Optical waveguides – Polarization without modulation
Reexamination Certificate
2002-06-04
2004-12-28
Lee, John D. (Department: 2874)
Optical waveguides
Polarization without modulation
C359S490020
Reexamination Certificate
active
06836575
ABSTRACT:
BACKGROUND OF THE INVENTION
Optical circulators are commonly used in optical communication systems and optical measurement systems.
FIG. 1
a
shows a three-port Polarization Maintenance (“PM”) circulator
100
that has ports
1
,
2
, and
3
. Each of ports
1
,
2
, and
3
can be coupled to a PM fiber. As shown in
FIG. 1
, a polarized optical signal S
1
entering port
1
exits from port
2
as a polarized optical signal S
2
. A polarized optical signal S
2
′ entering port
2
exits from port
3
as a polarized optical signal S
3
.
SUMMARY OF THE INVENTION
In one aspect, the invention provides an optical device. The optical device includes a non-reciprocal combination-device and a polarizer. The non-reciprocal combination-device has a principal direction and a reverse principal direction. The non-reciprocal combination-device includes a first birefringent wedge, a second birefringent wedge, and a non-reciprocal rotating element. The polarizer receives a first light signal from the second birefringent wedge traveling in the principal direction and transmits a second light signal to enter the second birefringent wedge in the reverse principal direction. The first birefringent wedge has a first optical axis perpendicular to the principal direction. The second birefringent wedge has a second optical axis perpendicular to the principal direction, and the second optical axis forms a first angle with respect to the first optical axis. The non-reciprocal rotating element is optically coupled between the first and the second birefringent wedge. The non-reciprocal rotating element is designed to rotate the polarization of light passing through the non-reciprocal rotating element by a second angle.
In another aspect, the invention provides a method of using a non-reciprocal combination-device as a three-port PM circulator. The non-reciprocal combination-device has a principal direction and a reverse principal direction. The non-reciprocal combination-device includes a first birefringent wedge, a second birefringent wedge, and a non-reciprocal rotating element. The first birefringent wedge has a first optical axis perpendicular to the principal direction. The second birefringent wedge has a second optical axis perpendicular to the principal direction, and the second optical axis forms a first angle with respect to the first optical axis. The non-reciprocal rotating element is optically coupled between the first and the second birefringent wedge. The non-reciprocal rotating element is designed to rotate the polarization of light passing through the non-reciprocal rotating element by a second angle. The method includes the step of providing a first, a second, and a third PM fiber. The method includes the step of directing a first light signal exiting from the first PM fiber with a polarization parallel to the first optical axis to enter the first birefringent wedge in an input direction. The method includes the step of directing the first light signal exiting from the second birefringent wedge with a polarization perpendicular to the second optical axis to enter the second PM fiber. The method includes the step of directing a second light signal exiting from the second PM fiber with a polarization perpendicular to the second optical axis to enter the second birefringent wedge in the reverse principal direction. The method includes the step of directing the second light signal exiting from the first birefringent wedge with a polarization perpendicular to the first optical axis to enter the third PM fiber.
In another aspect, the invention provides a method of using a non-reciprocal combination-device as a three-port PM circulator. The non-reciprocal combination-device has a principal direction and a reverse principal direction. The non-reciprocal combination-device includes a first birefringent wedge, a second birefringent wedge, and a non-reciprocal rotating element. The first birefringent wedge has a first optical axis perpendicular to the principal direction. The second birefringent wedge has a second optical axis perpendicular to the principal direction, and the second optical axis forms a first angle with respect to the first optical axis. The non-reciprocal rotating element is optically coupled between the first and the second birefringent wedge. The non-reciprocal rotating element is designed to rotate the polarization of light passing through the non-reciprocal rotating element by a second angle. The method includes the step of providing a first, a second, and a third PM fiber. The method includes the step of directing a first light signal exiting from the first PM fiber with a polarization perpendicular to the first optical axis to enter the first birefringent wedge in an input direction. The method includes the step of directing the first light signal exiting from the second birefringent wedge with a polarization parallel to the second optical axis to enter the second PM fiber. The method includes the step of directing a second light signal exiting from the second PM fiber with a polarization parallel to the second optical axis to enter the second birefringent wedge in the reverse principal direction. The method includes the step of directing the second light signal exiting from the first birefringent wedge with a polarization parallel to the first optical axis to enter the third PM fiber.
Among the advantages of the invention are one or more of the following. Implementations of the invention provide a three-port PM circulator that can have small insertion loss, compact size, and reduced manufacturing cost. The three-port PM circulator can include isolation function. Other advantages will be readily apparent from the attached figures and the description below.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
a
illustrates a three-port PM circulator
100
including ports
1
,
2
, and
3
.
FIG. 1
b
illustrates an implementation of a non-reciprocal combination-device.
FIG. 1
c
illustrates a specific configuration of birefringent wedges and a Faraday rotator of
FIG. 1
b.
FIGS. 1
d
-
1
f
illustrate alternative configurations of the birefringent wedges and the Faraday rotator of
FIG. 1
b.
FIG. 2
a
illustrates the paths traveled by light that enters the non-reciprocal combination-device of
FIG. 1
b
in the principal direction.
FIG. 2
b
illustrates that light entering the first birefringent wedge as an e-ray in the principal direction exits from the second birefringent wedge as an o-ray in the first output direction.
FIG. 2
c
illustrates that light entering the first birefringent wedge as an o-ray in the principal direction exits from the second birefringent wedge as an e-ray in the second output direction.
FIG. 3
a
illustrates the paths traveled by light that enters the non-reciprocal combination-device of
FIG. 1
b
in the first and the second input direction.
FIG. 3
b
illustrates that light entering the second birefringent wedge as an e-ray in the first input direction exits from the second birefringent wedge as an o-ray in the principal direction.
FIG. 3
c
illustrates that light entering the first birefringent wedge as an o-ray in the second input direction exits from the second birefringent wedge as an e-ray in the principal direction.
FIG. 4
a
illustrates the paths traveled by light that enters the non-reciprocal combination-device of
FIG. 1
b
in the reverse principal direction.
FIG. 4
b
illustrates that light entering the second birefringent wedge as an e-ray in the reverse principal direction exits from the first birefringent wedge as an e-ray in the reverse principal direction.
FIG. 4
c
illustrates that light entering the second birefringent wedge as an o-ray in the reverse principal direction exits from the first birefringent wedge as an o-ray in,the reverse principal direction.
FIGS. 5
a
and
5
b
illustrate that a polarized optical signal S
1
exiting from PM fiber
510
enters PM fiber
520
as a polarized optical signal S
2
.
FIGS. 6
a
and
6
b
illustrate that a polarized optical signal S
2
′ exiting from PM fiber
520
enters PM fiber
530
as
Fish & Richardson P.C.
Lin Tina M
Oplink Communications Inc.
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