Wavelength conversion device and image display device
View Patent ↗The present application discloses a wavelength conversion device. The wavelength conversion device includes a light source for generating excitation light, a laser medium for generating fundamental light from the excitation light, a resonator mirror for forming a resonator for the fundamental light in cooperation with the laser medium, and a wavelength convertor for converting wavelength from the fundamental light into harmonic light. The wavelength convertor includes a first end surface inclined by an angle θ from a surface orthogonal to an optical axis of the resonator and a second end surface parallel to the first end surface.
1. A wavelength conversion device comprising:
a light source configured to generate excitation light;
a laser medium configured to generate fundamental light from the excitation light;
a resonator mirror configured to form a resonator for the fundamental light in cooperation with the laser medium; and
a wavelength convertor configured to convert wavelength from the fundamental light into harmonic light, wherein
the wavelength convertor includes a first end surface inclined by an angle θ from a surface orthogonal to an optical axis of the resonator and a second end surface parallel to the first end surface, and
the angle θ satisfies a relationship represented by Formulas 1 to 5 described below:
Spreading
Angle
of
Harmonic
Light
<
θ
<
θ
1
=
1
2
tan
-
1
(
ϕ
1
+
ϕ
2
2
L
1
)
[
Formula
1
]
where,
L 1 : length of the laser medium in an optical axis direction,
and φ1 and φ2 are defined by Formula 2:
ϕ
1
=
2
(
λ
2
π
)
4
L
(
R
-
L
)
ϕ
2
=
ϕ
1
1
+
2
(
L
1
)
2
(
π
n
0
ϕ1
2
4
λ
)
2
[
Formula
2
]
where,
λ: wavelength of the fundamental light,
L: resonator length,
π: circular constant,
R: curvature radius of the resonator mirror,
and n 0 is defined by Formula 3:
n
0
=
n
′
L
′
[
Formula
3
]
where n′ is defined by Formula 4 and L′ is defined by Formula 5:
n
′
=
n
1
L
1
+
n
2
(
L
2
-
L
1
)
+
L
2
-
L
1
cos
2
θ
+
L
1
cos
{
sin
-
1
(
n
1
n
2
sin
2
θ
)
}
[
Formula
4
]
where,
n 1 : refractive index of the laser medium,
n 2 : refractive index between the laser medium and the wavelength convertor,
L 2 : distance from the laser medium to the wavelength convertor,
L
′
=
L
2
+
L
2
-
L
1
cos
2
θ
+
L
1
cos
{
sin
-
1
(
n
1
n
2
sin
2
θ
)
}
.
[
Formula
5
]
2. A wavelength conversion device comprising:
a light source configured to generate excitation light;
a laser medium configured to generate fundamental light from the excitation light;
a resonator mirror configured to form a resonator for the fundamental light in cooperation with the laser medium; and
a wavelength convertor configured to convert wavelength from the fundamental light into harmonic light, wherein
the wavelength convertor includes a first end surface inclined by an angle θ from a surface orthogonal to an optical axis of the resonator and a second end surface parallel to the first end surface, and
the angle θ satisfies a relationship represented by Formulas 6 to 10 described below:
Spreading
Angle
of
Harmonic
Light
<
θ
<
θ
1
=
1
2
tan
-
1
(
ϕ
1
+
ϕ
2
2
n
1
L
1
+
n
2
L
2
)
[
Formula
6
]
where,
L 1 : length of the laser medium in an optical axis direction,
L 2 : distance from the laser medium to the wavelength convertor,
n 1 : refractive index of the laser medium,
n 2 : refractive index between the laser medium and the wavelength convertor,
and φ1 and φ2 are defined by Formula 7:
ϕ
1
=
2
(
λ
2
π
)
4
L
a
(
R
-
L
a
)
ϕ
2
=
ϕ
1
1
+
{
2
(
n
1
L
1
+
n
2
L
2
)
}
2
(
π
n
0
ϕ1
2
4
λ
)
2
[
Formula
7
]
where,
λ: wavelength of the fundamental light,
π: circular constant,
R: curvature radius of the resonator mirror,
and L a and n 0 are defined by Formula 8:
L
a
=
n
1
L
1
+
n
2
L
2
+
n
3
L
3
+
n
4
L
4
n
0
=
n
′
L
′
[
Formula
8
]
where,
L 3 : length of the wavelength convertor in the optical axis direction,
L 4 : distance from the wavelength convertor to the resonator mirror,
n 3 : refractive index of the wavelength convertor,
n 4 : refractive index between the wavelength convertor and the resonator mirror,
and n′ is defined by Formula 9 and L′ is defined by Formula 10:
n
′
=
n
1
L
1
+
n
2
L
2
+
n
3
L
2
cos
2
θ
+
n
4
L
1
cos
{
sin
-
1
(
n
1
n
2
sin
2
θ
)
}
[
Formula
9
]
L
′
=
L
1
+
L
2
+
L
2
cos
2
θ
+
L
1
cos
{
sin
-
1
(
n
1
n
2
sin
2
θ
)
}
.
[
Formula
10
]
3. The wavelength conversion device according to claim 1 , wherein the spreading angle is defined as a value of a half of full width at half maximum.
4. The wavelength conversion device according to claim 1 , wherein the spreading angle is no more than 0.2 degrees.
5. The wavelength conversion device according to claim 1 , wherein parallelism between the first and second end surfaces is no more than 0.2 degrees.
6. The wavelength conversion device according to claim 1 , further comprising transmission films formed on the first and second end surfaces, wherein
the transmission films have transmittance no less than 99.7% for the fundamental light.
7. The wavelength conversion device according to claim 1 , wherein
the fundamental light has an elliptical beam shape, and
the wavelength convertor is inclined around a major axis of the elliptical beam shape.
8. The wavelength conversion device according to claim 1 , wherein
the wavelength convertor includes a polarization-reversed region, and
the first end surface is inclined around an axis extending in a polarization reversal direction of the region.
9. The wavelength conversion device according to claim 1 , wherein a distance between the laser medium and the wavelength convertor is no longer than 1 mm.
10. The wavelength conversion device according to claim 1 , wherein a length of the resonator in the optical axis direction is no longer than 10 mm.
11. The wavelength conversion device according to claim 1 , wherein an angle between the wavelength convertor and the fundamental light is a Brewster's angle.
12. The wavelength conversion device according to claim 1 , wherein the wavelength convertor is mechanically fixed so that rotation around an axis extending in a polarization direction of the fundamental light and rotation around the optical axis are restricted.
13. An image display device comprising:
an illuminator including laser sources; and
a spatial modulator illuminated by the illuminator to create image light, wherein
the laser sources include a red laser source configured to emit laser light of a red hue, a green laser source configured to emit laser light of a green hue, and a blue laser source configured to emit laser light of a blue hue, and
the green laser source includes the wavelength conversion device according to claim 1 .
14. The image display device according to claim 13 , wherein
the spatial modulator is rectangular, and
the wavelength convertor is inclined around a minor axis of the spatial modulator.