U.S. patent application number 10/422891 was filed with the patent office on 2003-11-13 for filament organizer with accessory positioner.
This patent application is currently assigned to 3M Innovative Properties Company. Invention is credited to Afflerbaugh, Martin G., Cronk, Bryon J., Howard, Patrick Charles, Wiegand, Gordon.
Application Number | 20030210884 10/422891 |
Document ID | / |
Family ID | 25248183 |
Filed Date | 2003-11-13 |
United States Patent
Application |
20030210884 |
Kind Code |
A1 |
Afflerbaugh, Martin G. ; et
al. |
November 13, 2003 |
Filament organizer with accessory positioner
Abstract
A filament organizer, for attaching an accessory to a section of
filament, comprises a frame including a plurality of filament
guides. The frame accommodates an accessory positioner adapted for
sliding engagement therewith. A pair of spools, attached to the
accessory positioner, has a section of filament extending from one
to the other so that the filament passes around the plurality of
filament guides of the frame to selectively position the section of
filament. The accessory positioner includes an accessory cradle
that moves from a retracted position to a proximate position. In
its retracted position the accessory cradle receives an accessory
to be placed in axial alignment with the section of filament. The
accessory cradle then moves into the proximate position to attach
the accessory to the filament section. Preferably, the filament is
an optical fiber that includes a refractive index grating, and the
accessory provides temperature compensation to stabilize the
wavelength and facilitate wavelength tuning of the grating.
Inventors: |
Afflerbaugh, Martin G.;
(Austin, TX) ; Cronk, Bryon J.; (Round Rock,
TX) ; Howard, Patrick Charles; (Austin, TX) ;
Wiegand, Gordon; (Austin, TX) |
Correspondence
Address: |
3M INNOVATIVE PROPERTIES COMPANY
PO BOX 33427
ST. PAUL
MN
55133-3427
US
|
Assignee: |
3M Innovative Properties
Company
|
Family ID: |
25248183 |
Appl. No.: |
10/422891 |
Filed: |
April 24, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10422891 |
Apr 24, 2003 |
|
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09827043 |
Apr 5, 2001 |
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6591054 |
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Current U.S.
Class: |
385/135 |
Current CPC
Class: |
G02B 6/3616 20130101;
G02B 6/0218 20130101; G02B 6/444 20130101; G02B 6/4457 20130101;
G02B 6/022 20130101 |
Class at
Publication: |
385/135 |
International
Class: |
G02B 006/00 |
Claims
What is claimed is:
1. A tuning apparatus for precise adjustment of the wavelength of a
refractive index grating, formed in a section of optical fiber,
said tuning apparatus comprising: a pair of spaced apart cantilever
arms having the section of optical fiber suspended therebetween; a
clamp immobilizing the section of optical fiber; a tuning blade to
apply force to at least one of said pair of cantilever arms; and an
actuator connected to said tuning blade, said actuator having a
controller for moving said tuning blade under a prescribed force
and distance causing displacement of said at least one of said pair
of cantilever arms to increase the separation between said pair of
cantilever arms, thereby changing the length of the section of
optical fiber to adjust the wavelength of a refractive index
grating formed therein.
2. The tuning apparatus of claim 1, wherein said pair of cantilever
arms are metal cantilever arms.
3. The tuning apparatus of claim 2, wherein said metal cantilever
arms are aluminum cantilever arms.
4. The tuning apparatus of claim 1, wherein said actuator includes
a voice coil mechanism that responds to signals from said
controller.
5. The tuning apparatus of claim 4, wherein said controller
includes a microprocessor.
6. A tuning apparatus for precise adjustment of the wavelength of a
refractive index grating, formed in a section of optical fiber
suspended by attachment between a pair of spaced-apart cantilever
arms each having connection by an end cap to a ceramic rod lying in
the accessory cradle of an accessory positioner, said tuning
apparatus comprising: an accessory positioner mount used for
orientation of an accessory positioner; an accessory clamp,
contacting an end cap to immobilize the ceramic rod in the
accessory cradle; a tuning blade inserted in a slot adjacent to the
accessory cradle to apply force to a said cantilever arm; and an
actuator connected to said tuning-blade, said actuator having a
controller for moving said blade under a prescribed force and
distance causing displacement of a said cantilever arm to increase
the separation between the pair of said cantilever arms, thereby
changing the length of said section of optical fiber to adjust the
wavelength of a refractive index grating formed therein.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. Ser. No.
09/827,043, filed Apr. 5, 2001 now allowed, the disclosure of which
is herein incorporated by reference.
FIELD OF THE INVENTION
[0002] The invention relates to an article used as a filament
storage device to facilitate filament positioning during
modification of a filament. More particularly the invention
provides a filament organizer including a detachable positioner for
conveniently handling an accessory to be attached to a filament,
especially an optical fiber to produce a functional optical device.
Such a device includes a temperature compensated optical fiber
Bragg grating that may be precisely tuned to a prescribed
wavelength using a tuning apparatus according to the present
invention.
BACKGROUND OF THE INVENTION
[0003] Technological advancements, particularly in
telecommunications, have caused a migration from systems and
devices based upon electronics to those that integrate electronics
with optics. These systems and related devices are known
collectively as optoelectronics. The movement of signals using
photons instead of electrons provides advantages of speed,
information-carrying capability, immunity from interference, lower
cost, and higher reliability.
[0004] Growth of optoelectronic systems occurs as phone companies
increasingly promote the use of fiber-optic cable and related
devices for developing ever-expanding telecommunications networks.
Success in telecommunications markets has produced a demand for
innovations in fiber-optic technology. Increasing demand for
products typically translates into a need to accelerate the output
rate and assembly of products and systems desired by consumers.
Acceleration of output rates depends upon efficiency in
manufacturing operations, usually through process automation.
[0005] Methods used currently for assembly and testing of
optoelectronic systems and devices are largely manual and time
consuming. This applies particularly to processes for introducing
special features such as periodic refractive index gratings into
optical fibers. Formation of a refractive index grating, or Bragg
grating, into an optical fiber requires a number of steps for
manually handling lengths of optical fiber during a series of
manufacturing operations.
[0006] A optical fiber Bragg grating provides a periodic variation
of refractive index within a length of an optical fiber. The
grating may be formed or written during exposure of a
photosensitive optical fiber to an appropriate pattern of
ultraviolet radiation. Applications for Bragg gratings exist in
telecommunications systems to control the wavelength of laser
light, to introduce dispersion compensation, for example. The
characteristics of Bragg gratings change with changes of strain and
temperature. A change in temperature will change the wavelength of
light transmitted via a Bragg grating, with undesirable
consequences. One solution to this problem is the use of a
temperature compensating structure attached to the portion of an
optical fiber containing the Bragg grating. This is usually
accomplished by clamping a Bragg grating containing optical fiber,
under tension, into a mechanical structure combining a low
expansion material with a high expansion material. This method of
passive temperature compensation is well known as a means for
improving wavelength stability of optical fiber Bragg gratings.
United States patent U.S. Pat. No. 5,042,898 discloses an apparatus
for temperature compensation of a fiber Bragg grating comprising
two juxtaposed compensating members with the required differences
in thermal expansion. The apparatus applies either tensile or
compressive stress to the grating. Other references addressing
temperature compensation of optical fiber Bragg gratings, using
fiber length variation, include United States patents U.S. Pat. No.
5,991,483, U.S. Pat. No. 6,101,301 and WIPO publication WO
98/59267. Japanese publication JP 9211348 describes the use of a
piezoelectric transducer to modulate the strain in a fiber in
response to electrical signals. Such devices are effective but
costly.
[0007] Temperature compensated optical fiber Bragg grating
packages, as previously discussed, are typically large, exhibiting
variation of reflection wavelength from one package to another. In
some cases, the design of temperature compensating structures is
complex requiring multiple points of connection to form a package
having a negative coefficient of thermal expansion. Some
temperature compensated packages include fine adjustment of the
grating wavelength but this may involve complicated procedures such
as the extension or compression of the total package as described
in WO 98/59267.
[0008] Regardless of the availability of solutions for compensating
the temperature drift of optical fiber Bragg gratings, little has
been revealed for automating processes either for forming Bragg
gratings or attaching structures or accessories to optical fibers
to perform a desired function such as temperature compensation.
With increasing demand for optoelectronic systems there is a need
to improve optical fiber handling to achieve more cost effective
production of large quantities of optical fiber devices.
SUMMARY OF THE INVENTION
[0009] The present invention satisfies the need for effective and
compact handling of filamentary materials during manufacturing
operations including process steps that include attaching
accessories to a filament and producing structural and related
changes in the filament. When applied to optical fibers, an
article, also described herein as a filament organizer, provides
compact containment of an optical fiber during the writing of an
optical fiber Bragg grating and further processing to provide a
temperature compensated optical fiber Bragg grating package.
Preferably the filament organizer includes a detachable accessory
positioner. The filament organizer allows relatively precise
positioning of at least a section of optical fiber to facilitate
attachment of accessories, such as thermal compensators, held
temporarily in an accessory cradle of an accessory positioner.
[0010] An accessory positioner, adapted for variable positioning in
a filament organizer, conveniently allows placement of an accessory
in the accessory cradle when there is a spaced relationship between
the accessory positioner and a filament, preferably an optical
fiber. Using suitable means to move the accessory positioner in the
filament organizer, an accessory may be moved towards a filament
with precise alignment of the two before joining them together.
Means to facilitate movement of an accessory positioner between
positions include sliding motion on e.g. racks, or tracks or
movement based upon the use of bearings, bars, hinges, cams and the
like.
[0011] A filament organizer according to the present invention may
be used to assemble filamentary devices, particularly devices
including optical fibers. An example of such use involves either
changing the inherent characteristics of an optical fiber or
incorporating an optical fiber into a functional assembly. The
inherent characteristics of an optical fiber change with adjustment
of its refractive index properties, as in the formation of a
variety of fiber Bragg gratings. Incorporation of an optical fiber
into a functional assembly provides useful devices such as
temperature compensated fiber Bragg gratings. Refractive index
changes and functional assembly production, according to the
present invention, use a filament organizer during the formation of
a temperature compensated optical fiber Bragg grating. Thereafter
an optical fiber Bragg grating may be precisely tuned using an
accessory positioner with a tuning jig according to the present
invention.
[0012] More particularly, the present invention provides a filament
organizer for attaching an accessory to a section of filament. The
filament organizer comprises a frame including a plurality of
guides. Also, the filament organizer includes an accessory
positioner adapted for sliding engagement with the frame between a
first position and a second position. The accessory positioner
includes a first spool and a second spool having a filament
extended between them to pass around the guides. This locates the
section of filament for attachment of an accessory. An accessory
cradle, included with the accessory positioner, receives an
accessory in the first position to transport it to the second
position from which the accessory is attached to the section of
filament.
[0013] An accessory positioner according to the present invention
preferably comprises a support having a forward edge and a first
surface opposite a second surface. The support further includes a
first hub having separation from a second hub. A first spool,
engaging the first hub, is mounted for rotation on the support. The
accessory positioner also includes a second spool, engaging the
second hub, mounted for rotation on the support. A separation
exists from the first spool to the second spool for suspension of a
section of filament between the two to locate the section of
filament before attaching an accessory to the filament. The
accessory positioner further has an accessory cradle to receive an
accessory to be attached to the section of filament.
[0014] A preferred embodiment of an accessory positioner may be
used for attaching an accessory to a section of a filament when the
accessory positioner is mounted in a substantially rectangular
frame that includes a plurality of forward guides and a plurality
of rear guides. In this case the accessory positioner moves in
sliding engagement with the frame. The movable accessory positioner
has a first surface opposite a second surface, a front edge and a
rear edge. A first spool occupies a position adjacent to the first
surface, between the front edge and the rear edge. A second spool
also lies adjacent to the first surface between the front edge and
the rear edge. The use of a filament restrictor transmits a force
to each of the first spool and the second spool to apply tension to
a filament extended therebetween. The filament passes around the
rear guides and the forward guides to locate a section of filament
between the forward guides. A movable accessory positioner also has
an accessory cradle at its front edge to move from a retracted
position to a proximate position relative to a filament. The
accessory cradle, in the retracted position receives a accessory
for placement in axial alignment with the section of filament when
the accessory cradle moves into the proximate position to attach
the accessory to the section of filament.
[0015] Accessory attachment according to the present invention
preferably uses an attachment fixture for arranging at least one
filament organizer for attaching an accessory to a filament. The
attachment fixture comprises a base plate that includes at least
one organizer slot and has a first end and a second end. A first
support is secured to the first end of the base plate and a second
support is secured to the second end of the base plate. At least
one rod extends between the first support and the second support so
that the rod contacts a filament organizer positioned in an
organizer slot.
[0016] A Bragg grating may be tested or optically proofed according
to the present invention using an optical proofing fixture for
arranging a plurality of accessory positioners for organizing
optical fiber pigtail ends to monitor light passing between the
pigtail ends. The optical proofing fixture comprises a first
faceplate, and a second faceplate. At least one support bar
connects the first faceplate to the second faceplate. Each of a
plurality of pigtail mounts, coupled between the first faceplate
and the second faceplate, includes a resilient grip having a grip
retention slit to releasably retain pigtail ends of an optical
fiber. The optical proofing fixture further includes a flange
connected between the first faceplate and the second faceplate.
[0017] The present invention includes a tuning apparatus for
precise adjustment of the wavelength of a refractive index grating,
formed in a section of optical fiber. The tuning apparatus
comprises a pair of spaced-apart cantilever arms having the section
of optical fiber suspended between them. A clamp immobilizes the
section of optical fiber to allow a tuning blade to apply force to
at least one of the pair of cantilever arms. An actuator connected
to the tuning blade has a controller for moving the tuning blade
under a prescribed force and distance causing displacement of the
cantilever arm. This increases the separation between the pair of
cantilever arms, thereby changing the length of the section of
optical fiber and adjusting the wavelength of a refractive index
grating formed in the optical fiber.
[0018] The present invention further includes a process for
attaching an accessory to a filament, preferably in the form of an
optical fiber. The process comprises the steps of providing a
filament held in a filament organizer. A filament organizer
comprises a frame including a plurality of guides and an accessory
positioner mounted on the frame for movement between a first
position and a second position. The accessory positioner includes a
first spool and a second spool having a filament extended between
them to pass around the guides to locate a section of filament for
attachment of an accessory. The accessory positioner further has an
accessory cradle to receive the accessory, in the first position,
for transportation of the accessory to the second position for
attachment to the section of filament. An accessory may be placed
in the accessory cradle when the accessory positioner is in the
first position. The accessory has a pair of spaced apart cantilever
arms, each including a contact point. Moving the accessory
positioner into the second position places the section of filament
adjacent to the accessory to contact the contact points for bonding
the accessory to the section of filament at each of the contact
points.
[0019] An attachment fixture may be used during attachment of the
filament to the accessory, at its contact points. The fixture
facilitates processing of a plurality of filament organizers at the
same time. An attachment fixture comprises a base plate including a
plurality of organizer slots and having a first end and a second
end. A first support is secured to the first end and a second
support is secured to the second end. The fixture includes at least
one rod extending between the first support and the second support
to contact each of the plurality of filament organizers positioned
in each of the plurality of organizer slots. A rod may be made of a
conducting material that acts as a heating element to assist with
elevated temperature bonding of a filament to contact points of the
accessory.
[0020] Definitions
[0021] The term "filament" as used herein refers to a threadlike
structure particularly an optical fiber and related optical
waveguides, including those having a refractive index grating or
Bragg grating formed therein.
[0022] The term "thermal compensator" means an accessory for
attachment to a filament, particularly an optical fiber that
includes a Bragg grating, to provide a temperature compensated
Bragg grating, which maintains a target wavelength independent of
temperature variation.
[0023] The term "filament organizer" refers to an article for
convenient containment and handling of extended lengths of
filament, particularly optical fiber, during processing. A filament
organizer according to the present invention includes a movable
mini-tray as an accessory positioner.
[0024] The term "accessory positioner" describes a movable,
detachable portion of a filament organizer. An accessory positioner
includes at least a pair of spaced-apart spools for holding a
filament and to allow access to a section of filament during
processing of a filament.
[0025] The term "tuning jig" refers to a device used for adjusting
a temperature compensated optical fiber Bragg grating to a target,
tuned wavelength.
[0026] The term "attachment fixture" is used to describe an
apparatus that may be used with one or more filament organizers to
facilitate attachment of an accessory to a filament.
[0027] The term "proofing" applies to a filament in the form of an
optical fiber containing a Bragg grating and means the process of
monitoring optical properties during thermal cycling to confirm
attainment of target values of e.g. optical fiber Bragg grating
wavelength response within a prescribed temperature range.
[0028] The term "proofing fixture" refers to an apparatus that may
be used with one or more accessory positioners during proofing and
related evaluation of the properties of one or more optical fiber
Bragg gratings.
[0029] The term "tensioner" or "filament restrictor" describes a
device or structure used with a filament containment assembly, e.g.
a pair of spools, to restrain a filament so that it does not become
slack.
[0030] The term "fiber tensioning" refers to the process of
attaching a weight or applying tension to a section of filament to
place the filament under strain. Fiber tensioning of an optical
fiber precedes fiber-modifying operations such as the writing of a
Bragg grating in the fiber and attachment of a thermal compensator
to the optical fiber.
[0031] The term "coupled" indicates the existence of intervening
parts in an attachment structure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] Notwithstanding any other forms which may fall within the
scope of the present invention, preferred forms of the invention
will now be described, by way of example only, with reference to
the accompanying drawings in which:
[0033] FIG. 1 provides a perspective view of an accessory
positioner according to the present invention.
[0034] FIG. 2 shows a perspective view of a filament organizer
according to the present invention including a positioner located
at a first position.
[0035] FIG. 3 shows a perspective view similar to that of FIG. 2
except for the locating of a positioner in a second position
relative to a filament organizer according to the present
invention.
[0036] FIG. 4 is a perspective view of an accessory, described
herein as a thermal compensator, for stabilizing an optical fiber
Bragg grating over a range of temperatures.
[0037] FIG. 5 is a perspective view showing a plurality of filament
organizers positioned in an accessory attachment fixture to
facilitate attachment of an accessory to a section of a
filament.
[0038] FIG. 6 provides a cross sectional view of an assembled
optical fiber Bragg grating showing an optical fiber attached to a
thermal compensator.
[0039] FIG. 7 provides a perspective view showing a plurality of
accessory positioners in an optical proofing fixture according to
the present invention.
[0040] FIG. 8 shows a perspective view of an optical proofing
fixture.
[0041] FIG. 9 is a perspective view of a tuning fixture for an
optical fiber Bragg grating.
[0042] FIG. 10 provides a perspective view showing a portion of an
accessory positioner engaged with operative parts of a tuning jig
for an optical fiber Bragg grating package according to the present
invention.
DESCRIPTION OF THE PREFERRED AND OTHER EMBODIMENTS
[0043] A filament organizer according to the present invention
provides a means for attaching an accessory to a filament. In its
preferred embodiment the filament organizer facilitates precise,
reproducible assembly of tunable, temperature-compensated fiber
Bragg grating packages.
[0044] Referring now to the Figures wherein like numerals refer to
like parts throughout the several views, FIG. 1 shows an accessory
positioner 10 that includes an accessory cradle 12 connecting a
first plate 14 to a second plate 16. The first plate 14 has a first
axle 18 and the second plate 16 has a second axle 20 connected at a
surface of each of the first plate 14 and the second plate 16. The
first axle 18 engages a first hub 22 of a first spool 26 and the
second axle 20 engages a second hub 24 of a second spool 28. The
spools 26, 28 act as storage devices for a length of filament (not
shown) extending between them 26, 28. Each hub 22, 24 of the first
spool 22 and the second spool 24 has a diameter slightly less than
the diameter of each of the first axle 18 and the second axle 20 to
provide a friction fit between each axle 18, 20 and hub 22, 24.
Friction between these parts restricts rotational movement between
an axle 18,20 and a hub 22, 24. A filament wound between the first
26 and second 28 spools exists under slight tension due to
frictional forces that restrict rotation of a spool 26, 28 about an
axle 18, 20. Without further modification of the accessory
positioner 10, a filament will pass over the accessory cradle 12 so
that there is alignment of the filament axis to the longitudinal
axis of the accessory cradle 12. With this alignment, a filament
will also extend along the length of an accessory 56 placed in the
accessory cradle 12.
[0045] As an alternative to the separated first 14 and second 16
plates shown in FIG. 1 the accessory cradle 12 could be attached to
a single plate having axles on its surface to engage the hubs of
spools, as described above. In this case, Other aspects of an
accessory positioner 10 for filament storage and the use of
frictional restriction to apply tension to a filament would remain
as before.
[0046] FIG. 2 shows an accessory positioner 10 mounted between
opposing ends 36, 38 of a frame 34 that is held together by a
connecting structure 40 between the opposing ends 36, 38. The frame
34, has a plurality of guides including a first 42, and a second 44
forward guide, and a first 46 and a second 48 rear guide for
threading a filament 30 from the first spool 26 to the second spool
28, when the accessory positioner 10 is mounted on the frame 34.
Each of the opposing ends 36, 38 of the frame 34 includes a
filament clamp 50, 52 for isolating a section of a filament 30
between the filament clamps 50, 52. At least one of the opposing
ends 36, 38 includes a notch 54 that the filament 30 traverses
between a forward guide 42, 44 and a filament clamp 50, 52. The
notch 54 provides access to a filament 30 to allow application of
weighted tension that produces a selected force acting on the
section of filament 30 between the forward guides 42, 44.
[0047] The configuration illustrated in FIG. 2 provides a filament
organizer 32 in which there is separation between the accessory
cradle 12 and the filament 30. This places the accessory positioner
10 in its retracted position allowing an accessory 56 to be placed
in the accessory cradle 12. The method of mounting the accessory
positioner 10 in the frame 34 provides movement between them so
that the position of the accessory positioner 10 is adjustable
inside the frame 34. Any one of a number of known methods may be
used to provide movement between an accessory positioner 10 and a
frame 34 of a filament organizer 32 according to the present
invention. Such methods include the use of a T-slot, V-slot,
dovetail, ball and groove configuration, linear ball slide, rack
and pinion system, three or four bar linkage, cams, hinges, or
pneumatic or mechanical actuators (for automated use). FIG. 2 shows
a preferred method of mounting an accessory positioner 10 on a
frame 34. In this case, the connecting structure 40 joins the frame
end plates 36, 38 together using connecting studs 57 on the
connecting structure 40 movably retained in grooves 59 formed in
each end plate 36, 38. The connecting structure 40 has movement
forwards or rearwards that is limited by the positioning of the
studs 57 in each groove 59. As indicated in the previous
description, the connecting structure 40 may move to a variety of
positions limited only by the length of the grooves 59 and the
position of studs 57 located within each groove 59. Movement of the
connecting structure 40 imparts movement to an accessory positioner
10 detachably mounted on the connecting structure 40. Detachable
mounting of an accessory positioner 10 to a connecting structure 40
may use any of a number of attachment components including screws,
nut and bolt combinations and related mechanical fasteners.
[0048] Comparison of FIG. 3 with FIG. 2 shows the change between
optional locations of an accessory positioner 10 mounted on a
connecting structure 40. An accessory 56 inserted in the accessory
cradle 12 of an accessory positioner 10, in its retracted position,
may be moved into a proximate position near to the section of
filament 30, as shown in FIG. 3. During movement of the accessory
positioner 10 the rear guides 46, 48 act against the frictional
forces between the axles 18, 20 and hubs 22, 24, causing the spools
26, 28 to rotate. This releases filament 30 from each spool 26, 28
thereby allowing the accessory positioner 10 to move from the
retracted position to the proximate position. In this way, there is
an increase in the length of a filament 30 between a spool 26, 28
and a rear guide 46, 48, while the section of filament 30, between
the filament clamps 50, 52 remains unchanged. From the proximate
position of an accessory positioner 10, an accessory 56 may become
attached to the approximate center of the section of filament 30.
After attachment of an accessory 56 to the section of filament 30
the accessory positioner 10 may be removed to the retracted
position. A biasing means such as a spring or cam may be used to
rotate the spools 26, 28 to readjust the filament 30 between the
spools 26, 28 and the rear guides 46, 48 to their shorter
lengths.
[0049] A preferred filament 30 is an optical fiber that includes a
Bragg grating to provide an optical signal within a prescribed
wavelength envelope. Variation of temperature is known to cause
wavelength drift of an optical fiber Bragg grating. This may be
overcome using an accessory 56 for an optical fiber Bragg grating
that compensates for temperature variation. Such an accessory 56 is
referred to herein as a thermal compensator.
[0050] FIG. 4 shows an accessory 56 in the form of a thermal
compensator including a cylindrical ceramic rod 60, preferably a
quartz rod, that allows a first end cap 62, and a second end cap 64
to slide to selected positions along its length. Any of a variety
of securing means may be used to retain the end caps 62, 64 in the
selected positions at opposing ends of the ceramic rod 60. Suitable
securing means include mechanical bonding, or bonding using
adhesives, low melting glasses, and metal solders. The length of a
thermal compensator is about 10 cm. or less which is also the
length of the rod 60.
[0051] It is known that effective thermal compensation of optical
fiber Bragg gratings depends on constructing a thermal compensator
that balances the thermal expansion characteristics of materials
used for its construction. Typically, the balance is established
according to precise dimensional and positional relationships
between materials having a low coefficient of thermal expansion
(CTE) and materials having a high CTE. During temperature variation
the length and strain characteristics of a temperature-compensated
optical fiber Bragg grating will stay essentially unchanged,
provided that the thermal compensator components have the correct
dimensions and positional relationships.
[0052] Using a filament organizer, as illustrated in FIG. 2 and
FIG. 3 it will readily be appreciated how a thermal compensator,
placed in an accessory cradle 12, may be moved from the retracted
position to the proximate position of the accessory positioner 10.
Adjustment of the proximate position of the accessory positioner 10
in a filament organizer 32 according to the present invention
brings a thermal compensator into precise alignment and contact
with an optical fiber, i.e. the filament 30. Alignment of an
accessory 56, such as a thermal compensator, to an optical fiber
precedes the actual attachment of a thermal compensator to an
optical fiber 30. Attachment of an optical fiber 30 to a thermal
compensator uses a first cantilever 68 extending from the first end
cap 62 and a second cantilever 70 extending from the second end cap
64. A first contact point 72 on the first cantilever 68 and a
second contact point 74 on the second cantilever 70 provide points
on the thermal compensator to which a fiber 30 under tension,
between first 50 and second 52 filament clamps may be firmly
attached (see FIG. 6). A number of available means for firmly
attaching an optical fiber 30 to the cantilevers 68, 70 includes
mechanical bonding or bonding using epoxy adhesives, low melting
glasses, metal solders and the like.
[0053] The process for attaching an optical fiber 30 to a thermal
compensator benefits from the precise alignment of a section of an
optical fiber 30 with a thermal compensator, using an accessory
positioner 10 according to the present invention. After
establishing correct alignment, the section of optical fiber 30
between the filament clamps 50, 52 requires the application of a
prescribed tension. The desired load may be applied to the section
of optical fiber 30 by weighting the optical fiber 30 in the notch
54 of the accessory positioner 10. A free weight or related fiber
tensioning device, e.g. a force or chatillon gauge, may be used to
place a desired load on the optical fiber 30. Preferably a section
of fiber 30, between filament clamps 50,52, exists under a positive
load. The applied load may be in a range from about 1 g to about 50
g, preferably from about 5 g to about 20 g.
[0054] A temperature compensated optical fiber package requires
attachment of an optical fiber 30 to a thermal compensator during
the application of the prescribed load to the section of optical
fiber 30 between the filament clamps 50, 52. In a preferred
process, optical fiber 30 attachment requires heating of the
thermal compensator and the optical fiber 30 to a temperature
sufficiently high to cure a quantity of adhesive applied to the
optical fiber 30 and the cantilevers 68, 70 at each of the contact
points 72, 74. An adhesive drop, sufficient to bond an optical
fiber 30 to a contact point 72, 74, represents a typical quantity
of adhesive. Adhesive drops bond the optical fiber 30 to the
cantilevers 68, 70 at the contact points 72, 74 during curing of
the adhesive at elevated temperature. Preferably the adhesive is an
epoxy adhesive, cured at approximately 100.degree. C. for a period
of about one (1) hour. Effective bonding of an optical fiber 30 to
each cantilever 68, 70 of a thermal compensator may include slight
separation between the optical fiber 30 and a cantilever 68, 70 to
facilitate penetration of the adhesive into the interface between
the optical fiber 30 and a cantilever 68, 70. Following bonding of
an optical fiber 30 to a thermal compensator, the temperature
compensated section of optical fiber 30 cools to ambient
temperature with retention of the prescribed tension on the optical
fiber 30 between the contact points 72, 74.
[0055] FIG. 5 shows a plurality of filament organizers 32 arranged
in an accessory attachment fixture 80. The fixture 80 comprises a
base plate 82 having a plurality of organizer slots 84
corresponding to the number of filament organizers 32 contained
within the accessory attachment fixture 80. The base plate 82 has a
first end 86 including a first support 90 and a second end 88
having a second support 92. At least one rod 94 extends between the
first support 90 and the second support 92. FIG. 5 includes two
rods 94 positioned adjacent to each end of an accessory 56,
preferably a thermal compensator, with the accessory positioner 10
in its proximate position. The thermal compensator accessory 56 is
shown more clearly in FIG. 3 and FIG. 4. Preferably each rod 94 is
electrically conducting and acts as a heating element to raise the
temperature at the ends of thermal compensators positioned in each
accessory cradle 12 and aligned with optical fibers contained by
the filament organizers 32 in the accessory attachment fixture 80.
The use of an accessory attachment fixture 80 provides a convenient
way for attaching an accessory 56 to an optical fiber 30 in each of
a plurality of filament organizers 32.
[0056] Attachment of thermal compensators to optical fibers 30, as
previously described, may use an accessory attachment fixture 80 to
simultaneously produce a number of thermally compensated optical
fibers 30. Production of such thermally compensated structures
under essentially the same conditions leads to optical devices with
similar performance characteristics, depending on material
consistency.
[0057] The previous general discussion, for attaching accessories
to filaments, may be beneficially applied to the production of
temperature compensated refractive index gratings 66, also referred
to herein as a Bragg gratings. A stable periodic refractive index
grating 66, free from wavelength drift, requires the preparation of
a thermally compensated package 100 that positions a Bragg grating
66, under tension, between the contact points 72, 74 of a thermal
compensator as shown in FIG. 6.
[0058] Methods for forming optical fiber Bragg gratings are well
known as are means whereby gratings' packages may include
temperature compensation, so as to provide a grating having a
consistent wavelength response over a significant range of
temperatures. The distinguishing feature of the present invention
is the use of a filament organizer 32 with an accessory positioner
10 that allows repeated, precise positioning of an accessory 56
particularly, in this case, a thermal compensator, for attachment
to an optical fiber section that contains a Bragg grating 66.
Selected fixtures may be used with filament organizers 32 according
to the present invention. An accessory attachment fixture 80, as
previously described, facilitates the bonding of an optical fiber
30 to contact points 72, 74 of a thermal compensator. This produces
a thermally compensated optical fiber Bragg grating package
100.
[0059] FIG. 6 illustrates the construction of an optical fiber
Bragg grating package 100 that includes a thermal compensator
comprising a rod 60, such as a quartz rod, having end caps 62, 64
at each of its opposing ends. The end caps include cantilevers 68,
70 extending towards the center of the rod 60. Using a filament
organizer 32 that includes an accessory positioner 10, the thermal
compensator aligns with an optical fiber 30 when the accessory
positioner 10 is in its proximate position. This allows attachment
of the optical fiber 30 to the thermal compensator, as previously
described, to produce the structure shown in FIG. 6 having an
optical fiber Bragg grating 66 bonded between the contact points
72, 74 on the cantilevers 68, 70 of the end caps 62, 64.
[0060] After formation of optical fiber Bragg grating packages 100,
filament organizers 32 are removed from the accessory attachment
fixture 80 and disassembled by removing the accessory positioner 10
from each frame 34. Optical fiber 30 containment between the first
spool 26 and second spool 28 may require rotation of the spools 26,
28 to wind in the length of optical fiber 30 previously extended
over the forward 42, 44 and rear 46, 48 guides of the filament
organizer 32. The process of winding in excess optical fiber 30
places the optical fiber Bragg grating package 100 in the accessory
cradle 12 in preparation for thermal cycling and proofing the
package 100. Thermal cycling of an optical fiber Bragg grating
package 100 occurs within a temperature range from -40.degree. C.
to 80.degree. C. Proofing includes monitoring light signals within
an optical fiber Bragg grating, during thermal cycling, to
determine the operating characteristics, particularly the
wavelength, of an optical fiber Bragg grating package 100.
[0061] FIG. 7 shows an optical proofing fixture 102, used during
thermal cycling and evaluation of a number of optical fiber Bragg
grating packages 100 arranged in the fixture 102. The optical
proofing fixture 102 includes a first face plate 104 and a second
faceplate 106 at either end of a pair of support bars 108 for
engaging a first indent 110 and a second indent 112 formed in the
accessory cradle 12 of each accessory positioner 10. When each
accessory positioner 10 has been seated in the optical proofing
fixture 102, a pigtail section of optical fiber 30 is unwound from
each spool 26, 28. The pigtail sections of optical fiber 30 allow
connection of each optical fiber Bragg grating package 100 to an
optical spectrum analyzer so as to monitor the wavelength of each
grating 66 during thermal cycling and property evaluation. An
optical proofing fixture 102 according to the present invention
includes pigtail organizing components including a pigtail channel
114 to direct optical fiber pigtails from the second spool 28, over
the support bars 108, towards the first spool 26. In the vicinity
of each first spool 26, the optical proofing fixture 102 includes a
pigtail mount 116 that has a pigtail grip 118 to receive pigtail
ends from both the first spool 26 and the second spool 28. Each
pigtail grip 118 comprises a resilient material, preferably a
polymeric foam, having a retention slit 120 formed in the resilient
material. The retention slit 120 associated with each accessory
positioner 10 holds a pair of pigtail ends for positioning
according to the height of the pigtail mount 116. Pigtail grips 118
arranged in a common plane, as shown in FIG. 7, provide
organization of optical fiber pigtails that may be transformed into
a parallel array using a stepped organizer 121. A parallel array
may also be achieved in the absence of a stepped organizer 121 by
changing the heights of pigtail mounts 116 to provide a stepped
relationship between pigtail grips 118. The parallel-array fiber
organizing scheme, while not limiting, provides a convenient
arrangement of optical fiber pigtails for connection to an optical
spectrum analyzer. FIG. 8 provides additional detail of an optical
proofing fixture before inserting accessory positioners 10. In this
case the retention slits 120 have a horizontal orientation.
Rotational repositioning of pigtail grips 118 to produce vertically
orientated retention slits represents a possible alternative
structure compared to the optical proofing fixture shown in FIG. 7
and FIG. 8.
[0062] After the processes of thermal cycling and proofing the
optical fiber Bragg grating 66 exists under tension that was
applied during the production of the package 100. It is known that
the spectral wavelength of a periodic refractive index grating may
be varied by changing the amount of tension applied to the optical
fiber 30 that is bonded between the contact points 72, 74 of the
thermal compensator. Adjustment in tension applied to an optical
fiber Bragg grating 66 provides a method for tuning the wavelength
response of the grating.
[0063] During initial attachment of a fiber 30, to a thermal
compensator, the Bragg wavelength setting is not critical, but
preferably is lower than that desired of the final package 100.
Subsequent adjustment and tuning of the wavelength of the Bragg
grating 66 requires application of torsional force to the
cantilevers 68, 70. During this process, the ends of the
cantilevers 68, 70 are bent away from the surface of the rod 60
using an appropriate jig. This increases the distance between the
cantilevers 68, 70, and the distance separating the optical fiber
30 from the rod 60. The increase in distance between the
cantilevers 68, 70 raises the tension in the optical fiber 30 and
adds to its length causing a change in the wavelength setting of
the Bragg grating 66. The range of increase in length, required to
provide a full range of tuning, for most applications, is typically
less than 5 .mu.m. The post tuning operation is preferably carried
out at the temperature of operation of the device thereby providing
a resulting optical fiber grating package 100 which operates at an
accurate wavelength at any given temperature across an operating
temperature range.
[0064] Although not requiring temperature compensation, some
optical fiber Bragg gratings, e.g. those used in a constant
temperature environment, may be packaged using the accessory 56
shown in FIG. 4 to provide a supporting structure for an optical
fiber. In this case there is no need to set accessory dimensions to
provide temperature compensation. However, the need may still exist
for tuning the wavelength of a Bragg grating held by the accessory
56. The tuning method for a temperature compensated Bragg grating
may also be applied to a similar optical fiber Bragg grating
package designed for use in a constant temperature environment.
[0065] Post tuning an optical fiber grating package 100 according
to the present invention is a computer controlled, automated
process using an optical spectrum analyzer to compare the grating
wavelength with a target wavelength. Deviations from the target
wavelength may be overcome using a cantilever displacement
mechanism to apply force to the cantilevers 68, 70 of the optical
fiber grating package 100. The cantilever displacement mechanism
responds to a computer-generated signal based upon the deviation of
the grating 66 wavelength from the target wavelength.
[0066] The automated tuning process provides rapid wavelength
adjustment without operator intervention except to place an optical
fiber Bragg grating package 100, retained in an accessory
positioner, into a tuning jig 122. After making connection between
the package 100 and an optical spectrum analyzer the operator
designates the target wavelength to which the grating 66 should be
tuned. Each optical fiber Bragg grating package 100 undergoes fine
tuning of its wavelength using a grating tuning jig 122 shown in
FIG. 9. Each accessory positioner 10 needs to be orientated to
place a blade slot 124, formed in the accessory cradle 12, to
receive an accessory tuning blade 126. Orientation includes setting
the accessory positioner 10 to a selected height. In FIG. 9, the
correct height is set using a pair of shaped blocks 132. One of the
pair of shaped blocks 132 includes a locating pin 134 that fits in
a positioning hole 136 in an accessory positioner (see FIG. 1). The
other block 132 has a threaded opening (not shown) to receive a
large-headed thumbscrew 138 that passes through a channel 140 in an
accessory positioner 10 to secure the accessory positioner 10 to
the block 132. Support means, other than shaped blocks 132, could
be used to set the correct height and orientation of an accessory
positioner according to the present invention. Therefore, support
means used to attach accessory positioners 10 to tuning jigs 122
are not limited to those specifically illustrated herein.
[0067] The accessory tuning blade 126, of the tuning jig 122,
enters or withdraws from the accessory positioner blade slot 124
under the control of a voice coil actuator 128. An accessory clamp
130 applies force to the end cap 64 to hold an optical fiber Bragg
grating package 100 (not shown) in the accessory cradle 12 of an
accessory positioner 10 during adjustment of a cantilever 70 that
responds to force applied through the accessory tuning blade 126.
This adjusts the length of the Bragg grating 66 as described
previously.
[0068] FIG. 10 provides a detailed view of the tuning jig 122 to
clarify the process of precisely fine tuning a Bragg grating 66 to
a target wavelength. Initially the pigtail ends of an optical fiber
30, held in an accessory positioner 10, are connected to a test
system that includes a computer. Preferably the test system uses an
optical spectrum analyzer and a light source. Other instruments
known to those skilled in the art would also suffice.
[0069] Preparation for fine tuning the wavelength of a Bragg
grating 66 entails mounting an accessory positioner 10, containing
an optical fiber Bragg grating package 100, on a tuning jig) 122. A
suitably positioned accessory positioner 10 places the accessory
cradle 12 to allow the tuning blade 126 to enter the blade slot
124. The tuning blade includes a pair of fingers (not shown) that
pass around either side of the rod 60 of the grating package 100.
Each finger touches an edge of a cantilever 70 on its underside.
Without some form of restraint, the application of force to the
underside of the cantilever 70 would push the grating package 100
out of the accessory cradle 12. An accessory clamp 130 prevents
such an occurrence by applying a force to the end cap 64, from
which the cantilever 70 extends. The starting position for Bragg
wavelength adjustment therefore requires stabilization of the
optical fiber Bragg grating package 100 in the accessory cradle 12
by contact of the accessory clamp 130 with the end cap 64. A
computer controlled voice coil actuator then moves the tuning blade
126 into the blade slot until the fingers touch the underside of
the cantilever 70.
[0070] Tuning the wavelength of a Bragg grating 66 to a target
wavelength begins with input of the desired wavelength value into
the computer of the test system. The computer probes the current
wavelength of the Bragg grating 66 before comparing it with the
target wavelength. Having determined the difference between the
current wavelength and the target wavelength, the computer provides
a signal to the voice coil actuator 128 to move the tuning blade
126 against the cantilever 70. The tuning blade 126 applies a force
to the cantilever 70 which is typically made from a metal,
preferably aluminum. This force, corresponding to the
computer-generated signal, usually exceeds the elastic limit of the
material, causing plastic deformation of the cantilever 70. Such
plastic deformation repositions the cantilever 70 and introduces a
permanent strain into the Bragg grating 66. Several test cycles may
be used until the target wavelength is met. With each cycle the
tuning blade produces a permanent bend in the cantilever 70. The
permanence of the position of the cantilever 70 thereafter retains
the Bragg grating 66 in a condition for dedicated operation at the
target wavelength.
[0071] During precise fine tuning of Bragg gratings 66, according
to the present invention, the advantageous use of a voice coil
actuator 128 provides a linear output force corresponding to an
input current that may be finely controlled. A high precision power
supply with a voice coil actuator 128 produces a stable signal
leading to an output force that is remarkably constant. This allows
selection of a wide range of output force, limited only by the
magnitude of energy transfer between a coil and a magnet. The
output force of the actuator is proportional to the input current,
similar to a DC motor. Cantilever 70 adjustment based upon a voice
coil actuator 128 offers a precise, consistent and reliable method
for fine control of force applied through the tuning blade 126.
[0072] A filament organizer including a movable accessory
positioner has been described to show how an accessory may be
attached to a filament. The filament organizer allows compact
handling and transfer of filaments between various types of
processing equipment. A filament organizer, as described
previously, is particularly useful for mass producing multiple
temperature compensated optical fiber Bragg gratings of
substantially reproducible wavelength characteristics. Preferably a
plurality of filament organizers is arranged in fixtures that
facilitate the manufacture of performance consistent temperature
compensated devices. Temperature compensated optical fiber Bragg
grating packages according to the present invention may be
individually tuned using a tuning apparatus controlled by a
microprocessor. The use of special fixtures and tuning apparatus
facilitates automation of at least parts of the process for
manufacturing temperature compensated Bragg gratings, unlike
previous similar processes that rely upon operator skill for
correct fiber positioning and attachment of a thermal
compensator.
[0073] As required, details of the present invention are disclosed
herein; however, it is to be understood that the disclosed
embodiments are merely exemplary. Therefore, specific structural
and functional details disclosed herein are not to be interpreted
as limiting, but merely as a basis for the claims and as a
representative basis for teaching one skilled in the art to
variously employ the present invention.
* * * * *