Optical phase shifter, optical switch and 90 degrees optical hybrid
An optical phase shifter in which a phase shift amount is kept constant in a wide wavelength region is provided. One aspect is the optical phase shifter constituting of two waveguides of a basic width, and configured so that two lights propagating through each waveguide have a phase difference, including a different type waveguide arranged in at least one of the two waveguides and having a waveguide width different from the basic width, and a configuration of the different type waveguide and a parameter of the two waveguides and different type waveguide are optimized.
1 . An optical phase shifter including two waveguides having a basic width W 0 and configured such that two light beams propagating through the respective two waveguides have a phase difference ξ, the two waveguides comprising:
a first waveguide; and
a second waveguide,
wherein the first waveguide comprises:
a waveguide having a basic width W 0 ; and
a first different type waveguide having a width W 1 different from the basic width W 0 and a length L 1 , and
the second waveguide comprises a waveguide having the basic width W 0 ,
wherein the first waveguide and the second waveguide are different in length by a difference ΔL, and when an equivalent refractive index of a waveguide having a width w is defined as n(w), a propagation distance along a light propagation path in the first different type waveguide from a starting point of the first different type waveguide is defined as z 1 , and a width of the first different type waveguide at the propagation distance z 1 is set to W(z 1 ), in a phase difference Δφ,
Δ
ϕ
=
2
π
n
(
W
0
)
·
Δ
L
+
∫
0
L
1
{
n
(
W
(
z
1
)
)
-
n
(
W
0
)
}
·
dz
1
λ
[
Math
.
1
]
for a wavelength λ of a predetermined wavelength range, the length L 1 and the difference ΔL are set so that
∫
(
Δϕ
-
ξ
)
2
d
λ
[
Math
.
2
]
becomes minimum.
2 . The optical phase shifter according to claim 1 , the first waveguide further comprising:
a second different type waveguide having a width W 2 different from the basic width W 0 and satisfying a relation of the width W 2 <the basic width W 0 <the width W 1 and having a length L 2 , wherein
when a propagation distance along a light propagation path in the second different type waveguide from a starting point of the second different type waveguide is defined as z 2 and a width of the second different type waveguide at the propagation distance z 2 is set to W(z 2 ), in a phase difference Δφ,
Δ
ϕ
=
2
π
n
(
W
0
)
·
Δ
L
+
∫
0
L
1
{
n
(
W
(
z
1
)
)
-
n
(
W
0
)
}
·
dz
1
+
∫
0
L
2
{
n
(
W
(
z
2
)
)
-
n
(
W
0
)
}
·
dz
2
λ
[
Math
.
3
]
for a wavelength λ of a predetermined wavelength range, the length L 1 , the length L 2 , and the difference ΔL are set so that
∫
(
d
Δ
ϕ
d
W
)
2
d
λ
[
Math
.
4
]
becomes minimum and
∫
(
Δ
ϕ
-
ξ
)
2
d
λ
[
Math
.
5
]
becomes minimum.
3 . The optical phase shifter according to claim 1 , the second waveguide further comprising:
a third different type waveguide having a width W 3 different from the basic width W 0 and satisfying a relation of the width W 3 <the width W 1 and having a length L 3 , wherein
when a propagation distance along a light propagation path in the third different type waveguide from a starting point of the third different type waveguide is defined as z 3 , and a width of the third different type waveguide at the propagation distance z 3 is set to W(z 3 ), in a phase difference Δφ,
Δ
ϕ
=
2
π
n
(
W
0
)
·
Δ
L
+
∫
0
l
1
{
n
(
W
(
z
1
)
)
-
n
(
W
0
)
}
·
dz
1
-
∫
0
L
3
{
n
(
W
(
z
3
)
)
-
n
(
W
0
)
}
·
dz
3
λ
[
Math
.
6
]
for a wavelength λ of a predetermined wavelength range, the length L 1 , the length L 3 , and the difference ΔL are set so that
∫
(
d
Δ
ϕ
d
W
)
2
d
λ
[
Math
.
7
]
becomes minimum and
∫
(
Δϕ
-
ξ
)
2
d
λ
[
Math
.
8
]
becomes minimum.
4 . An optical switch comprising:
two two-input two-output optical couplers connected by the first waveguide and the second waveguide of the optical phase shifter according to claim 1 , wherein
the optical switch is a Mach-Zehnder interferometer constituting of the two waveguides.
5 . The optical switch according to claim 4 , wherein
the two-input two-output optical coupler is a wavelength independent optical coupler (Winc) constituted by a Mach-Zehnder interferometer including two interference arms connecting two directional couplers, and the two directional couplers are connected so that an order in a propagation direction of light of the two directional couplers and an arrangement of the two interference arms are symmetrical.
6 . The optical switch according to claim 4 , wherein
the two-input two-output optical coupler is a directional coupler including an optical coupling portion in which two waveguides having different waveguide widths are close to each other, and the waveguides of the optical coupling portion are connected so as to be symmetrical in an arrangement.
7 . The optical switch, wherein
the optical switch is constituted by a double gate type switch element in which two optical switches according to claim 4 , are connected in cascade.
8 . The optical switch, wherein
the optical switch is constituted by a matrix switch including N 2 optical switches according to claim 4 between N input line waveguides and N output line waveguides.
9 . The optical switch, wherein
the optical switch is constituted by a tree switch including N optical switches according to claim 4 between one input line waveguide and N output line waveguides.
10 . A 90 degrees optical hybrid, wherein
a first optical coupler and a second optical coupler arranged in a front stage, a third optical coupler and a fourth optical coupler arranged in a rear stage, and
one output of the first optical coupler and one output of the second optical coupler are connected to an input of the third optical coupler by a pair of waveguides,
an other output of the first optical coupler and an other output of the second optical coupler are connected to an input of the fourth optical coupler by a pair of waveguides, and
at least one of the pair of waveguides is constituted by the first waveguide and the second waveguide of the optical phase shifter according to claim 1 .
11 . The optical phase shifter according to claim 1 , wherein the first different type waveguide is replaced at the starting portion by a tapered waveguide having a width gradually changed from the basic width W 0 to the width W 1 and is replaced at the terminating portion by a tapered waveguide having a width that gradually changed from the width W 1 to the basic width W 0 .
12 . The optical phase shifter according to claim 2 , wherein
the first different type waveguide is replaced at the starting portion by a tapered waveguide having a width gradually changed from the basic width W 0 to the width W 1 and is replaced at the terminating portion by a tapered waveguide having a width that gradually changed from the width W 1 to the basic width W 0 and
the second different type waveguide is replaced at the starting portion by a tapered waveguide having a width gradually changed from the basic width W 0 to the width W 2 and is replaced at the terminating portion by a tapered waveguide having a width that gradually changed from the width W 2 to the basic width W 0 .
13 . The optical phase shifter according to claim 3 , wherein
the first different type waveguide is replaced at the starting portion by a tapered waveguide having a width gradually changed from the basic width W 0 to the width W 1 and is replaced at the terminating portion by a tapered waveguide having a width that gradually changed from the width W 1 to the basic width W 1 and
the third different type waveguide is replaced at the starting portion by a tapered waveguide having a width gradually changed from the basic width W 0 to the width W 3 and is replaced at the terminating portion by a tapered waveguide having a width that gradually changed from the width W 3 to the basic width W 0 .