External resonator laser
A tunable external resonator laser is mode-hop-free for broadband and has a laser chip which emits light; a lens which collimates the light emitted from the laser chip, a diffraction grating which diffracts the light collimated by the lens, a support body to which the diffraction grating is fixed, and a movable mirror which reflects the light diffracted by the diffraction grating, wherein the diffraction grating is arranged a prescribed distance apart from a Littman-type tunable external resonator laser arrangement in which the movable mirror rotates on a pivot which is the intersection point of the surface of said movable mirror and the surface of the diffraction grating.
1. A tunable external resonator laser which suppresses mode hop, said laser comprising:
a laser chip for emitting light;
a lens for collimating the light emitted from the laser;
a diffraction grating for diffracting the light collimated by the lens;
a support body to which the diffraction grating is fixed, and
a movable mirror for reflecting the light diffracted by the diffraction grating, the movable mirror being rotatable about a pivot located on an intersection line of planes containing surfaces of the movable mirror and a first plane which is parallel to the diffraction grating surface and is movable from the first plane to a second plane parallel to the first plane,
wherein an offset D G of the diffraction grating surface and said pivot is determined by the following formula
D
G
=
(
d
2
n
1
(
λ
)
d
λ
2
❘
λ
0
l
+
d
2
n
2
(
λ
)
d
λ
2
❘
λ
0
t
)
(
1
-
(
λ
0
d
-
sin
α
)
2
)
3
d
2
wherein λ 0 is a desired center wavelength, n 1 (λ) is an effective refractive index of a waveguide mode of the laser chip, n 2 (λ) is a refractive index of the collimation lens, d 2 n 1 (λ)/dλ 2 or d 2 n 2 (λ)/dλ 2 is respectively quadratic differential coefficient for each wavelength of refractive index, l is the chip length of the laser chip, t is the effective thickness of the collimation lens, d is an interval of grooves of the diffraction grating, α is an incident angle between collimated light and the diffraction grating, with the collimating light being incident.
2. A tunable external resonator laser which suppresses mode hop, said laser comprising:
a laser chip for emitting light;
a lens for collimating the light emitted from the laser chip;
a diffraction grating for diffracting the light collimated by the lens, the diffraction grating being positioned at a second position which is offset from a previous position such that a plane containing a diffracting surface thereof is parallel to a plane containing the diffracting surface at the previous position;
a support body to which the diffraction grating is fixed, and
a movable mirror for reflecting the light diffracted by the diffraction,
wherein the movable mirror rotates on a pivot which is located on an intersection line of planes containing surfaces of the movable mirror and a first plane which is parallel to the diffraction grating surface, and an offset D G of the diffraction grating surface and said pivot is determined by the following formula
D
G
=
(
d
2
n
1
(
λ
)
d
λ
2
❘
λ
0
l
+
d
2
n
2
(
λ
)
d
λ
2
❘
λ
0
t
)
(
1
-
(
λ
0
d
-
sin
α
)
2
)
3
d
2
,
wherein λ 0 is a desired center wavelength, n 1 (λ) is the effective refractive index of a waveguide mode of the laser chip, n 2 (λ) is the refractive index of the collimation lens, d 2 n 1 (λ)/dλ 2 or d 2 n 2 (λ)/dλ 2 is respectively a quadratic differential coefficient for each wavelength of refractive index, l is the chip length of the laser chip, t is the effective thickness of the collimation lens, d is the interval of grooves of the diffraction grating, and α is the incident angle between collimated light and the diffraction grating, with the collimating light being incident.
3. A tunable external resonator laser for suppressing mode hop, said laser comprising:
a laser chip for emitting light;
a lens for collimating the light emitted from the laser;
a support body to which a diffraction grating is fixed, said support body being rotatable about a pivot which is contained in a plane containing surfaces of the half mirror and a first plane which is parallel to the diffraction grating surface and movable from a first plane to a second plane parallel to the first plane, and
a half mirror for reflecting part of the light incident thereon and transmitting another part of the incident light,
wherein the movable mirror rotates on a pivot which is located on an intersection line of planes containing a surface of the movable mirror and the first plane, and an offset D G of the diffraction grating surface and said pivot is determined by the following formula
D
G
=
(
d
2
n
1
(
λ
)
d
λ
2
❘
λ
0
l
+
d
2
n
2
(
λ
)
d
λ
2
❘
λ
0
t
)
(
1
-
(
λ
0
d
-
sin
α
)
2
)
3
d
2
wherein λ 0 is a desired center wavelength, n 1 (λ) is the effective refractive index of a waveguide mode of the laser chip, n 2 (λ) is the refractive index of the collimation lens, d 2 n 1 (λ)/dλ 2 or d 2 n 2 (λ)/dλ 2 is respectively the quadratic differential coefficient for each wavelength of refractive index, l is the chip length of the laser chip, t is the effective thickness of the collimation lens, d is the interval of grooves of the diffraction grating, and α is the incident angle between collimated light and the diffraction grating, with the collimating light being incident.
4. A tunable external resonator laser which suppresses mode hop, said laser comprising:
a laser chip for emitting light;
a lens for collimating the light emitted from the laser;
a diffraction grating for diffracting the light collimated by the lens;
a half mirror for reflecting the light diffracted by the diffraction grating; and
a support body to which the half mirror is fixed,
wherein the diffraction grating is rotatable about a pivot located on an intersection line of planes containing surfaces of the half mirror and a first plane which is parallel to the diffraction grating surface, and
the offset D G of the diffraction grating surface and said pivot is determined by the following formula
D
G
=
(
d
2
n
1
(
λ
)
d
λ
2
❘
λ
0
l
+
d
2
n
2
(
λ
)
d
λ
2
❘
λ
0
t
)
(
1
-
(
λ
0
d
-
sin
α
)
2
)
3
d
2
wherein λ 0 is a desired center wavelength, n 1 (λ) is the effective refractive index of waveguide mode of the laser chip, n 2 (λ) is the refractive index of the collimation lens, d 2 n 1 (λ)/dλ 2 or d 2 n 2 (λ)/dλ 2 is respectively the quadratic differential coefficient for each wavelength of the refractive index, l is the chip length of the laser chip, t is the effective thickness of the collimation lens, d is the interval of groove of the diffraction grating, α is the incident angle between collimated light and the diffraction grating, with the collimating light being incident.
5. A tunable external resonator laser which suppresses mode hop, said laser comprising:
a laser chip for emitting light;
a lens for collimating the light emitted from the laser;
a diffraction grating for diffracting the light collimated by the lens;
a support body to which the diffraction grating is fixed, and
a movable mirror for reflecting the light diffracted by the diffraction grating, the movable mirror being rotatable about a pivot located on an intersection line of planes containing surfaces of the movable mirror and a first plane which is parallel to the diffraction grating surface,
wherein an offset D G of the diffraction grating surface and said pivot is determined by the following formula
D
G
=
(
d
2
n
1
(
λ
)
d
λ
2
❘
λ
0
l
+
d
2
n
2
(
λ
)
d
λ
2
❘
λ
0
t
)
(
1
-
(
λ
0
d
-
sin
α
)
2
)
3
d
2
wherein λ 0 is a desired center wavelength, n 1 (λ) is the effective refractive index of a waveguide mode of the laser chip, n 2 (λ) is the refractive index of the collimation lens, d 2 n 1 (λ)/dλ 2 or d 2 n 2 (λ)/dλ 2 is respectively the quadratic differential coefficient for each wavelength of refractive index, l is the chip length of the laser chip, t is the effective thickness of the collimation lens, d is the interval of grooves of the diffraction grating, and α is the incident angle between collimated light and the diffraction grating, with the collimating light being incident.
6. A tunable external resonator laser which suppresses mode hop, said laser comprising:
a laser chip for emitting light;
a lens for collimating the light emitted from the laser chip;
a diffraction grating for diffracting the light collimated by the lens,
a support body to which the diffraction grating is fixed, and
a movable mirror for reflecting the light diffracted by the diffraction,
wherein the movable mirror rotates on a pivot which is located on a first plane which is parallel to the diffraction grating surface, and an offset D G of the diffraction grating surface and said pivot is determined by the following formula
D
G
=
(
d
2
n
1
(
λ
)
d
λ
2
❘
λ
0
l
+
d
2
n
2
(
λ
)
d
λ
2
❘
λ
0
t
)
(
1
-
(
λ
0
d
-
sin
α
)
2
)
3
d
2
,
wherein λ 0 is a desired center wavelength, n 1 (λ) is the effective refractive index of a waveguide mode of the laser chip, n 2 (λ) is the refractive index of the collimation lens, d 2 n 1 (λ)/dλ 2 or d 2 n 2 (λ)/dλ 2 is respectively a quadratic differential coefficient for each wavelength of refractive index, l is the chip length of the laser chip, t is the effective thickness of the collimation lens, d is the interval of grooves of the diffraction grating, and α is the incident angle between collimated light and the diffraction grating, with the collimating light being incident.
7. A tunable external resonator laser which suppresses mode hop, said laser comprising:
a laser chip for emitting light;
a lens for collimating the light emitted from the laser;
a diffraction grating for diffracting the light collimated by the lens;
a half mirror for reflecting the light diffracted by the diffraction grating; and
a support body to which the half mirror is fixed,
wherein the diffraction grating is rotatable about a pivot located on a first plane which is parallel to the diffraction grating surface, and
the offset D G of the diffraction grating surface and said pivot is determined by the following formula
D
G
=
(
d
2
n
1
(
λ
)
d
λ
2
❘
λ
0
l
+
d
2
n
2
(
λ
)
d
λ
2
❘
λ
0
t
)
(
1
-
(
λ
0
d
-
sin
α
)
2
)
3
d
2
wherein λ 0 is a desired center wavelength, n 1 (λ) is the effective refractive index of waveguide mode of the laser chip, n 2 (λ) is the refractive index of the collimation lens, d 2 n 1 (λ)/dλ 2 or d 2 n 2 (λ)/dλ 2 is respectively the quadratic differential coefficient for each wavelength of the refractive index, l is the chip length of the laser chip, t is the effective thickness of the collimation lens, d is the interval of groove of the diffraction grating, α is the incident angle between collimated light and the diffraction grating, with the collimating light being incident.