JP4968234B2 - Optical element and display device - Google Patents

Description

  The present invention relates to an optical element having a polarization separation function 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.
JP 2002-372749 A

  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.

Accordingly, an object of the present invention is to provide an optical element capable of suppressing adverse effects due to reflected light.
Another object of the present invention is to provide a high-performance display device configured using the optical element.

An optical element according to the present invention is an optical element having a function of polarizing and separating incident light, and includes a substrate transparent to the incident light and a plurality of convex portions having a sawtooth shape in cross section. A diffractive structure provided on one side, and a grid part including a plurality of fine lines extending in one direction, provided on one side of the substrate and along the upper surface of the diffractive structure, The grid portion reflects one polarization component of the incident light and transmits another polarization component, the wavelength of the incident light is λ, the mutual distance between the plurality of thin wires is d, and the plurality of projections These parameters satisfy the relationship of d <λ and λ / n <δ ≦ λ, where δ is the mutual interval and n is the refractive index of the constituent material of the substrate.

  An optical element according to the present invention is an optical element having a function of polarizing and separating incident light, and includes a substrate transparent to the incident light, and a plurality of convex portions having a sawtooth shape in cross section, A diffractive structure portion provided on one surface side of the substrate, and a grid portion including a plurality of fine lines extending in one direction and provided on the one surface side of the substrate and along the upper surface of the diffractive structure portion; The wavelength of the incident light is λ, the incident angle width of the incident light is ± θ, 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 These parameters satisfy the relationship of d <λ and λ / (n−sin θ) <δ ≦ λ / (1 + sin θ).

  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, the height of the convex portion of the diffractive structure portion is set to mλ / 2n. Here, m is an integer greater than or equal to 1 (1, 2, 3,...).
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 direction of each of the plurality of convex portions of the diffractive structure portion and the extending direction of each of the plurality of thin lines of the grid portion can be made substantially parallel. Further, the extending direction of each of the plurality of convex portions of the diffractive structure portion may intersect with the extending direction of each of the plurality of fine lines of the grid portion.

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

  In the optical element, for example, a second substrate having a refractive index substantially equal to that of the substrate may be bonded to the one surface of the substrate via an adhesive layer having a refractive index substantially equal to that of the substrate.

  By joining a second substrate having a refractive index substantially equal to the substrate to one surface of the substrate having the diffraction structure portion via an adhesive layer having a refractive index substantially equal to the substrate, the light transmitted by the diffraction structure portion is transmitted. The influence of can be further suppressed.

  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.

  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.

  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 is formed by a plurality of convex portions 3a. In addition, in the figure, the code | symbol is attached | subjected about each one convex part 3a for convenience. As shown in the figure, the diffractive structure 3 composed of these convex portions 3a has a sawtooth shape in cross section. Here, the sawtooth-shaped cross-sectional shape is an asymmetrical shape with respect to a straight line passing through the apex and perpendicular to the bottom side, with the length of the hypotenuse of the substantially triangular cross-sectional shape being different. In addition, it includes a shape in which the apex of a substantially triangular cross-sectional shape is rounded, a shape in which a hypotenuse is a curve, or a shape formed in a minute step shape. In addition, the slopes of the hypotenuses may be different in the cross section of each projection 3a. 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. The light attenuating unit 5 can be omitted.

  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 perspective view showing a part of the grid portion 4 in an enlarged manner. Based on this FIG. 4, 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. 5 is a schematic plan view showing a part of the pattern of the diffractive structure section 3. As shown in FIG. 5A, the diffractive structure 3 has a plurality of convex portions 3a extending in one direction (the Y direction shown in the figure). These convex portions 3a have a stripe shape as shown in the figure, and are periodically arranged along the X direction. In addition, each convex part 3a is not limited to the one-dimensional array as shown in FIG. 5 (A), for example, as shown in FIG. 5 (B), each convex part 3a is arranged two-dimensionally. Also good.

FIG. 6 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. 6, the structure of the diffraction structure part 3 and the grid part 4 is demonstrated still in detail. As shown in the drawing, the mutual interval (period of the convex structure) of the convex portions 3a of the diffractive structure section 3 is δ (nm), the mutual interval (grid period) of the thin wires 4a of the grid section 4 is d (nm), and incident. The wavelength of light is λ (nm), the incident angle width of incident light is ± θ, the refractive index of the constituent material of the substrate 2 is n, and the refractive index of air around the substrate 2 is n _air (= 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−sin θ) <δ ≦ λ / (1 + sin θ) (1)

For example, when the wavelength of incident light is λ = 600 nm, the incident angle width is θ = 10 degrees, and the refractive index of the constituent material of the substrate 2 is n = 1.46 (for example, in the case of SiO ₂ ), the above (1) In order to satisfy this relationship, for example, the grid period can be set to d = 140 nm, and the period of the concavo-convex structure can be set to δ = 490 nm.
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 formula (1) will be described in detail below.

(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 = sin θ / n + 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 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−sin θ) <δ (3)
(B) Derivation of the relationship of 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 = −sin θ / n + 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 + sinθ) (5)
Since nsin θc = 1 under the total reflection condition, the above equation (5) is as follows.
δ ≦ λ (1 + sin θ) (6)
From the above equations (3) and (6), a relationship of λ / (n−sin θ) <δ ≦ λ / (1 + sin θ) is derived.

Next, a preferable condition for the depth of the concavo-convex structure of the diffractive structure 3 (height of the convex portion 3a) will be described. As shown in FIG. 6, the depth of the concavo-convex structure is defined as g. Also, consider a situation where the incident light on the optical element 1 is substantially orthogonal to the other surface 2 b of the substrate 2. At this time, 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 expression.
gr = mλ / 2n: m = 1, 2,... (7)
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 = mλ / (n−1): m = 1, 2,... (8)
From the above equations (7) and (8), it can be seen that the depth gr at which the diffraction effect of the reflected light is maximized is different from the depth gt at which the diffraction effect of the 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 = 1, gr = 205 nm and gt = 1304 nm. However, it is assumed that the refractive index n is 1.46. Therefore, for example, if the depth g of the diffractive structure 3 is set to 205 nm equal to gr, most of the transmitted light amount can be made 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.

In order to further suppress the influence of the diffractive structure 3 on the transmitted light, a substrate made of the same material as the substrate 2 used for the diffractive structure 3 via an adhesive layer 10 on the grid 4 as shown in FIG. 20 is pasted. At this time, the refractive index n of the adhesive layer 10 is made substantially equal to the refractive index n of the substrate 2.
Note that the two substrates 2 and 20 to be bonded with the diffractive structure 3 sandwiched therebetween do not need to be made of the same material, and the refractive indexes n of both are substantially equal and both are transparent to the transmitted light. .

  By making the cross-sectional shape of the diffractive structure part 3 into a sawtooth shape, the reflected light from the grid part 4 can be confined and propagated inside the substrate 2. In FIG. 6, the first-order diffracted light generated inside the substrate 2 is totally diffracted by the diffraction structure unit 3 after being totally reflected on the other surface side of the substrate 2. At this time, part of the light leaks to the outside (dotted arrows in the figure). In order to reduce this leaking light as much as possible, it is desirable that the cross-sectional shape of the diffractive structure 3 is a sawtooth shape.

FIG. 8A is a graph showing the relationship between the diffracted light intensity and the depth g of the diffractive structure 3 when the diffractive structure 3 has a sawtooth cross section. In FIG. 8A, the curve I (+) indicates the + 1st order, the curve I (0) indicates the 0th order, and the curve I (−) indicates the −1st order.
As shown in FIG. 8A, most energy of incident light can be transferred to + 1st order diffracted light by selecting an appropriate depth g (for example, 6 to 7 rad). Even when the + 1st order diffracted light is diffracted again, almost no light leaks out of the substrate 2.

FIG. 8B is a graph showing the relationship between the diffracted light intensity and the depth g of the diffractive structure 3 when the cross-sectional shape of the diffractive structure 3 is rectangular. In FIG. 8B, the curve I (+) indicates the + 1st order, the curve I (0) indicates the 0th order, and the curve I (−) indicates the −1st order.
As shown in FIG. 8B, by selecting an appropriate depth g (for example, 3 to 3.3 rad), energy of about 80% of incident light is transferred to + 1st order and −1st order diffracted light. Can do. However, when the + 1st order and −1st order diffracted light is diffracted again, a certain amount of light (about 20%) leaks out of the substrate.

  FIG. 9 is a schematic plan view showing the arrangement of the diffractive structure section 3 and the grid section 4. 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. 9A, each convex portion 3a of the diffractive structure portion 3 extends along the Y direction shown in the drawing, and these convex portions 3a extend along the X direction. Are arranged. 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 convex part 3a and the extending direction of the thin wire 4a are parallel.

  Moreover, as shown in FIGS. 9B and 9C, the mutual arrangement relationship between the diffractive structure portion 3 and the grid portion 4 is such that the extending direction of each convex portion 3a and the extending direction of each thin wire 4a. It is also preferable to cross each other at a certain angle. Specifically, in the example shown in FIG. 9B, each convex portion 3a of the diffractive structure portion 3 extends along the Y direction shown in the drawing, and these convex portions 3a extend along the X direction. Are arranged. 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. Are arranged along the direction.

  In the example shown in FIG. 9C, each convex portion 3a of the diffractive structure portion 3 extends along the Y direction shown in the drawing, and these convex portions 3a are arranged along the X direction. . 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 arranged along a direction orthogonal to the intersecting direction (that is, the Y direction). Thus, by making the convex part 3a and each thin wire | line 4a cross, formation of the thin wire | line 4a in the vicinity of the level | step difference of each convex part 3a becomes easier. What is necessary is just to set suitably the intersection angle of the extension direction of each convex part 3a, and the extension 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.

Next, an example of a method for manufacturing the optical element 1 will be described.
10 and 11 are schematic process diagrams showing an example of a method for manufacturing the optical element 1. 10 and 11, a part of the cross section of the optical element 1 is shown in an enlarged manner.

  First, the diffractive structure 3 including the convex portions 3a is formed on one surface of the substrate 2 (FIG. 10A). 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 the photosensitive film is exposed and developed using an exposure mask having an exposure pattern corresponding to each convex portion 3a. 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 height of the convex portion 3a (that is, the depth g of the diffraction structure portion 3) is, for example, 205 nm as described above. This depth g is controlled by the etching time or the like.

  Next, a metal film 7 covering the convex portion 3a is formed on one surface of the substrate 2 (FIG. 10B). 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. 10C). 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. 10C). 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 with the respective protrusions 3a and to make the film surface substantially flat as shown. In this case, the difference between the film thickness of the photosensitive film 9 at the upper part of the diffractive structure 3 (the apex of the convex part 3a) and the film thickness of the photosensitive film 9 at the lower part of the diffractive structure part 3 (a region corresponding to the bottom of the convex 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. 11A). 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 the laser is split into an appropriate two laser beams, thereby intersect at a predetermined angle theta _L as shown. Thereby, light (interference light) including interference fringes composed of periodic brightness and darkness is generated. Pitch of the interference fringes (the period of light and dark) is determined by the crossover angle theta _L. For example, by setting the crossing angle theta _L to 72 °, the pitch of the interference fringes can be 140 nm. 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. 11B). 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. 11C). 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 along the surface of each convex part 3a of the diffraction structure part 3 on one surface of the board | substrate 2 like illustration.

In the above manufacturing method, it is also preferable to provide an extremely 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, after the step of forming the antireflection film 8, the step of forming the SiO ₂ film may be performed prior to the step of forming the metal film 7. The SiO ₂ 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 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.

  FIG. 12 is a schematic diagram illustrating a configuration example of a projection display device using the optical element according to the present embodiment. FIG. 12 shows only one optical system for explaining the principle configuration. The display device shown in FIG. 12 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.

  Next, a configuration example of a projection display device having three optical systems will be described as an application example of the above-described projection display device. Note that, in each of the following application examples, components common to the display device illustrated in FIG. 12 are denoted by the same reference numerals, and detailed description thereof is omitted.

  FIG. 13 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. 13, 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 faces 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.

  The optical elements 51R, 51G, and 51B shown in FIG. 13 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. 14 is a schematic diagram showing another configuration example of a projection display device having three optical systems. Unlike the projection display apparatus shown in FIG. 13, 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 disposed on the rear stage side (mirror or dichroic mirror side) on the optical path, and the other surface side is the front stage side (liquid crystal light valve) on the optical path. 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.

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. 13 or FIG. 14, 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 (8) above 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, when conditions such as the wavelength of incident light and the incident angle differ depending on the position on the substrate, the depth, width, shape, etc. of the convex portions of the diffractive structure are varied on the same substrate in accordance with the conditions. Also good.
In the above-described embodiment, the diffractive structure is formed by performing processing such as etching on one side of the substrate. However, 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. 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. Alternatively, the diffraction structure can be formed by forming another film (for example, an inorganic film such as SiO ₂ ) on the substrate and selectively etching the film.

  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 in embodiment of this invention. It is a schematic diagram which shows the cross-section of the optical element in embodiment of this invention. It is a schematic diagram which shows the cross-section of the optical element in embodiment of this invention. It is the typical perspective view which expanded and showed a part of grid part in the embodiment of the present invention. It is a typical top view which shows a part of pattern of a 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 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 a convex part. It is a typical top view which shows arrangement | positioning of a diffraction structure part and a grid part. 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 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.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,1a Optical element, 2 board | substrate, 3 diffraction structure part, 3a convex part, 4 grid part, 4a fine wire, 5 light attenuation part, 10 adhesive layer, 20 board | substrate (2nd board | substrate), 50 light source, 51R, 51G, 51B optical element, 52R, 52G, 52B liquid crystal light valve, 53R, 53G, 53B optical element, 54, 55 projection lens, 80 incident light, δ mutual distance, d mutual distance, λ wavelength, θ incident angle width, n refractive index

Claims (10)

An optical element having a function of polarizing and separating incident light,
A substrate transparent to the incident light;
The cross-sectional shape includes a plurality of convex portions having a sawtooth shape, and a diffractive structure portion provided on one surface side of the substrate;
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
The grid portion reflects one polarization component of the incident light and transmits another polarization component,
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:
satisfying the relationship of d <λ and λ / n <δ ≦ λ.
Optical element. An optical element having a function of polarizing and separating incident light,
A substrate transparent to the incident light;
The cross-sectional shape includes a plurality of convex portions having a sawtooth shape, and a diffractive structure portion provided on one surface side of the substrate;
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
The wavelength of the incident light is λ, the incident angle width of the incident light is ± θ, 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. When these parameters are
d <λ, and λ / (n−sin θ) <δ ≦ λ / (1 + sin θ).
Optical element. When m is an integer of 1 or more, the height of the convex portion of the diffractive structure portion is set to mλ / 2n.
The optical element according to claim 1. The extending direction of each of 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 convex portions of the diffractive structure portion and the extending direction of each of the plurality of fine lines of the grid portion intersect,
The optical element according to claim 1. A second substrate having a refractive index substantially equal to the substrate is bonded to the one surface of the substrate via an adhesive layer having a refractive index substantially equal to the substrate;
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. 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. The optical element according to any one of claims 1 to 7 is used as the first optical element, and the optical element is provided with one surface provided with the diffractive structure portion and the grid portion on the rear stage side. To be
The display device according to claim 8. The light source is a laser light source;
The display device according to claim 8 or 9.

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