The present invention is a hybrid cell that utilizes a PBS pair in conjunction with a wedge tuner and a crystal to achieve a more stable interleaver. A first PBS splits an incoming optical signal into two orthogonally polarized beams which follow different optical paths through the cell. The length of the wedge tuner and crystal are selected such that the periodicity of the cell is approximately inversely proportional to the free spectral range at a target frequency. The length of the wedge tuner and crystal are also selected such that there is no change in an optical path difference between the two optical paths with respect to a change in temperature over an operating temperature range.
1. An optical device through which propagates a first beam and a second beam, the first beam propagating through the optical device along a first optical path and the second beam propagating through the optical device along a second optical path, the optical device comprising:
a first optical component having a first length, the first optical component receiving the first beam along the first optical path;
a second optical component optically coupled to said first optical component, said second optical component having a second length and being adapted to receive the first beam and the second beam, and
a first polarizing beam splitter and a second polarizing beam splitter, said first polarizing beam splitter being optically coupled to said first optical component and said second polarizing beam splitter being disposed between said first optical component and said second optical component,
wherein said first length of said first optical component and said second length of said second optical component are selected such that an optical path difference between the first optical path length of said first optical path and a second optical path length of said second optical path is approximately inversely proportional to a free spectral range of a target wavelength of either the first beam or the second beam, and
wherein said first length and said second length are defined by the equations
(
n
air
-
n
g
)
L
w
+
(
n
o
-
n
e
)
L
c
=
c
FSR
-
4
n
g
d
sin
α
and
[
(
n
air
-
n
g
)
α
1
-
β
1
]
L
w
+
(
β
2
+
α
2
(
n
o
-
n
e
)
)
L
c
=
-
4
d
sin
α
(
β
1
+
α
1
n
g
)
,
where
n air = refractive index of air.
n g = group index of the glass.
L 2 = length of first optical component.
n o = ordinary index of refraction of the second optical component.
n e = extraordinary index of refraction of the second optical
component.
L c = length of the second optical component.
c = speed of light in a vacuum.
FSR = free spectral range.
d = distance between a first interface and a second
interface of the first polarizing beam splitter.
α = angle of the first interface with respect to horizontal.
α 1 = thermal expansion coefficient of said first and said second
polarizing beam splitters.
α 2 = thermal expansion coefficient of said second optical component.
β
1
=
∂
n
g
∂
T
,
where
∂
T
is the change in ambient temperature.
β
2
=
∂
(
n
o
-
n
e
)
∂
T
,
where
∂
T
is the change in ambient temperature.
2. The optical device of claim 1 , wherein said first optical component comprises a wedge tuner.
3. The optical device of claim 1 , wherein said second optical component comprises a birefringent optical crystal.
4. The optical device of claim 1 , wherein said target wavelength is in any one of the C, L, and S bands.
5. The optical device of claim 1 , wherein said first length and said second length are selected such that said optical path difference does not change over a given temperature range.
6. An optical component comprising:
a first polarizing beam splitter that receives an input light beam and splits said input light beam into a first beam along a first optical path and a second beam along a second optical path;
a wedge tuner having a first length optically coupled with said first polarizing beam splitter along said first optical path;
a second polarizing beam splitter optically coupled with said wedge tuner along said first optical path, said second polarizing beam splitter being optically coupled with said first polarizing beam splitter along said second optical path; and
an optical crystal optically coupled with said second polarizing beam splitter, said optical crystal having a second length,
wherein said second polarizing beam splitter combines said first and said second beams and passes said combined beam to said optical crystal and wherein said first length and said second length are selected such that an optical path difference between a first optical path length of said first optical path and a second optical path length of said second optical path is approximately inversely proportional to a free spectral range of a target wavelength of said input light beam, and
wherein said first length and said second length are defined by the equations
{
β
1
(
γ
c
)
-
[
(
n
air
(
γ
c
)
-
n
g
(
γ
c
)
]
}
L
w
-
[
β
2
(
γ
c
)
+
α
2
Δn
(
γ
c
)
]
L
c
=
-
4
dsin
α
[
β
1
(
γ
c
)
+
α
1
n
g
(
γ
c
)
]
and
{
[
n
air
(
γ
2
)
γ
2
-
n
air
(
γ
1
)
γ
1
]
-
[
n
g
(
γ
2
)
γ
2
-
n
g
(
γ
1
)
γ
1
]
}
L
w
+
[
Δn
(
γ
2
)
γ
2
-
Δn
(
γ
1
)
γ
1
]
L
c
=
(
γ
2
-
γ
1
)
FSR
c
-
4
d
sin
α
[
n
g
(
γ
2
)
γ
2
-
n
g
(
γ
1
)
γ
1
]
where
n air = refractive index of air.
n g = group index of the glass.
L w = length of first optical component.
Δn = n e − n o , where n o is ordinary index of refraction of the second
optical component and n e is extraordinary index of refraction of
the second optical component.
L c = length of the second optical component
c = speed of light in a vacuum
FSR = free spectral range
d = distance between a first interface and a second interface of the
first polarizing beam splitter
α = angle of the first interface with respect to horizontal
α 1 = thermal expansion coefficient of said first and said second
polarizing beam splitters.
α 2 = thermal expansion coefficient of said second optical component.
β
1
=
∂
n
g
∂
T
,
where
∂
T
is the change in ambient temperature.
β
2
=
∂
(
n
o
-
n
e
)
∂
T
,
where
∂
T
is the change in ambient temperature.
γ 1 , γ 2 = upper and lower boundaries for the operating wavelength range
γ c = (γ 2 + γ 1 )/2.
7. The optical component of claim 6 , wherein said target wavelength is in any one of the C, L, and S bands.
8. The optical component of claim 6 , wherein said first length and said second length are also selected such that said optical path difference does not change over a given temperature range.
9. The optical component of claim 8 , wherein the temperature range is from approximately −45 to approximately 85 degrees C.
10. The optical component of claim 6 , wherein said free spectral range is about 100 GHz, said first length is approximately 4.87 mm and said second length is approximately 3.42 mm.
11. The optical component of claim 6 , wherein said first and second polarizing beam splitters comprise glass.
12. The optical component of claim 6 , wherein said first and second polarizing beam splitters and said wedge tuner comprise glass.
13. The optical component of claim 6 , wherein said optical crystal comprises any one of an Yttrium Orthovanadate (YVO 4 ) Crystal, a Calcite (CaCO 3 ) crystal, a rutile (TiO 2 ) crystal, and an alpha-BBO crystal.
14. The optical component of claim 6 , wherein the optical component functions as an interleaver/de-interleaver.