JP2008008990A - Wavelength plate, image projector, and optical pick-up - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wavelength plate which can suitably secure the desired phase difference and transmissivity without using an auxiliary layer of a low refractivity thin film to improve the transmissivity even when placing this high refractivity thin film on the surface of this plate to secure a desired phase difference. <P>SOLUTION: In a wavelength plate, a phase difference is produced between two linear polarized light beams when they pass through the transparent substrate with their polarization plane perpendicularly crossing each other in their polarization plane. In this wavelength plate, a thin film 2 is formed in a periodic structure with fine irregularities arranged in a certain direction on the substrate 1 by using a material having a refractivity higher than the material of the substrate 1. For instance, the fine irregularities may be trigonous or trapezoidal in their cross section. Further, thin films 2a, 2b may be formed on both surfaces of the substrate 1, or a thin film 2 may be formed on one surface with an anti-reflection coating 3 formed on the other surface. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a wave plate, an image projection device, and an optical pickup device, and in particular, a low refractive index thin film for improving transmittance by providing a high refractive index thin film having a fine uneven periodic structure on a substrate surface. The present invention relates to a wave plate and the like that can suitably ensure a desired phase difference and transmittance without further using an auxiliary layer.

  A wave plate known as a kind of optical element has an optical function of giving a phase difference between mutually orthogonal polarization components, and is used in various optical devices. Conventionally, a wave plate using a uniaxial anisotropic crystal exhibiting birefringence, such as artificial or natural rutile, calcite, or quartz, is known, but an artificial one can grow a crystal uniformly. Difficult, natural crystals are optically uniform and large shapes are difficult to obtain and expensive.

  On the other hand, a wave plate having a periodic structure (sub-wavelength structure) shorter than the wavelength of transmitted light, more specifically, a wave plate in which a grating pattern is formed on the substrate surface with a periodic pitch shorter than the wavelength of transmitted light, etc. Has been proposed. Since such a wave plate exhibits optical anisotropy (birefringence) based on the grating pattern, a phase difference can be generated for two linearly polarized light whose polarization planes are orthogonal to each other.

  By the way, the transmittance and the phase difference are particularly important properties in the wave plate. As the wave plate, a wave plate having a high transmittance and capable of generating a desired phase difference with respect to the two linearly polarized lights whose polarization planes are orthogonal to each other is desirable. More specifically, the phase difference is expressed as a function of the refractive index of the material of the substrate, the depth of the grooves of the grating pattern formed on the substrate, and the like. The larger the refractive index of the material of the substrate and the deeper the groove of the lattice pattern, the larger the phase difference can be generated. However, as in the latter case, it is very difficult to produce a lattice pattern having deep grooves by molding or the like, and in particular, when considering mass productivity, a decrease in yield is inevitable.

  On the other hand, in Patent Document 1, for example, a dielectric medium having a sufficiently large refractive index compared to the refractive index of the substrate is coated or filled on the lattice pattern formed on the substrate, and the period equal to the lattice pattern is obtained. There has been proposed a wave plate adapted to form a pitch grating pattern. In such a wave plate, a dielectric medium having a sufficiently large refractive index as compared with the refractive index of the substrate forms a lattice pattern with a periodic pitch equal to the lattice pattern formed on the substrate, so that a larger phase difference is generated. To be able to. That is, the depth of the groove of the grating pattern formed on the substrate can be set smaller, and as a result, the wave plate can be manufactured more easily.

  Certainly, according to the wave plate proposed in Patent Document 1, it is possible to secure a large amount of the phase difference that can be generated by the wave plate. However, when the dielectric medium having a sufficiently large refractive index compared to the refractive index of the substrate is coated or filled on the lattice pattern formed on the substrate, the dielectric material is incident when light enters the wave plate. The amount of light reflected on the surface of the medium increases, and the transmittance decreases. That is, in the wave plate according to Patent Document 1, although the above-described dielectric medium is provided, the phase difference is improved, but the transmittance due to the dielectric medium is unavoidable. End up.

  On the other hand, for example, Patent Document 2 discloses the following wave plate. That is, a high refractive index film made of a film material having a refractive index higher than the refractive index of the material of the substrate is formed on the surface of the transparent substrate on which a lattice pattern is formed at a constant periodic pitch. In addition, a low refractive index film made of a film material having a lower refractive index than the film material of the high refractive index film is further formed on the surface of the high refractive index film. Then, in order to secure a desired phase difference, a wave plate that can suitably improve the transmittance while providing a film material having a higher refractive index than that of the substrate on the surface of the substrate. Is realized.

As described above, in the wave plate according to Patent Document 2, in order to secure a desired phase difference, a film material having a higher refractive index than that of the substrate is provided on the surface of the substrate to realize a wave plate with high transmittance. ing. However, the number of processes for further forming a low refractive index film is increased, and it is necessary to design in consideration of three layers of a substrate, a high refractive index film, and a low refractive index film that form a rectangular shape, and from the viewpoint of process control. Will also be complicated.
JP-A-7-99402 JP 2005-099099 A

  The present invention has been made in view of the above-mentioned circumstances, and although a high refractive index thin film is provided on the surface of the substrate to secure a desired phase difference, an auxiliary such as a low refractive index thin film for improving transmittance is provided. It is an object of the present invention to provide a wave plate that can suitably secure a desired phase difference and transmittance without further using a layer.

  In order to achieve such an object, the invention described in claim 1 is a wave plate that transmits a light-transmitting substrate and generates a phase difference between two linearly polarized light whose polarization planes are orthogonal to each other. A high refractive index thin film made of a high refractive index material having a refractive index higher than the refractive index is formed on the substrate, and the high refractive index thin film has a periodic structure in which fine concavo-convex structures are arranged in one direction as a sub-wavelength structure. It is characterized by having as.

  Specifically, the fine concavo-convex structure means that the pitch is smaller than the wavelength used (the wavelength of light when used as a wave plate). Further, the above substrate may be a parallel flat glass whose both surfaces are parallel, or a wedge-shaped flat plate in cross section.

  According to a second aspect of the present invention, in the wave plate according to the first aspect, the fine concavo-convex structure has a triangular cross section.

  In general, reflection of light is caused by a rapid change in refractive index. Therefore, by moderately changing the refraction, the reflectance can be lowered and the transmittance can be improved. In this respect, according to the triangular structure as the wave plate, the light entering the wave plate from the air having a refractive index of approximately 1 has a gradual change in the refractive index because its cross-sectional shape is triangular. As a result, it is possible to improve the transmittance of two linearly polarized light whose polarization planes are orthogonal to each other.

  In addition, when the refractive index difference between the substrate (glass flat plate or the like) and the high refractive index material is large, reflection also occurs here, resulting in a decrease in transmittance. In this case, it is good also as a structure which forms the thin film of the said high refractive index material on the glass substrate in which the antireflection coating was previously given.

  According to a third aspect of the present invention, in the wavelength plate according to the first aspect, the fine concavo-convex structure has a trapezoidal cross section.

  According to a fourth aspect of the present invention, in the wave plate according to the second or third aspect, the high refractive index thin film has a flat portion having a plane parallel to the substrate in a recessed portion of the fine concavo-convex structure. It is characterized by that.

  Further, the invention according to claim 5 is the wavelength plate according to any one of claims 1 to 4, wherein the high refractive index thin film has the fineness when the wavelength of light incident on the wavelength plate is λ. The pitch of the concavo-convex structure: P / λ and groove depth: H / λ are set so as to satisfy the conditions (1) 0 <P / λ <0.4 and (2) H / λ> 0.5. It is characterized by that.

  FIG. 20 shows a rectangular fine pattern in which a land and a space are formed at a ratio of 1: 1 on a substrate having a refractive index n = 1.5 with a pitch P / λ = 0.32 as shown in FIG. The relationship between the groove depth H / λ (horizontal axis) and the zero-order transmittance (vertical axis) in the periodic structure is shown.

  FIG. 21 shows a rectangular shape in which a land and a space are formed at a ratio of 1: 1 on a substrate having a refractive index n = 2.3, as shown in FIG. 19, with a pitch P / λ = 0.32. 2 shows the relationship between the groove depth H / λ (horizontal axis) and the zero-order transmittance (vertical axis) in the fine periodic structure. In FIG. 21, it can be seen that the transmittance is significantly reduced as compared with FIG.

  Although details will be described later, by satisfying the relationship described in claim 5, it is possible to obtain a transmittance higher than the transmittance (90%) of the rectangular cross section of FIG. 20 without providing an auxiliary layer or the like. .

  The invention according to claim 6 is the wave plate according to any one of claims 1 to 4, wherein the high refractive index thin film has the fine structure when the wavelength of light incident on the wave plate is λ. The pitch of the concavo-convex structure: P / λ and groove depth: H / λ satisfy the conditions: (1) 0 <P / λ <0.5, (2) 1.0 <H / λ <1.5 It is set and formed.

  Although details will be described later, by satisfying the relationship described in claim 6, it is possible to obtain a transmittance higher than the transmittance (90%) of the rectangular cross section in FIG.

  According to a seventh aspect of the present invention, in the wave plate according to the fifth or sixth aspect, the high refractive index thin film is formed on both front and back surfaces of the substrate.

  The wave plate according to any one of claims 1 to 6, wherein the high refractive index thin film is formed on one surface of the substrate and the antireflection film is formed on the other surface. Is formed.

  According to a ninth aspect of the present invention, in the image projection apparatus for guiding a light beam from a light source to a liquid crystal display element and projecting a display image of the liquid crystal display element onto a display surface by a projection lens, the light source and the projection The wave plate according to any one of claims 1 to 8 is arranged between the lenses.

  According to a tenth aspect of the present invention, in the optical pickup device that records and / or reproduces information by condensing and irradiating a light beam from a light source to an optical recording medium via an objective lens, the light source and the objective The wave plate according to any one of claims 1 to 8 is arranged between the lenses.

  According to the present invention, although a high refractive index thin film having a higher refractive index than that of the substrate is provided on the surface of the substrate in order to secure a desired retardation, an auxiliary layer such as a low refractive index thin film is used to improve the transmittance. Thus, a wave plate or the like that can suitably ensure a desired phase difference and transmittance can be realized.

  Hereinafter, embodiments of the present invention will be described. The embodiment is classified into a wave plate, an image projection device, and an optical pickup device. The wave plate is described in Embodiments 1 to 4, the image projection device is described in Embodiments 5 to 8, and the optical pickup device is described in Embodiment 9. .

[Embodiment 1]
FIG. 1 is a diagram for explaining a wave plate according to a first embodiment of the present invention. FIG. 1A is a perspective view showing the configuration of the wave plate of this embodiment. The wave plate has thin films 2 on both sides of a parallel plate-like glass plate 1 (for example, quartz substrate: refractive index 1.5). It has a formed configuration. The thin film 2 is formed of a material having a refractive index of 1.6 or more, and a “fine concavo-convex structure having a triangular cross section” is formed as a subwavelength structure as a surface shape thereof.

  FIG. 1B and FIG. 1C are diagrams for explaining the structure of the thin film of the wave plate. As will be described later, FIG. 1D and FIG. 1E are diagrams showing modifications of the element configuration of the wave plate. The unevenness of the fine unevenness structure has a triangular cross-sectional shape, and such triangular unevenness is formed with a uniform cross-sectional shape in the Y-axis direction. The pitch of the fine concavo-convex structure having a triangular cross section is P, and the groove depth is H. The aspect ratio is H / P, and the greater the aspect ratio, the greater the groove depth H with respect to the pitch P. The aspect ratio is preferably as small as possible from the viewpoint of easy formation of the fine relief structure.

  As is well known, when the fine concavo-convex structure is a sub-wavelength structure, it exhibits birefringence with respect to incident light. That is, as shown in FIG. 1C, in the incident light incident on the fine concavo-convex structure from the air region, the polarization component TM that vibrates parallel to the periodic direction (left-right direction in the drawing) of the fine concavo-convex structure (Y-axis direction ( The fine concavo-convex structure acts like a medium having a different refractive index with respect to the polarization component TE oscillating in parallel in a direction orthogonal to the drawing. For this reason, the phase of the polarization component TE is delayed by δ with respect to the polarization component TM in the transmitted light.

  That is, when the groove depth H is used, the optical thickness of the fine concavo-convex structure is H × n (TM) with respect to the polarization component TM and H × n (TE) with respect to the polarization component TE. A phase delay δ is generated according to H × {n (TE) −n (TM)}, which is a difference in optical thickness. This phase delay δ is retardation. If H × {n (TE) −n (TM)}, which is the difference in optical thickness, is D and the wavelength is λ, then δ = 2πD / λ.

As a high refractive index material for forming a thin film, a higher refractive index (for example, 1.6 or more) than quartz (n = 1.5) often used as a substrate material or BK7 (n = 1.5) manufactured by HOYA. You can choose the material. Inorganic materials such as TiO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ , ZrO ₂ , ITO (SnO ₂ + In ₂ O ₅ ), TiO ₂ , ZrO ₂ , Sb ₂ O ₅ , ITO, Al ₂ O _3, etc. A sol / gel material in which an element is bonded to the material, or a mixed material in which fine particles (5 nm to 100 nm) of the inorganic material are dispersed in a sol / gel material having a SiO ₂ skeleton, or photocuring A mold resin or a thermosetting resin having a refractive index of 1.6 or more can be used. The mixed material can be mixed and blended according to the characteristics. As the photocurable resin or thermosetting resin, for example, a resin having excellent optical characteristics such as a light transmitting adhesive is used.

  The inorganic material forms a thin layer by a film forming technique such as sputtering or vapor deposition. A sol / gel material, a mixed material, a photocurable resin, or a thermosetting resin forms a thin layer on a glass plate by spin coating or the like. A thin layer made of an inorganic material has a heat resistance of 200 ° C. or more, and is suitable as a thin layer of a wave plate or an optical element used in a high temperature environment.

  For example, a fine concavo-convex structure is formed by forming a resist layer on which a latent image is formed by scanning an electron beam on a thin layer, and drawing a pattern corresponding to the fine concavo-convex structure on the resist with an electron beam. And developing this to obtain a resist pattern corresponding to the fine relief structure, and etching the thin layer to a desired groove depth by etching such as RIE (reactive ion etching) using this resist pattern as a mask Can be formed. Moreover, when a thin layer is comprised with a thermosetting resin, it can also form with a thermal nanoimprint method.

  FIG. 2 is a diagram showing the optical characteristics of the wave plate of the present embodiment, in which light of wavelength λ is incident on a thin layer having a refractive index n = 2.3, and the pitch P / λ is used as a parameter. Depth: represents the relationship between H / λ (horizontal axis) and zero-order transmittance (vertical axis). 2A shows the transmittance of the TE direction component corresponding to the Y axis direction of FIG. 1A, and FIG. 2B shows the transmission of the TE direction component corresponding to the Y axis direction of FIG. Indicates the rate.

As shown in FIG. 20, in order to obtain a transmittance higher than the transmittance (90%) of the rectangular cross section, as a range of pitch P / λ and groove depth H / λ,
0 <P / λ <0.4
H / λ> 0.5
Is preferable (the range A 1 surrounded by a broken line in FIGS. 2A and 2B).

Further, as shown in FIG. 20, in order to obtain a transmittance higher than the transmittance (90%) of the rectangular cross section, the present invention is not limited to the above range, but pitch: P / λ, groove depth: H / As the range of λ,
0 <P / λ <0.5
1.0 <H / λ <1.5
However, it may be (range B 1 surrounded by a broken line in FIGS. 2A and 2B).

  FIG. 3 is a diagram showing the optical characteristics of the wave plate of the present embodiment. The groove depth H / λ (horizontal axis) when the refractive index n = 2.3 and the pitch P / λ = 0.32. This represents the relationship of retardation (vertical axis: wavelength unit). It can be seen that the retardation increases linearly as the groove depth H / λ increases. This means that H × {n (TE) −n (TM)}, which is the difference between the optical thickness of the fine concavo-convex structure with respect to the polarization component TM and the polarization component TE, is a linear function of the groove depth H. by. What is necessary is just to be able to ensure a desired phase difference in the range which satisfies said high transmittance | permeability. For example, in order to realize a ¼ wavelength plate, the retardation may be 0.25λ, and for that purpose, 0.72 may be selected as the groove depth: H / λ.

  Further, in order to realize a half-wave plate, the retardation only needs to be 0.5λ, and it is only necessary to select twice the groove depth H / λ of the quarter-wave plate. As shown in FIG. 1 (d), a thin film 2a and a thin film 2b having a high refractive index are formed on both surfaces of a glass flat plate 1, and a triangular cross section is formed on each surface, each corresponding to a quarter wavelength plate. The groove depth H / λ may be selected to be 0.72. The aspect can be reduced as compared with the case where the half-wave plate is formed with a structure of only one side.

  Further, when the wave plate is configured only on one side as shown in FIG. 1A, the antireflection film 3 may be formed on the other plane of the glass flat plate 1 as shown in FIG. In this case, for example, the antireflection film 3 may be formed by depositing an antireflection film having a four-layer structure in which high refractive index layers and low reflectance layers are alternately stacked, as conventionally known. Thereby, the transmittance | permeability of the wavelength plate as an element is securable. In addition, when a double-sided structure as shown in FIG. 1D is used, this step is not necessary. Therefore, when a high retardation wave plate is formed, a double-sided structure is desirable.

[Embodiment 2]
FIG. 4 is a diagram for explaining the wave plate according to the second embodiment of the present invention. 4A is a cross-sectional view showing the configuration of the wave plate of the present embodiment, and FIG. 4B is a diagram for explaining the structure of the thin film of the wave plate. The element configuration is not limited to the one in which the cross-sectional triangle shape is continuous in one direction as in the first embodiment, and a certain space is interposed between adjacent triangles as shown in FIG. It may be.

  FIG. 5 is a diagram showing the optical characteristics of the wave plate of the present embodiment. In a configuration formed on a thin layer having a refractive index n = 2.3, light having a wavelength λ is incident and the pitch P / λ is set as a parameter. The relationship between the groove depth H / λ (horizontal axis), 0th-order transmittance (vertical axis), and ± 1st-order diffracted light efficiency (vertical axis) is shown. As shown in FIG. 4B, assuming that triangles are continuously arranged without a space, the triangle height at that time is H ′, and the actual triangle height is H. FIGS. 5A to 5D show 0th-order transmittance and ± 1st-order diffraction efficiency when H / H ′ = 1, and FIGS. 5E to 5H show H / H ′ = 0. FIG. 5 (i) to (l) show the 0th-order transmittance and ± 1st-order diffraction efficiency when H / H ′ = 0.8. 5 (m) to 5 (p) show 0th-order transmittance and ± 1st-order diffraction efficiency when H / H ′ = 0.7.

As described in the first embodiment, the range of the pitch P / λ and the groove depth H / λ for obtaining a transmittance higher than the transmittance (90%) of the rectangular cross section shown in FIG.
0 <P / λ <0.4
H / λ> 0.5
Is preferred, but is not limited to the above range,
0 <P / λ <0.5
1.0 <H / λ <1.5
But you can.

  For example, when FIG. 5 (o) is compared with FIG. 5 (c), as H / H ′ decreases, ± first-order diffracted light remains even when the groove depth H / λ increases. From the viewpoint of transmittance, it is desirable that H / H ′ is large.

  FIG. 6 is a diagram showing the optical characteristics of the wave plate of the present embodiment. The groove depth H is set with H / H ′ as a parameter when the refractive index n = 2.3 and the pitch P / λ = 0.32. This represents the relationship between / λ (horizontal axis) and retardation (vertical axis: wavelength unit). Similar to the first embodiment, the retardation increases linearly as the groove depth H / λ increases. Although it is only necessary to ensure a desired phase difference within a range satisfying the above high transmittance, the retardation is constant when H / H ′ is in the range of 0.25 to 0.75. From the viewpoint of securing, it is desirable that H / H ′ is large. For example, in order to realize a quarter wavelength plate, the retardation may be 0.25λ, and 0.63 may be selected as the groove depth H / λ.

[Embodiment 3]
FIG. 7 is a diagram for explaining a wave plate according to a third embodiment of the present invention. FIG. 7A is a cross-sectional view showing the configuration of the wave plate of this embodiment, and FIG. 7B is a diagram for explaining the structure of the thin film of the wave plate. The element configuration is not limited to one in which the triangular cross section is continuous in one direction as in the first embodiment, and the trapezoidal cross section is continuous in one direction as shown in FIG. May be.

  FIG. 8 is a diagram showing optical characteristics of the wave plate of the present embodiment. In a configuration formed on a thin layer having a refractive index n = 2.3, light having a wavelength λ is incident and the pitch P / λ is set as a parameter. The relationship between the groove depth H / λ (horizontal axis), 0th-order transmittance (vertical axis), and ± 1st-order diffracted light efficiency (vertical axis) is shown. As shown in FIG. 7B, assuming that the triangles are continuously arranged without spaces, the height of the triangle is H ′ and the height of the trapezoid is H. 8 (a) to (d) show 0th-order transmittance and ± 1st-order diffraction efficiency when H / H ′ = 1, and FIGS. 8 (e) to 8 (h) show H / H ′ = 0.9. FIG. 8 (i) to (l) show the 0th order transmittance and the ± 1st order diffraction efficiency when H / H ′ = 0.8. 8 (m) to (p) indicate 0th-order transmittance and ± 1st-order diffraction efficiency when H / H ′ = 0.7.

  Further, as shown in FIG. 20, the range of the pitch P / λ and the groove depth H / λ for obtaining a transmittance higher than the transmittance (90%) of the rectangular cross section is the same as in the first and second embodiments. .

  For example, when FIG. 8 (o) is compared with FIG. 8 (c), as H / H ′ decreases, ± first-order diffracted light remains even if the groove depth H / λ increases. H ′ is preferably larger from the viewpoint of transmittance. Further, the structure of the present embodiment is more desirable than the structure of the second embodiment because the ± first-order diffraction efficiency is smaller than that of the second embodiment (FIG. 5). In contrast to Embodiments 1 and 2, which have a triangular shape and the tip of the convex portion is sharp and sharp, in this embodiment, the tip is flat, so there is no risk of damage due to contact or accidents. And process management can be simplified in the sense that mechanical strength becomes high.

  FIG. 9 is a diagram showing the optical characteristics of the wave plate of the present embodiment. The groove depth H is set with H / H ′ as a parameter when the refractive index n = 2.3 and the pitch P / λ = 0.32. This represents the relationship between / λ (horizontal axis) and retardation (vertical axis: wavelength unit). Similar to the first embodiment, the retardation increases linearly as the groove depth H / λ increases. What is necessary is just to be able to ensure a desired phase difference in the range which satisfies said high transmittance | permeability. For example, in order to realize a ¼ wavelength plate, the retardation may be 0.25λ. When H / H ′ is 0.75, 0.63 is selected as the groove depth H / λ. Good.

[Embodiment 4]
FIG. 10 is a diagram for explaining a wave plate according to a fourth embodiment of the present invention. FIG. 10A is a cross-sectional view showing the configuration of the wave plate of this embodiment, and FIG. 10B is a view for explaining the structure of the thin film of the wave plate. The element structure is not limited to the one in which the cross-sectional triangle shape is continuous in one direction as in the first embodiment, and a certain space is interposed between adjacent trapezoids as shown in FIG. It may be.

  FIG. 11 is a diagram showing the optical characteristics of the wave plate of the present embodiment. In a configuration formed on a thin layer having a refractive index n = 2.3, light having a wavelength λ is incident and the pitch P / λ is set as a parameter. The relationship between the groove depth H / λ (horizontal axis), 0th-order transmittance (vertical axis), and ± 1st-order diffracted light efficiency (vertical axis) is shown. As shown in FIG. 10B, assuming that triangles are continuously arranged without spaces, the height of the triangle is H ′ and the height of the trapezoid is H. 11 (a) to 11 (d) show 0th-order transmittance and ± 1st-order diffraction efficiency when H / H ′ = 1, and FIGS. 11 (e) to 11 (h) show H / H ′ = 0.9. FIGS. 11 (i) to 11 (l) show the 0th order transmittance and the ± 1st order diffraction efficiency when H / H ′ = 0.8. 11 (m) to (p) indicate the 0th-order transmittance and ± 1st-order diffraction efficiency when H / H ′ = 0.7.

  Further, as shown in FIG. 20, the range of the pitch P / λ and the groove depth H / λ for obtaining a transmittance higher than the transmittance (90%) of the rectangular cross section is the same as in the first to third embodiments. .

  For example, when FIG. 11 (o) is compared with FIG. 11 (c), as H / H ′ decreases, ± first-order diffracted light remains even when the groove depth H / λ increases. H ′ is preferably larger from the viewpoint of transmittance.

  FIG. 12 is a diagram showing the optical characteristics of the wave plate of the present embodiment. The groove depth H is defined by using H / H ′ when the refractive index n = 2.3 and the pitch P / λ = 0.32 as parameters. This represents the relationship between / λ (horizontal axis) and retardation (vertical axis: wavelength unit). Similar to the first embodiment, the retardation increases linearly as the groove depth H / λ increases. Further, the retardation tends to increase as H / H ′ increases. For example, in order to realize a ¼ wavelength plate, the retardation may be 0.25λ. When H / H ′ is 0.75, 0.58 is selected as the groove depth H / λ. Good.

[Embodiment 5]
FIG. 13 is a diagram showing the configuration of the image projection apparatus in the embodiment of the present invention. The image projection apparatus 100 includes three liquid crystal display elements 110, 111, and 112 that individually form images of the respective colors corresponding to the three primary colors, and a cross prism 113 that combines the image lights of the respective colors emitted from these liquid crystal display elements. In addition, the three optical paths between the liquid crystal display elements and the cross prism 113 include the wave plates 116, 117, and 118 corresponding to the half-wave plates in the above-described embodiment.

  White light emitted from the white light source 101 is reflected by the reflector 102 and enters the dichroic mirror 103. The dichroic mirror 103 transmits light having a blue wavelength or less and reflects light having a wavelength longer than the blue wavelength. Therefore, among the white light incident on the dichroic mirror 103, the blue component is transmitted through the dichroic mirror 103, and the green component and the red component are reflected by the dichroic mirror 103 and incident on the dichroic mirror 104.

  The dichroic mirror 104 transmits light having a wavelength longer than the red wavelength and reflects light having a wavelength shorter than the red wavelength. Therefore, of the light incident on the dichroic mirror 104, the green component is reflected by the dichroic mirror 104 and the red component is transmitted through the dichroic mirror 104. In this manner, the white light from the white light source 101 is color-separated by the dichroic mirrors 103 and 104 into three primary color component lights of red, green, and blue.

  The blue component light transmitted through the dichroic mirror 103 is reflected by the mirror 105 and enters the liquid crystal display element 110, and the green component light reflected by the dichroic mirror 104 enters the liquid crystal display element 111. The red component light transmitted through the dichroic mirror 104 follows the optical path formed by the relay lens 108, the mirror 106, the relay lens 109, and the mirror 107 and enters the liquid crystal display element 112. The relay lenses 108 and 109 perform optical path length correction of red component light.

  The liquid crystal display elements 110, 111, and 112 have a liquid crystal layer sandwiched between a pair of polarizers, and the pair of polarizers sandwiching the liquid crystal layer have their polarization directions orthogonal to each other. Each color component light passes through the incident side polarizer of the corresponding liquid crystal display element and becomes linearly polarized light and enters the liquid crystal layer. Image signals are applied to the liquid crystal display elements 110, 111, and 112 so as to display a blue image, a green image, and a red image, respectively, and the light transmitted through the liquid crystal layer at the pixel position of the image to be projected is polarized. The surface rotates 90 degrees, and has the same polarization direction as that of the exit-side polarizer and passes through the exit-side polarizer.

  In this way, the liquid crystal display element 110 emits blue component light (hereinafter referred to as blue video light) that is two-dimensionally intensity-modulated according to the blue image. Similarly, the liquid crystal display element 111 emits green component light that is two-dimensionally intensity-modulated according to the green image (hereinafter referred to as green video light), and the liquid crystal display element 112 outputs 2 according to the red image. Red component light (hereinafter referred to as red image light) that is dimensionally intensity-modulated is emitted. That is, the liquid crystal display elements 110, 111, and 112 individually form images corresponding to the three primary colors (blue, green, and blue).

  Each color image light emitted from each liquid crystal display element has a polarization direction parallel to the plane of the drawing. The blue image light emitted from the liquid crystal display element 110 is incident on the wave plate 116, and the green image light and red image light emitted from the liquid crystal display elements 111 and 112 are incident on the wave plates 117 and 118, respectively.

  The wave plates 116, 117, and 118 are ½ wavelength plates, and give a phase difference of ½ wavelength to two orthogonal components of transmitted light. Since each color image light incident on these wave plates is polarized in a plane parallel to the drawing as described above, the transmitted light is rotated by 90 degrees from the direction of incidence of the transmitted light and is orthogonal to the drawing. It becomes a light beam polarized in the direction and enters the cross prism 113 from the corresponding surface.

  The cross prism 113 is a rectangular parallelepiped made of a light-transmitting material having a square cross-sectional shape when viewed from a direction orthogonal to the drawing, and has reflection surfaces 113a and 113b orthogonal to each other. The reflective surface 113a is a dichroic mirror that reflects light having a wavelength less than or equal to the blue wavelength and transmits light having a wavelength longer than the blue wavelength, and the reflective surface 113b reflects light having a wavelength that is greater than or equal to the red wavelength. The dichroic mirror transmits light having a wavelength shorter than the wavelength.

  Of the color image lights incident on the cross prism 113, the blue image light is reflected on the reflection surface 113a, the red image light is reflected on the reflection surface 113b, and the green image light is transmitted through the reflection surfaces 113a and 113b. The colors are synthesized and emitted from the cross prism 113. The emitted light beam is incident on the projection lens 114 and enlarged and projected on the screen 115 as a display surface by the projection lens 114 to display a projected image.

  Here, the reflecting surfaces 113a and 113b have directionality with respect to the polarization axis of the reflected light or transmitted light. In general, it has higher transmittance for one polarization direction. Therefore, in order to optimize the polarization direction of the incident light to the cross prism and the polarization axis of the reflecting surface, a half-wave plate is appropriately inserted in front of the cross prism. FIG. 13 shows the case where a half-wave plate is inserted for any of blue, green, and red wavelengths, but a half-wave plate is inserted for only one of the input wavelengths. It may be configured to.

[Embodiment 6]
FIG. 14 is a diagram illustrating the configuration of the image projection apparatus according to the embodiment of the present invention. This embodiment is a modification of the image projection apparatus according to the fifth embodiment. In order to avoid complications, those that are not likely to be confused are given the same reference numerals as in FIG. 13, and the explanations relating to FIG.

  The image projection apparatus according to this embodiment is obtained by adding a uniform illumination unit 201 (optical integrator) and a polarization conversion element 202 between the white light source 101 and the dichroic mirror 103 to the image projection apparatus according to the fifth embodiment. is there.

  The uniform illumination unit 201 that is an optical integrator is a unit that makes the amount of light irradiated to the liquid crystal display element substantially uniform. For example, a well-known unit composed of a fly-eye lens, a rod lens, a rectangular lens array, or the like can be used as appropriate.

  The liquid crystal display elements 110, 111, and 112 use the polarization characteristics of the liquid crystal and can achieve high contrast. However, since the liquid crystal is sandwiched between a pair of polarizers, If the irradiation light incident on the liquid crystal display element is in a naturally polarized state, half of the amount of illumination light is blocked when passing through the incident side polarizer of each liquid crystal display element, and the light utilization efficiency is reduced. bad.

  The polarization conversion element 202 is used to effectively use the light from the white light source 101 and align the polarization direction of the light incident on the liquid crystal display element in order to brighten the projected image on the screen. The polarization conversion element 202 converts the polarization state of the illumination light from the light source side from the natural polarization state to the linear polarization state while substantially preserving the light intensity of the illumination light. If the polarization direction of the linearly polarized illumination light is aligned with the polarization direction of the incident-side polarizer in the liquid crystal display element, approximately 100% of the illumination light from the light source side can be used for displaying a projected image. Can do.

  FIG. 15 is a diagram illustrating the configuration of the uniform illumination unit and the polarization conversion element in the image projection apparatus according to the present embodiment. The white light beam from the light source 101 is uniformized by the uniform illumination unit 201 and the polarization state is converted by the polarization conversion unit 202. It is a figure for demonstrating the state converted.

  The white light beam from the light source 101 side is transmitted through a known uniform illumination unit 201 configured by arranging a pair of condensing lens arrays (fly eye lens arrays) so as to be incident on the polarization conversion unit 202.

  The polarization conversion means 202 has an optical base 202A and a wave plate portion 202B. As shown in FIG. 15A, the optical base 202A has a polarization separation surface 2021 and a reflection surface 2022 inclined by 45 degrees with respect to the optical axis of the illumination light.

  The polarization separation surface 2021 divides incident light into reflected light S (hereinafter referred to as S component) and transmitted light P (hereinafter referred to as P component) whose polarization surfaces are orthogonal to each other. The reflecting surface 2022 reflects the S component and directs it in the direction substantially the same as the traveling direction of the P component.

  Further, the combination of the polarization separation surface 2021 and the reflection surface 2022 is one unit, and a plurality of such units are provided over the transmission region of the illumination light, forming a so-called polarization prism lens array, and the individual elements constituting the array. For each polarizing prism, the transmitted illumination light is divided into an S component and a P component.

  The wave plate portion 202B rotates the polarization plane of the S component emitted from the optical substrate 202A by 90 degrees and aligns it with the polarization direction of the P component. In this way, linearly polarized illumination light having a uniform polarization direction is obtained. Of course, the polarization direction of the illumination light is the same as the polarization direction of the incident-side polarizer of each liquid crystal display element.

  As shown in FIG. 15 (b), the wave plate portion 202B includes a fine concavo-convex structure 2021B having a rectangular cross section on the surface of a thin layer 202B2 made of a material having a refractive index of 1.6 or more formed on one surface of a glass flat plate 202B1. 2022B, 2023B, and the like are formed as sub-wavelength structures, and each fine concavo-convex structure 2021B is provided with a function as a half-wave plate.

  The glass flat plate 202B1 is integrated with the surface of the optical base body 202A on the side where the illumination light having the same direction is emitted, and the fine concavo-convex structure 2021B and the like are formed in the portion where the S component is emitted. The wave plate portion 202B and the optical base body 202A may be joined with the thin layer 202B2 on the side of the optical base body 202A. In this way, the fine uneven structure can be better protected by the glass flat plate 202B1. Further, the thin layer 202B2 may be directly formed on the optical base 202A without using the glass flat plate 202B1.

[Embodiment 7]
FIG. 16 is a diagram illustrating the configuration of the image projection apparatus according to the embodiment of the present invention. This embodiment is a modification of the image projection apparatus according to the fifth embodiment. The image projection apparatus according to the present embodiment is a single-plate liquid crystal image projection apparatus. As shown in FIG. 16, an illumination device 300 that can emit white light and a color image formed by modulating the emitted white light. And a liquid crystal display element 308 that projects and a projection lens 309 that projects a color image.

  The illuminating device 300 is roughly configured by an LED chip 301 that emits white light, a substrate 302 on which the LED chip 301 is mounted, and a rod lens 303 that equalizes the illuminance distribution of the emitted light from the LED chip 301. .

  Further, the quarter-wave plate 306 and the polarizing plate 307a of the above-described embodiment are disposed on the light emitting side end face 303b of the rod lens 303. A color filter 308 a that converts white light into RGB light is disposed on the light incident surface of the liquid crystal display device 308, and a polarizing plate 307 is disposed on the light exit surface of the liquid crystal display device 308.

  The illumination device 300 emits white light from the LED chip 301 when power is supplied to the LED chip 301. White light propagates through the filler 304 a and enters the surface of the recess 304 that is a boundary surface with the rod lens 303. Since the filler 304 a has a higher refractive index than the rod lens 303, the white light is refracted at the boundary surface and propagates into the rod lens 303.

  The white light propagating in the rod lens 303 is totally reflected in the rod lens 303 to make its illuminance distribution uniform, and is emitted from the light emitting side end face 303b. White light with uniform illuminance distribution is incident on the quarter-wave plate 306, but since the white light emitted from the LED chip 301 is randomly polarized light, it is randomly polarized even if it passes through the quarter-wave plate 306. It is emitted as it is.

  The white light is incident on the polarizing plate 307a, the p-polarized light (one polarized light) is transmitted through the reflective polarization separation layer as it is, and is emitted toward the liquid crystal display device 308, and the s-polarized light (the other polarized light) is the polarizing plate. Reflected by 307a. The reflected s-polarized light reenters the quarter-wave plate 306, is converted into, for example, clockwise circularly polarized light, and is emitted toward the rod lens 303.

  The clockwise circularly polarized light propagating through the rod lens 303 is incident on the reflection layer 305 formed on the LED side end surface 303a of the rod lens and is reflected again toward the polarizing plate 307a. Also, when reflected by the reflective layer 305, clockwise circularly polarized light is converted into counterclockwise circularly polarized light.

  The counterclockwise circularly polarized light propagates through the rod lens 303 and enters the quarter-wave plate 306 and is converted to p-polarized light. Since the p-polarized light can pass through the polarizing plate 307 a, it is transmitted as it is and emitted toward the liquid crystal display device 308.

  In this way, the p-polarized light of the white light emitted from the illumination device 300 is incident on the entire surface of the liquid crystal display device 308 with a uniform illuminance distribution. The white light incident on the liquid crystal display device 308 is first converted into RGB color light by the color filter 308a, and then modulated by the liquid crystal display device 308 to form a color image. The synthesized color image is then projected onto the screen 310 by the projection lens 309.

  According to the above, the image projection apparatus has the configuration of the single plate type image projection apparatus including one illumination device 300 including the LED chip 301 that emits white light and one liquid crystal display device 308 including the color filter 308a. Can be reduced in size, weight, and cost.

  In addition, although this embodiment demonstrated using the LED chip 301 which radiate | emits white light, you may arrange | position the LED chip which radiate | emits RGB color light, respectively. In addition, when LED chips that emit RGB color light are arranged instead of the LED chip 301, the LED chip 301 may be made to continuously emit light simultaneously using the color filter 308a as in the present embodiment. The RGB LED chip 301 may be caused to emit alternating light without using 308a. In this case, since it is not necessary to use the color filter 308a, the price of the image projection apparatus can be further reduced.

[Embodiment 8]
FIG. 17 is a diagram illustrating the configuration of the image projection apparatus according to the embodiment of the present invention. This embodiment is a modification of the image projection apparatus according to the fifth embodiment. The image projection apparatus is not limited to the one using the above-described transmission type liquid crystal display element, and may be one using a reflection type liquid crystal display element, for example.

  The image projection apparatus according to the present embodiment performs the polarization conversion of the light incident from the rod lens 411 and the rod lens 411 for uniformizing the illuminance of the white light emitted from the LED 410 that can emit white light. The quarter wavelength plate 412 and the polarizer 413 of the above-described embodiment are sequentially provided.

  White light from the LED 410 is incident on a polarization beam splitter (PBS) 414. Only the S wave component of the light incident on the PBS 414 is reflected by the joint surface, and is incident on the reflective liquid crystal display element 415.

  The reflective liquid crystal display element 415 spatially modulates incident light in accordance with a video signal, converts it into a polarization plane component orthogonal to the polarization plane of the incident light, and reflects it. In this embodiment, high-speed switching is performed. An LCOS (Liquid Crystal On Silicon) element that can be used is used.

  Then, the reflected light that has been modulated based on the video signal and converted to P-polarized light passes through the S-polarized reflection surface and enters the projection lens 416. In this way, the light given the video information is enlarged and projected on the screen 417 via the projection lens 416.

[Embodiment 9]
FIG. 18 is a diagram showing the configuration of the optical pickup device in the embodiment of the present invention. The wave plate of the above-described embodiment may be used as an optical module other than the image projection apparatus, and can be used for an optical pickup apparatus, for example.

  The optical pickup device 501 includes a light source 502, a diffraction grating 503, a polarizing beam splitter 504, a quarter wavelength plate 505, a collimator lens 506, an objective lens 507, an optical recording medium 509, a cylindrical lens 510, and a photodetector 511. is doing.

  In addition, the optical pickup device 501 converts the light emitted from the light source 502 such as a laser diode into a diffraction grating 503, a polarizing beam splitter 504, a quarter wavelength plate 505, a collimator lens 506, and an objective, which are separately provided. The lens 507 is sequentially transmitted to irradiate the optical recording medium 509, and the reflected light is transmitted through the objective lens 507 and the quarter-wave plate 505, and then orthogonal to the transmission direction in the polarization beam splitter 504. It is configured to reflect in the direction.

  The reason why the light is reflected by the polarization beam splitter 504 is that the polarization of the light changes when it passes through the quarter-wave plate 505 twice. For example, if the light from the light source 502 is s-polarized light, the light transmitted through the quarter-wave plate 505 twice becomes p-polarized light.

  The light reflected by the polarization beam splitter 504 is collected by the cylindrical lens 510 and then received by the photodetector 511 to be used as read data or the like.

  According to the above-described embodiment, a high refractive index thin film made of a high refractive index material having a refractive index higher than that of the glass flat plate material is formed on the glass flat plate, and the thin film has a fine concavo-convex structure having a triangular cross section. Since the subwavelength structure has a periodic structure arranged in one direction, a desired phase difference and transmittance can be suitably ensured without providing an auxiliary layer such as a low refractive index layer.

  Further, according to the embodiment described above, a high refractive index thin film made of a high refractive index material having a refractive index higher than the refractive index of the glass flat plate material is formed on the glass flat plate, and the thin film is a depression of a fine uneven structure. Since a flat portion having a plane parallel to the glass flat plate is formed in the portion, a desired phase difference and transmittance can be suitably ensured without providing an auxiliary layer such as a low refractive index layer.

  Further, according to the embodiment described above, the high refractive index thin film made of the high refractive index material having a refractive index higher than the refractive index of the material of the substrate is formed on the glass flat plate, and the thin film has a fine unevenness having a trapezoidal cross section. Since the subwavelength structure has a periodic structure in which the structures are arranged in one direction, a desired phase difference and transmittance can be suitably ensured without providing an auxiliary layer such as a low refractive index layer. Moreover, since the triangular tip is flat, the strength against contact is improved. Therefore, an optical element having an antireflection structure that is easy to manufacture and has high mechanical strength is realized.

  Further, according to the embodiment described above, a high refractive index thin film made of a high refractive index material having a refractive index higher than the refractive index of the glass flat plate material is formed on the glass flat plate, and the thin film is a depression of a fine uneven structure. Since a flat portion having a plane parallel to the glass flat plate is formed in the portion, a desired phase difference and transmittance can be suitably ensured without providing an auxiliary layer such as a low refractive index layer. Moreover, since the triangular tip is flat, the strength against contact is improved. Therefore, an optical element having an antireflection structure that is easy to manufacture and has high mechanical strength is realized.

  Further, according to the above-described embodiment, when the wavelength of light incident on the wave plate is λ, the high refractive index thin film has a range of fine concavo-convex structure pitch: P / λ and groove depth: H / λ. , (1) Since 0 <P / λ <0.4 and (2) H / λ> 0.5, the high transmittance can be secured.

  Further, according to the above-described embodiment, when the wavelength of light incident on the wave plate is λ, the high refractive index thin film has a range of fine concavo-convex structure pitch: P / λ and groove depth: H / λ. Since (1) 0 <P / λ <0.5 and (2) 1.0 <H / λ <1.5, the high transmittance can be secured. it can.

  Further, according to the above-described embodiment, the high refractive index thin film having the fine uneven structure is formed on both the front and back surfaces of the glass flat plate, so that the aspect of the structure can be reduced.

  Further, according to the above-described embodiment, the high refractive index thin film having a fine concavo-convex structure is formed on one surface of the glass plate, and the antireflection film is formed on the back surface on which the thin film is formed. It is possible to further reduce the transmittance loss as a wave plate.

  Further, according to the above-described embodiment, in the image projection apparatus that guides the light flux from the light source to the liquid crystal display element and projects the display image of the liquid crystal display element on the display surface by the projection lens, the light source and the projection lens Since the wave plate to which the present invention is applied is mounted in between, it is possible to reduce the cost of the optical device and to ensure the transmittance characteristic and the retardation characteristic.

  Further, according to the above-described embodiment, the present invention is applied between the light source and the objective lens in the optical pickup device that records and reproduces information by collecting and irradiating the light flux from the light source to the optical recording medium via the objective lens. Since the wavelength plate to be mounted is mounted, it is possible to reduce the cost of the optical device, and to ensure the transmittance characteristics and the retardation characteristics.

  The above-described embodiment is a preferred embodiment of the present invention, and the scope of the present invention is not limited to the above-described embodiment alone, and various modifications are made without departing from the gist of the present invention. Implementation is possible.

It is a figure for demonstrating the wave plate which concerns on embodiment of this invention. It is the figure which showed the optical characteristic of the wavelength plate which concerns on this embodiment of this invention. It is the figure which showed the optical characteristic of the wavelength plate which concerns on this embodiment of this invention. It is a figure for demonstrating the wave plate which concerns on embodiment of this invention. It is the figure which showed the optical characteristic of the wavelength plate which concerns on this embodiment of this invention. It is the figure which showed the optical characteristic of the wavelength plate which concerns on this embodiment of this invention. It is a figure for demonstrating the wave plate which concerns on embodiment of this invention. It is the figure which showed the optical characteristic of the wavelength plate which concerns on this embodiment of this invention. It is the figure which showed the optical characteristic of the wavelength plate which concerns on this embodiment of this invention. It is a figure for demonstrating the wave plate which concerns on embodiment of this invention. It is the figure which showed the optical characteristic of the wavelength plate which concerns on this embodiment of this invention. It is the figure which showed the optical characteristic of the wavelength plate which concerns on this embodiment of this invention. It is the figure which showed the structure of the image projection apparatus which concerns on embodiment of this invention. It is the figure which showed the structure of the image projection apparatus which concerns on embodiment of this invention. It is the figure which showed the structure of the uniform illumination means and the polarization conversion element in the image projection apparatus which concerns on embodiment of this invention. It is the figure which showed the structure of the image projection apparatus which concerns on embodiment of this invention. It is the figure which showed the structure of the image projection apparatus which concerns on embodiment of this invention. It is the figure which showed the structure of the optical pick-up apparatus which concerns on embodiment of this invention. It is a figure for demonstrating the fine periodic structure in the conventional wavelength plate. It is the figure which showed the optical characteristic of the conventional wavelength plate. It is the figure which showed the optical characteristic of the conventional wavelength plate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Glass flat plate 2, 2a, 2b Thin film 3 Antireflection film 100 Image projection apparatus 101 White light source 102 Reflector 103,104 Dichroic mirror 105,106,107 Mirror 108,109 Relay lens 110,111,112,308 Liquid crystal display element 113 Cross Prism 113a, 113b Reflecting surface 114 Projection lens 115 Screen 116, 117, 118 Wavelength plate 201 Uniform illumination means 202 Polarization conversion element 202A Optical substrate 202B Wavelength plate portion 202B1 Glass flat plate 202B2 Thin layer 2021B, 2022B, 2023B Fine uneven structure 301,410 LED chip (LED)
302 Substrate 303, 411 Rod lens 303a LED side surface 303b Light emission side end surface 304 Concave 304a Filler 305 Reflective layer 306, 412, 505 1/4 wavelength plate 307, 307a Polarizing plate 308a Color filter 309, 416 Projection lens 310, 417 Screen 413 Polarizer 414, 504 Polarizing beam splitter (PBS)
415 Reflective liquid crystal display element 501 Optical pickup device 502 Light source 503 Diffraction grating 506 Collimator lens 507 Objective lens 509 Optical recording medium 510 Cylindrical lens 511 Photo detector

Claims (10)

In a wave plate that causes a phase difference between two linearly polarized lights that are transmitted through a translucent substrate and orthogonal to each other in the plane of polarization,
A high refractive index thin film made of a high refractive index material having a refractive index higher than that of the material of the substrate is formed on the substrate,
The wave plate according to claim 1, wherein the high refractive index thin film has a subwavelength structure having a periodic structure in which fine uneven structures are arranged in one direction.   The wave plate according to claim 1, wherein the fine concavo-convex structure has a triangular cross section.   The wave plate according to claim 1, wherein the fine uneven structure has a trapezoidal cross section.   4. The wave plate according to claim 2, wherein the high refractive index thin film is formed with a flat portion having a surface parallel to the substrate in a depressed portion of the fine concavo-convex structure. In the high refractive index thin film, when the wavelength of light incident on the wave plate is λ, the pitch of the fine concavo-convex structure is P / λ and the groove depth is H / λ (1) 0 <P / λ < 0.4
(2) H / λ> 0.5
5. The wave plate according to claim 1, wherein the wave plate is formed so as to satisfy the above. In the high refractive index thin film, when the wavelength of light incident on the wave plate is λ, the pitch of the fine concavo-convex structure is P / λ and the groove depth is H / λ (1) 0 <P / λ < 0.5
(2) 1.0 <H / λ <1.5
5. The wave plate according to claim 1, wherein the wave plate is formed so as to satisfy the above.   The wave plate according to claim 5, wherein the high refractive index thin film is formed on both front and back surfaces of the substrate.   The wavelength plate according to claim 1, wherein the high refractive index thin film is formed on one surface of the substrate, and an antireflection film is formed on the other surface. In an image projection apparatus that guides a light beam from a light source to a liquid crystal display element and projects a display image of the liquid crystal display element on a display surface by a projection lens,
9. An image projection apparatus, wherein the wave plate according to claim 1 is disposed between the light source and the projection lens. In an optical pickup device that records and / or reproduces information by condensing and irradiating a light beam from a light source onto an optical recording medium via an objective lens,
9. An optical pickup device, wherein the wave plate according to claim 1 is disposed between the light source and the objective lens.

Images