Coherent light generators – Optical fiber laser
Reexamination Certificate
2002-08-20
2004-07-13
Dang, Hung X. (Department: 2873)
Coherent light generators
Optical fiber laser
C372S020000, C385S037000
Reexamination Certificate
active
06763043
ABSTRACT:
TECHNICAL FIELD
The present invention relates to dispersion compensators, and more particularly to a tunable dispersion compensator based on a Bragg grating that allows the dispersion characteristics of a Bragg grating element to be tuned.
BACKGROUND ART
Fiber Bragg gratings can be used as effective filter elements in a range of applications in optical communications networks. The dispersion characteristics of a communication link are crucial in determining performance and transmission fidelity. Gratings, particularly chirped gratings can be used effectively for dispersion compensation. The ability to tune the dispersion introduced by a grating element is important in providing an adjustable element for performance optimization.
As optical networks evolve, there is a trend towards the development of “all-optical” networks, in which communications signal are dynamically routed in the optical domain. One of the issues that affect the ability of network engineers to increase transmission distances & data rates is signal impairments. One of the important parameters of a link is the dispersion of the system, which can create a serious deleterious effect on the signal quality in a high-Gbit optical transmission systems such as 10 Gbits/s and 40 Gbits/s.
Chirped Bragg gratings can be used to compensate for dispersion in a communications link.
FIG. 1
depicts a known optical transmission system
10
. Optical data
12
, which is generated by a laser transmitter
14
, is transmitted along a fiber link
16
, that may or may not contain optical amplifiers and other devices (that may in themselves be dispersive) to a receiver
18
. During the transmission along the fiber link
16
, the optical data
12
will be corrupted to a certain degree by differential group delay experienced by different wavelength components of a given wavelength signal. This group delay “smears-out” the data
12
producing poor contrast in the received bit stream
20
at the receiver end. The differential group delay in a signal can be compensated for by the use of an appropriately chirped grating
22
. As shown, the light (or received bit stream)
20
from the fiber link
16
is coupled though a circulator
24
to a chirped grating
22
. The chirped grating
22
has a bandwidth B and length L. The chirping of the grating
22
results in a strong group delay that can be chosen to be equal to, but opposite to that of the fiber link
16
. For example, for a grating length of 10 cm, the differential group delay for a wavelength component reflected from the front of the grating compared to one reflected from the rear of the grating is ~1000 ps. If the grating has a bandwidth of 1 nm, then it's effective dispersion is 1000 ps
m. Currently, the grating
22
has to be designed to match a given dispersion induced group delay error in a communications link.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a tunable dispersion compensator having a Bragg grating that allows the dispersion characteristics of a Bragg grating element to be tuned.
In accordance with an embodiment of the present invention, an optical waveguide includes an outer cladding disposed about an inner core. A portion of the cladding of the waveguide includes a tapered region. The cladding has a minimum cross-sectional dimension of 0.3 mm. A chirped grating is written in the inner core of the tapered region of the cladding.
In accordance with another embodiment of the present invention, a tunable dispersion compensator includes an optical waveguide having an outer cladding disposed about an inner core. A portion of the cladding has a tapered region. The cladding has a minimum cross-sectional dimension of 0.3 mm. A chirped grating is written in the inner core of the tapered region of the cladding.
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Bailey Timothy J.
Kersey Alan D.
Putnam Martin A.
CiDRA Corporation
Dang Hung X.
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