Optical waveguides – Accessories – Attenuator
Reexamination Certificate
2001-01-17
2003-04-22
Kim, Robert H. (Department: 2882)
Optical waveguides
Accessories
Attenuator
C359S577000, C359S888000, C359S578000, C359S588000, C359S589000
Reexamination Certificate
active
06553175
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to optical fiber attenuators, and more particularly to a variable optical attenuator.
BACKGROUND OF THE INVENTION
In optical systems, certain optical signals often need to be attenuated. As such, optical systems often include optical attenuators. A particular type of attenuator is a variable optical attenuator, which can vary the amount of attenuation. Such attenuators have a variety of potential uses in optical systems. For example, variable optical attenuators can be used to compensate for variable input strengths to achieve a constant output strength, or to compensate for variable path length attenuation to produce equal strength signals for signals that travel different paths. Alternatively, variable optical attenuators can be used to compensate for variable input strengths to achieve desired but differing lower signal strengths.
Some objectives in the field of variable optical attenuators are to provide such attenuators in a manner that is both cost effective and highly reliable. One prior solution, for example, is illustrated in
FIGS. 1A
,
1
B and
1
C. A variable optical attenuator
10
is provided with a housing
12
that supports a motor
14
. A drive shaft
16
extends from the motor
14
passes through, and mounts together with, a device
18
for converting the rotational motion to linear motion, (e.g., rack & pinion, threaded screw & nut, worm gear, cam, and the like). A rectangular shaped filter
22
mounts on one end of the device
18
. An input optical fiber
24
enters the housing
12
and terminates with an input collimator
26
. Also provided is an output collimator
28
, which is in optical communication with output optical fiber
30
. The output optical fiber
30
exits the housing
12
at a second end, thus transmitting any light signals out of the attenuator
10
. In addition, a potentiometer
32
mounts, for example, at a distal end of the drive shaft
16
extending from the motor
14
. The potentiometer
32
indicates a rotational position of the drive shaft
16
.
The rectangular filter
22
is illustrated in FIG.
1
B. The rectangular filter
22
is a neutral density filter with a linearly increasing gradient. As a light signal travels through input optical fiber
24
and input collimator
26
the light signal passes through rectangular filter
22
before entering output collimator
28
and output optical fiber
30
. The motor
14
activates the device
18
for converting rotational motion to linear motion and linearly slides the rectangular filter
22
to a desired attenuation position. This form of optical attenuator
10
has a significant number of moving parts. The device
18
, depending on its particular configuration, can experience an amount of backlash or play, which makes specific placement of the rectangular filter
22
and the subsequent attenuation level more difficult to achieve. There is also a concern that the backlash or play can be affected by vibrations from surrounding machinery, which might ultimately cause creep and a subsequent unintentional change in attenuation level.
FIG. 1C
illustrates a graphical representation of a level of attenuation versus amount of linear motion on the part of the rectangular filter
22
. As can be seen, this relationship is substantially linear.
A second conventional solution to variable optical attenuation, for example, is illustrated in
FIGS. 1D
,
1
E, and
1
F. As shown, an optical attenuator
34
has a housing
36
that supports a motor
38
. The motor
38
has a drive shaft
40
extending therefrom. A circular filter
42
mounts on the drive shaft
40
of the motor
38
such that the drive shaft
40
passes through a center point of the circular filter
42
. An input optical fiber
44
enters the housing
36
at one end and mounts to input collimator
46
. In addition, an output collimator
48
is in optical communication with an output optical fiber
50
. The output optical fiber
50
extends out a second end of the housing
36
. Once again, a potentiometer
52
is provided at a distal end of the drive shaft
40
to indicate the rotational position of the drive shaft
40
and the circular filter
42
.
In this version of variable optical attenuator
34
, input optical fiber
44
provides a light signal to input collimator
46
. The light signal passes through circular filter
42
and enters output collimator
48
to subsequently exit the housing
36
through the output optical fiber
50
.
The attenuation level in this version of attenuator
34
adjusts as follows. The motor
38
activates to rotate the drive shaft
40
and subsequently the circular filter
42
. As the circular filter
42
rotates, the various levels of attenuation pass in front of the light signal as it exits from input collimator
46
and enters the output collimator
48
and subsequently, the output optical fiber
50
.
As illustrated in
FIG. 1E
, the circular filter
42
is a neutral density filter. The filter
42
has circularly varying attenuation levels along radians of the circle structure. The relationship of attenuation level to rotation of the circular filter
42
is illustrated in FIG.
1
F. As can be seen, this relationship is also substantially linear. One concern in this type of optical attenuator
34
is that there exists a significant relative cost of forming the circularly varying attenuation levels of circular filter
42
, in a predictable, monotonically increasing, fashion.
SUMMARY OF THE INVENTION
For the foregoing reasons, there exists in the art a need for a variable optical attenuator that is both cost efficient to manufacture and mechanically stable and reliable. The present invention is directed toward further solutions in this art.
In accordance with example embodiments of the present invention, a variable optical attenuator is provided having a housing. A motor mounts within the housing, and a drive shaft extends from the motor. A filter is mounted on the drive shaft of the motor such that the drive shaft passes through a substantially center point of the filter. The filter has a filter gradient that begins at a lower optical density (appears more clear) first edge of the filter and gradually increases in optical density (appears more opaque) toward a second edge of the filter, the second edge being diametrically opposed from the first edge. The filter gradient can be linear, substantially linear, monotonically increasing, and the like. An input optical fiber provides a light signal to be attenuated. The input optical fiber introduces the light signal, which passes through a first collimator, through the filter, through a second collimator, and to an output optical fiber which exits the housing. When activated, the motor rotates the drive shaft to position the filter to a desired attenuation position for attenuating the light signal.
In one aspect of the present invention, the filter element is a neutral density filter, and is substantially circular in shape. In still another aspect of the present invention, the filter element has a linear filter gradient, which gradually increases in optical density from a first edge of the filter to a second, diametrically opposed, edge of the filter.
In still another aspect of the present invention, the housing is sealed to prevent unwanted and undesired light from entering the housing.
In yet another aspect of the present invention, a potentiometer is provided within the housing. The potentiometer is in communication with the drive shaft to aid in determining the rotational position of the drive shaft.
In still another aspect of the present invention, a surface of the filter has placed thereupon, an entirely reflective coating to prevent stray light from interfering with the light signal. In yet another aspect of the present invention, the input optical fiber and collimator, and the output optical and collimator, are angled with respect to each other such that a reflection from the filter element of the light signal is not received in either of the input or output optical fibers or collimators.
REFERENCES:
patent: 4
Kim Robert H.
Lahive & Cockfield LLP
Sycamore Networks, Inc.
Wang George
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