Optical isolator using multiple core fibers

Details Optical isolator using multiple core fibers Optical isolator using multiple core fibers

2000-09-12

2001-11-13

Ben, Loha (Department: 2873)

Optical: systems and elements

Optical modulator

Light wave temporal modulation

C359S281000, C359S282000, C359S256000, C359S324000, C359S484010, C385S126000, C385S047000, C385S011000, C324S096000, C324S244100

Reexamination Certificate

active

06317250

ABSTRACT:

FIELD OF THE INVENTION
The present invention pertains to the field of fiber optics, more particularly, the present invention relates to optical isolators using multiple core fibers.
BACKGROUND OF THE INVENTION
The field of fiber optics is currently undergoing rapid growth. A good portion of this rapid growth is driven by the desire to provide larger bandwidth capability to communication systems. Many approaches have been utilized to increase the existing communication system's current infrastructure. Improvements in amplifiers, encoding and decoding techniques, as well as others, has had some success. Of technologies currently available, optical fibers hold great promise for increasing available bandwidth. Thus, optical components that are able to assist in attaining increased bandwidth are of interest.
One of the optical components that is of value is an optical isolator. By providing the ability to transfer light in essentially one direction only, the optical isolator may “shield” those components whose performance suffers from light traveling in a reverse direction. Devices such as optical amplifiers, lasers, and other components suffer performance degradation from light entering in a “reverse” direction.
One prior optical isolator provides single fiber optical isolation. However, such an approach also introduces polarization mode dispersion because of the differing optical paths. These differences in optical path length may be due to such factors as differences in refractive indices, and differences in physical paths. For example,
FIG. 1
illustrates an optical isolator
100
, in which differing optical paths for different polarizations introduces polarization mode dispersion. In this prior art, incoming light and exiting light are coaxial. Incoming light
104
has random polarization as illustrated by horizontal and vertical components
102
. The incoming light
104
upon entering a birefringent crystal
150
travels different paths depending upon polarization. Path
106
is the path for the horizontally polarized component of the incoming light
104
, while path
105
is the path for the vertically polarized component of the incoming light
104
. The horizontally polarized component of the incoming light
104
upon exiting the birefringent crystal
150
continues
108
traveling through
110
the Faraday rotator
160
, then
112
through
114
a half wave plate
170
, then
116
through
118
a second birefringent crystal
180
, and exiting
120
. The vertically polarized component of incoming light
104
upon exiting the birefringent crystal
150
continues
107
traveling through
109
the Faraday rotator
160
, then
111
through
113
a half wave plate
170
, then
115
through
117
a second birefringent crystal
180
, and exiting
120
.
The optical path length for the horizontally polarized component of the incoming light
104
, in this example, is shorter than the optical path length for the vertically polarized component of the incoming light
104
. It is this difference that contributes to the polarization mode dispersion. That is, incoming light
104
may have vertical and horizontal polarization components that are coincident with respect to each other upon entering the isolator
100
, however upon exiting the isolator
100
, the horizontally polarized component of the incoming light
104
, in this example, travels a shorter distance than the vertically polarized component of the incoming light
104
and so the horizontally polarized component of the incoming light
104
will exit the optical isolator
100
before the vertically polarized component of the incoming light
104
with which it was initially coincident. Because of this spreading, signals must be spaced further apart in order to resolve them. This results in less than optimum information capacity.
Another prior single fiber optical isolator solution concentrates on lowering polarization mode dispersion. Yet, other optical isolators use components that try to address the assembly of thermally expanded core fibers via the use of V-groove techniques.
FIG. 2
illustrates a V-groove assembly
200
in which individual fibers
204
,
206
,
208
, and
210
are positioned within V-shaped grooves
214
,
216
,
218
and
220
respectively that are fabricated on a substrate
202
. V-groove assemblies require steps to place and secure the individual fibers within the V-grooves. Additionally the pitch between the fibers is currently in the 250 &mgr;m range. The alignment of an input V-groove assembly with other optical components and then with an output V-groove assembly presents challenges.
The prior art discloses single fiber optical isolators that may suffer from the introduction of polarization mode dispersion and multiple core assemblies that may suffer from assembly difficulties.
SUMMARY OF THE INVENTION
An apparatus for optically isolating multiple core optical fibers is disclosed. Two multiple core fibers are coupled to an optical isolator.
Other features of the present invention will be apparent from the accompanying drawings and from the detailed description that follows.


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patent: 5982539 (1999-11-01), Shirasaki
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