Low cost isolator/polarization beam combiner hybrid component

Details Low cost isolator/polarization beam combiner hybrid component Low cost isolator/polarization beam combiner hybrid component

2002-01-03

2004-02-10

Epps, Georgia (Department: 2873)

Optical: systems and elements

Optical modulator

Light wave temporal modulation

C359S641000, C359S615000, C359S494010, C359S490020, C385S011000

Reexamination Certificate

active

06690501

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to optical systems, and more particularly to a method and system for providing an isolator/polarization beam combiner.
BACKGROUND OF THE INVENTION
In fiber optic communication, the optical signal propagates inside an optical fiber. Due to the nature of optical fibers, optical signal attenuation always exists. To overcome this signal attenuation in long distance communication systems, optical signal amplification using an optical amplifier is required. Both Erbium Doped Fiber Amplifier (EDFA) or Raman Amplifier can be utilized as the optical amplifier. In order for the optical signal to propagate a longer distance, an optical amplifier with high output power is preferred.
Pump lasers with high output power are used in order to achieve high output power in high power optical amplifiers. In current technology, the output power of a single pump laser is limited. Higher pump power can be achieved by combining two pump signals having orthogonal polarization states. Furthermore, an optical isolator is required to prevent any back reflected signal from getting back to the pump so that a stabilized combined pump power can be achieved.
FIG. 1
depicts a conventional isolator/polarization beam combiner
10
. The conventional isolator/polarization beam combiner includes a dual fiber collimator
16
, a Wollaston prism
22
, a polarization beam displacer
24
, an isolator core
26
and a single fiber collimator
28
. The collimators
16
and
28
include pigtails
18
and
32
, respectively, lenses
20
and
30
, respectively. The lenses
20
and
30
are both GRIN lenses. Furthermore, the optical signals input from the fibers
12
and
14
cross at the face of the GRIN lens
20
.
The conventional isolator/polarization beam combiner
10
accepts a first optical signal from fiber
12
and a second optical signal from the fiber
14
. The polarizations of the optical signals are typically perpendicular. In addition, the fibers
12
and
14
are typically polarization maintaining (PM) fibers. The dual fiber collimator
16
collimates the optical signals such that the optical signals cross at the face of the GRIN lens
20
. The optical signals are then deflected to travel horizontally by the Wollaston prism
22
and combined by the polarization beam displacer
24
. The combined optical signal is transmitted by the isolator core
26
, which also prevents back reflections from the single fiber collimator
28
from being provided back to the input fibers
12
and
14
. The single fiber collimator
28
then focuses the combined signals and outputs this combined signal through the fiber
34
.
Although the conventional isolator/polarization beam combiner
10
functions, one of ordinary skill in the art will readily recognize that there are several drawbacks to its operation. First, a large number of discrete components are used: the dual fiber collimator
16
, the Wollaston prism
22
, the polarization beam displacer
24
, the isolator core
26
and the single fiber collimator
28
. Because of the large number of components, a large insertion loss is introduced. Moreover, the large number of components makes assembly of the conventional isolator/polarization beam combiner
10
more difficult. In addition, the conventional isolator/polarization beam combiner
10
is expensive, due in part to the use of a large number of optical components and the expense of certain optical components. For example, the GRIN lenses
20
and
30
are expensive to purchase. Furthermore, the conventional isolator/polarization beam combiner
10
has a higher polarization dependent loss because of the separated ordinary and extraordinary beams introduced by the isolator core
26
. Thus, the conventional isolator/polarization beam combiner
10
has relatively high losses and is expensive and difficult to assemble.
Accordingly, what is needed is a system and method for combining and isolating two signals with a lower insertion loss, lower PDL and a lower cost. The present invention addresses such a need.
SUMMARY OF THE INVENTION
The present invention provides a method and system for providing an isolator/polarization beam combiner. The method and system comprise providing a first collimator, a core and a second collimator. The first collimator collimates a plurality of optical signals traveling in a first direction. The core receives the plurality of optical signals from the first collimator. The core includes a first birefringent wedge, a second birefringent wedge and a rotator between the first and second birefringent wedges. The first collimator, the first birefringent wedge and the rotator transmit the plurality of optical signals such that the plurality of optical signals cross at an interface between the rotator and the second birefringent wedge. The core transmits the plurality of optical signals with a deflection, combines the plurality of optical signals to provide a combined optical signal and prevents a reflected portion of the plurality of optical signals from traveling opposite to the first direction. The second collimator receives and collimates the combined optical signal.
According to the system and method disclosed herein, the present invention provides a low cost isolator/polarization beam combiner.


REFERENCES:
patent: 2002/0191881 (2002-12-01), Chen et al.
patent: 2003/0049009 (2003-03-01), Vaganov et al.

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