JPWO2014013712A1 - Optical device and display device using the same - Google Patents

Abstract

[PROBLEMS] To provide an optical device that converts random polarized light having a high etendue into light having a low etendue consisting of only a polarized light component in a specific direction. [Solution] A light guide layer having a periodic structure on a first surface and a metal layer provided on the first surface, wherein the light guide layer transmits light into the light guide layer. And at least one incident surface for incident light, and at least one light emitting surface for emitting light inside the light guide layer to the outside of the light guide layer except for the incident surface and the first surface.

Description

  The present invention relates to an optical device and a display device using the same.

  In recent years, an LED projector using an LED (Light Emitting Diode) as a light source has attracted attention. The LED projector includes an LED, an illumination optical system into which light emitted from the LED is incident, a modulation element that modulates and emits light from the illumination optical system according to a video signal, and projects light from the modulation element onto a screen. And a projection optical system.

  In such an LED projector, in order to increase the brightness of the projected image, it is required to efficiently use the emitted light from the light source as the projected light. In order for the light emitted from the light source to be efficiently used as the projection light, the etendue obtained by the product of the light emitting area and the radiation angle of the light source has an acquisition angle determined by the light receiving area of the modulation element and the F number of the illumination optical system. Must be less than product value.

  In addition, in an LED projector, a modulation element having polarization dependency such as a liquid crystal panel may be used. In this case, since the emitted light of the LED is random polarized light, in order to efficiently use the emitted light of the light source as projection light, it is necessary to convert the random polarized light into a specific polarization state.

  Patent Document 1 can be exemplified as a technique for converting random polarization into a specific polarization state. For example, a planar optical device disclosed in Patent Document 1 includes a light guide 10, a polarization direction changing member 13 provided on the lower surface of the light guide 10, and a stepped microprism 14 as shown in FIG. A light guide plate 3 including a reflection plate 6, a polarization separation film 11 provided on the upper surface of the light guide 10, and a top cover 12 provided on the upper surface of the polarization separation film 11. The polarization separation film 11 has a configuration in which a metal thin film is sandwiched between a first low refractive index transparent medium and a second low refractive index transparent medium.

  In the above planar optical device, the light emitted from the LED 2 enters the light guide 10 and propagates through the light guide 10 while being angle-converted by the microprism 14. When incident light is totally reflected at the first boundary, which is the boundary between the light guide 10 and the first low-refractive-index transparent medium, surface plasmons are excited in the metal thin film by the evanescent wave generated at that time.

  When surface plasmon is excited in the metal thin film, a transition process opposite to the surface plasmon excitation process occurs at the second boundary, which is the boundary between the second low-refractive-index transparent medium and the top cover 12, and the second Light is generated at the boundary. The light generated at the second boundary is emitted through the top cover 12.

  In the above planar optical device, among the light incident on the first boundary, the light that excites the surface plasmon is only the P-polarized light whose electric field component is parallel to the first boundary. The light generated at the second boundary is generated by the reverse process of the excitation process of the surface plasmon, and thus has the same P polarization as the light that excites the surface plasmon. Therefore, the above planar optical device can emit random polarized light after converting it into a specific polarization state.

JP 2003-295183 A

  However, in the planar optical device according to the related art described above, the light traveling in the light guide 10 is propagated not only in a specific direction but also in various directions, and enters the first boundary surface from various directions. To do. As a result, surface plasmons propagating in various directions are generated in the plane of the metal thin film surface, and light generated at the second boundary is emitted in various directions. For this reason, there is a problem that it is difficult to obtain light in a specific polarization state, which is a low etendue state in which the emission direction is set in a specific direction.

  Therefore, a main object of the present invention is to provide an optical device and a display device that can convert random polarized light with high etendue into light of a specific polarization state with low etendue.

  In order to solve the above problems, an optical device includes a light guide layer having a periodic structure on a first surface and a metal layer provided on the first surface, and the light guide layer guides light. At least one incident surface that is incident on the inside of the layer, and at least one emission surface that emits light inside the light guide layer to the outside of the light guide layer, excluding the incident surface and the first surface. It is characterized by including.

  According to the present invention, it is possible to convert random polarized light having a high etendue into light having a specific polarization state which is a low etendue state in which the emission direction is set in a specific direction.

1 is a perspective view schematically showing an optical device according to a first embodiment of the present invention. It is explanatory drawing explaining operation | movement of the optical apparatus of 1st Embodiment. It is sectional drawing which shows typically the shape example of the periodic structure of 1st Embodiment. It is a graph which shows an example of operation | movement of the optical apparatus of a 1st Example. It is a perspective view which shows typically the optical apparatus of the 2nd Embodiment of this invention. It is explanatory drawing for demonstrating operation | movement of the optical apparatus of 2nd Embodiment. It is a graph which shows an example of operation | movement of the optical apparatus of a 2nd Example. It is a perspective view of the optical apparatus of the 3rd Embodiment of this invention. It is explanatory drawing for demonstrating operation | movement of the optical apparatus of 3rd Embodiment. It is a perspective view of the optical apparatus of the 4th Embodiment of this invention. It is explanatory drawing for demonstrating operation | movement of the optical apparatus of 4th Embodiment. It is a perspective view of the optical apparatus of the 5th Embodiment of this invention. It is a perspective view of the optical apparatus of the 6th Embodiment of this invention. It is a perspective view of the optical apparatus of the 7th Embodiment of this invention. It is a top view of the display apparatus of the 8th Embodiment of this invention. It is a top view of the display apparatus of the 9th Embodiment of this invention. FIG. 11 is an explanatory diagram for explaining the operation of the planar optical device of Patent Document 1.

[First Embodiment]
A first embodiment of the present invention will be described. FIG. 1 is a perspective view schematically showing an optical device 100 according to the first embodiment of the present invention. In an actual optical device, the thickness of each layer is very thin and the difference in thickness between the layers is large, so it is difficult to illustrate each layer with an accurate scale and ratio. For this reason, in the drawings, the layers are not schematically drawn but are shown schematically.

  The optical device 100 includes a light source 101, a light guide layer 102, and a metal layer 103.

  The light source 101 is disposed on the outer periphery of the light guide layer 102 and emits randomly polarized light to the light guide layer 102. The light source 101 may be disposed at a position away from the light guide layer 102, may be disposed so as to contact the light guide layer 102, or optically via a light guide member such as a light pipe. The light guide layer 102 may be connected.

  The upper surface (first surface) of the light guide layer 102 is provided with a one-dimensional periodic structure, and has a specific incident angle with respect to the periodic structure in the light guide layer 102 described later and the period of the periodic structure. The P-polarized light having the main component in the direction parallel to the direction is diffracted through the surface plasmon, and is emitted to the outside from the lower surface (emission surface) of the light guide layer 102.

  The light guide layer 102 is made of a transparent material that transmits at least visible light, and serves as a medium that propagates light. Further, as will be described later, the light guide layer 102 has a specific refractive index described later with respect to visible light.

  The metal layer 103 is made of a material that does not transmit at least visible light, and the single metal layer reflects light. As will be described later, the metal layer 103 is formed of a metal capable of exciting surface plasmons on the surface by visible light.

  The light guide layer 102 receives light emitted from the light source 101 and propagates the incident light inside. A structure having a period in the X direction, extending in the Y direction, and having irregularities in the Z direction is formed on the upper surface of the light guide layer 102 as a one-dimensional periodic structure. The light guide layer 102 is formed of, for example, a dielectric having a refractive index of about 1.46 to about 1.50 with respect to visible light. Examples include acrylic resins such as quartz glass, PET (polyethylene terephthalate), and PMMA (polymethyl methacrylate resin). The periodic structure of the upper surface of the light guide layer 102 has a period of about 220 nm to about 400 nm and an unevenness depth of about 120 nm or less.

  The refractive index of the light guide layer 102 is not limited to about 1.46 or more and about 1.50 or less. More specifically, it is sufficient that the diffraction angle of reflected diffracted light from the metal layer 103 to be described later is smaller than the critical angle at the interface between the lower surface of the light guide layer 102 and the outside of the light guide layer 102, and a P polarization component to be described later. It is sufficient that the intensity of is higher than the intensity of the S-polarized component.

  If the thickness of the light guide layer 102 is about 0.5 mm as a guide, it will function without problems. However, the thickness of the light guide layer 102 is not particularly limited.

  Note that the period of the periodic structure on the upper surface of the light guide layer 102 is not limited to about 250 nm or more and about 400 nm or less. More specifically, it is sufficient that the diffraction angle of reflected diffracted light from the metal layer 103 to be described later is smaller than the critical angle at the interface between the lower surface of the light guide layer 102 and the outside of the light guide layer 102, and a P polarization component to be described later. It is sufficient that the intensity of is higher than the intensity of the S-polarized component.

  The light guide layer 102 has a flat plate shape in the present embodiment, but is not limited to a flat plate shape in practice, and may have a wedge shape or a sawtooth shape.

  The metal layer 103 is formed of a metal that can excite surface plasmons on the surface by visible light. An example is Ag (silver). The thickness of the metal layer 103 is about 500 nm or more and about 2 μm or less.

  The metal layer 103 is not limited to Ag, and may be Al (aluminum) or Au (gold). More specifically, surface plasmons may be excited at the interface between the light guide layer 102 and the metal layer 103 described later. Further, the thickness of the metal layer 103 is not limited to about 500 nm or more and about 2 μm or less. More specifically, it is sufficient that the energy of the surface plasmon generated at the interface between the light guide layer 102 and the metal layer 103, which will be described later, is so thick that it does not ooze out to the upper surface of the metal layer 103. It only needs to be thick enough to reflect light and S-polarized light.

  The optical device 100 can be manufactured by the following procedure, for example. First, a one-dimensional concavo-convex structure is formed on the upper surface of quartz glass using a fine processing technique such as photolithography or nanoimprint, and Ag is formed thereon by a vapor deposition method such as sputtering. However, it is not limited to photolithography, nanoimprint, and vapor deposition.

  Note that a bonding layer of Ti or the like may be provided at the interface between the light guide layer 102 and the metal layer 103 with a thickness of about 5 nm or less in order to improve bonding properties.

  FIG. 2 is a diagram for explaining the operation of the optical device 100 in detail. FIG. 2 is a cross-sectional view orthogonal to the Y axis of the optical device 100. Of the light existing in the light guide layer 102, the light A is P-polarized light, that is, light whose electric field vibration direction is parallel to the ZX plane. The light B is S-polarized light, that is, light in which the vibration direction of the electric field is orthogonal to the ZX plane.

Next, the principle that surface plasmons are excited and light is generated from the surface plasmons will be described. Surface plasmons are dense waves of a group of electrons that propagate through the interface between a metal and a dielectric. Here, when the angular frequency of light in vacuum is ω and the speed of light is c, the wave number of light in vacuum is represented by k ₀ = ω / c. The wave number k _{SP of the} surface plasmon is calculated from the wave number k ₀ of light in vacuum, the dielectric constant ε _{m of the} metal, and the dielectric constant ε _d of the dielectric, k _SP = k ₀ ((ε _d · ε _m ) / (ε _d + ε _m )) ^1/2 ... (1)
Determined by

When the dispersion relationship, which is the relationship between the angular frequency of the surface plasmon and the wave number, matches the dispersion relationship of the light propagating in the dielectric, that is, the wave number of the light of a specific wavelength existing in the dielectric is the wave number of the surface plasmon. The surface plasmon is excited by the light.
However, in the case of only the interface between a flat metal and a flat dielectric, the surface plasmon dispersion relationship does not match the light dispersion relationship in the dielectric. Therefore, even if light is incident on the metal from the dielectric, the surface plasmon is not excited. Therefore, in order to excite the surface plasmon, it is necessary to change the dispersion relation of the light in the dielectric so that the dispersion relation of the surface plasmon and the dispersion relation of the light in the dielectric coincide.

  As a method of exciting surface plasmons by changing the light dispersion relationship, a grating coupling method in which a diffraction grating (grating) is provided at the interface between a metal and a dielectric is known.

In the grating coupling method, when light is incident on the diffraction grating at an incident angle θ _inc within a plane parallel to the periodic direction of the diffraction grating, the wave number of the light diffracted by the diffraction grating is parallel to the periodic direction of the diffraction grating. The component k _Λ is expressed by Equation 2 using the refractive index n of the dielectric, the integer m ₁ , the grating pitch Λ, and the grating vector K = 2π / Λ.
k _Λ = nk ₀ sin θ _inc + m ₁ K (2)
Here, when k _SP = k _{Λ at a} specific incident angle with respect to the diffraction grating, that is, when the dispersion relation of the surface plasmon and the dispersion relation of the diffracted light in the dielectric coincide, Surface plasmons having a wave number k _Λ at the interface between the body and the metal are excited in a direction parallel to the periodic direction of the diffraction grating. The incident light that excites the surface plasmon propagating in a specific direction due to the surface plasmon being a dense wave is only linearly polarized light whose electric field component is parallel to the specific direction.

Therefore, as shown in FIG. 2, the interface between the light guide layer 102 and the metal layer 103 has a one-dimensional periodic structure having a period in the X direction. The light capable of exciting the surface plasmon k _x = k _Λ is limited to P-polarized light having an electric field component in the X direction and having a specific incident angle with respect to the periodic structure at the interface between the light guide layer 102 and the metal layer 103 It becomes possible to do.

With respect to the periodic structure at the interface between the light guide layer 102 and the metal layer 103, light is incident at an incident angle θ ₁ that satisfies k _x = k _SP , and surface plasmons are formed at the interface between the light guide layer 102 and the metal layer 103. Is excited in the X direction, part of the energy of the surface plasmon becomes heat loss in the metal layer 103, and part of it is diffracted in combination with light in the dielectric.

The wave number component k _{x, d} of light diffracted from the interface between the light guide layer 102 and the metal layer 103 is expressed by using an integer m ₂ .
k _{x, d} = k _SP + m ₂ K (3)
It is expressed. The wave number k _{x, d} of light diffracted from the interface between the light guide layer 102 and the metal layer 103 is parallel to the wave number component of the surface plasmon excited at the interface between the light guide layer 102 and the metal layer 103.

Therefore, the diffracted light has an electric field component in the X direction, similar to the light incident on the interface between the light guide layer 102 and the metal layer 103, and the periodic structure at the interface between the light guide layer 102 and the metal layer 103. Is P-polarized light having a specific diffraction angle θ ₂ .

The P-polarized light diffracted at the diffraction angle θ ₂ at the interface between the light guide layer 102 and the metal layer 103 propagates through the light guide layer 102 and enters the lower surface of the light guide layer 102 at an incident angle θ ₃ . In the present embodiment, the light guide layer 102 has a flat plate shape, and θ ₃ = θ ₂ . Here, the medium A of the refractive index n _A, the critical angle at the time when the light is incident on the interface between the medium B of refractive index n _B and the medium A is
θ _c = sin ⁻¹ (n _B / n _A ) (4)
It is represented by When the refractive index of the light guide layer 102 is n ₁ , the refractive index outside the light guide layer 102 is n _0, and the light incident on the lower surface of the light guide layer 102 satisfies θ ₃ <θ _c , To the outside.

  Further, P-polarized light and S-polarized light that do not excite surface plasmons at the interface between the light guide layer 102 and the metal layer 103 are diffracted or mirror-reflected by the metal layer 103, and the light guide layer 102 is within the light guide layer 102. The light is guided while being totally reflected between the upper surface of the light guide layer 102 and the lower surface of the light guide layer 102, and is not emitted from the lower surface of the light guide layer 102 to the outside of the light guide layer 102. The light existing in the YZ plane in the light guide layer 102 is diffracted or specularly reflected by the metal layer 103 and guided while being totally reflected between the upper surface of the light guide layer 102 and the lower surface of the light guide layer 102. The light is not emitted from the lower surface of the light guide layer 102 to the outside of the light guide layer 102.

From the above, among the light that exists in the light guide layer 102, conductive only certain incident angle theta ₁ of the light A to the interface between the light guiding layer 102 and the metal layer 103 is diffracted through the surface plasmon Extracted from the optical layer 102.

  That is, since a one-dimensional periodic structure having a period in the X direction exists at the interface between the light guide layer 102 and the metal layer 103, light can be extracted only from surface plasmons having a specific wave number in the X direction. Thus, it is possible to obtain outgoing light whose main component is a polarization component propagating in the ZX plane which is a specific direction.

  Even when light propagating in a direction other than the ZX direction is incident on the interface between the light guide layer 102 and the metal layer 103 at various angles, the incident angle of the projected light projected onto the ZX plane is the excitation of the surface plasmon. If the angle satisfies the condition, light having a specific polarization component can be obtained. In that case, first, similarly to the light A, the surface plasmon having a specific wave number in the X direction is excited at the interface between the light guide layer 102 and the metal layer 103 by the polarization component parallel to the X direction. Further, part of the surface plasmon is diffracted at the interface between the light guide layer 102 and the metal layer 103 and is extracted from the light guide layer 102 as light having a specific polarization component in the X direction.

  As described above, in this embodiment, by providing a periodic structure at the interface between the light guide layer 102 and the metal layer 103, light having high angle selectivity and polarization selectivity and having a polarization component in a specific direction can be obtained. can get.

FIG. 3 shows an example of a cross section in the ZX plane of the periodic structure at the interface between the light guide layer 102 and the metal layer 103 in the present embodiment. As the periodic structure at the interface between the light guide layer 102 and the metal layer 103, (a) rectangular shape, (b) stepped shape, and (c) sinusoidal shape can be used. Further, any plurality of shapes (a) rectangular shape, (b) stepped shape, and (c) sinusoidal shape may be mixed in the periodic structure.
[First embodiment]
The effect of the above operation was confirmed by simulation. FIG. 4 is a graph illustrating an example of a simulation result for confirming the effect of the optical device 100. The simulation is performed for an example of the first embodiment and does not limit the present invention.

4 represents the diffraction angle θ ₂ from the interface between the light guide layer 102 and the metal layer 103 in the ZX plane of the optical device 100, and the vertical axis represents the diffraction efficiency D.D. normalized to a maximum value of 50%. E. (Diffraction Efficiency) is shown. (A) shows the case where the light incident on the interface between the light guide layer 102 and the metal layer 103 is S-polarized light, and (b) shows the light incident on the interface between the light guide layer 102 and the metal layer 103 converted into P-polarized light. Shows the case.

The diffraction angle θ ₂ indicates a range within the critical angle θ _{c at} the interface between the lower surface of the light guide layer 102 and the outside of the light guide layer 102 described later. For the simulation, a two-dimensional rigorous coupled wave analysis method (RCWA method: Rigorous Coupled Wave Analysis method) was used.

  In the simulation of the first embodiment, the light guide layer 102 is PET having a refractive index of 1.46. The metal layer 103 is made of Ag and has a thickness of 2 μm. The periodic structure at the interface between the light guide layer 102 and the metal layer 103 has a rectangular shape shown in FIG. 3A, a depth of 60 nm, and a pitch of 300 nm. The outside of the light guide layer 102 was air having a refractive index of 1.

  4A and 4B, the full width at half maximum of the diffraction efficiency in the light guide layer 102 of the P-polarized component is about 20.0 deg, and the interface between the lower surface of the light guide layer 102 and the outside of the light guide layer 102 The full width at half maximum in air after passing through is about 33.0 deg. Therefore, it can be confirmed that light having a high angle selectivity can be obtained as compared with the full width at half maximum (45.0 deg) of the emitted light having a Lambertian distribution like LED in the air.

In addition, when comparing the peak value of the diffraction efficiency of the P-polarized component and the peak value of the diffraction efficiency of the S-polarized component, the P-polarized component is more than four times larger, so that light having polarization selectivity can be obtained. I can confirm.
[Second Embodiment]
Next, a second embodiment of the present invention will be described. In addition, about the same element as each component in 1st Embodiment, description is abbreviate | omitted suitably using the same code | symbol.

  FIG. 5 is a perspective view schematically showing an optical device 200 according to the second embodiment of the present invention. The optical device 200 shown in FIG. 5 includes a dielectric layer (first dielectric layer) 204 between the light guide layer 102 and the metal layer 103 as compared to the optical device 100 of the first embodiment. The point is different.

  The dielectric layer 204 is made of a transparent material that transmits at least visible light, and serves as a medium that propagates light. Further, the dielectric layer 204 has a specific refractive index to be described later with respect to visible light. The lower surface of the dielectric layer 204 is in contact with the light guide layer 102 and has a periodic structure. The upper surface of the dielectric layer 204 is flat. Note that the upper surface of the dielectric layer 204 is not flat and may have a random uneven structure or a periodic structure.

  The dielectric layer 204 may have a portion having a thickness in the Z direction of zero. That is, the light guide layer 102 and the metal layer 103 may be in contact with each other at the convex portion on the upper surface of the light guide layer 102.

  The dielectric layer 204 has a refractive index different from that of the light guide layer 102. The dielectric layer 204 is air having a refractive index of 1, for example. The dielectric layer 204 is not limited to a refractive index of 1.

  The optical device 200 can be manufactured, for example, according to the following procedure. A one-dimensional concavo-convex structure is formed on the upper surface of the quartz glass by a microfabrication technique such as photolithography or nanoimprinting to form a substrate A. On the other hand, Ag is formed on the surface of the Si substrate or the like by a vapor deposition method such as sputtering to obtain a substrate B.

  The substrate A and the substrate B are bonded to each other in the one-dimensional concavo-convex structure of quartz glass and the Ag layer of the Si substrate by a bonding method such as optical carving. However, the manufacturing method of the optical device 200 according to the first embodiment is not limited to photolithography, nanoimprinting, vapor deposition, or optical carving.

  FIG. 6 is a cross-sectional view of the optical device 200 perpendicular to the Y axis. Of the light existing in the light guide layer 102, the light A is P-polarized light, that is, light whose electric field vibration direction is parallel to the ZX plane. The light B is S-polarized light, that is, light in which the vibration direction of the electric field is orthogonal to the ZX plane.

Next, the principle that surface plasmons are excited and light is generated from the surface plasmons will be described. When light is incident on the periodic structure at the interface between the light guide layer 102 and the dielectric layer 204 at an incident angle θ ₁ , diffracted light that satisfies k _x = k _SP is generated in the dielectric layer 204.

  When the surface plasmon is excited in the X direction at the interface between the dielectric layer 204 and the metal layer 103 by the diffracted light generated in the dielectric layer 204, a part of the energy of the surface plasmon is a heat loss in the metal layer 103. Thus, a part is diffracted by the periodic structure at the interface between the light guide layer 102 and the dielectric layer 204.

The wave number k _{x, d} of light diffracted from the interface between the light guide layer 102 and the dielectric layer 204 is parallel to the wave number component of the surface plasmon excited at the interface between the dielectric layer 204 and the metal layer 103.

Therefore, the diffracted light has an electric field component in the X direction, and the period of the interface between the light guide layer 102 and the dielectric layer 204, similar to the light incident on the interface between the light guide layer 102 and the dielectric layer 204. P-polarized light having a specific diffraction angle θ ₂ with respect to the structure.

  Further, P-polarized light and S-polarized light that do not excite surface plasmons at the interface between the dielectric layer 204 and the metal layer 103 are mirror-reflected by the metal layer 103, and the upper surface of the light guide layer 102 in the light guide layer 102. The light is guided while being totally reflected between the light guide layer 102 and the lower surface of the light guide layer 102, and is not emitted from the lower surface of the light guide layer 102 to the outside of the light guide layer 102.

  From the above, among the light existing in the light guide layer 102, only the light A having a specific incident angle θ1 with respect to the interface between the light guide layer 102 and the dielectric layer 204 is diffracted and guided through the surface plasmon. Extracted from the optical layer 102.

  That is, since a one-dimensional periodic structure having a period in the X direction exists at the interface between the light guide layer 102 and the dielectric layer 204, light can be extracted only from surface plasmons having a specific wave number in the X direction. Therefore, it is possible to obtain outgoing light whose main component is a polarization component propagating in the ZX plane which is a specific direction.

  Even when light propagating in a direction other than the ZX direction is incident on the interface between the light guide layer 102 and the dielectric layer 204 at various angles, the incident angle of the projected light that projects the light on the ZX plane is the surface plasmon If the angle satisfies the excitation condition, light having a specific polarization component can be obtained. In that case, first, similarly to the light A, the surface plasmon having a specific wave number in the X direction is excited at the interface between the dielectric layer 204 and the metal layer 103 by the polarization component parallel to the X direction. Further, a part of the surface plasmon is diffracted at the interface between the light guide layer 102 and the dielectric layer 204 and is extracted from the light guide layer 102 as light having a specific polarization component in the X direction.

Thus, in this embodiment, by providing the dielectric layer 204 between the light guide layer 102 and the metal layer 103, the metal layer 103 is formed on the light guide layer 102, for example, as in the first embodiment. Even when it is difficult to provide directly, the periodic structure at the interface between the upper surface of the light guide layer 102 and the dielectric layer 204 and the grating at the interface between the dielectric layer 204 and the metal layer 103 through the dielectric layer 204. By applying the combination method, light having high angle selectivity and polarization selectivity and having a polarization component in a specific direction can be obtained.
[Second Embodiment]
The effect of the above operation was confirmed by simulation. FIG. 7 is a graph illustrating an example of a simulation result for confirming the effect of the optical device 200. The simulation is performed for an example of the second embodiment and does not limit the present invention.

7 represents the diffraction angle θ ₂ from the interface between the light guide layer 102 and the dielectric layer 204 in the ZX plane of the optical device 200, and the vertical axis represents the diffraction efficiency D normalized at a maximum value of 50%. . E. (Diffraction Efficiency) is shown. (A) shows the case where the incident light on the interface between the light guide layer 102 and the dielectric layer 204 is S-polarized light, and (b) shows the incident light on the interface between the light guide layer 102 and the dielectric layer 204 as P. This shows the case of polarized light.

The diffraction angle θ ₂ indicates a range within the critical angle θ _{c at} the interface between the lower surface of the light guide layer 102 and the outside of the light guide layer 102 described later. For the simulation, a two-dimensional rigorous coupled wave analysis method (RCWA method: Rigorous Coupled Wave Analysis method) was used.

  In the simulation of the second embodiment, the light guide layer 102 is PET having a refractive index of 1.46. The metal layer 103 is made of Ag and has a thickness of 2 μm. The dielectric layer 204 was air and had a thickness of 60 nm. The shape of the periodic structure at the interface between the light guide layer 102 and the dielectric layer 204 was a rectangular shape shown in FIG. 3A, the depth was 60 nm, and the pitch was 300 nm. That is, on the upper surface of the light guide layer 102, the convex portion is in contact with the metal layer 103, and the lower surface of the metal layer 103 is flat. The outside of the light guide layer 102 was air having a refractive index of 1.

  7A and 7B, it can be seen that the P-polarized light diffracted in the light guide layer 102 is obtained in the vicinity of −23 deg and +21 deg according to the diffraction order. The full width at half maximum of the diffraction efficiency in the light guide layer 102 for the P-polarized light component is about 3.0 deg for the diffracted light D1 obtained in the vicinity of −23.0 deg, and about 8.8 for the diffracted light D2 obtained about +21.0 deg. 0 deg. Further, the full width at half maximum in air after passing through the interface between the lower surface of the light guide layer 102 and the outside of the light guide layer 102 is about 5.0 deg for the diffracted light D1 and about 13.0 deg for the diffracted light D2. . Therefore, it can be confirmed that light having a high angle selectivity can be obtained as compared with the full width at half maximum (45.0 deg) of the emitted light having a Lambertian distribution like LED in the air.

  Further, comparing the peak value of the diffraction efficiency of the P-polarized component and the peak value of the diffraction efficiency of the S-polarized component, the P-polarized component is about 1.7 times the diffracted light D1 and about 3 times the diffracted light D2. Since it is 3 times larger, it can be confirmed that light having polarization selectivity can be obtained.

  In addition, when using for the display apparatus mentioned later, you may utilize either the diffracted light D1 or the diffracted light D2.

Further, by diffracting the diffracted light D1 or the diffracted light D2 using an angle conversion layer or the like (not shown) and making the propagation directions of the diffracted light D1 and the diffracted light D2 parallel, both the diffracted light D1 and the diffracted light D2 are converted. May be used.
[Third Embodiment]
Next, a third embodiment of the present invention will be described. In addition, about the same element as each component in each embodiment mentioned above, description is abbreviate | omitted suitably using the same code | symbol. FIG. 8 is a perspective view schematically showing an optical device 300 according to the third embodiment of the present invention.

  The optical device 300 shown in FIG. 8 is provided with a phase modulation layer 305 on the lower surface of the light guide layer 102 and the phase modulation layer 306 outside the lower surface of the light guide layer 102 as compared with the optical device 100 of the first embodiment. Is different. Note that the phase modulation layer 305 may be provided not inside the light guide layer 102 but inside the light guide layer 102. Further, the dielectric layer shown in the second embodiment may be provided between the light guide layer 102 and the metal layer 103.

  The phase modulation layers 305 and 306 are made of a transparent material that transmits at least visible light, and serve as a light propagation medium. The phase modulation layers 305 and 306 have an optical axis in the XY plane, and give a phase difference to a component in a direction perpendicular to a component parallel to the optical axis of the phase modulation layer of transmitted light. As an example of such phase modulation layers 305 and 306, a λ / 4 plate can be used.

  The optical device 300 can be manufactured, for example, by the following procedure. First, a one-dimensional concavo-convex structure is formed on the upper surface of quartz glass by a fine processing technique such as photolithography or nanoimprint, and Ag is formed thereon by a vapor deposition method such as sputtering. Further, a λ / 4 plate layer is provided on the lower surface of the quartz glass by optical carving, and the λ / 4 plate is disposed outside the lower surface of the quartz glass.

  However, the manufacturing method of the optical device 300 is not limited to photolithography, nanoimprinting, vapor deposition, and optical carboxylating.

  FIG. 9 is a cross-sectional view orthogonal to the Y axis of the optical device 100. Of the light existing in the light guide layer 102, the light A is P-polarized light, that is, light whose electric field vibration direction is parallel to the ZX plane. The light B is S-polarized light, that is, light in which the vibration direction of the electric field is orthogonal to the ZX plane.

P-polarized light diffracted at the diffraction angle θ ₂ at the interface between the light guide layer 102 and the metal layer 103 propagates through the light guide layer 102 and enters the phase modulation layer 305 at an incident angle θ ₃ . In the present embodiment, the light guide layer 102 has a flat plate shape, and θ ₃ = θ ₂ .

  Here, from Snell's law, the critical angle at the interface between the lower surface of the phase modulation layer 305 and the outside of the phase modulation layer 305 with respect to the light existing in the light guide layer 102 is the light guide except for the phase modulation layer 305. The critical angle at the interface between the layer 102 and the outside of the phase modulation layer 305 can be considered the same.

That is, using θ _c obtained from Equation 4, θ ₃ <θ _c is satisfied, and light incident on the phase modulation layer 305 from the light guide layer 102 is transmitted through the phase modulation layer 305 and outside the phase modulation layer 305. Exit. The P-polarized light transmitted through the phase modulation layer 305 is phase-modulated by the phase modulation layer 305 and converted from linearly polarized light to circularly polarized light.

  The light converted into circularly polarized light enters the phase modulation layer 306 and passes through the phase modulation layer 306. The circularly polarized light transmitted through the phase modulation layer 306 is phase-modulated by the phase modulation layer 306 and converted into linearly polarized light.

  Further, light that is not emitted to the outside of the light guide layer 102 but is multiple-reflected in the light guide layer 102 and the phase modulation layer 305 passes through the phase modulation layer 305 and is converted from linearly polarized light to circularly polarized light. The light converted into circularly polarized light is totally reflected at the interface between the phase modulation layer 305 and the outside of the phase modulation layer 305, and is incident on the phase modulation layer 305 again. When the light passes through the phase modulation layer 305 again, it becomes linearly polarized light in a direction orthogonal to the forward path and enters the light guide layer 102.

From the above, the phase modulation layer 305 converts the polarization state of the light not emitted to the outside of the phase modulation layer 305, returns it to the light guide layer 102, and reuses it, so that the optical device 100 of the first embodiment is used. Compared to the above, the light utilization efficiency can be increased.
[Fourth Embodiment]
Next, a fourth embodiment of the present invention will be described. In addition, about the same element as each component in each embodiment mentioned above, description is abbreviate | omitted suitably using the same code | symbol. FIG. 10 is a perspective view schematically showing an optical device 400 according to the fourth embodiment of the present invention.

  The optical device 400 illustrated in FIG. 10 includes an angle conversion layer 407 on the lower surface of the light guide layer 102 as compared to the optical device 100 of the first embodiment. Note that the dielectric layer described in the second embodiment may be provided between the light guide layer 102 and the metal layer 103.

  The angle conversion layer 407 of the present invention is made of a transparent material that transmits at least visible light, and serves as a medium that propagates light. Further, the angle conversion layer has a specific refractive index described later with respect to visible light. The angle conversion layer 407 converts the propagation angle of the incident light at least with respect to the X direction component.

  Examples of the angle conversion layer 407 include a plurality of prisms having periodicity in the X direction and extending in the Y direction. Another example of the angle conversion layer 407 includes a single prism extending in the Y direction. The refractive index of the angle conversion layer 407 is equal to the refractive index of the light guide layer 102, but is not particularly limited.

  The optical device 400 can be manufactured, for example, according to the following procedure. First, a one-dimensional concavo-convex structure is formed on the upper surface of quartz glass by a fine processing technique such as photolithography or nanoimprint, and Ag is formed thereon by a vapor deposition method such as sputtering. In addition, a prism is provided on the lower surface of the quartz glass by optical carving.

  However, the manufacturing method of the optical device 400 is not limited to photolithography, nanoimprinting, vapor deposition, or optical carboxylating.

FIG. 11 is a cross-sectional view of the optical device 400 perpendicular to the Y axis. The P-polarized light diffracted at the diffraction angle θ ₂ at the interface between the light guide layer 102 and the metal layer 103 propagates through the light guide layer 102 and enters the angle conversion layer 407 at an incident angle θ ₃ .

The light that has entered the angle conversion layer 407 enters the lower surface of the angle conversion layer 407 at an incident angle θ ₃ . Here, when θ ₃ (= θ ₂ + α) <θ _c , where α is an angle formed between the lower surface of the angle conversion layer 407 and the lower surface of the light guide layer 102, the light incident on the angle conversion layer 407 is angle converted. The light is emitted to the outside of the layer 407.

  In addition, the light that is not emitted to the outside of the angle conversion layer 407 but is multiple-reflected in the light guide layer 102 and the angle conversion layer 407 is converted in angle when reflected by the angle conversion layer 407.

From the above, the angle conversion layer 407 converts the angle of light that does not exit the angle conversion layer 407 that does not satisfy the plasmon excitation condition at the interface between the light guide layer 102 and the metal layer 103 to the light guide layer 102. By returning and reusing the light, the light use efficiency can be increased as compared with the optical device 100 of the first embodiment.
[Fifth Embodiment]
Next, a fifth embodiment of the present invention will be described. In addition, about the same element as each component in each embodiment mentioned above, description is abbreviate | omitted suitably using the same code | symbol. FIG. 12 is a perspective view schematically showing an optical device 500 according to the fifth embodiment of the present invention.

  The optical device 500 is different from the optical device 300 of the third embodiment in that the angle conversion layer 407 described in the fourth embodiment is additionally provided. Note that the dielectric layer described in the second embodiment may be provided between the light guide layer 102 and the metal layer 103.

  The optical device 500 can be manufactured, for example, by the following procedure. First, a one-dimensional concavo-convex structure is formed on the upper surface of quartz glass by a fine processing technique such as photolithography or nanoimprint, and Ag is formed thereon by a vapor deposition method such as sputtering.

  In addition, a λ / 4 plate and a prism are provided on the lower surface of the quartz glass by optical carving, and the λ / 4 plate is disposed outside the lower surface of the quartz glass.

  However, the manufacturing method of the optical device 500 is not limited to photolithography, nanoimprinting, vapor deposition, and optical carboxylating.

With such a configuration, the phase modulation layer 305 and the angle conversion layer 407 can be used to convert the polarization state and angle of light not emitted to the outside of the angle conversion layer 407 and return it to the light guide layer 102 for reuse. Thus, the light use efficiency can be increased as compared with the optical device 300 of the third embodiment.
[Sixth Embodiment]
Next, a sixth embodiment of the present invention will be described. In addition, about the same element as each component in each embodiment mentioned above, description is abbreviate | omitted suitably using the same code | symbol. FIG. 13 is a perspective view schematically showing an optical device 600 according to the sixth embodiment of the present invention.

  The optical device 600 is different from the optical device 500 of the fifth embodiment in that a polarizer layer 608 is additionally provided. The polarizer layer 608 is disposed on the lower surface side of the phase modulation layer 306, and its optical axis exists in the XY plane. Then, the polarized light having the main component in the X direction is transmitted, and the polarized light having the main component in the Y direction is reflected or absorbed to be blocked.

  As the polarizer layer 608, a wire grid, a multilayer structure of PVA (polyvinyl alcohol) or TAC (triacetyl cellulose), a photonic crystal, or the like can be used. However, the example of the polarizer layer 608 is not limited to a multilayer structure of PVA (polyvinyl alcohol) or TAC (triacetyl cellulose), a wire grid, or a photonic crystal.

  The optical device 500 can be manufactured, for example, according to the following procedure. First, a one-dimensional concavo-convex structure is formed on the upper surface of quartz glass by a fine processing technique such as photolithography or nanoimprint, and Ag is formed thereon by a vapor deposition method such as sputtering. Further, a λ / 4 plate and a prism are provided on the lower surface of the quartz glass by optical carving, and a wire grid in which the λ / 4 plate is bonded to the lower surface of the quartz glass by optical carving is disposed.

  However, the method for manufacturing the optical device 500 according to the fifth embodiment is not limited to photolithography, nanoimprinting, vapor deposition, or optical carboxylating.

  With such a configuration, the polarizer layer 608 transmits the P-polarized light diffracted at the interface between the upper surface of the light guide layer 102 and the metal layer 103 and blocks the S-polarized light. Therefore, the optical device 500 of the fifth embodiment. The polarization selectivity can be increased compared to the above.

Further, when the polarizer layer 608 is of a reflective type that reflects S-polarized light, the reflected S-polarized light is returned to the light guide layer 102 and reused, so that light is used as compared with the optical device 600 of the fifth embodiment. Efficiency can be increased.
[Seventh Embodiment]
Next, a seventh embodiment of the present invention will be described. In addition, about the same element as each component in each embodiment mentioned above, description is abbreviate | omitted suitably using the same code | symbol. FIG. 14 is a perspective view schematically showing an optical device 700 according to the seventh embodiment of the present invention.

  The optical device 700 is different from the optical devices 100 to 600 of the first to sixth embodiments except for an incident port 709 that is an incident region where light is incident from the light source 101 and a light emission surface. The difference is that a reflective portion (reflective layer) 710 is additionally provided on the outer wall surface (that is, the side surfaces of the optical devices 100, 200, 300, 400, 500, and 600). Note that a dielectric layer (second dielectric layer) may be inserted between the entrance 709, the outer wall surface excluding the light exit surface, and the reflecting portion 710.

  Since the reflection unit 710 can suppress light from being emitted from the side surface of the optical device 700, the light use efficiency can be increased as compared with the optical devices of the above-described embodiments.

  In addition, although the reflection part 710 was provided in all the side surfaces except the entrance 709, you may be provided only in the one part surface among the side surfaces. Moreover, the reflection part 710 may be a diffuse reflector that diffusely reflects light, or may have a saw shape.

  Such a reflection part 710 is comprised with the material which reflects visible light, for example, although Ag and Al can be used, it is not limited to these.

  The dielectric layer is made of a material that transmits visible light. For example, air, an optical gel, and an optical adhesive can be used, but not limited thereto.

  Thus, since the reflection part is provided in the outer wall surface etc., the light which leaks through an outer wall surface can be suppressed. Therefore, the light use efficiency is improved.

In each of the above-described embodiments, one light source is described as an example, but a plurality of light sources may be used. At that time, each light source may emit light having a different wavelength. More specifically, the wavelengths of the plurality of light sources may be different to such an extent that surface plasmons are excited on the metal surface.
[Eighth Embodiment]
Next, an eighth embodiment of the present invention will be described. In addition, about the same element as each component in each embodiment mentioned above, description is abbreviate | omitted suitably using the same code | symbol. The present embodiment relates to a projector (display device) including the optical device described so far.

  FIG. 15 is a schematic diagram of the projector 3A of the present embodiment. The projector 3A includes optical devices 800R, 800G, and 800B, liquid crystal panels (spatial light modulation elements) 811R, 811G, and 811B, a cross dichroic prism 812, and a projection optical system 813.

  The optical devices 800R, 800G, and 800B are the optical devices in the above-described embodiments. The optical devices 800R, 800G, and 800B generate light having different wavelengths. Hereinafter, it is assumed that red light is emitted from the optical device 800R, green light is emitted from the optical device 800G, and blue light is emitted from the optical device 800B.

  Optical devices 800R, 800G, and 800B change each color light to a predetermined polarization state and guide it to liquid crystal panels 811R, 811G, and 811B.

  The liquid crystal panels 811R, 811G, and 811B spatially emit light of each color carrying the image by carrying the image on each color light by two-dimensionally modulating each colored light according to the video signal. It is a modulation element.

  The cross dichroic prism 812 combines and outputs the modulated lights emitted from the liquid crystal panels 811R, 811G, and 811B.

  The projection optical system 813 projects the combined light emitted from the cross dichroic prism 812 onto the screen 814 and displays an image corresponding to the video signal on the screen 814.

In such a projector, when randomly polarized light emitted from a light source is converted into a specific polarization state, it is converted into a low etendue state in which the emission direction is set to a specific direction. Therefore, a projector with improved light utilization efficiency can be provided.
[Ninth Embodiment]
Next, a ninth embodiment of the present invention will be described. In addition, about the same element as each component in each embodiment mentioned above, description is abbreviate | omitted suitably using the same code | symbol.

  The display device in the eighth embodiment uses a plurality of optical devices. In contrast, the display device of the present embodiment includes one optical device.

  FIG. 16 is a schematic diagram of the projector 3B of the present embodiment. The projector 3B includes an optical device 900, a liquid crystal panel 911, and a projection optical system 913.

  The optical device 900 has the same configuration as the optical devices 800R, 800G, and 800B described in the eighth embodiment, but includes three light sources.

  The liquid crystal panel 911 modulates the incident combined light according to the video signal and emits it. The projection optical system 913 projects the modulated light emitted from the liquid crystal panel 911 onto the screen 814 and displays an image corresponding to the video signal on the screen 814.

  In the eighth and ninth embodiments, the liquid crystal panel is used as the light modulation element. However, the light modulation element is not limited to the liquid crystal panel and can be changed as appropriate. For example, in the projectors shown in FIGS. 15 and 16, DMD (Digital MICROMIRROR Device) may be used instead of the liquid crystal panels 811R, 811G, 811B or the liquid crystal panel 911.

  As described above, since an image can be displayed by one optical device, the configuration can be simplified and the cost can be reduced. In addition, these effects can further reduce the size of the projector.

  Further, as a modification of the display device of the eighth embodiment and the ninth embodiment, the surface of the display device may be configured to be substantially perpendicular to the polarization component in a specific direction such as the + X direction. Good. Thereby, since it can condense efficiently to a projection optical system, without using optical systems, such as a mirror and a lens, an optical system can be omitted. The above modification only shows the applicability of the present invention, and does not limit the present invention.

A part or all of the above-described embodiment can be described as in the following supplementary notes, but is not limited thereto.
(Appendix 1)
A light guide layer having a periodic structure on a first surface;
A metal layer provided on the first surface,
The light guide layer includes at least one incident surface on which light enters the light guide layer;
An optical apparatus comprising: at least one emission surface that emits light inside the light guide layer to the outside of the light guide layer except for the incident surface and the first surface.
(Appendix 2)
The light guide layer guides the light by multiple reflection between the first surface and the emission surface, and emits the light generated on the first surface from the emission surface. The optical apparatus according to Supplementary Note 1.
(Appendix 3)
The optical apparatus according to any one of appendices 1 and 2, wherein a first dielectric layer is provided at least at a part between the first surface and the metal layer.
(Appendix 4)
4. The optical device according to appendix 3, wherein a surface of the metal layer that is in contact with the first surface and the first dielectric layer or a surface that is in contact with the first dielectric layer is flat.
(Appendix 5)
The optical apparatus according to any one of appendices 1 to 4, wherein the periodic structure is a one-dimensional periodic structure.
(Appendix 6)
The optical apparatus according to any one of appendices 1 to 5, wherein a period of the periodic structure is 250 nm or more and 400 nm or less.
(Appendix 7)
The optical apparatus according to any one of appendices 1 to 5, wherein a period of the periodic structure is 400 nm or more and 800 nm or less.
(Appendix 8)
The optical device according to any one of appendices 1 to 7, wherein the periodic structure is rectangular.
(Appendix 9)
The optical device according to any one of appendices 1 to 7, wherein the periodic structure has a step shape.
(Appendix 10)
The optical device according to any one of appendices 1 to 7, wherein the periodic structure is sinusoidal.
(Appendix 11)
The optical apparatus according to any one of appendices 1 to 10, wherein a phase modulation layer is provided between the first surface and the exit surface.
(Appendix 12)
The optical device according to any one of appendices 1 to 11, wherein an angle conversion layer is provided on the exit surface.
(Appendix 13)
The optical apparatus according to appendix 12, wherein the angle conversion layer has a sawtooth shape.
(Appendix 14)
14. The optical device according to any one of appendices 1 to 13, wherein the light guide layer includes a reflective layer on a surface excluding the incident surface and the emission surface via a second dielectric layer.
(Appendix 15)
The optical apparatus according to any one of appendices 1 to 14, wherein a plurality of the light sources are provided, and the wavelengths of the plurality of light sources are the same or different from each other.
(Appendix 16)
The light guided in the light guide layer excites surface plasmons by the periodic structure, and the surface plasmon wave number k _SP is:
Using the angular frequency of light in a vacuum as ω, the speed of light as c, the dielectric constant ε _{m of the} metal, and the dielectric constant ε _d of the dielectric,
k _SP = (ω / c) * (ε _d · ε _m / (ε _d + ε _m )) ^1/2
The optical device according to any one of appendices 1 to 15, wherein the optical device is given by:
(Appendix 17)
The periodic structure is formed of a diffraction grating, and the wave number component k _Λ parallel to the periodic direction of the diffraction grating of the light diffracted by the diffraction grating is:
In the plane parallel to the periodic direction of the diffraction grating, the incident angle of the light is θ _inc , the refractive index of the dielectric is n, the grating pitch is Λ, the grating vector is K = 2π / Λ, and the integer is m ₁ .
k _Λ = nk ₀ sin (θ _inc ) + m ₁ K
17. The optical device according to any one of appendices 1 to 16, wherein
(Appendix 18)
The optical device according to any one of appendices 1 to 17,
A display device comprising: a spatial light modulator that converts light emitted from the optical device into a predetermined polarization state.
(Appendix 19)
The display device according to appendix 18, wherein the spatial light modulator is a liquid crystal panel.
(Appendix 20)
Item 19. The display device according to appendix 18, wherein the spatial light modulation element is a digital micromirror device.

  This application claims the priority on the basis of Japanese application Japanese Patent Application No. 2012-160419 for which it applied on July 19, 2012, and takes in those the indications of all here.

3A, 3B Projector 100-700 Optical device 101 Light source 102 Light guide layer 103 Metal layer 204 Dielectric layer 305 Phase modulation layer 306 Phase modulation layer 407 Angle conversion layer 608 Polarizer layer 709 Entrance 710 Reflector 800R, 800G, 800B, 900 Optical device 811R, 811G, 811B, 911 Liquid crystal panel 812 Cross dichroic prism 813, 913 Projection optical system 814 Screen

Claims (10)

A light guide layer having a periodic structure on a first surface;
A metal layer provided on the first surface,
The light guide layer includes at least one incident surface on which light enters the light guide layer;
An optical apparatus comprising: at least one emission surface that emits light inside the light guide layer to the outside of the light guide layer except for the incident surface and the first surface.   The light guide layer guides light by multiple reflection between the first surface and the emission surface, and emits light generated on the first surface from the emission surface. The optical device according to claim 1.   The optical device according to claim 1, wherein a first dielectric layer is provided at least at a part between the first surface and the metal layer.   The optical device according to claim 1, wherein the periodic structure is a one-dimensional periodic structure.   5. The optical device according to claim 1, wherein a period of the periodic structure is 250 nm or more and 400 nm or less.   The optical device according to claim 1, wherein a phase modulation layer is provided between the first surface and the emission surface.   The optical device according to claim 1, wherein an angle conversion layer is provided on the emission surface.   8. The optical device according to claim 1, wherein the light guide layer includes a reflective layer on a surface excluding the incident surface and the emission surface via a second dielectric layer. 9.   The optical apparatus according to claim 1, wherein a plurality of the light sources are provided, and the wavelengths of the plurality of light sources are the same or different from each other. An optical device according to any one of claims 1 to 9,
A display device comprising: a spatial light modulator that converts light emitted from the optical device into a predetermined polarization state.

Images