Note: Descriptions are shown in the official language in which they were submitted.
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APPARATUS AND METHOD FOR CONTROLLED HEATING AND
DEFORMING OF AN OPTIC FIBER
RELATED APPLICATIONS
This application claims priority from U.S.
provisional application 60/040,875, filed on March 21,
1997, incorporated herein by reference. This application
is a continuation-in-part application of U.S. application
serial number 08/718,727, filed on September 24, 1996,
incorporated herein by reference.
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to an apparatus and
method for controlled heating and deforming of an optical
device, such as a waveguide or an optical fiber, and more
particularly, to an apparatus and method to accurately
and reliably control and monitor the formation of an
optical device, such as an optical fiber biconical taper.
Backqround of the Related Art
Currently, various techniques for stretching,
shaping or fusing optical fibers have been performed.
For example, one technique involves heating the optical
fiber(s) at constant temperature and pulling at a
constant rate in an attempt to achieve desired optical
properties in the optical fiber or device. Due to the
inherent uncertainties in this process, this technique
necessitates various estimates or guesses when the
heating and pulling should be stopped to achieve the
desired properties.
Accordingly, the resulting processed optical
fiber(s) or device often times does not meet with the
predetermined optical requirements. Thus, this process
does not provide good yield results. Further, this crude
process limits the types of optical devices that can be
produced.
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It is therefore desirable to provide accurate and
consistent production of high quality fiber optic
devices. It is also desirable to provlde better device
production techniques for a passive fiber optic component
manufacturer.
It is further desirable to provide accurate and
consistent production of high quality fiber devices,
including, for example, an optical fiber biconical taper.
SUMMARY OF THE INVENTION
A feature and advantage of the invention is in
providing accurate and consistent production of high
quality fiber optic devices.
Another feature and advantage of the invention is
that its principal use is, for example, in device
production for a passive fiber optic component
manufacturer.
Another feature and advantage of the invention is in
providing accurate and consistent production of high
quality fiber devices, including, for example, an optical
fiber biconical taper.
The present invention is based, in part, on the
realization or identification of the problem that during
standard coupler production, the monitored optical
properties, such as coupling ratio, do not accurately
correspond to the actual post-production optical
properties. This requires that a guess, which must take
into account many small variations in production
conditions, be made as to the monitored optical
properties at which to terminate production of the
coupler. This guess creates tremendous uncertainties in
the process, thereby lowering the yield of the formation
process for fiber optic devices.
Advantageously, I have discovered that the heating
temperature and rate of stretch of the optical fiber are
main variables that may be beneficially used to achieve
accurate formation of optical devices. Further, I have
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discovered that the optical properties, such as the
coupling ratio, may be beneficially monitored to drive or
control the formation or formation conditions of the
optical device, such as the heating temperature and/or
the rate of stretch of the optical fiber(s).
In accordance with one embodiment of the invention,
a new method of forming a fiber optic device having
optical properties is provided. The method includes the
sequential, substantially simultaneous or sequence
independent steps of applying energy to heat at least one
region of at least one optical fiber or optical fiber
~evice using at least one energy source positioned a
predetermined distance therefrom, resulting in the
deformation of the heated at least one optical fiber or
optical fiber device, and monitoring at least one of the
optical properties of the at least one optical fiber or
optical fiber device. The method also includes the steps
of controlling at least one of the energy and the shaping
or deforming, responsive to the monitoring step prior to
completion of the method, and producing the at least one
optical fiber or optical fiber device responsive to the
controlling step.
An optical fiber or optical fiber device is also
provided that is produced by the process.
These together with other ob~ects and advantages
which will be subsequently apparent, reside in the
details of construction and operation as more fully
herein described and claimed, with reference being had to
the accompanying drawings forming a part hereof wherein
like numerals refer to like elements throughout.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an example of an apparatus to produce
fused-biconical tapered couplers;
FIG. 2 is a diagram showing perspective, top and
side views of one example of a clamp used this process;
FIG. 3 is a fused biconical taper;
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FIG. 4 shows an example of a graph, displaying
percentage of optlcal coupling at a single wavelength
between two optical fibers as a function of both
stretching distance and stretching time, during the
standard production of a fused-biconical tapered (FBT)
coupler;
FIG. 5 shows an example of a graph, displaying
percentage of optical coupling at a single wavelength
between two optical fibers as a function of both
stretching distance and stretching time, during the
production of a FBT coupler; and
FIG. 6 is another example of a graph, displaying
percentage of optical coupling at a single wavelength
between two optical fibers as a function of both
stretching distance and stretching time, during the
production of a FBT coupler.
DES~RIPTION OF PREFERRED EMBODIMENT OF THE INVENTION
The present invention is used on, and provides
accurate and reliable production of, optical fibers and
fiber optic devices such as couplers, switches, wave-
division multiplexers (WDM), filters, attenuators,
polarizers, waveguides, and the like, that provide
substantially similar optical responses, properties
and/or indicators. These various fiber optic devices,
such as the WDM, may be constructed of different
materials such as glass, crystal, metal, plastic, ceramic
and the like.
One principal advantage of this method is that it
allows the accurate and consistent production of high
quality fiber optic devices. A principal use of this
method could be in device production, for example, for a
passive fiber optic component manufacturer.
To illustrate this method, I will conceptually
discuss the production of a single-wavelength FBT
coupler. The production of other fiber optic devices
would be similar (with the exception that some steps may
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be added and/or omitted based on the specific optical
device being formed), including production of single
optical fibers and/or devices.
FIG. 1 is an example of an apparatus to produce
fused-biconical tapered couplers. This apparatus may
also be used for production of single optical fibers
and/or devices. The apparatus 2 includes a pair of
moveable optical fiber holding stages 10, 12 with a
plurality of optical fiber clamps 100-114 attached to the
holding stages 10, 12. The optical fiber clamps 100-114
hold a pair of optical fibers 116, 118 in alignment
between the holding stages 10, 12.
The fused-biconical tapered coupler (described below
in connection with FIG. 2) is produced by heating and
fusing together a portion of the stripped section of the
optical fibers at area 120 between the holding stages 10,
12. The holding stages 10, 12 are selectively moved
apart when the optical fibers are sufficiently heated,
thereby stretching the optical fibers. This stretching
and heating process facilitates the fusion of the optical
fibers together, forming a fused region with generally a
biconical taper, for example, at area 120.
Alternative process steps to stretching may also be
used so long as the optical fiber or fiber optic device
is shaped or formed using such alternative process steps.
Thus, the present invention contemplates use of a process
step that is able to deform, form, shape, compress or
stretch the optical fiber or fiber optic device to alter
in the some manner the optical properties relating
thereto. Further, the present invention also
contemplates various different process steps that control
the rate of shaping the optical fiber or fiber optic
devlce.
The optical changes are monitored using standard
optical sources and detectors attached to the ends (e.g.,
116a, 116b, 118a, 118b) of the optical fibers 116, 118.
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Coupler production is terminated when desired optical
properties are achieved. Advantageously, I have
discovered that the heating temperature and rate of
stretch of the optical fibers 116, 118 are main variables
that may be beneficially used to achieve accurate
formation of optical devices.
The process described herein, beneficially uses the
monitored optical property(s) (in this case, the coupling
ratio) as a control variable(s) to selectively and
variably control the rate of stretching and heat applied
to the optical fibers. This process can, of course, also
be applied to other optical devices or single optical
fibers or devices as discussed above. The variable
heating of the optical device may be performed by
increasing/decreasing the heat, intensity, power, or
energy of the heat source, or by moving the heat source
closer/further to/from the optical device, at the same or
different regions.
Various types of heat sources can be used, such as
lasers, flames, furnaces, electric, and the like, or any
other device that can cause the optical fiber or device
to be heated. The variable stretching of the optical
device may be performed by increasing/decreasing the rate
or acceleration of pull by moving, for example, the
holding stages further/closer from/to each other. Other
techniques or devices for holding and/or stretching the
optical fiber or device may also be used.
While the above process describes that the heating,
stretching and fusing occur, in part, simultaneously, the
present invention also contemplates that the above steps
be performed sequentially, and/or independently. The
present invention is also based on my realization or
postulation that this process is sufficiently effective,
in part, when the optical fiber or device is heated
generally between its softening and anneal points (e.g.,
the anneal range), where variation in optical properties
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is more stable or less significant. Additionally, the
present invention is also based, in part, on my
realization or postulation that this process is
- sufficiently effective when the optical fiber or device
is formed or produced while or during a period of time
when the heat applied to the optical fiber or device is
reduced. Various ranges or values of heating may be
used, and/or various heating patterns may also be used.
FIG. 2 is a diagram showing perspective, top and
side views of one example of a clamp used in this
process. Of course, any standard clamping device may be
used. As shown in FIG. 2, the base 100 includes a slot
206 having a width corresponding to the diameter of a
bare optical fiber, and a depth corresponding to 1-1/2
times the diameter of an exposed optical fiber. Hence,
the slot 206 is adapted to accommodate two optical
fibers, where the second exposed optical fiber sits on
top of the first optical fiber and is seated halfway
within the slot 206. The first optical fiber inserted
into the slot 206 is secured by a firs-t vacuum region
generated by a first series of vacuum holes 208 located
at the base of the slot 206. The base 100 also includes
guiding surfaces 210 for guiding an optical fiber into
the slot 206. The guiding surfaces 210 also include a
second series of vacuum holes 212 for generating a second
vacuum region for securing the corresponding surface 210a
of the clamp cover 204a to the base 100.
Hence, an exposed optical fiber is secured in the
clamp 100 by placing the optical fiber within the
vicinity of the guiding surfaces 210. As the optical
fiber is lowered into position of the slot 206, the first
series of vacuum holes 208 generate a first vacuum region
that secures the first optical fiber within the slot 206.
A second optical fiber can then be added on top of the
first optical fiber within the slot 206. After the first
and second optical fibers have been inserted into the
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slot 206, the cover 204a is engaged with the base 100.
The cover 204a engages the base 100 using a support arm
204b fixed to the cover 204a. The cover 204a has a
groove 214 corresponding to the second optical fiber in
the slot 206, enabling the first and second optical
fibers to be secured within the clamp 100 upon engagement
of the cover 204a with the base 100. As recognized in
the art, the groove 214 may be substituted with an
extension (not shown) that extends into the slot 206 in
order to secure a single exposed optical fiber within the
primary clamp 100 upon engagement of the cover 204a with
the base 100. Hence, different covers 204a may be used,
depending on whether one or two optical fibers are to be
secured within the clamp 100.
Additional details regarding alternative clamping
devices may be found in U.S. Patent No. 5,395,101 to
Takimoto et al., the disclosure of which is incorporated
in its entirety herein by reference.
FIG. 3 is a fused biconical taper. The biconical
taper consists of a pair of tapered regions 122, 124 that
guide light between the optical fibers, and an optical
coupling region 126. The shape and thickness of the
biconical taper, such as the length and slope of the
tapered regions and the length and thickness of the
optical coupling region, determine the optical properties
of the biconical taper. The conditions under which the
biconical taper is produced, such as heating temperatures
and the rates/accelerations at which the biconical taper
is stretched, for example, determine the shape and
thickness of the biconical taper. Other variables are
also contemplated that may produce equivalent or
substantially similar reliable optical responses,
properties and/or indicators.
FIG. 4 shows an example of a graph, displaying
percentage of optical coupling at a single wavelength
between two optical fibers as a function of both
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stretching distance and stretching time, during the
standard production of a FBT coupler. The standard FBT
coupler is produced using a constant heating temperature
and a constant rate of stretching; hence, as shown on the
graph at area 128, coupling ratio is the same as a
~ function of either stretching distance or stretching
time. Line 127 represents the distance of stretch of the
optical fiber or device, and line 129 represents the time
of stretching the optical fiber or device.
During standard coupler production, the monitored
coupling ratio does not accurately correspond to the
actual post-production coupling ratio. This requires
that a guess, which must take into account many small
variations in coupler production conditions, be made as
to the monitored coupling ratio at which to terminate
production of the coupler. This discrepancy, between the
monitored coupling ratio and the post-production coupling
ratio, is displayed on the graph as jump 130 in the
coupling ratio (shown on the graph between the dashed 50%
and 75% lines) as a function of stretching time. That
is, when the stretching and resulting stretching distance
or length of the optical device is stopped or fixed, the
optical properties continue to change in an undetermined,
uncontrolled, and/or uncontrollable manner.
FIG. 5 shows an example of a graph, displaying
percentage of optical coupling at a single wavelength
between two optical fibers as a function of both
stretching distance and stretching time, during the
production of a FBT coupler using my new method. My new
method, after fusing the optical fibers, varies the
heating temperature and the rate of stretching to produce
the FBT coupler; hence, as shown on the graph, the
coupling ratio differs as a function of stretching
distance and stretching time. During coupler production
using my new method, the monitored coupling ratio does
substantially and/or accurately correspond to the actual
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post-production coupling ratio, making my new method
insensitive to production conditions.
My new method, in response to monitored optical
properties, optionally slowly and proportionally
decreases both heating temperature and rate of
stretching, which decreases the rate of change of the
coupling ratio shown at line 134 over time, in comparison
with the standard production illustrated at line 132 over
distance. Note that distance lines 127 (FIG. 4) and 132
can be substantially similar. My method also allows
coupler production to be terminated when, as shown on the
graph, the monitored coupling ratio converges on the
desired post-production value 136. Note that area 137 is
a conceptual representation of the jump that the process
described herein was able to avoid by providing the
appropriate control from a point substantially early on
in the stretching/heating process.
FIG. 6 is another example of a graph, displaying
percentage of optical coupling at a single wavelength
between two optical fibers as a function of both
stretching distance and stretching time, during the
production of a FBT coupler using my new method at line
138. This graph displays some of the control possible
using my new method. My new method, in response to
monitored optical properties, can slowly and
proportionally change both heating temperature and rate
of stretching, which varies the rate of change of the
coupling ratio, and allows complete and accurate control
of the coupler production process.
The many features and advantages of the invention
are apparent from the detailed specification, and thus,
it is intended by the appended claims to cover all such
features and advantages of the invention which fall
within the true spirit and scope of the invention.
Further, since numerous modifications and variations will
readily occur to those skilled in the art, it is not
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11
desired to limit the invention to the exact construction
and operation illustrated and described, and accordingly,
all suitable modifications and equivalents may be
resorted to, falling within the scope of the invention.
