Optical device, optical element, and image display device
Disclosed are an optical device, an optical element, and an image display device that can achieve an improved absorption efficiency of excitation light. The optical device includes: a light-emitting element; a carrier generation layer on which light from the light-emitting element is incident and in which carriers are generated; a plasmon excitation layer that excites a plasmon, stacked on the upper side of the carrier generation layer and has a plasma frequency higher than a frequency of light generated when the carrier generation layer is excited by the light from the light-emitting element; and an exit layer that converts light or a surface plasmon generated on a surface of the plasmon excitation layer into light having a predetermined exit angle and from which the light having the predetermined exit angle exits. The optical device further includes a polarization conversion layer on the lower side of the carrier generation layer.
1. An optical device comprising:
a light-emitting element;
a carrier generation layer on which light from the light-emitting element is incident and in which carriers are generated;
a plasmon excitation layer that excites a plasmon, the plasmon excitation layer being stacked on an upper side of the carrier generation layer and having a plasma frequency higher than a frequency of light generated when the carrier generation layer is excited by the light from the light-emitting element; and
an exit layer that converts light or a surface plasmon generated on a surface of the plasmon excitation layer into light having a predetermined exit angle and from which the light having the predetermined exit angle exits,
wherein the optical device further comprises a polarization conversion layer on a lower side of the carrier generation layer.
2. The optical device according to claim 1 , wherein
the polarization conversion layer is a 1/4 wavelength plate.
3. The optical device according to claim 1 , wherein
a dielectric layer is stacked on at least one surface of the plasmon excitation layer.
4. The optical device according to claim 1 , wherein
the distance between a carrier generation layer side-surface of the plasmon excitation layer and a plasmon excitation layer side-surface of the carrier generation layer is shorter than an effective interaction distance of a surface plasmon excited on the carrier generation layer side-surface of the plasmon excitation layer.
5. The optical device according to claim 4 , wherein
the carrier generation layer is disposed within a distance in the range from 1 to 200 nm from the plasmon excitation layer.
6. The optical device according to claim 1 , wherein
the exit layer has a surface periodic structure.
7. The optical device according to claim 6 , wherein
the surface periodic structure is a photonic crystal structure.
8. The optical device according to claim 1 , wherein
the carrier generation layer has a surface periodic structure and serves also as the exit layer.
9. The optical device according to claim 1 , further comprising a polarization converter that sets axially symmetric polarized light exiting from the exit layer in a predetermined polarization state.
10. The optical device according to claim 1 , wherein
an incident side portion that comprises an entire structure provided on the light-emitting element side of the plasmon excitation layer and a medium in contact with the light-emitting element has a lower effective dielectric constant than an exit side portion that comprises an entire structure provided on the exit layer side of the plasmon excitation layer and a medium in contact with the exit layer.
11. The optical device according to claim 1 , wherein
an incident side portion that comprises an entire structure provided on the light-emitting element side of the plasmon excitation layer and a medium in contact with the light-emitting element has an effective dielectric constant higher than or equal to an effective dielectric constant of an exit side portion that comprises an entire structure provided on the exit layer side of the plasmon excitation layer and a medium in contact with the exit layer, and
an end of the exit layer on the plasmon excitation layer side is disposed so that a distance between the end and an exit layer side-surface of the plasmon excitation layer is within an effective interaction distance of the surface plasmon.
12. The optical device according to claim 10 , wherein
the effective dielectric constant (∈ eff ) is represented by either one of the following Equation (1) and Equation (7):
ɛ
eff
=
(
∫
∫
∫
D
Re
[
ɛ
(
ω
,
x
,
y
,
z
)
]
exp
(
2
j
k
spp
,
z
z
)
∫
∫
∫
D
exp
(
2
j
k
spp
,
z
z
)
)
2
(
1
)
ɛ
eff
=
∫
∫
∫
D
Re
[
ɛ
(
ω
,
x
,
y
,
z
)
]
exp
(
2
j
k
spp
,
z
z
)
∫
∫
∫
D
exp
(
2
j
k
spp
,
z
z
)
(
7
)
where an x axis and a y axis are directions parallel to an interface of the plasmon excitation layer; a z axis is a direction perpendicular to the interface of the plasmon excitation layer; ωis an angular frequency of light exiting from the carrier generation layer; ∈(ω, x, y, z) is a dielectric constant distribution of dielectric substances in the incident side portion or the exit side portion; an integration range D is a range of three-dimensional coordinates in the incident side portion or the exit side portion; k spp,z is a z component of a wave number of a surface plasmon; j is an imaginary unit; and Re[ ] is a sign indicating a real part of a numerical value in the square brackets, and
the z component k spp,z of the wave number of the surface plasmon and an x and y components k spp of the wave number of the surface plasmon are represented by the following Equation (2) and Equation (3), respectively:
k
spp
,
z
=
ɛ
eff
k
0
2
-
k
spp
2
(
2
)
k
spp
=
k
0
Re
[
ɛ
eff
ɛ
metal
ɛ
eff
+
ɛ
metal
]
(
3
)
where ∈ metal is a real part of a dielectric constant of the plasmon excitation layer; and k 0 is a wave number of light in a vacuum.
13. The optical device according to claim 4 , wherein
the effective interaction distance d eff is represented by the following Equation (4):
d
eff
=
Im
[
1
k
spp
,
z
]
(
4
)
where Im[ ] is a sign indicating an imaginary part of a numerical value in the square brackets.
14. The optical device according to claim 1 , wherein
an incident angle of the light incident on the carrier generation layer is set to 40° or more.
15. An optical element comprising:
a carrier generation layer on which light from a light-emitting element is incident and in which carriers are generated;
a plasmon excitation layer that excites a plasmon, the plasmon excitation layer being stacked on an upper side of the carrier generation layer and having a plasma frequency higher than a frequency of light generated when the carrier generation layer is excited by the light; and
an exit layer that converts light or a surface plasmon generated on a surface of the plasmon excitation layer into light having a predetermined exit angle and from which the light having the predetermined exit angle exits,
wherein the optical element further comprises a polarization conversion layer on a lower side of the carrier generation layer.
16. The optical element according to claim 15 , wherein
the polarization conversion layer is a ¼ wavelength plate.
17. An image display device comprising:
the optical device according to claim 1 ; and
an image display section that can display an image.
18. The image display device according to claim 17 , further comprising a projection optical system that projects a projection image using light exiting from the image display section.
19. The optical device according to claim 2 , wherein a dielectric layer is stacked on at least one surface of the plasmon excitation layer.
20. The optical device according to claim 2 , wherein the distance between a carrier generation layer side-surface of the plasmon excitation layer and a plasmon excitation layer side-surface of the carrier generation layer is shorter than an effective interaction distance of a surface plasmon excited on the carrier generation layer side-surface of the plasmon excitation layer.