Light control device and light control system using the same
A light control device includes a substrate, a first reflective layer, a light modulating film in which the refractive index varies according to an applied electric field, a transparent electrode, and a second reflective layer having a reflection characteristic such that the reflection band and transmission band exhibit a steep switching pattern at a specified wavelength. The device is configured such that the specified wavelength and the resonant wavelength of a Fabry-Perot resonator defined by the first reflective layer, the light modulating film, the transparent electrode, and the second reflective layer are substantially the same. The reflection-type light control device has improved light utilization efficiency.
1. A light control device comprising:
a substrate;
a first reflective layer provided on the substrate;
a light modulating film provided on the first reflective layer and in which the refractive index varies according to an applied electric field;
a transparent electrode provided on the light modulating film; and
a second reflective layer provided on the transparent electrode and having a reflection characteristic such that the reflection band and transmission band exhibit a steep switching pattern at a specified wavelength; wherein
the specified wavelength and the resonant wavelength of a Fabry-Perot resonator defined by the first reflective layer, the light modulating film, the transparent electrode, and the second reflective layer are substantially the same.
2. The light control device according to claim 1 , wherein a thickness t p of the light modulating film is such that
t
p
=
λ
c
{
2
π
m
+
(
π
-
ϕ
)
}
4
π
n
p
cos
θ
p
-
n
i
cos
θ
i
n
p
cos
θ
p
t
i
,
where λ c is the specified wavelength, n p is the refractive index of the light modulating film, n i is the refractive index of the transparent electrode, t i is the thickness of the transparent electrode, θ i is the angle of incidence of light incident on the light control device, θ p is the angle of incidence of light incident on the light modulating film from the transparent electrode, φ is the phase variation amount of light reflected by the first reflective layer, and m is the order number.
3. The light control device according to claim 2 , wherein the order number m is an integer in the range of 4≦m≦10.
4. The light control device according to claim 1 , wherein the second reflective layer has a laminated structure including a plurality of dielectric films having different refractive indices.
5. The light control device according to claim 4 , wherein at least one of the plurality of dielectric films is a silicon oxide film.
6. The light control device according to claim 4 , wherein at least one of the plurality of dielectric films is a silicon nitride film.
7. The light control device according to claim 4 , wherein the number of laminations of the dielectric films in the second reflective layer is 19 to 23 layers.
8. The light control device according to claim 1 , wherein the light modulating film is made from an electro-optic material whose refractive index varies in proportion to the square of the applied electric field.
9. The light control device according to claim 8 , wherein the electro-optic material is lead titanate zirconate or lanthanum lead titanate zirconate.
10. The light control device according to claim 1 , wherein the light control device is arranged on a semiconductor substrate.
11. A light control system comprising:
the light control device according to claim 1 ;
a light-emitting portion that illuminates the light control device with light; and
a light-receiving portion that receives the light emitted from the light control device.