Optical: systems and elements – Optical amplifier – Correction of deleterious effects
Reexamination Certificate
2002-02-21
2003-07-29
Hellner, Mark (Department: 3663)
Optical: systems and elements
Optical amplifier
Correction of deleterious effects
C359S337130, C359S199200
Reexamination Certificate
active
06600594
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to optical transmission systems and more particularly to variable optical attenuators (VOAs) within optical transmission systems. Even more particularly this invention relates to circuits and methods for automatically adjusting variable optical attenuators and to methods and systems for calibrating variable optical attenuators to allow for the automatic adjustment of the variable optical attenuators.
2. Description of Related Art
Variable optical attenuators (VOA) are well known in the art and permit the attenuation of optical or light signals as they are transferred in an optical transmission system. Variable optical attenuators are of two fundamental types, mechanical and non-mechanical. The mechanical variable optical attenuators have moving parts such as stepper motors to adjust an optical filter to vary the attenuation. In non-mechanical variable optical attenuators, the mechanism employed to adjust the attenuation is either a magneto-optic effect or thermo-optic effect that modifies the light waveguide. The attenuation settings of a non-mechanical variable optical attenuator are generally wavelength dependent. Mechanical variable optical attenuators on the other hand provide adjust the optical attenuation in a manner that provides relative independence of wavelength.
Mechanical variable optical attenuators such as described in U.S. Pat. No. 6,149,278 (Mao, et al.) have a pair of substantially parallel mirrors that attenuate an optical signal based, at least in part, on the rotation angle of the mirrors. When the pair or mirrors is in a predetermined position, an input optical signal is directed from an input port to an output port with a minimum insertion loss. As the pair of mirrors is rotated, the optical signal is shifted in a parallel fashion. This provides increased insertion loss and an attenuated signal at the output port. The pair of mirrors are rotated a stepper motor or similarly controlled mechanism.
An alternate mechanical variable optical attenuator is described in U.S. Pat. No. 4,398,806 (Bennett, et al.). Bennett et al. describes a variable optical attenuator that has wedge shaped plates that are adjusted for form Fresnel lens structures. Each of plates has two surfaces defined by an angle of convergence, a pair plates are supported with two of the surfaces of each plate being spaced apart and in parallel alignment and with the angle of convergence of the two plates being in opposite directions. A second pair of plates are supported with two of the surfaces of each plate being spaced apart and in parallel alignment and with the angle of convergence the plates. One plate of each pair of plates is adjusted to modify the attenuation of the variable optical attenuator.
As the demand for communication networks has increased, wavelength division multiplexing (WDM) is becoming the technique used for increasing the amount of information that can be carried on-fiberoptic cables. Variable optical attenuators are employed within the network to allow the equalization of the gain of the bands of light frequencies transmitted on the fiberoptic cables. Further, the variable optical attenuators allow the addition and removal of selected bands or channels at various terminal points of the communication network.
Refer now to
FIG. 1
for an overview of an application of a variable optical attenuator.
FIG. 1
illustrates an amplification and balancing device for a fiberoptic communication channel. The light
10
from a fiberoptic cable in a wavelength division multiplexed communication system is composed of multiple wavelengths &lgr;
1
, &lgr;
2
, &lgr;
3
, . . . , &lgr;
n
. Prior to equalization and balancing each of the wavelengths &lgr;
1
, &lgr;
2
, &lgr;
3
, . . . , &lgr;
n
have non-equal amplitudes or gains. For proper operation these amplitudes or gains must be equal or balanced.
The light
10
from a fiberoptic cable is the input to an optical demultiplexer
15
. The optical demultiplexer
15
separates the wavelengths &lgr;
1
, &lgr;
2
, &lgr;
3
, . . . , &lgr;
n
of the multiplexed light signal
10
into the individual light signals
20
a
,
20
b
, . . . ,
20
n
. The individual light signals
20
a
,
20
b
, . . . ,
20
n
are each applied respectively to variable optical attenuators
25
a
,
25
b
, . . . ,
25
n
. The outputs of the variable optical attenuators
25
a
,
25
b
, . . . ,
25
n
are then the inputs to the multiplexer
30
. The individual light signals
20
a
,
20
b
, . . . ,
20
n
are then recombined to form the input light signal input to the erbium-doped fiber amplifier (EDFA)
35
. The erbium-doped fiber amplifier
35
amplifies the light signal to form the output light signal
40
that is transferred to a subsequent fiberoptic cable.
The variable optical attenuators
25
a
,
25
b
, . . . ,
25
n
are each calibrated to adjust the gain of the wavelengths &lgr;
1
, &lgr;
2
, &lgr;
3
, . . . , &lgr;
n
of the individual light signals
20
a
,
20
b
, . . . ,
20
n
such that outputs of the variable optical attenuators
25
a
,
25
b
, . . . ,
25
n
are approximately equal. The recombined and amplified light signal
40
now has wavelengths &lgr;
1
, &lgr;
2
, &lgr;
3
, . . . , &lgr;
n
that have equal gain and are balanced.
An alternate application for variable optical attenuators is shown in FIG.
2
. This application illustrates a switching application when separate wavelength channels within different light signals
110
,
125
,
130
, and
175
are added and removed for redirection to receiving and transmitting nodes (not shown) of the communication network. Generally the light signals
110
and
130
are demultiplexed to their individual wavelength channels. Those individual wavelength channels that are to be removed from the light signals
110
and
130
are separated and transferred to the receiving nodes. The individual wavelength channels that are to be added are combined with the remaining wavelength channels to form the light signals
125
and
175
. In order for the removed wavelength channels and the newly formed light signals to have appropriate balance and gain across all the wavelength channels, a variable optical attenuator is added to each channel to perform the attenuation to equalize the gain of each channel.
Referring now to
FIG. 2
for a more detailed discussion. The light signals
110
and
130
are respectively the inputs to the demultiplexers
115
and
135
. The demultiplexers
115
and
135
decompose the light signals
115
and
135
-into their component wavelength channels. Those wavelength channels
116
that are to be transferred to the light signal
125
become a first set of inputs to the multiplexer
120
. Those wavelength channels
117
that are to be removed from the decomposed light signal
110
are transferred to the set of variable optical attenuators
150
. Similarly, those wavelength channels
136
that are to be transferred to the light signal
175
are transferred to the multiplexer
170
and those wavelength channels
137
that are to be removed from the decomposed light signal
130
are the inputs to the set of variable optical attenuators
150
.
The variable optical attenuators
150
attenuate the wavelength channels
117
to balance and equalize the light signals to form the wavelength channels
119
. The wavelength channels
119
are the inputs to the demultiplexer
140
, which decomposes the wavelength channels into the individual light signals
142
that are transferred to the receiving nodes of the communication system. Similarly, the variable optical attenuators
150
attenuate the wavelength channels
137
to balance and equalize the light signals to form the wavelength channels
139
. The wavelength channels
139
are the inputs to the demultiplexer
160
, which decomposes the wavelength channels into the individual light signals
162
that are transferred to other receiving nodes of the communication system.
To add wavelength channels to the light signals
125
, and
175
the multiplexers
145
and
155
from the tran
Ko Jimmy
Tseng Kevin
Ackerman Stephen B.
Hellner Mark
Lightech Fiberoptics Inc.
Saile George O.
LandOfFree
Intelligent variable optical attenuator with controller and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Intelligent variable optical attenuator with controller and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Intelligent variable optical attenuator with controller and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3019152