Wavelength selective switch
View Patent ↗Provided is a wavelength selective switch, which includes: an input/output unit; a dispersive portion; a condensing optical system; and the deflection portion. The input/output unit has input/output ports. The dispersive portion disperses signal light incident from the input/output ports. The condensing optical system condenses a plurality of signal light beams dispersed by the dispersive portion. The deflection portion has a plurality of deflection elements. The deflection elements deflect, along a second direction, the signal light beams condensed by the condensing optical system. In the condensing optical system, the aberration amount of the meridional component in a sagittal coma aberration remains substantially constant irrespective of an angle formed between the optical axis of the condensing optical system and a signal light beam incident on the condensing optical system from the input/output portion, at an incident position of the incident signal light beam at a certain height in the second direction.
1. A wavelength selective switch, comprising:
an input/output portion including at least twenty input/output ports;
a dispersive portion for dispersing wavelength-multiplexed signal light incident from the input/output port;
a condensing optical system for condensing a plurality of signal light beams dispersed by the dispersive portion; and
a deflection portion having a plurality of deflection elements for deflecting, along a second direction perpendicular to the dispersion direction of the dispersive portion, the plurality of signal light beams condensed by the condensing optical system, so as to allow the signal light beams to be incident on any of the input/output ports,
the condensing optical system having the aberration amount of the meridional component in a sagittal coma aberration maintained substantially constant irrespective of an angle formed between the optical axis of the condensing optical system and the signal light beam incident on the condensing optical system from the input/output portion, at an incident position of the incident signal light beam at a certain height in the second direction.
2. The wavelength selective switch according to claim 1 , wherein the condensing optical system has a curved surface in an aspherical shape in the dispersion direction.
3. The wavelength selective switch according to claim 2 ,
wherein the curved surface is a reflective surface,
wherein Z asp (h) is an amount of sag of the aspherical shape, which is obtained by Expression (1):
Z
asp
(
h
)
=
c
×
h
2
1
+
1
-
(
1
+
k
)
×
c
2
×
h
2
+
∑
i
=
2
A
i
h
2
i
,
(
1
)
where c represents a curvature, k represents a conic coefficient, and A i (i is an integer of 2 or more) represents an aspherical coefficient of 2i-th order,
wherein Z sp (h) represents an amount of sag of a spherical shape that is paraxial to the aspherical shape, which is obtained by Expression (2):
Z
sp
(
h
)
=
c
×
h
2
1
+
1
-
c
2
×
h
2
,
(
2
)
wherein Expression (3) has a maximum value of less than 0.02:
(
Z
asp
(
h
)
Z
sp
(
h
)
-
1
)
×
f
H
ω
,
(
3
)
where f represents the focal length of the condensing optical system, H represents a distance from each of the signal light beams passing through the condensing optical system to the optical axis of the condensing optical system, relative to the second direction, ω represents an angle formed between a light beam passing through the condensing optical system and the optical axis of the condensing optical system in the dispersion direction.
4. The wavelength selective switch according to claim 2 ,
wherein the curved surface is a transmission surface,
wherein Z asp (h) represents an amount of sag of the aspherical shape, which is obtained by expression (4):
Z
asp
(
h
)
=
c
×
h
2
1
+
1
-
(
1
+
k
)
×
c
2
×
h
2
+
∑
i
=
2
A
i
h
2
i
,
(
4
)
where c represents a curvature, k represents a conic coefficient, and A i (i is an integer of 2 or more) represents an aspherical coefficient of 2i-th order,
wherein Z sp (h) represents an amount of sag of a spherical shape that is paraxial to the aspherical shape, which is obtained by Expression (5):
Z
sp
(
h
)
=
c
×
h
2
1
+
1
-
c
2
×
h
2
,
(
5
)
wherein Expression (6) has a maximum value of less than 0.2:
(
Z
asp
(
h
)
Z
sp
(
h
)
-
1
)
×
f
H
ω
,
(
6
)
where f is the focal length of the condensing optical system, H is a distance from each of the signal light beams passing through the condensing optical system to the optical axis of the condensing optical system, relative to the second direction, ω is an angle formed between a light beam passing through the condensing optical system and the optical axis of the condensing optical system in the dispersion direction.
5. The wavelength selective switch according to claim 2 , wherein the condensing optical system includes a mirror having the curved surface.
6. The wavelength selective switch according to claim 2 , wherein the condensing optical system includes, as an optical element, a lens having the curved surface.
7. The wavelength selective switch according to claim 6 , wherein the optical element having the curved surface has a refractive index of 2.8 or more, and includes a medium for transmitting the signal light beams.
8. The wavelength selective switch according to claim 7 , wherein the medium of the optical system is any one of silicon, gallium arsenide, aluminum arsenide, gallium phosphide, and aluminum antimonide.
9. The wavelength selective switch according to claim 6 , wherein the optical element having the curved surface is a Grin lens.
10. The wavelength selective switch according to claim 6 , wherein the optical element having the curved surface has a surface formed in a Fresnel shape.
11. The wavelength selective switch according to claim 1 , wherein the condensing optical system has a curved surface which is a free-form surface.
12. The wavelength selective switch according to claim 1 ,
wherein the condensing optical system includes an optical element, the optical element having an incident surface for receiving the signal light beams incident thereon and a curved surface for reflecting the signal light beams incident on the incident surface, and the optical element refracting the signal light beams to be transmitted from the incident surface to the reflective surface.
13. The wavelength selective switch according to claim 1 , wherein the condensing optical system has a curved surface discontinuous in the second direction.
14. The wavelength selective switch according to claim 1 ,
wherein, assuming that a diaphragm is disposed on a front focal position of the condensing optical system, the diaphragm being in a size equal to a distance D between the passage positions of two light beams passing through both ends of the dispersive portion in the second direction, among the light beams passing through the twenty input/output ports,
the maximum field angle ω is represented by Expression (7), with the total dispersion angle being defined as γ with respect to the wavelength range of the dispersive portion:
±
ω
=
γ
2
(
7
)
wherein Expression (8) or Expression (9) is satisfied:
(
sin
α
2
…
m
-
sin
β
2
…
m
)
-
(
sin
α
1
-
sin
β
1
)
sin
(
ω
2
…
m
-
ω
1
)
×
50
W
<
0.003
(
8
)
(
sin
α
2
…
m
-
sin
β
2
…
m
)
-
(
sin
α
1
-
sin
β
1
)
sin
(
ω
2
…
m
-
ω
1
)
×
50
W
<
2.1
×
10
-
7
×
(
N
u
)
2
+
1.8
×
10
-
9
×
(
N
u
)
(
9
)
where ω 1 represents a minimum field angle, ω 2 . . . m represents an arbitrary field angle in a range from the maximum field angle ω to the minimum field angle ω 1 , α 1 represents an incident angle of a light beam passing through the center in the dispersion direction of the diaphragm at a position of the diaphragm when the field angle is ω 1 , β 1 is an incident angle, relative to the dispersion direction on the deflection elements, of a light beam passing through an arbitrary height H within a range of the size D of the diaphragm in the dispersion direction at the position of the diaphragm when the field angle is ω 1 , α 2 . . . m represents an incident angle, relative to the dispersion direction on the deflection elements, of a light beam passing through the center of the diaphragm in the dispersion direction at a position of the diaphragm when the field angle is ω 2 . . . m , β 2 . . . m represents an incident angle, relative to the dispersion direction on the deflection elements, of a light beam passing through the height H in the dispersion direction at a position of the diaphragm when the field angle is ω 2 . . . m , the frequency interval of the deflection elements is W(GHz), N represents a total number of the input/output ports, and u represents a value of a spot radius which makes a light intensity of 1/e 2 with respect to the maximum value, which is defined as 1, of the light intensity in the second direction of the deflection elements.