Optical: systems and elements – Polarization without modulation – Depolarization
Reexamination Certificate
2001-07-05
2003-09-30
Chang, Audrey (Department: 2872)
Optical: systems and elements
Polarization without modulation
Depolarization
C359S485050, C359S488010, C359S490020, C385S031000, C385S039000
Reexamination Certificate
active
06628461
ABSTRACT:
BACKGROUND
1. Field of the Disclosure
The disclosure relates generally to fiber optics, and in particular, to a polarization beam splitter/combiner featuring an integrated optical isolator.
2. The Prior Art
BACKGROUND
Fiber optical networks are becoming increasingly faster and more complex. For example, networks compliant with the OC48 standard for synchronous optical networks (capable of a 2.5 Gb/s data rate) are being replaced by newer networks compliant with OC192 (10 Gb/s). Networks compliant with OC768 (40 Gb/s) networks are already on the horizon. At the same time, research is underway to transmit more and more channels down a single fiber through the use of dense wavelength division multiplexing (DWDM) technology. Eighty-channel systems are currently being deployed; it is anticipated that network density will increase in the future.
Key to this expansion are technologies such as thin film deposition and diffraction gratings which allow optical components to be manufactured in increasingly smaller packages. As optical networks continue to carry more channels at faster rates, component size is becoming a key limiting factor.
Central to any optical network are optical amplifiers. Optical amplifiers such as Raman and erbium-doped fiber amplifiers (EDFA) are responsible for amplifying and transmitting optical signals over long distances.
FIG. 1
shows a prior art operational block diagram of a typical Raman pump model
100
. The Raman pump
100
is formed using several discrete components, including four isolators
110
,
112
,
114
, and
116
; and two polarization beam combiners (PBC)
118
and
120
in addition to pump lasers (not shown).
In operation, two light sources
102
and
104
feed the two isolators
110
and
112
, respectively. The output of the isolators
110
and
112
are fed to PBC
118
, where the two signal are combined into a single signal. Likewise, two light sources
106
and
108
feed the isolators
114
and
116
, respectively. The output of isolators
114
and
116
feed PBC
120
, where the two signals are combined into one signal. The two signals from the PBCs
118
and
120
are then multiplexed and output by WDM
122
.
As is appreciated by those skilled in the art, isolators and PBCs are essential components of any optical amplification system. Currently, optical amplifiers must separately employ isolators and PBCs as discrete components. As the complexity of optical networks continues to grow, utilizing discrete components has certain disadvantages. For example, discrete components take up space and are expensive. Furthermore, discrete components must be optically coupled, which may lead to performance degradation.
SUMMARY
An integrated optical polarization beam splitter/combiner and isolator (IPBC) is disclosed. In one aspect, a disclosed IPBC may comprise a first birefringent crystal optically configured to receive two rays incident at an angle &ggr;; a rotator configured to rotate the two rays received from the first wedge; a second birefringent crystal positioned to receive the two rays from the rotator; and wherein the integrated optical polarization beam splitter/combiner and isolator is configured to combine the two rays in a forward direction, and isolate the two rays in a reverse direction.
In another aspect of a disclosed IPBC, the first and second birefringent crystals may comprise the same material, and have the same wedge angle &thgr;.
In a further aspect of a disclosed IPBC, the relationship between the wedge angle &thgr; and the angle &ggr; may be defined as:
&ggr;=2·arc Sin [(
n
o
−n
e
)·tan &thgr;].
In yet a further aspect of a disclosed IPBC, the crystals may have optic axes which are 45° apart. Furthermore, the two rays may have orthogonal polarizations, and may be combined interior to the second crystal, and exit the second crystal as a third ray.
In a further aspect of a disclosed IPBC, an incoming beam port may be employed for launching the two rays through a lens into the first crystal. The incoming beam port may comprise a plurality of PM fibers, the PM fibers each having corresponding principal axes; the plurality of PM fibers disposed together as a grouping, the grouping having corresponding secondary axes; and whereby each the plurality of PM fibers is aligned such that the corresponding principal axes of each the plurality of the PM fiber and the secondary axes of the grouping intersect at a predetermined angle.
Another aspect of a IPBC is disclosed, which may comprise a first birefringent means for receiving and refracting a first ray and a second ray incident at an angle &ggr; such that the first ray comprises an e-ray with respect to the first wedge, and the second ray comprises an o-ray with respect to the first wedge; rotating means for rotating the two rays received from the first wedge; second birefringent means for receiving and refracting the first and second rays from the rotator such that the first ray comprises an o-ray with respect to the second wedge, and the second ray comprises an e-ray with respect to the second wedge; and wherein the second crystal is optically configured to combine the first and second rays in a forward direction, and the first crystal is optically configured to diverge the first and second rays in a reverse direction.
A method for combining light in a forward direction and isolating light in a reverse direction is disclosed. In one aspect, the method may comprise refracting a first ray and a second ray incident at an angle &ggr; such that the first ray comprises an e-ray with respect to the first wedge, and the second ray comprises an o-ray with respect to the first wedge; rotating the two rays received from the first wedge; and refracting the first and second rays from the rotator such that the first ray comprises an o-ray with respect to the second wedge, and the second ray comprises an e-ray with respect to the second wedge.
REFERENCES:
patent: 4548478 (1985-10-01), Shirasaki
patent: 5402509 (1995-03-01), Fukushima
patent: 6018418 (2000-01-01), Pan et al.
patent: 6038357 (2000-03-01), Pan
patent: 0 50 199 (1992-12-01), None
patent: 59176721 (1984-10-01), None
patent: 60130934 (1985-07-01), None
patent: 61130921 (1986-06-01), None
patent: 06113920 (1994-04-01), None
Huang Yonglin
Ma Meng
Ma Shuging
Chang Audrey
Curtis Craig
Finisar Corporation
Workman & Nydegger & Seeley
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