T ₁ as shown in FIG. 20, the diffraction efficiency is 50% and the transmittance is 50%. When the film thickness of the second hologram element is T ₂ as shown in FIG. 20, the diffraction efficiency is 100% and the transmittance is 0%. That is, the efficiency of the second diffracted polarized light shown in FIG. 20 is 50%, and the efficiency of the first transmitted straight light is 50%, and the light intensity of the two light beams can be evenly divided. Although not shown here, the third hologram element and the fourth hologram element having the same grating pitch and the same grating inclination are appropriately arranged on the optical axis of the first transmitted straight light, and the film thicknesses of both hologram elements (cell Let T ₂ be the gap. In this case, the third and fourth hologram elements have a diffraction efficiency of 100% and a transmission efficiency of 0%, and the intensity and optical path length of the first transmitted straight light can be set through two diffractions.

  From the above, when the first hologram element to the fourth hologram element having different film thicknesses (cell gaps) are arranged in multiple stages as a configuration of the light beam dividing element, the light beam can be divided into light beams having the same optical path length. By properly setting the film thickness, the strength can be set evenly.

  Next, another embodiment of the light beam splitting element of the present invention will be described.

First, in the configuration in which the hologram elements having the same film thickness (cell gap) as shown in FIG. 18 are arranged in multiple stages as described above, the film thickness (cell gap) T ₂ that maximizes the diffraction efficiency is set. Even when the hologram element is used, the light beam is not split when the incident polarization direction is polarized light that is substantially parallel (p-polarized light) to the periodic structure of the hologram element and polarized light that is perpendicular (s-polarized light). For example, as shown in FIG. 21, when the polarization direction parallel to the arrangement direction of the periodic structure is incident, the intensity of the incident light includes substantially no s-polarized component and substantially only the p-polarized component. The transmitted light hardly generates transmitted light related to the s-polarized component, and generates only diffracted light (polarized component 1) related to the p-polarized component.

  However, when the same incident light is incident with the polarization direction slightly inclined from the direction parallel to the arrangement direction of the periodic structure as shown in FIG. 22, the intensity of the incident light is separated into the s-polarized component and the p-polarized component. The p-polarized light component is larger than the s-polarized light component, the diffracted light related to the p-polarized light is emitted larger, and a small amount of transmitted light related to the s-polarized light is emitted. Further, as shown in FIGS. 23 and 24, when the polarization direction is inclined at 45 ° (or 135 °) with respect to the arrangement direction of the periodic structure, the incident light intensity is equal to the s-polarization component at an equal ratio. This is equivalent to a mixture of p-polarized components, and this mixed incident light is separated by the beam splitting element, and the two split lights, which are the diffracted light related to the p-polarized component and the transmitted light related to the s-polarized component, are emitted equally. Is done.

  As described above, the ratio of the first diffracted polarized light and the first transmitted straight light of the first hologram element depends on the ratio of the light intensity of the s-polarized component and the p-polarized component of the incident light.

  Therefore, even when the film thickness (cell gap) of the first hologram element and the second hologram element is substantially the same as shown in FIG. 18, the intensities of the p-polarized component and the s-polarized component of the incident light The incident polarization direction is set so that the ratio is substantially uniform, and as described above, the incident light beam is divided into two light beams, the polarized light by diffraction of the first hologram element and the straight light by transmission, and polarized by diffraction. Light can be polarized by re-diffraction of the second hologram element, and the traveling direction and light intensity of the divided two light beams can be set. In such a configuration, it is necessary to adjust the setting of the incident polarization direction. However, since the device can be manufactured by a production process under a certain condition so as to have the same film thickness, productivity is improved.

  As shown in FIGS. 22 and 23, when linearly polarized light having a polarization direction different from the arrangement direction of the periodic structure is incident and the intensities of the p-polarized component and the s-polarized component are appropriately adjusted, the p-polarized component in the first hologram element is The first diffracted polarized light is obtained, and the s-polarized light component is the first transmitted straight light. Next, in the second hologram element, the p-polarized component becomes the second diffracted polarized light, the s-polarized component becomes the second transmitted light, and the light beam is split. Here, the setting of the incident polarization direction is performed using a general retardation plate such as a polarizing plate, a Glan-Thompson prism, a Gran Taylor prism, a Glan laser prism, a Wollaston prism, a half-wave plate, a quarter-wave plate, etc. Can be used. Further, when using polarized light such as LD as the light source, it can be set by selecting the polarization direction of the light source (rotating the light source itself).

Although not illustrated in the same manner as described above, the third hologram element and the fourth hologram element having the same grating pitch and the same grating inclination are appropriately arranged on the optical axis of the first transmitted straight light, and the film thicknesses of both hologram elements (cell gap) and T _2. In this case, the diffraction efficiency of the third and fourth hologram elements is 100%, the transmittance is 0%, and the intensity and optical path length of the first transmitted straight light can be set with two diffractions. However, in the above configuration, since the first transmitted straight light has only the s-polarization direction component, the third and fourth hologram elements diffract the s-polarization component different from the first and second hologram elements, and p It is configured to have polarization selectivity that transmits the polarization component. The first and second hologram elements have polarization selectivity that diffracts the s-polarized component and transmits the p-polarized component, and the third and fourth hologram elements diffract the p-polarized component and s-polarized component. It is good also as a structure of the polarization selectivity which permeate | transmits. The difference in polarization selectivity depends on the refractive index modulation amount (or refractive index difference) of the periodic structure. For example, the polarization component of the polarization structure that is desired to be diffracted is large and the polarization component that is desired to be transmitted. When the refractive index modulation amount of the periodic structure is small, and when the refractive index modulation amount of the periodic structure of the polarization component desired to be diffracted is small, the refractive index modulation amount of the periodic structure of the polarization component desired to be transmitted is large. It is desirable to select the case. Such setting of the refractive index modulation amount for the polarization component can be realized by selecting the refractive index of the material forming the periodic structure.

<Sixth Embodiment>
Next, a sixth embodiment of the light beam splitter according to the present invention will be described with reference to FIG.

  As shown in FIG. 24, in the sixth embodiment, the ridge line directions (directions perpendicular to the arrangement direction of the periodic structure) of the gratings of the first and second hologram elements and the third and fourth hologram elements are substantially orthogonal to each other. Arrange. As described above, the polarization direction of the incident light is inclined by approximately 45 ° from the direction parallel to the arrangement direction of the periodic structure. In such a configuration, the polarization selectivity of the first and second hologram elements and the third and fourth hologram elements do not need to be different from the polarization components to be diffracted as described above, and are all hologram elements having the same structure. realizable.

  From the above, first to fourth hologram elements having substantially the same film thickness (cell gap) are arranged in multiple stages as a configuration of the light beam splitting element, and the ratio of the intensity of the p-polarized component and the s-polarized component of the incident light is By setting the incident polarization direction so as to be substantially uniform, it can be divided into light beams having the same optical path length, and by setting the film thickness appropriately, the intensity can be set evenly.

  FIG. 25 shows an ideal relationship between the diffraction efficiency of the light beam splitter and the incident polarization direction when the configuration shown in FIG. 18 is adopted. From FIG. 25, when the incident polarization direction is approximately 45 ° or approximately 135 ° (45 ° + 90 °) with respect to the arrangement direction of the periodic structure, the luminous flux is divided with a split intensity balance of approximately 50%. However, there is no problem even if it is used as a general optical element.

  Further, when a quarter wave plate (quarter λ plate) is used as a phase difference plate to obtain circularly polarized light or elliptically polarized light, the circularly polarized light has p-polarized component and s-polarized light of incident light as shown in FIG. The intensity of the component is set evenly, and the incident light can be divided equally. Even in elliptically polarized light, the ratio of the intensity of the p-polarized component and the s-polarized component can be set by appropriately setting the azimuth angle. In FIG. 26, the circularly polarized light is rotated to the left (left-handed), but the rotation direction may be either left or right. In this way, when circularly polarized light (elliptical polarized light) is incident, the axis may be set with respect to the polarization direction on the light source side, and setting of the polarization direction to the polarization hologram element becomes unnecessary.

  The light beam splitting element of the present invention is divided into a zero-order light beam and a primary light beam by the first periodic structure (first hologram element), and the second periodic structure (second hologram element) is divided into 1 The third periodic structure (third hologram element) diffracts the zeroth order light beam and the fourth periodic structure (fourth hologram element) has the third period described above. The 0th-order light beam diffracted by the structure is diffracted again to form a divided first light beam, which is emitted.

  Hereinafter, although the light beam splitting element of this invention is demonstrated concretely by an Example, this invention is restrained by the following Examples and is not limitedly interpreted.

FIG. 27 is a diagram showing a cellular body for forming a lattice structure constituting a light beam splitting element formed in a cellular shape. As shown in FIG. 27, an antireflection film for blue light and red light is formed on one surface of a 0.7 mm thick glass substrate 1, and each adhesive is mixed with bead spacers having diameters of about 4 μm and 8 μm, respectively. A sheet of glass substrate was bonded together. The adhesive is applied on the surface opposite to the antireflection film forming surface, as shown in the top view of FIG. 27 (b), at the two edges of the substrate (as shown in FIG. 27 (b)). 2 places). The material for forming a lattice structure having a photopolymer resin, crosslinkable liquid crystal, non-crosslinkable liquid crystal, etc. is composed of a mixture of the following materials 1 to 5 from the direction indicated by the arrow in FIG. The composition was injected into the cell by the capillary method while being heated on a hot plate to form composition layers having thicknesses of about 4 μm and 8 μm. In addition, since this composition showed reactivity (light curing reactivity) to light having a shorter wavelength than green, it was handled in a dark room using red light.
1 nematic liquid crystal (Merck Δε> 0) 25 parts by weight 2 urethane prepolymer (manufactured by Kyoeisha Chemical) 75 parts by weight 3 diacrylate (manufactured by Kyoeisha Chemical) 10 parts by weight 4 methacrylate (manufactured by Kyoeisha Chemical) 5 parts by weight 5 bisacylphos Fin oxide photopolymerization initiator (Ciba Geigy) 1 part by weight

  When the above compositions 1 to 5 were injected into the cell, this composition was isotropic at room temperature.

  Next, a two-beam interference exposure system was prepared using a He—Cd laser having a wavelength of 442 nm. The two-beam interference exposure apparatus is shown in FIG.

  As shown in FIG. 28, this two-beam interference exposure apparatus includes an exposure laser apparatus 101 (light source having coherence), a spatial filter including an objective lens 102 and an aperture 103, a collimator lens 104, and a half mirror. 5 and a two-beam interference exposure apparatus composed of mirrors 106a and 106b, a recording material 107 (cell shown in FIG. 27), and a temperature control stage for heating the recording material 107 shown in 108. Yes. As the exposure laser device 101, a krypton ion laser (oscillation wavelength 407 nm), a helium cadmium laser (oscillation wavelength 442 nm), an argon laser (oscillation wavelength 488 or 514 nm), etc. can be used. I just need it. When a single longitudinal mode oscillation laser is used for the exposure laser device, a coherence length is increased and a diffraction grating with less noise can be manufactured. A spatial filter is not always necessary, but noise may be added to the laser beam by an optical element up to the half mirror 105 and the like, which is useful for improving the beam quality. When the laser beam is bisected by the half mirror 105 and beams are superimposed at a predetermined angle by the mirrors 106a and 106b, interference fringes are generated, and the recording material (sample to be exposed) is disposed at the position where the interference fringes are generated. A diffraction grating corresponding to the interference fringe pitch can be produced. Here, the spatial filter 102 + 103 and the collimating lens 104 are disposed in front of the half mirror 105, but may be disposed after each of the mirrors 106a and 106b. Furthermore, by arranging a converging lens (not shown) after the collimating lens, interference exposure using convergent light becomes possible. When interference exposure using convergent light is used, the convergence position when reproducing can be set.

  In this embodiment, the laser light source 101 is divided and enlarged to form parallel light, and interference fringes having a period of about 1 μm are generated corresponding to the interference fringes of two-beam interference. With the cell substrate heated, two-beam interference exposure was performed for about 1 minute to produce a liquid crystal hologram element. At this time, it was set so that the two light beams were incident at an angle of about 7 degrees with respect to one incident optical axis.

  Characteristic evaluation of the liquid crystal hologram element obtained by the exposure was performed by irradiating the manufactured element with linearly polarized semiconductor laser light having a wavelength of 650 nm and rotating the + first-order light at an incident angle of 0 ° perpendicular to the substrate. The 0th-order light and the + 1st-order diffracted light intensity with respect to the folding angle and the incident light intensity were measured. A linearly polarizing plate and a half-wave plate (λ / 2 plate) are placed in the incident optical path, and the polarization direction (p-polarized light, s-polarized light) incident on the element is switched by rotating the optical axis of the half-wave plate by 45 degrees. Possible configuration. At this time, the p-polarized light was in a direction orthogonal to the interference fringes during interference exposure, and the s-polarized light was in the same direction as the interference fringes. The characteristics of liquid crystal hologram elements having film thicknesses of 4 μm and 8 μm are shown below.

Here, the liquid crystal hologram element 1 is a first hologram element, the liquid crystal hologram element 2 is a second hologram element, the liquid crystal hologram element 3 is a third hologram element, and the liquid crystal hologram 4 is a fourth hologram element. As shown in Fig. 4, a beam splitting element was produced by arranging in multiple stages. The incident polarization direction to the element is p-polarized light, the distance L _1-2 , L _3-4 element between the array elements of the first hologram element and the second hologram element, and the third hologram element and the fourth hologram element. The minimum distance at which no interference occurs is about 20 mm. When the light use efficiency of the divided first light beam and the divided second light beam with respect to the incident light of this light beam splitting element was measured, the light use efficiency of the divided first light beam: the divided second light beam was 40.2%: 42.9%. There was a good division. Further, when the light receiving distance AB of the divided light beam was measured at 100 mm and 200 mm, the divided light beam was positioned almost symmetrically with respect to the incident optical axis at both measurement positions, and the distance A′-B ′ between the divided light beams was It was 34 mm. That is, in the light beam splitting element configured as shown in FIG. 2, a split light beam that is parallel to the optical axis of the incident light beam and has the same intensity and optical path length can be generated.

  The same liquid crystal hologram elements 1 to 4 as in the first embodiment are used, and the liquid crystal hologram elements 1 to 4 are arranged in multiple stages as shown in FIG. Was made.

The incident polarization direction to the element is p-polarized light, and the distances L _1-2 and L _3-4 between the array elements of the first hologram element and the second hologram element, and the third hologram element and the fourth hologram element are: The minimum distance at which the element does not interfere was set to about 10 mm. When the light use efficiency of the divided first light beam and the divided second light beam of the light beam splitting element was measured, the light use efficiency of the divided first light beam: the divided second light beam was 40.4%: 42.7%. There was a good division. Further, when the light receiving distance AB of the split light flux was measured at 100 mm and 200 mm, the split light flux was located almost symmetrically with respect to the incident optical axis at both measurement positions, and the split light flux interval A′-B. 'Was 17 mm. That is, in the light beam splitting element having the configuration shown in FIG. 7, it is possible to generate a split light beam that is parallel to the optical axis of the incident light beam and has the same intensity and optical path length. Furthermore, the minimum distance at which the elements do not interfere with each other can be set to about half that of Example 1.

  The liquid crystal hologram elements 1 to 4 similar to those of the first embodiment are used, and the liquid crystal hologram elements 1 to 4 are respectively configured as a first hologram element to a fourth hologram element in a multistage arrangement shown in FIG. An element was produced.

The incident polarization direction to the element is p-polarized light, and the distances L _1-2 and L _3-4 between the array elements of the first hologram element and the second hologram element, and the third hologram element and the fourth hologram element are: The minimum distance at which the element does not interfere was set to about 8 mm. When the light use efficiency of the divided first light beam and the divided second light beam of the light beam splitting element was measured, the light use efficiency of the divided first light beam: the divided second light beam was 41.1%: 42.1%. And could be divided well. Further, when the light receiving distance AB of the split light flux was measured at 100 mm and 200 mm, the split light flux was positioned almost symmetrically with respect to the incident optical axis at both measurement positions, and the split light flux spacing A′-B ′. Was 14 mm. That is, in the light beam splitting element configured as shown in FIG. 9, a split light beam that is parallel to the optical axis of the incident light beam and has the same intensity and optical path length can be generated. Further, the minimum distance at which the element does not interfere can be set smaller than those in Examples 1 and 2, and the light beam splitting element can be thinned.

  A liquid crystal hologram element 1 ′ was produced in the same manner as in Example 1.

  Using the liquid crystal hologram element 1 ′ and the liquid crystal hologram elements 2 to 4, the liquid crystal hologram element 1 ′ is the first hologram element, the liquid crystal hologram element 2 is the second hologram element, and the liquid crystal hologram element 3 is the third hologram element. Then, the liquid crystal hologram 4 was used as a fourth hologram element, and a multi-stage arrangement shown in FIG.

  Here, the first and second hologram elements are set to have the same grating ridge line direction, and the third and fourth hologram elements have the same grating ridge line direction. The lattice ridge line directions of the third and fourth hologram elements were arranged so as to be substantially orthogonal. The incident polarization direction to the element was set to the y direction (in all elements, a direction inclined by 45 ° or 135 ° from the lattice ridge line direction), and the p polarization component and the s polarization component were set to be substantially equal.

  The position of the second hologram element is set to 20 mm in the x direction and −17 mm in the y direction with respect to the optical axis, and the position of the fourth hologram element is 20 mm in the x direction and 17 mm in the y direction with respect to the optical axis. The distance between the array elements of the first hologram element and the second hologram element, and the third hologram element and the fourth hologram element was set such that the hologram elements did not interfere with each other, and was about 20 mm. When the light use efficiency of the divided first light beam and the divided second light beam of the light beam splitting element was measured, the light use efficiency of the divided first light beam: the divided second light beam was 41.8%: 41.5%. It was possible to divide well. Further, when the light receiving distance of the split light flux was measured at 100 mm and 200 mm, the split light flux was located almost symmetrically in the y direction with respect to the position where the incident optical axis was shifted by 20 mm in the x direction at both measurement positions. The spacing was 34 mm. That is, in the light beam splitting element configured as shown in FIG. 24, a split light beam that is parallel to the optical axis of the incident light beam and has the same intensity and optical path length can be generated. Furthermore, since all can be realized using elements having the same film thickness, productivity is improved.

  In a light beam splitting element similar to that in Example 4, the incident polarization direction to the element was made circularly polarized using a λ / 4 plate, and the optical axis and light utilization efficiency characteristics of the split light beam were almost the same as in Example 4. It was. That is, it was possible to split the light beam only by installing the λ / 4 plate without adjusting the polarization direction of the incident light beam.

  As described above, the light beam splitting element of the present invention splits the incident light into the 0th order diffracted light beam and the 1st order diffracted light beam.

  Specifically, the first to fifth embodiments are shown as examples divided in the horizontal direction (H direction) in the drawings, and the sixth embodiment is shown as an example divided in the vertical direction (V direction). Although described, these directions may of course be divided in any arbitrary direction, and are merely prescriptions for explanation. However, in the present invention, the first to fourth periodic structure elements (first hologram element to fourth hologram element) are mounted in place of these directions H, V, or H → V, V → H, and are spatially mounted. It is also possible to divide in the direction specified in the above, and the present invention includes these inventions.

  By combining a plurality of the light beam splitting elements of the present invention, it can be used as a light beam splitting element having various intensity distributions or as a light beam splitting element group for splitting the same intensity into two or more light beams. In addition, since these divisions can be appropriately combined in the vertical direction and the horizontal direction, the light beam dividing element (light beam dividing element group) of the present invention can be used as an equal light beam dividing element into a space. For example, the incident light beam is split into equal intensities in the vertical and horizontal directions (1 / n: n is a positive integer greater than or equal to 2), the polarization direction of each split light beam is set to a specific direction, or is made entirely random Etc., and can be freely adjusted. For example, the outgoing light shown in FIG. 24 is used as an incident light beam, the divided first light beam is divided into two in the horizontal direction (H), and the divided second light beam is divided into two in the vertical direction (V) to obtain respective p-waves. And the intensity of the s-wave component are substantially the same, and the applicability of the light beam splitting element (group) is also excellent.

  Such a light beam splitting element of the present invention is used in a field in which a light beam is split and used, a scanning device, a field in which the number of light source elements such as a light source of an image forming apparatus is limited, a video field or an optical computer element. It can be widely used in the field of using.

It is a figure which shows the structure outline of 1st Embodiment of the light beam splitting element of this invention, (a) is a top view, (b) is a perspective view. 1 is a layout diagram illustrating a schematic configuration of a first embodiment of a light beam splitter according to the present invention. It is a figure which shows the cross-section structure model of the hologram element used for this invention. It is a figure which shows the structure outline of 2nd Embodiment of the light beam splitting element of this invention, (a) is a top view, (b) is a perspective view. It is a figure which shows the structure outline of 3rd Embodiment of the light beam splitting element of this invention, (a) is a top view, (b) is a perspective view. It is a figure which shows the structure outline of 4th Embodiment of the light beam splitting element of this invention, (a) is a top view, (b) is a perspective view. It is an arrangement figure showing the composition outline of a 4th embodiment of the light beam splitting element of the present invention. It is a figure which shows the structure outline of 5th Embodiment of the light beam splitting element of this invention, (a) is a top view, (b) is a perspective view. It is an arrangement drawing showing the outline of composition of a 5th embodiment of a light beam splitting element of the present invention. It is an example of a hologram element used for a light beam splitting element, and is an example of an element having a periodic structure composed of isotropic regions having different refractive indexes. It is an example of a hologram element used for a light beam splitting element, and is an example of an element having a periodic structure composed of regions exhibiting different optical anisotropies. It is an example of a hologram element used for a light beam splitting element, and is an example of an element having a periodic structure including a region showing optical anisotropy and a region showing optical isotropy. It is a figure which shows the cross-sectional structure about HPDLC before interference exposure. It is a figure which shows typically the formation process of the hologram element by phase separation. It is a figure which shows the structure outline of the cross section of a HPDLC (polarization hologram) element. FIG. 16 is a diagram for explaining a functional operation of the hologram element shown in FIG. 15. It is a figure which shows the relationship between the diffraction efficiency of a volume type refractive index modulation hologram element, the transmittance | permeability, and a film thickness. The vertical axis represents efficiency (%), and the horizontal axis represents film thickness. It is explanatory drawing at the time of making the incident polarization direction of a multi-stage arrangement | sequence parallel to the arrangement direction of a hologram periodic structure by using the polarization hologram element which has the same film thickness (cell gap) as a 1st hologram element and a 2nd hologram element. . When polarization hologram elements having the same film thickness (cell gap) are arranged in multiple stages as a first hologram element and a second hologram element, both components in which the incident polarization direction is perpendicular to the arrangement direction of the hologram periodic structure are orthogonal to each other. It is explanatory drawing in the case of including. Explanatory drawing when the incident polarization direction when the first hologram elements and the second hologram elements having different film thicknesses (cell gaps) are arranged in multiple stages includes both components that are orthogonal to and parallel to the arrangement direction of the hologram periodic structure It is. It is explanatory drawing when the polarization direction parallel to the arrangement direction of a periodic structure of the structure which arranged the hologram element which has the same film thickness (cell gap) in multistage is incident. It is explanatory drawing in the case of making it incline a little with a polarization direction from the direction parallel to the arrangement direction of a periodic structure. It is explanatory drawing in the case where it injects with the polarization direction inclined 45 degrees (or 135 degrees) on the basis of the arrangement direction of a periodic structure. It is an example which shows the outline of composition of a 6th embodiment of the present invention, and is an explanatory view in case a polarization hologram element is arranged in multiple stages, and it injects with a polarization direction inclined 45 degrees (or 135 degrees). It is a figure which shows the ideal relationship between the diffraction efficiency of a light beam splitting element at the time of employ | adopting the structure shown in FIG. 18, and an incident polarization direction. It is explanatory drawing at the time of arranging a polarization hologram element in multiple stages and making circularly polarized light (left-handed rotation) enter. It is a figure which shows the cellular body for forming the lattice-like structure which comprises the light beam splitting element formed in the cell form, (a) is the sectional view on the AA 'line shown to the cell top view of (b). (B) is a top view of a cellular body. It is a figure which shows a two-beam interference exposure apparatus schematic structure.

Explanation of symbols

01 incident light beam 1 substrate 1 ′ antireflection film 2 sealant 11 first periodic structure element (first hologram element)
12 Second periodic structure element (second hologram element)
13 Third periodic structure element (third hologram element)
14 Fourth periodic structure element (fourth hologram element)
21 First-order diffracted light beam (first diffracted polarized light)
22 Split second light beam (second diffracted polarized light)
23 Diffracted light of the 0th order diffracted light beam (third diffracted polarized light)
24 split first light beam (fourth diffracted polarized light)
31 0th order diffracted light beam (first transmitted straight light)
40 Optical axis of incident light beam 51 First refractive index medium 52 Second refractive index medium 101 Laser apparatus for exposure (light source having coherence)
102 Objective lens 103 Aperture 104 Collimating lens 105 Half mirror 106a, 106b Mirror 107 Recording material (recording material cell)
108 Temperature control stage

Claims (18)

A light beam splitting element comprising a periodic structure element having a periodic structure in which two layers having different refractive indexes of at least one of an optically isotropic region or an optically anisotropic region are repeated,
The beam splitting element is
A first periodic structure element that divides an incident light beam into a transmitted light beam of zero-order light and a diffracted light beam of primary light;
A second periodic structure element that diffracts the diffracted light beam again to form a second divided light beam;
A third periodic structure element that diffracts the transmitted light beam;
A fourth periodic structure that diffracts the light beam from the third periodic structure element into a first light beam;
The optical axis of the split light is adjusted by transmission and diffraction of the first to fourth periodic structure elements,
In the adjustment, each split light of the emitted light is emitted substantially in parallel,
In the light beam splitting element, the adjustment is performed such that the optical path difference lengths of the split lights of the outgoing light are substantially the same . According to claim 1, beam splitting device and each pitch p of the periodic structure of the first to fourth periodic structure elements and the grating inclination φ is characterized substantially the same der Rukoto. According to claim 1 or 2, the gap between the first to fourth periodic structure elements periodic substrate film is a thickness of the structure of the light-flux splitter to the same or different, wherein Rukoto. 4. The first to fourth periodic structure elements according to claim 1, wherein the first to fourth periodic structure elements have a periodic structure, and the inter-substrate gap, which is the film thickness of the elements, is substantially constant. The periodic structure is formed in a direction substantially orthogonal to the periodic structure element in which the transmitted light divided into two light beams by diffraction and transmission is diffracted,
Polarized light in a direction substantially parallel to the arrangement direction of the periodic structure is p-polarized light,
When polarized light in a direction substantially perpendicular to the arrangement direction of the periodic structure is s-polarized light,
The light beam splitting element, wherein the light beam incident on the periodic structure element is split into a p-polarized component and an s-polarized component and emitted with substantially equal intensity . In claim 4, the light-flux splitter polarization of the light beam the incident, wherein the linear polarization der Rukoto. 6. The polarization direction of the incident light beam according to claim 5, with reference to the arrangement direction of the periodic structure of the periodic structure element as a reference, approximately + 45 ° or substantially about the arrangement direction of the periodic structure of the periodic structure element. beam splitting element characterized that you have facing -45 °. In claim 4, the light-flux splitter polarization of the light beam the incident and said circular or elliptical polarization der Rukoto. The pitch p and the lattice inclination φ of the first and second periodic structure elements or the third and fourth periodic structure elements are substantially the same and the lattice inclination φ is arranged in the same direction, The light beam splitting element according to any one of claims 1 to 7, wherein a lattice inclination φ between the periodic structure element and the third periodic structure element is arranged in the opposite direction or the same direction . Each pitch p and each grating inclination φ of the first and second periodic structure elements or the third and fourth periodic structure elements are substantially the same, and the first and second periodic structure elements, The light beam splitting element according to any one of claims 1 to 8, wherein the third and fourth periodic structure elements are arranged substantially in parallel . The periodic structure of the periodic structure element according to any one of claims 1 to 9, wherein a composition composed of a non-polymerizable liquid crystal and a polymerizable monomer or a prepolymer is held between a pair of transparent substrates. A polymer-dispersed liquid crystal hologram element in which a periodic phase separation structure of a layer mainly composed of a polymer and a layer mainly composed of a non-polymerizable liquid crystal is formed by multi-beam interference exposure with a composition having two or more beams. A light beam splitting element. 10. The method according to claim 1, wherein at least one region of the periodic structure of the periodic structure element is a region exhibiting optical anisotropy, and the region is made of a material having birefringence. Characteristic light beam splitting element. The light beam splitting element according to claim 1, wherein the region showing the optical anisotropy of the periodic structure element includes a non-polymerizable liquid crystal or a polymerizable liquid crystal . 13. The light beam splitting element according to claim 1, wherein a region exhibiting optical isotropy having a different refractive index of the periodic structure element is obtained from a photosensitive polymer . In Claim 8, lattice inclination (phi ) of said 1st periodic structure element and said 3rd periodic structure element is reverse direction, and at least any one of said 2nd periodic structure element and said 3rd periodic structure element beam splitting element but characterized by Rukoto disposed in the next stage of the first periodic structure elements. According to claim 14, wherein the second periodic structure elements and said third periodic structure element which is arranged in parallel to the next stage of the first periodic structure element beam splitting element characterized Rukoto. 16. The light beam splitting element according to claim 1, wherein the split first light beam and the split second light beam are split in a vertical direction or a horizontal direction . A method of splitting one light beam using the light beam splitting element according to claim 1 ,
The light beam splitting method, wherein the outgoing light beam split by the method is substantially parallel to the incident light beam. A method of splitting one light beam using the light beam splitting element according to claim 1 ,
Beam splitting method the divided emitted split light, characterized in Rukoto to have a substantially same light intensity.

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