JP5040847B2 - Optical element, liquid crystal device, display device - Google Patents

Description

  The present invention relates to an optical element having a polarization separation function, and a liquid crystal device and a display device using the optical element.

  As one of optical elements having a polarization separation function, a wire grid type polarization separation element is known. This wire grid type polarization separation element is made by arranging a lot of fine wires (for example, aluminum fine wires) on the surface of a glass substrate or the like, and the mutual interval (period) of each wire is set shorter than the wavelength of light. Is done. The wire grid type polarization separation element is characterized by being excellent in light resistance since the constituent material is inorganic in addition to high polarization separation performance. For this reason, in various optical systems, it has been studied to substitute for a conventional polarization separation element made of a polymer. One application example of the wire grid type polarization separation element is a projection display device such as a liquid crystal projector.

In the above-described projection display device, the wire grid type polarization separation element is disposed on at least one of the front surface and the back surface of the liquid crystal panel (liquid crystal light valve). In the projection display device, light having a relatively high intensity is input to the liquid crystal panel in order to improve the brightness of a displayed image. However, in principle, the wire grid type polarization separation element transmits almost all TM polarized components of incident light, but reflects almost all TE polarized components. Therefore, the reflected light (TE polarized components) is again applied to the liquid crystal panel. There is concern that the operation of the liquid crystal panel may become unstable due to incidence. Further, such a concern is not limited to the projection display device, but can be commonly applied to various optical devices configured using a wire grid type polarization separation element. This is because it is not preferable that unnecessary reflected light is generated on the optical path in any optical device.
JP 2002-372749 A

A specific aspect of the present invention has an object to provide an optical element capable of suppressing adverse effects due to reflected light.
It is another object of a specific aspect of the present invention to provide a high-performance liquid crystal device configured using the above-described optical element.
Another specific object of the present invention is to provide a high-performance display device configured using the above-described optical element.

  An optical element according to the present invention is an optical element having a function of polarizing and separating incident light, and (a) a substrate that is transparent to the incident light, and (b) a cross-sectional shape that is rectangular and alternately arranged. A diffractive structure portion provided on one surface side of the substrate, and (c) a plurality of fine lines extending in one direction, the diffractive structure on the one surface side of the substrate. A grid portion provided along the upper surface of the portion, the wavelength of the incident light is λ, the distance between the plurality of thin wires is d, the distance between the plurality of protrusions is δ, and the constituent material of the substrate These parameters satisfy the relationship of d <λ and λ / n <δ ≦ λ.

  In this optical element, one polarization component of incident light is reflected by the action of the grid portion, and the other polarization component is transmitted. Further, the reflected polarization component (reflected light) is diffracted at a sufficiently large angle by the action of the diffraction structure portion. When the above-described parameter relationship is satisfied, the diffracted reflected light is totally reflected at the interface between the other surface of the substrate and the surrounding medium (for example, air), propagates in the substrate, and reaches the edge of the substrate. Head. Therefore, when the optical element according to the present invention is used in a desired optical system, most of the reflected light generated by the grid portion does not return to the front stage side of the optical path, and adverse effects due to unnecessary reflected light are suppressed. .

  Preferably, in the optical element, a step between the concave portion and the convex portion of the diffractive structure portion is set to (2m + 1) λ / 4n. Here, m is an integer greater than or equal to 0 (0, 1, 2,...). λ is the wavelength of the incident light as described above, and n is the refractive index of the constituent material of the substrate.

  By satisfying this condition, it is possible to sufficiently enhance the diffraction effect of the reflected light in the diffraction structure portion of the optical element and sufficiently suppress the diffraction effect of the transmitted light (transmitted polarization component). As a result, most of the transmitted light amount is a non-diffracting component, so that the light utilization efficiency can be further increased.

  In the optical element, for example, the extending directions of the plurality of concave portions and the plurality of convex portions of the diffraction structure portion and the extending directions of the plurality of thin lines of the grid portion are substantially parallel. be able to. The extending directions of the plurality of concave portions and the plurality of convex portions of the diffractive structure portion may intersect with the extending directions of the plurality of fine lines of the grid portion.

  When each concave part and convex part intersect with each thin line, it becomes easier to form a thin line near the step between each concave part and each convex part. The intersecting angle is arbitrary, and can be set to 45 ° and multiples of 90 °, 135 °, etc., for example.

  The above-described optical element preferably further includes a light attenuating portion disposed on the end side of the substrate. The light attenuating unit may be disposed in contact with the substrate end or may be disposed at a position separated from the substrate end. The light attenuating part is, for example, a dark resin film or an antireflection film.

  Thereby, the intensity of light confined in the optical element can be reduced by absorbing the reflected light that has propagated through the substrate and reached the edge of the substrate, or by letting it escape to the outside.

In the optical element described above, the thickness of the substrate in the normal direction of the one surface is T, the width of the substrate in the direction in which the first-order diffracted light diffracted by the diffraction structure portion travels on the one surface as viewed in plan is W, and the diffraction It is also preferable that these parameters satisfy the relationship of θ> tan ⁻¹ (W / 2T), where θ is a diffraction angle formed by the first-order diffracted light diffracted by the structure portion and the normal direction.

  Thus, first-order or higher-order diffracted light of the reflected light in the diffractive structure part is reflected and diffracted on the other surface of the substrate, and then enters the end surface in the width direction of the substrate. Therefore, the light reflected and diffracted on the other surface does not directly enter one surface and is not re-diffracted by the diffractive structure. Therefore, the re-diffracted light does not return to the front stage side of the optical path, and adverse effects due to the light returning to the front stage side are suppressed. As the width W of the substrate, for example, when the recess has a groove shape, the width W of the substrate in the direction orthogonal to the extending direction of the recess may be defined. In addition, for example, when the concave portion has a substantially rectangular hollow shape in plan view and there are a plurality of directions in which the first-order diffracted light travels on one surface in plan view, the width of the substrate is the direction in which the width of the substrate is minimized in the plurality of directions. W may be defined.

The optical element described above preferably includes a planarizing layer for planarizing the plurality of concave portions and the plurality of convex portions on one surface side of the substrate, and the refractive index of the planarizing layer and the refractive index of the substrate are preferably substantially the same. .
As a result, the transmitted light is hardly diffracted by the diffractive structure, and most of the transmitted light amount is a non-diffracted component, so that it is possible to further improve the light utilization efficiency.

  The liquid crystal device according to the present invention is a transmissive liquid crystal device that modulates and emits light incident from a light source, and includes (a) a first substrate disposed on the incident side, and (b) the first substrate disposed on the emission side. A second substrate disposed opposite to the first substrate; (c) a liquid crystal layer provided between the first substrate and the second substrate; and (d) an opposite side of the second substrate to the liquid crystal layer. And an optical element having a polarization separation function, and the optical element according to the present invention is used as the optical element.

  In this liquid crystal device, light emitted from the liquid crystal layer is polarized and separated by an optical element, and light transmitted through the optical element is used for image display and the like. Moreover, the light incident on one surface of the optical element is reflected and diffracted at a sufficiently large angle by the action of the diffraction structure portion. The diffracted reflected light is totally reflected at the interface between the substrate and the gap of the optical element, propagates through the substrate, and travels toward the end of the substrate. Therefore, most of the reflected light generated by the grid portion does not enter the second substrate or the liquid crystal layer again, and adverse effects due to unnecessary reflected light are suppressed. In addition, since the optical element and the second substrate are bonded via a gap, adverse effects due to the heat of the optical element being transferred to the second substrate side are also suppressed.

In the liquid crystal device, the second substrate and the optical element are joined together via a sealing material that annularly surrounds the gap, and the gap is sealed by the second substrate, the optical element, and the sealing material. It is preferable that
This prevents dust from entering the gap between the second substrate and the optical element. Therefore, it is not necessary to attach dust-proof glass that prevents dust from entering the image light as a shadow, and the liquid crystal device can be downsized.

  A projection display device according to the present invention includes (a) a light source such as a mercury lamp, (b) a first optical element having a polarization separation function and disposed on the rear stage side of the light source, and (c) A liquid crystal light valve having a function of modulating incident light and disposed on the rear stage side of the first optical element; and (d) a liquid crystal light valve having a polarization separation function and disposed on the rear stage side of the liquid crystal light valve. 2 and (e) a projection lens disposed on the rear side of the second optical element, and the optical element according to the present invention is used as at least the second optical element. At this time, in the optical element, one surface provided with the diffraction structure portion and the grid portion is arranged on the rear side.

  By using the optical element as at least the second optical element, it is possible to prevent the reflected light from the grid portion from entering the liquid crystal light valve. Thereby, the stable operation of the liquid crystal light valve is not hindered by the incidence of unnecessary light. Specifically, for example, when a thin film transistor is included in the liquid crystal light valve, there may be inconveniences such as causing a malfunction of the thin film transistor when unnecessary light is incident, thereby reducing display quality. According to the display device of the present invention, such inconvenience is avoided. Moreover, since it uses as a polarization separation element by the grid part which consists of a some metal fine wire, the display apparatus excellent in light resistance is realizable. Therefore, according to the present invention, a high-performance display device can be provided.

  In the above display device, it is also preferable that the optical element according to the present invention is used as the first optical element. At this time, in the optical element, one surface provided with the diffraction structure portion and the grid portion is arranged on the rear side.

  By using the optical element as the first optical element, it is possible to avoid the reflected light from the grid portion from returning to the previous stage (for example, the light source). Moreover, since it uses as a polarization separation element by the grid part which consists of a some metal fine wire, the display apparatus excellent in light resistance is realizable. Therefore, it is possible to provide a display device with higher performance and higher quality.

  Preferably, the display device further includes a field lens disposed on the rear side of the second optical element and on the front side of the lens.

  By providing such a field lens, more transmitted diffracted light can be incident on the projection lens. Thereby, the brightness of the display image can be further improved.

  In the display device, the light source may be a laser light source.

  Since the laser light source has a very narrow wavelength range of light, the light controllability by the optical element according to the present invention is further improved. Thereby, the display quality of the display device can be further improved.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each figure, the dimensions and ratios of the constituent elements are appropriately changed from the actual ones in order to make the constituent elements large enough to be recognized on the drawings.

  FIG. 1 is a schematic diagram showing a cross-sectional structure of an optical element according to an embodiment to which the present invention is applied. The optical element 1 according to this embodiment shown in FIG. 1 includes a substrate 2, a diffraction structure portion 3, a grid portion 4, and a light attenuation portion 5. The optical element 1 has a function of polarizing and separating incident light by the action of the grid portion 4.

  The substrate 2 is a substrate that is transparent to the wavelength of incident light. As the substrate 2, for example, a substrate made of an inorganic material such as a glass substrate (quartz substrate) is used. The thickness of the substrate 2 is, for example, about 0.7 mm. A diffractive structure 3 is provided on one surface side of the substrate 2. The other surface of the substrate 2 is a plane as shown in the figure.

  The diffractive structure 3 is provided on one side of the substrate 2. The diffractive structure portion 3 includes a plurality of concave portions 3a and convex portions 3b arranged alternately. In addition, in the figure, the code | symbol is attached | subjected about each one recessed part 3a and the convex part 3b for convenience. As shown in the figure, the diffractive structure part 3 composed of the concave part 3a and the convex part 3b has a rectangular cross section. The shape may have a slight taper. In the present embodiment, the diffractive structure 3 is formed by processing one side of the substrate 2. That is, the substrate 2 and the diffractive structure 3 are integrally formed.

  The grid portion 4 is provided on the one surface side of the substrate 2 and along the upper surface of the diffractive structure portion 3. The grid portion 4 includes a plurality of fine wires (fine wires) 4a extending in one direction. In the figure, only one thin line 4a is provided with a reference for convenience. Each thin wire 4a is a metal film such as aluminum.

  The light attenuating unit 5 is provided at each end of the substrate 2. The light attenuating portion 5 is, for example, a dark resin film. The light attenuating portion 5 is diffracted light that is generated in the diffraction structure portion 3 and totally reflected at the interface between the other surface of the substrate 2 and air. The light attenuating unit 5 absorbs the incident diffracted light or attenuates its intensity. In addition to the case where the light attenuating portion 5 is disposed in contact with each end portion of the substrate 2, the light attenuating portion 5 may be provided at a position separated from each end portion of the substrate 2 as shown in FIG. 2.

  FIG. 3 is a schematic cross-sectional view illustrating another aspect of the optical element. The optical element 1a shown in FIG. 3 has the same configuration as the optical element 1 shown in FIG. 1, and further has an antireflection film 6 on the other surface of the substrate 2. The antireflection film 6 is a dielectric multilayer film, for example. Components other than the antireflection film 6 are denoted by the same reference numerals as those of the optical element 1 in FIG. 1, and description thereof will be omitted. By having the antireflection film 6, it is possible to suppress reflection of a part of the light component incident from the other surface side of the substrate 2.

  FIG. 4 is a schematic cross-sectional view illustrating another aspect of the optical element. The optical element 1b shown in FIG. 4 has the same configuration as the optical element 1 shown in FIG. 1, and an antireflection film made of an AR film or the like is provided as an optical attenuating part 5a at each end of the substrate 2. Yes. Here, a light absorbing member 5b that absorbs light that has passed through the light attenuating portion 5a is provided at a position separated from each end portion. When the antireflection film is provided, the reflectance of light is remarkably reduced at the interface between the end and air, so that the intensity of the light reflected at this interface is attenuated as compared with that before reflection. As a result, the light reflected at the interface of the end portion is remarkably reduced from entering the grid portion 4 again. Further, the light that has passed through the light attenuating portion 5a is absorbed by the light absorbing portion 5b, and this light is prevented from becoming stray light. The light absorbing member 5b may have a cooling means such as a heat radiating plate, so that the heat due to light absorption can be managed and released.

  FIG. 5 is a schematic cross-sectional view illustrating another aspect of the optical element. An optical element 1c shown in FIG. 5 has the same configuration as the optical element 1 shown in FIG. 1, and a planarizing film 3c is provided on the side of the diffraction structure portion 3 of the substrate 2. The flattening film 3c flattens the step between the concave portion 3a and the convex portion 3b, and is provided so as to cover the concave portion 3a, the convex portion 3b, and the fine wire 4a. The planarizing film 3c is formed by depositing SOG (Spin On Glass), polysilazane, or the like using a liquid phase method such as a coating method. The planarizing film 3c has substantially the same refractive index as that of the substrate 2, and light transmitted through the optical element 1b is not affected by the step between the concave portion 3a and the convex portion 3b. As a result, the light transmitted through the optical element 1b is hardly diffracted, so that the light use efficiency can be further increased.

  FIG. 6 is a schematic perspective view showing a part of the grid portion 4 in an enlarged manner. Based on this FIG. 6, the function which the grid part 4 has is demonstrated. In the incident light 80 to the grid portion 4, a component p (TE polarization component) having a polarization axis parallel to the extending direction (major axis direction) of each thin wire 4a is reflected, and is orthogonal to the extending direction of each thin wire 4a. A component s (TM polarization component) having a polarization axis is transmitted. That is, the grid unit 4 has a function (polarization separation function) for separating the incident light 80 into reflected light 80r and transmitted light 80t having different polarization states. In the optical element 1 of the present embodiment, a grid portion 4 that performs such a polarization separation function is provided on one surface side of the substrate 2.

  FIG. 7 is a schematic perspective view showing a part of the diffractive structure 3 in an enlarged manner. As shown in FIG. 7A, the diffractive structure portion 3 has a plurality of concave portions 3a and convex portions 3b extending in one direction (the Y direction shown in the drawing). These concave portions 3a and convex portions 3b have a stripe shape as shown in the figure, and are periodically arranged along the X direction. In addition, each recessed part 3a and the convex part 3b are not limited to the one-dimensional arrangement | sequence as shown to FIG. 7 (A), For example, as shown to FIG. 7 (B), each recessed part 3a and the convex part 3b are two-dimensional. It may be arranged in a shape.

FIG. 8 is a schematic cross-sectional view showing a part of the diffraction structure portion 3 and the grid portion 4 in an enlarged manner. Based on this FIG. 8, the structure of the diffraction structure part 3 and the grid part 4 is demonstrated still in detail. As shown in the figure, the mutual interval (period of the concavo-convex structure) of the convex portions 3b of the diffractive structure portion 3 is δ (nm), the mutual interval (grid cycle) of the fine wires 4a of the grid portion 4 is d (nm), and incident The wavelength of light is λ (nm), the refractive index of the constituent material of the substrate 2 is n, and the refractive index of the air around the substrate 2 is nair (= 1). In the optical element 1 of the present embodiment, the following relationship exists between the wavelength λ of the incident light and the diffraction structure and the grid structure.
d <λ and λ / n <δ ≦ λ (1)

  For example, when the wavelength of incident light is λ = 600 nm and the refractive index of the constituent material of the substrate 2 is n = 1.5 (for example, in the case of SiO 2), in order to satisfy the relationship (1), for example, a grid The period can be set to d = 140 nm, and the period of the concavo-convex structure can be set to δ = 600 nm. Further, when a member is provided around the substrate 2, the ratio of the refractive index of the constituent material of the substrate 2 to the refractive index of this member is set to n (> 1), and the grid period and the concavo-convex structure period are set. Can do. Light incident on the optical element 1 from the other surface 2 b of the substrate 2 is polarized and separated by the action of the grid portion 4. That is, as described above, the TE polarization component is reflected, and the TM polarization component is transmitted through the substrate 2. In addition, the TE polarization component is diffracted at a large angle by the action of the diffractive structure portion 3 together with this. The diffracted TE polarization component causes total reflection at the interface between the air and the substrate 2, thereby propagating through the inside of the substrate 2 and traveling toward the end of the substrate 2. When the light attenuating unit 5 is provided on the substrate 2 as described above, the TE-polarized component propagating through the substrate 2 is absorbed by the light attenuating unit 5 or the intensity is reduced. The conditions for the TE polarization component thus generated by diffraction to cause total reflection at the interface between the substrate 2 and the air, that is, the condition of the above equation (1) will be described in detail.

(A) Derivation of the relationship of λ / n <δ In order for the m-th order diffracted light to exist inside the substrate 2, the following relational expression must be satisfied.
sin θm = mλ / (nδ) <1 (2)
However, as shown, the diffraction angle inside the substrate 2 is θm. As described above, λ is the wavelength of incident light in the air, n is the refractive index of the constituent material of the substrate 2, and δ is the period of the concavo-convex structure. When all the diffracted light is confined inside the substrate 2, the diffraction order is m = 1 in the above equation (2). As a result, the following expression (3) is derived.
λ / n <δ (3)
(B) Derivation of the relationship δ ≦ λ In order to confine the m-th order diffracted light inside the substrate 2, the diffraction angle θm is larger than the critical angle θc (the angle at which total reflection occurs), that is, the substrate 2 and the air It is necessary that the incident angle θi of the m-th order diffracted light at the interface is larger than the critical angle θc. For that purpose, it is necessary to satisfy the following expression.
sin θm = mλ / (nδ) ≧ sin θc (4)
When all the diffracted light is confined inside the substrate 2, the diffraction order is set to m = 1 in the above equation (4). As a result, the following expression (5) is derived.
δ ≦ λ / (nsinθc) (5)
Since nsin θc = 1 under the total reflection condition, the above equation (5) is as follows.
δ ≦ λ (6)
From the above equations (3) and (6), the relationship of λ / n <δ ≦ λ is derived.

In addition, it is also preferable that the diffraction angle θm of the first-order diffracted light coincides with the critical angle θc. Specifically, it is as follows.
sin θm = mλ / (nδ) = sin θc (7)
Since nsin θc = 1 under the total reflection condition, the above equation (7) is as follows with m = 1.
δ = λ (8)
That is, by making the wavelength λ of the incident light equal to the period δ of the concavo-convex structure of the diffractive structure 3, the diffraction angle θm of the first-order diffracted light and the critical angle θc can be matched.

The above description has been given for the case where the incident medium is air. However, when the incident medium is different from air, the conditions for confining the mth-order diffracted light inside the substrate 2 are as follows.
Even when the incident medium is different from air, it is necessary that the diffraction angle θm be larger than the critical angle θc in order to confine the m-th order diffracted light inside the substrate 2, and the above equations (4) and (5) It is necessary to satisfy the formula. When the incident medium is different from air, the total reflection condition is expressed as n sin θc = ns using the refractive index ns of the incident medium. Therefore, the following relationship is derived from the total reflection condition and the equation (5).
δ ≦ mλ / ns (9)

  Thus, when the incident medium is different from air, the upper limit of the period of the concavo-convex structure can be set using the equation (9). That is, it can be seen that it is necessary to satisfy the relationship of σ ≦ λ / ns when m = 1 in the equation (9).

  Next, a preferable condition for the depth of the concavo-convex structure of the diffractive structure 3 (step between the concave portion 3a and the convex portion 3b) will be described. As shown in FIG. 8, the depth of the concavo-convex structure is assumed to be g. Consider a situation where the incident light on the optical element 1 is perpendicular to the other surface 2 b of the substrate 2. The intensity of the m-th order diffracted light in the intensity of the polarized light reflected by the other surface 2b is defined as the m-th order reflection diffraction efficiency.

The 0th-order reflection / diffraction component of the TE polarization component is folded back by 180 ° by reflection and is emitted from the optical element 1 along the same optical axis as that at the time of incidence. From the viewpoint of minimizing this component, it is considered preferable that the zero-order reflection diffraction efficiency of the TE polarization component is minimized. Assuming that the period of the concavo-convex structure is sufficiently larger than the wavelength, and performing approximation in the scalar region, the polarization dependence of the reflection diffraction efficiency can be ignored. The depth g (hereinafter referred to as “gh” for convenience) when the zero-order reflection diffraction efficiency is minimized is expressed by the following formula for both the TE polarization component and the TM polarization component.
gh = λ / 4n (10)
On the other hand, if the period of the concavo-convex structure is approximately equal to or less than the wavelength, the polarization dependence of the reflection diffraction efficiency is increased, and thus consideration in the vector region is necessary.

  FIG. 9 is a graph showing a result of obtaining an exact solution of the reflection diffraction efficiency with respect to the depth of the concavo-convex structure using a technique of strict coupled wave analysis in consideration of polarization. FIG. 9A shows the reflection diffraction efficiency of the TE-polarized component incident substantially perpendicularly to the other surface 2b, and FIG. 9B incident substantially perpendicularly to the other surface 2b. The reflection diffraction efficiency of the TM polarization component is shown. 9A and 9B are examples of solutions for λ = 633 nm and n = 1.46.

As the value of g at which the zero-order reflection diffraction efficiency of the TE polarization component is minimized, the value calculated from the equation (10) is about g = 108 nm, whereas it is obtained from the graph of FIG. The value is about 190 nm.
As the value of g at which the zero-order reflection diffraction efficiency of the TM polarization component is minimized, the value calculated from the equation (10) is about g = 108 nm, whereas it is obtained from the graph of FIG. 9B. The value is about 100 nm.

  As described above, when the period of the concavo-convex structure is equal to or less than the wavelength, it is understood that g may be set based on the result of consideration in the vector region.

The depth g (hereinafter referred to as “gr” for convenience) when the diffraction effect of the reflected light is maximized is approximately given by the following equation.
gr = (2m + 1) λ / 4n: m = 0, 1, 2, (11)
On the other hand, the depth g (hereinafter referred to as “gt” for convenience) when the diffraction effect of transmitted light is maximized is approximately given by the following equation.
gt = (2m + 1) λ / 2 (n-1): m = 0,1,2, ... (12)
From the above equations (11) and (12), it can be seen that the depth gr at which the diffraction effect of reflected light is maximized is different from the depth gt at which the diffraction effect of transmitted light is maximized. Therefore, if the depth g of the diffractive structure 3 is made equal to gr, it is possible to sufficiently suppress the diffraction effect of the transmitted light. For example, when λ = 600 nm, for m = 0, gr = 100 nm and gt = 600 nm. However, it is assumed that the refractive index n is 1.5. Therefore, for example, assuming that the depth g of the diffractive structure 3 is set to 100 nm equal to gr, 96% of the transmitted light amount can be a non-diffracted component. For example, if a lens is arranged at the rear stage of the optical element 1, almost all light can be incident on the lens.

  FIG. 10 is a schematic perspective view showing the diffractive structure portion 3 and the grid portion 4 partially enlarged. Based on this figure, the arrangement relationship between the diffraction structure portion 3 and the grid portion 4 will be described. The mutual arrangement relationship between the diffractive structure portion 3 and the grid portion 4 can be, for example, as shown in FIG. Specifically, in the example shown in FIG. 10A, each concave portion 3a and each convex portion 3b of the diffractive structure portion 3 extend along the Y direction shown in the drawing, and these concave portions 3a and convex portions are formed. The parts 3b are alternately arranged along the X direction. Similarly, each thin line 4a of the grid part 4 extends along the Y direction shown in the figure, and these thin lines 4a are alternately arranged along the X direction. That is, the extending direction of each recessed part 3a and each projecting part 3b and the extending direction of the thin wire 4a are parallel.

  Further, as shown in FIGS. 10B and 10C, the mutual arrangement relationship between the diffractive structure portion 3 and the grid portion 4 is such that the extending directions of the concave portions 3a and the convex portions 3b and the thin wires 4a. It is also preferable to intersect with the extending direction at a certain angle. Specifically, in the example shown in FIG. 10B, each concave portion 3a and each convex portion 3b of the diffractive structure portion 3 extend along the Y direction shown in the drawing, and these concave portions 3a and convex portions are formed. The parts 3b are alternately arranged along the X direction. On the other hand, each thin line 4a of the grid portion 4 extends along a direction intersecting with the illustrated Y direction at an angle of approximately 45 °, and these thin lines 4a are orthogonal to the intersecting direction. It is alternately arranged along the direction. In the example shown in FIG. 10C, each concave portion 3a and each convex portion 3b of the diffractive structure portion 3 extend along the Y direction shown in the drawing, and these concave portions 3a and convex portions 3b are in the X direction. Are arranged alternately. On the other hand, each thin line 4a of the grid portion 4 extends along a direction intersecting at an angle of approximately 90 ° with respect to the illustrated Y direction (that is, the X direction), and these thin lines 4a are They are alternately arranged along a direction perpendicular to the intersecting direction (that is, the Y direction). In this way, by making the concave portions 3a and the convex portions 3b intersect with the thin wires 4a, it is easier to form the thin wires 4a in the vicinity of the step between the concave portions 3a and the convex portions 3b. What is necessary is just to set suitably the intersection angle of the extending direction of each recessed part 3a and each convex part 3b, and the extending direction of each thin wire | line 4a. The crossing angles of 45 ° and 90 ° as an example above are preferable because they are often used in optical systems in general.

The optical element 1 of the present embodiment has the above-described configuration. Next, an example of a method for manufacturing the optical element 1 will be described.
11 and 12 are schematic process diagrams illustrating an example of a method for manufacturing the optical element 1. A part of the cross section of the optical element 1 is shown enlarged.

  First, the diffractive structure 3 including the concave portion 3a and the convex portion 3b is formed on one surface of the substrate 2 (FIG. 11A). This step can be realized using, for example, a well-known photolithography technique and etching technique. Specifically, a photosensitive film (resist film or the like) is formed on one surface of the substrate 2, and this photosensitive film is exposed using an exposure mask having an exposure pattern corresponding to each concave portion 3a and convex portion 3b. develop. Thereafter, dry etching or wet etching is performed using the developed photosensitive film as an etching mask. Thereby, a predetermined uneven shape is formed on one surface of the substrate 2 of the pattern of the exposure mask. Here, the board | substrate 2 is a glass substrate, for example as mentioned above, The plate | board thickness is 0.7 mm, for example. Further, the step between the concave portion 3a and the convex portion 3b (that is, the depth g of the diffractive structure portion 3) is, for example, 100 nm as described above. This depth g is controlled by the etching time or the like.

  Next, a metal film 7 is formed on one surface of the substrate 2 so as to cover the concave portions 3a and the convex portions 3b (FIG. 11B). This metal film 7 is processed in a later process and becomes each thin wire 4a constituting the grid portion 4 described above. The metal film 7 is, for example, an aluminum film, a silver film, or a nickel film, and the film thickness is, for example, about 120 nm. Such a metal film 7 can be formed by using, for example, a physical vapor deposition method such as a vacuum evaporation method or a sputtering method.

  Next, an antireflection film 8 that covers the metal film 7 is formed on one surface of the substrate 2 (FIG. 11C). This antireflection film 8 is used for the purpose of improving the exposure accuracy when exposing the photosensitive film in a later step. As such an antireflection film 8, for example, a SiON (silicon oxynitride) film, a SnO (tin oxide film), an ITO (indium tin oxide) film or the like is suitable. The thickness of the antireflection film 8 is, for example, about several tens of nm. Whether a film can be used as an antireflection film depends on the complex refractive index of the material of the film. For example, the real part value of the complex refractive index is +1.4 or more, and the imaginary part value of the complex refractive index is It is desirable to be about -0.1 to -1.5.

  Next, a photosensitive film 9 that covers the antireflection film 8 (or the metal film 7) is formed on one surface of the substrate 2 (FIG. 11C). The photosensitive film 9 is, for example, a negative or positive resist film. The photosensitive film 9 can be formed using, for example, a spin coating method. The film thickness of the photosensitive film 9 may be set as appropriate, but it is desirable to cover at least all the regions overlapping the concave portions 3a and the convex portions 3b and to make the film surface substantially flat as shown. In this case, the difference between the film thickness of the photosensitive film 9 in the upper part of the diffractive structure part 3 (area corresponding to the convex part 3b) and the film thickness of the photosensitive film 9 in the lower part of the diffractive structure part 3 (area corresponding to the concave part 3a). Is substantially equal to the depth g of the diffractive structure 3 described above.

  Next, laser interference exposure is performed on the photosensitive film 9 formed on one surface of the substrate 2 (FIG. 12A). As a light source used for laser interference exposure, for example, a continuous wave DUV (Deep Ultra Violet) laser having a wavelength of 266 nm may be mentioned. The laser beam output from this laser is appropriately branched into two laser beams and crossed at a predetermined angle θL as shown. Thereby, light (interference light) including interference fringes composed of periodic brightness and darkness is generated. The pitch of interference fringes (brightness / darkness cycle) is determined by the crossing angle θL. For example, the interference fringe pitch can be set to 140 nm by setting the crossing angle θL to 72 °. By irradiating the photosensitive film 9 with such interference light, a latent image pattern corresponding to the pitch of the interference fringes is formed on the photosensitive film 9. At this time, as described above, since the antireflection film 8 is provided on the lower side of the photosensitive film 9, the disadvantage that the laser light is reflected by the metal film 7 and the exposure accuracy is reduced can be avoided.

  Next, the photosensitive film 9 on which the latent image pattern is formed using the interference light is developed (FIG. 12B). As a result, a photosensitive film pattern 9a having a period corresponding to the pitch of the interference fringes is formed as shown. For example, when the pitch of the interference fringes is 140 nm, the period of the photosensitive film pattern 9a is approximately 140 nm.

  Next, etching (for example, dry etching) is performed using the photosensitive film pattern 9a as a mask (FIG. 12C). As a result, the pattern of the photosensitive film pattern 9 a is transferred to the antireflection film 8 as shown in the drawing, and the pattern is further transferred to the metal film 7. Thereafter, the photosensitive film pattern 9a and the antireflection film 8 are removed. Thereby, the grid part 4 (namely, each thin wire | line 4a) is formed on one surface of the board | substrate 2 along the surface of each recessed part 3a and the convex part 3b of the diffraction structure part 3 like illustration.

  In the above-described manufacturing method, it is also preferable to provide a very thin SiO 2 film (for example, about 20 nm) between the antireflection film 8 and the metal film 7. As a result, the etching selectivity with respect to the metal film 7 can be further improved, and the photosensitive film 9 can be made thinner. This means that the latent image pattern becomes shallow, which is more advantageous in terms of performing stable exposure. In this case, the step of forming the SiO 2 film may be performed after the step of forming the antireflection film 8 and the step of forming the metal film 7. The SiO2 film can be formed by, for example, chemical vapor deposition. Further, the antireflection film 8 can be omitted depending on process conditions and the like.

  The above-described optical element 1 of the present embodiment can be used by being incorporated into various liquid crystal devices. Hereinafter, a liquid crystal light valve will be described as an example of the liquid crystal device.

  FIG. 13 is a schematic diagram illustrating a configuration example of a liquid crystal device including the optical element according to the present embodiment. FIG. 13A shows a schematic perspective view of a liquid crystal light valve (liquid crystal device) 70, and FIG. 13B shows a cross-sectional view of the main part of the liquid crystal device 70.

  As shown in FIG. 13A, the liquid crystal light valve 70 includes a first substrate 71 disposed on the incident side and a second substrate 72 disposed on the emission side. As shown in FIG. 13B, a liquid crystal layer 73 is provided between the first substrate 71 and the second substrate 72. On the opposite side of the second substrate 72 from the liquid crystal layer 73, an optical element 727 is bonded via a sealing material 725. The optical element 727 includes the optical element according to the present embodiment. The sealing material 725 has a frame shape that overlaps the peripheral edge of the second substrate 72 in a planar manner. A region surrounded by the frame-shaped sealing material 725 is a gap 726 between the second substrate 72 and the optical element 727. The gap 726 is hermetically sealed so that dust does not enter the gap 726.

  The first substrate 71 is formed using a transparent substrate 71A made of glass, quartz or the like as a base. A common electrode 711 is provided on the liquid crystal layer 73 side of the transparent substrate 71A. An alignment film 712 for controlling the alignment state of the liquid crystal layer 73 is provided between the common electrode 711 and the liquid crystal layer 73. On the opposite side of the transparent substrate 71A from the liquid crystal layer 73, a polarizing plate 713 is provided.

  The second substrate 72 is of an active matrix type, for example, and is formed using a transparent substrate 72A made of glass, quartz or the like as a base. A thin film transistor (hereinafter referred to as TFT) 721 that functions as a switching element is provided on the liquid crystal layer 73 side of the transparent substrate 72A.

  The TFT 721 is formed using, for example, polycrystalline silicon technology. The source region of the TFT 721 is electrically connected to a signal source that supplies an image signal via a data line (not shown). A gate electrode of the TFT 721 is electrically connected to a signal source that supplies a scanning signal via a scanning line (not shown).

  An interlayer insulating film 722 is provided so as to cover the TFT 721, and an island-shaped pixel electrode 723 is provided in a portion overlapping the pixel in the interlayer insulating film 722. A contact hole is provided in the interlayer insulating film 722, and the pixel electrode 723 is electrically connected to the drain region of the TFT 721 through the contact hole. An alignment film 724 that controls the alignment state of the liquid crystal layer 73 is provided between the pixel electrode 723 and the liquid crystal layer 73. An optical element 727 is provided on the opposite side of the transparent substrate 72A from the liquid crystal layer 73 with a gap 726 interposed therebetween. In the optical element 727, the depth of the unevenness is adjusted so that the zero-order reflection diffraction efficiency of the TE polarization component is minimized.

  In the liquid crystal light valve 70 configured as described above, when a scanning signal is supplied to the gate electrode of the TFT 721, the TFT 721 is turned on. When the TFT 721 is turned on, an image signal is transmitted to the pixel electrode 723 via the data line and the TFT 721. Then, a voltage corresponding to the image signal is applied between the pixel electrode 723 and the common electrode 712, and an electric field is applied to the liquid crystal layer 73 for each pixel. Thereby, the azimuth angle of the liquid crystal molecules of the liquid crystal layer 73 is controlled according to the applied electric field.

  On the other hand, light that has entered the first substrate 71 from a light source (not shown) passes through the polarizing plate 713 and enters the liquid crystal layer 73 as predetermined polarized light (for example, linearly polarized light). The light incident on the liquid crystal layer 73 changes its polarization state in accordance with the azimuth angle of the liquid crystal molecules, and is incident on the second substrate 72 as, for example, linearly polarized light in a direction different from that upon incidence on the liquid crystal layer. The light incident on the second substrate 72 enters the optical element 727 through the gap 726. The TE polarization component of the light incident on the optical element 727 is reflected by the optical element 727, and the TM polarization component is transmitted through 727. The light that has passed through the optical element 727 becomes light having a gradation according to the image signal by separating the TM polarization component.

  The TE polarization component reflected by the optical element 727 is set to minimize the intensity of the 0th-order diffracted light as described above. Further, first-order or higher-order diffracted light is totally reflected at the interface between the gap 726 and the optical element 727. As described above, most of the TE-polarized components are prevented from passing through the gap 726, and the reflected light caused by the TE-polarized components is remarkably reduced from entering the second substrate 72 again. Accordingly, malfunction occurs when the reflected light is incident on the TFT 721, heat is generated when the reflected light is absorbed between the first substrate 71 and the second substrate 72, and the first substrate 71 from the light source is generated. Adverse effects such as a reduction in contrast due to interference between the light incident on and the reflected light can be avoided.

In addition, since the gap 726 between the second substrate 72 and the optical element 727 is hermetically sealed, and dust does not enter here, it is prevented that the light passing through the gap 726 is shaded by dust. Therefore, it is not necessary to provide dust-proof glass or the like for preventing dust from entering, and the liquid crystal light valve 70 can be downsized. In addition, since the second substrate 72 and the optical element 727 are interposed via the gap 726, the heat of the optical element 727 hardly propagates to the second substrate 72, and the heat resistance of the liquid crystal light valve 70 is improved.
In the above description, a configuration in which TE polarized light is reflected and TM polarized light is used for image formation has been described. However, a configuration in which TM polarized light is reflected and TE polarized light is used for image formation is also possible. In addition to the liquid crystal light valve, examples of the liquid crystal device to which the optical element of the present invention can be applied include a liquid crystal device used in a direct-view type liquid crystal display device.

  The above-described optical element 1 of the present embodiment can be used by being incorporated into various optical devices. Hereinafter, as an example of the optical device, a projection type display device (liquid crystal projector) using a liquid crystal light valve will be described. In this example, unlike the liquid crystal device described above, the optical element 1 is provided independently of the liquid crystal light valve.

  FIG. 14 is a schematic diagram illustrating a configuration example of a projection display device including the optical element according to the present embodiment. FIG. 14 shows only one optical system for explaining the principle configuration. The display device shown in FIG. 14 includes a light source 50 such as a mercury lamp, an optical element 51, a liquid crystal light valve (liquid crystal panel) 52, an optical element 53, a pupil 54a, and a projection lens 54. A one-dot chain line in the drawing indicates an optical path of light output from the light source 50. On the optical path, an optical element 51, a liquid crystal light valve 52, an optical element 53, and a projection lens 54 are arranged in this order. In this display device, at least the optical element according to the present embodiment is used as the optical element 53.

  The optical element 51 is an element having a polarization separation function. That is, when the light output from the light source 50 enters the optical element 51, only one polarization component is transmitted, and the other polarization component is not transmitted. The optical element 51 is a polymer-type polarizing plate obtained, for example, by uniaxially stretching a resin. Further, the optical element 51 may be one in which a large number of fine fine lines such as the above-described grid portion are provided on a transparent substrate. The optical element having such a structure is excellent in light resistance, and reflects a polarized light component parallel to each thin line in incident light and transmits a polarized light component orthogonal to each thin line.

  In the liquid crystal light valve 52, a liquid crystal material (liquid crystal layer) is disposed between two transparent substrates disposed opposite to each other. The liquid crystal light valve 52 controls the alignment state of the liquid crystal molecules by appropriately applying a voltage to the liquid crystal material through the electrodes provided on each transparent substrate. By controlling the alignment state of the liquid crystal molecules, the polarization state of the light transmitted through the optical element 51 can be appropriately changed. Based on the change in the polarization state of the light, an image to be projected on the screen 60 is formed. In other words, the liquid crystal light valve 52 functions as a light modulation device (light modulation means).

  The optical element 53 is an optical element according to this embodiment as described above. In this optical element 53, one surface 53a provided with a diffractive structure portion and a grid portion (not shown) is disposed on the rear side of the optical path, and the other surface 53b provided with no diffractive structure portion or the like is provided on the front side of the optical path. It is arranged on the side (light source 50 side). With this arrangement, the TE component of the light transmitted through the liquid crystal light valve 52 is diffracted and totally reflected as described above, and propagates through the substrate of the optical element 53 toward the substrate end. As a result, the return light to the liquid crystal light valve 52 is remarkably reduced, and problems such as malfunction of the liquid crystal light valve 52 can be prevented.

  Note that the optical element according to the present embodiment may also be used for the optical element 51 described above. In that case, it is arranged in the same manner as the optical element 53. That is, in this case, the optical element 51 has a surface 51a provided with a diffractive structure portion and a grid portion (not shown) disposed on the rear side of the optical path (the liquid crystal light valve 52 side). The other surface 51b that is not provided is disposed on the front side (light source 50 side) of the optical path.

  An image formed by the optical element 51, the liquid crystal light valve 52, and the optical element 53 is incident on the projection lens 54 through the pupil 54a, and is magnified by the projection lens 54 to form an image on the screen 60. As a result, the enlarged image is displayed on the screen 60.

  FIG. 15 shows a modification of the optical system shown in FIG. In addition, the same code | symbol is attached | subjected about the component which is common in each figure, and those description is abbreviate | omitted. In the projection display device shown in FIG. 15, a field lens 55 is further added. The field lens 55 is disposed on the optical path after the optical element 53 and before the projection lens 54 (that is, between the optical element 53 and the projection lens 54). By using such a field lens 55, more transmitted diffracted light can be collected on the pupil 54a of the projection lens 54. Therefore, the brightness (luminance) of the image on the screen 60 can be further increased.

  Next, a configuration example of a projection display device having three optical systems will be described as a further application example of the above-described projection display device. In the following application examples, components common to the display device shown in FIG. 14 are given the same reference numerals, and detailed descriptions thereof are omitted.

  FIG. 16 is a schematic diagram illustrating a configuration example of a projection display device having three optical systems. In the projection type display device shown in FIG. 16, the optical element 51B, the liquid crystal light valve 52B, and the optical element 53B are arranged to face each other on one of the four surfaces of the prism (light combining means) 56, as shown in the figure. The optical element 51G, the liquid crystal light valve 52G, and the optical element 53G are arranged to face each other on one surface, and the optical element 51R, the liquid crystal light valve 52R, and the optical element 53R are arranged to face each other on the other surface.

  In this projection display device, the light output from the light source 50 enters the dichroic mirror 58a. Of this incident light, the blue component is transmitted and the remaining components are reflected. The transmitted blue component (hereinafter referred to as “blue light”) is reflected by the mirror 57a, enters the optical element 51B, is appropriately modulated by the liquid crystal light valve 52B, passes through the optical element 53B, and passes through one surface of the prism 56. Is incident on. The light component reflected by the dichroic mirror 58a is incident on the dichroic mirror 58b. Of this incident light, the red component is transmitted and the green component is reflected. The transmitted red component (hereinafter referred to as “red light”) is reflected by the mirrors 57b and 57c, enters the optical element 51R, is appropriately modulated by the liquid crystal light valve 52R, passes through the optical element 53R, and passes through the optical element 53R. Incident on the other surface. The reflected green component (hereinafter referred to as “green light”) enters the optical element 51G, is appropriately modulated by the liquid crystal light valve 52G, passes through the optical element 53G, and enters the other surface of the prism 56. Blue light, green light, and red light respectively incident on the three surfaces of the prism 56 are combined by the prism 56 and emitted from the other surface of the prism 56. The emitted combined light is magnified by the projection lens 55 and projected onto the screen 60.

  Note that the optical elements 51R, 51G, and 51B shown in FIG. 15 correspond to the optical element 51 of the above embodiment, the liquid crystal light valves 52R, 52G, and 52B correspond to the liquid crystal light valve 52 of the above embodiment, and the optical elements 53R, 53G and 53B correspond to the optical element 53 of the above embodiment. In each of the optical elements 53R, 53G, and 53B, one surface side on which the diffractive structure portion and the grid portion are provided is disposed on the rear stage side (prism side) on the optical path, and the other surface side is on the front stage side (liquid crystal light valve side) on the optical path. Be placed. In addition, when the diffractive structure is provided also in each of the optical elements 51R, 51G, and 51B, each optical element 51R, 51G, and 51B has the one side where the diffractive structure and the grid are provided on the rear side of the optical path ( It is arranged on the liquid crystal light valve side, and the other surface side is arranged on the front stage side (mirror or dichroic mirror side) on the optical path.

  FIG. 17 is a schematic diagram showing another configuration example of a projection display apparatus having three optical systems. Unlike the projection display apparatus shown in FIG. 12, the configuration example is a projection display apparatus configured without using a prism.

  In this projection display device, the light output from the light source 50 enters the dichroic mirror 58a. Of this incident light, only the red component is reflected and the remaining components are transmitted. Each transmitted component enters the dichroic mirror 58b. Of this incident light, the green component (green light) is reflected and the blue component (blue light) is transmitted. The transmitted blue light enters the optical element 51B, is appropriately modulated by the liquid crystal light valve 52B, passes through the optical element 53B, and enters the mirror 57b. The blue light incident on the mirror 57b is reflected, incident on the dichroic mirror 58d, reflected by the dichroic mirror 58d, and incident on the projection lens 55. The red light reflected by the dichroic mirror 58a enters the mirror 57a and is reflected. The reflected red light enters the optical element 51R, is appropriately modulated by the liquid crystal light valve 52R, passes through the optical element 53R, and enters the dichroic mirror 58c. The red light incident on the dichroic mirror 58c passes through the dichroic mirror 58c and enters the dichroic mirror 58d. The red light incident on the dichroic mirror 58d passes through the dichroic mirror 58d and enters the projection lens 55. The green light reflected by the dichroic mirror 58b enters the optical element 51G, is appropriately modulated by the liquid crystal light valve 52G, passes through the optical element 53G, and enters the dichroic mirror 58c. The green light incident on the dichroic mirror 58c is reflected by the dichroic mirror 58c, enters the dichroic mirror 58d, passes through the dichroic mirror 58d, and enters the projection lens 55. The combined light (the combined light of blue light, green light, and red light) finally combined and incident on the projection lens 55 is enlarged by the projection lens 55 and projected onto the screen 60.

  Also in this example, the optical elements 51R, 51G, 51B correspond to the optical element 51 of the above embodiment, the liquid crystal light valves 52R, 52G, 52B correspond to the liquid crystal light valve 52 of the above embodiment, and the optical elements 53R, 53G. , 53B corresponds to the optical element 53 of the above embodiment. In each of the optical elements 53R, 53G, and 53B, one surface side on which the diffractive structure portion and the grid portion are provided is arranged on the rear stage side (mirror or dichroic mirror side) on the optical path, and the other surface side is the front stage side on the optical path (liquid crystal light valve Side). In addition, when the diffractive structure is provided also in each of the optical elements 51R, 51G, and 51B, each optical element 51R, 51G, and 51B has the one side where the diffractive structure and the grid are provided on the rear side of the optical path ( It is arranged on the liquid crystal light valve side, and the other surface side is arranged on the front stage side (mirror or dichroic mirror side) on the optical path.

  Note that it is preferable that the projection display apparatus of the embodiment shown in FIGS. 16 and 17 further includes a field lens (see FIG. 15). Further, in the projection display device of each embodiment, the light source 50 may be a laser light source. In that case, since the wavelength width of light is extremely narrow, the controllability of light by the optical element according to the present embodiment is further improved.

  In addition, it is also preferable that the structures of the diffractive structure portion and the grid portion of each optical element are optimized in accordance with the wavelength λ of the target light. For example, in the optical system shown in FIG. 16 or FIG. 17, the wavelength λ is 450 nm for the optical element 53B corresponding to blue light, and the wavelength λ is 550 nm for the optical element 53G corresponding to green light. For the optical element 53R corresponding to the above, it is possible to optimize the structure of each optical element for each wavelength by applying the relational expressions (1) to (12) with a wavelength λ of 650 nm. it can.

  Thus, according to the optical element of this embodiment, one polarization component of incident light is reflected by the action of the grid portion, and the other polarization component is transmitted. Further, the reflected polarization component (reflected light) is diffracted at a sufficiently large angle by the action of the diffraction structure portion. When the above-described parameter relationship is satisfied, the diffracted reflected light is totally reflected at the interface between the other surface of the substrate and the surrounding medium (for example, air), propagates in the substrate, and reaches the edge of the substrate. Head. Therefore, when the optical element according to the present invention is used in a desired optical system, the reflected light generated by the grid portion does not return to the previous stage of the optical path, and adverse effects due to unnecessary reflected light are suppressed.

  Further, according to the projection display device of the present embodiment, the above-described optical element having the diffractive structure part and the grid part is used as an optical element on the rear side of the liquid crystal light valve, so that the reflected light from the grid part is reflected. It is possible to avoid entering the liquid crystal light valve. Thereby, the stable operation of the liquid crystal light valve is not hindered by the incidence of unnecessary light. Moreover, since it uses as a polarization separation element by the grid part which consists of a some metal fine wire, the display apparatus excellent in light resistance is realizable. Therefore, according to the present invention, a high-performance display device can be provided. Further, when the above-described optical element having a diffractive structure part and a grid part is used as an optical element on the front side of the liquid crystal light valve, it is possible to provide a display device with higher performance and higher quality. Become.

  The present invention is not limited to the contents of the above-described embodiments, and various modifications can be made within the scope of the gist of the present invention.

  For example, in the above-described embodiment, the diffractive structure portion is formed by performing processing such as etching on one surface side of the substrate, but other manufacturing methods may be employed. Specifically, an optical element similar to the above may be formed by forming a polymer (polymer resin) film on one surface of the substrate and then performing photomask exposure and wet etching on the polymer film. Is possible. An example of the structure of an optical element formed by this method is shown in FIG. In the optical element 101 shown in FIG. 18, a diffractive structure portion 103 formed using a polymer film is disposed on one surface side of a substrate 102 such as glass. The diffractive structure portion 103 includes a concave portion 103a and a convex portion 103b, and a grid portion 104 composed of a plurality of thin wires 104a is disposed along the surfaces of the concave portion 103a and the convex portion 103b. In addition to this, a substrate having a diffractive structure portion may be integrally formed using a light refractive index glass (n = about 2.0) that can be molded. In this case, since the refractive index is high, the depth g of the diffractive structure portion can be further reduced, which is preferable in forming the grid portion. In addition, the diffractive structure portion can be formed by forming another film (for example, an inorganic film such as SiO 2) on the substrate and selectively etching the film. An example of the structure of an optical element formed by this method is shown in FIG. In the optical element 111 shown in FIG. 19, a diffractive structure portion 113 formed using a film such as SiO 2 is disposed on one surface side of a substrate 112 such as glass. The diffractive structure portion 113 includes a concave portion 113a and a convex portion 113b, and a grid portion 114 composed of a plurality of thin lines 114a is disposed along the surfaces of the concave portion 113a and the convex portion 113b.

  In the above-described embodiment, the projection display device is illustrated as an example of the use of the optical element. However, the application example of the optical element according to the present invention is not limited to this. The projection display device is only an example of an optical device including the optical element according to the present invention. The optical element according to the present invention can also be applied to, for example, a liquid crystal display that requires a polarization separation layer. Of course, the optical device according to the present invention is not limited to the optical device for display of the optical element according to the present invention, and the optical element according to the present invention can be used for various optical devices in general that require a polarization separation function.

It is a schematic diagram which shows the cross-section of the optical element of one Embodiment. It is a schematic diagram which shows the cross-section of the optical element of one Embodiment. It is a schematic diagram which shows the cross-section of the optical element of one Embodiment. It is a schematic diagram which shows the cross-section of the optical element of one Embodiment. It is a schematic diagram which shows the cross-section of the optical element of one Embodiment. It is the typical perspective view which expanded and showed a part of grid part. It is the typical perspective view which expanded and showed a part of diffraction structure part. It is the schematic cross section which expanded and showed a part of diffraction structure part and a grid part. It is a graph which shows the reflection diffraction efficiency with respect to the depth of an uneven structure. It is a schematic plan view which expands and shows a diffraction structure part and a grid part partially. It is a schematic process drawing which shows an example of the manufacturing method of an optical element. It is a schematic process drawing which shows an example of the manufacturing method of an optical element. It is a schematic diagram which shows the structural example of a liquid crystal device. It is a schematic diagram which shows the structural example of a projection type display apparatus. It is a schematic diagram which shows the structural example of a projection type display apparatus. It is a schematic diagram which shows the structural example of the projection type display apparatus which has three optical systems. It is a schematic diagram which shows the structural example of the projection type display apparatus which has three optical systems. It is a schematic diagram which shows the cross-section of the optical element of other embodiment. It is a schematic diagram which shows the cross-section of the optical element of other embodiment.

Explanation of symbols

1: optical element, 2: substrate, 3: diffractive structure part, 3a: concave part, 3b: convex part, 4: grid part, 4a: fine wire, 5: light attenuation part, 6: antireflection film, 7: metal film, 8: Antireflection film, 9: Photosensitive film, 50: Light source, 51R, 51G, 51B: Optical element, 52R, 52G, 52B: Liquid crystal light valve, 53R, 53G, 53B: Optical element, 54: Projection lens, 55: Field lens, 56: prism, 70: liquid crystal light valve (liquid crystal device), 71: first substrate, 72: second substrate, 73: liquid crystal layer, 725: sealant, 726: gap, 727: optical element

Claims (13)

An optical element having a function of polarizing and separating incident light,
A substrate transparent to the incident light;
A diffractive structure section provided on one surface side of the substrate, including a plurality of recesses and projections alternately arranged in a rectangular cross-sectional shape,
A grid portion including a plurality of fine lines extending in one direction, provided on one side of the substrate and along the upper surface of the diffraction structure portion;
With
When the wavelength of the incident light is λ, the distance between the plurality of thin wires is d, the distance between the plurality of protrusions is δ, and the refractive index of the constituent material of the substrate is n, these parameters are d <Λ and satisfy the relationship of λ / n <δ ≦ λ.
Optical element. When m is an integer greater than or equal to 0, the step between the concave portion and the convex portion of the diffractive structure portion is set to (2m + 1) λ / 4n.
The optical element according to claim 1. The extending direction of each of the plurality of concave portions and the plurality of convex portions of the diffractive structure portion and the extending direction of each of the plurality of fine lines of the grid portion are substantially parallel.
The optical element according to claim 1. The extending direction of each of the plurality of concave portions and the plurality of convex portions of the diffractive structure portion intersects with the extending direction of each of the plurality of fine lines of the grid portion,
The optical element according to claim 1. A light attenuator disposed on the end side of the substrate;
The optical element according to claim 1. The thickness of the substrate in the normal direction of the one surface is T, the width of the substrate in the direction in which the first-order diffracted light diffracted by the diffraction structure portion travels on the one surface as viewed in plan is W, and is diffracted by the diffraction structure portion 1 These parameters satisfy the relationship θ> tan ⁻¹ (W / 2T), where θ is the diffraction angle that the next diffracted light makes with the normal direction,
The optical element according to claim 1. A planarizing layer for planarizing the plurality of concave portions and the plurality of convex portions on one surface side of the substrate, wherein the refractive index of the planarizing layer and the refractive index of the substrate are substantially the same;
The optical element according to claim 1. A transmissive liquid crystal device that modulates and emits light incident from a light source,
A first substrate disposed on the incident side;
A second substrate disposed opposite to the first substrate on the emission side;
A liquid crystal layer provided between the first substrate and the second substrate;
An optical element bonded to the second substrate on the opposite side of the liquid crystal layer via a gap and having a polarization separation function;
With
The optical element according to any one of claims 1 to 7 is used as the optical element.
Liquid crystal device. The second substrate and the optical element are bonded via a sealing material that annularly surrounds the gap,
The gap is sealed by the second substrate, the optical element, and the sealing material;
The liquid crystal device according to claim 8. A projection display device,
A light source;
A first optical element having a polarization separation function and disposed on the rear side of the light source;
A liquid crystal light valve having a function of modulating incident light and disposed on the rear side of the first optical element;
A second optical element having a polarization separation function and disposed on the rear stage side of the liquid crystal light valve;
A projection lens disposed on the rear side of the second optical element;
Including
The optical element according to any one of claims 1 to 7 is used as the second optical element, and the optical element has one surface provided with the diffractive structure portion and the grid portion arranged on the rear stage side. To be
Display device. Furthermore, the optical element of any one of Claims 1 thru | or 7 is used as said 1st optical element, and the one surface in which the said diffraction element part and the said grid part were provided for the said optical element is a back | latter stage side. Placed in the
The display device according to claim 10. A field lens disposed on the rear side of the second optical element and on the front side of the projection lens;
The display device according to claim 10 or 11. The light source is a laser light source;
The display device according to any one of claims 10 to 12.

Images